Abstract
Introduction The concept of accelerated degeneration of adjacent disc levels as a consequence of increased stress caused by interbody fusion of the lumbar spine has been widely postulated. Total disc arthroplasty may offer the same clinical benefits as fusion while providing motion that may protect the adjacent level discs from the abnormal and undue stresses associated with fusion. The goal of this study was to prospectively analyse the results of the Maverick Lumbar Disc Prosthesis (Medtronic, USA) at 4 years follow-up.
Methods We conducted a prospective analysis of the Maverick Lumbar Disc Prosthesis implanted in the first 50 consecutive patients for the treatment of degenerative disc disease of the lumbar spine resistant to conservative treatment for more than 1 year. 253 Maverick have been implanted in our spine unit and these 50 have the longest follow-up. The outcome data collected included the Oswestry Questionnaire and Visual Analog Scale (VAS) preoperatively and at routine scheduled follow-ups. Radiographic analysis included sagittal balance parameters on standing full length lateral radiographs of the spine and range of motion on flexion/extension dynamic radiographs. 3 European centres were included in the study. The offset on AP x-rays was calculated for all patients and correlated with clinical outcomes.
Results There were 32 females and 28 males with an average age of 43, 4 years and average follow-up of 3.1 years (22 to 48 months). The Maverick was implanted at L5S1: 20 cases; L4L5: 17 cases; 3 patients had 2 levels arthroplasty and 10 had a fusion at L5S1 and a prosthesis at L4L5. Clinical success, defined by the FDA as improvement of at least 25% on the Oswestry, was 76% and 81%, at 6 months and 1 year follow-up respectively. The VAS showed an improvement in back pain from 7.1 (+/− 2, 1) pre-operatively to 3.0 (+/− 1.8) post-operatively. Leg pain was significantly higher according to VAS when patients have been previously operated for disc herniation (HD).
At the latest follow-up, there was no measurable subsidence of the devices except in one case at L5S1 due to a technical error and no evidence of device migration. The measured range of motion in flexion-extension ranged from 3 to 16 degrees (mean range of motion, 6 +/− 4 degrees). L4–L5 level is more mobile: average 8.4 degrees. With regards to sagittal balance, there was no significant change in any of the variables studied including sacral tilt, pelvic tilt, or overall lordosis after placement of total disc arthroplasty. Only the lordosis at the level above the prosthesis was significantly decreased. The position of the implant on AP and lateral x ray was analyzed and correlated with the clinical results. Less than 19% of offset on AP view had no influence on clinical results. One complication, a ureter injury occurred during the approach in one procedure. One left iliac vein injury occurred per-operatively and treated with vascular clip. One patient with two discs with persistent low back was re-operated for posterior fusion with a significant improvement of pain at two years. This patient had been operated 3 times before for disc herniation and recurrence of HD.
Discussion These results of total disc arthroplasty compare favorably with the mid-term clinical outcomes associated with anterior lumbar discectomy and fusion reported in the literature. Unlike fusion however, it appears that the prosthesis has enough freedom of motion to allow the patient to maintain the natural sagittal and spinopelvic balance with radiographic evidence of normal range of motion. However, these early favorable clinical results in addition to the influence on adjacent motion segments can be assessed only after long term follow-up. Previous surgery for HD isn’t the better indication to restore the motion.
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.
