FR2699065A1 - Self-compressing screw for treating bone end fractures - comprises hollow threaded rod with distal tip and bush with self-tapping surfaces - Google Patents

Abstract

The screw comprises a hollow rod (1) which can be fitted onto a guide pin, with its distal end having a self-tapping tip (1a) for anchoring in the spongy tissue of the bone. The remainder of the rod has a threaded surface (1b) of smaller and finer pitch which can receive a threaded bush (2). The bush has the same internal thread as the rod and an external thread of larger pitch, but slightly smaller than that of the distal tip (1a). The bush is shaped to receive a key which rotates and tensions it. The bush can be in different shapes, depending on the type of bone fragments to be joined, and the rod can be of any length, e.g. cut to length after fitting. USE/ADVANTAGE - For treating bone end fractures. Assembled from small range of standardised components.

Description

 Self-compressing screw For the treatment of primary and / or osteochondral fractures.

 We know that certain bone fractures, especially in the epiphyseal area, require the use of screws for their repair. In the case of osteochondral fractures, i.e. bone fractures with cartilage fragment, screws are also used.

 A large number of epiphyseal fractures, such as those of the condyles of the femur, are osteosynthesized using screws. In this regard, after reduction of the fracture and placement of the screw, the latter exerts compression at the fracture site, ensuring a. good stability. The compression is exerted via the threaded anchoring zone in the bone and, conversely, by the screw head which rests on the bone cortex. By cons, after placing the screw, its head appears to overflow from the bone, which is not rational. Note also that the pressure exerted by the screw head on the external surface of the bone is not always well tolerated.

 In the case of osteochondral invoices, that is to say comprising a fragment coated with a cartilaginous layer, the use of a conventional screw is hardly possible, given its head which appears protruding , prohibiting any movement of articulation. Figure 1 shows a reduced osteochondral fracture using a conventional screw.

 In an attempt to remedy these drawbacks, a self-compressive screw having no head has been proposed. This type of screw is described in HERBER T patent DE 2807364. This self-compressing screw makes it possible to obtain inter-fragmentary compression without apparent protrusion at the level of the external part of the cortex. Such a screw can therefore be used in the case of osteochondral fractures.

 This type of screw has, at its proximal end, a tapped surface cooperating with the bone, in particular cortical. The distal end of this screw also has a tapped bearing of diameter smaller than the other bearing and of a reduced pitch to ensure compression. Figure 2 shows the principle of reduction of a fracture, using the HERBER T screw. Note that this screw is hollow to be engaged on a guide pin previously placed at the fracture site.

 However, given its design, it is necessary to have a large number of sizes. In addition, the thread of the proximal end at the cortex of the bone is very often insufficiently anchored to maintain compression, so that this screw is difficult to use in an elderly subject.

 The object of the invention is to remedy these drawbacks in a simple, safe, effective and rational manner.

 The problem which the invention proposes to solve is to produce a self-compressing screw of a single size making it possible to treat epiphyseal fractures, even in the elderly, and osteochondral fractures.

 To solve such a problem, it was designed and developed, a self-compressive screw comprising a hollow rod capable of being engaged on a guide pin placed at the fracture, said rod having at its distal end, a threaded seat self-tapping, capable of being anchored in the cancellous bone and, at its opposite end, a threaded seat of smaller diameter and not more reduced, intended to receive a threaded socket of corresponding pitch and whose outer diameter is threaded d '' a determined step, to be anchored in the bone fragment, while compressing it.

 To solve the problem of ensuring compression, the outside diameter of the sleeve is very slightly greater than the outside diameter of the distal end. The thread pitch of the socket is very slightly lower than that of the distal end.

 To solve the problem posed of setting up the socket, the latter has arrangements for being operated from the outside.

 These arrangements are constituted either by two diametrically opposite notches capable of cooperating with arrangements complementary to an operating key, or by a screw head, capable of cooperating with a screwdriver.

 To solve the problem of having a single-size autocompressive screw, the threaded seat of smaller diameter and of reduced pitch, extends beyond the distal end, over almost the entire length of the rod, to be cut to the desired length after installation.

The invention is set out below in more detail using the appended drawings, in which:
Figure 1 is a perspective view showing an osteochondral fracture of the end of the femur, reduced by a conventional screw.

 Figure 2 is a view corresponding to Figure 1, in the case where the fracture is reduced by means of a HERBERT screw.

 Figure 3 is a perspective view of the components of the screw according to the invention.

 Figure 4 is a longitudinal sectional view of the rod and the socket before assembly.

 Figure 5 is a view corresponding to Figure 4 after installation of the sleeve.

 Figure 6 is a longitudinal sectional view of another embodiment of the sleeve.

 Figures 7, 8, 9, 10, 11, 12, 13 and 14 are perspective views showing the technique for installing the self-compressive screw according to the invention.

 Figure 15 is a view corresponding to Figures 1 and 2, in the case where the fracture is reduced by the autocompressive screw according to the invention.

 As shown in Figures 3 and 4, the screw comprises a hollow rod (1) intended to be engaged on a guide pin (B) placed at the fracture, as will be indicated in the following description. This rod (1) has, at its distal end, a self-tapping threaded seat (la) intended to cooperate with the cancellous bone.

At its opposite end, the rod (1) has a threaded seat (1b) intended to receive a threaded socket (2) of corresponding pitch.

 Importantly, the threaded seat (lob) at a pitch of length (I) less than the length of the step (L) of the distal threaded seat (la). The scope (lob) therefore has a step "faster" than that of the scope (la), so that the sleeve (2), screwed onto the scope (it), will move quickly.

 The external diameter (D) of the sleeve (2) is very slightly greater than the external diameter (d) than the threaded distal seat (la). In addition, the length of the pitch (11) of the socket thread (2) is greater than the length of the pitch (I) of the bearing thread (lob) and very slightly less than the length (L) of the thread pitch of the distal range (1 a). The threaded seat (lb) extends over almost the entire length of the rod.

 The socket (2) has arrangements for being operated from the outside, so as to be screwed onto the threaded surface (lob). These arrangements can be constituted by two diametrically opposite vertical notches (2a) intended to cooperate with lugs that have an operating key (Figures 4 and 5). Or these arrangements can be constituted by a screw head (2b) shaped to be operated, for example, by a screwdriver.

 It is now necessary to analyze the operating mode for the installation of the autocompressive screw according to the invention, as defined and illustrated. We refer to Figures 7 to 15.

 Firstly, after reduction of the fracture, the guide pin (B) is put in place (Figure 7). On this spindle, a forest is engaged up to the level of the cortex opposite the point of introduction (Figure 8).

 A tapping is then carried out with a diameter corresponding to that of the threaded seat (la) (FIG. 9), thus producing a tapped intra-bone tunnel. Then engaged in this tunnel thus formed, the entire rod (1) engaged from its distal end (la).

For the screwing of the rod, one can use for example, a drill turning at low speed. The guide pin (B) is still in place.

 At this stage we see that the rod (1) passes successively into the initially fractured bone fragment, then into the bone on which it has been reduced (Figure 10). The distal end (la) must not perforate the opposite cortex. This threaded seat (la) is anchored in the bone and holds the entire rod (1). The threaded seat (lob) extends well beyond the bone (Figure 11). On the projecting part of the seat (lob), is screwed the sleeve (2) which is anchored in the bone fragment while compressing it, since each turn has the effect of anchoring said sleeve in the fragment, while by simultaneously ensuring a faster approximation, taking into account the difference in pitch between the ranges (lob) and (la). This produces compression (Figure 12).

The projecting end of the threaded surface (lob) is then sectioned by means, for example, of a cutting and crushing pliers ensuring the locking in translation of the sleeve (2) (Figures 13 and 14).

 Note that the choice of socket is determined based on the type of fracture. For example, if one is in a free zone, that is to say if the screw head is not annoying, the socket used is of the type described and illustrated in FIG. 6. On the other hand, if the 'we are in the chondral zone, the socket used is of the type illustrated in Figure 4 and will be screwed to be inserted 1 to 2 mm from the surface of the cartilage.

The advantages are clear from the description, in particular it is emphasized and recalled that the self-compressing screw can be used:
- as a specific single-size screw, for osteochondral fractures,
- as a standard one-size screw with the consequence that the thread of the socket relieves the pressure exerted by the part of the rod on the external face of the cortex.

 The assembly of the screw, namely the rod and the socket, can be made of any type of material, in particular titanium or stainless material.

Claims (7)

-1- Self-compressing screw for the treatment of epiphyseal and / or osteochondral fractures comprising a hollow rod (1) capable of being engaged on a guide pin placed at the level of the fracture, characterized in that said rod (1) has its distal end, a self-tapping threaded seat (la), capable of being anchored in the cancellous bone and, at its opposite end, a threaded seat (lb) of smaller diameter and not smaller, intended to receive a threaded sleeve (2) of corresponding pitch and whose external diameter is threaded with a determined pitch, to be anchored in the bone fragment, while compressing it. -2- Screw according to claim 1, characterized in that the outside diameter of the sleeve (2) is very slightly greater than the outside diameter of the distal end (1a). -3-- Screw according to claim 1, characterized in that the pitch of the thread of the sleeve (2) is very slightly less than that of the distal end (la).  -4- Screw according to claim 1, characterized in that the sleeve (2) has arrangements to be operated from the outside. -5- Screw according to claim 4, characterized in that the arrangements are constituted by two notches (2a) diametrically opposite, adapted to cooperate with arrangements complementary to an operating key. -6- Screw according to claim 4, characterized in that the arrangements are constituted by a screw head (2b), capable of cooperating with a screwdriver. -7- Screw according to claim 1, characterized in that the threaded seat (lob) of smaller diameter and of reduced pitch, extends beyond the distal end, over almost the entire length of the rod, for be cut to the desired length after installation.