WO2008044057A1

WO2008044057A1 - Spinal implant

Info

Publication number: WO2008044057A1
Application number: PCT/GB2007/003927
Authority: WO
Inventors: Peter Seddon
Original assignee: Quadrant Medical Limited
Priority date: 2006-10-13
Filing date: 2007-10-15
Publication date: 2008-04-17
Also published as: EP2079405A1; GB0620400D0

Abstract

A spinal fusion implant (1) comprises a first and second body member (2, 3) having perforated vertebra-engaging surfaces. The members define a cylindrical body with a rounded end in the collapsed condition. An axially extending threaded activating member (13) within the body is rotated by means of an elongate tool (28) to move the members apart by means of linkages (22). The linkages carry bone engaging elements (27) which are contained within the body in the collapsed condition but which are driven to protrude through apertures (11a - 11c) in the first vertebra-engaging surfaces as the implant reaches its fully expanded condition. The linkages (22) are such that the degree of expansion at the rounded end exceeds that at the other end, to account for the lordotic curve of the patient's spine. The rate of expansion of the implant per evolution of the activating member (13) reduces as the implant reaches its fully expanded condition.

Description

Spinal Implant

Field of the invention The present invention relates to an improved spinal implant for use in spinal fusion surgery and particularly, but not exclusively, to a spinal implant for use in lumbar spinal fusion surgery.

Background

In a healthy spine adjacent vertebrae are separated by intervertebral discs which separate the vertebrae and allow relative movement of adjacent vertebrae. This provides movement in the spine. Conditions such as degenerative disc disease cause degradation of the intervertebral discs resulting in significant problems for sufferers.

These conditions, and other ailments affecting the intervertebral discs, cause instability in the spine and movement of adjacent vertebral segments which can cause significant pain, discomfort and often a reduction in the mobility for an individual.

The lower portion of the spine, the lumbar spine, is connected to the pelvis and is the region in which most spinal movement occurs and where the greatest loads are placed on the spine. Damage to or degeneration of the intervertebral discs in this particular region is therefore a significant problem and cause of back pain.

A number of techniques and methods have been developed to alleviate the pain and problems caused by these conditions and specifically in the lumbar portion of the spine. One such technique is lumbar spinal fusion in which two adjacent vertebral elements are caused to grow or fuse together. Although this technique prevents two adjacent elements from moving relative to one another, thereby reducing mobility for the individual, it does alleviate the intense pain which can be caused by these conditions and is therefore a preferred method for surgeons.

Fusing vertebrae together in this way presents other problems. For example, causing bones to fuse together requires a bone graft inside the intervertebral cavity which is difficult to reach. In addition, fusing the bones in exactly the correct position can be a significant challenge. Adjacent vertebrae are by their very nature prone to movement and uneven fusion can result in poor alignment of the bones, hi the worst cases poorly fused vertebrae can cause a reduction in the spacing of adjacent vertebrae and a distorted or shortened spine.

To solve these problems spinal implants known as "interbody cages" are commonly used to maintain the spacing of adjacent vertebrae as the bones fuse together. Interbody cages are simple elements, commonly made of titanium, which are inserted into the space between adjacent vertebrae. Once inserted the cages maintain a space between the adjacent vertebrae as the bones fuse together. Typically, two spinal implants are used in parallel. In contrast in a "T-LIFT" operation a single relatively longer spinal implant is used.

Simple rigid (that is to say non-expanding) spinal cage implants are known (see for example US2007/0027544; US 2006/0293748, and US2006/0095136). However, such implants require a larger incision, in order to expose the insertion site and cannot be conveniently re-sited by a surgeon after an initial implantation.

Intervertebral spacers are also used on a temporary basis during surgery for adjusting the space between vertebrae as described in WO2004/000166, for example when preparing the opposing surfaces of adjacent vertebrae. WO2004/000166 discloses such a spacer which is expanded by a surgeon in a patient but is generally designed to be removed from the patient after surgery. Expansion of the spacer is controlled by axial movement of a pull arm in the spacer. Although it is suggested that in one embodiment of the spacer may remain within the patient, the only disclosure of means for locking the spacer in an expanded condition is in relation to locking means provided by a tool used to insert the spacer rather than by the spacer itself. Accordingly, the spacer is only locked in an expanded condition whilst the tool is attached, there is no disclosure of means for locking the spacer independently of the tool.

The insertion of interbody cages involves traumatic invasive surgery requiring an incision into the body at least as large as the cage and in some cases over 2.54 cm (1 inch) in size. Access to the spine can either be made through the front of the body in a procedure known as Anterior Lumbar Interbody Fusion (ALIF) or from the rear of the body in a procedure known as Posterior Lumbar Interbody Fusion (PLIF). Both of these techniques are complicated and highly invasive procedures.

Attempts have been made to provide interbody cages which simplify these procedures and which reduce the trauma experienced by the patient both during and after surgery. An example of such a cage is shown in US6, 126,689. The interbody cage shown in this patent has a relatively high number of joints which are potential areas of weakness.

Although some interbody cages, do provide some improvements they still cause significant trauma to the patient and fail to provide surgeons with a reliable device which can accommodate an individual patient's anatomical needs. Furthermore, existing devices fail to provide a simple and efficient means to allow for complications in the procedure to be remedied. In particular, the device of US6127597 may be difficult to withdraw once positioned and this can lead to complications if the interbody cage is not initially correctly positioned.

There is therefore a need for a suitable implant for use in a lumber spinal fusion procedure which addresses the known problems with prior art products, and specifically reduces the trauma experienced by the patient and the associated post operation recovery time.

Summary of the invention

According to one aspect of the invention there is provided an interbody spinal fusion implant comprising a first elongate body member having a first vertebra-engaging surface for engaging a first vertebra, a second opposed body member having a second vertebra-engaging surface for engaging a second vertebra, there being a space defined between the first and second body members, a rotary activating member extending longitudinally in the space between the first and second body members, a first linkage system connected between the first body member and the rotary activating member, and a second linkage system connected between the second body member and the rotary activating member, whereby the rotary activating member may be operated to move the first and second body members apart between a collapsed condition and an expanded condition; wherein the first body member is arranged to provide a first recess or aperture defined by the first vertebra-engaging surface, and the first linkage system is connected to a first bone-engaging element which is arranged so that it does not extend beyond the first vertebra-engaging surface of the first body member when the body members are in the collapsed condition and which is arranged to be urged into the first recess or aperture by the first linkage system as the body members are moved to the expanded condition so as to protrude from the first vertebra-engaging surface; and wherein the second body member is arranged to provide a second recess or aperture defined by the second vertebra-engaging surface, and the second linkage system is connected to a second bone-engaging element which is arranged so that it does not extend beyond the second vertebra-engaging surface of the second body member when the body members are in the collapsed condition and which is arranged to be urged into the second recess or aperture by the second linkage system as the body members are moved to the expanded condition so as to protrude from the second vertebra-engaging surface, and in which the implant comprising means for maintaining the implant in an expanded condition.

The spinal implant of the invention is advantageous in several respects. The rotary activating member permits careful control of expansion and contraction of the spinal implant. This is advantageous during delicate surgery and facilitates repositioning of the implant. The spinal implant of the invention is advantageous in that the bone-engaging elements are kept within the perimeter of the body members until they are deployed as the implant is operated into an expanded condition. Significantly, compared with certain prior art devices, the spinal implant of the invention may be returned to a collapsed condition in order to permit re-siting by a surgeon. The implant is maintained in an expanded condition by means integral with the implant which is advantageous over systems in which the implant is maintained in an expanded condition by an external tool. Typically, the implant is monitored in an expanded condition by the resistance to rotation of the rotary activating member.

The first and second body members are arranged to provide two opposing surfaces or 'jaws' which contact the surfaces of the vertebrae and which can accommodate the forces applied when the patient is again active. The upper body member is arranged to contact the upper vertebrae within the cavity and the lower body member is arranged to contact the lower vertebrae within the cavity. The body members may have any suitable shape or profile suitable for use in a vertebral cavity.

Preferably, the first and second body members each have a generally semicircular cross- section. In one particularly preferred embodiment, the body members have substantially flat opposed surfaces bordered by radiussed edges. The lower body member is preferably provided with a generally 'U' shaped profile and the upper member with an opposing inverted ¹U¹ profile. The two body members are preferably generally identical in profile such that when opposing body members are placed together the implant is generally circular in cross-section and generally tubular in shape. Thus, in a collapsed position the implant is generally smooth in profile thereby facilitating insertion into the body and minimising damage as the implant is put into position.

It will be appreciated that other profiles may also be used such as an elliptical shape or other shape having a generally smooth outer profile.

The first and second body members may define respective first and second recesses. The first and second body members preferably each define four recesses or apertures. Each of the first and second body members may be associated with four bone-engaging elements.

A bone-engaging element may be pivotally connected to an associated first or second body member. A bone-engaging element may be pivotally connected to a linkage mechanism. Preferably a bone-engaging element associated with the first body member engages a bone-engaging element associated with the second body member. This provides support between adjacent bone-engaging elements enhancing the stability of the implant. For example, a bone-engaging element associated with the first body member may have a geared portion which engages a geared portion of a bone-engaging element associated with the second body member. Preferably geared portions of the bone-engaging elements associated with the first body member engage with geared portions of the bone-engaging elements associated with the second body member. The gearing facilitates coordinated movement of the bone-engaging elements.

The bone engaging elements may be arranged at any suitable angle to the surface of the body members. The bone engaging members may be arranged at an angle between 20 and 60 degrees, preferably between 30 and 50 and more preferably between 30 and 50 degrees. Most preferably the bone-engaging elements are arranged to engage with the bone at an angle of 45 degrees to the surface of the body members.

The bone-engaging elements may be any suitable element arranged to penetrate the bone surface. Any suitable shape may be used such as a cone, 'spike' or other suitable profile which can engage with the bone surface. The bone-engaging elements themselves may be provided with surfaces arranged to facilitate movement into the bone. For example, the elements may be arranged with serrated edge or the like.

The bone-engaging elements are preferably integral with the linkage connecting the elongate members and threaded rod. Most preferably the bone-engaging elements are in the form of a portion of the linkage extending from the pivot point at which the elongate members are connected to the respective linkage or coupling. Thus, as the linkage moves and rotates the portion extending beyond this pivot point moves in an arc from a generally flat orientation (generally parallel with the axis of the device) to an expanded orientation or position where the portion extends beyond the surface of the elongate member and into the bone.

In a preferred embodiment, a bone-engaging element pivots to an over-centre position when the first and second body members are in a fully expanded condition whereby the implant is stabilised in the fully expanded condition. This provides excellent stability for the implant.

The first and/or second linkage system may comprise a trunnion which is driven by the rotary activating member. Preferably the first and second linkage systems comprise two trunnions. The trunnions may be pivotally connected to the bone-engaging elements. In a preferred embodiment, the first linkage system comprises two axially spaced first links connected to the first body member at axially spaced positions, and the second linkage system comprises two axially spaced second links connected to the second body member at axially spaced positions. Preferably when each of the first links is connected to a respective first bone-engaging element which is within the hollow space when the body members are in the collapsed condition and which is arranged to be urged into a first recess or through a respective first aperture by the first linkage system as the body members are moved to the expanded condition; and each of the second links is connected to a respective second bone-engaging element which is within the hollow space when the body members are in the collapsed condition and which is arranged to be urged into a second recess or urged through a respective second aperture by the second linkage system as the body members are moved to the expanded condition. Each of the first links of the first linkage system may comprise two laterally spaced arms connected to the first body member, and each of the second links of the second linkage system may comprise two laterally spaced arms connected to the second body member. Each of the arms of the first links of the first linkage system may be provided with a respective first bone-engaging element which is within the space between the body members when the body members are in the collapsed condition and which is arranged to be urged into a first recess or through a respective first aperture by the first linkage system as the body members are moved to the expanded condition; and wherein each of the arms of the second links of the second linkage system is provided with a respective second bone-engaging element which is within the space between the body members when the body members are in the collapsed condition and which is arranged to be urged through a respective first recess or through a respective second aperture by the second linkage system as the body members are moved to the expanded condition.

The rotary activating member may comprise a first threaded portion extending from a central region towards one end of the implant, and a second, coaxial threaded portion extending from a central region towards the other end of the implant, the first and second threaded portions having threads of opposite senses, the first threaded portion engaging a first threaded follower which is connected to one of the pair of first links and one of the pair of second links, and the second threaded portion engaging a second threaded follower which is connected to the other of the pair of first links and the other of the pair of second links. The first threaded follower may be pivotally connected to one of the pair of first links, that one of the pair of first links being pivotally connected to the first body member; the first threaded follower is also pivotally connected to one of the pair of second links, said one of the pair of second links being pivotally connected to the second body member; the second threaded follower is pivotally connected to the other of the pair of first links, said other of the pair of first links being pivotally connected to the first body member; and the second threaded follower is also pivotally connected to the other of the pair of second links, said other of the pair of second links being pivotally connected to the second body member. The pitches of the first and second threaded portions may differ, so that in the fully expanded condition the first and second members are separated by more at one end of the implant than at the other. Thus, the lordotic curve of a patient's spine can be matched by selecting an appropriate thread pitch of the respective ends of the implant. More preferably the lordotic curve of the patient may be accommodated by providing the cage with linkages of a suitable length such that in use the cage may form a 'wedge shape¹ once in situ i.e. with one end separated more than another. Preferably, the pitch of one threaded portion is about 0.4. Preferably, the pitch of the other threaded portion is about 0.35.

As noted above, resistance of the rotary activating member may monitor the implant in an expanded condition. Other suitable means for achieving this are contemplated. For example, a releasable catch may be provided for monitoring the implant in an expanded condition.

Alternatively, in order to produce the wedge shape, one of the first links is larger than the other of the first links, and one of the second links is larger than the other of the second links, so that in the fully expanded condition the first and second members are separated by more at one end of the implant than at the other.

The leading end of the implant, i.e. the end which is entered into the body first is preferably arranged to prevent tissue damage, and more importantly nerve damage, as the implant is located into the body. Any suitable profile may be used. Preferably, the end of the implant is of a generally rounded shape such that the implant resembles a capsule or bullet shape. The leading end of the implant is preferably hemispherical in a collapsed position so as to provide a smooth outer surface at the leading end of the device. Other elongate profiles may also be conveniently used.

Preferably the portion of the body member which is arranged to engage with the vertebrae is flat or truncated so as to increase the contact area of the elongate member and the bone.

The body members are preferably arranged to provide a path through which bone can grow. Preferably the body members are provided with a plurality of holes or orifices passing through the member. Thus, once the implant is in situ a path is provided through which bone can grow in a generally vertical direction to meet the opposing vertebrae. In this way the bone can conveniently fuse together through, as well as around, the implant. This advantageously makes the fused bone more homogeneous and less prone to fracture, failure or the like. Alternatively, dimples may be formed in the surface of the elongate members which facilitate engagement with bone as it grows.

In use the rate of separation of the first and second body members when moving from the collapsed condition to the fully expanded condition preferably decreases as the separation increases, at least over a range of movement adjacent the fully expanded condition. This gives a surgeon enhanced control over expansion and/or collapse of the implant during surgery.

In a fully expanded condition, longitudinally spaced bone-engaging elements of the implant may diverge. Preferably, in the fully expanded condition, laterally spaced bone- engaging elements diverge.

Preferably in the fully expanded condition bone- engaging elements extend laterally beyond the body members. In this way, in use the bone-engaging elements engage a patient's vertebrae. Preferably in the fully expanded condition, the bone-engaging elements protrude beyond the respective first and second vertebrae-engaging surfaces.

The rotary activating member may comprise an axially extending connector for connecting to a tool which can be operated to expand or contract the implant. The first and second body members may be provided with means for receiving latches provided on the tool.

In accordance with another aspect of the invention there is provided a spinal implant in accordance with the invention in combination with an elongate tool having at one end means for engaging with the axially extending connector on the rotary activating member.

Preferably the tool comprises latches for engaging with the latch receiving means on the first and second body members.

According to another aspect of the invention there is provided an interbody spinal fusion implant comprising a first body member having a first vertebra-engaging surface for engaging a first vertebra; a second opposed body member having a second vertebra- engaging surface for engaging a second vertebra; a rotary activating member extending axially between the first and second body members; a linkage system connected between the rotary activating member and the first and second body members, whereby the rotary activating member may be operated to move the first and second body members between a collapsed condition and an expanded condition; the body members in the collapsed condition defining an elongate body which is rounded at one end of the implant, the elongate body containing the rotary activating member and the linkage, and in which the implant comprising means for maintaining the implant in an expanded condition; wherein at the other end of the implant the rotary activating member comprises an axially directed connector for connecting to an axially extending tool for use in rotating the activating member.

According to another aspect of the invention there is provided an interbody spinal fusion implant comprising a first body member having a first vertebra-engaging surface for engaging a first vertebra; a second opposed body member having a second perforated vertebra-engaging surface for engaging a second vertebra; a rotary activating member disposed between the first and second body members; a linkage system connected between the rotary activating member and the first and second body members, whereby the rotary activating member may be operated to move the first and second body members between a collapsed condition and an expanded condition; the body members in the collapsed condition defining a body containing the rotary activating member and the linkage; wherein the arrangement of the rotary activating member and the linkage is such that in use the rate of separation of the first and second body members when moving from the collapsed condition to an expanded condition decreases as the separation increases, at least over a range of movement adjacent a fully expanded condition.

According to a further aspect of the invention there is provided an interbody spinal fusion implant comprising a first body member having a first textured vertebra- engaging surface for engaging a first vertebra; a second opposed body member having a second textured vertebra-engaging surface for engaging a second vertebra; an activating member extending axially between the first and second body members; a linkage system connected between the activating member and the first and second body members, whereby the activating member may be operated to move the first and second body members between a collapsed condition and an expanded condition; the body members in the collapsed condition defining a body containing the activating member and the linkage; wherein there are provided a plurality of bone-engaging elements which are contained within the body in the collapsed condition and which are connected to the rotary activating member such that as the body members move apart to an expanded condition, the bone-engaging elements protrude through recesses defined by the first and second vertebra-engaging surfaces, and in which the implant comprising means for maintaining the implant in an expanded condition.

According to a further aspect of the invention there is provided an interbody spinal fusion implant comprising a first body member having a first perforated vertebra- engaging surface for engaging a first vertebra; a second opposed body member having a second perforated vertebra-engaging surface for engaging a second vertebra; an activating member extending axially between the first and second body members; a linkage system connected between the activating member and the first and second body members, whereby the activating member may be operated to move the first and second body members between a collapsed condition and an expanded condition; the body members in the collapsed condition defining a body containing the activating member and the linkage; wherein there are provided a plurality of bone-engaging elements which are contained within the body in the collapsed condition and which are connected to the rotary activating member such that as the body members move apart to an expanded condition, the bone engaging elements protrude through apertures in the first and second vertebra-engaging surfaces, and in which the implant comprises means for maintaining the implant in an expanded condition.

Associated with each of the first and second vertebra-engaging surfaces there may be longitudinally spaced bone-engaging elements which, in the fully expanded condition, protrude through apertures in the associated vertebra-engaging surfaces, or through recesses defined by those vertebrae-engaging surfaces, and which diverge in the longitudinal direction. Preferably associated with each of the first and second vertebra- engaging surfaces there are laterally spaced bone-engaging elements which, in the fully expanded condition, protrude through apertures in the associated vertebra-engaging surfaces and which diverge in the lateral direction. Most preferably in the fully expanded condition, the bone-engaging elements protrude beyond the body members.

There may be the provision of means which allows the surgeon to adjust the implant to match the dimensions of the intervertebral cavity of the individual patient by controlling the extent to which the body members move apart. However, for simplicity of construction it may be preferred to have a range of implants of different sizes.

The implant and its components may be made of any material suitable for use in the human body and suitable for accommodating the loads once the implant is in position in the spine. For example, the implant may be manufactured from titanium or the like which advantageously allows the surgeon to view the position of the implant during and/or after surgery, using radiography. Furthermore, materials such as titanium allow the individual components to be designed with high strength to weight ratios thereby reducing the overall weight of the implant. This is an important factor for components which are to remain in the body. Alternatively, or additionally, all or parts of the implant may be made from a suitable biomaterial. All or parts of the implant may be manufactured from a suitable polylactide or other biocompatible material. For example the implant may be manufactured (all or in part) from polyetheretherketone (PEEK) or the like. This also advantageously allows the surgeon to observe the position of the implant by means of radiography. In such a case the implant is manufactured all or in part using a suitable biosoluble material so that the implant is absorbed by the body over a period of time and of course after the bones have fused. Any suitable material may be used such as a polylactide or the like.

The implant may additionally be provided with a suitable coating arranged to stimulate bone growth. Such a coating may be any suitable bone growth inducing material such as hydroxyapetite or the like. Additionally, or alternatively, the implant may be provided with a suitably rough surface (e.g. protuberances, or dimples) which acts as a 'key' to encourage bone growth around the implant.

The outer dimensions of the cage are preferably selected to minimise the size of incision necessary to access the spine and to allow for convenient positioning between adjacent vertebrae. The overall outer diameter of the implant in a collapsed consition is preferably between 5 mm and 10 mm, more preferably between 6 and 8 mm and most preferably 6.5 mm.

The implant may be physically moved and expanded from the collapsed to the expanded position using any suitable means. Preferably, this is achieved by means of a drive or actuator extending along the longitudinal axis of the implant. Thus, the implant can be inserted into the body and expanded along a single axis and thereby along a single incision. This reduces further the tissue damage caused by conventional surgery of this type since the means to locate the implant in the vertebral cavity and also the means to expand the implant to fill the cavity can be achieved through a narrow incision. In effect the operation can be performed using minimally invasive surgery techniques. According to a further aspect of the invention there is provided a kit comprising a spinal implant and an applicator tool which can be operated to control operation of the implant between collapsed and expanded conditions.

According to another aspect of the invention there is provided a method of spinal surgery comprising introducing a spinal implant according to the invention in a collapsed condition between adjacent vertebrae of a patient, operating the rotary activation member of the spinal implant so as to expand the spinal implant whereby the spinal implant engages the adjacent vertebrae, the implant remaining in an expanded condition unless the rotary activation member is subsequently operated.

The implant is provided with bone engaging elements which are arranged in use to penetrate the bone surface when the implant is expanded. Any suitable element may be used which extends from the implant into the bone. This thereby prevents movement of the implant in the axial direction of the implant once in position. Preferably the elements are arranged at angles to the surface of the elongate members to optimise the axial load which can be accommodated. Most preferably the elements extend in opposing directions so as to prevent movement in either axial direction of the implant once the elements are engaged with the bone.

It will be appreciated that features of aspects, examples and embodiments described herein may be used in any convenient combination.

Brief description of the drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, Figures 1 to 19, in which:

Figure 1 shows a first view of the device in a collapsed condition;

Figure 2 shows a second view of the device again in a collapsed condition;

Figure 3 shows the outer surface of a jaw; Figure 4 shows the inner surface of a jaw;

Figure 5 shows the implant in an expanded condition;

Figure 6 shows the threaded rod forming part of the expansion driver means;

Figure 7 shows a rotatably mounted member arranged to connect to the threaded rod;

Figure 8 shows the linkages with integral bone engaging elements;

Figure 9 shows the implant in a partially expanded condition;

Figure 10 shows a sectional view of the implant in a fully expanded condition;

Figure 11 is a perspective view of the implant in a fully expanded condition;

Figure 12 is a view of a tool for use with the implant;

Figure 13 is a sectional view showing the tool engaged with the implant;

Figure 14 is a view showing the tool engaged with the implant;

Figure 15 is a perspective view of another implant in accordance with the invention in an open condition;

Figure 16 a perspective view of the implant of figure 15 in a closed condition;

Figure 17 is an exploded view of the implant of figure 15 showing various components of the implant in more detail;

Figure 18 is a detail view of a rotary activating member and trunnions of the implant of Figure 15; and Figure 19 is a schematic view showing the intra- vertebral insertion of implants of

Figures 15-18.

Detailed disclosure

Spinal Implant According to First Embodiment Common reference numerals are used throughout the description to refer to the same components.

Figure 1 shows the spinal implant 1 according to one embodiment of the invention. In Figure 1 the implant is shown in a closed position ready for use by a surgeon.

The implant 1 comprises a first upper jaw 2 and second lower jaw 3 which align when the implant is in a closed or collapsed position to form an elongate implant having a generally smooth outer profile as shown. The left hand end of the implant shown in Figure 1 (referred to as the proximate end 4) is arranged to couple to an expanding device (discussed below). The right hand end (referred to as the distal end 5) is arranged in the preferred embodiment to be generally hemispherical in shape to facilitate insertion into the incision in the patient's body.

Figure 2 shows the view of the implant from the proximate end 4 of the implant 1 again in the closed position ready for insertion. As shown the proximate end 4 is provided with a coupling 6 within the recess 7. The coupling 6 is arranged to connect to a rotational drive device (not shown in this figure) to rotate the coupling and expand the implant from the collapsed position to an expanded position. The operation of the device is described below.

Figures 3 and 4 show the upper and lower jaws respectively of the device. The jaws 3, 4 are largely identical components formed from titanium such that when aligned form the hemispherical distal end and smooth outer surface. The jaws differ as shown in the figures in that the pivot points 12a-12d on the opposing jaws are positioned to allow the device to fold into a flat arrangement as described below. The jaw are arranged in use to engage with the surfaces of the vertebrae and in the embodiment shown have substantially flat upper and lower contacting or engaging surfaces. The flat outer vertebra-engaging surfaces of the jaws are provided with a plurality of orifices 10 extending from the contacting surface through the jaw. The orifices 10 are disposed along the length and width of the upper and lower jaw surfaces and provide a path through which the bone graft can contact the bone surface and through which the bone can grown. Thus, bone is able to grow through the device after a period in the patient's body.

Figures 3 and 4 also show four further orifices or apertures 11a - Hd which pass through the jaws and which provide a path through which the articulated locking members can pass as described below. In addition Figures 3 and 4 show the four recesses and housings 12a - 12d arranged to receive a second pivoting shaft for the articulated locking members.

Figure 5 shows the device in an expanded or open position with common reference numerals being used to identify the individual components. Figure 5 also shows the drive mechanism which moves the upper and lower jaws 2, 3 apart. The drive mechanism comprises the coupling 6 which is connected to an elongate threaded rod 13.

As shown in more detail in Figure 6, the coupling 6 has two flat parallel engaging portions 14a, 14b disposed on either side of the coupling 6. These portion 14a, 14b provide the surfaces by which the rod 13 can be rotated by means of engagement with an implant positioning and expanding tool described later.

The rod 13 is itself formed of two portions 15 and 16. The first portion 15 has a thread 15a running in a first direction and the second portion 16 has a thread 16a running in the opposite direction. The two portion 15, 16 are separated by the stop 17. Thus, on rotation of the rod the first and second portions act to drive thread mounted components together or apart.

Referring back to Figure 5, the threaded rod 13 is provided with two rotatably mounted members or followers 18 and 19 mounted on the first and second portions of the threaded rod. Figure 7 shows one of the members in more detail. The members are each provided with opposing threads for engagement with the threaded rod described below. The members 18, 19 shown in Figure 7 comprise a central threaded bore 20 for engagement with the threads of the rod 13. The outer surface of the member is provided with 4 radially extending shafts 21a - 21 d formed by pins which are inserted to holes or recesses formed in the members 18, 19. This thereby facilitates assembly of the implant. Shafts 21a, 21c, and 21b 21d are disposed on opposite sides of the member 18/19 as shown in figure 7. The shafts 21a - 21 d are arranged to provide a support and pivot for the two jaws 2 and 3 and for the vertebra-engaging elements described below. The vertebral engaging elements are four identical components which are arranged to mount on the members 18/19 at either end of the implant 1. Two engaging elements are arranged to extend in a generally upward direction on expansion of the implant so as to engage with a vertebrae above the implant and two in a generally downward direction so as to engage with a vertebra below the implant.

Figure 8 shows an engaging element 22 in detail which can also be seen in-situ in Figure 5. The engaging element 22 is provided at a first end with two shaft connection arms 23, 24. The arms are arranged to extend over the rotatably mounted member 18/19 shown in Figure 7. The element 22 is rotatably mounted onto the element 18/19 by means of the bores 25, 26. The combined component of the element 22 and member 18/19 can be formed by aligning the bores 25 26 with the corresponding bore holes for the shafts 21a - 21d on the member 18/19 and then inserting the shafts 21a - 21d.

The distal end of the engaging element 22 from the connection arms 23, 24 is provided with two elongate bone engaging portions 27. The bone engaging portions 27 are arranged at approximately 45 degree angles to the longitudinal axis of the engaging element 22. As shown in Figure 8 the two bone engaging portions are in the form of sharp points or spikes which are arranged to penetrate the vertebrae surface and provide an anchor point in the bone surface.

The engaging element 22 is also arranged to receive a second pair of shafts into bores 28, 29 located at the opposing end of element 22 to the bores 25, 26. The bores 28, 29 are arranged to align with the bores in the housings 12a - 12d shown in Figures 3 and 4. A corresponding shaft is inserted through the housings 12a - 12d and into the bores 28, 29. Thus, the engaging elements 22 mechanically couple the engaging elements (which are rotatably mounted onto the threaded rod 13) and the jaws 2, 3. Once connected the bone engaging portions are arranged to align with the holes 11a - Hd of the upper and lower jaws.

The engaging element 22 is also provided with a recess 30 extending along the central portion of the element which is arranged to accommodate the curvature of the threaded rod. Thus, in a collapsed position the overall dimensions of the implant can be minimised.

In use the spinal implant operates as follows:

The operation of the implant is independent of the surgical procedure which the surgeon has selected for placing the implant into the patient's spine. This may be implanted percutaneously or using an open posterior or anterior approach.

The implant arrives in a collapsed position as shown in Figures 1 and 2. In this position the bone engaging elements are contained within the implant such that the outer surface of the implant is substantially smooth. The surgeon couples the implant to the positioning and expanding tool described later by means of the coupling 6.

The implant is then directed into the intervertebral cavity. The position of the implant is typically monitored using radiography so that the surgeon can accurately position one or more implants with the cavity.

Once correctly positioned the coupling 6 is rotated in a clockwise direction using the positioning and rotation tool. The coupling is, as described above, connected to the threaded rod 13 which rotates under the surgeon's control. It will be appreciated that the implant may be conveniently arranged to expand and collapse on rotation of the device in opposite directions. This permits fine adjustment during position, and collapse if it is ever necessary to remove the implant. This is a significant improvement over existing spinal implants which are difficult to remove after insertion. Figure 9 shows the implant in a partially expanded position. The rotatably mounted members 18, 19 are in contact either the central collar 17 in a collapsed position. As the rod rotates the rotatably mounted member 19 moves along the thread portion 15 away from the collar 17. Conversely the rotatably mounted member 18 moves away from the collar 17 in the opposite direction. Thus, the two rotatably mounted members move apart under the surgeon's control of the threaded rod 13. Figure 9 shows the implant partially expanded and before the body engaging spikes have extended through the holes 1 Ia - 1 Id in the upper and lower jaws.

Two of the four engaging elements 22 are mounted onto the first rotatably mounted members 19 and two to the second rotatably mounted member 18.

As the rotatably mounted members move the engaging elements provide a linkage arrangement by means of the respective pivot points which causes the engaging elements to rotate about the first pivot A shown in Figure 9 (one of the pivots being labelled). Thus, the engaging element rotates from the horizontal position toward the vertical as the rotatably mounted member moves along the threaded rod 13. This rotating movement is a result of the cooperation of the first and second pivots A and B in cooperation with the engaging element 22 and jaws which acts as linkages. The second pivot B, as illustrated in Figure 9, connects the distal end of the engaging element 22 to the jaw (the lower jaw in this illustration in figure 9).

As the threaded rod rotates the engaging elements 22 rotate about the pivot A. Simultaneously, the pivot point A moves axially along the threaded rod. As described above this arrangement is duplicated, in a reverse orientation, at either end of the implant with the two upper engaging elements being connected to the upper jaw and the two lower engaging elements being connected to the lower jaw. Thus, as the rod rotates the engaging elements move and simultaneously rotate causing the upper and lower jaws to move apart. The linkages carrying the bone engaging elements are of differing lengths such that one end expands more than the other. This provides a wedge shape on full expansion which accommodates the lordotic curve. As the jaws move apart the external surfaces of the jaws come into contact with the vertebrae which can be detected by an increase in torque required to expand the implant or, as above, by means of radiography or other suitable imaging.

The position shown in Figure 9 is immediately before the bone engaging spikes begin to extend from the surfaces of the jaw. It will be recognised that as the engaging elements rotate the distal end of the element will move in an arc about the pivot B shown in Figure 9. Thus, the distal end of the element begins to move out of the orifice in the jaw as the element rotates. The distal ends rotate smoothly and synchronously with the movement of the members 22 so that the expansion and engagement of the implant with the bone occurs in one smooth operation.

Figure 10 shows a section through the longitudinal axis of the implant in a fully expanded position. As shown the rotatably mounted members 18, 19 have reached the ends of the threaded rod 13. The movement along the rod is limited by the coupling 6 which prevents the rotatably mounted member 19 moving any further along the rod. This provides a fail-safe indicator that the implant is fully expanded and prevents the members 18, 19 from being disconnected from the rod. As also shown in the Figure the members 22 have rotated into vertical orientations. This orientation maximises the compressive load the implant can accommodate. In this position the vertical orientation of the linkages minimises any longitudinal forces on the followers 18, 19 (as a result of the pivot points) which would act to force the followers together thereby driving the implants into a collapsed condition.

Additionally or alternatively, the thread of the threaded rod 13 is selected so that the threads are 'auto-locking' that is that the rotatably mounted elements cannot move along the threaded rod without being driven. Thus, once the rotation of the rod has stopped the members will not move and, in effect, lock out. This allows the implant to be expanded and set with a variable height to accommodate specific vertebral spacing of patients. Preferably, though, for maximum security an implant of an appropriate size is chosen and expanded to a fully expanded condition where there will be additional resistance to collapse as described above. The links 22 adjacent one end of the implant, in this case the rounded end, are longer than the links at the other end, meaning that in the folly expanded condition as shown in Figure 10, the spacing between the members 2, 3 at that end is greater than at the other end. The implant thus adopts a somewhat wedged shape, which assists in accounting for the lordotic curve of the patient's spine. In the folly collapsed state, on the other hand, the members (2, 3) are parallel.

The arrangement of the linkages 22 connected to the followers 18 and 19 is such that as the folly expanded condition is reached, the degree of movement apart of the members 2 and 3 per revolution of the threaded rod 13 is reduced. Thus, the surgeon has greater control over expansion of the implant at this time.

Figure 9 also shows the distal end 27 of the engaging element 22 which has rotated such that the distal end extends beyond the surface of the jaw. The engaging element is arranged such that the angle between the distal end 27 and the surface of the implant (illustrated by lines C and D) is 45 degrees. Thus, at foil extension the distal ends 27 of the engaging elements 22 extend beyond the surfaces of the upper and lower jaws into the vertebrae at 45 degrees to the horizontal. It will be recognised by those skilled in the art that this angle optimises the engagement of the implant with the bone in terms of the axial and vertical forces which can be accommodated by the engaging element without failure. The elements at opposite ends of the implant diverge with respect to each other.

Once the surgeon is happy with the position of the spine and the level of expansion the surgeon can disconnect the positioning and expansion tool and begin implanting the bone graft.

Once in-situ the outer surfaces of the jaws are in contact with the vertebrae and counteract the compression forces through the spine. Thus, the vertebrae cannot move in a vertical direction. Furthermore, the distal ends of the engaging members mechanically engage with the bone and prevent and axial and lateral movement of the implant thereby preventing movement of adjacent vertebrae in a horizontal plane. The implant (or implants since two are conventionally inserted between two vertebrae) thereby prevents movement of the vertebrae in the x, y and z directions.

The next stage of the process involves inserting bone graft in and around the implant. This can be done using a variety of techniques which are known to those skilled in the art.

The bone graft is inserted into the vertebral cavity along the axis of the implant. The small cross-section of the threaded rod and contoured edges to the expansion mechanism allow the graft to flow easily into the cavity thereby filling and 'packing out' the entire space within the implant. The plurality of orifices in the upper and lower jaws allow the graft to contact the bone tissue of adjacent vertebrae which, over time, allows the two adjacent bone to fuse together through the implant which has an advantageously open central profile.

In the event of problems with positioning of the implant or complications with the procedure the implant can be advantageously lowered and if necessary removed. It will be recognised that by rotating the threaded rod in the clockwise direction reverses the movement of the rotatably mounted elements thereby lowering the jaws and retracting the distal ends of the engagement elements 27.

Figure 11 shows the implant in a fully expanded position with the engagement 'points' or 'spikes' extending from the surfaces of the jaws 2, 3.

Figure 12 shows an elongate tool 28 for inserting and operating the implant. At one end there is a portion 29 which, in a commercial embodiment would be provided with a suitable handle with controls. The portion 29 includes an elongate rotatable shaft 30 which extends through the tool 28 to a socket 31 at the distal end. As shown in Figure 13, this engages the coupling 6. This, by rotating the shaft 30 the implant can be expanded as discussed earlier (and as shown in Fig 14). At the handle end there are also two members 32 which control latches 33 at the distal end. These engage in portions 34 provided on the implant 1, to secure the implant to the tool and to stop it from rotating. The surgeon can hold the tool 28 and rotate shaft 30 to expand the implant. Once the implant is fully expanded, the members 32 are operated to release the tool 28 from the implant 1, so that the tool can be withdrawn.

Spinal Implant According to Second Embodiment

The implant 10 shown in Figures 15 and 16 comprises upper vertebra-engaging member 12 and lower vertebra-engaging member 14. The members 12 and 14 have dimpled major surfaces indicated generally, for example at 13. The upper and lower vertebrae engaging members 12 and 14 correspond to the jaws of the previously described implant 1 shown, for example in Figures 3 and 4. The upper and lower vertebra- engaging members 12 and 14 each define four recesses (15a-h respectively, 15g-h obscured) in pairs on either side.

The upper and lower vertebra- engaging members 12 and 14 are supported by elongate cranks 16, 17, 18, 19, 20, 21, 22 and 23. The crank 16-23 provide the bone-engaging elements. Each crank is geared at one end e.g. 24 and has a tooth at its opposite end e.g.

The elongate cranks 16-23 are arranged in pairs with a geared end of one crank in a pair engaging the geared end of the other crank in the pair. For example, geared end 24 of crank 22 engages with geared end 26 of crank 16. The cranks are pivotally mounted on solid pins e.g. 27 which are held by the respective vertebra-engaging members 12 and 14. This solid pin arrangement provides significant structural strength to the spinal implant.

A rotary drive mechanism is provided by screw 28 which is received within trunnions 30, 32. The elongate cranks 16-23 are each additionally pivotally mounted on the trunnions 30, 32 adjacent their respective geared ends, by stub axles e.g. 33,35, whereby upon rotation in one direction of the screw 28, the trunnions 30, 32 move outwardly causing the cranks 16-23 to rotate about the stub axles whereby the vertebra-engaging members 12 and 14 move outwardly to the position shown in Figure 15. The cranks go 10° over centre, engaging stops on the upper and lower vertebra-engaging members 12 and 14. This advantageously removes any loading from the gears and the screw mechanism when the implant is in a fully expanded condition. At one end of the screw is formed a nut 34. The gearing on the cranks helps to ensure parallel opening of the implant in use.

The thread of screw 28 is carefully designed to ensure parallel opening of the vertebrae- engaging members 12 and 14. The screw 28 has different threads front and rear in order to instigate different opening heights. Specifically the thread has a pitch of 0.4 at the front and 0.35 at the rear to ensure parallel opening. Parallel operation of the spinal implant is also ensured by the gearing at the ends of the cranks. Resistance to rotation of screw 28 monitors the implant in an expanded condition.

The dimples on the major surfaces of vertebra-engaging members 12 and 14 provide a rough surface for bone graft to attach to. The spinal implants 10 of Figure 15 is shown in a closed condition in Figure 16. In this condition, the spinal implant has a relatively smooth profile which facilitates insertion into the inter- vertebral space.

In use, the implant 10 is inserted between into the inter- vertebral space as generally described above in relation to spinal implant 1. Some bone graft material may be inserted anteriorily of the spinal implant prior to use. The surgeon may use real bone material or a substitute. The spinal implant 10 is introduced into the space in a closed condition the screw is then operated by a tool which engages nut 34 so that the spinal implant is expanded, driving the upper and lower vertebra-engaging members 12 and 14 apart so as to engage upper and lower vertebrae 40 and 42 as shown in Figure 19. Figure 19 shows two spinal implants 10 and 50 introduced between the two adjacent vertebrae in a typical arrangement. After insertion of spinal implants 10, a second spinal implant 50 is introduced as for spinal implant 10. The tool 60 includes a drive mechanism which engages with nut 34 and can be operated by a surgeon in order to rotate screw 28 whereby the spinal implant is operated from a closed condition to an open condition. The teeth at the ends of the elongate cranks protrude through recesses 15a-h above the plane of the major surface of the vertebra-engaging members 12, 14, so as to engage with the adjacent vertebra 40, 42. Significantly, compared to prior art devices the position of the spinal implants can be checked and regularly adjusted by the surgeon prior to the subsequent introduction of bone graft material. This is not possible with most prior art spinal implants. Once the surgeon is happy with the positioning of the spinal implants, the tool 60 can be disengaged from the spinal implant and removed from the patient's body.

The spinal implant 10 is produced in a surgical grade titanium. The implant is designed to withstand a loading of 250N in going from a closed position to a folly open condition. In a folly open condition, the implant is designed to withstand a loading of 2500N. Thus the implant provides significant structural strength compared to prior art spinal implants.

Only a few components of the spinal implant are specifically indicated in Figure 15 and 16 for clarity. More detail of the components of the spinal implant is shown in the expanded view of Figure 17.

Claims

1. An interbody spinal fusion implant comprising a first body member having a first vertebra-engaging surface for engaging a first vertebra, a second opposed body member having a second vertebra-engaging surface for engaging a second vertebra, there being a space defined between the first and second body members, a rotary activating member extending longitudinally in the space between the first and second body members, a first linkage system connected between the first body member and the rotary activating member, and a second linkage system connected between the second body member and the rotary activating member, whereby the rotary activating member may be operated to move the first and second body members apart between a collapsed condition and an expanded condition; wherein the first body member is arranged to provide a first recess or aperture defined by the first vertebra-engaging surface, and the first linkage system is connected to a first bone-engaging element which is arranged so that it does not extend beyond the first vertebra-engaging surface of the first body member when the body members are in the collapsed condition and which is arranged to be urged into the first recess or aperture by the first linkage system as the body members are moved to the expanded condition so as to protrude from the first vertebra-engaging surface; and wherein the second body member is arranged to provide a second recess or aperture defined by the second vertebra-engaging surface, and the second linkage system is connected to a second bone-engaging element which is arranged so that it does not extend beyond the second vertebra-engaging surface of the second body member when the body members are in the collapsed condition and which is arranged to be urged into the second recess or aperture by the second linkage system as the body members are moved to the expanded condition so as to protrude from the second vertebra-engaging surface, and in which in the implant comprising means for maintaining the implant in an expanded condition.

2. An implant according to claim 1 in which the first and second body members define respective first and second recesses.

3. An implant according to claim 1 in which the first and second body members define respective first and second apertures.

4. An implant according to claim 2 or 3 in which the first and second body members each define four recesses or apertures.

5. An implant according to any preceding claim in which each of the first and second body members is associated with four bone-engaging elements.

6. An implant according to claim 5 in which a bone-engaging element is pivotally connected to an associated first or second body member.

7. An implant according to claim 5 or 6 in which a bone-engaging element is pivotally connected to a linkage mechanism.

8. An implant according to claim 5, 6 or 7 in which a bone-engaging element associated with the first body member engages a bone-engaging element associated with the second body member.

9. An implant according to claim 8 in which bone-engaging elements associated with the first body member engage bone-engaging elements associated with the second body member.

10. An implant according to claim 8 or 9 in which a bone-engaging element associated with the first body member has a geared portion which engages a geared portion of a bone-engaging element associated with the second body member.

11. An implant according to claim 10 in which geared portions of the bone-engaging elements associated with the first body member engage with geared portions of the bone-engaging elements associated with the second body member.

12. An implant according to claim any one of claims 5 to 11 in which a bone- engaging element pivots to an over-centre position when the first and second

13. Body members are in a fully expanded condition whereby the implant is stabilised in the fully expanded condition.

14. An implant according to any preceding claim in which the first and/or second linkage system comprises a trunnion which is driven by the rotary activating member.

15. An implant according to claim 13 in which the first and second linkage systems comprise two trunnions.

16. An implant according to claim 14 in which the trunnions are pivotally connected to the bone-engaging elements.

17. An implant as claimed in claim 1 to 5, wherein the first linkage system comprises two axially spaced first links connected to the first body member at axially spaced positions, and the second linkage system comprises two axially spaced second links connected to the second body member at axially spaced positions.

18. An implant as claimed in claim 16, and wherein each of the first links is connected to a respective first bone-engaging element which is within the hollow space when the body members are in the collapsed condition and which is arranged to be urged into a first recess or through a respective first aperture by the first linkage system as the body members are moved to the expanded condition; and each of the second links is connected to a respective second bone- engaging element which is within the hollow space when the body members are in the collapsed condition and which is arranged to be urged into a second recess or urged through a respective second aperture by the second linkage system as the body members are moved to the expanded condition.

19. An implant as claimed in claim 16 or 17, wherein each of the first links of the first linkage system comprises two laterally spaced arms connected to the first body member, and each of the second links of the second linkage system comprises two laterally spaced arms connected to the second body member.

20. An implant as claimed in claim 16, 17 or 18, wherein each of the arms of the first links of the first linkage system is provided with a respective first bone- engaging element which is within the space between the body members when

21. The body members are in the collapsed condition and which is arranged to be urged into a first recess or through a respective first aperture by the first linkage system as the body members are moved to the expanded condition; and wherein each of the arms of the second links of the second linkage system is provided with a respective second bone-engaging element which is within the space between the body members when the body members are in the collapsed condition and which is arranged to be urged through a respective first recess or through a respective second aperture by the second linkage system as the body members are moved to the expanded condition.

22. An implant as claimed in any of claims 16 wherein the rotary activating member comprises a first threaded portion extending from a central region towards one end of the implant, and a second, coaxial threaded portion extending from a central region towards the other end of the implant, the first and second threaded portions having threads of opposite senses, the first threaded portion engaging a first threaded follower which is connected to one of the pair of first links and one of the pair of second links, and the second threaded portion engaging a second threaded follower which is connected to the other of the pair of first links and the other of the pair of second links.

23. An implant as claimed in claim 20, wherein the first threaded follower is pivotally connected to one of the pair of first links, said one of the pair of first links being pivotally connected to the first body member; the first threaded follower is also pivotally connected to one of the pair of second links, said one of the pair of second links being pivotally connected to the second body member; the second threaded follower is pivotally connected to the other of the pair of first links, said other of the pair of first links being pivotally connected to the first body member; and the second threaded follower is also pivotally connected to the other of the pair of second links, said other of the pair of second links being pivotally connected to the second body member.

24. An implant as claimed in claim 20 or 21, wherein the pitches of the first and second threaded portions differ, so that in the fully expanded condition the first and second members are separated by more at one end of the implant than at the other.

25. An implant according to claim 22, in which the pitch of one threaded portion is about 0.4.

26. An implant according to claim 22 or 23, in which the pitch of one threaded portion is about 0.35.

27. An implant as claimed in any of claims 16 to 24, wherein one of first links is larger than the other of the first links, and one of the second links is larger than the other of the second links, so that in the fully expanded condition the first and second members are separated by more at one end of the implant than at the other.

28. An implant as claimed in any preceding claim, wherein at least one of the first and second vertebra-engaging surfaces is textured.

29. An implant according to claim 26 in which the or each vertebrae-engaging surface is dimpled.

30. An implant according to claim 26 or 27, in which the or each vertebrae-engaging surface is perforated.

31. An implant as claimed in any preceding claim, wherein in the collapsed condition one end of the implant is substantially rounded.

32. An implant as claimed in any preceding claim, wherein the arrangement is such that in use the rate of separation of the first and second body members when moving from the collapsed condition to the fully expanded condition decreases as the separation increases, at least over a range of movement adjacent the fully expanded condition.

33. An implant as claimed in any one of claims 4 to 30 in which, in the fully expanded condition, longitudinally spaced bone-engaging elements diverge.

34. An implant as claimed in any one of claims 5 or 31 wherein, in the fully expanded condition, laterally spaced bone-engaging elements diverge.

35. An implant as claimed in any preceding claim wherein, in the fully expanded condition bone engaging elements extend laterally beyond the body members.

36. An implant according to any preceding claim wherein, in the fully expanded condition, the bone-engaging elements protrude beyond the respective first and second vertebrae-engaging surfaces.

37. An implant as claimed in any preceding claim, wherein the rotary activating member comprises an axially extending connector for connecting to a tool which can be operated to expand or contract the implant.

38. An implant as claimed in claim 35, wherein the first and second body members are provided with means for receiving latches provided on the tool.

39. An implant as claimed in any preceding claim, in combination with an elongate tool having at one end means for engaging with the axially extending connector on the rotary activating member.

40. An implant according to claim 37 in which the tool comprises latches for engaging with the latch receiving means on the first and second body members.

41. An interbody spinal fusion implant comprising a first body member having a first vertebra-engaging surface for engaging a first vertebra; a second opposed body member having a second vertebra-engaging surface for engaging a second vertebra; a rotary activating member extending axially between the first and second body members; a linkage system connected between the rotary activating member and the first and second body members, whereby the rotary activating member may be operated to move the first and second body members between a collapsed condition and an expanded condition; the body members in the collapsed condition defining an elongate body which is rounded at one end of the implant, the elongate body containing the rotary activating member and the linkage, and in which the implant comprising means for maintaining the implant in an expanded condition; wherein at the other end of the implant the rotary activating member comprises an axially directed connector for connecting to an axially extending tool for use in rotating the activating member.

42. An interbody spinal fusion implant comprising a first body member having a first vertebra-engaging surface for engaging a first vertebra; a second opposed body member having a second perforated vertebra-engaging surface for engaging a second vertebra; a rotary activating member disposed between the first and second body members; a linkage system connected between the rotary activating member and the first and second body members, whereby the rotary activating member may be operated to move the first and second body members between a collapsed condition and an expanded condition; the body members in the collapsed condition defining a body containing the rotary activating member and the linkage; wherein the arrangement of the rotary activating member and the linkage is such that in use the rate of separation of the first and second body members when moving from the collapsed condition to an expanded condition decreases as the separation increases, at least over a range of movement adjacent a fully expanded condition.

43. An interbody spinal fusion implant comprising a first body member having a first textured vertebra-engaging surface for engaging a first vertebra; a second opposed body member having a second textured vertebra-engaging surface for engaging a second vertebra; an activating member extending axially between the first and second body members; a linkage system connected between the activating member and the first and second body members, whereby the activating member may be operated to move the first and second body members between a collapsed condition and an expanded condition; the body members in the collapsed condition defining a body containing the activating member and the linkage; wherein there are provided a plurality of bone-engaging elements which are contained within the body in the collapsed condition and which are connected to the rotary activating member such that as the body members move apart to an expanded condition, the bone-engaging elements protrude through recesses defined by the first and second vertebra-engaging surfaces, and in which the implant comprising means for maintaining the implant in an expanded condition.

44. An interbody spinal fusion implant comprising a first body member having a first perforated vertebra-engaging surface for engaging a first vertebra; a second opposed body member having a second perforated vertebra-engaging surface for engaging a second vertebra; an activating member extending axially between the first and second body members; a linkage system connected between the activating member and the first and second body members, whereby the activating member may be operated to move the first and second body members between a collapsed condition and an expanded condition; the body members in the collapsed condition defining a body containing the activating member and the linkage; wherein there are provided a plurality of bone-engaging elements which are contained within the body in the collapsed condition and which are connected to the rotary activating member such that as the body members move apart to an expanded condition, the bone engaging elements protrude through apertures in the first and second vertebra-engaging surfaces, and in which the implant comprises means for maintaining the implant in an expanded condition.

45. An implant as claimed in claim 41, wherein associated with each of the first and second vertebra-engaging surfaces there are longitudinally spaced bone- engaging elements which, in the fully expanded condition, protrude through apertures in the associated vertebra-engaging surfaces, or through recesses defined by those vertebrae-engaging surfaces, and which diverge in the longitudinal direction.

46. An implant as claimed in claim 42, wherein associated with each of the first and second vertebra-engaging surfaces there are laterally spaced bone-engaging elements which, in the fully expanded condition, protrude through apertures in the associated vertebra-engaging surfaces and which diverge in the lateral direction.

47. An implant as claimed in claim 43 wherein, in the fully expanded condition, the bone-engaging elements protrude beyond the body members.

48. A kit comprising an implant according to any one of claims 1 to 36 or 38 to 45 and an applicator tool which can be operated to control operation of the implant between collapsed and expanded conditions.

49. A method of spinal surgery comprising introducing a spinal implant according to any one of claims 1 to 36 or 38 to 45 in a collapsed condition between adjacent vertebrae of a patient, operating the rotary activation member of the spinal implant so as to expand the spinal implant whereby the spinal implant engages the adjacent vertebrae, the implant remaining in an expanded condition unless the rotary activation member is subsequently operated.