Resorptive intramedullary implant between two bones or two bone fragments

Abstract

The invention relates to a resorptive intramedullary implant between two bones or two bone fragments. The implant includes a single-piece body (1) having a generally elongate shape and having, at each end, areas for anchoring to the bone portions in question, characterized in that one of said areas (A1) has a cylindrical cross-section while the other area (A2) has a flat cross-section.

Description

FIELD OF THE INVENTION

The invention relates to the technical field of orthopedic implants, particularly for arthrodesis and osteosynthesis.

More particularly, the invention relates to an intramedullary implant for arthrodesis between two bone parts or osteosynthesis between two bone fragments, particularly in the case of the hand or foot.

BACKGROUND OF THE INVENTION

Different solutions have been proposed to achieve these functions.

For example, a solution comes from the teaching of patent application FR 2,884,406 [US 2008/0177262], of which the applicant of the present application is also the applicant. This patent describes an intramedullary osteosynthesis device constituted of an elongated body whose ends constitute anchor zones cooperating with the bone parts to be immobilized. The anchor zones are shaped and made of a material selected to enable insertion into the bone parts, then to ensure an anchor in the bone parts by preventing any rotational movement by resisting traction and by maintaining a compression force.

Another solution also comes from patent application FR 07.02003 [US 2010/0131014], also from the same applicant. This document describes an implant in the form of two anchor zones connected by a central zone and whose general shape is substantially inscribed in a very elongated rectangle of X-shape, so as to form in the anchor zones two legs adapted to move apart by elastic or shape-memory effect.

From this design, different criteria have been established to make the implant easy to place and efficient in order to create a primary and secondary stability for the osteosynthesis or arthrodesis site.

However, these solutions are not adapted for the case of an implant made of resorptive material.

BRIEF SUMMARY OF THE INVENTION

From this state of the art, the object that the invention proposes to attain is further improving the anchor and the stability of the implant as well as its adaptation to the morphology of the implantation site when the implant is made of resorptive material.

To solve such a problem, a resorptive intramedullary implant between two bones or two bone fragments has been designed and developed; it is constituted, in a known manner, of a single-piece body having a general elongated shape with, at each end, zones for anchoring to the bone parts being considered. According to the invention, one of the zones has a cylindrical shape, whereas the other zone is flat.

Advantageously, the implant is made of a resorptive material whose mechanical properties are determined to last the time necessary for the consolidation, so that the implant is resorbed after six months. For example, the implant is composed of lactic acid polymer or copolymer (PLA, PGA . . . ).

Considering the specific mechanical characteristics of resorptive materials, and to solve the given problem of improving anchor and stability, the cylindrical cross-section is threaded and tapers in the direction of its free end.

To solve the given problem of enabling a deformation by elasticity, thus causing an expansion adapted to the geometry of the site and to the properties of the material, the flat cross-section zone has, substantially in its median portion, an opening adapted to enable elastic deformation of the zone. The opening defines at least two anchor arms.

It therefore appears that the combination of a cylindrical and threaded anchor zone and a flat-sectioned anchor zone is particularly advantageous considering the problem to be solved.

To solve the given problem of resisting the shear and flexion forces susceptible of occurring in the area of the bone site, between the two anchor zones, the body has a central zone of transition adapted to resist the shear and flexion forces occurring in the area of the bone site and adapted to serve as an abutment.

From this basic design of the implant, the anchor zones are either coaxial or angularly offset by between about 1° and 30° and, advantageously, by 10°. The bend between the anchor zones is located so as to substantially correspond to an arthrodesis line of the bones being considered.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail hereinafter with reference to the attached drawings, in which:

FIG. 1 is a perspective view of the implant;

FIG. 2 is a front view of the implant before insertion into the bone part in question;

FIG. 3 is a side view corresponding to FIG. 2;

FIG. 4 is a view like FIG. 2 showing the position of the anchor arms of the flat section after insertion;

FIG. 5 is a perspective view of another advantageous embodiment of the implant;

FIGS. 6 and 7 show the installation of the implant into two bone parts.

DETAILED DESCRIPTION

The implant according to the invention has a one-piece body 1 of elongated shape and having a first proximal zone A1 and a second distal zone A2. The entire implant body is made of a resorptive material whose mechanical properties are determined for the implant to be resorbed in no less than about 6 months. In one embodiment, the implant is composed of lactic acid polymer or copolymer (PLA, PGA . . . ).

As will be described later in the description, the zones A1 and A2 have anchor formations for the respective bone parts. Taking into account the specific characteristics of the resorptive material and to attain the given object of anchor and stability, the zone A1 is of a cylindrical shape section whereas the other zone A2 is flat.

The zone A1 has a generally cylindrical outer surface 1a with a limited taper toward its free end. The surface 1a has a helical rib forming a screwthread 1a1.

The zone A2 is flat and has substantially in its center, an opening 1b adapted to enable elastic deformation of the zone A2. More particularly, the opening 1b defines at least two anchor arms 1c and 1d, each having at least one outwardly projecting tooth 1c1, 1d1.

Advantageously, between the two zones A1 and A2 the body 1 has a central zone C for transition adapted to resist shear and flexion forces that can occur at the end of a bone. By way of nonlimiting example, this median zone C can have a length of about 3.5 mm and a thickness of about 2 mm, for an overall implant length comprised between about 15 and 25 mm and a diameter of about 2 or 3 mm at the zone A1.

In the embodiment shown in FIG. 1, the two zones A1 and A2 are coaxial.

To solve the problem of adaptation to the shape of the implantation site, the anchor zones A1 and A2 can be offset at an angle α adapted to the geometry of the bone site. This angle α is comprised between about 1° and 30° and, advantageously, on the order of 10° when the implant is for foot arthrodesis (FIG. 5).

In this embodiment in which the two anchor zones are angularly offset, the bend is located so as to correspond substantially to the arthrodesis line of the bone parts being fused.

FIGS. 6 and 7 schematically show the positioning of the implant according to the invention between two bone parts O1 and O2. After suitable holes have been made in the bone by a rasp-type tool, the operator screws the thread 1a into the bone part O1 substantially up to step 2 of the median zone C providing a surface that, as shown, faces towards thread 1a in a direction parallel to a longitudinal axis defined by zones A1, A2 and serves as an abutment preventing the implant from sinking too deeply into the bone (see FIGS. 1, 5, 6, and 7). The operator then fits the second bone part O2 back onto the anchor arms 1d and 1c of the zone A2, the anchor arms then spread and tighten by elasticity (FIG. 7).

The operative technique can be the following:

• • Drilling of the two holes with a conventional drill;
  • Preparation of the holes with a rasp for the flat side and a bone tap to form the inner screw thread on the cylindrical side;
  • Use of a screwdriver with a gripper end;
  • Screwing in the cylindrical side P1 [A1] for an arthrodesis IPP of the foot;
  • Fitting of the bone back onto the flat side [A2] of the implant.

The advantages are readily apparent from the description; in particular, it is to be emphasized and understood that the combination of the two anchor zones A1 and A2 of cylindrical and a flat shape, respectively, significantly enhances anchor and stability of the implant adapted to the geometry of the bone site and to the material properties, namely, a resorptive material.

Claims

1. An intramedullary implant for insertion into first and second bone parts, the implant being a one-piece body, the one-piece body comprising: a threaded first end for anchoring to the first bone part; anda second end extending from the first end for anchoring to the second bone part, the second end comprising: a body portion defining a longitudinal axis thereof;a first arm and a second arm projecting from the body portion;a first projection and a second projection spaced apart from the first projection, the first and the second projections extending from the first arm away from the longitudinal axis; anda third projection extending from the second arm in a different direction than the first projection,wherein the second end extends from the first end to form a step, the step having a surface facing in a direction parallel to the longitudinal axis and away from the second end.

2. The intramedullary implant of claim 1, wherein the third projection extends in a different direction than the second projection extends from the first arm.

3. The intramedullary implant of claim 1, wherein a fourth projection spaced apart from the third projection extends from the second arm.

4. The intramedullary implant of claim 1, wherein the first and the second projections extend in a same direction.

5. The intramedullary implant of claim 1, wherein the step defines a plane perpendicular to the longitudinal axis.

6. The intramedullary implant of claim 1, wherein entireties of the first and the second arms are spaced from the longitudinal axis to define an opening therebetween.

7. The intramedullary implant of claim 1, wherein the intramedullary implant is made of a polymer.

8. The intramedullary implant of claim 1, wherein the first projection includes a first flat portion, the second projection includes a second flat portion, and the third projection includes a third flat portion, and wherein the first, the second, and the third flat portions are coplanar.

9. The intramedullary implant of claim 1, wherein the first projection includes first and second opposing surface portions, the second projection includes third and fourth opposing surface portions, and the third projection includes fifth and sixth opposing surface portions, and wherein each of the first, the third, and the fifth opposing surface portions define a first plane and each of the second, the fourth, and the sixth opposing surface portions define a second plane parallel to the first plane.

10. An intramedullary implant for insertion into first and second bone parts, the implant being a one-piece body, the one-piece body comprising: a threaded first end for anchoring to the first bone part; anda second end extending from the first end for anchoring to the second bone part, the second end comprising: a body portion defining an opening in a median portion thereof;a first plurality of projections extending from a first side of the body portion and extending away from the opening, each one of the first plurality of projections including a respective one of a first set of flat surface portions, the first set of flat surface portions being coplanar; anda second plurality of projections extending from a second side of the body portion opposite the first side and extending away from the opening, each one of the second plurality of projections including a respective one of a second set of flat surface portions, the second set of flat surface portions being coplanar.

11. The intramedullary implant of claim 10, wherein the projections of the first plurality of projections extend away from the opening in a same direction.

12. The intramedullary implant of claim 11, wherein the projections of the second plurality of projections extend away from the opening in a same direction.

13. The intramedullary implant of claim 10, wherein the body portion includes a pair of arms and the opening is defined by the pair of arms.

14. The intramedullary implant of claim 10, wherein the body portion defines a longitudinal axis, and wherein the second end extends from the first end to form a step defining a plane perpendicular to the longitudinal axis.

15. The intramedullary implant of claim 10, wherein the intramedullary implant is made of a polymer.

16. The intramedullary implant of claim 10, wherein the first and the second sets of flat surface portions are coplanar.

17. The intramedullary implant of claim 10, wherein the first and the second sets of flat surface portions are coplanar.

18. The intramedullary implant of claim 17, wherein the first plurality of projections include a third set of flat surface portions opposite respective ones of the first set of flat surface portions, the third set of flat surface portions being coplanar, and wherein the second plurality of projections include a fourth set of flat surface portions opposite respective ones of the second set of flat surface portions, the fourth set of flat surface portions being coplanar, and wherein each of the first, the second, the third, and the fourth sets of flat surface portions lie in parallel planes.

19. An intramedullary implant for insertion into first and second bone parts, the implant being a one-piece body, the one-piece body comprising: a threaded first end for anchoring to the first bone part; anda second end extending from the first end for anchoring to the second bone part, the second end having a body portion, a first projection extending from a first side of the body portion, a second projection extending from a second side of the body portion opposite the first side, and a third projection extending from the first side of the body portion in a direction away from a longitudinal axis defined by the body portion, the first and the second projections extending in different directions away from the longitudinal axis and the third projection being spaced from the first projection,wherein the second end extends from the first end to form a step defining a plane perpendicular to the longitudinal axis, the step having a surface facing in a direction parallel to the longitudinal axis and away from the second end,wherein the first projection includes first and second opposing surface portions, the second projection includes third and fourth opposing surface portions, and the third projection includes fifth and sixth opposing surface portions, andwherein each of the first, the third, and the fifth opposing surface portions define a first plane and each of the second, the fourth, and the sixth opposing surface portions define a second plane parallel to the first plane.

20. The intramedullary implant of claim 19, wherein the first and the second projections are in alignment relative to and spaced apart from the longitudinal axis.

21. The intramedullary implant of claim 19, wherein the second end includes separated arms defining an opening, and wherein each of the first and the second projections extends from the separated arms.