BACKGROUND TO THE INVENTION

THIS invention relates to an interspinous stabilisation device.

Posterior spinal stabilisation devices are sometimes used by surgeons in cases where fusion or disc replacement is inappropriate or unwarranted. One known class of spinal stabilisation device is installed interspinously, i.e. between the spinous processes of adjacent vertebrae.

An example of a known interspinous stabilisation device is the DIAM (Device for Intervertebral Assisted Motion) device produced by the Sofamor Danek division of Medtronic Inc. This is a flexible spinal implant designed to provide support between posterior elements of the spine, namely the spinous processes of adjacent vertebrae, and thereby relieve pain caused by degenerative spinal diseases. The device includes a resiliently flexible spacer made of medical grade silicone which is implanted between adjacent spinous processes, typically in the lumbar region of the spine, to resist extension and reduce interdiscal pressure. The spacer, which is typically encapsulated in a flexible sheath providing protection against abrasive wear from the spinous processes, has upper and lower notched edges to receive the respective processes and is tethered in place by means of separate, flexible cords which are tied about the processes or passed about the processes and tied to one another. The tethering of the spacer using these cords is a time-consuming and inconvenient procedure, and may in some cases require suturing of the cords to adjacent ligamentous structures of the spine.

Another example of interspinous stabilisation device is the so-called Walllis Cage produced by Spine Next, SA. It includes a moulded plastics body, typically of PEEK™ which is positioned between the spinous processes. Like the DIAM device the Wallis Cage is tethered in position by means of an anchoring clip and cords which are tied about the processes. The tethering procedure suffers from similar problems to those experienced in DIAM implantation.

Yet another interspinous stabilisation device is the Fixano interspinous fixation system produced by Fixano SA. This device has a U-shaped body made of titanium which is implanted between the spinous processes. Wings or lugs projecting upwardly and downwardly from respective legs of the Li- shape are clamped to the respective processes to hold the body in position. Once again, installation and fixation of the device are time-consuming and inconvenient procedures.

In each of the above cases, the stabilisation device is placed in position posteriorly and can, as a result, cause damage to or even destroy the interspinous process ligament.

It is an objective of the present invention to provide an alternative interspinous stabilisation device which can be implanted and fixed in position relatively quickly and easily.

SUMMARY OF THE INVENTION

According to the present invention there is provided an interspinous stabilisation device comprising:

- a resiliency flexible, moulded plastics body shaped and dimensioned to be located between adjacent spinous processes in order to provide support between the associated vertebrae, and

- elongate, flexible ties carried in use by the body, the ties being arranged to be looped over the respective processes and engaged in one or more openings associated with the body.

In the preferred embodiment, the body includes an operatively upwardly facing notch therein and an operatively downwardly facing notch therein and is shaped for reception of respective spinous processes in the notches when the body is placed between such processes. Conveniently the notches are defined between a pair of operatively upwardly facing projections on the body and a pair of operatively downwardly facing projections on the body, respectively. Thus the body may have a bow-tie like shape.

The ties are moulded integrally with the body and the body may be moulded with at least one tie-receiving opening therein.

The ties are preferably engagable in the opening(s) by interaction of teeth on the ties with tooth-engaging pawls associated with the opening(s). In this case, the teeth are typically of ratchet form and the pawls are arranged to engage with the teeth, when the ties are passed through the opening(s), in a manner preventing withdrawal of the ties through the opening(s).

Conveniently, the body has a pair of openings therein, one for each tie, and each opening has a pawl associated therewith to engage the teeth on a respective tie.

It is preferred that the body be sufficiently resiliently flexible to be compressed vertically to an extent allowing lateral insertion of the body between adjacent spinous processes.

Other features of the invention are described below and are set forth in the appended claims.

BRlEF 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 shows a perspective view of an interspinous stabilisation device according to this invention;

Figure 2 shows how ties can be looped over and engaged with the body of the device seen in Figure 1 ; and

Figure 3 illustrates the use of the device in a posterior view of a spine segment.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

The interspinous stabilisation device 10 seen in Figure 1 has a central body 12 with a pair of ties 14 extending from the body in opposite directions. The body and ties are formed integrally, as a one-piece moulding, of a resilient plastics material, in this case a radiation cross-linked LDPE (low density polyethylene).

As illustrated the body 12 has a bow-tie like shape and includes pairs of opposed projections 16 which define intermediate notches 18 facing in opposite directions. Openings 20 extend centrally through the body in a side by side relationship with a web of material 22 between the openings. Extending inwardly from opposite sides of the openings 20 are pawls 24 having hook formations at their ends.

The ties 14 are formed with ratchet-like teeth 28 along their lengths and terminate at their extremities in toothless end regions 29.

In use, as illustrated in Figure 2, each tie 14 can be looped over and passed through a respective opening 20, with the pawl associated with that opening allowing passage of the tie as indicated by the arrow 30. However the hook formation of the pawl, while allowing passage of the teeth in the direction 30, interacts with the teeth in a manner to prevent withdrawal of the tie through the opening in the opposite direction 32, as will be apparent from the enlargement in Figure 2. The end regions 29 facilitate initial entry of the ties into the openings.

It will be recognised that the combination of a tie 14, opening 20 and pawl 24 can be likened to the structure of a conventional, so-called "cable tie".

In other embodiments, not illustrated, there may be multiple pawls 24 in each opening 20, the pawls being arranged to engage spaced apart teeth on the ties 14 thereby to increase the security with which the ties are engaged.

In use, the body 12 is implanted posteriorly between the spinous processes 36 of adjacent vertebrae 38 in a spine after appropriate distraction of those vertebrae. The body is oriented such that the processes locate in the notches 18.

It will be understood that the body 12 is accurately dimensioned for proper location between the processes, although it would of course be possible to have different devices 10, with bodies 12 of different size, to suit different applications and spinal segments.

The invention envisages that the material of which the device 10 is made will have sufficient flexibility to allow posterior-lateral placement of the body 12, thereby leaving the interspinous process ligament intact. In particular the projections 16 should be sufficiently resiliently deformable to allow them to pass the spinous processes with a lateral component of movement, thereby avoiding potentially damaging contact with the ligament.

After location of the body 12, the ties are looped over the respective spinous processes and are then fed through the respective openings 20 and pulled tight whereafter the ends of the ties can be cut off and disposed of. The pawls 24, by preventing subsequent withdrawal of the ties through the openings, ensure that the device 10 is firmly anchored in position.

An advantage of the illustrated device 10 is the speed and simplicity of the fastening procedure compared to the conventional DIAM, Wallis Cage and Fixano devices mentioned earlier.

Numerous variations are possible. It would for instance be possible to have a single opening in the body 12 to receive both ties, with pawls projecting into the opening in opposite directions. It would also be possible for the body 12 and ties to be separately manufactured, or for the device to include a body and separately manufactured cable ties which are connected to the body when the body is implanted between the spinous processes.