[Long-term osseous changes in the posterior arch after laminectomy for lumbar stenosis]

Many studies have indicated favorable results of decompressive surgery for symptomatic lumbar spinal stenosis. However, little is known about the osseous changes that occur at the operative sites. Postacchini in 1992 and Chen in 1994 have studied, only from plain radiographs, osseous changes at the operative sites, and have suggested that bone regrowth possibly affects the neurologic result. The aims of this study were: to assess bone regrowth at the operative site, to compare the bone regrowth rate calculated from plain radiographs and CT-Scan examinations, to determine the effects of bone regrowth on clinical outcome, to investigate the factors promoting the bone regrowth.

28 patients who underwent decompressive surgery for lumbar spinal stenosis were retrospectively studied with an average follow-up of 8.4 years. In order to evaluate the degree of bone regrowth at the posterior arch, early postoperative radiographs and CT images of the operative sites were compared with those obtained at final follow-up. Bone regrowth at the sites operated upon was evaluated as a percentage of regrowth of the original laminectomy site based upon plain radiographs and CT images.

Decompressive lumbar spinal stenosis is responsible for bone regrowth at the operative site in most patients. However, this regrowth was mild, the mean bone regrowth rate evaluated from plain radiographs was 12 per cent in average and the obtained from CT images was 8.2 per cent in average. Changes were found to be predominant at the facet joint level compared to the pedicle level. The evaluation of regrowth obtained from plain films and CT image examinations were compared. Radiographs seem to overestimate bone regrowth. Postoperative spinal instability was statistically significantly associated with new bone development. This variable was the only factor that affected the degree of bone regrowth. No relationship between bone regrowth and clinical outcome was found.

Natural course of laminectomy defect includes probably new bone formation in most patients. New bone results from gradual regrowth of the laminae and articular processes partially resected at surgery and from coalescence of islets of bone tissue within the tissue filling the laminectomy defect. In the present study bone regrowth rate was moderate but in other ones it was marked. If some factors (like postoperative destabilization) promoting bone regrowth were identified many remain unknown. Factors influencing rapidity of regrowth progression remain also unknown. Patient's intrinsic features such as spinal stenosis characteristics are probably closely related to quantitative and kinetic characteristics of regrowth. Consequences of bone regrowth are also variable: in some cases regrowth may reproduce pathological conditions identical previous ones, in other ones new bone spreads around the dura a mater without any nerves roots compression. Study of bone regrowth requires further research including prospective studies and using a more precise method for the regrowth evaluation.