Abstract
INTRODUCTION: Intervertebral degeneration is characterised by instability due to permanent decrease in the stiffness of the intervertebral segment and concentration of stress upon the posterior portion of the disc, and by morphologic changes in the posterior elements due to posterior displacement of loading, notably enlargement of the lamina and zygapophyseal joints. These changes lead to reduction in the cross-sectional area of the vertebral canal.
In order to counterbalance these changes, an implant has been developed with an interspinous blocker and an artificial ligament made of Dacron. This obviates the need for a permanent fixation in the vertebral bone, avoiding the risk of loosening. Inhibition of hyperextension limits narrowing of the posterior canal, resulting in an increase in its cross-sectional area of up to 40%.
A first-generation implant for nonrigid stabilisation of lumbar segments was developed in 1986 with a titanium interspinous blocker. Following an initial observational study in 1988 and a prospective controlled study from 1988 to 1993, more than 300 patients have been treated for degenerative lesions with significant resolution of residual low back pain with no serious adverse effects.
After careful analysis of the points that could be improved,a second-generation,improved implant called the ‘Wallis implant’ was developed with a redesigned blocker made of PEEK (polyetheretherketone), a more resilient material.
METHODS: Biomechanical studies were used to verify the effectiveness of this implant in increasing intervertebral stiffness, reducing mobility, and unloading the facet joints and the posterior portion of the disc.
A prospective multicenter international observational study was begun a year ago.
RESULTS: Preliminary results confirm the clinical efficacy of this treatment on low back pain and nerve root symptoms, especially in recurrent disc herniation and canal stenosis.
DISCUSSION: Nonrigid intervertebral fixation with the Wallis implant clearly appears to be a useful technique in the management of initial forms of degenerative intervertebral lumbar disc disease. The method should rapidly assume a specific role along with total disc prostheses in the new step-wise surgical strategy to obviate definitive fusion of degenerative intervertebral segments. Moreover, dynamic stabilisation with the Wallis system is totally reversible and leaves all other options open.
Wallis is recommended for patients with lumbar disc disease who have: (i) discectomy for massive herniated disc leading to substantial loss of disc material, (ii) a second discectomy for recurrence of herniated disc, (iii) discectomy for herniation of a transitional disc with sacralization of L5, (iv) degenerative disc disease at a level adjacent to a previous fusion or prosthesis, (v) isolated disc resorption, notably with concomitant type-1 Modic changes, associated with low back pain, or (vi) symptomatic narrow canal treated by resection of the superior aspect of the laminae.
These abstracts were prepared by Dr Robert J. Moore. Correspondence should be addressed to him at Spine Society of Australia, Institute of Medical and Veterinary Science, The Adelaide Centre for Spinal Research, Frome Road, Adelaide, South Australia 5000.
