Osteosynthesis Device

Abstract

In one embodiment, the present invention includes an intramedullary osteosynthesis or arthrodesis implant including a central body, a first pair of legs extending from the central body to a pair of leg tips, and a second pair of legs extending from the central body, in a direction opposite the first pair of legs, to a pair of leg tips such that the central body, first pair of legs and second pair of legs are positioned alongside a longitudinal axis.

Claims

1. An intramedullary osteosynthesis or arthrodesis implant comprising: a central body, a first pair of legs extending from the central body to a pair of leg tips, and a second pair of legs extending from the central body, in a direction opposite the first pair of legs, to a pair of leg tips such that the central body, first pair of legs and second pair of legs are positioned alongside a longitudinal axis; the central body having a width; the pair of tips of the first pair of legs having a width in a closed position and a width in an open position, the width in the closed position is less than the width of the central body and the width in the open position is greater than the width of the central body; and the pair of tips of the second pair of legs having a width in a closed position and a width in an open position, the width in the closed position is less than the width of the central body and the width in the open position is greater than the width of the central body.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The invention is described in greater detail below in conjunction with the appended drawings in which:

[0032] FIG. 1 shows an exemplary implant of the invention in its full open position in 3 dimensions,

[0033] FIG. 2 shows the same example in its closed introduction position in its main plane,

[0034] FIG. 3 shows an exemplary implant of the invention in its full open position, in its main plane,

[0035] FIG. 4 shows an example of a bent implant according to the invention in its full open position,

[0036] FIGS. 5 (5a to 5f) shows the implantation sequence: closed, half introduced still stressed, fully introduced on one side (free in the bone), and the same sequence on the other side.

SPECIFIC DESCRIPTION

[0037] The implant is in the form of 2 anchoring zones A1 and A2 connected by a central zone C (FIG. 1) and optionally intermediate connecting zones such that in the closed position, the shape is substantially inscribed in a very elongated rectangle (FIG. 2), and in the open shape, corresponds to a wider X-shape due to the spreading of the anchoring zones A1 and A2 (FIG. 3).

[0038] The anchoring zones A1 and A2 each have two legs P1 and P2 having lengths L1 and L2 (FIG. 3).

[0039] The cross-section of the implant is adapted to the implantation sites, but preferably flat in order to have good mechanical strength and reduced size (typically the thickness e is about 1 to 2 mm) (FIG. 1).

[0040] FIG. 2 shows the closed position with the various widths of the implant: Lab is the width of the central zone C, L1ab and L2ab are the widths at the base of the anchoring zones A1 and A2. These 3 widths may be equal or slightly different to adapt to the bone site. Typically, the widths are about 2 to 5 times the thickness (or 2 to 10 mm). These dimensions are adapted to the various dimensions of the hand and foot but are not limiting because they depend on the bone site of the operated patient.

[0041] The anchoring zones A1 and A2 are suitable for separation by elastic effect or by shape memory effect at their base, so that the maximum width in the open position at the tips La1 and La2 (FIG. 3) is at least equal to the width of the base of the same anchoring zone in the closed position plus 50% minimum, or plus a minimum of 1.5 mm. This means that La1>L1ab+50% or La1>L1ab+1.5 mm and that La2>L2ab+50% or La2>L2ab+1.5 mm. This opening criterion is necessary to have sufficient fixation in the bone.

[0042] As shown in FIG. 3, the legs P1 and P2 are substantially straight at their base (on about ⅓ to half of their length) and are then rounded inwardly at their tips (on about ⅓ to half of their length). In the open position, the straight inner portions of the legs P1 and P2 make positive outward angles a1 and a2 with the longitudinal implant axis A (FIG. 3), whereas in the closed position, these angles become inward negative angles b1 and b2 (FIG. 2). The upper or outer portions (toward the tip) of the legs P1 and P2 virtually undergoes no particular deformation between the two open and closed shapes.

[0043] This particular geometric arrangement ensures that in the closed position, the legs virtually touch at the tips (FIG. 2), and that the widths at the tips in the closed position Lalf and La2f are lower than the widths at the respective bases L1ab and L2ab, thereby allowing easy introduction without distraction of the distal bone fragment and also obtaining the opened/closed movement by a local deformation at the base of the legs, that is by leaving the distal zone free for introducing this zone into the bone.

[0044] In order to obtain both easy introduction and sufficient opening movement, the angles a1 and a2 are preferably between +5 degrees and +25 degrees and the angles b1 and b2 between 0 degrees and −15 degrees.

[0045] Preferably, the width of the tips of the anchoring zones in the closed position La1f and La2f are lower than the widths of the bases of the zones L1ab and L2ab, minus 20%: La1f<L1ab-20% and La2f<L2ab-20%.

[0046] The legs or anchoring zones are thus “articulated” at their base, and can therefore be secured in the closed position on a support or even better a clamp, positioned at an appropriate location defined in particular in the case of an elastic material (for a shape memory material, this is not absolutely necessary since the shape does not change as long as the activation temperature is not reached), this clamp not covering more than half of the length of the legs, thereby allowing introduction of at least half of the implant into its recess.

[0047] The inside tangents at the tip of the legs P1 and P2 in the open position make angles β1 and β2 with the longitudinal axis A of the implant close to 0 degrees, in order to have a good bone contact area along the whole lengths of the legs in the open position and to prevent the bone from being touched by the tips alone (FIG. 3).

[0048] In the implant site, at body temperature, the implant can still be in the closed position, or parallel or with semiopen legs so that the force exerted by opening of the legs is transmitted to the bone and ensures proper fixation.

[0049] This “olive” arrangement of the legs, associated with an “articulation” of the base and associated with a minimal introduction of half of their length allows completion of the insertion, once the clamp has been removed.

[0050] In order to guarantee satisfactory operation, the elasticity or memory of the piece must allow a transition from the closed shape (typically width 2 to 4 mm according to the size of the site) to an open shape with a significant movement (+1.5 to +3 mm approximately).

[0051] Similarly, the force of expansion of the legs (or swelling of the olive) must be significant: typically 1 to 3 kg for an arthrodesis of the tips (force measured at 37° C. in the blocked introduction position), without being excessive: it is important for the legs to avoid opening completely and for the bone to resist so as to have a real holding force.

[0052] The legs P1 and P2 or fins may have a rough surface or even better notches D (FIG. 3) on their outer surfaces intended to be press into the spongy bone and form a good anchorage. The typical depth of these notches H1 and H2 is about 0.5 mm. The opening of the legs must be at least 1.5 times this depth in order to ensure good engagement of the notches in the bone or 1.5 mm.

[0053] The legs P1 and P2 may also have a surface covered with an osseointegration coating such as hydroxyapatite (HAP) intended to facilitate the anchorage.

[0054] To facilitate introduction into the bone, the tips of the legs P1 and P2 are bevelled with an inward angle to the longitudinal axis A of the implant W1 and W2 (FIG. 3). This angle is typically between −20 degrees and −40 degrees.

[0055] By tests on fresh cadavers and experience, an optimal level of the force was determined with a minimum allowing anchorage of the notches in the spongy bone and a maximum force to be certain to avoid damaging the implantation site.

[0056] After tests and experience, an ideal zone was found with a maximum 20% of the elastic limit of the bone measured in a blocked closed shape at 37° C., which, considering the dimensions of the implant, gives rise to maximum values of about 3 kg, and the need for a rapid lowering as soon as the anchorage is obtained, or a force divided by 2 in the semi-open position (a force of 0.5 to 1.5 kg allows good holding). In fact, if the opening force is higher than about 3 kg, introduction into the bone becomes much more difficult, or even impossible above 4 kg. Finally, in order to guarantee a damage-free site, it is necessary for the force to become negligible for a virtually complete opening. These values are indicative and depend on the arthrodesis site and the bone quality.

[0057] In one version of the invention, the notches D1 and D2 on the outside of the legs P1 and P2 allow the positioning of a clamp and introduction at the base of the legs P1 and P2 (FIG. 3). These notches are symmetrical by pairs of legs and their spacing d is the same on the legs PI and on the legs P2.

[0058] The central zone C must have a minimum length Lc equal to the length d between the notches D1 and D2 so that even in case of movement of the implant during final impaction, this zone C remains in the arthrodesis focus and performs its resistance function.

[0059] In one version of the invention, an orifice Or is provided in this central zone for positioning a holding pin to prevent migration of the implant at the time of final impaction.

[0060] As shown in FIG. 4, this central zone may be bent at an angle Ag defined between the 2 main planes formed by the legs P1 on the one hand and P2 on the other hand to adapt to the surgical requirements for adjusting the position of the arthrodesis. In most cases, the angle Ag is fixed between 0° (typically flat position for an index) and 30° (typically for a little finger).

[0061] As an example, an operating technique of implantation of the inventive device for the case of an elastic or superelastic implant is described as follows as shown in FIG. 5:

DETAILED DESCRIPTION OF THE FEATURES OF THE INVENTION AND EXEMPLARY EMBODIMENTS

[0062] Approach by dorsal path [0063] Resection of cartilages and osteophytes [0064] Centromedullary perforation using an appropriate instrument to make a calibrated rectangular hole having a width of substantially L1ab or L2ab and thickness of substantially e (by a suitable rasp) [0065] Closure of the clamp side P1 (FIG. 5a) [0066] Implant introduction side P1 to minimum half (FIG. 5b) [0067] Clamp removal [0068] Complete introduction side P1 (FIG. 5c) [0069] Closure of the clamp side P2 (FIG. 5d) [0070] Placement of the bone side P2 on the implant side P2 to about half (FIG. 5e) [0071] Removal of the clamp [0072] Manual impaction of the bone side P2 on the bone P1 (FIG. 5f)

[0073] In a particular embodiment, intended for a distal interphalangeal arthrodesis (hand), the implant is prepared from a superelastic Nitinol alloy (nickel-titanium in the weight proportion 55.8% nickel and 44.2% titanium).

[0074] The cross-section of the central zone C is Lab×e=2.8×1.2 mm and the legs are asymmetrical to adapt better to the shapes of the bone, minimize the implanted metal section and allow sufficient expansion for good anchorage. The length of the legs is L2=6.5 mm distal side P2 and L1=9 mm proximal side P1. The length of the central zone C is 3 mm, allowing a slight offset during closure, without affecting the shear strength. To adapt to the surgeon's choice, this central zone may be bent (typically flat or 15° or 25°).

[0075] In the closed position, the width of the proximal base L1ab is 3.8 mm and of the distal base L2ab is 3.0 mm. The opening of the legs P1 and P2 is 2.5 mm or 2.2 mm, that is La1 is 6.3 mm and La2 is 5.2 mm. In the open position the angle at the base of the legs is a1=10° and a2=22°. The straight portion is about 45% of the total length. The curvature of the distal tip of the legs is calculated so that the angle of the tangent at the tip is β1=−5° and β2=−3°. In the closed position, the angle at the base of the legs is b1=−4°, b2=−2°. And the width at tip is La1f=2.5 mm and La2f=2.1 mm.

[0076] In one embodiment of the invention, the 0.5 mm deep notches are distributed on the legs (1 notch at approximately 0.8 mm spacings).

[0077] The angle of incidence of the tip of the legs (including notches) is w1=33° and w2=24°, allowing easy introduction without the distraction effect between the two bone pieces to be osteosynthesized.

[0078] The rounded design of the anchoring zones serves to obtain a maximized contact area over the entire length in the open shape, with an impaction effect in the spongy bone, and hence a spongy packing effect.

[0079] In another example, more appropriate for arthrodesis of the thumb, the dimensions are rather the following:

Closed widths: L1ab=6.5 mm, L2ab=5 mm, with an opening of 3 to 4 mm approximately to obtain: La1=11 mm and La2=8 mm and L1=13 mm and L2=9 mm.