TOTAL PHALANGEAL JOINT PROSTHESIS C 2308068
The present invention relates to the field of bone joint prostheses and more particularly concerns total prostheses for the joints between bones in the hand or foot.
By way of preferred application, the invention relates to a total prosthesis for the joint between the phalangeal bones and, more specifically, the metacarpophalangeal and/or interphalangeal joints.
The natural metacarpophalangeal and interphalangeal joints are subjected to intensive forces and wear, the result of which is a tendency towards wear or degradation, or to the onset of inflammatory disorders or chronic impairment.
is when the impairment or degradation reaches a degree incompatible with the function to be fulfilled by the joint, or with the joint pain which it induces, it is generally desired to operate on the joint surfaces in question in order, using a prosthesis, to try to provide an artificial substitute for the natural joint.
However, an operation of this type encounters difficulties due essentially to two reasons.
The first results from the presence, in this type of joint, of surfaces with little imbrication or congruence compared to that involving greater complementary shape imbrication, such as the coxofemoral joint.
The second is due to the fact that the congruent surfaces of-the bones in question have small dimensions and that it is therefore difficult and tricky to fit a prosthesis of the total type while respecting the need to take account of relatively large individual dimensional variations in view of the inherent dimensions of the bones and the natural requirement to leave, by means of the natural ligaments, a tension which is sufficiently taut to maintain the natural interaction ratio between the bone parts in question in order to avoid detrimental luxation.
With the aim of achieving the above objects, it should be mentioned that the prior art includes a proposal for a total phalangeal joint prosthesis in which the distal and proximal parts interact by means of a structural connec- tion which makes them interdependent. A connection of this type may be embodied by a transverse pin, by a ball joint, or by a fold when this is allowed by the constituent material of the pieces to be fitted.
These proposals for a total prosthesis with connected complementary pieces are not satisfactory for various reasons.
Prostheses with connected complementary pieces are not suitable for fitting as metacarpophalangeal prostheses, the anatomical structure of which involves a flexion degree of freedom combined with the possibility of abduction and adduction.
This twofold requirement cannot be met using a prosthesis with connected complementary pieces.
Irrespective of whether the connection involves a pin or a ball joint, connected prostheses require their relative bulk to be taken into account for installing them and require the practitioner to perform extensive resection of the distal part and of the proximal part of the constituent bones of the joint which is to be restored.
In view of the small surface area and the relatively short length of the bones in the foot or hand, extensive resection is difficult to perform suitably because of the insertion sites of the lateral ligaments which must 3 always be preserved in order for the functioning of the artificial joint to be adapted suitably to the function to be fulfilled.
Furthermore, when extensive resection of the epiphyseal parts is carried out, the practitioner has little if any safety margin to complete adaptation which is moreover compromised and needs or requires orientation or angulation adjustments.
Furthermore, connected total prostheses of this type also have a problem of functional complementarity, in particu lar with the extensor-flexor tendons for which free passage should be preserved.
A total prosthesis of the type which is connected by means of a fold could be considered not to give rise to all of the above drawbacks, but the nature of its constituent material is not capable of providing long- term reliable service because premature fractures have been known and may occur as a result of wear or. excessive functional loading.
Prostheses of this type furthermore have an imposed installation direction, so that the hinge fold which they include is arranged in close relation with the flexing plane of the joint, which raises the problem of preserving the integrity of the tendons and sheaths which fulfil the function of extending the constituent bones of the joints in question.
As a general rule, joints of the connected type are also provided with internal linings made of antifriction material, so as to facilitate the functionality of the art-ificial joint. Linings of this type further increa a the bulk of the joint, with the drawbacks which have been mentioned.
The object of the invention is to overcome the above - 4 drawbacks by providing a novel total phalangeal joint prosthesis, which is designed to include two installation pieces, respectively distal and proximal, Which have the characteristic of being free and not mutually connected, while having interacting parts with congruent surfaces, functionality of which is established by means of the natural ligaments and tendons.
The invention proposes characteristic technical means which are of the same nature for a so-called metacarpo- phalangeal total prosthesis or a so-called interphalangeal total prosthesis.
To achieve the above object, the total prosthesis according to the invention is characterized in that the interacting parts do not have means for structurally connecting them together and consist in the case of one of them, of a metal head which, on the opposite side from the stem, provides at least one convex surface for contact and sliding, and, in the case of the other, of a seat f or contact and sliding which is on a metal plate and provides a surface congruent with the convex surface of the distal piece.
Other characteristics will emerge from the description which is given below, with reference to the appended drawings which show embodiments of the invention by way of nonlimiting examples.
Fig. 1 is a schematic plan view of the skeleton of a hand, making it possible to demonstrate theintended application of the invention.
Fig. 2 is a half-elevation and half-section taken along the line II-II in Fig. 1.
Fig. 3 is a plan view taken along the line III-III in Fig. 2.
Fig. 4 is a transverse view taken along the line IV-IV in Fig. 2.
Fig. 5 is a cross-section taken along the line V-V in Fig. 2.
Fig. 6 is a transverse view taken along the line VI-VI in Fig. 2.
Fig. 7 is a cross-section taken along the line VII-VII in Fig. 2.
Fig. 8 is a view, partly in elevation and partly in cutaway section, corresponding to a general line VIII-VIII in Fig. 1 and illustrating another embodiment of the subject of the invention.
Fig. 9 is a section taken along the line IX-IX in Fig. 8.
is Fig. 10 is a transverse view taken along the line X-X in Fig. 8.
Fig. 11 is a section taken along the line XI-M in Fig. 8.
Fig. 12 is a transverse view taken along the line XII-XII in Fig. 8.
Fig. 13 is a cross-section taken along the line XIII-MII in Fig. 8.
In order to clarify the subject of the invention, Fig. 1 sho-ws a hand skeleton which, in conventional fashion, comprises the carpus 1, the metacarpus 2 and the phalanges 3.
The subject of the invention relates to a total prosthe- - 6 sis intended to be fitted as a replacement for the metacarpophalangeal or interphalangeal joints, which joints may, for present requirements, be grouped under the definition phalangeal joints.
For application to a metacarpophalangeal joint, as formed by the metacarpal bone 4 and the phalanx 5 of the middle finger 6, the total prosthesis according to the invention is of the type illustrated by Fig. 2.
The total prosthesis comprises a first, so-called distal (relative to the bone 4) piece or implant P, and a second, so-called proximal (relative to the phalanx 5) piece or implant P2.
As more particularly illustrated by the complementary f igures 3 to 5, the distal piece P, includes a stem 10 for engagement and immobilization inside the medullary cavity of the metacarpal bone 4. In cross-section, this stem 10 has an elliptical shape with a flat 11. In addition, the stem 10 may have a cross-section which increases from a so-called engagement tip 12 and may also include successive transverse grooves 13 intended to promote natural anchoring or anchoring by means of a cement.
Preferably, the stem 10 is also off-centred downwards relative to a reference plane p-p' and the flat is inclined diverging relative to this plane from the tip 12.
On the opposite side from the tip 12, the piece P, includes, secured to the stem 10, a metal head 14 which, on its opposite face from the tip 12, provides a surface 15 for contact and s--iding which is substantially produced in the form of a portion or a sector of a spherical cap, without this definition being intended in its strict geometrical meaning.
The head 14 is formed by a kind of shield which has a constant small thickness and, relative to the horizontal plane p-p, (Fig. 2), forms a downward return 16 and an upward extension 17. The qualifications up and down 5 should be taken to mean relative to the line II-II in Fig. 1, according to which the hand which is illustrated is oriented so that the palm is directed horizontally while being turned downwards. The return 16 extends over an angular range such that its extreme part is substantially parallel to the plane p-p,, while the extension 17 rises so that its general plane, as illustrated by a dotdash line in Fig. 2, may be considered as substantially perpendicular to the plane p-p'.
The shield 14 is furthermore produced so that the contour delimiting the surface 15 presents two lateral recesses 18. reserved for passage of the lateral ligaments of the joint, as specified below, and a plane part 18. reserving passage for the flexor nerve. The shield 14 is furthermore produced so as to define, on the opposite side from the surface 15, an internal surface 19 which is concave but has substantially the same geometrical shape.
In the above application, the total prosthesis comprises, as mentioned before, the proximal piece P2 which also includes a stem 20 presenting substantially the same configuration as the stem 10 and having a progressively increasing elliptical cross-section with a flat 21 reserved for adaptation in the intramedullary cavity of the phalanx 5. The stem 20 includes a tip 22 reserved for this purpose and also has transverse grooves 23.
In contrast to the stem 10, the stem 20 is off-centred upwards relative to the plane p-p, while, like the stem 10,_ having a flat 21 which is inclined liverging from the tip 22 relative to the said plane.
On the opposite side from the tip 22, the stem 20 is 35 provided with a metal plate 24 which, via its surface on the opposite side from the tip 22, has a seat 25 providing a surface congruent to the surface 15. As can be seen from Figs. 6 and 7, the plate 24 has an elliptical geometrical contour whose centre passes through the flat 21, which is oriented in the same direction as the flat 11 of the distal piece P, The structural characteristic of the total prosthesis resides in the fact that, further to the property of adaptation to the anatomical form presented by the stems 10 and 20, the head 14 and the plate 24 are thin and are directly adapted so as to benefit from only simple resection of the congruent natural anatomical parts, principally formed by articular cartilages.
In this way, fitting a total prosthesis of the type described above consists in resecting the cartilage of the distal epiphysis of the metacarpal bone 4, so as if possible to leave the bone mass of this epiphysis and so as to give it a surface that can promote adaptation of the surface 19 of the shield 14. The distal piece is fitted after the medullary cavity has been drilled in order to allow engagement of the stem 10 which can be held in place with a suitable orientation that respects the direction of the top and bottom parts, on the one hand because of the particular shape of the stem 10, which is elliptical with a flat and, on the other hand, because of the shape of the surface 19, the shape of the shield 14, its position relative to the stem 10 and the surrounding return 16.
As regards the proximal part P2, it is then suf f icient to resect the proximal epiphysis of the phalanx 5 in order to define a bearing plane corresponding to the rear face of_the plate 24, which is preferably defined as perp i dicular to the plane p-p'. Resection is performed only over the thickness of the plate 24 and, after the medullary cavity has been drilled, the piece P2 can be engaged via the stem 20 whose particular shape defines 9 - the orientation of the proximal piece, so that the seat 25 is provided for interaction with the surface 15. The seat 25 and the surface 15 then constitute congruent parts which fulfil the function of an artificial joint, substituting for the natural joint.
Because the shield 14 and the plate 24 are thin, the required resection of the articular epiphyses is limited to a minimal value, so that it is possible to leave in place the lateral ligaments as well as the flexor and extensor tendons, the natural function of which can here be exercised in order to keep the congruent surfaces 15 and 25 interacting with frictional contact, without luxation.
Because of the recesses 18. and the flat 18b, the functionality of the lateral ligaments and of the flexorextensor tendons is not impaired, so that interaction between the surfaces 15 and 25 can be established continuously during flexion from the maximum extension position as illustrated by Fig. 2.
Preferably, the pieces P, and P2 are made of a metal alloy which is suitable, in particular, for prostheses of this type, and have surface conditions for the shield and the plate which provide a uniformity and a polish which are beneficial to direct metal-on-metal contact.
By way of information, the metal alloy chosen is, for example, based on chromium-cobalt.
The total prosthesis described above is of the nonconnected type, given that the distal P, and proximal P2 pieces do not have means for structurally connecting them together and are kept cooperating via their congruent surfaces solely by the natural action of the ligaments and tendons of the joint which has been replaced.
There are many applications of a total prosthesis of this - 10 type in the event of damage to a metacarpophalangeal joint suffering from arthrosis or broken during an accident, or degraded by a disease such as rheumatoid polyarthritis.
Using the means described above, it becomes possible to fit a total prosthesis without entailing extensive resection of the opposing articular surfaces, without impairing the natural function of the ligaments and tendons, and while eliminating any risk of functional hazards which are ordinarily associated with the presence of a structural joint of the connected type.
By way of comparative indication, the total prosthesis described above can be fitted while entailing only a small resection thickness of the order of 2 mm in total, is while a connected prosthesis as known in the prior art requires resection by at least 10 mm.
There is a clear benefit in leaving as much as possible of the epiphysis of each constituent bone part of the joint, so as at least to preserve the natural functional nature of the tendons and ligaments, and also to afford the possibility of readaptation over time, if necessary.
In the intended application, the absence of a structural connection between the distal and proximal pieces presents the additional advantage of providing a joint with a possible potential for sliding which does not make the articular centre spatially fixed and consequently gives greater compatibility with the natural joint which satisfies such a characteristic of requiring several degrees of freedom.
Alt-ho-gh the functioning of the total prosthesis described above involves direct metal-on-metal contact between the congruent surfaces, it is in some cases not impossible to resort to interposing a film or a layer or a coating of plastic deposited suitably on one and/or the 11 - other of the congruent surfaces, this plastic being chosen from those which promote relative sliding between the congruent surfaces. A layer of this type may be provided in a relatively small thickness, given that the joint represented by the total prosthesis which is fitted is only very rarely and weakly subjected to a compressive stress.
Figs. 8 to 13 illustrate an alternative embodiment of the total prosthesis for a joint of the interphalangeal type, as illustrated in Fig. 1, formed by the proximal phalanx 35 and the middle phalanx 36 of the third finger 37. As in the previous example, the total prosthesis of this type comprises a distal piece P', and a proximal piece P',, relative to the middle phalanx 36.
is The distal piece P', is intended to be fitted starting from the distal epiphysis of the phalanx 35 and, for this purpose, comprises a stem 40 having a constant elliptically shaped cross-section with a flat 41. This crosssection is oriented so that the major axis is directed horizontally and corresponds to the plane p,-p', on which the stem 40 is centred such that the flat is parallel to the said plane.
The stem 40 includes an insertion tip 42 and on the opposite side therefrom, a head 44 consisting of a shield of constant small thickness providing a congruent surface 45 which includes a bottom part 46 and a top part 57, when considering the fitting direction as illustrated by Fig. 8 and which corresponds to an orientation of the hand such that the palm is situated horizontally and directed downwards. The shield 44 is connected to the stem 40 in such a way that, towards the tip 42, the bot_tom part 46 forms. type of return extending substantially parallel to the axis of the stem 40. This shield 44 is connected to the stem 40 by stiffening ribs or gussets 48.
0 12 - The congruent surface 45 defines two types of condyls 49 which have parallel axes and develop with a curvature directed substantially perpendicular to the plane p-p,. The curvature of the condyls is designed longitudinally and transversely so as to define an intercondylar space 49, between them.
The shield 44 is made of metal, for example an alloy such as chromiumcobalt, and preferably also forms an integral part with the stem 40.
The proximal piece P'2 comprises a stem 50 presenting an elliptical shape with a flat 51. This stem 50 furthermore has, starting from an end tip 52, a cross-section which increases progressively in the plane Pi-P'i, corresponding to the major axis of the ellipse. In addition, the stem 50 has grooves or incisions 53 which are intended to promote natural immobilization or immobilization by means of a fastening cement after fitting in the middle phalanx 36, as described below.
The stem 50 is also centred on the plane P-P' I, as is shown by Fig. 8, so that the flat 51 is parallel to the said plane.
on the opposite side from the tip 52, the stem 50 is provided with a plate 54, of rectangular general shape, the length of which is oriented parallel to the plane p, p'-. Via its face on the opposite side from the tip 52, the plate 54 defines a seat comprising two glenoid cavities 56 which have substantially parallel axes and are separated by a spine 57, the overall combination defining a congruence surface for interacting with the distal piece P',, as mentioned above.
The general transverse plane of the congruent surface of the plate 54 may, as illustrated by Fig. 8, be considered to be substantially perpendicular to the plane p,-p',. As in the previous example, the plate 54 is made of metal, 9 13 as the stem 50 preferably is, and in such a case an alloy of the chromium- cobalt type is advantageously chosen.
As shown by Fig. 9, the plate 54 and the shield 44 are thin, so that fitting a total interphalangeal prosthesis starting with the distal P',. and proximal P'2 pieces entails only minor resection of the articular surfaces of the distal epiphysis of the proximal phalanx and the proximal epiphysis of the middle phalanx, and makes it possible to retain the integrity of the lateral ligaments, which ensure constant interaction of the opposing congruent surfaces 55, 49 and 56, 49,.
As in the previous example, it is sufficient to perform minor resection of the cartilaginous surfaces for the distal epiphysis of the proximal phalanx 35 and for the proximal epiphysis of the middle phalanx 36, in order then to allow the medullary cavities to be drilled and to allow the distal P, and proximal P, pieces to be fitted.
The return 46 formed by the shield 44 is advantageously designed to protect the superficial flexor tendon, while allowing rotation of the middle phalanx relative to the proximal phalanx through an angular range of the order of 900, as allowed by the natural joint.
As in the previous illustrative embodiment, a choice may advantageously be made to keep metal-on-metal contact between the congruent surfaces 55, 49 and 56, 49,, even though a suitable plastic lining may be interposed on one and/or the other of these congruent surfaces.
As in the previous example, by means of the stems 40 and and by virtue of the form of the head 44 and the plate 54,_ the form of the distal P11 and proximal P' 2 pif,es allows oriented fitting without the risk of subsequent rotation in the proximal phalanx 35 and in the middle phalanx 36, irrespective of whether this fitting is carried out with or without imposing a connecting cement.
14 It is clear that the advantages attributed to the previous embodiment are also applicable to the interphalangeal total prosthesis embodiment because of the simila rity of the designs.
Although the invention was described above with reference to an application to the phalangeal joints in the hand, it must be borne in mind that it may also be applied to the corresponding joints in the foot.
The invention is not limited to the examples which have been described and represented, since various modifica tions may be derived therefrom within its scope.
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