FR2763835A1 - Carpometacarpal implant - Google Patents

Abstract

The implant consists of a shank (1) with a collar (12) and a projecting tip (11), lengthwise fins (135) beneath the collar to prevent the shank rotating about its lengthwise axis, and a head (2) with a lengthwise hole (21) to receive the tip with a clearance. The implant incorporates a ring (3) of a supple elastomer material, preferably polyurethane, which fits between the head and the collar and has the tip passing through it. The upper end of the shank, adjacent to the collar, is toothed to prevent lengthwise movement. A ligament (40) of a synthetic material, e.g. polyester, is fitted between the collar and the top of the shank. More convenient to fit and giving improved joint movement.

Description

Carpometacarpal implant
The present invention relates to a carpometacarpal implant to replace a defective joint or bone in the hand, particularly in the thumb between the scaphoid and the first metacarpal.

 The choice of therapeutic methods applicable to peritrapézienne osteoarthritis remains very wide. One of the essential characteristics of the interventions that can be proposed must be good long-term reliability, which obviously all interventions do not bring for sure.

 If the ligamentoplasties could bring in the immediate indolence and the stability in the préradiologic forms of the osteoarthritis, their long-term future is not as favorable as the promoters might have initially thought.

 Trapezometacarpal arthrodeses pose the long-term problem of overloading the neighboring trapezo-scaphoid and metacarpophalangeal joints. The adjustment of the fusion position also remains a difficulty and a compromise as well as that of the very fusion of the joint.

Some marginal indications for trapeziometacarpal arthrodesis still appear to remain.

This is the case of post-traumatic arthritis, in young subjects, in particular force workers for whom there is no reliable arthroplasty over time.

 Prosthetic replacements by coupled prostheses which can bring brilliant results in the short term, do not seem to be immune to more or less early mechanical type setbacks, such as loosening, trapezium fracture or dislocation of the implant, and as such, should see their indications reduced or at least limited as regards the usual osteoarthritis of the subject of middle age.

 Simple trapezectomies provide indolence. Their major shortcoming is the slowness of the operative suites, the lack of residual strength and the inevitable shortening of the thumb. Changes in the dynamics of the thumb column associated with this process may also be poorly tolerated.

A complete artificial trapezium replacement, in particular of the SILASTIC type, whether it is a complete implant with or without an intramedullary tail, placed after a total trapezectomy, or a partial implant of the KESSLER type or
ASHWORTH-BLATT provide immediately, at the cost of a rigorous technique, a painless thumb retaining good mobility and good stability.

 These implants present a major risk which is that of wear of the materials, with the consequences of synovitis or peripheral reactions to foreign bodies. The progressive decentering of the implant by asymmetrical wear or by destabilization seems to favor the risk of occurrence of these complications. Therefore, this type of arthroplasty seems abandoned mainly because of the insufficient resistance of the material, the complications can be formidable in the medium term and the therapies to be brought to it extremely difficult.

 The present invention aims to remedy the drawbacks of the aforementioned known carpometacarpal implants. More particularly, the invention aims to provide a carpometacarpal implant by means of which an arthroplasty of the base of the thumb transforms a trapezo-metacarpal and sometimes scapho-trapezoid-trapezoid arthritis painful and stiff joint into a painless and mobile joint without this lead to a shortening of the thumb or a reduction in the gripping and gripping forces as is regularly the case with the other known arthroplasties.

 To this end, a carpometacarpal implant for the hand comprising a tail having a collar, a stud projecting from the collar along a longitudinal axis of the tail, and a longitudinal portion extending behind the collar and supporting means for preventing a rotation of the tail around the longitudinal axis, and a head comprising a longitudinal hole for partially receiving the stud, comprises a flexible washer which is crossed by the stud and located between the head and the collar.

 The washer is made of elastomer, preferably polyurethane, and the nipple is housed with a slight clearance, typically a few tenths of a millimeter in the head hole, so that the head has an angular movement of the order of 50 relative to to the longitudinal axis of the tail, as in the carpometacarpal connection in the thumb, and the relative thrusts of the scaphoid and the first metacarpal towards each other are damped between the head and the collar.

 The implant of the invention replaces a pathological trapezoid and in particular the bearing surfaces thereof in contact with the scaphoid, the trapezoid and the first metacarpal. The materials of the implant have a high resistance and surface states which are durably resistant to frictional forces. The damping produced by the intermediate washer between the tail flange and the head reduces the rigidity of the implant of the invention and thus limits, for the purpose of long-term tolerance, the stress peaks which are always harmful to the residual cartilage on which the implant is in support.

 The means for preventing rotation of the tail may include at least one rib rising in a plane substantially diametrical to the nipple. For example, two triangular ribs are crossed on longitudinal faces of said longitudinal portion, under the collar, and are completely embedded in biocompatible cement during the implantation of the tail, preventing any axial rotation of the latter.

 According to another characteristic of the invention, the implant comprises means for preventing a longitudinal translation of the tail towards the head, so that the tail remains linked to the first metacarpal.

According to a first embodiment, the means for preventing a longitudinal translation of the tail comprises transverse slots extending successively longitudinally to said longitudinal portion, for example located on one or two opposite longitudinal faces of said longitudinal portion. According to a second embodiment which can be combined with the first embodiment for more efficiency, the means for preventing a longitudinal translation of the tail comprises frustoconical teeth extending successively longitudinally on one end of said longitudinal portion, which end may be itself even tapered.

 Preferably, the head is cylindrical, substantially similar in shape to the trapezoid bone to be replaced, and has a countersink, cylindrical or frustoconical, to partially receive the washer and thus keep the washer centered under the head.

The hole in the second element may have a height at most substantially equal to the difference in height of the stud and the washer.

 The head may include a recess substantially in a spherical cap in a face of the head opposite to that in contact with the washer so that the head is in sliding contact with the distal capsule of the scaphoid.

 According to another characteristic of the invention, a plastic ligament has strands applied against a shoulder between the collar and the longitudinal portion and is added to strengthen and stabilize the connection between the assembly of the implant with tail, head and puck with the first metacarpal bone and the scaphoid. More specifically, the ligament may comprise a loop, bypassing the large palmar muscle, from which the strands extend to be applied substantially diametrically opposite against said shoulder, substantially parallel to the aforementioned ribs, and have crossed portions substantially against the head. , with ends saturated with the scaphoid capsule.

Other characteristics and advantages of the present invention will appear more clearly on reading the following description of several preferred embodiments of the invention with reference to the corresponding appended drawings in which
- Figure 1 is a partial schematic front view of the skeleton of a right hand
- Figure 2 is an exploded front view, partially in axial section, of a carpometacarpal prosthetic implant according to the invention
- Figure 3 is a side view of the prosthetic implant assembled according to the invention
- Figure 4 is a palmar front view similar to Figure 1, after total dissectomy of the trapezium and partial trapezoid of the hand of Figure 1, showing a loop of a stabilizing ligament associated with the prosthetic implant of invention
- Figure 5 is a palmar front view partially in axial section of the prosthetic implant implanted in the first metacarpal and in place of the trapezium of the hand shown in Figure 1
and
FIG. 6 is a side view of the implant already implanted as in FIG. 5.

Figure 1 shows the relative arrangement of the bones of a right hand between the carpus and the metacarpus, in the thumb PO and the index finger IN. Thumb
PO, the trapezius bone T, also called "trapezium", is located between the scaphoid SC and the first metacarpal
M1. At the level of the index IN, the trapezoid bone TR, also called "trapezoid" 11, is located between the large bone
GO and the second metacarpal M2. The trapezoid T and the trapezoid TR are joined in the second row of the carpus of the hand. In FIG. 1 is also represented the large palmar muscle GP which extends from the epitrochlea of the humerus to the second metacarpal M2.

 As shown in Figures 2 and 3, a carpometacarpal prosthetic implant according to the invention essentially comprises first and second rigid monolithic elements 1 and 2 made of metal, such as titanium, or else of resistant plastic, such as polyethylene, and an intermediate part 3 in flexible damping material such as certain elastomers, for example a polyurethane. The first element is a distal "metacarpal" tail 1 to be implanted in the first metacarpal. The second element is a trapezoidal proximal cylindrical head 2 to replace the trapezoid. The intermediate piece is a washer 3 located on the tail and under the head. These three elements have symmetrical profiles with respect to a longitudinal trapezoid-metacarpal axis YY '. As will be seen below, the implant also comprises a stabilizing ligament 4 made of synthetic material, such as polyester.

 The tail 1 essentially comprises a centering pin 11, a collar 12 and a longitudinal portion 13-14 extending successively in the trapezoido-metacarpal direction along the axis YY '.

 The centering stud 11 is smooth cylindrical to penetrate with a small clearance of a few tens of millimeters into a blind cylindrical hole 21 of the head 1 through the washer 3. The internal diameter of the washer 3 is equal to the diameter of the stud 11. The circular collar 12 has an external diameter substantially equal to that of the head 2 and somewhat greater than the external diameter of the washer 3. The collar 12 constitutes a support base for the washer and has a diameter typically of about 13 mm.

 The longitudinal portion 13-14 of the tail 1 comprises an intermediate antirotation and antitranslation portion 13 and a distal antitranslation portion 14.

 The intermediate portion 13 has a generally parallelepiped shape with an almost square cross section completely inscribed in the contour of the flange 12, and arises from the flange 12, opposite the centering stud 11.

Each of two narrower parallel sides of this intermediate portion 13 is crenellated longitudinally and has, according to the illustrated embodiment, four transverse linear slots 131 to 134 which are equally distributed longitudinally from the flange, and the first 131 of which forms an underlying lateral shoulder with the collar. On the other two sides of the intermediate portion 13 project perpendicularly two median ribs 135 in a right triangle whose short sides are diametrically opposite under the flange 12 and whose long sides are parallel to the axis YY '. The two ribs 135 are substantially inscribed in an equilateral triangle, two sides of which are substantially collinear with the hypotheses of the ribs and one diametrical side of which is collinear with the short sides of the ribs.

 The distal antitranslation portion 14 of the tail is substantially conical, with a proximal base located substantially at the distal vertices of the triangular ribs 135 and an angle at the distal vertex of a few degrees, typically about 5.

On this distal portion 14 of the tail is provided a frustoconical serration which comprises, according to the illustrated embodiment, seven frustoconical teeth 141 spaced apart longitudinally. The teeth 141 have an apex angle of about 20 to 250 and each converge in a distal direction, towards the axis YY '. As a variant, the distal tops of the ribs 135 are extended in the teeth 141 so as to facilitate the machining of the sides of the portion 13 from which the ribs are raised.

 Approximately depending on the size of the tail adapted to the physiology of the hand where it is to be implanted, the distribution of the three portions 11, 12, 13 and 14 with respect to the length of the tail is as follows: at most 1 / 4 approximately in tail length of the order of 30 to 35 mm for the centering pin 11 and the flange 12, between 1/4 and 1/3 approximately in tail length for the intermediate portion 13, and at most 1 / About 2 of tail length for the distal tapered portion 14.

 The proximal head 2 comes from the machining of a cylindrical solid metal part in which the blind cylindrical hole 21 is made to receive with play the centering pin 11 of the distal tail 1. The depth of the hole 21 is substantially equal to half -height of the head and substantially greater than the difference in the heights of the centering pin 11 and of the washer 3, as shown in FIGS. 5 and 6.

 In the distal face of the head 2 located opposite the tail flange 12, a shallow counterbore 22 is provided at the mouth of the hole 21 for sliding therein a short proximal portion of the washer 3. The washer 3 and the counterbore 22 are substantially frustoconical and complementary, the washer having a large base applied to the flange 12.

 A concave recess 23 is made in the proximal face of the head 2 to conform to the contour of the distal capsule of the scaphoid SC. The axial height of the recess 23 is 1 to 2 mm.

 The height of the head 2 with the washer 3 embedded in the counterbore 22 and the diameter of the head are approximately equal to those of the pathological trapezoid T to be replaced, respectively.

The thickness of the washer 3 is approximately 2 mm, 1 mm of the latter being housed in the counterbore 22, and the height of the head 2 is approximately 10 mm.

 The carpometacarpal implant of the invention is implanted in the following manner.

 Previously, the pathological trapezium T, weakened or fragmented, is approached externally or palmar. A dissectomy of the trapezium releases an interosseous space EO between the scaphoid SC and the first metacarpal M1, in front of the trapezoid TR, as shown in Figure 4. Then a partial dissectomy of the trapezoid TR, on the side of this one facing the trapezoid, enlarges the interosseous space EO up to below the large palmar muscle GP, as appears by comparing Figures 1 and 4, so as to subsequently accommodate the proximal head 2.

Then we remove the osteophyte
OT which developed at the periphery of the capsule of the first metacarpal M1, in particular near the proximal end of the second metacarpal M2, and at a partial dissection of the large palmar GP. The bone parts which have thus undergone a dissectomy are hatched in FIG.

 Referring now to Figures 5 and 6, the medullary canal of the first metacarpal M1 is hollowed out of the cancellous bone by means of a tool having a square section rod with a pointed end, of length, typically 28 mm, somewhat greater than that of the longitudinal tail portion 13-14. The rotation of a discoid base of the rod having four sectors with radial cutting edges, like a milling cutter, and adjustable in position along the rod prepares a flat bearing surface SA for the flange 12 of the distal tail 1 on the proximal capsule of the first metacarpal M1, substantially orthogonal to the medullary canal.

 Then by means of a frustoconical rasp, the medullary canal is shaped into a medullary cavity Cv intended to accommodate a test tail having a profile analogous to the tail 1 of the carpometacarpal implant according to the invention. When the medullary cavity CV inside the first metacarpal M1 is substantially larger than the volume occupied by the tail 1, the medullary cavity CV is filled with a biocompatible cement CM. The portions 13 and 14 of the tail i supporting the washer 3 applied against the collar 12 and the head 1 self-centered on the stud 11 are immersed in the soft cement CM contained in the cavity Cv until the collar 12 is applied to the bone support surface SA, the cement thus being compressed between the longitudinal portion 13-14 and the wall of the bone cavity CV. The ribs 135 are oriented substantially parallel to the palmar and dorsal sides of the hand. After hardening of the cement, the ribs 135 stabilize in rotation the tail 1 around the axis YY '; the transverse slots 131 to 134 and the tapered teeth 141 offer crevices in intimate contact with the cement CM which prevent any translation of the tail, and in particular any withdrawal of the tail 1 from the cavity CA in the direction of the head 2.

During the sealing of the tail 1 in the metacarpal medullary cavity CV, the synthetic ligament 4 is passed behind the large palmar GP to form a loop 40 in front of the resected side of the trapezoid
TR. From the loop 40 arise strands of the ligament which run against the shoulders formed by the first slots 131 between the flange 12 and the anti-rotation and antitranslation portion 13, substantially parallel to the ribs 135. Intermediate sections 41 and 42 of the strands are thus embedded in the CM soft cement under the collar 12.

Then after having exerted a traction on the ends of the ligament strands in the direction of the head 2 so as to tighten the collar 12 and the large palmar GP, end sections 43 and 44 of the ligament strands are stretched and crossed against the cylindrical periphery of the head 2, approximately halfway up the latter, as shown in FIG. 6.

Portions of the strands between the sections 41, 42 and 43, 44 and of the ends 45 and 46 of the strands are sutured respectively on the proximal capsule of the first metacarpal M1, on or near the bearing surface SA of this leveled capsule, and on the periphery of the distal capsule of the scaphoid SC.

 Ligament 4 thus reinforces -iF the joint which is located between the first metacarpal M1 and the scaphoid SC. The implant of the invention functions in a similar manner to the joint at the level of the thumb and the palm of the hand, thanks to the sliding of the distal capsule of the scaphoid SC over the spherical recess 23 of the head 2 and by virtue of the damping washer 3 which can more or less be compressed particularly towards the palmar face or the dorsal face of the hand following a slight tilting of the head 2 of approximately 50 relative to the axis YY 'of the stud 11.

 The use of synthetic stabilizing ligament 4, biologically well tolerated and rehabitable, definitively stabilizes the joint.

The peripheral stabilization provided by the ligament is an integral part of the concept of replacement arthroplasty with the cushioned implant to avoid the defects of force so often encountered in the aftermath of other surgical procedures.

 In total, the cushioned and stabilized implant attempts to correct most of the faults of the other processes used in reconstructions of destroyed joints at the base of the thumb.

The implementation of the implant of the invention cushioned by ia washer 3 and stabilized in particular by the ligament 4 overcomes the disadvantages of the implants of the prior art described above
- by maintaining or providing physiological mobility at the base of the thumb
- by avoiding the shortening of the thumb and the mechanical troubles of the coupled prostheses
- the materials of the implant elements are reliable both for their long-term resistance and for their friction capacities; pathology due to wear debris is thus avoided; and
- the damping properties provided to the implant by the flexible washer limits the stresses on the residual scaphoid cartilage.

Claims (13)

 1 - Carpometacarpal implant comprising  - a tail (1) having a collar (12), a stud (11) projecting from the collar along a longitudinal axis (YY ') of the tail, and a longitudinal portion (13-14) extending behind the flange and supporting means (135) for preventing rotation of the tail about the longitudinal axis (YY '), and  - a head (2) comprising a longitudinal hole (21) for partially receiving the stud,  characterized in that it comprises a flexible washer (3) which is crossed by the stud (11) and located between the head (2) and the flange (12).  2 - Carpometacarpal implant according to claim 1, wherein the washer (3) is made of elastomer, preferably polyurethane.  3 - Carpometacarpal implant according to claim 1 or 2, wherein the stud (11) is housed with play in the hole (21).  4 - Carpometacarpal implant according to claims 1 to 3, wherein the hole (21) in the second element (2) has a height at most substantially equal to the difference in height of the stud (11) and the washer (3).  5 - carpometacarpal implant according to any one of claims 1 to 4, wherein the means for preventing rotation of the tail comprises at least one rib (135) standing in a plane substantially diametrical to the stud (11).  6 - Carpometacarpal implant according to any one of claims 1 to 5, comprising means (131-134, 141) for preventing a longitudinal translation of the tail (1) towards the head (2).  7 - carpometacarpal implant according to claim 5 or 6, wherein the means for preventing a longitudinal translation of the tail comprises transverse slots (131-134) extending successively longitudinally to said portion (13-14).  8 - Carpometacarpal implant according to claim 6 or 7, wherein the means for preventing a longitudinal translation of the tail (1) comprises frustoconical teeth (141) extending successively longitudinally on one end (14) of said longitudinal portion.  9 - carpometacarpal implant according to any one of claims 1 to 8, wherein the head (2) is cylindrical.  10 - carpometacarpal implant according to any one of claims 1 to 9, wherein the head (2) has a countersink (22) to partially receive the washer;).  11 - Carpometacarpal implant according to any one of Claims 1 to 10, in which the head (2) has a recess (23) substantially in a spherical cap in a face of the head opposite to that in contact with the washer (3) .  12 - Carpometacarpal implant according to any one of claims 1 to 11, comprising a ligament made of synthetic material (4) having strands (41, 42) applied against a shoulder (131) between the flange (12) and the longitudinal portion (13 14).  13 - carpometacarpal implant according to any one of claims 1 to 11, comprising a ligament made of synthetic material (4) comprising a loop (40) from which strands (41, 42) are applied substantially diametrically opposite against a shoulder (131) between the flange (12) and the longitudinal portion (13-14), and have portions (43, 44) crossed substantially against the head (2).