Posterolateral arthroscopic discectomies of the thoracic and lumbar spine.

Posterolateral arthroscopic discoscopies were performed on the lumbar and thoracic spine of the cadaver of a 6-foot-tall man. The purpose of this study was to determine the anatomic relationships of the discotomies and to examine the feasibility of the procedure for thoracic discectomies. At most levels in the thoracic spine, the rib neck acted as a guide to the posterolateral disc and as a safeguard against penetration of the pleural cavity. The average distance from the dura to the discotomy was 0.79 cm, with this distance increasing caudally. The thoracic nerve roots were found, in general, to be at less risk of damage because of their initial posterolateral course as they entered the subcostal groove. In the lumbar spine, the average distance from discostomy to the dura was 11.5 mm. Access to the triangular working zone could be gained with angles of insertion ranging from 38 degrees to 65 degrees. At angles less than 35 degrees, there was a significant risk of nerve injury. It is concluded that some thoracic discs can be safely removed through this approach and that the lumbar ventral ramii are very vulnerable to injury because of their proximity to the annulotomy.