198 - An Ipsilateral Bi-portal Arthroscopic Trans-iliac Approach to L5-S1 Di...

#198 An Ipsilateral Bi-portal Arthroscopic Trans-iliac Approach to L5-S1 Disc and Foramen. A Cadaver Study

Oral Posters: MIS

Presented by: S. Osman

Author(s):

S.G. Osman (1)

(1) American Spine Center, Frederick, MD, USA

Abstract

Background: Multiple MIS procedures have been added to the armamentarium of surgical approaches of the lumbar spine including X-LIF, MIS TLIF, AxiaLIF, laparoscopic, and endoscopic approaches. The downside of the posterior endoscopic approach is violation of the spinal canal. The X-LIF cannot access the L5-SI because of the intervening iliac bone. AxiaLIF, in addition to possible injury to the bowel, cannot tackle intra-canal pathology, and laparoscopic approach risks injuries to the major vessels, the bowel and pre-sacral plexus. The arthroscopic micro-discectomy approach can access the L5-S1 disc and foramen in most cases, however, in a deep-seated L5-S1, a supra-iliac crest approach may not access the disc in its axial plane and may lean on the exiting L5 nerve root causing injury.

Objectives: To determine the feasibility of a trans-iliac approach to L5-S1 disc and foramen, and to evaluate the safely of this approach by studying the anatomical relationship to the trans-iliac access cannula.

Materials and Methods: 5 fresh cadavers were used for the study. Pre-operative axial CT scan was taken, in the plane of the disc equator to determine the portal site and angle of instrumentation. Under fluoroscopic guidance, a guide wire is driven through the iliac crest through the iliac wing and into the postero-lateral corner of the disc. A core-drill was used to excise a cylinder of iliac bone from around the guide wire after insertion of access cannula. 18-gauge spinal needle was inserted through the iliac bone window into the posterolateral disc. The rest of instrumentation was carried out as described by Kambin et al(1). Another cannula was inserted supra-iliac to triangulate with the trans-iliac in the foramen and bi-portal arthroscopic procedure is performed. Distances from vital structures were measured and the integrity of the skeletal structures was investigated.

Results: The access cannula passed through the Gluteus Maximus and Medius in 4 cadavers and only through Glut. Maximus in 1. Distances from the trans-cannula to: (a) PSIS = 4.16 cm; (b) iliac crest = 2.24 cm; (c) lumbo-sacral trunk = 1.93 cm; (d) superior gluteal nerve =4.8 cm. The volume of iliac bone dowel was 3.93 cc. There were no injuries to the facet joints, sacro-iliac joints or ilio-lumbar ligaments.

Conclusion: Access to the L5-S1 disc and foramen is possible through trans-iliac approach. Vital structures were at safe distances from the path of the access channel, and no injury to the skeleton' other than the trans-iliac window, was recorded. [Key words: arthroscope, bi-portal, ipsilateral, supra-iliac, trans-iliac.

References: 1. Kambin P. Arthroscopic Micro-discectomy. Arthroscopy 1992; 8:287-95.