Background: To asses the safety and efficacy of the Wallis Stabilization System in degenerative disorders of the lumbar spine.

Methods: A prospective international multicentre clinical and radiological outcome assessment study. The study is ongoing. The study group comprises 260 consecutive patients meeting inclusion and exclusion criteria with respect to diagnosis (and levels affected), age, medical conditions and prior surgery. 61% were male, 39% female and the mean age was 44 years. The principal diagnosis was massive disc herniation in 37%, degenerative disc disease (with Modic type I change) in 27%, canal stenosis in 13%, recurrent disc herniation in 9% and disc herniation above a transitional segment in 5%. L4/5 was the operated level in 88%. Clinical assessment has been performed using a p atient completed questionnaire incorporating SF-36, JOA (Japanese Orthopaedic Association score), VAS (lumbar pain Visual Analogue Score, 0–100), ODI (Oswestry Disability Index) and Odem’s Criteria. Any adverse or serious adverse events were documented. Pre-operative static and dynamic radiographs and MRI scans have been undertaken, and the radiographs are then repeated at 3 and 6 months post-operatively and yearly thereafter. Post-operative MRI scans are obtained on a yearly basis up to 5 years post-surgery.

Results: Mean operating time has been 74 minutes overall, with mean implantation time of 19 minutes. Blood loss averaged 180 mls. The pre-operative mean VAS of 71 improved to 21 at 3 months (p< 0.01) with further improvement at 6 months (VAS 18) and 1 year (VAS 11). SF-36 scores improved in every category from 3 months onwards, this improvement being statistically significant in all categories except general health. At 1 year SF-36 scores were not distinguishable from an age and sex matched general population. JOA scores improved significantly from 6.1 (15 point scale) pre-operatively to 12.5 at 3 months and 13.7 at 12 months (p< 0.01). Odem’s criteria provide additional evidence of efficacy, with 80% of subjects categorized as ‘good’ or ‘excellent’ at 3 months, this proportion improving to 89% at 1 year. Of those graded as ‘fair’ at 3 months, half had improved to ‘good’ or ‘excellent’ by 1 year.

From the series of 260 cases there were only 3 implant related complications (1.2%).

Conclusion: Previous biomechanical and finite element analysis studies have shown that the Wallis stabilization system off-loads the intervertebral disc and improves the biomechanical characteristics of the degenerative lumbar motion segment. The surgical procedure is simple, minimally invasive and non destructive, preserving surgical options for the future.

This study provides preliminary evidence with respect to the safety and efficacy of the Wallis Stabilization System.

No matter what form of anterior scoliosis instrumentation a spinal surgeon chooses to use it is generally accepted that complete clearance of the intervertebral discs over the levels being instrumented should be undertaken. This improves the flexibility of the curve, potentially enhancing the correction that can be achieved but, perhaps more importantly, reduces the forces that must be exerted on the spine through the instrumentation, particularly at the upper and lower levels. Complete disc clearance may also facilitate intervertebral fusion.

The most challenging aspect of disc clearance is removal of the posterior aspect of the annulus and the posterior longitudinal ligament The standard surgical technique involves initial excision of the convex lateral and anterior annulus, followed by the gelatinous nuclear material. This is relatively easily and quickly achieved. However, careful, patient and painstaking piecemeal removal of the posterior annulus is then necessary and this is more time consuming. Care is clearly required to avoid injury to the adjacent dura and neurological structures. Access to the posterior annulus with a ronger becomes more difficult towards the far concave aspect of the disc.

Little information is published concerning the time required for standard disc clearance. However, in the author’s experience, and from personal information provided by other surgeons, 30 minutes per level is generally required.

Coblation is a relatively new surgical technology by which tissue is removed by vaporisation achieved through the production of an ionized plasma vapour. The depth of vaporisation is very limited and is achieved with virtually no heat production, resulting in minimal thermal damage to adjacent tissue.

The author has used coblation in anterior correction of scoliosis, and in his view the technique allows simpler, more controlled and thus ultimately safer clearance of the posterior annulus. Clearance is also achieved more quickly, the time required for each level undertaken being reduced to approximately 15 minutes.

The technique involves standard exposure and then excision of the bulk of the disc. The disc must be exposed back to the neural foramen and the convex lateral annulus cleared to this point The anterior annulus is also exposed in the usual manner and excised together with the nuclear material and as much of the posterior annulus that can be easily removed with a ronger. At this point a blunt dissector is introduced into the neural foramen and held in position. Starting at the convex aspect of the posterior annulus and working towards the concave side a ‘Versitor’ coblator wand is then used to remove the posterior annulus, working back to the tip of the dissector . The dissector is not particularly required for safety , the depth of vaporisation being only 0.5 mm, but to establish the posterior extent of the annulus. As this is vaporised the dissector is advanced as necessary .

No complications have been observed in the small number of cases undertaken thus far. Current generated by the sodium plasma can result in local neurological stimulation causing muscle twitching, similar to that seen with the use of diathermy, but this has not been associated with any neurological deficit