GB2154144A - Bone fixation device - Google Patents

Abstract

An external minifixation apparatus for use as a bone lengthener, comprises a rigid bar (3) bearing two clamps (5) and (9) for holding pins (8), each clamp consisting of two jaws (4, 6, 10, 11) which are closeable by means of a screw (7) at least one of the clamps being displaceable longitudinally of the axis of the bar, the clamp having one of its jaws (10) provided with a carriage (12) which is displaceable within an opening (13) in the bar by rotation of a threaded rod (14) which passes through a cavity in the carriage (12), the cavity having a thread mating with the thread on the rod (14) and the lower part of the jaw (10) having surfaces (15) for resting against the bar. <IMAGE>

Description

SPECIFICATION External Axial Fixation Device The invention relates to orthopedic fixation devices, namely, minifixators, particularly adapted to controlled fixation of small bones, such as phalanges, metacarpal and metatarsal bones.

U.S. Patent No. 4,312,336 describes a monolateral external fixation device having a variety of features designed to give the surgeon flexibility in applying it to a number of bone-fixation situations, particularly involving large bones. However, the relative complexity and bulk of the device make it inapplicable to fixation of small bones of the hand or foot. A mere reduction in scale of this device does not meet the surgeon's requirements for simplicity, strength, bone anchorage and elongation, in a broken or otherwise defective small-bone situation.

An object of the invention is to provide a device with pin mounts to provide monolateral support of two spaced regions of a small bone wherein all axes of bone engagement are in a single plane and wherein this coplanar relation is maintained during a bone-elongation procedure, such as diaphyseal bone elongation, in chondroepiphyseal distraction, in losses of bone substance, in synthesis of articular fractures of the hand, for arthrodesis, for axial deviations, of the digits as well as in cases of hallux valgus, of metatarsus primus varus, and the like.

According to the present invention an external minifixation apparatus for use as a bone lengthener, comprises a rigid bar bearing two clamps and for holding pins, each clamp consisting of two jaws which are closeable by means of a screw at least one of the clamps being displaceable longitudinally of the axis of the bar, the clamp having one of its jaws provided with a carriage which is displaceable within an opening by rotation of a threaded rod which passes through a cavity in the carriage, the cavity having a thread mating with the thread on the rod and the lower part of the jaw having surfaces for resting against the bar.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which:~ Fig. 1 is a plan, with clamp pins partly broken away; Fig. 2 is a section on the line 2-2 of Fig. 1; Fig. 3 is a section similar to Fig. 2, showing a modification; and Figs. 4 and 5 are fragmentary sectional views showing further modifications.

The external minifixation apparatus shown in Figs. 1 and 2 of the drawings comprises an elongate metal bar 3 with general external conformance to a parallelepiped. One end of bar 3 integrally includes a projection 4 constituting a fixed jaw of a clamp 5, the second jaw 6 of which may be secured to jaw 4 by means of a screw 7. Mutually facing surfaces of jaws 4 and 6 are formed with spaced parallel cylindrically arcuate grooves, for reception and location of shanks of two pins 8 therebetween. The shanks of pins 8 are cylindrical and are securely clamped in parallel relation, upon tightening the screw 7 therebetween.

The other clamp 9 is movably guided along bar 3 and comprises two jaws 10~11 which have correspondingly grooved confronting faces and a single screw 7' therebetween, for secure clamping of the shanks of two further pins 8.

For adjustably guided positioning of the movable clamp 9, the length of bar 3 is characterized by a slot 13 extending between closed ends of the bar and between spaced parallel side members or rails 13', and downwardly extending carriage guide block 12 integrally formed with jaw 10 is guided within slot 13. Block 12 has a threaded longitudinal bore, in constant engagement with a threaded rod 14, and rod 14 is journaled in the respective closed ends of bar 3, with access for wrenched rotary actuation via one exposed end thereof. A transverse pin 14' driven into a bore at the fixed-clamp end of bar 3 is slightly offset from intersection with the axis of threaded rod 14 but it has locating engagement with a circumferential groove at the end of rod 14, thus axially stabilizing rod 14 without impairing rotation thereof.

It is apparent that adjusted rotation of rod 14 imparts longitudinal displacement to block 12 and thus also to the movable clamp 9 and its clamped pins 8. In such displacement, jaw 10 derives longitudinally extensive support from its continuous sliding engagement (at 15) with the spaced rails of bar 3, so that coplanarity is assured for clamped pins 8 at both clamps 59, whatever the adjusted displacement of clamp 9.

In one specific embodiment of the invention, applicable to monolateral small-bone fixation, distraction or compression, bar is 8-cm long, 1 .2#m wide, and 0.8-cm thick; and the section of slot 13 available for stabilized guidance of block 12 is a 0.8-cm square. Each of the clamps 59 is designed to secure two identical pins 8 at 1.2-cm spacing, and these pins are suitably self-perforating and selfthreading standard cortical screws, e.g., 40x 1.5 mm or 50x 1.8 mm, having cylindrical shank diameters of 2.5 mm. The thread pitch on rod 14 is 20/cm, and the elongation span available for adjustable displacement of the movable clamp 9 is substantially 4-cm.

In use with self-threading cortical screws at 8, there is no need for drilling, but if drilling should be desired, the two clamps 59 may first be set at desired spacing and with their clamp screws 7-7' setto thereby establish jig bores (at the pin grooves) for precise guidance of the drilling operation.

The minifixator described herein has been successfully used in phalanges, metacarpal and metatarsal contexts, in the following clinical and surgical areas: (a) Bone diaphysis lengthening, (b) Hemipiphyseal distraction, (c) Loss of bone substance, and (d) Synthesis of non-articularfractures.

Locking means may be provided for anchoring rod 14 against rotation, as by set-screw application to one of the ends of rod 14. Also, as shown in Fig. 3, the jaw 5 may be a duplicate of jaw 9 and thus also longitudinally positionable along slot 13, in which case it is preferred that rod 14 be formed with opposing thread advances for each of two exposed halves of its length; in this event; the blocks 12 of the respective clamps 59 will have corresponding oppositely threaded bores, engaged to the respective half lengths of rod 14, whereby a single rotary adjustment of rod 14 will impart distraction or compression displacements of both clamps 59 at the same time. As is apparent from Fig. 3, the added advantage is presented that ready wrench access to rod 14 is via either of its ends.

Still further, it will be seen that a feature of angular adjustment of pins 8 held at clamp 5 and/or clamp 9 may be provided, as shown in Figs. 4 and 5.

In Fig. 4, the semicylindrical grooves which locate pins 8 with respect to fixed projection 4 are formed in an intermediate jaw pad or washer 4' which, in unclamped condition, is rotatable about the clamp screw 7, in view of a sliding interface 16 between parts 4~4'. The clamp Sin Fig. thus can be set to retain both the longitudinal position of pins 8 in their respective semicylindrical grooves (in jaw members 4'-6) and the angular orientation of these pins with respect to the elongation of bar 3.

In Fig. 5, the same kind of angular-adjustment feature is provided for the jaw 9 on movable block.

Specifically, the semicylindrical grooves which locate pins 8 with respect to slide block 12 are formed in an intermediate jaw pad or washer 12' which, in unclamped condition, is rotatable about the clamp screw 7', by reason of a sliding interface 17 between parts 12-12'.

Claims (7)

1. An external minifixation apparatus for use as a bone lengthener, comprising a rigid bar bearing two clamps and for holding pins, each clamp consisting of two jaws which are closeable by means of a screw at least one of the clamps being displaceable longitudinally of the axis of the bar, the clamp having one of its jaws provided with a carriage which is displaceable within an opening by rotation of a threaded rod which passes through a cavity in the carriage, the cavity having a thread mating with the thread on the rod and the lower part of the jaw having surfaces for resting against the bar.

2. An apparatus as claimed in claim 1, in which the jaw of the movable clamp is rotatable with respect to the carriage around an axis perpendicular to the longitudinal axis of the opening and is lockable in the selected position.

3. An apparatus as claimed in claim 1 or 2, in which the jaw of the clamp is rotatable with respect to the bar around an axis perpendicular to the longitudinal axis of the bar and is lockable in a selected position.

4. An apparatus as claimed in claim 1, 2 or 3 in which the plane containing the axes of the pins of one clamp also comprises the axes of the pins of the other clamp.

5. An apparatus as claimed in any of claims 1 to 4, in which the bar is of said elongate metal having an elongate slot therein, the slot extending continuously between parallel inner sidewalls and terminating short of integrally closed ends of the bar, the clamps having multiple-pins, at least one of clamps having one jaw with surfaces configurated for elongate stabilized sliding support on the bar at opposed regions spanning the slot, the one jaw further including a block of substantially the slot width and projecting into stabilized guided relation with the sidewalls of the slot, and a lead screw journaled for rotation in the respective closed ends of the bar and having threaded engagement to the block.

6. An apparatus as claimed in claim 5, in which the other of the clamps also has one jaw configurated for elongate stabilized sliding support on the bar at opposed regions of spanning the slot, the one jaw of the other clamp also including a block of substantially the slot width and projecting into stabilized guided relation with the sidewalls of the slot and a lead screw oppositely threaded in its respective longitudinal halves and journaled for rotation in the respective closed ends of the bar, the block of one clamp having threaded engagement to the lead screw in one of its longitudinal halves and the block of the other clamp having threaded engagement to the lead screw in the other of its longitudinal halves.

7. An external minifixation apparatus for use as lengthener constructed and arranged to operate substantially as herein described with reference to and as illustrated in any of the Figs. of the accompanying drawings.