WO2000040164A1

WO2000040164A1 - Self-compressive osteosynthesis screw for small bone surgery

Info

Publication number: WO2000040164A1
Application number: PCT/FR1999/003321
Authority: WO
Inventors: Louis Samuel Barouk; Vincent Coulange; Jean-Michel Gaume
Original assignee: Depuy France
Priority date: 1998-12-30
Filing date: 1999-12-30
Publication date: 2000-07-13
Also published as: JP2002534151A; AU776105B2; EP1139893A1; FR2787989B1; FR2787989A1; AU3049600A

Abstract

The invention concerns a self-compressive and atraumatic osteosynthesis screw (1), comprising a threaded proximal head (2), a body (4) forming a threaded distal portion (5) and, between the head and the distal part, a smooth section (6) of short length relatively to the distal portion length, the threading (7) thereof having a greater pitch than that of the proximal head threading (3), and a longitudinal channel (8) provided from one end to the other of said screw to receive a guide pin; said screw comprises means enabling it to fix small bones or small bone fragments of the skeleton after an osteotomy or a fracture, and in particular one of the five metatarsals (13, 14) of a human foot, said means comprising a threading diameter (d1) of the distal portion (5) slightly greater than the diameter (d2) of the thread root (3) of the proximal head (2) and the diameter of the channel (8) ranges between about 0.8 and 1.0 mm. Said screw miniaturised compared to the BAROUK screws of prior art advantageously replaces them as well as the cleavable screws with self-rupturing end piece for all the small bones, and bone fragments, in particular the five metatarsal bones.

Description

Self-compressing osteosynthesis screw for small bone surgery.

The present invention relates to an autocompressive and atraumatic osteosynthesis screw for the surgery of small bones or small bone fragments, in particular those of the foot.

French patent 2,722,086 (94 08 445) describes a BAROUK screw, comprising a threaded proximal head, a body forming a threaded distal part and, between the head and the distal part, a smooth section of short length relative to the length of the distal part. The thread of the latter has a pitch greater than that of the thread of the proximal head, and a longitudinal channel is arranged from one end to the other of the body of the screw to receive a guide pin. The difference between the steps of the two threads causes compression of the two bone fragments one on the other during screwing.

This cannulated screw has a relatively large diameter due to its longitudinal channel and therefore can only be used for fixation of fractures or for bone osteotomies of sufficient size, in particular the first metatarsal in the so-called osteotomy. "Scarf". Indeed the diameter of the threaded head of this screw at the bottom of the thread is about 3mm. For smaller bones such as the other four metatarsals, we must, when we want to perform an osteotomy described by Dr. WEIL, to correct an excess of length of these metatarsals, use a screw of smaller dimensions such as that described by French patent No. 2,721,819 (94 08 373). Such a screw is extended by a self-breaking end piece thanks to a rupture line formed between the head of the screw and the base of the end piece. The reduction in the diameter of this breakable screw is obtained by the fact that it is not pierced with a longitudinal channel for guiding a spindle.

None of these anterior screws can be used universally for osteotomy or fixing small bone fractures, especially the metatarsals. Indeed, the screw according to patent 2,722,086 has too large a diameter for the four metatarsals other than the first metatarsal of which it can cause bursting, as well as for other small bones or bony fragments of the skeleton. For its part, if the bone of these four lateral metatarsals is porotic, the screw with breakable tip may prove to be too small and its strength insufficient. Similarly, if the first metatarsal is actually small, as is the case for some patients, the cannulated screw with threaded head according to the aforementioned patent may cause it to burst. The object of the invention is to propose an osteosynthesis screw of the aforementioned type, for the surgery of small bones or small bone fragments, which can be used in place of the two known screws mentioned above, not only for one any of the five metatarsals, but also for osteotomies of small bones or small bone fragments as well as for the fixation of fractures in other applications than foot surgery, for example for bones of the hand.

According to the invention, the autocompressive and atraumatic osteosynthesis screw includes means to allow it to fix small bones or small bone fragments of the skeleton after an osteotomy or a fracture, and in particular any one of the five metatarsals of a human foot.

Thus the screw according to the invention advantageously replaces the two screws, cannulated and breakable, of the prior art set out above. According to one embodiment of the invention, said means comprise a diameter of the thread of the distal part slightly greater than the diameter of the bottom of the thread of the proximal head, as well as the fact that the diameter of the channel is between 0.8 and 1.0mm approx.

This achieves a miniaturization of the anterior screws while maintaining the arrangement of a longitudinal channel opening at the two ends of the screw, which allows it to be guided in place by a pin.

The diameter of the bottom of the thread of the proximal head is approximately 2.2 to 2.7mm, and the outside diameter of the thread of the distal part is between approximately 2.5 and 3.0mm approximately. A screw is thus produced whose dimensions are sufficiently reduced compared to the screw according to French patent 2,722,096 to allow it to be used in osteotomies or fixation of fractures of small bones such as average metatarsals without risk of causing bursting of these bones, and retaining enough strength in the screw to withstand the stresses experienced during their period of use.

Other features and advantages of the invention will become apparent during the description which follows, given with reference to the appended drawings which illustrate an embodiment thereof by way of nonlimiting example.

Figure 1 is a longitudinal elevational view on an enlarged scale of an embodiment of the osteosynthesis screw according to the invention.

FIG. 2 is an end view along arrow F1 of the screw of FIG. 1. Figure 3 is an end view along arrow F2 of the screw of Figure

1.

Figure 4 is a schematic top view of the bones of a human foot, the first phalanx having a hallux valgus and the first metatarsal a metatarsus varus which can be corrected by means of screws according to the invention.

Figure 5 is a longitudinal elevational view on an enlarged scale of the first metatarsal of Figure 4 showing the longitudinal and transverse section lines of the metatarsal bone to be treated. Figure 6 is a longitudinal elevational view on an enlarged scale, illustrating the use of a screw according to the invention in a Weil osteotomy of a middle metatarsal.

The osteosynthesis screw 1 for the surgery of small bones or small bone fragments shown in FIGS. 1 to 3 comprises a proximal head 2 provided with a thread 3, as well as a body 4 forming a threaded distal part

5. Between the head 2 and the distal part 5, a smooth section 6 is made, of short length compared to that of the distal part 5.

The thread 7 of the latter has a pitch p1 greater than the pitch p2 of the thread 3 of the proximal head 2. A longitudinal channel 8 is arranged axially from one end to the other of the screw 1 and opens at its two opposite ends, this channel 8 being provided to be able to receive a guide pin not shown. Two self-tapping notches 9 are arranged at the distal end of the part 5. In the head 2, the axial channel 8 widens to delimit a housing 11 whose wall constitutes a hexagonal imprint 12 adapted to receive a tool for corresponding screw not shown.

The outside diameter d1 of the thread 7 of the distal part 5 is slightly greater than the diameter d2 of the bottom 10 of the thread 3 of the head 2. Therefore, taking into account the height of the threads of the thread 3, the outside diameter d3 of that - This can be of the order of for example 3.1 mm for a diameter d2 of 2.2mm and a diameter d1 of 2.6mm. This external diameter d3 of 3.1 mm is a maximum acceptable by the four lateral metatarsals and is also suitable for the first metatarsal which requires screws of a minimum size.

The thread 3 has a maximum depth sufficient to ensure satisfactory bone attachment, without, on the other hand, reaching the wall of the impression 12 with a hexagon. The fact that the top of the distal thread 7 has a diameter d1 barely greater than the diameter d2 of the bottom of the thread 3 prevents this distal thread from damaging the entry of the hole into the bone. Otherwise, the proximal thread 3 would interfere with the distal thread of different pitch, which is obviously undesirable for obtaining satisfactory bone anchoring.

If for example the outside diameter d1 of the distal thread 7 is 2.6mm for a diameter d2 of 2.2mm, we obtain a radial width of 0.2mm of the thread 3 in the wall of the bone at the entrance of the hole . This low insertion value of the thread 3 avoids substantially damaging the bone. It should also be noted that the outside diameter d1 of the distal thread 7 cannot be reduced too much, otherwise it would not ensure sufficient bone bonding.

It has moreover been found that the best results with respect to imprints of different profiles are obtained with a hexagonal profile of the wall 12, and a distance e between two opposite faces 12a of the hexagonal wall 12 of between approximately 1.3 mm. and 1.7mm. Indeed, with such an imprint, associated with a cannula screwdriver with a diameter for example of 0.9 mm, it can be seen that the screwdriver can exert on the screw 1 a high torque without "ripping" on the hexagonal wall 12.

Tests have established that the outside diameter d1 of the distal thread 7 must be between approximately 2.3 and 2.8mm, the diameter d2 must be between approximately 2.0mm and 2.5mm, while the outside diameter d3 of the proximal thread 3 must be between substantially 2.8mm and 3.5mm. The length of the screw is between 10 and 22mm. It covers all morphotypes and roughly corresponds to the different thicknesses of the metatarsals.

The table below contains an example of the characteristics of an anterior BAROUK screw and an embodiment of the self-compressive and atraumatic screw 1 according to the invention.

We see that all the dimensions of the screw according to the invention are significantly reduced. Despite this reduction in dimensions, the tearing force and the torsional torque of the screw remain much greater than that of a breakable or “Twist-off” screw with the same head outside diameter.

Figures 4 and 5 schematically illustrate a hallux valgus treatment which can be carried out through the use of self-compressive and atraumatic screws 1 according to the invention.

Among the five metatarsals 13 and 14, the first metatarsal 14 is deformed in the medial direction (arrow F3 and position 14a shown in phantom), constituting the metatarsus varus. The surgical method for the treatment of this metatarsus varus consists, for short, in carrying out a longitudinal section of the metatarsal bone 14 along a longitudinal plane 15 and transverse planes 16 inclined at angles of 60 ° to the longitudinal plane 15.

In a subsequent step, the surgeon moves laterally, ie towards the metatarsals 13, the lower bone fragment 14b. Then the surgeon inserts fixing screws 1 to firmly assemble and compress one over the other the two bone fragments 14b and 14c. Finally, the surgeon partially cuts the bone portion 17 which forms a medial projection relative to the bone fragment 14b.

FIG. 6 illustrates a second example of implementation of the screw 1 according to the invention, in the context of a Weil osteotomy. In this application the screw 1 is used to fix the plantar part 13b of a metatarsal 13 previously cut longitudinally into two parts 13a and

13b, and moved back to the desired position.

The pitch of the screws 1 is of the order of 1 mm, substantially equal to that of the earlier, more bulky BAROUK screws. This increases the strength of the screw in the bone, which is often porotic or small. The screw can be made of any suitable biocompatible material, such as a titanium alloy.

Claims

1. Self-compressive and atraumatic osteosynthesis screw (1), comprising a threaded proximal head (2), a body (4) forming a threaded distal part (5) and, between the head and the distal part, a smooth section (6 ) of short length compared to the length of the distal part, the thread (7) of the latter having a pitch greater than that of the thread (3) of the proximal head, and a longitudinal channel (8) arranged at one end to the other of said screw to receive a guide pin, characterized in that it comprises means for enabling it to fix small bones or small bone fragments of the skeleton after an osteotomy or a fracture, and in particular one any of the five metatarsals (13, 14) of a human foot.

2. Screw according to claim 1, characterized in that said means comprise a diameter (d1) of the thread (7) of the distal part (5) slightly greater than the diameter (d2) of the bottom of the thread (3) of the proximal head (2), as well as the fact that the diameter of the channel (8) is between

0.8 and 1.0mm approximately.

3. Screw according to claim 1 or 2, characterized in that in the proximal head (2) is formed an impression with a hexagonal wall (12) for a screwing tool, and the distance (e) between two opposite faces (12a) of this footprint is approximately 1.3mm to 1.7mm.

4. Screw according to one of claims 1 to 3, characterized in that the outside diameter (d1) of the thread (7) of the distal part (5) is between 2.3 and 2.8 mm approximately, the diameter ( d2) from the bottom of the thread (3) of the proximal head (2) is approximately 2.0 mm to 2.5 mm and the outside diameter (d3) of the thread of the head is between substantially 2.8 mm and 3 , 5mm.