POSTERIOR SURGICAL APPROACH TO THE LUMBAR SPINE AND ITS EFFECT ON THEMULTIFIDUS MUSCLE

Study Design. This study investigated the changes in the lumbar muscle s after posterior fusion of the lumbar spine and the potential correla tion between muscular changes and the persistence of low back pain. Ob jectives. To evaluate prospectively the effect of the posterior approa ch to the spine on the lumbar erector spinae. Summary of Background Da ta. The posterior approach to the spine leads to considerable alterati on of the erector spinae muscles. An eventual correlation between thes e changes and persisting pain or other clinical symptoms has not been investigated previously. Methods. Seventy-five patients undergoing spo ndylosyndesis for different indications (43 patients) or a second oper ation for the removal of internal fixation (32 patients) were allotted to the study. In each patient, four biopsy specimens from the lumbar multifidus muscle were harvested; in 14 patients, biopsies were taken at both operations. Size and distribution of the fiber types (I, IIA, IIB, IIC) were determined, and pain scoring (visual analogue scale) an d the presence of neurologic deficits were recorded. Results. At the t ime of the first operation, 88% of the patients showed pathologic chan ges (altered internal structure, atrophy, type grouping) in one or mor e biopsies. Statistical analysis showed a correlation between both age and pain and type II (A + B) atrophy. After surgery, the patients sho wed significantly more biopsies with denervation signs than before sur gery. No correlation could be made, however, between the intensity of pain before or after surgery and the relative number of biopsies with signs of denervation. Conclusions. Posterior surgery causes muscular a lterations; however, no correlation with pain or other clinical sympto ms could be established. Therefore, in the case of unsatisfactory resu lts after surgery of the lumbar spine, reasons other than muscle damag e caused by use of the posterior approach must be considered.