Abstract
Introduction The aim of this study was to assess the safety and effectiveness of the Wallis Stabilization System through a prospective international multi-center study.
Methods 262 consecutive patients (39% female, 61% male; mean age of 44 years), treated with the Wallis system, were enrolled into the study, which was undertaken in 8 centers in 6 countries. The two principal indications for surgery were massive disc herniation (37% patients) and degenerative disc disease with Modic type 1 change (27% patients).
Clinical outcomes variables, assessed preoperatively and at 3, 6, 12 and 24 months, included the Japanese Orthopaedic Association score (JOA) for low back pain, SF-36, lumbar and leg pain visual analog scale (VAS), and Odom score. At these assessments flexion/extension radiographs were performed and yearly MRIs have been obtained.
Results Mean time of surgery overall was 74 minutes, with an average of 19 minutes required for implantation. Average blood loss was 180 cc.
Pre-operatively, the mean VAS was 70.3/100. At three months, VAS was significantly reduced (P< 0.01) to a mean 18.3 with further reductions to 17.0 at 6 months and 14.6 at 24 months. At 3 months post-operation, all categories of the SF-36 scores (except general health) had shown significant improvement compared with preoperative values. At 1 year, and sustained at 2 years, the SF-36 scores were comparable with an aged and sex matched normal population form France. The JOA score (15 point scale) significantly improved (P< 0.01) from 6.0 preoperatively to 12.9 at 24 months after reaching a plateau at 3 months (12.5).
From Odom’s assessment at 3 months 85% of subjects were categorized as ‘good’ or ‘excellent’, this being sustained over the period of the study, with results at 6 months and 24 months 90% and 88%, respectively.
Of the total cohort of 262 cases, only four implant-related failures have been observed to date.
Discussion The objective of the study was to determine the safety and efficacy of the Wallis stabilization system in treating symptomatic degenerative lumbar motion segments. The medium term results at 2 years have been very encouraging, with the significant clinical improvement seen at 1 year being sustained through to 2 years. This, coupled with the survivorship analysis for the first generation implant, give grounds for optimism for the future.
The few implant related failures all occurred in the first year, after which some minor implant modifications were made. There have been no subsequent implant related failures.
The abstracts were prepared by Assoc Prof Bruce McPhee. Correspondence should be addressed to him at the Division of Orthopaedics, The University of Queensland, Clinical Sciences Building, Royal Brisbane Hospital, Herston, Brisbane, 4029, Australia.
