OBJECTIVESTo provide the anatomical basis for surgical treatment of extraforaminal lumbar disc herniation (EFLDH) by paraspinous muscle splitting approach and to investigate the effect of its application.

METHODSThe relationship among the intertransverse processes, lateral margin of the pars interarticularis, anterior ramus of the lumbar nerve, and anterior ramus of the lumbar artery was studied in 34 cadaveric specimens. From October 1993 to October 1999, eleven cases of extraforaminal lumbar disc herniation were treated by paraspinous muscle splitting approach and retroperitoneal approach.

RESULTSIn the extraforaminal region, the anterior ramus of the lumbar artery and venus locate ventrally to the superior half of the intertransverse space, and the anterior ramus of the lumbar artery runs downward behind the nerve. The distance from the lateral margin of the pars interarticularis to the nerve root and the angle between the nerve root and midline sagittal plane were 1.0 - 2.0 cm and 7 degrees - 25 degrees respectively which increased gradually from L(1) to L(5). The period of follow up in 10 of 11 cases was 23 - 98 months. Evaluation according to Low Back Outcome Score showed excellent results in 8 cases, and good in 2.

CONCLUSIONSurgical treatment of EFLDH by paraspinous muscle splitting approach is safe, effective and minimal invasive.