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.