AU732244B2

AU732244B2 - Skeletal implant

Info

Publication number: AU732244B2
Application number: AU28734/97A
Authority: AU
Inventors: Fred Zacouto
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-07-22
Filing date: 1997-07-21
Publication date: 2001-04-12
Anticipated expiration: 2017-07-21
Also published as: EP0820731A3; DE69722320D1; AU2873497A; FR2751202B1; EP0820731B1; EP0820731A2; FR2751202A1; CA2213063A1

Description

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AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION NAME OF APPLICANT(S): Fred Zacouto ADDRESS FOR SERVICE: S S *5 DAVIES COLLISON CAVE Patent Attorneys 1 Little Collins Street, Melbourne, 3000.

INVENTION TITLE: Skeletal implant The following statement is a full description of this invention, including the best method of performing it known to me/us:- S.

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P:oprslbU8734-97rs.doc-23/) I/0 I -1A- BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a skeletal implant, and more particularly to an 5 implant of this type to be used for connecting at least two elements of the skeleton, which implant is embodied in at least two parts, each of which is capable of being connected to one of these elements.

Background and Material Information There are known implants of this type that are capable of being used, for example, in the case of a performance of a bone graft or during the formation of a callus following a fracture. The two ends of the implant, which are rigidly connected to one another, for example because they are embodied in one piece, are each attached, for example screwed, to a bone element located on either side of the graft. When the graft has consolidated, the implant can be removed.

However, there are numerous cases where the implant is left in place. This is particularly the case when the implant is used to replace a bone structure which is impossible to restore or to construct.

:3 *o P:ope:sb\28734-97r-.doc-23/O I I -2- In such cases, the rigidity of the implant, which is often indispensable at the beginning of the implantation, during the formation of the callus, later constitutes a drawback. In effect, the bone structures no longer sustain sufficient mechanical stress. Therefore, they do not reconstitute themselves in an optimal way, this reconstitution being tied to a satisfactory stressing of the bone, the disturbance of which has consequences which can result in postsurgical pain that is very difficult to treat.

Moreover, when the implant is to be used to connect two bones elements which are normally capable of moving relative to one another, as in the case of a rachidian implant, this rigidity results in a functional handicap in the patient in whom it is implanted, and excessive stress on the neighbouring joints.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

SUMMARY OF THE INVENTION The present invention provides a skeletal implant of the type to be used for connecting at least two elements of the skeleton, said implant comprising at least two parts, each of which is capable to be connected to one of said elements, said at least two parts being movable with respect to each other, wherein there is provided, between said two parts, a variable volume element containing a fluid adapted to exert "a force and/or a displacement and/or a damping effect between said at least two parts, and wherein said variable volume element is capable of receiving fluid under high pressure, wherein there is provided a refill element connected to a low fluid source, said refill element being responsive to movements of corporal parts where it is implanted to withdraw fluid from this low pressure fluid source and increase the pressure of the withdrawn fluid such that this variable volume element can be refilled with high pressure fluid.

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P:\opcsbU28734-97rs.doc-23A) I/01 -2A- The present invention also provides a skeletal implant of the type to be used for connecting at least two elements of the skeleton, said implant comprising at least two parts, each of which is capable to be connected to one of said elements, said at least two parts being moveable with respect to each other, wherein there is provided a damping device having an adjustable damping coefficient between said at least two parts, said damping device being responsive to control means to adjust said adjustable damping coefficient when implanted.

Embodiments of the invention relate to an articulated implant, and more particularly to an implant of this type intended either to be intercalated between two bone elements in relative motion, such as an artificial intervertebral disk, or to replace a joint or an element of a joint, such as an artificial head of the femur.

As regards the intercalated implant, it can be beneficial to assist the adjacent bone structures and the ligaments during rapid, or event violent movements. On the other hand, it may be preferable to allow these structures and ligaments to work during slow movements or simple static loads in order to prevent atrophy or weakening.

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P: pcraSsbU8734-97r-d.-23/ IA) I -3- As regards the articulated implant itself, a completely rigid structure fully transmits the shocks and vibrations to the other element of the joint, resulting in a risk of dystrophy or rupture of this other element.

To this end, the subject of embodiments of the invention is a skeletal implant of the type to be used for connecting at least two elements of the skeleton, which implant is embodied in at least two parts, each of which is capable of being connected to one of these elements, characterised in that it comprises between two parts at least one shock-absorbing device with an adjustable coefficient of resistance.

It is noted, first of all, that the adjustment can be discreet as well as continuous, and for example, can include only two positions of adjustment.

The shock-absorbing device is a device generally comprising two chambers of variable volume filled with a hydraulic fluid and connected by a calibrated opening. A device of this type is intended to "cushion" the movements between two elements, one of which is connected to a structure of one of the chambers, the other being connected to an element in which the calibrated opening is formed.

o 20 When the two elements move relative to one another, the volumes of the two S" chambers vary in inverse proportion to one another, the hydraulic fluid being laminated at the level of the calibrated opening. The result is a force which opposes the relative movement between the two elements which, as will be shown, is proportional to the speed of this movement.

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P:\pcssbU28734-97.dc-23/0 1/01 -4- Used in embodiments of the invention, a device of this type applied to an implant of the consolidating and/or connecting type has the advantage of allowing the bone structures to function, and thus to develop, in a practically normal way at moderate relative speeds between the bone elements connected by the implant, particularly in the case of static stresses. On the other hand, the greater the relative speeds, particularly in the case of voluntary rapid movement or shock, that is, dynamic stresses, the greater the portion of the stress absorbed by the implant.

The result is that the osteo-ligamentous structure, weakened by the situation which justified the insertion of the implant, can nevertheless function and thus reconstitute normally as long as the stresses remain moderate. But the greater these stresses, the more the natural structure is assisted by the implant.

Moreover, the coefficient of resistance being adjustable, it is possible to reduce it progressively as the bone structure reconstitutes. The latter can also sustain more and more dynamic stresses until, eventually, it returns to normal function.

It has already been suggested in the prior art to endow prostheses with viscous and/or elastic means intended to absorb shocks. Likewise, it is well known to provide, in 20 certain prostheses, regulating or adjusting means. However, no prothesis with a functional characteristic of viscous resistance has yet been proposed wherein the coefficient of resistance would be adjustable. This combination is essential in the primary function of the invention, which is to allow a progressive reconstitution of the bone structure and an optimal continuous adaptation to the state of this structure.

eQ *i P:opb\.28734-97r- doc-23/0 II0 When applied to an articulated implant, embodiments of the invention make it possible to give the articulation greater flexibility, which, as in the prior art, allows it to absorb shocks, but in this case also allows the neighbouring bone structures and ligaments to work.

Finally, the consequence of this shock-absorbing characteristic is to protect the implant itself, as well as joints located above and below the implant, from shocks.

In one particular embodiment, the implant comprises removable means for locking the shock-absorbing device at a predetermined length.

The implant according to this embodiment can function during a first period in the traditional way, like a rigid implant. This phase of functioning is for example that of the formation of the callus in the case of a graft. During a second period the locking means are removed and the implant functions according to embodiments of the invention, exerting between the elements to which it is connected a force which is proportional to their relative one:speed and is therefore a function of the stresses exerted in the graft.

o" In another particular embodiment, the implant comprises means for limiting the a a travel of the shock-absorbing device.

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*.i This has the advantage of rendering the implant rigid in the case where the stresses reach a certain limit. Thus, there is no risk of reaching the rupture stress point.

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asst 25 Advantageously, these means for limiting the travel are adjustable.

too o'2 0The travel of the shock-absorbing device can therefore be adapted to the patient and possibly increased progressively as the graft strengthens.

1 r 4 P:\op~fSb 8734-97s.dow-23/ I/01 -6- An implant according to an embodiment of the invention can be embodied in the form of an elongated element such as a screw, or a pin such as a coxofemoral prosthesis pin, or event the neck, the body or the head of a femora prothesis, comprising two end parts connected by a flexible middle part, the middle part comprising two chambers filled with hydraulic fluid, disposed on either side of a neutral axis and designed such that one of them increases in volume while the other decreases in volume when the implant flexes, these chambers being liked by at least one calibrated conduit.

This embodiment can be used to connect the two parts of a fractured bone to one another, for example the femur at the level of the neck or diaphysis. The screw is positioned so that its middle part is located at the point of the fracture, with its neutral axis disposed as near as possible to the plane of maximum flexion under stress. Thus, after the formation of the callus, the implant will continue to assist it during sudden efforts, the hydraulic fluid being forced from the chamber whose volume decreases to the chamber whose volume increases, through the calibrated opening. On the other hand, the callus will sustain the static stresses on its own.

More particularly, these end parts can be connected by an elastic wall delimiting these chambers with a peripheral bellows.

0 0t 0 *"As will be seen below, it is often advantageous to add an elastic component to the eviscous component of the implant's behaviour.

The calibrated conduit can be embodied in the form of borings in at least one of the visou25 end parts.

This produces a very compact embodiment that is well suited to the embodiment of the implant in the form of a screw.

Advantageously, a valve is provided on the calibrated conduit.

This valve can initially be closed during the formation of the callus. Thus the implant is perfectly rigid and behaves like a classic screw. The valve is then opened so that the implant funrctions according to the invention, with its shock-absorbing function. A valve with a progressive opening makes also makes it possible to provide the function for adjusting the coefficient of resistance.

The control of the valve is preferably housed at the end of the implant, nearest the skin, Thus, a completely non-invasive intervention allows the valve to be opened and possibly adjusted.

bon a particular embodiment which is especially well suited to the performance of a boegraft for the purpose of replacing an injured vertebra, the shock-absorbing device is. 1 comprises at least one chamber formed of two semi-chambers joined by a bellows, each of the semi-chambers being connected to one of the parts of the implant, this chamber being filled with a hydraulic fluid, and at least one calibrated opening being provided in a wall of this chamber for connecting this chamber with another chamber.

This disposition has the advantage of being very compact and preventing the relative slippage of the mechanical parts, with the resulting risk of hydraulic fluid leakage. However, in certain cases a traditional cylinder-and-piston shock-absorber may be preferred.

-7- More particularly, these semi-chambers can be in the form of cupels whose openings face one another.

The above-mentioned locking means can in this case comprise a removable elongated locking element, inserted into a fold of the bellows so as to prevent it from collapsing.

The elongated lacking element can be embodied in any appropriate way, for example in the form of a metal beaded chain.

The above-mentioned means for limiting the travel can comprise a stop ring screwed onto one of the semi-chambers and designed to cooperate with a shoulder of the other semichamber to prevent the two semi-chambers from moving toward one another beyond a certain limit.

The other chamber can be housed in a supporting skirt mounted on one of the semichambers around the calibrated opening, opposite the oilier semi chamber.

This other chamber can also be formed of two semi-chambers joined by a bellows.

a preferred embodiment the implant according to the invention also includes elastic means between these two parts.

In effect, it is often beneficial for the resistance to the relative displacement of the *aa.two parts of the implant to be proportional not only to the speed of this displacement, but 4 also to the value of this displacement itself relative to a nominal position, Thus, the implant's assistance to the surrounding bone structures is even more efficient when they are farther 20 apart than in their normal configuration.

J Advantageously, the coefficient of elasticity .is adjustable.

Thus, it is possible to adjust the elasticity of the imnplant and, for example, to render it increasingly flexible as the surrouniding structures re-establish themselves.

This type of elasticity cani be obtained in an implant comprising two chambers filed with hydraulic fluid and joined by a calibrated opening, at least one of which chambers contains a compression ampulla at ambient pressure with elastic walls, When a movement between the two parts of the implant begins, it produces a pressure variation in the chambers, and thus an elastic reaction of the compressible amnpulla.

The wall of this ampulla can have progressive elasticity, one of the chambers being capable of being joined to a source of fluid under pressure.

Thus, in this ease, it is possible to regulate the elasticity of the implant by adjusting the pressure in the chambers.

Means can be provided for adjusting the cross section of the calibrated opening.

S. In particular, these means for adjusting the cross section of the calibrated opening can comprise a hydraulically controlled needle valve.

Another embodiment of the present invention is an implant of the type described ***:above wherein the shock-absorbing device comprises at least two chambers, specifically two low-pressure chambers whose walls are made of elastic material, these chambers being joinedb y P15709. S01 at least one calibrated conduit and filled with hydraulic fluid, and designed to sustain a differential pressure variation during a relative movement of the elements.

This type of design makes it possible to easily obtain implants which, as above, not only have a viscous resistance which is a function of the speed, but also an elastic resistance which is a function of the displacement.

In this case, the cross-section of the conduit can advantageously be determined by the prevailing pressure in a high-pressure chamber which is capable of compressing this conduit.

As a result of this design, the coefficient of resistance of the implant can be regulated very easily by adjusting the pressure in the high-pressure chamber, In particular, one of the low-pressure chambers can have a wall of relatively low rigidity relative to the rigidity of the walls of the other chamber.

This design allows the implant to function even when the two chambers are not stressed differently. During a movement which creates excessive pressure, the pressure increases more in the rigid-walled chamber, resulting in a flow of the hydraulic fluid from 2.5 this chamber to the chamber with the less rigid wall, and thus a shock-absorbing effect.

In one particular embodiment, a high-pressure chamber and a low-pressure chamber can be connected, in the low-pressure to high-pressure direction, by a non-return valve.

As will be seen, this disposition makes it possible to increase the pressure difference between the high-pressure and low-pressure chambers. It also makes it possible to maintain this difference despite possible leaks in the high-pressure to low-pressure direction, The anti-return valve can comprise a flexible tube connected to the low-pressure chamber, one free end of which is inserted into a free end of a tube connected to the high.

pressure chamber.

This type of valve is very small and also has the advantage of being even more tightly closed when the pressure difference is greater.

Preferably, it is also arranged for these chambers to be connected by a pressure regulation valve in parallel with the anti-return valve.

It will be seen that the anti-return valve is preferably disposed between the highrigidity, low-pressure chamber and the high-pressure chamber.

In one particular embodiment, the implant according to the invention comprises a first annular low-pressure chamber, and a second rotating chamber it the center of the first chamber, the calibrated conduits being formed radially in the wall separating the two chambers.

9Advantageously, the outer wall of the first low-pressure chamber is relatively thin, 15 and the wall separating the two low-pressure chambers is relatively thick.

This implant can comprise at least one annular high-pressure chamber formed within the thickness of the wall separating the two low-pressure chambers, and designed to compress the calibrated conduits, In another embodiment, this conduit is at least partially embodied in the form of a tube of elastic material surrounded by a tube that is substantially more rigid, these tubes _11- I I P:Koperb\28734-97 sdoc-23/0 I/01 -12being joined into rings at their ends, the compressed volume between the two tubes forming a high-pressure chamber.

In another particular embodiment, the implant is substantially disk-shaped, comprising a plurality of low-pressure chambers in sectors, joined by the calibrated conduits, which alternate inside the thickness of the disk with the high-pressure chambers.

Advantageously, the implant comprises means for adjusting the distance between the elements it connects.

This type of design makes it possible, in particular, to alleviate possible postoperative pain by adjusting this distance appropriately. It is also particularly advantageous in the case of prostheses intended for children who are still growing.

These adjusting means can comprise a bellows designed to receive a hydraulic fluid, and means for connecting this bellows to a source of fluid under pressure.

Another embodiment of the invention is a pair of implants as described above, the low-pressure chamber of each of the implants being connected by the anti-return valve to 20 the high-pressure chamber of the other implant.

*A pair of implants of this type can particularly be provided, in the case of a graft of the vertebral column, to assist the graft in case of lateral flexion.

25 More generally, a pair of implants according to an embodiment of the invention can include means for automatically adapting to the movements of the wearer of the implants, .o Up to this point, bone consolidation implants embodied according to the invention have been described. It will now be shown that the invention is also well suited to the embodiment of articulated implants.

In this case, each part of an implant as described above is articulated to the other, More particularly, these parts can have complementary surfaces which rest against one another, forning a ball-and-socket joint.

An articulated implant of this type can include, in particular, a pivot integral with one of the parts and housed in a space formed between a plurality of low-pressure chambers in the form of sections, which are integral with the other part of the implant and joined by the calibrated conduits, which themselves alternate with high-pressure chambers.

These embodiments are suitable as intervertebral disks.

In a particular application to a coxofemoral joint, the implant according to the invention comprises an articulating hollow sphere whose wall is open so as to allow the ::*insertion of the end of a connecting pin, the shock-absorbing device being disposed inside 0 15 this sphere between the wall of the latter and the end of the connecting pin.

More particularly, this shock-absorbing device can comprise an end element of the connecting pin designed to slide through a slot of a partition inside the sphere, which C...partition delitnits two chambers in the sphere, and at least one calibrated opening is formed 0..0 inside this end element between the two chambers.

-13a 0 In another embodiment, this shock-absorbing device can include an end element of the connecting Pin disposed between two shock-absorbing elements, each of which includes at least two low-pressure chambr whose walls are made of elastic material, these chambers being connected by at least one calibrated conduit and filled with hydraulic fluid, and designed to sustain a differential pressure variation during a relative movement of thle sphere and the connecting pin, Another embodiment of the invention is a pair of implants as described above, used particularly within the scope of an arthrodesis of the vertebral column, each of the implants being mechanically connected in series to a connecting pin of a known type.

More particularly, each of the implants can include ineans for adjusting the distance between the two elements it connects.

It is thtus possible, using a pair of implants of this type, not only to perform the arthrodesis, but also to adjust the angle and the distance between the two parts of the vertebral column connected by the prosthesis, In one particular mode of embodiment, these adjusting means include, for each implant an expandable element such as a bellows, designed to receive a hydraulic fluid, and means for connecting this bellows to a source of fluid under pressure, This source of fluid under pressure can comprise a high-pressure fluid reservoir.

Advantageously, this high-pressure reservoir is common to both implants, each expandable element is also connected to a low-pressure reservoir, and an expandable refill :cell is mechanically connected in series to each pin, each refill cell being connected to the -14- 0 1 I P:%opcrssb\28734-97r sdoc.23 l /01 high-pressure and low-pressure reservoirs by two anti-return valves, one of which allows a flow of fluid from the low-pressure reservoir to the refill cell, the other allowing a flow of fluid from the refill cell to the high-pressure reservoir.

It will be seen that this type of design makes it possible to produce a pump activated by the movements of the wearer of the implants.

In another particular embodiment, the above-mentioned pair of implants is formed of implants in which the shock absorbing device comprises at least two chambers, these chambers being connected by at least one calibrated conduit filled with hydraulic fluid, and designed to sustain a differential pressure variation during a relative movement of these elements, the cross section of this calibrated conduit being determined by the prevailing pressure in a high pressure chamber, and the high-pressure chambers of the implants are connected to the high-pressure reservoir by a controllable valve.

Another embodiment of the invention is a skeletal implant as described above, S. specifically belonging to a pair of implants, which includes sensors of physical quantities, including pressure, supplied with electric power and controlled from outside the body in a Sonon-invasive way, and designed to transmit their information to display means.

o More particularly, this implant can also include adjusting actuators which are also supplied with electric power and controlled from outside the body in a non-invasive way.

BRIEF DESCRIPTION OF DRAWINGS 0 P:\opcrsb\28734-97rs.doc-23/01/01 -16- Particular embodiments of the invention will now be described, by way of a nonlimiting example, in reference to the appended schematic drawings, in which: Figs, la and lb schematically illustrate an embodiment of the invention applied to the formation of a callus after the fracture of a long bone; Fig. 2 schematically illustrates a femoral reconstruction process after a fracture of the neck; Fig. 3 shows a screw according to an embodiment of the invention which can be used to implement the process of Fig. 2; Fig. 4 is a larger scale view of the detail IV of Fig. 3; Fig. 5 is an even larger-scale axial section of the detail IV; Fig. 6 is a schematic axial section illustrating the functioning of this screw; Fig. 7 is a schematic axial section of a shock-absorbing device which can be used 20 in an implant according to an embodiment of the invention; Fig. 8 is a partial view of the device of Fig. 7 showing a certain number of improvements; Fig. 9 is a partial section along the line IX-IX of Fig. 8; Fig. 10. is a view in perspective of elements Figs. 8 and 9; 1 P:pers-sb\28734-97res.doc-23/0 I/O -17- Figs. 11 a and lb are also partial views of the device of Fig. 7 showing other improvements, in two successive phases of the utilisation of the device; Fig. 12 is a front view in partial section of a rachidian implant according to an embodiment of the invention; Fig. 13 shows the utilisation of two implants according to an embodiment of the invention within the scope of a rachidian arthrodesis; 0 Fig. 14 shows in detail, in axial section, the implants of Fig. 13, in section along the line XIV-XIV of Fig. 15, and their interconnections; Fig. 15 is a cross sectional view along the line XV-XV of Fig. 14; Fig. 16 is a diagram of the device in Figs. 13 through Fig. 17a through 17d illustrate the functioning of the devices of Figs. 13 through 0* Fig. 18 shows a top view, in partial cross-section, of a rachidian prosthesis according to another embodiment of the invention; Fig. 19 is a sectional view along the line XIX-XIX of Fig. 18; Fig. 20 is a sectional view along the line XX-XX of Fig. 18; Fig. 21 is a sectional view along the line XXI-XXI of Fig. 18; F 1 0, 1, P:operssb\28734-97es.doc-23/0 -18- Fig. 22 illustrates the interconnection of the chambers of the prosthesis of Fig. 18; Fig. 23 shows another possible assembly of two implants like those shown in Fig.

14; Fig. 24 illustrates a variant of Fig. 23; Fig. 25 is a schematic axial section of an application of an embodiment of the invention to an intervertebral prosthesis; Fig. 26 shows the implantation of the prosthesis of Fig. Fig. 27 is an axial sectional view of a "ligament" of Fig. 26; Fig. 28 shows a schematic top view of an intervertebral prosthesis according to an embodiment of the invention; Fig. 29 is a sectional view along the line XXIX-XXIX of Fig. 28; 20 Fig. 30 is a sectional view along the line XXX-XXX of Fig. 28; Fig. 31 is a sectional view along the line XXXI-XXXI of Fig. 28; Fig. 32 is a view in perspective showing in greater detail the implantation of the 25 intervertebral prosthesis of Figs. 28 through 31; o* o* I Q P:'opcrssb28734-97rs.doc-23/01/01 -19- Fig. 33 is a view in perspective of an anti-return valve which can be used in an implant according to an embodiment of the invention; Fig. 34 is an axial sectional view; Fig. 35 and 36 are views in perspective of a coxofemoral prosthesis according to an embodiment of the invention; Fig. 37 is a schematic cross-sectional view; Fig. 38 is a sectional view of the head of the prosthesis of Figs. 35 through 37; Fig. 39 is a partially exploded view of the prosthesis of Figs. 35 through 38; Fig. 40 shows another implant which can be used in place of those in Fig. 13; Fig. 41 is a view in perspective of an element of the implant of Fig. Fig. 42 is an axial sectional view; Fig. 43 is a view similar to Fig. 41 of another embodiment; 9 *99o Fig. 44 is an axial sectional view of this embodiment; 25 Fig. 45 illustrates the functioning of the elements of Figs. 41 through 44; Fig. 46 illustrates another mode of functioning of this embodiment; 1 7.

Fig. 47 is a schematic view of the entire hydraulic circuit of an arthrodesis of the vertebral colunm using implants of the same type as the one in Fig. Fig. 49 is an electrical wiring diagram of the control of an implant according to an embodiment of the invention; DETAILED DES CRIPTION O1P Mh RFRE ENMODIMdRJ]S Figs. I a and l b represent a long bone I in whose middle part 2 a graft 3 has been formed, between two end elements 4 and An imnplant, generally designated by the reference number 6, is provided in order to consolidate the graft 3. For this purpose, the implant 6 comprises two parts 7 and 8, each of which is screwed into one of the bone elements 4 and 5, respectively. According to the invention, the opposite ends of the parts 7 and 8 are connected by a shock-absorbing device.

The shock absorber 9 is composed in a known way of a cylinder 10 which forms two closed chambers 11 and 12 respectively, separated by a piston head 13, mounted such that it slides in the cylinder. For thi pupoete cylinder 10 is filed with a hydraulic fluid, S which can be laminated at the level of a calibrated opening (not represented) formed in the piston head 13.

Means of any known type, also not represented, are provided for adjusting the 5*5*5coeffcient of resistance, for example means for adjusting the cross-section of the calibrated s S20 opening, Adjusting means of this type are present in all the embodiments described below.

even in the cases where they are not mentioned.

The end of the part 7 Of the implant is connected to a piston rod 14 attached to the head 13 and passing through one of the end plates of the cylinder. The end of the part 8 of the implant is connected to the cylinder Moreover, a removable rigid connecting piece 15 initially connects the end parts 7 and 8 of the implant, thus making the shock absorber 9 inactivre.

The implant 6 is put in place with its connecting piece 15 (Fig. 1 which is retained as long as no callus has formed at the level of the graft. Due to this connecting piece, the implant behaves like a standard implant, sustaining both the static and dynamic stresses, When the callus has formed (Fig. lb), the connecting piece 15 is removed or inhibited.

Since the shock absorber exerts between the parts 7 and 8 of the implant 9 a force proportional to the relative speed of these two parts, the partially reconstituted bone will sustain all of the static stresses. On the other hand, it will be increasingly assisted by the shock absorber as the dynamic stresses it sustains become more substantial, thus causing high rates of strain, in this case tensile strain or compressive strain.

Figs. 2 through 6 show an application of the principle explained in reference to Figs.

l an and lb.

These figures show the top part of a femur 100 which has sustained a fracture at the *level of the neck 10 1. In a known way, a screw 103 is inserted into the body of the femur and into its head 104, in order to hold the latter in place until the formation of a callus and the suture of the two parts separated by the fracture.

1. 4.

The screw 103 is embodied in two rigid substantially cylindrical parts, namely a body 105, the part of the screw nearest the skin, and a threaded point 106, the part farthest from the skin, respectively. The part nearest the sin comprises, at its external end, a head 107 for turning the screw 103. The two end parts are connected by a flexible middle part 108.

The middle part 108 is formed by an annular bellows 109 which connects the peripheries of the inner ends of the body 105 and the point 106, A flat elastic blade 1 10 also connects these two ends, which blade contains their axis, thus allowing a relative pivoting movement between the two parts 105 and 106 in a plane perpendicular to the blade, while preventing such a movement in the plane of the blade, The blade 1 10 thus forms a neutral axis ina rotation between the parts 105 and 106 around an axis perpendicular to the axis of these parts and contained in the plane of the blade 1 Thus, the bellows 109 and the blade 110 delimit two chambers 1 11 and 112 disposed on either side of the neutral axis. During a bending of the screw, which causes a relative rotation of its parts 105 and 106 around the above-mentioned axis, the volume of one of the chambers (I111 in Fig. 6) increases while the volume of the other (112) decreases.

The chambers 111 and 112, as well as their connecting conduits as described above, are filled with a hydraulic fluid.

Borings 113 parallel to the axis of the screw each connect to one of the chamnbers 111 and 112 and connect to one another through a transverse boring 114. A valve 115 (not 20 represented in Fig. 6) mounted in the boring 114 makes it possible to open or close the *connection between the chamnbers I111 and 112, as well as to regulate the cross-section of thle passage between these chambers.

-22- The control rod 116 of the valve 115 is coaxial with the body 105 of the screw, and its control head, which for example is itself a screw, is included in the head 107 of the screw.

Thus it is disposed near the outside of the body of the patient where the screw is inserted.

The screw 103 is positioned in a known way, but such that its middle part 108 is disposed at the level of the fr-acture. Moreover, the screw is immobilized in axial rotation in such a way that the plane of the blade 1 10 is perpendicular to the plane of Fig. 2, in a way that can produce a relative rotation of the parts 105 and 105 of the screw around an axis perpendicular to this plane and passing through the level of the part 108.

During the implantation, the valve 115 is closed. Thus, no connection is permitted between the chambers I111 and 112, so that the screw is perfectly rigid throughout the time it takes for the callus to form. Once the callus has formed, a minor intervention allows access to the control head of the valve 115, making it possible to open this valve, and to adjust its opening and consequently the coefficient of resistance of the implant.

Figs. la and lb illustrate the utilization of a standard shock-absorbing device.

Generally, however, the shock-absorbing devices used will be better adapted to the particular use to be made of them.

Thus, Fig, 7 shows a shock-absorbing device in which each of the two chambers 220 and 221 has a variable volume due to the presence of a bellows 222 and 223, respectively.

The chamber 220 is formed of two semni-chambers in the shape of cupels 224 and 225 whose openings face one another. These cupels are connected by the bellows 222.

-23- Likewise, the chamber 221 is formed of two semi-chambers, one of which is constituted by a cylinder 226 welded to the outside of the bottom 227 of the cupel 225, and the other of which is a cupel 228 whose opening faces the cylinder 226. The cylinder 226 and the cupel 228 are connected by the bellows 223.

Each of the bellows in this case is embodied in the form of a toric, sector made of sheet metal welded along each of its edges and the edges of the eupels 224 and 225, in the cae of the bellows 222, and along the free edge of the cylinder 226 and the edge of the cupel 228 in the case of the bellows 223.

The chambers 220 and 221 are filled with a hydraulic fluid and connect through a calibrated opening 229 cut into the bottom 229 of the cupel 225 and opening into the cylinder 226. Thus, when a compressive stress is exerted on the cupels 224 and 225 of the chamber 220, tending to push them toward one another, the volume of this chamber decreases while the fluid passes through the opening 229 and is forced into the chamber 22 1, whose volume increases. The force which opposes the approach of the cupels 224 and 225 is is proportional to the approach speed, assuming that the bellows do not exert any force, particularly of an elastic nature.

When the compression stress stops, the bellows return the chambers 220 and 221 to their original configuration, In the embodiment represented, the chamber 221 is housed in a cylindrical stresstransmitting su~pport skirt 230, welded to the bottom 227 of the cupel 225 around the cylinder 226, In this case, the stresses are transmitted to the shock-absorbing device by the cupel 224 and the skirt 230, which two elements connect the two parts of the implant.

-24- .In Figs. 8 through 10, the cupel 224 comprises, in a cylindrical area, an extenal threading 240 onto which is screwed a stop ring 241 equipped with a cooperating internal threading. One end of the ring 241 faces a shoulder 242 of the cupel 225, in this case the edge of this cupel onto which one edge of the bellows 222 is welded.

Moreover, a beaded chain 243 is engaged in the annular space 244 delimited by the fold of the bellows 222, which includes the edge of the cupel 224, and the bottom of the ring 241. The beads of the chain in this case have a diameter substantially equal to the distance at equilibrium between the edges of the cupels 224 and 225 which face one another, One end 245 of this chain exits the annular space 224 through a slot 246 formed in the lateral wall of the stop ring 241, opposite the shoulder 242.

During the insertion of the implant, and in the subsequent consolidation phase, the chain 243 prevents the collapse of the bellows 222 in such a way that, under compression, the device behaves substantially like a traditional rigid implant. If the chain has a diameter smaller than the thickness of the space 244, the device has a partial shock-absorbing flunction .:so 15 in this phase.

:*00.0After consolidation, the chain 243 is removed by pulling on its end 245, the device then functioning entirely according to the shock-absorbing principal of the invention.

0 .0 However, a compression limit is obtained by the abutment of the edge of the ring 241 against so. 0.the shoulder 242 of the cupel 225. Thus, the device once again functions, under compression, 000 20 like arigid implant, 0 Figs. 11 a and I1I b illustrate an alternate embodiment of the locking system of the .00. chain 243 of Figs. 8 through 10. In this case an elastic needle 250 has one of its ends 251 0 so:welded to the inside of the cupel 224 of the chamber 220. Initially, the other end 252 of the needle 250 is engaged in the calibrated opening 229, which it obstructs, Due to the incompressibility of the hydraulic fluid contained in the chambers of the device, the device is perfectly rigid.

When desiring to make the device function according to the invention, it suffices to distance the cupels 224 and 225 from one another enough to disengage the end 252 of the needle 250 from the opening 229. This opening is then free to allow the passage of the hydraulic fluid and cannot in any case be re-blocked by the needle 250.

The rachidian implant 260 of Fig. 12 comprises two end parts 261 and 262 equipped with anchoring cones 263 and 264, respectively. The part 261 also includes a sleeve 265 connected to the anchoring cone by a length adjusting screw 266, A shock-absorbing device 267, in this case the same type as those described in reference to Figs. 7 through 11, has a cupel 224 integral with the sleeve 265 and a skirt 230 integral with the end part 262.

An implant of this type can be used during operations for restoring the funictioning is.. 1 or the integrity of the vertebral column. The vertebrae at least partially retain their structural functions in case of static stresses, On the other hand, the implant is more active when the dynamic mtesses are substantial, Fig. 13 shows an arthrodesis of the vertebral column in which two pins 3 01 and 3 02 are anchored in two vertebrae 303 and 304 so that in a known way, they provide a 20 connection between these two vertebrae. The pins 301 and 302 in this case are each embodied in two parts 301', 301" and 302', 302", respectively, each of these parts being -26- .9 I.

connected at one of its ends to one of the vertebrae 303 and 304, and at its other end to the other part, by means of a device 305 according to the invention.

An example of this type of device is described in reference to Figs. 14 and respectively in cross-section and in axial section.

The implant 305 comprises a shell constituted by two half-shells 306 and 306' which are upper and lower shells, respectively. Disposed inside this shell is an alveolar structure 307, particularly made of silicone, w1iich ensures both the elastic and shock-absorbing fu~nctions between the two half-shells 306 and 306'.

The structure 307 comprises an outer toric chamber 308 and a substantially cylindrical central chamber 3 09, these two chambers being separated by a partition 3 10. The partition 3 10 is constituted in the following way, It forms a thick wall 311 of low elasticity (of high elastic rigidity) relative to the external wall 312 of the outer chamber 308. Radial conduits 313 disposed inside this wall 311 connect the chambers 308 and 309. Annular chambers 314 which communicate freely with one another are fanned between the conduits 313, which conduits 313 and chambers ::*314 are distributed in layers perpendicular to the axis of the prosthesis.

The lower half-shell 306 in this case is connected by a bellows 315 to a base 316.

Means, not represented, make it possible to inject hydraulic fluid under pressure into the chamrber 317 delimited by the bottom of the half-shell 3 06, the bellows 3 15 and the base 316, 20 It is thus possible to adjust the axial thickness of the implant 305, Obviously, a differential adjustment of the two bellows 315 makes it possible to realign the vertebrae of Fig. 13.

By providing a range of adjustment that is sufficient to allow a substantial variation of the length of the device, it is possible to produce an adjustable internal fixation, allowing the repair of the vertebrae without the need for osseous fuision of the joints of these vertebrae.

Other means which are not represented, but which are included for most fluid injection sites or adjusting buttons implanted under the skin of the patient, make it possible to adjust the pressure in the chambers 308 and 309 on the one hand, and 314 on the other hand, the pressure at equilibriumn in effect being equal in the low-pressure chambers 308 and 3 09. and lower than the pressure in the high-pressure chamber 3 14.

Fig. 14 also shows that the central low-pressure chamber 309 of each prosthesis 305 is connected to the high-pressure chamber of the other prosthesis by conduits 318 equipped as described below.

Mounted in each conduit 3 18 is an anti-return valve 319 which can open from a lowpressure chamber 309 into the corresponding high-pressure chamber 314, when the pressure -i s in the chamber 309 becomes higher than that in the chamber 314. Moreover, a pressure control valve 320 is mounted in parallel with the valve 319, which valve is calibrated in a .**known way to establish a predetermined differential pressure between the low-pressure chamber 309 and the high-pressure chamber 314.

It is noted that the conduits between the low-pressure chambers could, in a variant, 20 be disposed outside the shell. One such embodiment would involve producing a conduit of this type at least partially in the form of a catheter made of elastic material surrounded by a substantially more rigid tube, the catheter and the tube being joined into rings at their ends, -28- 1. 1.

for example by means of adhesive bonding or welding, The high-pressure chamber in this case is constituted by the volume between the catheter and the tube.

Refer now to Fig. 16, in which the same reference numbers used in Figs. 14 and have been repeated, combined with the letters D and G for the right and left implants, respectively (seen from the rear of the patient wearing the prosthesis).

In Fig. 16, the various chambers are comparable to pressure cylinders wherein the body constitutes the chamber itself. These cylinder bodies are considered to be fixed, which means that the lower parts 3 01' and 3 02' of the pins 3 01 and 3 02, the bases 3 16, and the lower half-shells 306 are assumed to be fixed, The pistons 3 09D' and 309G' and 3 14D' and 3 14G' illustrate the stresses exerted on the corresponding chambers by the upper half-shells 306' when the patient bends laterally, to the left in Fig, 16 as seen from behind- As for the pressure cylinders 308D and 308G, the elasticity of the walls is only symbolized, by the springs 321D and 321G, the pressure va riations in the chambers 308 in practice resulting only in movements of fluid though the conduits 313 due to this elasticity.

Finally, these conduits 313 are symbolized by flexible restrictions compressed to a greater or lesser degree by the fluid contained in the higl -pres sure chambers 314.

The behavior of the left implant, which is compressed during the movement, will now be examined. Due to the thickness of the Wall 311 and thus its low elasticity, the central lowpressure chamber 309 can increase in diameter only slightly to compensate for the decrease in its height. The fluid it contains will then be expelled through the conduits 313 to the -29- P15709. SOI peripheral low-pressure chamber 308, Thus, the desired shock-absorbing function is obtained.

Furthermore, the elasticity of the wall 312, symbolized by the spring 321 of Fig. 16, will simultaneously have the tendency to resist the expansion of the chamber 308, and therefore the entry of the fluid into this chamber. Thus, the function of elastic resistance is obtained.

It is noted that, as the left half-shells 306 and 306' move closer together, the left highpressure chambers 314 also move closer to one another, which has the effect of increasing the coefficient of resistance by reducing the cross-sections of the conduits 3 13.

On the right side, where conversely, the half-shells 3 06 and 3 06' have a tendency to move apart, the fluid will move in the opposite direction. Due to the rigidity of its walls, the cross-section of the chamber 309 will not vary much. But as its height, and therefore its volume, increases, fluid will enter it from the chamber 308 through the conduits 313. The cross-sections of the latter will increase, which will have the effect of reducing the coefficient of resistance on this side, thus compensating for its increase on the other side.

This elastic behavior will result from most of the stresses exerted on the lateral wall .:of the chamber 309.

Consequently, it is noted that during the patient's movement, the implant essentially sustains the high-amplitude or high-speed stresses. But it is the bone graft which will sustain the moderate static loads or loads resulting from relatively slow movements. The result is a 0.0.

reduction in the risk of osteoporosis.

P15709. Sol It will now be seen, in reference to Figs. 1 7a through 1 7d, how the differential pressure between the high-pressure and low-pressure chambers, which is essential for retaining the shook-absorbing characteristics of the implant, is regulated. These figures illustrate the pressure levels in the central low-pressure chamber and the high pressure chambers as a function of time.

It is assumed, in reference to Figs. 17a through 17d, that the patient successively bends to his right rapidly (Fig. 17a), or slowly (Fig, 17b), straightens himself (Fig. 17c), and bends again, but to his left (Fig. 1 7d). The solid lines (BPD and BPD) relate to the right implant, and the broken lines (HPG and BPG) relate to the left fimplant.

During a rapid mo~vement, a substantial pressure peak is observed which is positive on the bent side, and negative on the other side, in both the high-pressure and low-pressure chambers, The reason why this occurs in the high-pressure chambers will be explained below. In the low-pressure chambers, it is due to the rigidity of the walls of the chambers 309 and to the shock-absorbing effect of the conduits 313, which slow the flow of fluid from the chambers 309 to the chambers 308, The time t, that it takes for the patient to bend to the right, during which the pressure levels vay then stabilize, can be seen in Figs. 1 7a arnd l7b. The respective pressure levels were substantially equal before the movement, by reason of symmetry, but after the movement the pressure levels are obviously higher on the right than on the left.

When the movement is rapid enough, there is a period t.

2 included in tj during which the pressure in the right low-pressure chamber 309 becomes higher than the pressure i the left hig-pressure chamber 314. The anti-retur valve 3 19G then opens and allows the passage of fluid from the right low-pressure chambers to the left high-pressure chamber.

o z-31 11 1.

Sinultaneously, the pressure control valve 320G allows a flow in the opposite direction so as to Prevent the differential pressure between the high and low pressure from excceeding the set-point value.

Thus, if need be for any reason, the differential pressure predetermined by the calibration value of the pressure control valve is re-established, Thiis can occur continuously in the case of leaks from the high-pressure chambers to the low-pressure chambers, or when the low-pressure chambers are refilled by injection, or even when an adjustment is made to increase the differential pressure between the high and low pressure. The device then functions like a pump controlled by the movements of the patient.

If;, on the other hand, the bending movement is slow, as shown in Fig. 17b, the fluid has the time to flow from the right low-pressure chambers 309 to 308 without causing excessively high pressure levels. The anti-return valve 3190 does not open.

When the patient straightens, the pressure levels change as shown in Fig. 1 7c. Given that the pressure levels on the right side are initially higher than those on the left side, it is is not very probable that during the period t 3 of the movement, the prevailing low pressure mn the left chamber 309 will become greater than the prevailing high pressure in the right chamber 314.

It is only when the patient bends quickly enough to the left, as represented in Fig.

17d, which is symmetrical to the case in Fig. 17a, that the differential pressure between the right high-pressure chamber and the left low-pressure chamber re-establishes its set-point V....value. The period t 4 of the movement, and the period t5 during which the left low pressure 0 0becomes greater than the right high pressure, are shown in this figure.

-32- It is understood that what has just been described step-by-step in reference to Figs.

1 7a through 1 7d actually occurs continuously when the patient is moving normally, successively adopting various natural postures, Consequently, it is noted that this results in a continual biornechanical adaptation of the implants to the stresses imposed on it by the patient.

In light of the auto-refil principle explaied in reference to Figs. 1 7a through 17d, it may be seen that the pressure points that are too acute will flatten, out due to the fact that the fluid is laminated as it flows into the anti-return valve. This produces an additional shock-absorbing effect when the cell is stressed suddenly enough that the low pressure surpasses the high pressure. Taking into account the variability of the coefficient of resistance as a function of the loads, as described above, this proves to be a device endowed with an advantageous capacity for self-adjustment.

Another advantage of this mode of functioning resides in the fact that a practically continuous circulation of fluid occurs in the hydraulic circuit of the implant of the invention, i1 This circulation avoids the risk of collapse and thus limits the need for maintenance operations.

.Another embodiment 322 of the implants 305 is seen in Figs. 18 through 22.

The implant 322 is again embodied in the form of an alveolar structure made of elastomer contained in a shell composed of a lower half-shell 323 and an upper half shell 324.

-33- The alveolar structure of this embodiment is in the shape of a disk and forms three low-Pressure chambers 325 in the form of sectors, distributed substantially equally around the axis of the disk, at 1200 from one another. The three chambers 325 connect through a network of calibrated conduits 326, here disposed in two transverse layers, Three groups of high-pressure chambers 327, which communicate with one another by any appropriate means, are disposed between the low-pressure chambers 325. The chambers 327 are flat in shape, and each group has three of them, interposed between the layers of conduits 326. The pressure in the high-pressure chambers determines the crosssection of the conduits 326 and thus their characteristics of viscosity.

Fig. 22 shows that the low-pressure chambers are connected to the high-pressure chambers by a set of anti-return valves and pressure control valves. Each low-pressure chamber 325 is connected to the high-pressure chamber 327 that is diametrically opposed to it by an anti-return valve 328 which opens in the direction from the chamber 325 to the chamber 327, in parallel with a pressure control valve 329.

In this case, there is no intersection, as in the embodiment of Figs. 14 and 15, arid as symbolized in Fig. 17, of the connections between the low-pressure and high-pressure chambers of two implants mounted in parallel. Moreover, there is only one type of low- .9 9 pressure chamber.

*9.*During an axial compression, the fluid contained in the conduits 326 is, due to the S 20 thickness of the waills of the latter, expelled to the chambers 325 with a viscous fluid behavior. The walls of these chambers are then forc-ed toward the outside, giving the implant its elastic behavior. In this respect, this inaplant behaves like the one in the Preceding embodiment.

4 9 -34- On the other hand, this implant has a particular behavior relative to non-axial loads.

For example, in the case of a load exerted from the left side of Fig. 22, the low-pressure chamber 325a will be compressed, while the chambers 325b and 325c will be at low pressure. The wall of the chamber 325a will then expand, while part of the fluid contained in this chamber will flow into the chambers 325b and 325c through the conduits 326, further drawn by the prevailig low pressure in these chambers, When the movement is large enough and rapid enough, the outer wall of the lowpressure chamber 325a comes into contact with the shell. The elastic behavior of the implant is then blocked, so that the pressure rises sharply in the low-pressure chamber 325a- This pressure can then become greater than the prevailing pressure in the high-pressure chamber 327a which faces it engaging the process for regulating the differential pressure described above in reference to the preceding embodiment.

An implant according to this second embodiment could therefore be used alone, while retaining the differential pressure regulation function.

0*0 15 Various implantations other than that represented and described in reference to Fig.

13 can be envisaged for the implants just described.

see Co..

Fig. 23 shows a bone graft 330 disposed between two vertebrae 33 1. Two im plants 305 such as those in Figs. 14 and 15 have been placed in the graft, symmetrically relative to median plane of the patient's body. The interconnections between the implants and the I.0 20 functional principles are the same as those described in reference to Figs. 14 through 17.

Fig. 24 shows a single implant 332 as described in reference to Figs. 18 through 22, implanted in a graft 333, which is itself disposed between two vertebrae 334, A solution of this type ensures good performance with regard to lateral as well as frontal flexions, Articulated implants embodied according to the invention will now be described.

Fig. 25 shows an implant, or intervertebral, prosthesis 400 intended to be disposed, as shown in Fig. 26, between two vertebrae 401 in place of an intervertebral disk, This implant must therefore allow certain movements between the vertebrae 40 1, contrary to what occurs in the case of an arthrodesis.

The implant 400 is generally formxed by a shell comprising a bottom 402 and a cover 403. The cover 403 rests on the bottom 402 as a result of two spherical surfaces with the same radius, the surface 404 of the bottom which fares upward and the surface 405 of the cover which faces downward, Thus, the cover 403 can pivot relative to the bottom 402 around three axes, 0% The bottom 402 is hollow, so as to define a space 406 inside the implant The cover 15 403 forms a projection 407 into this space, the end of which projection is connected to the 01- bottom by three inner viscoelastic "ligaments" 408, which will now be described in reference to Fig. 27.

Each ligament 408 comprises a rigid hollow body 409 which is substantially .*.*cylindrical and has, at one of its ends, an opening to the ambient air 410. This opening is 20 sealed by an ampulla, or elastic bellows 411. The bellows 411 is a cylinder closed at its end opposite the opening 4 10 by a bottom 412, andl its lateral wall forms a helical fold 413 with a variable pitch which increases from the opening 4 10 to the bottom 412.

-36- The body 409 and the bellows 411 delimit a chamber 414 containing a hydraulic fluid which is supplied from, and whose pressure can be regulated by, a conduit 415 and a valve 416, At the other end of the body 409, the base 417 of this body supports an annular cylindrical chamber 418 whose inner wall 419 and outer wall 420 are also constituted by bellows. The chamber 418 contains a hydraulic fluid which is supplied from, and whose pressure is regulated by, a conduit 421 and a valve 422.

At the center of the annular chamber 418, the wall of another cylindrical chamber 423 is formed by a bellows 424. The chamber 423 connects to the chamber 414 through a calibrated opening 425 cut into the base 417 of the body 409. The chamber 423 is therefore supplied and pressurized from the chamber 414.

The end of the bellows 424 opposite the base 417 is sealed by a plate 426 which carries a support piece 427 passing through an opening 428 of an end plate 429 of the annular chamber 418. The end plates 426 and 429 are integral.

15Formed inside the chamber 423 is a chamber 430 mounted on the base 417 of the *.body 409 bymeans of posts 43 1. One of these posts 431 is hollow and makes it possible to supply and to pressurize the chamber 430.with hydraulic fluid from a conduit 432 and a valve 433.

T h w a lo.h.h m b r4., b t ee.h u c i n p o n s o h o s s 4 n h 00:..h aloftecabr40,btentejntinpit fte ot 3 n h o~o. 0 base 417, formas a bellows 434. The bottom of the chamber 430, which faces the base 417 of the body 409, carries a needle 435 which penaenates into the calibrated opening 42 1. o.o -37- The implant is anchored at the proJection 407 and at the bottom 402 by its elements 409 and 427.

It is easily understood that the length of the ligament 408 is a functiori of the pressure in the annular chamber 418, which determines the elongation of the bellows 419 and 420.

This length can be adjusted by means of the valve 422.

Moreover, the coefficient of resistance of the ligament 408 is a function of the free cross-section of the calibrated opening 425, and thus of the penetration depth of the needle 435. This coefficient can be adjusted by means of the valve 433.

Finally, with regard to its elasticity, the bellows is comparable to a helical spring with a variable pitch which becomes increasingly steep as it is compressed and its spires progressively come into contact. This bellows determines the elasticity of the ligament 408' since, when the latter is compressed, it elastically opposes the penetration of the hydraulic fluid into the chamber 414 through the opening 425. The coefficient of elasticity can **:therefore be adjusted by means of the valve 416 by pre-compressing the bellows 411 to a 15 greater or lesser degree, It is noted that a structure similar to that of the ligament just described could be used in place of the device of Fig. 7, in order to render its various functions adjustable.

An alveolar structure 500 made of elastomxer which could replace the three ligaments 408 of Fig. 25 will now be described in reference to Figs. 28 through 3 1.

20 This structure is practically identical to that of the implant 322 of Figs. 18 through 21 (Fig. 28 has been schematized). It is noted, however, that in this case the structure 500 has -38an opening 501 of triangular section for receiving a projection of the cover, similar to the projection 407 and intended to form a pivot between the bottom and the cover of the prosthesis, The interconnections between chambers are the same as in the case of the implant 322, and the functioning of the present prosthesis and the implant are the same from'the hydraulic standpoint.

The differences reside in the way in which the stresses are applied. In this case, essentially transverse stresses are applied to the low-pressure chamber 502 by the projection of the cover.

Fig. 32 shows one possible implantation of the prostheses of Figs. 25 through 3 1.

This figure shows the bottom 503 and the cover 504 of the prosthesis. The bottom 503 is equipped with fittings 505 and the cover 504 with fittings 506 for their respective attachment to a lower vertebra 507 and an upper vertebra not represented.

.The various hydraulic chambers are connected by conduits 508 to a set of 15 subcutaneous control buttons 509, particularly p'ush-buftons, disposed behind the vertebrae, Safety devices are preferably provided in order to prevent ill-timed operation of the buttons.

In a variant, fully hydraulic adjustment means could be provided, with a subcutaneous access site connected to the various chambers by a slide valve.

Figs. 33 and 34 show, in partial perspective and in cross-section, respectively, an 20 anti-return valve which can be used in the invention.

-39- This valve is composed of a conduit 5 10 connected to the high-pressure and a conduit 11 connected to the low pressure. These conduits are coaxial, and the end of the lowpressure conduit 511 is engaged inside the end of the high-pressure conduit 5 10, The end of the conduit 511 inside the conduit 5 10 is flat.

As long as the high pressure is greater than the low pressure, the end of the conduit 511 remains flat and the valve remains closed, thus preventing the possibility of a flow from the conduit 511 to the conduit 5 10, But when the low pressure becomes higher than the high pressure, the end of the conduit 511 opens and fluid flows from the conduit 511 to the conduit 5 Finally, Figs. 35 through 39 illustrate a coxofemoral prosthesis embodied according to the principles of the invention.

This prosthesis is intended to be used after a fracture of the neck of the femur and a resection of its upper part It comprises a pin 600, one end of which is intended to be attached to the remaining part of the femur, and a hollow sphere 601 whose wall includes an opening 602 to allow it to be penetrated by the other end of the pin 600.

*5The upper end of the pin 600, inside the sphere 60 1, is integral with a cylindrical head 603, The latter is capable of sliding and forming a piston in a circular opening 604 of an internal partition 605 of the sphere, The axis of the head 603 and of the opening 604 passes substantially through the other end of the femur, at the level of the knee joint The partition 605, along with the piston 603P delimits inside the sphere two chambers 606 and 607, which are respectively upper and lower chambers. The chambers 606 and 607 -4ocontain viscoelaslic devices which determine the relative movement of the pin 600 and the sphere 601, as a function of thie stresses applied.

In one particularly simple embodiment, these viscoelastic devices can be simply constituted by an elastic foam which fills the chambers 606 and 607, and a calibrated opening formed in the head 603. The foam contain a hydraulic fluid and an appropriate joint is disposed at the level of the opening 602.

However, the embodimnenti Figs. 38 and 39 is preferred.

In this case, the viscoelastic devices 608 are embodied in a form practically identical to that of the structures 307 in the implants 305. The difference resides in the fact that the structures 307 are generally of cylindrical shape, while the devices 608 have a shape which is generally hemispherical. But in a similar way, they are chiefly composed of a peripheral low-pressure chamber 609 and a center low-pressure chamber 6 10, separated by a wall 611.

**.Annular high-.pressure chambers 612 formed within the thickness of the wall 611, are interposed with calibrated conduits 613 which connect the low-pressure chambers 609 and 9 15 610. The intersecting interconnections between chambers are embodied as above.

:9....When the prosthesis is stressed, the head 603 compresses one of the devices 608, while the other device is at low pressure. Everything indicated relative to the functioning of the twin implants 305 remains valid in the present case.

It is noted that in this case, when a device 608 is compressed, its line of tangetcy 20 with the inner surface Of the sphere moves closer to the partition 605. The elastic outer wall *99: surface then decreases, which has the effect of increasing the elastic rigidity of the device, -41- The interconnections between chambers are embodied as shown in Fig. 39, by boring 614 formed in the head 603 and in the pin 600. These borings emerge at the level of a control button box 615 (Figs. 35 and 36). This box is disposed subcutaneously so as to be easily accessible, in order to allow the necessary adjustments.

The implant 700 of Fig. 40 generally comprises a viscoelastic cell 701, for example like that in the implant 305 of Fig. 13 and the subsequent figures, or like the ligament 408 of Fig. 27, as well as a distance adjusting element 702, in this case for adjusting the height, and a refill cell 703. These elements are mechanically disposed in series, in support with the half-pins 704, 704' of the artbrodesis, which can belong to the two vertical members of a frame. The half-pins 704, 704' consequently support the pressure of the patients body, which is variable as a function of his posture.

The adjusting element 702 cat be embodied as shown in Figs. 41 and 42, in the form of an expandable toric bellows, which can expand axially. Its central free space allows it to house a protuberance of the viscoelastic cell.

15 In a vaiant the adjusting element can be in the form of the disk-shaped bellows 702' of Figs. 43 and 44.

The adjusting element 702 (or 702') can be connected by a conduit 705 to a tube valve 706 which can itself be connected to a pump 707. Thus, it is possible to adjust the tbickniess of the element 702. It is therefore possible to adjust not only the total length of the 20 prosthesis, but also the angle formed between its upper par (the hl-pin 704) and its lower part (the half-pins 704') by means of a differential filling of two elements 702 of the prosthesis.

-42- It is noted that the valve 706 itself can be implanted, in which case it is accessed either by cutaneous incision or by means of an access site, or external, the conduit 705 being transcutaneous, In another embodiment, represented in Fig. 46, the filling of the adjusting elements i s carried out with the aid of a high pressure reservoir 708, in this case dilatable, and a slide valve 709. In a similar way, the emptying of these elements occurs into a low-pressure drainage collector 710, also dilatable, through another slide valve 711 (or in the same way, through a three-way valve).

Moreover, a filling valve 712 makes it possible to fill the reservoir 708, and a drainage valve 713 makes it possible to empty the reservoir 710. The reservoirs 708 and 710 are implanted and the valves 712 and 713 can be external or implanted, as in the ease of the valve 706. Generally, however, they will be implanted, since their access should be far less frequent than that of the valve 706.

The refill cells 703, whose funrction will be described below, are entirely similar to the adjusting elements 702. However, they are connected to the high-pressure and low.

pressure reservoirs 708 and 710 not by slide valves, but by anti-return valves 714 and 715, respectively. The anati-return valves 714 are connected from the cells 703 to the high-pressure reservoir 708, and the anti-return valves 715 are connected from the low-pressure reservoir 710 to the cells 703.

Te clls 03 erveas umpsforrefilling the high-pressure reservoir 708. In effect, when the patient bends, for example to the right, the cell 703D is compressed. When the pressure in this cell surpasses the pressure in the reservoir 708, the anti-return valve 714D -43opens and fluid passes from the cell 703 to the reservoir 708. Simultaneously, the left cell 703G draws in fluid from the low-pressure reservoir 710.

A pressure control valve 716 prevents the -high-pressure from exceeding a predeterm~ined value.

It is noted that if only angular corrections are desired, the refill device can be greatly simplified, and the refill cells in particular can be eliminated. In effect, in this case it suffces to connect the adjusting elements by means of a slide valve. When the patient bends, for example to the right, the valve is opened so that fluid passes from right to left, then is closed again. When the patient straightens, the height of the left side will be larger and that of the right side will be smaller.

The viscoelastic cells have not been described in this embodiment It is simply noted that in the case where they comprise high-pressure chambers, like for example the implants 3 05 or the ligaments 408, these chambers can be connected to the high-pressure reservoir 708 0%* by a valve, for example a slide valve. Thus it is possible to easily rigidify the viscous behavior of these cells. The low-pressure chambers of the viscoelastic cells, for their part, 9:.?:can also be connected to the low-pressure reservoir 710.

48 shows a possible implantation for the elements j ust described- The connecting conduits generally have the reference number 717. It is noted that all these elements can have very small dimensions, and the hydraulic volumes can be very low.

The physical characteristics of the implants just described can be modified postoperatively by any means, including entirely non-invasive means, whether in terms of -44their viscoelastic properties, their dimensions, their lateral or antero-posterior inclination, or their anti-rotational resistance.

By way of example, Fig. 49 illustrates an electronic control circuit for an implant of the type represented in Fig. 47.

This circuit is embodied in two parts, an extracorporeal part 720 and an implanted part 72 1. These two parts are in contact by means of two antennas 722 and 723, respectively.

The circuit part 720 comprises a power supply 724, a remote control device 725, a detection and amplification module 726, and a monitor 727. The remote control device 725 controls a radio frequency multiplexer 728 connected to the antenna 722.

The circuit part 721 also comprises a radio frequency multiplexer 729 connected to the antenna 723. The multiplexer 729 is connected to a radio frequency/D.C. voltage converter 73 0 which supplies electric power to the other modules of the circuit part 72 1, .namely a radio frequency oscillator 731 and sensors 732, as well as actuators 733.

In the case of Figs, 40 and 47, the sensors 732 can be, in particular, pressure sensors in the distance control elements 702, and possibly in the chambers of the viscoelastic cells 701. The actuators can comprise electrically operated valves such as the slide valves 709 and 711. More particularly, the pressure sensors can comprise, for each side of the patient one sensor for each low-pressure chamber and one sensor for the high-pressure chamber, Pressure sensors can also be provided on the means for attaching the implants, such as screws or hooks, as well as on the bone, possibly bridged- When the doctor wishes to know and possibly to adjust the pressure in the elements 702, for example, he operates the remote control device 725. The antenna 722, placed in proximity to the antenna 723, emnits a code that is detected and used by the implanted part 721. Moreover, the radio frequency is transf6nned into a D.C. supply voltage for the sensors 732, the oscillator 73 1, and the multiplexer 729. The implanted part then in turn emits a code containing the pressure information, which is detected and displayed on the monitor 727. The adjustment of the elements 702 by means of the electrically-controlled valves 733 occurs in the same way.

It is noted that thanks to the invention, it is possible to perform a detailed examination of the behavior of the implants, For example, in the case of a vertebral implant, it is possible to measure its frequency response, or its impulse response, by having the patient sit on a scat equipped with means for moving in any direction desired, and by recording the response of the pressure sensors. The adjustment of the various stationary pressure levels can thus be determined with great precision.

It is noted that an implant according to the invention can include analgesic neurostimulating means of a known type, as well as a programmable medication delivery Generally, for aJI of the implants described above which do not have remote control by means of radio frequencies or the like, devices ame provided which are accessible either directly, as in th e case of subcutaneous buttons, or by means of a benign intervention. The means for adjusting by remote control without physical contact can be rotary valves of the "1sluice" type which are multidirectional, whose rotation is induced by an external rotating magnetic field- A spiral spring re-establishes the equilibrium in the closed position, It is S Sadvantageous to be able to carry out the desired adjustments relatively often, either in a I. j. k P:opcrssb\28734-97rs.doc-23/0 1/01 -47planned way, for example in order to progressively reduce the coefficient of resistance as a graft consolidates, or as necessary, for example in order to relieve pain.

Likewise, all of the above-mentioned implants can be provided with improvements which have only been described in reference to certain embodiments. This is the case, for example, with the dimensional adaptation provided in the implants of Figs. 14 and 27. A disposition of this type is particularly useful in any implant intended for a child who is still growing, or an elderly person whose size is gradually decreasing.

The instant application is based upon French Priority Patent Application No. 96 09157, filed on July 22, 1996, the disclosure of which is hereby expressly incorporated by reference thereto.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and :see "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

5

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Claims

48- THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:- 1. A skeletal implant of the type to be used for connecting at least two elements of the skeleton, said implant comprising at least two parts, each of which is capable to be connected to one of said elements, said at least two parts being movable with respect to each other, wherein there is provided, between said two parts, a variable volume element containing a fluid adapted to exert "a force and/or a displacement and/or a damping effect between said at least two parts, and wherein said variable volume element is capable of receiving fluid under high pressure, wherein there is provided a refill element connected to a low fluid source, said refill element being responsive to movements of corporal parts where it is implanted to withdraw fluid from this low pressure fluid source and increase the pressure of the withdrawn fluid such that this variable volume element can be refilled with high pressure fluid. 2. A skeletal implant according to claim 1 wherein said low pressure fluid source receives fluid from said variable volume element. ;o o• 3. A skeletal implant according to claim 1 or 2 wherein there is provided a high :0 pressure reservoir to supply fluid under pressure to said variable volume element, and 20 wherein said refill element is connected to said high pressure reservoir in order to refill it 0with fluid under high pressure. A skeletal implant according to anyone of claims 1 to 3 wherein said refill element 0 is a differential variable volume element located in said implant between said variable 0000 25 volume element and one of said parts. 0ooo A skeletal implant as claimed in anyone of claims I to 4 wherein the intensity of said force is adjustable through said control means. 6. A skeletal implant as claimed in claim 1, wherein said means authorising a p displacement are, at least partially, reversible to authorise a displacement in a direction f P:\oprssb\2734-97res.doc-23/0/01 -49- opposite or different to a direction of precedent displacement. 7. A skeletal implant as claimed in claim 1 wherein said means authorising a displacement are also responsive to a sensor of force, pressure or displacement in said implant and/or in a bone element. 8. An implant according to anyone of claims 1 to 7 in which said variable volume element is a bellow means. 9. A pair of implants according to anyone of claims 1 to 8, for connection to bone elements of the vertebral column, each of the implants being mechanically connected in series to a connecting pin of a known type. A pair of implants according to claim 9 in which each of the implants comprises 15 means for adjusting the distance between said elements which it connects. *o*o 11. A pair of implants according to claim 9 in which said adjusting means comprise, for each implant, a variable volume element designed to receive a fluid, and means for connecting said element to a source of fluid under pressure. i 12. A pair of implants according to claim 11 in which said source of fluid under pressure is a reservoir of high-pressure fluid. 000*0 13. A pair of implants according to claim 12 in which said high-pressure reservoir is 25 common to both implants, each variable volume element is also connected to a low- :I pressure reservoir and a variable volume element refill cell is mechanically connected in series to each refill cell being connected to the high-pressure and low pressure reservoirs by two anti-return valve, one allowing of fluid from the low pressure reservoir to the refill cell, and the other allowing a flow of fluid from the refill cell to the high-pressure S reservoir. P:opcsb\287314-97s.doc-23/1 /01 14. A pair of implants according to claim 13 formed of implants according to claim 11, and in which the high pressure chambers of the implants are connected to the high-pressure reservoir by a controllable valve. 15. An implant according to claim 1 characterized in that it comprises a high-pressure reservoir, and a very high pressure variable volume element for sending fluid into the high- pressure reservoir, said high pressure reservoir being connected to the variable volume element via a high-pressure valve, the said variable volume element being connected to a low-pressure reservoir via a low-pressure valve. 16. A skeletal implant, according to claim 1 also comprising analgesic neusrostimulating means. 17. A skeletal implant according to claim 1 wherein the distance between said at least two parts is adapted to follow the growth of said elements of the skeleton. 9• 18. An implant according to claim 1 also comprising elastic means between said two 999 parts. o S 20 19. An implant according to claim 18 in which the coefficient of elasticity is adjustable. An implant according to claim 1 comprising at least two chambers filled with fluid and designated such that one increases in volume while the other decreases in volume; said oooo chambers being connected by at least one calibrated opening, and comprising means for o8 adjusting the cross-section of said calibrated opening. 21. An implant according to claim 20 in which said means for adjusting the cross- section of the calibrated opening comprises a hydraulically controlled needle valve. 22. An implant according to claim 20 wherein said calibrated opening is formed by a AW J., P:\opr\ssb\28734-97res.doc-23/0 I/OI -51 calibrated conduit, in which the cross section of said calibrated conduit is determined by the prevailing pressure in a high-pressure chamber which is capable of compressing this conduit. 23. An intervertebral implant according to claim 1 substantially in the form of a disk, comprising a plurality of low-pressure chambers in the form of sectors, connected by said calibrated conduits, which themselves are deformable within the thickness of the disk by high-pressure chamber means. 24. An invertebral implant being an artificial disk according to claim 23, wherein said two parts are normally parallel to form a disk and are movable and/or tiltable to modify the thickness and/or the diedral angle between said two parts of the disks. An invertebral implant, being an artificial disk, according to claim 1 wherein said two parts are movable with respect to each other in a direction allowing a variation of the thickness of the disk. be. 26. An vertebral implant being an artificial disk according to claim 1 wherein said two parts are movable with respect to each other, in order to modify the diedral angle between said two parts. 27. An invertebral implant according to claim 1 wherein said two parts have respective spherical surfaces articulated for pivotable movement thereof. S*e 25 28. An implant according to claim 1 in which said damping device comprises at least two chambers, said chambers being connected by at least one calibrated conduit and filled with a fluid, and designed to undeigo a differential pressure variation during a relative movement of said elements, the cross-section of said calibrated conduit being determined by the prevailing pressure in a high-pressure chamber. l l 29. A skeletal implant of the type to be used for connecting at least two elements of the P:\oper\ssb28734-97rs.doc-23/01/01 -52- skeleton, said implant comprising at least two parts, each of which is capable to be connected to one of said elements, said at least two parts being moveable with respect to each other, wherein there is provided a damping device having an adjustable damping coefficient between said at least two parts, said damping device being responsive to control means to adjust said adjustable damping coefficient when implanted. An implant according to claim 29 also comprising elastic means between said two parts. 31. An implant according to claim 30 in which the coefficient of elasticity is adjustable. 32. An implant according to claim 29 comprising at least two chambers filled with fluid and designated such that one increases in volume while the other decreases in volume; said chambers being connected by at least one calibrated opening, and comprising means for adjusting the cross-section of said calibrated opening. 33. An implant according to claim 32 in which said means for adjusting the cross- section of the calibrated opening comprises a hydraulically controlled needle valve. 34. An implant according to claim 32 wherein said calibrated opening is formed by a calibrated conduit, in which the cross section of said calibrated conduit is determined by the prevailing pressure in a high-pressure chamber which is capable of compressing this conduit. o, 35. An intervertebral implant according to claim 32 substantially in the form of a disk; comprising a plurality of low-pressure chambers in the form of sectors, connected by said calibrated conduits, which themselves are deformable within the thickness of the disk by high-pressure chamber means. 36. An invertebral implant being an artificial disk according to claim 32 wherein said 'V P:opcrssb\28734-97res.doc.23/01/01 -53- two parts are normally parallel to form a disk and are movable and/or tiltable to modify the thickness and/or the diedral angle between said two parts of the disks. 37. An inverterbral implant according to claim 35 wherein said two parts have respective spherical surfaces articulated for pivotable movement thereof. 38. An implant according to claim 29 in which said damping device comprises at least two chambers, said chambers being connected by at least one calibrated conduit and filled with a fluid, and designed to undergo a differential pressure variation during a relative movement of said elements, the cross section of said calibrated conduit being determined by the prevailing pressure in a high-pressure chamber. 39. A skeletal implant substantially as hereinbefore described :with reference to the drawings. 0ev OSOO .00.0 0 0 S S. S. 00 a 0 0000 00 0 G*:S 0S S 0 0 go0 0 0 0050 0 0 0000 S 0@SS 0 0 0000 00 DATED this 2 3 rd day of January, 2001 Fred Zacouto By his Patent Attorneys DAVIES COLLISON CAVE