This study investigated the operative results and factors involved in multiply operated back cases (M. O. B.). 639 cases of Lumbar canal stenosis were surgically treated over a 5 year period, 32 of whon (4.9%) were M. O. B.. Average improvememt rate according to the J. O. A. score using Hirabayashi's method was 52.0%. Many factors are involved with M. O. B.. The prinapal factors were instability at the affected level and insufficient decompression of lateral recess. It is relatively easy to resect adhesions in new stenotic damage, with an improvement rate was 53.7%. However, when the stenosis is long-term, with scar formation or compression on the dura and nerve root it is very difficult to release the nerve. In these cases, the improvementrate was 20-30%. For the prevention of M. O. B., adequate decompression and accurate fusion are necessary at the first operation.
