PARS-INTERARTICULARIS FRACTURE AFTER LAMI NOARTHRECTOMY - STUDY ON 31PATIENTS

Purpose of the study Pars interarticularis fracture is one possible so urce 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 3 1 patients operated for disc herniation or degenerative lumbar stenosi s were retrospectively studied. Clinical symptoms were evaluated befor e and 3 months after initial surgery, at the time of postlaminectomy r adiological examination and at last follow-up according to Beaujon rat ing 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, a nalysis of the postoperative stability of the spine both on static and dynamic radiographs. Any remaining disc herniation or stenosis were a lso noted. Results 39 pars interarticularis fractures were disclosed. These fractures were identified as a linear luency on plain radiograph s or on reformated CT imaging view. Asymetric widening of the facet jo int space just below the pars defect was easier to observe and was pre sent in 66 per cent of the cases on plain radiographs and in 79 per ce nt on CT imaging. After initial surgery 12 slipping appeared, In all o f these cases pars fracture was bilateral at the same level or associa ted to a complete unilateral facetectomy at the same level. The amount of bone resected just above the inferior facet process was 66 per cen t in average, range from 45 to 84 per cent. All the patients complaine d for low back pain and/or leg pain. In 62 per cent of cases symptoms occured within one year after surgery, at an average onset of 7.6 mont hs postlaminectomy. 27 patients were reoperated Revision surgery was i n all cases a posterolateral fusion with or without instrumentation; n ew decompression was performed in 15 cases. At last follow-up, accordi ng to our classification, results were very good in 9 cases, good in 1 5 cases and fair in the remaining 3 cases. Improvement rate obtained a fter the initial surgery was 75 per cent in average, it was 59 per cen t after revision surgery, difference was statistically significant. Co nclusion Pars interarticularis fractures may be a source of postlamine ctomy pain. They appear to be caused primarily by an excessive resecti on (more than one half) of the bone immediately superior to the inferi or articular process at the level of the laminectomy. These results su ggest that caution in resection of this bone or additional posterolate ral fusion in case of large resection of pars interarticularis, can av oid the problem. Asymetric widening of the joint space just bellow the defect seems to be the key to this diagnosis in the postoperative lum bar laminectomy patient with persistent or recurrent pain.