Purpose of the study: Indications for disc prosthesis is generally established on the basis of the MRI findings (MODIC classification) and the discography. We considered that knowledge of the preoperative disc height is also important. We report a multicentric study of the results of lumbar arthroplasties as a function of preoperative height of the operated disc.

Material and methods: A Mobidisc prosthesis was implanted in 93 patients and followed prospectively for at least one year (mean follow-up 5 years). Disc height was compared with the height of the suprajacent disc and divided into three groups: > 66% of height (GI) i.e. a subnormal disc height (n=30), 33–66% (GII) moderate impingement (n=36), < 33% (GIII) total impingement (n=27). A MODIC signal was found for 19% in GI, 42% in GII and 40% in GIII.

Results: The lumbar VAS improved from 6.7 to 3.2 (GI), 6.2 to 2 (GII) and 6.2 to 1.5 (GIII). The radicular VAS improved from 4.8 to 3.1 (GI), 5.7 to 2.4 (GII) and 5.5 to 1.6 (GIII), respectively 69, 75 and 85.5% of the patients were satisfied or very satisfied for relief of the lumbar or radicular pain. The Oswestry score improved from 50 to 22% (GI), 49 to 20% (GII) and 46 to 12% (GIII). By MODIC, the lumbar VAS improved from 6.5 to 2.8 (MODIC 0) and from 6.6 to 2 (MODIC 1). The radicular VAS was improved from 5.5 to 2.9 (MODIC 0) and from 5.3 to 2.1 (MODIC 1). The Oswestry score was improved from 52 to 24% (MODIC 0) and from 48 to 15% (MODIC 1). Independently of MODIC, the VAS was always better for very tight discs and lower if the disc height was preserved.

Discussion: An influence of the disc height was found for all parameters studied, irrespective of the type of disc disease as described by the MODIC classification. The presence of a tight preoperative disc height appeared as the essential prognostic factor for discal prostheses. For a MODIC 0 discopathy, without loss of disc height, only 67 and 61% of the operated patients were satisfied or very satisfied with relief of lumbar and radicular pain (VAS 3.6 and 3.4) for respectively 88 and 75% of the MODIC0 discopathies with discal impingement (VAS 1.5 and 1.5). Though it should not be formally ruled out, surgery for discopathy with a preserved disc height should be examined prudently before implanting a disc prosthesis.

Purpose of the study: Discectomy-anterior fusion has proven efficacy for many diseases of the cervical spine. Nevertheless, the loss of motion and the over-solicitation of adjacent levels are arguments in favor of disc replacement. This prospective study examined the early clinical and radiological results obtained in the first 41 patients treated with a new cervical disc prosthesis, Mobi-C.

Material and methods: A prospective multicentric clinical and radiological study is being conducted to analyze the safety and efficacy of Mobi-C for degenerative disease. Indications are radiculopathies due to discal herniation or foraminal osteophytic stenosis involving one or two levels from C3 to T1. An independent observer reviewed the patients. SF36, the Neck Disability Index, and a visual analogue scale for pain as well as radiographic mobility were noted.

Results: Mean age was 42 years (range 31–56 years). There were 23 men and 18 women. Eight patients had two disc replacements. Mean follow-up was six months (range 3–10 months). Mean operative time was 65 min, similar to operative time for fusion. Blood loss was 90 ml. NSAID were prescribed for the first 15 days. There were no intraopeartive complications and no revisions. Postoperative complications were minimal. There were no specific complications related to the prosthesis, its insertion or its function. The function and quality-of-life scores showed a significant improvement at last follow-up. Radiographically, motion was also improved in most patients.

Discussion: The early results on the safety and efficacy of this new cervical prosthesis are promising. Primary stability has been excellent and there have been no specific prosthesis-related complications. Furthermore, several operators have mentioned how easy it is to insert the Mobi-C.

Conclusion: The clinical results in terms of pain and function as well as the radiological results have been satisfactory both at the early and at the later assessments. Insertion of this prosthesis is a simple process, similar to insertion of an intersomatic cage, elements arguing in favor of a cervical disc prosthesis. Further follow-up will be needed to assess the long-term efficacy and possible effect on prevention of accelerated degeneration of the adjacent discs.

Purpose of the study: The theoretical usefulness of a disc prosthesis in comparison with arthrodesis would be to restore physiological segmental motion without perturbing the kinematics of the adjacent levels. The purpose of this study was to determine the rotation centers of the lumbar segments before and after implantation of a disc prosthesis with a mobile insert (Mobidisc™).

Material and methods: Lateral flexion and extension views in the sitting position with a stabilized pelvis were obtained before and after implantation of the lumbar disc prosthesis in 32 patients. Spineview™ was applied to the digitalized images for semi-automatic recognition of the vertebral body contours and calculation of the rotation centers. The detection threshold for this automatic system was 5° motion.

Results: Rotation centers were difficult to determine preoperatively because of the absence of mobility. A pathological position was found for three patients. Postoperatively, at three and twelve months, the position was «physiological» in 13 patients, in the posterior half of the disc or inferior body near the vertebral end plate. IN 14 patients, the center could not be determined because motion measured 5° or less. For three patients, the center was too anterior on a prosthesis implanted to anteriorly. There were no changes in the rotation centers for the adjacent levels.

Discussion: Demonstration of an abnormal rotation center could be an additional indication of presumed instability. In certain cases, a disc prosthesis appears to restore the physiological rotation center. But the position and the thickness of the implant can influence their localization.

Conclusion: Restoration of a physiological rotation center for the instrumented intervertebral segment and the absence of change in the rotation centers for the adjacent centers are arguments in favor of disc prosthesis for reducing the incidence of osteoarthritic degradation of adjacent discs in comparison with fusion, under the condition that the implantation and the size are correctly adapted.

Purpose: The purpose of this study was to analyse the results and morbidity of video-assisted minimally invasive thoracoctomy for anterior arthrodesis of thoracolumbar fractures treated with a two-stage procedure and to evaluate mid-term outcome.

Material and methods: This retrospective series included 6 patients with an unstable thoracolumbar fracture who underwent surgery between November 1997 and June 2002. A two-stage procedure was used: posterior reduction osteosynthesis and anterior arthrodesis with a tricortico-cancellous graft via video-assisted minimally invasive thoracotomy. The cohort included six women and eighteen men, mean age 34.5 years. Fractures were located at: L1 (n=4), T12 (n=10), T11 (n=2). At initial assessment the Franckel classification was: A (n=3), B (n=1), C (n=1), D (n=3), 3 (n=18). Time between the posterior procedure and the anterior thoracotomy was 30.2 days (range 6–86). Postoperative results as well as the time to fusion were recorded. Mean follow-up was 21 months (range 6–45) for functional and radiological assessment. No patient was lost to follow-up.

Results: Mean operative time was 188 min (range 80–240). Mean blood loss was 235 ml (range150–1000) with no intraoperative event requiring conversion to open thoracotomy. Mean duration of morphine administered postoperatively was 2.2 days, the same as for thoracic drainage. Residual pleural effusion was observed in one patient and residual pneumothorax in two; all resolved spontaneously. Mean hospital stay was 12 days (range 6–27). Twenty-five patients had achieved fusion at four months. One patient developed a radiological non-union which was asymptomatic at one year. At last follow-up, the Oswestry function score was 22.6% for the entire series, 18% for Franckel D or E patients (n=21) and 42% for Franckel A, B and C patients (n=5). Loss of angular correction of the spinal kyphosis and regional traumatic angulation between the postoperative films and the last follow-up films was 2 (mean).

Discussion: This series of complementary anterior arthrodesis by video-assisted minimally invasive thoracotomy confirmed the minimally invasive nature of this approach in comparison with thoracophrenolaparotomy and its complications. At mid term, this technique has provided satisfactory functional and radiographic results. Applied for thoracolumbar fractures, this combined surgical option can limit intraoperative morbidity and assure good mid-term results.