CA1331329C

CA1331329C - Bicompression external fixator for osteosynthesis

Info

Publication number: CA1331329C
Application number: CA000544088A
Authority: CA
Inventors: Juan Lazo-Zbikowski; Marcel Wagenknecht
Original assignee: Jaquet Orthopedie SA
Current assignee: Stryker GmbH
Priority date: 1986-08-11
Filing date: 1987-08-10
Publication date: 1994-08-09
Anticipated expiration: 2011-08-09
Also published as: ATE119010T1; EP0256984A2; DE3751103D1; DE3751103T2; EP0256984B1; EP0256984A3; ES2069533T3

Abstract

ABSTRACT OF THE DISCLOSURE
An external fixator comprising two groups of pins, each holding a bone fragment, and a telescopic piece comprising an internal bar and an external bar, each pin group being connected to one of the internal and external bars. The device is characterized in that one of the bars includes first guiding means destined to cooperate with corresponding second guiding means at least indirectly dependent on the other bar, said first and second guiding means being separated from each other by roller sliding means intended to reduce friction during relative movement of the bars. The guiding means comprise at least one longitudinal flat surface made in one of the bars and capable of being arranged parallel to the longitudinal axis of the fractured bone.

Description

13~ ~29 The present invention belongs to the field of osteosynthesis and more precisely concerns a bicompression external fixator.
External fixators have been known for many years and are used in bone surgery to maintain wires and transcutaneous pins inserted into the bones on each side of a fracture by means of external frames and fixation rods.
It has however been observed that in some cases, namely when using fixed systems giving an excellent stability, there 10 was a tendency toward delayed unions and scarce callus formation. -So-called"biocompression" has been proposed in order to avoid such disadvantages. Biocompression is a term applied to stresses (such as tractions and compressions) that have their origin in the deformation of a bone, under the loads of functional activities. The biocompression phenomena are also called, according to the authors, functional activity, mechanical stimuli, axial compression, load transmission or dynamization.
In fact, this biocompression has been stated to be an essential feature in fracture healing, which requires not only stability, which is not osteogenic in itself, but also physiologic biocompression. In fact, when a bone is loaded, it undergoes a deformation (strain) and at the same time, internal forces opposing this deformation (stresses) are built up.
Elastic deformations occur when the original shape is recovered once the deforming load is removed. External fixators have consequently to be considered both from rigidity and stability points of view, the rigidity meaning the absence of elasticity .- -., ~
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, . :, ~33~29 and the stability being the limitation to elastic deformations.
To perform such a biocompression, a device is needed allowing a sliding movement parallel to the bone axis in such a way that the muscular contraction is converted, at the fracture focus between the bone fragm^nts, into a compression equal in magnitude and opposite to said contraction. The external fixator must cancel out any angular, lateral or rotational movement, while maintaining a sliding displacement in the direction of the longitudinal axis of the fractured bone.
In the known systems, the compression is virtually invariable and its magnitude entirely empirical.
Many models of external fixators are already known, of various mechanical forms but essentially having the same principles: a plurality of transfixing pins or studs, j inserted into each fragment of the fractured bone are unified externally relative to the bone by means of metal frames or `j bars. The joining bars are of two types, namely neutralizing bars and compression bars.
The neutralizing bars are metal bars, generally made of steel, in several dimensions and shapes, which are connected to the bone pins by means of various clamping devices in order to constitute a fixed unit.
The compression bars are formed of endless blockable screw devices which make it possible to apply a permanent interfragmental compression which is constant and substantially invariable. When the screw is blocked, the pressure applied is theoretically maintained constant within the period between - ~^ two adjustments made by the physician. Alternatively, springs ., ~ ,~, i,.

; ~, 133~29 or rubber bands are used instead of screws.
A fixation system described in the Spanish Patent No. 483.191 is based on the utilization of telescopic sliding bars, formed by a double tube in which the exterior is greater in diameter and with an internal diameter corresponding to the outside of the interior tube. In order to fasten each one of the telescopic bars to one of the two fragments of a fractured bone, a bar is provided parallel to the principal axis of the bone to produce an axial compression in the area of the fracture under muscular action. The fact that the muscle is never totally relaxed, even if the member is at rest, is therefore used since there exists a permanent contraction named muscular "tonus". In other words, the fracture is permanently submitted to various compressions being, from least to greatest importance:
- muscular "tonus" (when the member is at rest, including gravitational force), - muscular contractions due to movements, - static load (patient's weight) - dynamic loading when walking (depending on weight multiplied by acceleration), all these stimulations being natural ones (hence the notion "biology" from the prefix "bio") and non-mechanical, such as those ~rought about by compression bars.
In order to avoid any angular displacement and any rotation at the site of the fracture, two telescopic bars are generally used, fixed on each extremity of the transfixing pins, i.e. pins extending from both sides of the .. ..

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member. As the sliding axis is to be disposed parallel to the longitudinal axis of the bone, these bars are maintained by means of clamping devices such as orientable jaws or ball-and -socket joints.
French Patent FR-82.19809 (US-4,612,921)describes a functional attachment system for osteosynthesis by means of external fixators coupling the clamping devices of the transfixing studs inserted into the bone fragments, on each side of the fracture, by means of telescopically sliding bars acting as biocompressors. These bars are connected to the transfixing studs by means of jaws, ball-and-socket joints or other clamping devices, the compression mechanical stimuli at the focus, of physiological magnitude corresponding to the muscular tonus and variable with the ~unctional activity, the static load and the dynamic load being used as a functional attachment system.
That patent describes a system having several compression bars, in order to ensure rotational stability.
It is consequently disadvantageously cumbersome for the patient, since the fixation frame extends on each side of transfixing pins, i.e. on each side of the fractured member.
The present invention aims to provide a device whose magnitude of compression is variable in function of parameters such as muscular tonus ~at rest), muscular contraction (from movements), the individual load (static) and the dynamic load (walk and weight by acceleration). This external fixator furthermore is advantageously the sole connection between the groups of pins on each side of the . . .

5 ~331~29 64680-430 fracture, which reduces the weight and the nuisance of the device for the patient.
Furthermore the device should be able to be very rapidly installed and adjusted, which is very important since the installation is made under anaesthesia, whose duration would consequently be significantly reduced.
The invention provides an external fixator for maintaining longltudinal axial alignment of bone fragments comprising: a first ele~ent comprising at least one pin and a second element comprising at least one pin, sald at least one pin of said f irst element to be placed into a f irst bone fragment and said at leas$ one pin of said second element to be placed in a second bone fragment; a telescopic piece comprising, in a coaxial relationship with respect to a central longitudinal axis of said tele~copic piece, an internal bar and an external bar, said first element being rlgidly connected to and supported by said internal bar and said second element being rigidly connected to and s supported by said external bar, said first and second elements extending at an angle to said central longitudinal axis of said ~0 telescopic piece so that a force generated by the loading of said $irst and æecond elements by axial compression of said bone fragments causes a bending moment to develop between said first and second bar, said external bar having a generally hollow interior for receiving said internal bar, the telescoping action of said internal bar within said external bar extending over a predetermined distance; a roller sliding means disposed between said internal and external bars and extending in the longitudinal direction over at least said predetermined distance, said roller ., ,'''~
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6 ~ 3~29 64680-430 sliding means having a roller contact bearing having a multiplicity of rotatable elements spaced around the perimeter of engagement between said inner and external bars to provide support along all sides of the int2rnal and external bars for spreading the forces generated by said bending moment over the entire length and perimeter of said roller sliding means; and guiding means disposed between said internal and external bars longitudinally spaced from said roller sliding means along said central longitudinal axis, said guiding mean3 engaging at least one longitudinally extending flat surface formed on one of said bars, said flat surfaces extending in a plane parallel to the central longitudinal axis, sald at least one longitudinally extending flat surface including a stop surface for engaging a stop surface connected to the other of said bars for limiting the relative longitudinal movement therebetween.
The sliding means intended to reduce friction can be realised in different ways, for example, by means of a needle bearing for instance with a square section and constituted by a cage, each side of which is made of a æeparator presenting a succession of openlngs fitted to receive a needle each.
Alternatively, the roller lider means may be a ball bushing, fitted between two dirt scraper rings. This ball bushing is positioned between the movable bar and a guiding piece attached to the fixed bar.
; The accompanying drawings show, by way of example, two embodiments of the preæent invention. In the drawings:
F~gure 1 is a general side elevation view schematically showing a fixator according to a first embodiment, as well as the ''' C .

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6a ~ 3 .~ ~ 3 2 9 64680-430 anchoring means in the fractured bone.
Figures 2 and 3 are partially enlarged views of the fixator shown in Figure 1, respectively a slde and a top vlew.
Figure 4 i~ a longitudinal sectioned view of the same device, further enlarged in order to show its principal parts.
Figures 5, 6 and 7 are transverse sectional views ta~en respectively along the lines V-V, VI-VI and VII-VII in Figures 2 and 3 and respectively presenting the clamping device of one of the bars, the guiding means of the movable bar and the mounting tip.
Figure 8 is a perspective view of a second embodiment of the device according to the invention.
Figure 9 is a part-sectlonal vlew of the device of Flgure 8, who~e cover has been removed.
Figure 10 i8 a longitudinal section of the device ~, ,j ,~' ' ' ' :
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. ,,, , , , ' 133~9 of Fi~ures 8 and 9, whilst Fi~uxe 11 is a transverse sectional view, taken along the line XI-XI in Figure 10.
In the schematic view represented in Figure 1, a fractured ~one 10 is shown in two parts 11 and 12. In each of the bone parts, one can distinguish a succession of studs or pins 20.
More precisely there are in Figure 1 a first group of three pins 21 inserted into the part 11 and a second group of pins 22 inserted into the bone part 12.
Each group of pins 21 or 22 is maintained in a corresponding binding piece 31 or 32, for instance a tightener, each jaw of which presents grooves for positioning and clamping the pins 21 and 22. The binding pieces 31 or 32 further connect the bars 41 and 42 to bind the two groups of pins 21 and 22, through the agency of a telescopic member 50. It is of course possible to replace the binding pieces 31 or 32 by orientable sockets according to any specific use.
Figures 2 and 3 show the enlarged telescopic member 50, 'i1, with the precedingly described bars, the bar 41 being a fixed bar and the bar 42 a movable bar. The rear wall 51 of the member 50 is adapted to clamp the bar 41, whilst the front wall is closed by a tip 60, externally screwed on the member 50 and presenting an opening for the movable bar 42. It will be noted in Figure 3 that the bar 41 presents an angulation ~, generally ~-comprised between 20 and 90 beyond which the rear bar 43 is straight.
The rear wall 51 presents a transverse slot 52 and a - longitudinal slot 53 in order to create two wings 54 and 55, slightly deformable in order to allow the clamping of the bar 41.

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As visible in the sectional view of Figure 5, the wing 55 presents a threaded opening 56 perpendicular to the slot 53 and adapted to receive a screw 57, freely crossing a corresponding opening in the wing 54, the screw head of which screw leans on the bottom of a recess 58. It is to be noted that the screw 57 presents a square head in order to cooperate with a corresponding securing wrench, and the head is substantially on the same level as the member 50 when secured, hidden in the recess 58.
The bar 42 has a medium portion 44 of a diameter greater than that of the bar 42, with two longitudinal, parallel flat surfaces 45 as can be seen in Figure 6 and able to guide the movable bar, in order to prevent its rotation.
Coming back to Figure 4, it is to be noted that the rear portion 46 presents a central cylindrical opening 47, whose dimension is slightly greater than the diameter of the bar 41. The external diameter of t~e rear portion 46 is greater than the medium portion 44, in order to create an abutment 48.
Although the movable bar has been described in distinct portions 42, 44 and 46, in order to clarify the description, it is only one piece obtained by manufacturing or eventually soldering the distinct parts.
The rear portion 46 of the movable bar is destined to cooperate with a ball bushing 70 in order to facilitate the relative sliding between bars 41 and 42 and, more precisely, between the member 50, connected to the bar 41, and the bar 42.
The ball bushing 70 is insexted in a corresponding central . opening presenting an abutment 59 and is fixed between two dirt b~

,~,f;'," ' ' , ' ': ~ ' ~'r, 133~:~29 scraper rings 71 and 72.
The ball bushing furthermore cooperates with a guiding member 80 constituted b~ a cylindrical piece limited on one frontal face by a collar 81, whose diameter is greater than that of the cylindrical member 80. The collar 81 is adapted to abut on the member 50, while the cylindrical member 80 is engaged in the central opening of the member 50. The collar 81 presents a slot 82 whose width corresponds to the distance between the two longitudinal flat surfaces 45 of the medium portion 44 of the movable bar. The guiding member 80 is connected to the member 50 through two openings 83 adapted to cooperate with corresponding projections of the member 50.
The guiding member 80 is fixed in the member 50 by means of a tip 60, to be externally screwed on the member 50.
The tip 60 has a circular opening 61 for the passage of the medium portion 44 of the movable bar. It furthermore presents two opposed holes 62 and 63 destined to receive two pins of a securing wrench in order to clamp together the different parts mentioned above.
In order to limit the weight of the fixator, the member 50, its tip 60 and the guiding member 80 will be made from a light metal, for instance aluminum, alloy.
To ensure the rigidity of the device, the movable and fixed bars 41 and 42 will prefexably be of stainless steel.
It is to be noted that all these materials are able to resist sterilization conditions.

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'~,, ~ ', ' 1~31~29 In the embodiment shown in Figures 8 to 11, there are a fixed bar 141 and a movable bar 142 having a medium portion 144 with a square section and whose dimension is greater than the diameter of the bar 142, in order to slide with respect to the member 150 and its top 160. This top presents two lateral lips 161 and 162 adapted to cooperate with two corresponding recesses in the member 150 (Figure ll).
It will be noted that the medium portion 144 presents a graduated scale 145 in order to measure the relative movement. Although this scale was not mentioned in the first embodiment described, that embodiment may of course be fitted with that scale also.
The second embodiment essentially distinguishes in the fact that the medium portion 144 of the movable bar is of ~ square cross-section. This portion is adapted to slide in a i needle bearing 170 constituted by a square prismatic casing, each side of which is made of a separator presenting a succession of rectangular openings 171 each fitted to receive I~ a nee~le 172. The medium portion 144 of the movable bar j 20 presents a central opening 147 adapted to receive the fixed ij bar 141 and its abutting plate 148.
, The needle bearing 170 is disposed in a corresponding recess 159 in the member 150 as shown in Figure 9, where the cover 160 is removed. It is to be noted that the member 150 is generally U-shaped, one end of which is closed by a fixed wall 151 and the other by a plate 180 having a square central opening 181 for the square bar 144. The ' ~"~, " ~

1 33~32~

cover 160 is adapted to slide along the member 150 and may be fixed to same by means of a screw 163 inserted into a corresponding recess 155 in the fixed wall 151. The fixed bar 141 is made solid with the mem~er 150 by means of a screw 1~7 cooperating with the tapping 156 therefor provided in the wall 151~
In the drawings the needle bearing 170 presents a square section. ~ithout going beyond the scope of the present invention, the section may differ and be replaced by another polygonal shape, for instance triangular, quadrangular or hexagonal.
The fixed bar 141 and the movable ones 142, 144 are generally made of stainless steel although other alloys are possible too, such as Cr-Co-Mo or titanium alloys, which have good mechanical properties and a relatively low weight.
~ The separators constituting the casing 170 may be i realised in plastic materials such as high density polyethylene, ^ nylon, polytetrafluoroethylene or others, provided the physical properties are appropriate and that they are resistent to sterilization temperatures in saturated steam up to 140C.
As already mentioned, the external fixator is - to be installed during an operation under anaesthesia.
Therefore it is particularly advantageous to have available a mounted telescopic member in order to reduce the duration of the anaesthesia.
In the example of Figures 8 to 11, the square bar 144 surrounded by its needle bearing 170, is arranged in the recess - :
. , ~331329 159 in the member 150. The lateral lips 161 and 162 of the cover 160 are slid along the corresponding recesses in the member 150, ana the cover 160 is fixed to the member 150 by means of the screw 163 passed through the opening 156 for the clamping screw 157 and inserted into the corresponding tapping 155. The front plate 180 is fixed by any known means, and the fixed bar 141 is clamped by means of the screw 157.
In the embodiment shown in Figures 2 to 7, the ball bushing 70 with its two lateral scraper rings 71 and 72, is arranged around the rear portion 46 of the movable bar and engaged in the member 50 against the abutment 59 of the central opening. The guiding member 80 is placed around the medium portion 44 of the movable bar, in order to prevent any rotation of the movable bar 42 with respect to the member 50, as the longitudinal flat surfaces 45 are aligned in the corresponding slot 82. The tip 60 is mounted and fixed by means of a special securing tool having two pins adapted to be introduced into the corresponding holes 62 and 63.
It is to be noted that, in any embodiment, the telescopic device, when mounted, is adapted to allow sterilization treatments.
According to any particular use, the length and the shape of the fixed bar 41 will be chosen with respect to the bone for which the device is used and to the distance at which the pins are inserted in the bone fragments.
During the operation, the process of putting the device in place is as follows. The physician first inserts the .':

~33~329 pins 21 and 22 into the bone fragrnents 11 and 12, on each side of the fracture. He then adjusts the telescopic member 50 or 150 parallel to the direction of the principal axis of the fractured bone 10, by means of the binding pieces 31 and 32.
To be sure that the compression displacement is parallel to the longitudinal axis of the fractured bone, the physician secures the fixed bar 41 or 141 within the rear wall 51 or 151 of the telescopic member 50 or 150, by turning the screw 57 or 157 in the corresponding tapping 56 or 156.
Coming back to Figure 3, showing a bar 41 with an angulated rear portion 43, one notes that the alignment between the telescopic member and the fractured bone is easily obtained by rotating the telescopic member.
The compression movement is limited when the end of the fixed bar 41 abuts against the central opening 47 of the movable bar and the extension movement is limited by means of the abutment 48 with the guid~ng member 80.

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Claims

1. An external fixator for maintaining longitudinal axial alignment of bone fragments comprising:
a first element comprising at least one pin and a second element comprising at least one pin, said at least one pin of said first element to be placed into a first bone fragment and said at least one pin of said second element to be placed in a second bone fragment;
a telescopic piece comprising, in a coaxial relationship with respect to a central longitudinal axis of said telescopic piece, an internal bar and an external bar, said first element being rigidly connected to and supported by said internal bar and said second element being rigidly connected to and supported by said external bar, said first and second elements extending at an angle to said central longitudinal axis of said telescopic piece so that a force generated by the loading of said first and second elements by axial compression of said bone fragments causes a bending moment to develop between said first and second bar, said external bar having a generally hollow interior for receiving said internal bar, the telescoping action of said internal bar within said external bar extending over a predetermined distance;
a roller sliding means disposed between said internal and external bars and extending in the longitudinal direction over at least said predetermined distance, said roller sliding means having a roller contact bearing having a multiplicity of rotatable elements spaced around the perimeter of engagement between said inner and external bars to provide support along all sides of the internal and external bars for spreading the forces generated by said bonding moment over the entire length and perimeter of said roller sliding means; and guiding means disposed between said internal and external bars longitudinally spaced from said roller sliding means along said central longitudinal axis, said guiding means engaging at least one longitudinally extending flat surface formed on one of said bars, said flat surfaces extending in a plane parallel to the central longitudinal axis, said at least one longitudinally extending flat surface including a stop surface for engaging a stop surface connected to the other of said bars for limiting the relative longitudinal movement therebetween.

2. An external fixator according to claim 1, wherein external bar presents a central tubular opening whose dimension is greater than the diameter of the internal bar.

3. An external fixator according to claim 2, wherein said opening is cylindrical.

4. An external fixator according to claim 1, wherein at least one of said bars presents a graduated scale.

5. An external fixator according to claim 1, wherein said roller sliding means comprises a needle bearing.

6. An external fixator according to claim 5, wherein internal and external bars are square in cross section and said needle bearing presents a square cross section.

7. An external fixator according to claim 6, wherein said needle bearing comprises a prismatic casing, each side of which is made of a separator presenting a succession of openings fitted to receive a needle each.

8. An external fixator according to claim 7, wherein said needles are made of steel.

9. An external fixator according to claim 7, wherein said separators are made of plastics.

10. An external fixator according to claim 1, wherein said roller sliding means comprises a ball bushing.

11. An external fixator according to claim 10, wherein said ball bushing is fitted between two scraper rings.