SPINAL FUSION IMPLANT

A spinal fusion implant comprises a rigid hollow elongate member for insertion in a direction parallel to the longitudinal extent of the member between the vertebrae of a human spine, the rigid member having a height (when considered in an use implanted position with a patient's spine vertical) greater than its width w so that the member can be inserted between the two vertebrae and then displaced angularly through 90° to an in use position. The member has a body portion which has a plurality of apertures for allowing bone growth inducing material introduced into the hollow member to extend therethrough and a plurality of arcuate teeth which bite into the vertebrae when the member is in an in use position.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1 to 3 of the drawings, the spinal fusion implant shown therein is intended for insertion between the end plates of two adjacent vertebrae of a human spine after removal of damaged spinal disc. The implant comprises a rigid hollow elongate member 10 which has a height h (when considered in an in use implanted position with the patient's spine vertical) greater than its width w so that the member can be inserted between two vertebrae and then displaced angularly through 90° to an in use position. This allows for the smooth entry of the implant into the intervertebral space before angularly displacing the implant to wedge it in place. The member 10 comprises a body portion 11 , which tapers from one end to the other when viewed from the top and the bottom 15 (as shown in FIG. 1 ) and when viewed from its two sides 16 (as shown in FIG. 2 ), and a plurality of arcuate teeth 12 . The top and the bottom of the body 11 are each provided with an elongate generally rectangular aperture 13 and each side of the body 11 is provided with three circular apertures 14 . These apertures 13 and 14 allow bone growth inducing material introduced into the hollow member 10 to extend therethrough. There are several sets of teeth 12 . In the embodiment shown, there are five sets of teeth 12 a to 12 e . The sets 12 a to 12 e are spaced apart in a direction parallel to the longitudinal extent of the rigid member 10 . Each set comprises four teeth. Two of the teeth extend from the top of the body portion 11 and are equi-angularly spaced from, and on opposite sides, of a plane p bisecting the width of the rigid member and the other two teeth extend from the bottom of the body portion 11 and are also equi-angularly spaced from, and on opposite sides of, the plane p. As clearly shown in FIGS. 1 and 3 , the teeth do not extend beyond the two sides 16 of the body portion 11 . This further promotes smooth entry of the implant into the intervertebral space. As shown clearly in FIG. 3 , the sharp edges of the teeth 12 of each set of teeth 12 a to 12 e lie on a common circle centred about a central longitudinal axis of the implant. The height of the teeth 12 varies along the longitudinal extent of the implant. The teeth 12 c midway or substantially midway between the ends 17 of the rigid member are higher than the teeth 12 a and 12 e at or adjacent to opposite ends 17 of the implant. This ensures anatomical contact between the implant 10 and the concave surfaces of the end plates of the vertebrae. Moreover, the tapered nature of the implant is designed to restore natural lordosis of the lumbar spine. The body portion 11 of the implant has threaded apertures 18 at opposite ends, respectively, for attachment of the rigid member 10 to an insertion tool (not shown). This allows the implant to be inserted posteriorly or anteriorly. The large central cavity in the body portion 11 provides good area surface contact between bone growth inducing material which is compacted into the body portion 11 prior to insertion into the intervertebral space. FIGS. 4 and 5 show an elongate tamping jig 20 for supporting the member 10 while bone growth inducing material is compacted therein. The jig 20 has a base 21 and two side walls 22 and 23 which define therebetween a tapered passage 24 for receiving and supporting the member 10 with the top or bottom uppermost. This exposes one of the generally rectangular apertures 13 whilst the other aperture 13 is covered by an elongate projection upstanding from the base 21 mid-way between the diverging sides of the passage 24 and whilst the circular apertures 14 are covered by the side walls 22 and 23 . Bone growth inducing material is compacted into the hollow member 10 through the said one generally rectangular aperture 13 whilst the member 10 is supported in the jig 20 . The elongate nature of the jig 20 allows members 20 of various different sizes to be supported. The implant is made of any bio-compatible material which is stronger than bone and is typically made from titanium alloy or non-metallic materials such as carbon fibre composites.