FR3066101B1 - IMPLANT FOR SURGICAL ARTHROPLASTY COMPRISING TWO PIECES - Google Patents

Abstract

The subject of the invention is an implant for the field of surgical arthroplasty, comprising an articular surface (24) and a rear anchoring rod (50) providing an anchorage in the bone, characterized in that it comprises two discrete parts forming a resurfacing head (20) comprising the articular surface (24) and an anchor piece (40) comprising the anchor rod (50), each piece having a bearing face (22, 42) in contact on the other bearing face, these bearing faces (22, 42) comprising an assembly system comprising pins (32, 44) each fitting into a bore (30) of the other piece .

Description

IMPLANT FOR SURGICAL ARTHROPLASTY COMPRISING TWO PIECES

The present invention relates to an implant for the field of arthroplasty for performing surgical repair of joints, used in particular in orthopedics for arthroplasties of the toes.

Various known implant systems for toes relate to hemi-arthroplasties including the replacement of a damaged joint surface by means of an implant, or arthroplasties comprising the replacement of the entire damaged joint by means of several implants. These implants make it possible to treat in particular the following diseases.

The realization of a hemi-arthroplasty for the treatment of Freiberg's disease, on heads of the second or third metatarsal radius. The realization of a hemi-arthroplasty of the heads of the second, third or fourth metatarsal radius for the treatment of osteoarthritis, subluxations or trauma. Achievement of arthroplasties of the joints, in particular arthroplasties of metatarsophalangeal joints of the foot for the treatment of osteoarthritis or trauma.

Different types of surgical implants are known to perform these operations.

One type of implant known for arthroplasty, presented in particular in US-B1-6319284, comprises a proximal shaft implanting in the metatarsal, a distal stem implanting in the proximal phalanx, and a central area recreating mobility joint with a pivot connection using a stiffness of a specific flexible material.

This type of prosthesis nevertheless has long-term, fair results and significant complications.

Another type of implant known for a hemi-arthroplasty of the base of the phalanx, presented in particular by the document US-A1-20150250602, comprises a head with an articular surface resurfacing of the base of the proximal phalanx, disposing of the back of a rod for anchoring in the bone. The articular surface has a condyle-like concavity that articulates on the articular surface of the adjacent metatarsal.

Another type of implant known for a hemi-arthroplasty of the metatarsal head, presented in particular by US-A1-20100262254, comprises a head with articular surface of the metatarsal head, having a rod for anchoring in the the bone. The articular surface has a condyle-shaped convexity that articulates on the articular surface of the adjacent proximal phalanx.

Another type of implant known for a total arthroplasty of the joint, presented in particular by the document FR-A1-2858545, comprises a first element having a head with articular surface of the metatarsal head, equipped with a rear stem for its anchorage in the metatarsal, and a second element having a head with articular surface of the proximal phalanx, also equipped with a back rod for anchoring in the phalanx. Both articular surfaces adapt to optimize joint mobility.

For these last three types of implant the results are relatively good although many complications may appear a few years after implantation. Nevertheless, the prostheses for the realization of hemi-arthroplasties of the base of the phalanx and for the realization of total arthroplasties are generally adapted only to the first metatarsal ray.

In addition, these different types of implant essentially solve the problem of wear of the articular surface, with a surface adapted for the opposite articular surface, and an anchor rod disposed directly behind the head. The problem of primary holding in the bone of the anchor rod is relegated to the background, with various shapes of this rod including in particular a cylindrical or conical shape.

Another type of known implant, presented in particular in WO-A1-2010079288, comprises two parts, and an assembly between the head having the articular surface and an anchor comprising a conical interlocking.

However, this type of assembly poses special problems to ensure optimum hold between the two parts. In particular the machining of small diameter interlocking cones with tight tolerances proves complex. In addition, the retaining force of the assembly is very dependent on the tolerances of the different parameters of the two cones fitting one into the other.

The present invention is intended to avoid these disadvantages of the prior art.

It proposes for this purpose an implant for the field of surgical arthroplasty, comprising a joint surface and a rear anchor rod performing an anchoring in the bone, this implant being remarkable in that it comprises two separate parts forming a resurfacing head comprising the articular surface and an anchoring piece comprising the anchoring rod, each part having a bearing face coming into contact with the other bearing face, these bearing faces comprising a bearing system; assembly comprising pins each fitting into a hole in the other part.

An advantage of this implant is that the bearing faces and the pins each fitting into a hole in the other part, allow to form a precise and rigid assembly in all directions, which can have good resistance with simple and economical machining that does not require a very low manufacturing tolerance.

It is thus possible to precisely adapt each piece for its particular use, in particular their materials, the head intended for resurfacing the surface of the joint, and the rear rod having specific shapes providing an anchorage in the reliable bone. The implant according to the invention may further comprise one or more of the following features, which may be combined with one another.

Advantageously, the assembly system comprises two pins having parallel axes, a bore receiving one of these pins having an elongated cross section in a direction passing through the axis of the two pins. In this way, the machining accuracy of the distance between the axis of these two pins is overcome.

In particular, each support face may comprise a single pin.

Advantageously, an assembly pin comprises an annular groove receiving a resilient circular element which is also engaged in an internal groove of the bore receiving said assembly pin. By simple interlocking is obtained a resistant assembly which can be produced economically.

Advantageously, the anchor comprises around its bearing face a shoulder disposed before the anchor rod. This shoulder avoids a depression of the anchor in the bone.

Advantageously, the anchor rod comprises in side view after the shoulder a first triangular portion.

In this case, the anchor rod may include in side view after the first triangular portion, a second straight portion which terminates in a point.

Advantageously, the anchor rod has a rectangular cross section.

Advantageously, the resurfacing head is made of a metal alloy comprising chromium and cobalt.

Advantageously, the anchor is made of a titanium alloy.

Advantageously, the anchor rod comprises a coating based on titanium powder. Other characteristics and advantages of the invention will emerge on reading the description which follows, given solely by way of example, with reference to the following appended figures: FIG. 1 shows the bones of a foot having undergone one hemi arthroplasty of the head of the second metatarsal ray, with an implant according to the invention; - Figures 2 and 3 show the two parts of this implant respectively comprising a head and an anchor rod; - Figures 4, 5 and 6 show the head of this implant seen from the rear, from above and from the side respectively; - Figures 7 and 8 are views in axial section respectively of the assembly of the bore of the head and the rod assembly of the rod, for the assembly of the two parts; - Figures 9 and 10 are views in axial section showing two successive steps of the input of the assembly pin in its assembly bore; - Figure 11 shows a spring surrounding the assembly pin; - Figure 12 shows a side view and four cross-sectional views of the anchor rod along the cutting planes A-A, B-B, C-C and D-D; and - Figure 13 shows three head sizes and three sizes of anchor rod compatible with each other.

For the sake of clarity, identical or similar elements are marked with identical reference signs throughout the figures.

FIG. 1 shows a right foot successively comprising the second toe, a metatarsal 2, a proximal phalanx 6, a middle phalanx 8 and finally a distal phalanx 10.

The head of the metatarsal 2 has undergone a hemi-arthroplasty surgery, receiving an implant 4 having an articular surface coming into contact with a corresponding surface of the proximal phalanx 6.

FIGS. 2, 3 and 4 show a resurfacing head 20 having on the front side indicated by the arrow "AV" an articular surface 24, two flat and parallel lateral sidewalls 26, and a flat rear support face 22 fitting on a plane front face 42 of an anchoring piece 40.

The anchoring piece 40 comprises behind the bearing front face 42, an anchoring rod 50 which gradually tapers towards the rear, intended to be implanted in the bone.

The bearing front face 42 of the anchor piece 40 comprises in a vertical median plane a cylindrical assembly pin 44, which fits into a main bore 30 disposed in the middle of the rear bearing face 22 of the resurfacing head 20.

The rear bearing surface 22 of the resurfacing head 20 has above its assembly piercing 30 an angular wedge pin 32 having a reduced diameter and length relative to the assembly pin 44, which adjusts in a setting bore 52 of the bearing front face 42 of the anchor piece 40.

Each lateral flank 26 of the resurfacing head 20 comprises in its central part a notch 28 inclined at 30 ° with respect to the flat bearing face 22, forming a recess at the same time on this lateral flank and on the rear face of FIG. support 22.

FIG. 5 shows a top view of the transverse radius RI of the articular surface 24, which is centered on a point lying on the main axis X of the locking pin 32.

Figure 6 shows in side view the sagittal radius R2 of the articular surface 24, which is centered slightly above the axis of the main bore 30.

The radii R1, R2 of the articular surface 24 are intended to be slightly smaller than the corresponding rays of the phalangeal base, to fit perfectly in the sagittal plane and in the transverse plane with a surface in significant contact.

In view from above, the radius RI is connected to the lateral flanks 26 by a small connecting radius 34. In side view the radius R2 ends on the top by a flat portion 36. By way of example, the transverse radius R1 may be 10mm and sagittal radius of 8.5mm. The thickness E of the resurfacing head 20 in the transverse plane may be 10 mm, and the height H in the sagittal plane of 16 mm.

The articular surface 24 undergoes a mirror polishing in order to reduce the coefficient of friction, to limit the fatigue of the cartilage facing and avoid wear over time may cause joint pain. Advantageously, the polishing has a roughness Ra of 0.05.

The material of the resurfacing head 20 has good tribological properties with the opposite bone cartilage, while being bio-compatible and implantable in the long term. In particular, a chromium-cobalt alloy can be used according to the standards ISO 5832-12 and ASTM F1537.

Figures 7 and 8 show the assembly pin 44 comprising starting from the front, a slightly conical front shape with a small bending, then an annular groove 46, and finally a cylindrical shape 48.

The assembly piercing 30 of the resurfacing head 20 has an inner annular groove 60.

FIG. 11 shows a helical spring 70 wound so as to fit in a toric volume, which fits both on the annular groove 46 of the assembly pin 44, and in the inner groove 60 of the assembly bore 30.

When assembled by pressing the resurfacing head 20 on the anchor 40, the conical front shape of the assembly pin 44 facilitates its insertion into the assembly bore 30, and then as shown in FIG. 9, is introduced in the toric spring 70 to compress it radially outwards.

In parallel, the wedge pin 32 of the resurfacing head 20, comprising an inlet chamfer at its end, penetrates into the wedging hole 52 of the anchoring piece 40.

Continuing the assembly as shown in FIG. 10, the toric spring 70 descends into the annular groove 46 while relaxing its turns, which forms a robust tear-resistant assembly, maintaining the two bearing faces 22, 42 of the two elements. in support of one another.

Advantageously, the wedge bore 52 comprises an oblong shape elongated radially in a direction passing through the axes of the pins 32, 42, having a width adjusted to receive the diameter of the wedge pin 32 in order to ensure precise angular wedging of the head of the resurfacing 20 relative to the anchor piece 40. This radially elongated shape has a height to overcome a precise manufacturing tolerance between the axes of the wedge pin 32 and the assembly pin 44.

The disassembly of the resurfacing head 20 in the event of error or of surgical revision, can be done with a pull on this head in order to compress again the toric spring 70. Advantageously to obtain a safety of operation, the resistance to the tearing is at least 50N.

Disassembly of the resurfacing head 20 is done with a clamp having jaws of pointed shape, which are positioned between the two bearing faces 22, 42 by fitting into the inclined notches 28 of this head to guide them, then sliding between these faces to separate them by applying a sufficient pulling force.

Figure 12 shows the anchor rod 50 having the front side after a transverse shoulder 80 surrounding the front support face 42, a rectangular cross section which is gradually reduced.

The anchoring rod 50 has successively a generally triangular front portion disposed in succession between the cutting planes AA and BB, then after a small connecting bend on the lower face ending at a first transverse plane 52, a substantially straight intermediate portion extending to a second transverse plane 54, and finally a final portion tapering slightly to the cutting plane DD, which then terminates in a point.

The anchoring rod 50 has a top view successively the front part with strongly tightening sides, then the intermediate portion which is straight, and finally the final part is tightened slightly to the end to finish with a small width . The intermediate portion and the end portion facilitate the insertion of the anchor rod 50 into the medullary canal of the bone.

The anchoring rod 50 also has the advantage by its rectangular section, to allow a peripheral cortical support which also blocks the rotational movements around its main axis. The transverse shoulder before 80 makes it possible to avoid a depression of the anchoring rod 50 during its implantation, or a migration into the metatarsal under the effect of physiological constraints. The transverse shoulder 80 has in particular a thickness of 0.5 mm, and a rectangular base having a width of 7 mm and a height of 10 mm. The anchor rod 50 may in particular have a length of about 25 mm.

The upper face of the anchoring rod 50 has an inclination α of 15 ° with respect to the plane perpendicular to the front support face 42, which corresponds to the angle of attack of the metatarsals with respect to the ground.

The long-term holding of the anchoring piece 40 is facilitated by the use of a material having a modulus of elasticity closest to that of the bone, which is for the cortical bone of about 15GPa, while providing sufficient mechanical strength. Advantageously, a titanium alloy of the "TA6V" type is used according to ISO 5832-3 and ASTM F136.

In this way reduces the risk of bone resorption caused by the mechanical stress of the implant on the bone at the anchor rod 50, also called "stress shielding" in English.

Advantageously, a coating is provided on part or all of the anchoring rod 50 to optimize the resistance in the bone by promoting osseointegration, but also to facilitate withdrawal in case of failure of the operation. In particular, this coating can be applied to the proximal half of the anchor rod 50. In particular, a coating comprising titanium powder according to ISO 13179 having a thickness of between 50 and 150 μm can be produced.

FIG. 13 shows three anchoring pieces 40 with various anchor rods 50, all having a front bearing face 42 and an identical assembly system, making it possible to adapt to three resurfacing heads 20 having various dimensions. In this way, according to the characteristics of the foot of the patient, it is possible to choose independently both the size of the anchoring rod 50 and that of the surface of the articulation 24.

Claims (11)

1. Implant for the field of surgical arthroplasty, comprising a joint surface (24) and a rear anchor rod (50) providing an anchorage in the bone, characterized in that it comprises two separate parts forming a head resurfacing device (20) comprising the articulating surface (24) and an anchor piece (40) comprising the anchor rod (50), each part having a bearing face (22, 42) coming into contact with the another bearing face, these bearing faces (22, 42) comprising an assembly system comprising pins (32, 44) each fitting into a bore (30, 52) of the other piece. 2. Implant according to claim 1, characterized in that the assembly system comprises two pins having parallel axes (32, 44), a bore (52) receiving one of these pins (32) having an elongated cross section in a direction passing through the axis of the two pins (32, 44). 3. Implant according to claim 1 or 2, characterized in that each bearing face (22, 42) comprises a single pin (32, 44). 4. Implant according to any one of the preceding claims, characterized in that an assembly pin (44) comprises an annular groove (46) receiving a resilient circular element (70) which is also engaged in an internal groove (60). ) of the bore (30) receiving said assembly pin (44). 5. Implant according to any one of the preceding claims, characterized in that the anchor (40) has around its bearing face (42) a shoulder (80) disposed before the anchor rod (50). . 6. Implant according to claim 5, characterized in that the anchor rod (50) comprises in side view, after the shoulder (80) a first triangular portion. 7. Implant according to claim 6, characterized in that the anchor rod (50) has in side view after the first triangular portion, a second straight portion which terminates in a point. 8. Implant according to any one of the preceding claims, characterized in that the anchor rod (50) has a rectangular cross section. 9. Implant according to any one of the preceding claims, characterized in that the resurfacing head (20) is made of a metal alloy comprising chromium and cobalt. 10. Implant according to any one of the preceding claims, characterized in that the anchor (40) is made of a titanium alloy. 11. Implant according to any one of the preceding claims, characterized in that the anchor rod (50) comprises a coating based on titanium powder.