|Número de publicación||US20070123993 A1|
|Tipo de publicación||Solicitud|
|Número de solicitud||US 11/645,503|
|Fecha de publicación||31 May 2007|
|Fecha de presentación||27 Dic 2006|
|Fecha de prioridad||12 Dic 2001|
|También publicado como||DE60235116D1, EP1453443A1, EP1453443B1, US7182787, US20050119757, WO2003049651A1|
|Número de publicación||11645503, 645503, US 2007/0123993 A1, US 2007/123993 A1, US 20070123993 A1, US 20070123993A1, US 2007123993 A1, US 2007123993A1, US-A1-20070123993, US-A1-2007123993, US2007/0123993A1, US2007/123993A1, US20070123993 A1, US20070123993A1, US2007123993 A1, US2007123993A1|
|Inventores||Michel Hassler, Cecile Real, Jean-Pierre Pequignot, Yves Allieu|
|Exportar cita||BiBTeX, EndNote, RefMan|
|Citada por (19), Clasificaciones (26), Eventos legales (1)|
|Enlaces externos: USPTO, Cesión de USPTO, Espacenet|
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.
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.
There exist several types of trapezal and trapezo-metacarpal implants.
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.
This implant has two principal drawbacks:
So as to increase the stability of this implant and avoid partial dislocation as shown in
Another solution is described in the article entitled “L'implant trapézien de Swanson dans le traitement de l'arthrose péri-trapézienne” (“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
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.
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.
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,
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.
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.
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 trapézien de Swanson dans le traitement de l'arthrose péri-trapézienne” (“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.
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.
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.
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.
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.
In the accompanying drawings:
The implant according to this first embodiment is a trapezo-metacarpal implant, in the general form of a nail. It comprises a stem 10 terminating, at a so-called proximal end, in a head 20 and whose opposite end, called the distal end, is constituted by a point 101.
Stem 10 is adapted to be inserted in the metacarpus of the thumb, and the head 20 to be disposed in a space obtained on the one hand by providing a cut or resection on the proximal end of the metacarpus and on the other hand by removing a portion of the trapezium facing the proximal portion of the metacarpus.
The head 20 has a flattened shape. Its longitudinal section is circular. Its surface is constituted by an annular and plane base 201 connected to the proximal end of the stem 10 and adapted to rest on the proximal portion of the metacarpus, a distal surface portion 202 opposite the base 201 and serving as a contact and friction surface with the remaining portion of the trapezium, and a rounded and annular lateral edge 203 connecting the distal surface portion 202 to the base 201. Among the surface portions 201, 202 and 203, only the distal portion 202 is liable to be in contact with the remaining portion of the trapezium. The distal surface portion 202 has a convex shape, and preferably consists in a spherical cap.
The stem 10 comprises a truncated conical portion 102 whose smaller diameter end is connected to the point 101 and larger diameter end is prolonged by a divergent connecting portion 103 connecting the base 201 of the head 20 to the truncated conical portion 102 of the stem 10.
According to the invention, the distal surface portion 202 of the head 20 is inclined relative to a longitudinal axis 104 of the stem 10 by a predetermined angle α, which is to say that the mean plane 204 tangent to the distal surface portion 202 forms with the longitudinal axis 104 of the stem 10 an angle β=90°−α different from 90°. In the embodiment shown in
The diameter D of the head 20 and the radius of curvature R of the distal surface portion 202 are selected to be sufficiently great to match as much as possible the anatomical curvature of the trapezo-metacarpal articulation. Typically, the implant according to the invention is designed in four different sizes. In each of these sizes, the ratio between the diameter D of the head, measured along a longitudinal axis of the head inclined relative to the longitudinal axis 104 of the stem in the same direction as the distal surface portion 202 and by an angle equal to the angle α, and the length L of the stem, measured along the longitudinal axis 104 of the stem between the distal end 101 and the point of intersection I between the plane 205 defined by the base 201 and the axis 104, is preferably equal to at least 0.84. The ratio between the radius of curvature R of the distal surface portion 202 and the length L of the stem is preferably equal at least to 0.6.
The thickness E of the head can be relatively small. Typically, the ratio between the thickness E of the head 20, measured perpendicularly to the base 201, and the length L of the stem, is at most equal to 0.42.
Preferably, the distal surface portion 202 of the head 20 is not only inclined, but also offset relative to the longitudinal axis 104 of the stem 10 to the side of the implant where the angle between the distal surface portion 202 and the axis 104 is smaller, which is to say the side designated in
In the example shown in
The implant according to the invention, constituted by the stem 10 and the head 20, or at least the distal surface portion 202 of the head 20, is preferably made of pyrocarbon. According to a preferred variant, the implant is constituted by a graphite substrate clad with a layer of pyrocarbon.
An oblique varus cut is provided in the proximal end 2 a of the metacarpus 2 and a portion of the trapezium 6 located facing this proximal end 2 a is removed, to provide a space adapted to accommodate the head 20. Then a straight hole is formed in the shaft of the metacarpus, along the longitudinal axis 2 b of this latter. The stem 10 of the implant is then force-fitted into the hole until the inclined base 201 of the head 20 comes into contact with the inclined surface 2 a of the metacarpus, such that the head 20 will be disposed in the mentioned space, in a varus position.
The stem 10 of the implant is thus positioned straight in the central soft portion of the metacarpus, delimited in
As in the first embodiment, the distal surface portion 202 a is preferably offset relative to the axis 104 a of the stem to the side C1.
The ratios indicated above between the diameter D of the head and the length L of the stem, and between the radius of curvature R of the distal surface portion of the head and the length L of the stem, also hold true for this second embodiment. On the other hand, the thickness of the head is necessarily greater.
When it is emplaced in the patient, this implant rests on a straight cut previously provided in the proximal end of the metacarpus, and not on an oblique cut as in the first embodiment.
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|Clasificación de EE.UU.||623/21.11|
|Clasificación internacional||A61F2/42, A61F2/00, A61F2/30|
|Clasificación cooperativa||A61F2230/0006, A61F2002/4258, A61F2002/30299, A61F2/4241, A61F2002/30616, A61F2/30767, A61F2230/0069, A61F2230/0052, A61F2230/0067, A61F2310/00173, A61F2310/00574, A61F2002/30878, A61F2002/30174, A61F2310/00161, A61F2002/30113, A61F2002/4276, A61F2230/0093, A61F2/4261, A61F2002/30224, A61F2002/3021|
|Clasificación europea||A61F2/42W, A61F2/42H|
|27 Dic 2006||AS||Assignment|
Owner name: BIOPROFILE, FRANCE
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:HASSLER, MICHEL;REAL, CECILE;PEQUIGNOT, JEAN-PIERRE;AND OTHERS;REEL/FRAME:018744/0044
Effective date: 20040624