FR2671717A1 - Expansion bolt for the fixation of a ligament prosthesis on the cortical wall of a bone - Google Patents

Abstract

The bolt comprises a barrel (10) which is generally cylindrical and capable of engaging in a hole formed in the cortical wall, and a screw (2) capable of being driven into an axial bore of the barrel in order to expand the latter radially and block it in the hole, the prosthesis being passed around the barrel and pressed against the bone by a collar (11) forming a cap at the end of the barrel. The screw, the barrel and the collar are made of physiologically acceptable metal. The barrel (10) and the collar (11) are made in one piece. The bore (17) is tapped to the pitch of the screw (2) from the collar (11) to a median cross-section (13), beyond which it narrows (12) to a diameter smaller than the diameter at the base of the thread of the screw (2), while the latter has a point (21) in the shape of a tapered cone. The barrel has slots (15) which extend in planes passing through the axis from an end edge (12a) of the barrel (10), opposite the collar (11), as far as an intermediate cross-section (17) between the median cross-section (13) and the collar (11).

Description

"Expansion bolt for fixing a prosthesis
ligament on the cortical wall of a bone "
The invention relates to a peg for anchoring an end of a ligament prosthesis on the cortical wall of a bone, comprising a generally cylindrical shaft suitable for engaging in a perforation made in the cortical wall and a screw capable of sinking in an axial bore of the barrel to expand it radially and block it in the perforation, the prosthesis being passed around the barrel and pressed onto the bone by a ferrule covering the barrel at the end.

 It goes without saying that a ligament prosthesis, generally constituted by a wick or a braid of a physiologically compatible textile with high tenacity, must be fixed on the bones, naturally connected by a ligament which the prosthesis must replace, in the vicinity of the points. insertion of the original ligament.

 Although prostheses are very generally intended to be rehabilitated by newly formed bone to constitute, in the long term, a secondary anchoring analogous to the natural anchoring of the ligament, it is advisable to ensure a primary anchoring by allogenic organs, if only to allow the formation of newly formed tissue.

 Self-tapping screws, conventional for fixing bone prostheses, were used to make a primary anchorage. A washer or ferrule placed under the head of the screw pressed the ligament prosthesis onto the bone, to promote rehabitation.

 However, the necessary tension of the prosthesis came to stress the screw transverse to its axis, which tended to have a bias relative to normal to the cortical wall, all the more since the thinness of the cortical wall accentuated the tendency of the screw to have a bias. In addition, the small thickness of the cortical wall, made it possible to involve in the fixation only a small number of threads of the self-tapping screw, threads whose pitch, moreover, is relatively large having regard to the mechanical properties of the cortex . The reliability of the anchors was insufficient.

We turned, then, to anchor bolts modeled on the devices used to fix various organs on the walls of buildings. These devices were of two kinds
- some, preferably suitable for solid walls, include a slightly frustoconical dowel of elastic material, with an axial orifice in which the penetration of a screw, of increasing section from the point to the head causes a radial expansion of the dowel , which is blocked in the perforation, practiced in the wall for the housing of the ankle
- the others, specially designed for honeycomb walls, with thin partitions delimiting the honeycombs, comprise a tubular metal barrel with a thin wall, the anterior end of which, pressed into a perforation, has longitudinal slots and a tapped anterior section; the rear end, flared in a ferrule, has a smooth hole through which passes a screw which engages in the tapped front end.

By tightening the screw, the head of which bears on the rear edge, the traction of the screw on the anterior end of the barrel causes a spouting of the barrel segments between the slots, which thus tighten the thin wall between the router and the ferrule.

 However, in fact, neither of these devices is really suitable for fixing to the cortical wall of a bone. Elastic ankle devices resist resistance to forces parallel to the surface of the cortex due to the elasticity of the ankle and the lack of depth of the perforation in the resistant cortical wall.

 Expansion devices in a spinning top have the drawback of occupying, during tightening in particular, an important place in the medullary cavity behind the cortex, with an attack on the integrity of the cord over a not insignificant volume; moreover, the interface between the medullary cavity and the cortex is made up of cancellous bone, mechanically not very resistant, and on which the blossoming in a spinning top does not find a secure support.

 To overcome these drawbacks, the invention offers a peg to anchor an end of a ligament prosthesis on the cortical wall of a bone, comprising a generally cylindrical shaft suitable for engaging in a perforation made in the cortical wall, and a suitable screw. to sink into an axial bore of the barrel to expand it radially and block it in the perforation, the prosthesis being passed around the barrel and pressed onto the bone by a ferrule covering the barrel at the end, characterized in that screws , barrel and ferrule being made of physiologically acceptable metal, with the ferrule in one piece with the barrel, the bore is tapped with the pitch of the screw from the ferrule to a median cross section beyond which it narrows to a diameter less than the diameter at the bottom of the thread of the screw, while the latter has a point in a tapered cone, the barrel having slots which extend in planes passing through the axis from a t end end of the barrel opposite the ferrule, up to a cross section intermediate between the middle straight section and the ferrule.

 With this structure, the barrel can be inserted without significant play in the perforation made in the cortex until intimate support of the prosthesis by the ferrule against the bone, after which the driving of the screw by rotation in the tapping of the the bore engages the conical point of the screw in the narrowed part of the bore beyond the middle section; the barrel segments between the slots are spaced apart, from the end of the slots in the intermediate section to the end edge of the barrel. The expansion of the barrel therefore increases from the intermediate section towards the end edge. The maintenance of the piton in the perforation results simultaneously from an expanding radial thrust on the deep part of the perforation in the cortex, opening into the cavity medullary, and of a longitudinal support of the spaced apart segments on the outlet of the perforation in the medullary cavity. It is thus possible to obtain a secure, resistant and play-free fixation, with the minimum of degradation of the bone, and of abnormal stresses of the cortex.

 Preferably, the piton will be of dimensions such that, inserted into the perforation of the cortical wall until the prosthesis rests on the bone by the ferrule, the so-called median and intermediate straight sections are respectively above and below the inner surface of the cortical wall.

 Due to this arrangement, blocking by radial expansion, which begins with the origin of the slits, occurs in the deep part of the perforation. In addition, the spacing stress produced by the penetration of the screw into the narrowed part of the bore is exerted in the middle straight section, with an amplitude of spacing in this section positively related to the difference in the diameters of the screw. and narrowed bore, while the spacing amplitude can be partially compensated by a deformation of the barrel segments, away from the middle section. The constraints of the cortical wall following the perforation are thus partially limited since the spacing at imposed amplitude occurs in the medullary cavity.

 Preferably the barrel, between the ferrule and the median cross-section, has on its outer surface annular projections suitable for opposing an extraction of the barrel from the perforation. It will be understood that these projections will be forced into the surface of the perforation advantageously these projections will be frustoconical, with the top of the cone directed in the same direction as the end edge of the barrel. This arrangement facilitates the insertion of the barrel into the perforation, and effectively retains this barrel against extraction forces.

 In a preferred arrangement, the ferrule has a flat bearing surface on the side of the barrel, and, on the opposite side, a rounded edge around a central bowl. The latter makes it possible to bring the screw head into contact with the ferrule, without the initiation of the thread under the head becoming stuck in the tapping.

Secondary characteristics and advantages of the invention will emerge from the description which follows by way of example, with reference to the accompanying drawings in which
Figure 1 shows in section a piton according to the invention
FIG. 2 represents the piton according to the invention, in the first phase of the anchoring of a ligament prosthesis
Figure 3 shows the peak of Figure 2, in the final anchoring phase, after expansion.

 According to the embodiment chosen and shown in the figures, the stud 1 is made of implantable stainless steel 316 L and comprises, in one piece, a generally cylindrical barrel 10 and a ferrule 11 forming a head.

 The ferrule 11 has, on the side of the barrel 10, a flat face 11a, and, on the side opposite the barrel, a central bowl 18, surrounded by a rounded edge 11b. In the center of the bowl 18 opens a tapped hole 17, directed along the axis of the barrel 10.

 This barrel 10 is drilled axially right through, with the internal thread 17 of the ferrule 11 to a median cross section 13, and, from the straight section 13 to an end edge 12a, on the side opposite the ferrule, a smooth bore 12 narrowed, relative to the thread 17, to a diameter less than the diameter at the bottom of the thread of a screw 2, which engages in the thread 17.

 The barrel 10 has, on the outer surface between the ferrule 11 and the middle section 13, stepped annular projections 14, shaped as truncated cones whose apex is directed in the same direction as the end edge 12a, and whose l The angle at the top is only a few 10 degrees.

This corrugated surface is designed to be able to sink relatively easily into a perforation calibrated in a relatively soft solid substance, such as the cortex of a bone, and to offer a significantly higher resistance to tearing.

 The barrel 10 further comprises four longitudinal slots 15, located in pairs in two planes passing through the axis of the barrel and orthogonal to each other; these slots 15 open into the end edge 12a, and extend towards the ferrule 11 to a straight section 16 intermediate between the middle section 13 and the ferrule 11, so that they initiate the thread 17 on a certain length towards its lower part which ends at the middle section 13.

 The stud 1 is completed by a screw 2 also in implantable stainless steel 316 L, with a rod 20 threaded at the same pitch as the thread 17 in which it engages. This rod 20 ends in a cone 21, with a half-angle at the top of the order of 200. In fact this cone 21 is truncated at its end to a section whose diameter is much smaller than that of bore 12, because its role will be to separate the barrel segments between the slots 15, which is why the presence of an acute point is unnecessary.

 The screw 2 has a domed head 22, the diameter of which is at least equal to that of the bowl 18. In this head 22 are formed two cylindrical holes 23, with axes parallel to the axis of the rod 20, and symmetrical by relative to this stem axis. In these holes will engage two cylindrical pins projecting from the end of a screwdriver adapted to the convex head 22, so that the screw can be forced into the thread 17 or removed from it without the head screw 22 escapes the screwdriver.

 The rod 20 of the screw 2 is of such length that, engaged in the internal thread 17 until the cone 21 comes into contact with the inlet of the narrowed bore 12, the head 22 remains spaced from the ferrule 11 by a distance which corresponds at least to the length of the cone 21 (see Figure 2).

 For the fixation of a ligament prosthesis 3 on the cortex 4 of a bone, reference is made to FIGS. 2 and 3.

 The screw 2 being engaged in the internal thread 17 until the cone 21 stops on the inlet of the narrowed bore 12, the weft and warp threads of the prosthesis 3 are spread apart, using a tool similar to a splicer, to provide an opening into which the barrel 10 of the stud 2 will penetrate, at a suitable location. A perforation 40 was made in the drill bit 40 in the cortical wall 4 of Laos, to a diameter corresponding to the diameter of the barrel 10 of the peak 1, in its cylindrical part comprised between the end edge 12a and the middle section 13. We engages the end of the barrel 10 in the perforation 40, then by striking axially on the ferrule 11 while carrying along the periphery of the bowl 18, engaging the ringed part 14 of the barrel in the cortex until fully tightening the prosthesis 3 between the external face 4a of the cortex 4, and the flat part 11a of the ferrule, in the position shown in FIG. 2. It can be seen in this figure that the stud 2 has dimensions such that the middle section 13 protrudes from the internal face 4b of the cortex 4 in the medullary cavity, while the intermediate section 16 does not emerge from the cortex beyond the internal wall 4b.

 At this moment, the pins of the screwdriver are engaged in the holes 23 of the head, and the rod 20 of the screw 2 is advanced by force into the bore 17, to force the cone 21 into the bore 12, which has the result of spreading outwards the barrel segments 10 between the slots 15. It will be noted that the bending torques of the segments act between the middle section 13, where the separation force occurs, and the intermediate section 16, where the slots 15 end, and where the resisting force consequently occurs. It will also be noted that the walls of the barrel at the height of the thread 17 are relatively thin and lend themselves to bending. The progression of the screw is continued until the head 22 stops on the ferrule 11.

 Thus, as shown in Figure 3, the barrel segments 10 between the middle section 13 and the end edge 12a are straight and divergent, while they begin to move away from the intermediate section 16, forcing on the wall of the perforation 40 in the cortex 4, in its deep part close to the internal wall 4b.

 It is thus understood that the fixing of the piton is resistant and without play, without however that the efforts of expansion of the piton risk causing the cortex to burst, all the more so as the expansion occurs where the cortex is most tender, and without the deformations of the piton in the medullary cavity causing serious damage in this region.

 It will be noted that the pins of the screwdriver can exceed the underside of the head 22, because they find their clearance in the bowl 18.

 Preferably, as shown in Figure 3, the screw 2 is held in place, to be sure that the internal thread of the barrel remains in good condition, and protected from invasion by tissues, in case the extraction of the piton would prove necessary.

To fix the ideas, a typical piton has a barrel 10 with a diameter of 4 mm and a length of 14.5 mm, while the ferrule 11 has a diameter of 13 mm and a thickness of 2.5 mm, and the central bowl 18 a diameter of 10 mm and a depth of 1 mm. Axial thread 17 is in step
M3, and the middle straight section 13, where this tapping ends, is 7.5 mm from the plane force of the ferrule lla.

 The diameter of the cylindrical bore 12 is 1.7 mm. The frustoconical annular projections 14 have a large base diameter of 4.3 mm, a small base diameter of 4 mm, and an axial extent of 1.5 mm. The length of the slots 15, from the end edge 12a to the intermediate cross section 16 is 10.5 mm.

The corresponding screw 2 has a rod 20 with a pitch of
M3 which extends over 10 mm and the conical tip 21 has a length of 2.5 mm, and is truncated to the diameter of 1 mm. The domed head 22 has an outside diameter of 10 mm and a thickness at the top of 2.5 mm, and has two holes 23 with an axis parallel to that of the rod and symmetrical with respect thereto, with a diameter of 1 , 2 mm and a center distance of 6 mm.

 Of course, the invention is not limited to the examples described, but embraces all of the variant embodiments thereof, within the scope of the claims.

Claims (8)

 1. Piton for anchoring an end of a ligament prosthesis on the cortical wall of a bone, comprising a generally cylindrical shaft suitable for engaging in a perforation made in the cortical wall, and a screw capable of being inserted into an axial bore of the barrel to expand it radially and block it in the perforation, the prosthesis being passed around the barrel and pressed onto the bone by a ferrule covering the barrel at the end, characterized in that screw (2), barrel (10) and ferrule (11) being made of physiologically acceptable metal, with the ferrule (11) in one piece with the barrel (10), the bore (17) is tapped with the pitch of the screw (2) from the ferrule (11 ) up to a median cross section (13) beyond which it narrows (12) to a diameter less than the diameter at the bottom of the thread of the screw (2), while the latter has a point (21) in a tapered cone, the barrel (10) having slots (15) which extend in planes passing through the axis from an end edge (12a) of the barrel (10) opposite the ferrule (11), to a straight section (17) intermediate between the middle straight section (13) and the ferrule (11) .  2. Piton according to claim 1, characterized in that it has dimensions such that, driven into the perforation (40) of the cortical wall (4) until the prosthesis (3) is supported by the ferrule (11) on the bone, said median (13) and intermediate (16) straight sections are respectively beyond and below the internal surface (4 # b) of the cortical wall (4).  3. Piton according to claim 1, characterized in that the barrel (10) between the ferrule (11) and the median cross section (13) has, on its outer surface, annular projections (14) adapted to oppose an extraction of the barrel (10) out of the perforation (40) of the cortical wall (4).  4. Piton according to claim 3, characterized in that the annular projections (14) are frustoconical, with their apex directed in the same direction as the end edge (12 # a).  5. Piton according to claim 1, characterized in that the ferrule (11), with a plane bearing surface (lla) on the side of the barrel (10), comprises, on the opposite side, a rounded edge (lek) around d '' a central bowl (18).  6. Piton according to claim 5, characterized in that the screw (2) has a domed head (22) suitable for covering the central cup (18) of the ferrule (11), with two holes (23) with parallel axes to the rod axis (20) and symmetrical with respect thereto.  7. Piton according to claim 1, characterized in that the barrel (10) has a diameter of 4 mm and a length of approximately 14.5 mm, the ferrule (11) has a diameter of 13 mm and a thickness of 2, 5 mm approximately, the screw, in pitch M3 has a rod (20) of approximately 12.5 mm, conical point (21) included, the middle straight section (13) is approximately 7.5 mm from the ferrule (11) , while the intermediate cross section (16) is approximately 10.5 mm from the end edge (12a).  8. Piton according to claims 2 and 7 taken together, characterized in that the annular projections (14) reach a diameter of about 4.3 mm.