| Trapezal or trapezo-metacarpal implant -> Monitor Keywords |
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Trapezal or trapezo-metacarpal implantRelated Patent Categories: Prosthesis (i.e., Artificial Body Members), Parts Thereof, Or Aids And Accessories Therefor, Implantable Prosthesis, Bone, Joint Bone, Wrist, Hand (e.g., Finger, Etc.)Trapezal or trapezo-metacarpal implant description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070123993, Trapezal or trapezo-metacarpal implant. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The present invention relates to a trapezal or a trapezo-metacarpal implant, comprising a stem terminating in a head. The stem is adapted to be inserted in the metacarpus of the thumb, and the head to be disposed in a space obtained particularly by removing all the trapezium, in the case of a trapezal implant, or a portion of the trapezium, in the case of a trapezo-metacarpal implant. [0002] The implant according to the invention can be used to treat rhizarthritis, a very frequent affliction consisting in an arthritis of the base of the thumb, essentially trapezo-metacarpal. STATE OF THE ART [0003] There exist several types of trapezal and trapezo-metacarpal implants. [0004] Among the most widely known are the so-called Swanson trapezal implant, constituted by a stem terminating in a head, the entirety made of silicone. In this implant, the head has a suitable size and shape to replace all the trapezium. [0005] This implant has two principal drawbacks: [0006] the material from which it is made is unsuitable: silicone gives rise in certain patients to an allergy known as siliconite; moreover, because of its insufficient hardness, the silicone wears in contact with the adjacent bones, giving rise to deterioration of the implant; [0007] it is not stable and, in particular, has a tendency to dislocate, fully or partially; FIGS. 1A, 1B and 1C show a trapezal implant 1, whose stem 1a is mounted in the metacarpus 2 and the head 1b completely replaces the trapezium; in FIG. 1A, the implant is normally positioned relative to the adjacent bones and particularly relative to the scaphoid 3 with which it is in contact; FIG. 1B shows a typical configuration of partial dislocation of the implant during a pinching effort involving the thumb and at least one other finger of the hand; FIG. 1C shows a typical arrangement of full dislocation of the implant after such a pinching effort. [0008] So as to increase the stability of this implant and avoid partial dislocation as shown in FIG. 1B or full dislocation as shown in FIG. 1C, it has been proposed to perforate its head from one side to the other so as to pass therethrough a tendinous tongue adapted to limit its movements, or to ligate it. These techniques complicate the task of the surgeon and limit the mobility of the implant, causing trouble for the patient. [0009] Another solution is described in the article entitled "L'implant trapezien de Swanson dans le traitement de l'arthrose peri-trapezienne" ("The Swanson trapezal implant in the treatment of peri-trapezal arthritis"), by Y. Allieu et al., which appeared in the review "Annales de Chirurgie de la Main" ("Annals of Surgery of the Hand"), Volume 3, No. 2, 1984. It consists in first carrying out an oblique cut at the proximal end of the metacarpus, and fixing the implant in the varus position, which is to say fixing it in an inclined manner relative to the axis of the metacarpus by orienting it inwardly of the hand, as shown in FIG. 2. Thus inclined, the implant is held in contact with the scaphoid, and has less tendency to dislocate. This solution thus significantly improves the stability of the implant. Nevertheless, fixing the implant in an inclined manner relative to the axis of the metacarpus requires providing an oblique hole in the shaft of the metacarpus, a delicate surgical operation to perform, which requires hollowing out the hard peripheral portion of the bone and which moreover renders this latter fragile. [0010] There are also known trapezo-metacarpal implants, such as the Swanson condylar implant, whose head is to be disposed in the space provided on the one hand by forming a cut on the proximal end of the metacarpus and on the other hand by removing a portion of the trapezium opposite this proximal end. These implants are also made of silicone. A titanium version of the Swanson condylar implant however has been proposed. [0011] In the same way as for the Swanson trapezal impant, the material from which these trapezo-metacarpal implants are made is unsuitable. As previously explained, silicone is too soft. As for titanium, it is too hard and wears the bones with which it is in contact. It also makes the implant painful for the patient. [0012] Moreover, these implants have a relatively thick and narrow head, adapted to be disposed in a cavity of matching shape previously formed in the trapezium. This co-action between a thick and narrow head and a deep and narrow cavity gives stability to the implant--which is the intended purpose--because the head is retained in the cavity, but does not take account of the anatomical curvature of the trapezo-metacarpal articulation, which is suitable for ample relative movements between the trapezium and the proximal end of the metacarpus. By way of illustration, FIG. 3 shows the Swanson condylar implant with its stem 5a inserted in the metacarpus 2 of the thumb and its head 5b disposed in a deep and narrow cavity in the trapezium 6. The small radius of curvature of the surface portion of the head in contact with the trapezium, made necessary by the thickness and narrowness of the head, limits the angular swing of the implant, which hinders movements of the thumb. OBJECTS AND SUMMARY OF THE INVENTION [0013] The present invention seeks particularly to provide a trapezal or a trapezo-metacarpal implant which will be at least as stable as the implants described above and which will be relatively easy to emplace. [0014] To this end, there is provided a trapezal or trapezo-metacarpal implant comprising a stem terminating in a head, the stem and the head being adapted respectively to be inserted in the metacarpus of the thumb and to be disposed in a space obtained particularly by removing at least a portion of the trapezium, the surface of the head being constituted by a base connected to the stem and adapted to rest on the proximal end of the metacarpus, a distal surface portion opposite the base and serving as a contact surface with the bone located facing the proximal end of the metacarpus, and a connection portion connecting the base and the distal surface portion of the head, characterized in that the distal surface portion of the head is inclined relative to a longitudinal axis of the stem by a predetermined angle, such that, when the head is mounted straight in the metacarpus, the distal surface portion of the head can be located in varus. Said bone facing the proximal end of the metacarpus is the scaphoid in the case of a trapezal implant, and the remaining portion of the trapezium in the case of a trapezo-metacarpal implant. [0015] Thus, according to the invention, the stability of the implant is given by the varus position of the distal surface portion of the head, as in the mentioned article by Y. Allieu et al. "L'implant trapezien de Swanson dans le traitement de l'arthrose peri-trapezienne" ("The Swanson trapezal implant in the treatment of peri-trapezal arthritis"). However, unlike this article, it is not the entire implant which is positioned in varus, but only a portion of the implant, including the distal surface portion of the head. [0016] The inclination of the distal surface portion of the head relative to the stem permits inserting the stem straight into the metacarpus, which is to say along the longitudinal axis of this latter. The stem can thus be placed exclusively in the soft central portion of the bone, which facilitates the work of the surgeon who does not have to cut into the hard peripheral portion. Such a positioning of the stem moreover avoids rendering the bone excessively fragile. [0017] There is no need, according to the invention, to ligate the implant or to pass a tendon through it. On the other hand, contrary to the trapezo-metacarpal implants of the prior art, the head can be wide and its distal surface portion can have a large radius of curvature corresponding substantially to the radius of curvature of the trapezo-metacarpal articulation. The head can also be flatter. The surgeon thus does not need to make a large cut on the proximal end of the metacarpus, nor to cut deeply into the trapezium, for which the removal of a small cap of large radius of curvature can suffice. [0018] The stability of the implant according to the invention can be further increased by designing this latter such that the distal surface portion of the head will be not only inclined but also offset relative to the longitudinal axis of the stem to the side of the implant where the angle between the distal surface portion of the head and the longitudinal axis of the stem is smaller. [0019] Preferably, at least the distal surface portion of the head is made of pyrocarbon. Pyrocarbon has a very good coefficient of friction with bone, which permits it to slide without adherence over the bones with which it is in contact and without giving rise to wear. In contrast to silicone, which is too soft, and titanium, which is too hard, pyrocarbon has a modulus of elasticity, also called Young's modulus, near that of bone. The reciprocal forces exerted on the implant and the neighboring bones thus distribute themselves evenly, thus reducing the risk of pain for the patient. BRIEF DESCRIPTION OF THE DRAWINGS [0020] In the accompanying drawings: [0021] FIGS. 1A, 1B and 1C, already discussed, show a portion of a hand in which has been implanted a trapezal implant according to the prior art, respectively in the rest position, in pinching position with the implant partially dislocated, and in pinching position with the implant fully dislocated, this portion of the hand being seen on the dorsal side, with the thumb and trapezo-metacarpal articulation in profile and the other fingers seen from above; [0022] FIG. 2, already discussed, shows, in the same type of view as that of FIGS. 1A, 1B and 1C, a trapezal implant according to the prior art mounted obliquely in the metacarpus of the thumb; Continue reading about Trapezal or trapezo-metacarpal implant... Full patent description for Trapezal or trapezo-metacarpal implant Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Trapezal or trapezo-metacarpal implant patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Trapezal or trapezo-metacarpal implant or other areas of interest. ### Previous Patent Application: Provisional orthopedic implant and recutting instrument guide Next Patent Application: Method and apparatus for reducing femoral fractures Industry Class: Prosthesis (i.e., artificial body members), parts thereof, or aids and accessories therefor ### FreshPatents.com Support Thank you for viewing the Trapezal or trapezo-metacarpal implant patent info. 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