GB2425958A - Collet type pin clamp for an external fracture fixator or distractor - Google Patents

Abstract

A pin clamp for an external fracture fixator or distractor comprising a split collet 3a or jaw which clamps the transfixion pin 2 or pin bush 1 perpendicular to the axis of the pin 2 to prevent movement. Preferably the angle of the pin 2 may be adjusted. The collet 3a may have a tapered threaded outer surface 4b and may be split to form jaws. The collet 3 may be inserted into a body 4 with a cooperating internal thread and held in place by a nut 5. The collet 3 may have a tapered inner expander 6 to release the pin 2. The body 4 may be provided with separate frame elements (11, fig 3) to link several pin clamps together. Also claimed is a split pin bush 1 for attachment to a pin which may be shaped to engage the collet 3.

Description

Title: A novel collet type pin clamp for external fixator and distractor

Applicant: Veterinary Innovations Ltd Abstract This patent is for a new compact coliet type pin clamp with excellent grip to be used with frame components to construct a bone distractor and external fixator that has a good range of adjustments for the positioning of transfixion pins in orthopaedic reduction of bone fractures and for fracture fixation pending the healing process [Fig. 3]

1. Introduction.

Fractures of the long bones may be treated by means of internal fixation devices such as pins, plates and screws. These are applied to the broken bones after the fragments have been properly aligned and fixed to maintain that alignment.

Alignment of bone fragments can be difficult to achieve before an internal fixation device is applied. To facilitate realignment or reduction of the fracture, devices known as fracture tables or reduction machines are sometimes used, or the services of a strong assistant to the operating surgeon. Usually clamps or pins are secured to the limb or directly to the bone fragments then manipulated and locked in the desired position while the internal device is being applied. A considerable amount of force is often required to stretch the soft tissue contraction that normally accompanies fracture injuries.

An alternative system for fracture fixation, known as an external fixator, comprises an adjustable frame clamped to transfixion pins that are screwed into appropriate positions in the fractured bone. By adjusting the frame attached to the pins, realignment of the bone fragments can be achieved. Then the frame and clamps are locked to function as an external fixator.

Such external fixators are often complex and have a number of joints which have to be secured against loss of position. The result is usually a bulky and costly construction that impedes radiographic checks on the quality of reduction. Alternatively a fracture reduction apparatus can be used on the transfixion pins to reduce the fracture. Then a minimally adjustable or non-adjustable external fixation device is fitted to hold the transfixion pins in the reduced positions.

2. Field of Invention.

2.1. This invention relates to a novel pin clamp that can be used with transfixion pins to effect both fracture reduction and fracture fixation. It could also be used in conjunction with a separate fixator frame and once the fracture is reduced and the frame is secured, be removed of the pins from below that frame.

3. Background

3.1. To be effective a pin clamp must grip the pin with sufficient force to resist loss of position and have sufficient adjustment to its three dimensional position to accommodate a useful range of transfixion pin positions. Also, if required, after fracture reduction allow easy access to the fracture site.

3.2. To provide optimal utility the pin clamp should preferably be capable of disengagement at any angle from the pin with minimal force applied to the pin.

3.3. To be manufactured of radiolucent material so as not to impede radiographic checks on the quality of the reduction.

3.4. The device described here meets all these requirements in a way not hitherto achieved.

4. Drawings 4.1. Figure 1. shows details of one version of the pin clamp.

4.1.1 Figure Ia. is an exploded view.

4.1.2 Figure lb. shows the same device fully assembled.

4.1.3. Figure ic. shows the collet detail at a greater scale.

4.1.4. Figure Id. shows a side elevation of the pin clamp assembled.

4.1.5. Figure le. shows a front elevation of the pin clamp.

4.1.6. Figure if. shows a mid section through the pin clamp about axis 1 Ob to a larger scale.

4.1.7. Figure 1g. shows a mid section through the pin clamp about axis 3b to a larger scale.

4.2. Figure 2. &2a show an exploded view of alternative pin clamp arrangements.

4.3. Figure 3. shows three pin clamps in different orientations connected together with two frame elements to form a possible fixator/ distractor arrangement. *

5. Description.

5.1. The concept is of a split collet which is made to grip a transfixion pin directly or by means of a split bush, which in turn grips the transfixion pin.

5.2. The bush (1) fits over the transfixion pin (2) and by virtue of the split (Ia) which passes substantially through the section but does not completely divide the bush, may be sprung open to fit onto the pin or clamped closed to grip it.

5.3. The bush (1) is pivotally located between the jaws (3a) of a split collet (3), the pivot axis (1 b) being substantially perpendicular to the jaws (3a) and the direction of the split (la). By this means the pin (2) can be clamped at any position along its length, at any angle about the pin axis (2a) and at any angle to the axis (3b) of the collet (3).

This provides three degrees of freedom in the adjustment. When clamped the pin or bush (1) is retained within the jaws (3a) by a combination of friction between the clamped surfaces and re-entrant geometry, which can only be released by separating the jaws (3a) of the collet (3). Leading geometry (3e) can be provided so that forcible engagement and separation can be effected when the jaws are unlocked by a wedging action between the counter surfaces of the re-entrant geometry. This is effected in a direction substantially perpendicular to the bush pivot axis (1 b).

5.4. The collet (3) is caused to clamp the pin or bush (1) by the interaction of an external taper (3d) with an internal taper (4a) of a body section (4). The force to achieve this is created by a nut (5) on a thread (3b). This nut drives the two tapers together locking the relative positions of the collet (3) and the body (4). Before locking, the collet can be set in any angular position about the collet axis (3b), thus adding a fourth degree of freedom to the position of the transfixion pin to the body.

5.5. A plurality of bodies can be connected together with frame elements which allow them to be brought closer together or further apart and at a variety of angular relationships so as to provide at least two more degrees of freedom to the relative positioning of a plurality of transfixion pins.

5.6. In order to release the pin or bush (1) from the jaws (3a), force can be applied as described in 5.3 above. However the jaws can be opened without applying a force to the transfixion pins by means of these additional features described below.

5.7. The collet (3) is provided with an axial through hole (31), terminating in a shoulder (3g) at the jaw end. An expander rod (6) passes along this hole from the jaw end and is prevented from passing through by a tapered section (6a) with a major diameter (6b) greater than the hole (31) by a difference at least equal to the total separation required of the jaws to release the re-entrant geometry that traps the bush in the jaws.

5.8. A collar (7) with a diameter greater than the major thread (3b) diameter of the collet (3) is attached to the end of the expander rod (6) thus preventing removal of the ro from the collet but allowing sufficient axial movement to disengage the taper (6a) from the shoulder (3g) whilst preventing it invading the space required for the action of the bush.

59. The collet is unlocked by unscrewing the nut (5) backing off the body (4) and releasing the tapers (3d) and (4a). Further unscrewing brings the nut (5) into contact with the collar (7) and then drives the expander taper (6a) into the hole (31). This action opens the jaws (3a) and allows force-free disengagemrit from the bush (1) in a direction substantially perpendicular to the pivot axis (I b) of the bush (1).

5.10. There are many possible geometries for the bush (1). The essential requirement is that the faces that engage the jaws of the collet (3) are surfaces of revolution about the pivot axis (ib). Three possible arrangements are illustrated in the figures 1 and 2.

5.11. Figure 1 shows a bush, which is spherical in outer form. This gives obvious additional limited degrees of adjustment to the relative position of the pin (2).

5.12. Figure 2 shows an alternative essentially cylindrical solution and figure 2a a solution without a bush. With this bush the jaws (8) are provided with a step feature (8a) to capture the bush (9). In this illustration additional capture is provided with prominences (9a) from the clamping faces (9b) of the bush (9) engaging recesses (Sc) in the jaws. Leading geometry (Sb) and (9c) in the jaws and prominences respectively allow forcible engagement and disengagement of the capture, when the jaws are released, whilst retaining substantial grip when the jaws are clamped shut.

5.13. Figure 3. shows one arrangement of a plurality of pin clamps and interconnecting frame elements.

5.13.1. In this case the Bodies (4) of the pin clamps are provided with threads (1 Oa) on an axis (lic) essentially perpendicular to the axis (3b) of the pin clamp. Two such threads may be provided diametrally apposed and have opposite handedness.

i.e. one right-handed (RH) thread and the other left-handed (LH).

5.13.2. Adjacent bodies are joined by connecting rods (11) provided with RH thread (11 a) at one end and LH thread (11 b) at the other so that by screwing in one direction causes adjacent bodies to separate and in the other direction for them to close together. Clearly the relative angular position of the bodies can also be varied about the connecting rod axis (1 ic).

5.14. Many other connecting arrangements are possible.

Claims (24)

Claims.

1. A pin clamp for use in a bone distractor or orthopaedic external fixator comprising a split collet or jaw capable of clamping the transfixion pin or the pin bush on an axis substantially perpendicular to the axis of the pin and the plane of the split so as to cause the collet or bush to clamp the pin and thus prevent all relative movement between collet and pin or pin bush and pin.

2. The inner surface of the collet is such that conforms to the outer surface of the pin or bush to permit adjustable angular relative positioning about an axis substantially perpendicular to the phine of the pin or the slit in the bush.

3. The collet is split over a substantial portion of its length so as to form two jaws that can be sprung towards each other provide a clamping pincer movement.

4. The collet is provided with a taper on the outside engaging a taper in a fixed body component so that when pressed into engagement the two tapers cause the jaws of the collet to close onto the pin or bush at any relative angle between collet and body on an axis substantially perpendicular to axis of freedom between the pin or bush and the collet.

5. A collet as above in which the gap between the jaws when relaxed to be sufficient to disengage from the pin or bush in a direction substantially perpendicular to the pin using minimal force.

6. A screw thread is provided to drive the tapers into engagement.

7. A collet fitted with an inner expander, which can open the collet from a normal closed position to release a trapped pin bush or pin.

8. An expander having a tapered section engaging a corresponding surface on the collet and driven by a screw thread.

9. A body that has a female thread engaging a male thread on the collet to drive together the tapers of the body and the collet.

I O.A separate nut that engages the thread on the collet to force the female taper in the body onto the male taper of the collet.

11. A pin bush with a hole through it to fit onto a transfixion pin.

12. The bush is split on a plane through the axis of the hole and through a substantial portion of the bush so that it can be snapped onto a pin in a direction substantially perpendicular to the pin axis and having sufficient flexibility to allow it to be squeezed onto the pin so as to prevent relative movement.

I 3. Sufficient section of the bush to remaining intact to prevent the bush falling into two hyçs.

14, The ofler form of the pin bush to be a surface of revolution about an axis perpendicular to the axis of the pin and the plane of the slit.

15. A pin bush that is spherical in outer form engaging a complementary surface in the collet.

16. A pin bush that has two flat faces, parallel to the plane of the split, engaging corresponding flat faces on the collet.

17. A pin bush as in 16. above, which has prominences on the flat surfaces to engage corresponding recesses in the collet.

18. A pin clamp as shown in Figure 1

19. The body is provided with means of attaching frame elements capable of joining two or more pin clamps together.

20. A frame arrangement as shown in Figure 3.

21. A means of rigidly though adjustably attaching one or more frames to the body or nut to hold two or more pin clamp assemblies in a variable fixed relationship to each other.

22. A frame or frames as above, which can be adjusted in length on axes substantially perpendicular to the axes of the collets

23. A collection of such pin clamps and frames combined into a structure capable of holding various fragments of a broken bone in an anatomical relationship with each other whilst healing occurs or to hold them in good position whilst an alternative fixation device is fitted.

24. A combination of pin clamps and frames as above made of radiolucent material.