[Fractures of the ischium after laminoarthrectomy. Retrospective study of a series of 31 patients].

PURPOSE OF THE STUDY

Pars interarticularis fracture is one possible source of pain after laminoarthrectomy. The purposes of this study were: to describe the pars defect, to determine its causes and to analyse its consequences on the functional final result.

MATERIAL AND METHOD

31 patients operated for disc herniation or degenerative lumbar stenosis were retrospectively studied. Clinical symptoms were evaluated before and 3 months after initial surgery, at the time of postlaminectomy radiological examination and at last follow-up according to Beaujon rating scale. Radiological evaluation included: description of the pars defect on plain radiographs and CT imaging, calculation of the amount of bone just above the inferior articular process that was resected, analysis of the postoperative stability of the spine both on static and dynamic radiographs. Any remaining disc herniation or stenosis were also noted.

RESULTS

39 pars interarticularis fractures were disclosed. These fractures were identified as a linear luency on plain radiographs or on reformed CT imaging view. Asymmetric widening of the facet joint space just below the pars defect was easier to observe and was present in 66 per cent of the cases on plain radiographs and in 79 per cent on CT imaging. After initial surgery 12 slipping appeared. In all of these cases pars fracture was bilateral at the same level or associated to a complete unilateral facetectomy at the same level. The amount of bone resected just above the inferior facet process was 66 per cent in average, range from 45 to 84 per cent. All the patients complained for low back pain and/or leg pain. In 62 per cent of cases symptoms occurred within one year after surgery, at an average onset of 7.6 months postlaminectomy. 27 patients were reported Revision surgery was in all cases a posterolateral fusion with or without instrumentation; new decompression was performed in 15 cases. At last follow-up, according to our classification, results were very good in 9 cases, good in 15 cases and fair in the remaining 3 cases. Improvement rate obtained after the initial surgery was 75 per cent in average, it was 59 per cent after revision surgery, difference was statistically significant.

CONCLUSION

Pars interarticularis fractures may be a source of postlaminectomy pain. They appear to be caused primarily by an excessive resection (more than one half) of the bone immediately superior to the inferior articular process at the level of the laminectomy. These results suggest that caution in resection of this bone or additional posterolateral fusion in case of large resection of pars interarticularis, can avoid the problem. Asymmetric widening of the joint space just below the defect seems to be the key to this diagnosis in the postoperative lumbar laminectomy patient with persistent or recurrent pain.