Metacarpal rod anchor for a trapezometacarpal prosthesis

Abstract

In one embodiment, the present invention is an anchoring rod that is elongated and tapered, the rod extends from a distal end toward a proximal end, the shape including a palmate side, a dorsal side and lateral sides, is the shape being flared on its palmate side without flaring on its dorsal side and flares on its lateral sides so as to form a flared proximal portion, said flared proximal portion having a substantially trapezoidal cross-section, with a dorsal face larger than the palmate face.

Claims

1. A metacarpal anchoring rod, particularly for a trapezo-metacarpal prosthesis, comprising an elongated and tapered shape extending from a distal end toward a proximal end, the shape including a palmate side, a dorsal side and lateral sides, the shape being flared on its palmate side without flaring on its dorsal side and flares on its lateral sides so as to form a flared proximal portion, said flared proximal portion having a substantially trapezoidal cross-section, with a dorsal face larger than the palmate face, wherein the lateral faces include grooves formed within the lateral faces, each groove delimiting, on its side turned toward said distal end, a steep wall flank, generally perpendicular to a longitudinal axis of the anchoring rod and, on its side turned toward said proximal end, an inclined wall flank; wherein a distal portion includes a boss with a rounded shape positioned on the palmate side.

2. The rod according to claim 1, wherein said palmate face has a curvature extending from an area near its distal end up to the edges of its proximal end.

3. The rod according to claim 2, wherein the shape has a rounded boss on its palmate side, in proximity to its distal end.

4. The rod according to one of claim 1, wherein the proximal side of said flared proximal portion includes more than one rounded ridge situated between the dorsal, palmate and lateral faces.

5. The rod according to claim 4, wherein the rounded ridges which separate each lateral face and the palmate face rejoin one another on the palmate side of the anchoring rod, such that said palmate face has, seen in cross-section, a rounded shape on the proximal side of said flared proximal portion.

6. The rod according to claim 1, wherein each lateral face includes two grooves at its flared proximal portion, and another groove at its distal portion.

7. The rod (4) according to one of claim 1, further comprising a porous bone inducing covering.

8. A set of modular elements allowing the constitution of a trapezo-metacarpal prosthesis including an anchoring rod according to one of claim 1, wherein: said anchoring rod includes an assembly cavity provided in its proximal end, this cavity having a slightly conical principal portion and a groove which extends radially from the principal portion of the assembly cavity; said set of elements includes a first articulation part capable of being assembled to this anchoring rod to constitute a metacarpal element of a first type, this first articulation part including a spherical articulation head and an assembly pin of slightly conical shape, capable of being accommodated in said principal portion of the assembly cavity and to be retained in this principal portion by wedging; said set of elements includes a second articulation part capable of being assembled to said anchoring rod to constitute a metacarpal element of a second type, forming an anatomical articulation surface and including an assembly pin having a slightly conical principal portion and a rib extending radially from the principal portion of the assembly pin, the principal portion and rib of the assembly pin being designed to be received respectively in said principal portion of the assembly cavity and in said groove which forms said cavity, and said principal portion of the assembly pin being intended to be retained in said principal portion of the assembly cavity by wedging.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a view in exploded perspective;

(2) FIG. 2 is a side view of an anchoring rod which includes this prosthesis;

(3) FIG. 3 is a view of this anchoring rod from the dorsal side of said rod;

(4) FIG. 4 is a view of this anchoring rod at the end, by the proximal end of said rod; and

(5) FIG. 5 is a view of the anchoring rod similar to FIG. 2, after placement of this rod in the first metacarpal.

DETAILED DESCRIPTION

(6) FIG. 1 shows a trapezo-metacarpal prosthesis 1 including a metacarpal element 2 and a trapezium element 3.

(7) The metacarpal element 2 is formed by the assembly of an anchoring rod 4 and an articulation part 5.

(8) The metacarpal element 2 is designed to be anchored to the first metacarpal 100 by insertion of the rod 4 into the marrow channel of this first metacarpal 100, as can be seen in FIG. 5. The rod 4 has, to this end, between its proximal end 4p and its distal end 4d, an elongated and tapered shape.

(9) As is visible on FIGS. 2 to 4, from this distal end 4d to this proximal end 4p, the rod 4 flares on its palmate side P without flaring on its dorsal side D, and flares on its lateral sides L. It thus forms a flared proximal portion offset on the palmate side P, which has a substantially trapezoidal cross-section, with a dorsal face that is larger than the palmate face, the two lateral faces of this portion consequently converging one toward the other in the direction of the palmate side P, as can be seen in FIG. 4.

(10) The ridges separating the dorsal face and the lateral faces, as well as the ridges separating the palmate face 6 and the lateral faces, are rounded at the proximal side of said proximal flared portion, see FIG. 4; the rounded ridges which separate each lateral face and the palmate face 6 rejoin each other on the palmate side P of the rod 4, such that said palmate face has a rounded section on this proximal side of said flared proximal portion.

(11) The palmate face 6 has moreover a curved shape from an area near the distal end 4d to the edges of the proximal end 4p, as shown in FIG. 2.

(12) The anchoring rod 4 also shows a rounded boss 7 on its palmate side P, located in proximity to its distal end 4d, and grooves 8 provided in its lateral faces, with a wolf teeth profile (see FIG. 3). Each groove 8 thus delimits, on its edge turned toward the distal end 4d, a steep wall flank 19, more or less perpendicular to the longitudinal axis of the anchoring rod 4, and on its side turned toward the proximal end 4p, an inclined wall flank 18.

(13) The anchoring rod 4 also includes a cavity 9 provided in its proximal end 4p, to assemble it to the articulation part 5. This cavity 9 is formed by a slightly conical principal portion and by a groove extending radially from this principal portion, on the dorsal side of the rod 4 in the example shown.

(14) The anchoring rod 4 also includes, outside of its proximal face, a porous bone-inducing covering, accomplished by projecting particles of titanium onto it by means of a plasma torch.

(15) The articulation part 5 includes a spherical articulation head 11 and a pin 12 of slightly conical form, this pin 12 being designed to be received in said principal portion of the cavity 9 and retained in that principal portion by wedging, so as to accomplish the assembly of the articulation part 5 into the anchoring rod 4 and to thus form the metacarpal element 2.

(16) The trapezium element 3, for its part, is constituted by a cup having on the outside anchoring ribs into the trapezium bone and forming interiorly an articulating cavity, designed to accommodate the head 11.

(17) In practice, as shown by FIG. 5, the anchoring rod 4 is pushed into the sponge-like bone of the first metacarpal 100 up to complete engagement of its flared proximal portion into the proximal end of this bone. In this position, this flared proximal portion is in adequacy with this proximal end of the first metacarpal, and the dorsal face of the rod 4 extends along the dorsal cortical bone and the curved palmate face 6 has a large support on the endo-cortical, ensuring a perfect seat of the rod 4 in the marrow channel of the first metacarpal 100. On the distal side, the boss 7 impresses itself into the sponge-like bone, thus accomplishing, in combination with the aforementioned shape of the rod 4 and with its aforementioned steep wall flanks, an anti-ejection function for that rod.

(18) Once the rod 4 is in place on the first metacarpal 100 as shown in FIG. 5, the articulation part 5 is put in place on the rod 4 so as to constitute the metacarpal element 2 of the prosthesis 1, by insertion of the pin 12 into the cavity 9, then the head 11 is engaged in the cavity of the trapezium element 3, put in place on the trapezium bone.

(19) It should be noted that the elements 3, 4, 5 are part of a set of elements including, besides several sizes of rods 4, a second articulation part forming an anatomic articulation surface, that is, reproducing more or less the shape of the native articulate surface(s), as a saddle; this second articulation part includes an assembly pin having a slightly conical principal portion, capable of being accommodated and wedged in the principal portion of the cavity 9, and a rib extending radially from this principal portion, capable of being engaged in the groove that this cavity 9 forms. The adequate angular mounting of said second articulation part with respect to the anchoring rod 4 is thus ensured.

(20) Said assembly of elements thus makes it possible to form, as desired, including during the operation, either a prosthesis of the guided type as shown in the figures, by the use of the articulation part 5, or a prosthesis of the anatomical type, by the use of said second articulation part.

(21) As shown by the foregoing, the invention provides a metacarpal rod, particularly for a trapezo-metacarpal prosthesis, which has, with respect to the homologous rods of the prior art, the determinant advantages of having a perfect seat in a metacarpal, to have a low tendency to ejection out of said bone, and to allow the adequacy of numerous articulated interfaces.