AU776010B2

AU776010B2 - Total metatarsophalangeal prosthesis with section plane

Info

Publication number: AU776010B2
Application number: AU15699/00A
Authority: AU
Inventors: Marc Augoyard; Louis Samuel Barouk; Michel Benichou; Vincent Coulange; Jean-Michel Gaume; Michel Maestro; Jacques Peyrot; Mathieu Ragusa; Bernard Valtin
Original assignee: DePuy France SAS
Current assignee: DePuy France SAS
Priority date: 1998-12-14
Filing date: 1999-12-13
Publication date: 2004-08-26
Anticipated expiration: 2019-12-13
Also published as: FR2787013B1; DE69933236T2; AU1569900A; JP2002532138A; JP4160727B2; EP1139928A1; FR2787013A1; DE69933236T8; EP1139928B1; DE69933236D1; WO2000035381A1

Description

P.\OPER\O\2436279 p l.doc-06/07/04 1 Total metatarso-phalangeal prosthesis with section plane The present invention relates to a total metatarsophalangeal prosthesis with a section plane complimentary to a cut surface of a bone, of the type comprising a metatarsal prosthesis with a bone anchoring rod, a phalangeal prosthesis and an articular plate adapted to be placed on the phalangeal prosthesis, this plate comprising an articular surface co-operating with a complementary articulation surface for the metatarsal prosthesis.

This type of prosthesis is adapted to be fitted in the big toe between the phalange and the metatarsal, in order to remedy certain pathological conditions, namely hallux rigidus or even arthrosic hallux valgus.

It is known that hallux valgus consists of lateral deformation of the big toe, combined with a medial deviation of the first metatarsal or metatarsus varus, resulting in the formation of painful lateral bursitis.

The second pathological condition in question, hallux rigidus, is associated with arthrosis and demonstrated by constriction of the interstice (space between the metatarsal and phalange), the cartilage having partially or completely disappeared on the opposing surfaces of the joint. Surgeons distinguish three stages of hallux rigidus: stage I, at a very early- stage of development, can be treated by osteotomy of the metatarsal which has a shortening and lowering effect. This may also be combined with shortening of the first phalange of the big toe, again with the aim of increasing the effect of longitudinal relaxation.

Stage II corresponds to more severe wear on the cartilages but the joint still has slight mobility.Surgical treatment may either be the same as in the previous stage or it may involve fitting a prosthesis.

Finally, at stage III, there is no cartilage left to work the joint, there is virtually no mobility and severe pain P:\OPER\DH\2436279 apal.do-06/O7/04 2 is experienced. The only possible surgical treatment is then arthrodesis or prosthesis.

There are total metatarso-phalangeal prostheses of the "section" and "resurfacing" types. "Section" prostheses involve preliminary cutting of planar surfaces on the metatarsal and phalange, to accommodate the components of the prosthesis. On the other hand, "resurfacing" prostheses only require resurfacing of the facing articular surfaces of the metatarsal and phalange, as they are shaped to replace only the cartilage.

Total prostheses for big toes are already known, e.g.

from US patent US-A-5 458 648 and French patents FR-A-2- 709 948 and 2 697 155. These prostheses are not entirely satisfactory, particularly because they adapt only imperfectly to the patient's natural anatomy.

In accordance with the invention, there is provided a section type metatarso-phalangeal prosthesis comprising a metatarsal implant having a body and a bone anchoring rod, a phalangeal implant and an intermediate plate adapted to be disposed on the phalangeal implant and having an articular surface co-operating with a complementary articulation surface of the body of the metatarsal implant, wherein the articular surface and the complementary articulation surface each are divided in two zones respectively located on both sides of a sagittal plane and having respectively different radii of curvature corresponding to the anatomy of the metatarsal and phalange, respectively.

Preferably, the prosthesis is for the big toe which, by its adapted geometry, restores 10 degrees of plantar flexion and 60 degrees of dorsal flexion; this prosthesis should perform satisfactorily in the pathological conditions known as stage II and stage III hallux rigidus, or even arthrosic hallux valgus.

Preferably, the zone with the greater radius of P:\OPER\OH\2436379 spal.d-06/07/04 3 curvature (R2) extends over approximately two thirds of the articular surfaces of the metatarsal implant and plate, and is comprised between 30 and 50 mm, and the smaller radius (RI) is comprised between 5 and 15 mm.

This double curvature of the two mating articulation surfaces of the prosthesis enables the latter to adapt advantageously to the patient's anatomy, forming two surfaces with excellent congruence, thereby also ensuring automatic recentring of the body of the phalangeal process on the metatarsal implant.

Thus, the prosthesis of the invention not only permits the range of movement described above but also allows the phalange to recover axial alignment relative to the metatarsal.

According to a further feature of the invention, the bone anchoring rod of the metatarsal implant is inclined by about 100 degrees to a distal planar bone support surface of the body of said implant to which said rod is fixed.

This distal planar surface bears on a corresponding section surface of the metatarsal, the inclination of the rod to the body of the metatarsal implant being such that when the prosthesis is in position the anchoring rod is coaxial with the axis of the metatarsal. Such an angular position has the advantage of avoiding any interference of the plantar end of the body of the metatarsal implant with the metatarso-sesamoid joint.

Moreover, as already mentioned, the prosthesis provided according to the invention is of the section type, which has the advantage of allowing accurate positioning of its components thanks to a suitable cutting aid which makes it easier to cut through the bone.

4 The radii of curvature of the metatarsal implant restore a dynamic valgus of 10 degrees after the implantation of the prosthesis, by the sliding of the phalangeal implant relative to the metatarsal implant.

Further features and advantages of the invention will become apparent from the description which follows, referring to the accompanying drawings which illustrate an embodiment thereof as a non-restrictive example.

Figure 1 is a side elevation on a reduced scale of the skeleton of a human right foot, showing in particular the metatarso-phalangeal joint of the big toe.

Figure 2 is a longitudinal semi-elevation, half in section, on a vertical plane, on a larger scale, of an embodiment of the total metatarso-phalangeal prosthesis according to the invention fitted to a metatarsophalangeal joint.

Figure 3 is an elevation of the metatarsal implant in Figure 2 in the direction of the arrow F, from the end of its anchoring rod.

Figure 4 is a view of the metatarsal implant in the direction of the arrow K in Figure 2.

Figure 5 is a perspective view, on a larger scale, of the intercalary plate between the metatarsal and phalangeal implants.

Figure 6 is a view of the intercalary plate in section along a dorsal plane, i.e. a plane perpendicular to that in Figure 2.

Figure 7 is an axial section, on a larger scale, of a component of the phalangeal implant.

Figure 1 shows a skeleton of a human right foot, showing the first metatarsal i, the phalange 2 articulated on the metatarsal i, the terminal phalangette 3 and the other bones of the foot (first cuneiform 4, scaphoid etc.). The phalange 2 is articulated about a point O, on either side of which it can flex, pulling the phalangette 3, either by plantar flexion (angle A) or by dorsal flexion The maximum plantar flexion is of the order 5 of 100 and the maximum dorsal flexion B is substantially 900 in a normal metatarso-phalangeal joint.

The sesamoid 41 is arranged (Figure 2) below the metatarsal head and connected to the metatarsal 1 and to the phalange 2 by respective tendons 42, 43.

The prosthesis illustrated in Figures 2 to 7 is a section-type total prosthesis intended to reproduce the joint between the metatarsal 1 and the phalange 2. This total prosthesis comprises a metatarsal implant 6, a phalangeal implant 7 and an intermediate plate 8 disposed on the phalangeal implant 7. The plate 8 has an articular surface 9 co-operating with a complementary articulation surface 11 provided on a body 12 of the metatarsal implant 6. This latter also has a bone anchoring rod 13 fixed to the body 12, the articular surface 11 of which has a rounded, substantially spherical contour with at least three different radii of curvature defined by an anatomical study. The body 12 is substantially L-shaped in section, viewed in a vertical plane (Figure 2) By contrast, the inner surface of the body 12, located nearest the anchoring rod 13, is segmented into three planar surfaces 14, 15, 16 machined so as to be capable of bearing precisely on corresponding distal and dorsal sections 14a and 16a, respectively, of the metatarsal i. The intermediate surface 15 bears on a bone chamfer 15a formed between the dorsal and distal sections.

The dorsal part of the body 12 has a length similar to that of the dorsal rod 13, which advantageously forms an angle C of about 100' with the plane of the distal surface 14. The axis of the rod 13 is thus coaxial with the axis of the metatarsal 1 when the prosthesis is in position.

In a dorsal plane, i.e. in the plane of Figures 4 and 6 which is perpendicular to that of Figure 2, the articular surface 17 of the intercalary plate 8 and the complementary articular surface 11 of the body 12 of the metatarsal implant 6 each have two zones with different radii of curvature corresponding to the anatomy of the 6 metatarsal 1 and the phalange 2, respectively. Thus, the articular surface 11 is divided over its entire length in the sagittal plane (Fig. 2) into a first zone 19 having a radius of curvature R1 and a second zone 21 having a radius of curvature R2 greater than RI. Similarly, the articular surface 17 of the plate 8, the contour of which is substantially circular, has a first zone 22 having a radius of curvature equal to R1 and a second zone 23 having a significantly greater radius of curvature equal to R2. Advantageously, the zones 19 and 22 extend over substantially one third of the total area of the respective surfaces 11, 17, the remaining two thirds of the surfaces consisting of the zones 21 and 23.

The radii R1 and R2 have values between those indicated above, i.e. 5 to 15 mm and 30 to 50 mm, respectively, depending on the height of the patient for whom the total prosthesis is intended.

This geometry reproduces the patient's anatomy as closely as possible and thereby ensures excellent congruence of the articular surfaces 17 and 11.

The phalangeal implant 7 comprises a rotational tubular base 24 (Figures 2 and 7) in the shape of a funnel, consisting of two coaxial conical parts 25 and 26.

The conical part 26 is larger in diameter than the conical part 25 and serves as a support for the intermediate plate 8 and for the phalangeal implant 7 on the phalangeal bone resection. The plate 8 is made of a plastic material with a low coefficient of friction such as polyethylene. The phalangeal implant 7 also comprises a bone anchoring member consisting, in the example shown, of a screw 27 for spongy bone, the thread of which is very deep for this reason.

The intermediate plate 8 is completed by an axial stud 28 integrally formed with the rest of the plate and adapted to engage axially in the conical part 25 of the phalangeal base 24 in order to prevent radial migration of the plate 8 relative to the phalangeal implant 7. This 7arrangement does, however, allow the plate 8 to move axially with respect to the base 24. Moreover, the phalangeal base 24 is internally profiled to enable it to accommodate the spongy bone screw 27 with predetermined angular play.

The screw 27 consists of a milled head 29 the conical surface of which adjoins a cylindrical portion 31 (Figure 2) extended by the threaded rod 32. Corresponding to this conical and cylindrical profile of the milled head 29 and the zone 31 is a mating profile formed on the inside of the conical part 25 of the base 24, consisting of a conical wall 33 (Figure 7) terminating in a flange 34.

The latter is extended in the direction of the screw 27 by a terminal collar 37 larger in diameter than the flange 34.

The conical wall 33 is connected, in the direction of the flared end 26, to a groove 35 in which is housed a joint 36 for holding the screw 27, this joint 36 being made of silicone, for example. As can be see from Figure 2, the milled head 29 bears on the conical part 33, thereby compressing the joint 36. This compression ensures that the screw 27 is retained, preventing it from escaping after it has been inserted in the base 24 as far as the position shown in Figure 2.

Moreover, the inner flange 34 is slightly larger in diameter than the smooth cylindrical part 31, so as to allow, together with the diameter of the flange 37, limited angular movement of the screw 27 relative to the phalangeal base 24 after the screw has been inserted therein.

When the bone screw 27 is put into position in the base 24, its head 29 compresses the joint 36 which thus ensures that the screw 27 is held in place.

It is possible to provide a suitably sized notch 38 (Figures 2 and 5) in the edge of the plate 8 opposite the dorsal plane, the advantage of which is that it prevents any contact between the edge of the plate 8 and the 8 sesamoid ridge 39 of the metatarsal bone 1 during plantar flexion, and thus avoids any consequent discomfort or pain to the patient.

The intermediate plate 8 may be made in several thicknesses to provide a suitable range from which the surgeon can select the plate which is most appropriate for the patient. The anti-migration stud 28 may be about 3 mm long, for example. The phalangeal base 24 is preferably covered on the outside with a layer of hydroxyapatite, which ensures secure fixing without the need for surgical cement.

In addition to the advantages outlined above, the total prosthesis according to the invention also has the following: The possibility of relative axial rotation between the intermediate plate 8 and the phalangeal base 24 makes it possible to reproduce the natural rotation between the phalange and the metatarsal when a person walks. This axial freedom of rotation also allows automatic selfcentring between the intermediate plate 8 and the metatarsal implant 6, which is itself linked to the double curvature R1, R2 of the articular surfaces.

The retention of the bone screw 27 in the base 24 by means of the joint 36 makes fitting easier for the surgeon by allowing him to handle a phalangeal implant 7 virtually as a single unit. It also prevents the screw 27 from pulling out and coming into contact with the polyethylene stud 28 after the operation, causing undesirable wear on the stud 28. This retention by the joint 36 nevertheless allows a slight angular movement, of the order of 30, which enables the screw 27 to orient itself automatically in the phalange 2.

The notch 38 in the plantar part of the plate 8 prevents any interference with the sesamoid ridge and indexes the positioning of the plate 8 relative to the metatarsal implant 6.

The stud 28 eliminates any risk of the plate 8 9 migrating relative to the phalangeal base 28 in which it is located.

The phalangeal implant 7 is firmly anchored by the screw 27 in the phalange 2, and its intermediate plate 8 restores the articular surface of the base of the phalange.

The movement of axial rotation between the plate 8 and the phalangeal implant 7 generates a very small, practically negligible, volume of debris under physiological conditions.

The articular surface 11 of the metatarsal implant 6 restores the sliding strip originally provided by the head of the metatarsus. In profile, the distal metatarsal section should be at an angle of about 100 relative to a plane perpendicular to the axis of the diaphysis. This section dips towards the plantar surface of the metatarsal 1 and makes contact with the location of the sesamoid 41 on the metatarsal, so as to be parallel to the phalangeal section. The dorsal section of the metatarsal 1 is flush with the dorsal cortex of the metatarsal, so that the implant 6 has three sectional planes: the dorsal section of the plane 16, the distal section 14 and a chamfer section corresponding to the surface 15, e.g. 2 mm between the two previous sections. The implant 6 has radii of curvature which make it possible to cover all the morphotypes, while its length in dorsal view should also meet this criterion.

Various embodiments of the invention are possible.

Thus, the ratio of one-third/two-thirds between the two zones of radii of curvature R1 and R2 may vary substantially depending on the patient's anatomy, as may the numerical values of the radii of curvature. The retention of the bone screw 27 in the base 24 may be achieved by any means equivalent to the retaining joint 36.

P:\OPER\DH\2436279 spal.doc-06/07/04 10 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.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "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.

Claims

2. Prosthesis according to claim i, wherein the zone with the greater radius of curvature (R2) extends over approximately two thirds of the articular surfaces of the metatarsal implant and plate, and is comprised between and 50 mm, and the smaller radius (RI) is comprised between 5 and 15 mm.
3. Prosthesis according to claim 1 or 2, wherein the phalangeal implant comprises a rotational tubular base in the shape of a funnel mounted on a bone anchoring member, and on which is supported the plate which is able to rotate relative to the phalangeal base.
4. Prosthesis according to claim 3, wherein the bone anchoring member is a screw for spongy bone. Prosthesis according to claim 3, wherein the plate is provided with an anti-migration stud adapted to engage axially in the phalangeal base. P:\OPER\DH\2436279 8pa.do-06/07/04 12
6. Prosthesis according to claim 3 and 4, wherein the base is internally profiled to enable it to accommodate the spongy bone screw with some angular play.
7. Prosthesis according to claim 6, wherein the base has an inner flange the diameter of which is slightly greater than that of a smooth cylindrical portion of the spongy bone screw located between the head and the threaded portion of said screw.
8. Prosthesis according to claim 3, wherein retaining means are provided for retaining the bone anchoring member on the phalangeal base to prevent it from coming into contact with the plate.
9. Prosthesis according to claim 8, wherein the head of the bone screw is milled, wherein said retaining means comprise a flexible joint housed in an inner groove of the phalangeal base and compressed by the milled head of the screw, while allowing angular movement of the screw. Prosthesis according to claim 3, wherein the tubular base is provided with a conical part forming a funnel on which the plate can bear.
11. Prosthesis according to claim i, wherein an edge of the plate opposite the dorsal plane is provided a notch intended to prevent any contact between said plate edge and the sesamoid ridge of the metartarsal bone during plantar flexion.
12. Prosthesis according to claim i, wherein the bone anchoring rode of the metatarsal implant is inclined by an angle of about 100 degrees to a distal planar bone support u P:\OPER\DH\2436279 sal.doc-06/07/04 13 surface of the body of the implant to which this rod is fixed, this inclination being such that when the implant is in position the anchoring rod is coaxial with the axis of the metatarsal.
13. Prosthesis, substantially as hereinbefore described with reference to the drawings and/or Examples. DATED 6 July 2004 0 DePuy France By DAVIES COLLISON CAVE Patent Attorneys for the applicant