RADIOGUIDED RETROPERITONEAL TRANSACRAL APPROACH TO THE L5-S1 DISC

Abstract

Purpose: Intersomatic L5-S1 arthrodesis is a common procedure in orthopaedic surgery of the spine. Two approaches are generally proposed: the anterior trans or retroperitoneal approach and the posterior approach via the spinal canal or laterally. We conducted an anatomic animal study to examine the feasibility of a new approach to the L5–S1 disc.

Material and methods: Five anatomic specimens were used. The approach consisted in introducing via posterior laterosacral access a blunt 5 mm trocar into the sacrococcygeal joint. A 2 cm incision was made to identify the anterior aspect of the sacrum. Anterior and lateral scopic control was used to follow the progression of the trocar. The guide was medialised and slid into the median part of the sacrum. A larger tube with an oblique end was slid over the guide and impacted on the inferior border of the S1–S2 disc. The blunt trocar was then removed and the tube was impacted into the S2 bone under scopic control. A hollow bit was then inserted into the tube to perforate S2 and reach the L5-S1 disc. Angled instruments allowed nucleoctomy without injuring the annulus. All specimens were then explored anteriorly. The technique was tested on five 40–50 kg living pigs. After inserting the hollow bit, laparoscopy was performed to visualise the trajectory of the tube and search for possible complications.

Results: The anatomic study was conducted with the animals placed in a ventral position. The blunt trocar easily detached the presacral infraperitoneal region without any perforation of the neighbouring organs (sigmoid, colon). The presacral membrane was fragile in two cases but appeared to have been weakened by prior intra-peritoneal surgery due to the presence of pseudomembranes. It was possible to achieve perforation of S1 and partial L5–S1 discectomy in all cases. Nucleoctomy was difficult due to insufficient instrument design. There was no problem in inserting the trocar and reaching the L5–S1 disc in any of the piglets.It was sometimes difficult to impact the tube into the S1 bone because of the small angle between the sacrum and the lumbar spine. Laparoscopy revealed a small pre-sacral haematoma in four cases without significant bleeding. In one case, the haematoma was much larger and related to arterial or venous bleeding from presacral vessels. Insertion of the trocar was difficult. The instrument slid toward the promontory probably causing injury to a branch of the sacral vessels which have a large diameter in the piglet.

Discussion: This anatomic study demonstrated the feasibility of a new approach to the L5–S1 disc. This approach could be an interesting alternative in several indications: revision surgery for nonunion after other methods, treatment of certain types of spondylolisthesis. For partial prosthetic replacements (nucleoplasty) this approach would have the advantage of avoiding the need to open the annulus, the principal element of disc stability. Other trials would be necessary to design adequate instrumentation, but this new approach appears promising because it involves a minimally vascularised area. Video assistance for the trocar would help optimise presacral dissection.