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: 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.

Background: Certain pelvic fractures with posterior shearing force lesions raise a difficult problem for stabilisation. Assemblies bridging the two sacroiliac joints and anchored in the vertebral pedicles have been proposed to overcome this difficult osteosynthesis problem. But this type of fixation bridges intact joints. We used an original computer-assisted osteosynthesis technique in a patient with an unstable non-union of a displaced fracture passing through the S1 pedicle and the sacral foramina associated with major pubic disjunction.

Case report: The instability of the half-pelvis led to pubalgia and movement of the non-union focus which in turn led to S1 sciatalgia preventing the sitting position. The fracture and the displacement could not be treated initially because of open visceral lesions which required definitive colostomy and a long period of intensive care. The technical problem was to stabilise the pelvis with a posterior osteosynthesis which could not use the S1 pedicle. The fixation had to be sufficiently rigid to compensate for the impossible anterior fixation of the pubic symphesis.

Operative technique: The original solution was to bridge the non-union transversally using two spinal bars (CD instrumentation) applied on the healthy side with two polyaxial screws in S1 (in the pedicle and the wing) and on the non-union side with two polyaxial screws inserted in the iliac wing passing between the internal and external corticals. The assembly was completed with two transiliosacral screws passing through S1 and S2 after demounting and avivement of the non-union.

Discussion: The computer superposed a virtual image of the instruments on the CT images allowing precise insertion of the two iliac screws which had to pass between the bone tables over a long trajectory. The two transiliosacral screws could thus be inserted into S1 and S2 percutaneously with minimal neurological risk. Monitoring the progression allowed safe avivement of the nonunion to the anterior border of the sacrum. The final assembly thus associated four screws and two bars on the posterior part of the sacrum and two anterior screws, enabling perpendicular compression of the nonunion while maintaining the spine and contralateral sacroiliac joint. At five years, the patient remains free of dysesthesia and can sit and walk with little limitation.

Conclusion: This particular case illustrates perspective computer-assisted osteosynthesis methods.

Purpose: Circumferential arthrodesis of the lumbar spine is necessary in certain selected situations (lumbar stenosis with instability and preserved disc height or spondylolisthesis). Posterior lumbar interbody fusion (PLIF) raises the risk of significant bleeding and fibrosis around the roots as well as neurological complications. Transforaminal lumbar interbody fusion (TLIF) can avoid excessive bleeding and root displacement. The cages are inserted via a unilateral approach.

Material and methods: This prospective single-centre study included twenty patients (nine men and eleven women), mean age 49 years. Indications for lumbar surgery were degenerative spondylolisthesis in nine patients and discal lumbar pain with foraminal stenosis in five. The clinical status was assessed with the Oswestry score, SF-36 and a visual analogue scale (VAS). Radiological assessment was based on inter-body fusion, segmentary lordosis, and lumbopelvic parameters. TLIF was associated with a posterior approach for insertion of titanium pedicular screws (CDH, Medtronic Sofamor Danek). Temporary unilateral distraction opened the foramen. Unilateral arthrectomy enabled a lateral approach to the disc without involving the roots and avoiding any movement of the dural sac. The disc was resected and the body endplates were prepared before introducing two cages (pyramesh) filled with macroporous ceramic granules (BCP) mixed with autologous bone marrow. Installation to two contourned rods enabled segmentary compression to stabilise the cages in association with posterolateral fusion.

Results: Mean operative time was three hours. Mean blood loss was 400 ml. The patients were verticalised on day three without a corset. Mean follow-up was six months with retrospective evaluation of the Oswestry score, SF-36, and VAS. Postoperative pain resolved rapidly. Two patients developed transient incomplete L5 deficit. Bony bridges around the cases and posterolaterally were identified on the six-month x-rays. Spine view confirmed the quality of the fusion and lumbopelvic parameters revealed restoration of segmentary lordosis.

Conclusion: The unilateral approach for TLIF is a reliable technique which does not compromise the roots. It enables very reliable primary stability and recovery of local segmentary lordosis. We are developing a minimally invasive percutaneous technique for this procedure.