ORTHOPAEDIC FASTENER"

BACKGROUND TO THE INVENTION

THIS invention relates to an orthopaedic fastener and, more particularly, an orthopaedic fastener designed to form a bridge between respective bones that are normally connected by way of ligaments that for some reason or another are rendered ineffective, or between a body structure such as tissue and a bone.

Whilst in no way being restrictive on the scope of the invention, one particular application for an orthopaedic fastener according to the invention is to locate the clavicle relative to the coracoid process of the scapula in the event of an injury such as acromioclavicular disruption or clavicle fracture with associated tearing of the coracoclavicular ligaments attaching the scapula to the clavicle.

It is to be understood that, whilst treatment of the aforesaid injuries will be particularly described in the following specification, the orthopaedic fastener of the invention can be applied in other applications such as, for example, in the case of Weber C fractures of the ankle.

With particular reference to injuries affecting the shoulder girdle, and in particular injuries such as distal clavicle fractures and AC-joint disruption that require the location of the clavicle or a part thereof relative to the coracoid process in order for healing to take place, existing treatments do have distinct disadvantages.

Some of the complications that can evidence themselves are erosion of bone by contact with a metal component, .late fracture through the implant holes in the bone, necessity of a second operative procedure in order to remove a fixation device, migration of pins or wires, metal failure, an unsightly scar and inadequate purchase of the fixation.

SUMMARY OF THE INVENTION

According to the invention there is provided an orthopaedic fastener for locating a body. structure relative to a bone, the fastener comprising:

a shank for passing through the body structure and having an anchor portion at an operatively distal end thereof which is anchorable in a hole drilled in the bone, a locking portion at an operatively proximal end thereof opposite to the distal end, and a connecting portion between the, anchor portion and the locking portion; and

a locking element engagable with the locking portion at a selected position on a section of the locking portion projecting from the body structure on a side thereof remote from the bone;

at least the connecting portion exhibiting limited flexibility to allow relative movement to take place between the body structure and the bone.

In the preferred embodiments the anchor portion is substantially rigid and has an external thread by means of which it be anchored in the hole in the bone. The locking portion and connecting portions may be continuous with one another and exhibit limited flexibility and elasticity. Most conveniently the shank is moulded integrally of a plastics material.

In order to provide the anchor portion with the required rigidity for anchorage in the bone, it may have a lateral dimension which is greater than that of the locking portion and connecting portion. Alternatively the anchor portion may be internally reinforced, typically by means of an internal reinforcing pin moulded into the plastics material of the anchor portion. As another alternative the anchor portion may be made of a relatively rigid material, for example a metal, and at least the -connecting portion may be made of ^" a relatively less rigid material, for example a plastics. According to yet another alternative the connecting portion can be made of spring steel.

Preferably the locking portion and locking element have cooperating formations thereon allowing the locking element to move along the locking portion in a direction towards the anchor portion but preventing movement of the locking element along the locking portion in the opposite direction. The cooperating formations may be of an opposing, sawtooth configuration.

The fastener may include a sleeve arranged to cover the shank where it passes through the body structure. The sleeve may carry a laterally projecting flange at an operatively proximal end thereof. There may in addition be a washer locatable on the flange around the locking portion. Typically the locking element is annular and is locatable around the locking portion against the washer. For this purpose the locking element and washer may have complementary, curved surfaces, and washer may be made of an elastic material.

Further according to the invention there is provided a method of locating a body structure relative to a bone, the method comprising the steps of providing a fastener according to any one of the preceding claims, forming a hole having a first portion extending through the body structure and a second portion extending into the bone, passing the shank of the fastener through the first portion of the hole, anchoring the anchor portion of the fastener in the second portion of the hole, and engaging the locking element of the fastener with a section of the locking portion of the shank which projects from the body structure on a side thereof remote from the bone.

Preferably the shank of the fastener is tensioned and the locking element is engaged with the locking portion so as to maintain the tension in the shank.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a partly sectioned elevation of one embodiment of fastener according to the invention;

Figure 2 shows an enlargement of part of the locking portion of the shank illustrated Figure 1 ;

Figure 3 shows the shank of the fastener illustrated in Figure 1 in elevation, in a manner indicating its flexibility;

Figure 4 diagrammatically illustrates a fastener according to the invention in use providing location of a clavicle relative to a coracoid process in a shoulder; and

Figure 5 illustrates, in elevation, a variation of the shank illustrated in Figure 1.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

In the embodiment of the invention illustrated in Figures 1 and 2, an orthopaedic fastener 1 has a shank 2 comprising an anchor portion 3 extending partway along the shank from a distal end 4 thereof and a locking portion 5 at the other end, the locking portion merging with an intervening connecting portion 6.

In this embodiment of the invention the shank is made as a one-piece injection moulding wherein the required variation of physical properties is achieved by varying the cross-sectional dimension of the shank and selecting the plastic material accordingly. Typically a suitable nylon is envisaged as being suitable. The anchor portion is of the largest diameter in order to render it substantially rigid. The anchor portion has an external screw thread enabling it to be anchored in a hole drilled and, if necessary, tapped, in a recipient bone.

Both the locking portion and the connecting portion have a series of formations 7 extending therealong. The illustrated formations are of a sawtooth configuration to cooperate with corresponding locking teeth 8, of opposing sawtooth configuration, in a central bore, through an annular locking element 9. The arrangement is such that the opposing sawtooth formations allow unidirectional movement of the locking element 9 in a direction from the free, proximal end 10 of the locking portion of the shank towards the anchor portion thereof.

The cross-sectional dimensions of the locking portion and connecting portion are selected so that limited flexibility, such as that indicated in Figure 3, is provided.

A sleeve 11 operatively extends over at least a part of the length of the shank as shown in Figure 1. The sleeve has an integral flange 12 at the end thereof corresponding to the locking element. An optionally elastic load distributing washer 13 is located between the flange of the sleeve and the locking element 9. In this embodiment of the invention the washer and locking element have cooperating, contoured surfaces 14 that include a part spherical recess or seat formed within the washer and a complementary part spherical outer surface on the locking element.

In use, and as illustrated schematically in Figure 4, the orthopaedic fastener 5 described above may be applied to the shoulder, for example in the event of injury such as tearing of the coracoclavicular ligaments 15, in order to locate the clavicle 16 relative to the coracoid process 17 of the scapula 18 at least during a healing process.

The installation procedure is performed surgically, typically with the aid of X-ray imaging. The surgical incision would typically be over the clavicle and the underlying coracoid process. The procedure is initiated by drilling a hole through the clavicle with the diameter of the hole being selected to accommodate the sleeve 11 of the fastener.

A hole is then drilled into the base of the coracoid process to accept the screw threaded anchor portion 3 of the shank. The hole may be tapped with a matching screw thread. The shank is then installed in position by securing the anchor portion 3 into the tapped hole using a tool (not shown) that conveniently could cooperate with a hexagonal formation 19 formed as part of the shank at the position where the connecting portion joins the anchor portion. The tool will typically be configured as a very deep socket so that it can pass through the drilled hole in the clavicle. The sleeve 11 is then slipped over the shank such that the flange 12 seats about the mouth of the hole in the clavicle.

The washer 13 is placed around the shank, resting on the flange 12, whereafter the locking element 9 is slipped over the locking portion and moved down that portion in order to press against the washer.

It will be understood that as the locking element 9 is pressed down against the washer 13, tension will be applied to the shank. If required, a tensioning device may be applied to the free end of the locking portion, while the locking element is moved down over that portion, in order to generate a predetermined tension in the shank. After appropriate tensioning of the shank, any excess length of the shank extending beyond the locking element 9 can be trimmed off to allow subsequent closure of the wound.

If necessary a second, similar fastener could be used at a different angle and be anchored more distally on the coracoid process in order to provide a replacement for the Conoid and Trapezoid ligament function.

It will be understood that the flexibility in the fastener allows limited movement to take place between the clavicle and scapula. The preferred fastener is designed to provide intrinsic elasticity and dynamics similar in nature to the ligaments in the natural state, thereby closely mimicking the ^{■ •} characteristics of the conoid and trapezoid ligaments in terms of strength, stabilization in respective motion planes, as well as dynamic properties allowing motion at the AC-joint as in the uninjured state.

The orthopaedic fastener of this invention does not need to be removed at a specific time interval, and failure of the device is not envisioned within normal physiological use of the shoulder joint. Rapid mobilization and recovery is foreseen with immediate post operative mobility limited by pain only.

It is perceived that the orthopaedic fastener could also be used for fixation at syndesmosis type joints e.g. Weber C fractures of the ankle, because of the inherent elastic mobility in the fastener, in which the shank allows for rigid fixation with a calculated amount of pressure over the joint yet allows slight natural mobility through its elastic properties. It is envisaged that the orthopaedic fastener of this invention could be used in any situation in which a surgeon requires fixation of bone, tissue or other body structure to an underlying bone, and needs to be sure of placement of the drill hole that will be obscured by an structure if that structure has a geometry which obscures the view of the deep anchor site when attempting to drill both layers simultaneously.

The shank of the fastener can be made in a number of different ways other than moulding the entire shank as one integral unit. For instance, a rigid metal pin 20 could be moulded within the anchor portion of the shank during injection moulding of the plastics, as illustrated in Figure. 5. In another variation the anchor portion of the shank could be made of metal and the connecting portion could be made of a suitable plastics material bonded or otherwise fixed to the metal anchor portion. In yet another variation, the connecting portion could be made of spring steel, for example spring steel wire. This could cooperate with a suitably resilient washer in order to impart required elasticity to the assembly.