ANTERIOR INSTRUMENTED FUSION OF THE LUMBAR SPINE IN SCOLIOSIS – ARE INTERBODY SPACERS NECESSARY FOR SAGITTAL PROFILE?

Abstract

Introduction: There have been reports of anterior fusion surgery advocating the routine use of interbody spacers in the lumbar and low thoracic spine. In contrast to these, many surgeons feel that the routine use of inter-body spacers is not warranted, provided appropriate surgical technique is used for discectomy, screw placement, and solid rod contouring. Rather, the insertion of spacers may, in fact, hinder correction of the overall deformity. Our hypothesis was that it is possible to create a satisfactory sagittal profile without the use of interbody spacers.

Methods and results: Study design: Retrospective examination of X-rays and appropriate notes. Patients of the senior author who had undergone an instrumented anterior fusion for scoliosis were reviewed. Some of these patients underwent a second stage posterior fusion to the same level distally. Analysis of the X-rays and notes was performed on a group of 27 patients who had undergone their surgery from July 1996 to December 2000. Follow-up varied from six months to three years.

Inclusion criteria: Diagnosis was adolescent idiopathic scoliosis. All surgery carried out by the one surgeon (BT). Anterior fusion, with a solid rod, extending into the lumbar spine. There were 15 who had anterior fusion only, and 12 who also underwent posterior fusion. The difference between the groups was that of the nature of the curves. One of the patients had the posterior fusion on a second admission for thoracic curve progression after anterior lumbar fusion. Lowest instrumented levels were 6 to L2, 15 to L3, and 6 to L4.

Variables measured: Assessment of AP and sagittal alignment was made, as was fusion across the levels. Methods and problems encountered with data collection will be discussed. Variables were AP Cobb; Sagittal angle variables were 1) L1-S1 2) TIV-LIV 3) LIV-S1 4) L4 5) S1. These were compared with previously published data; difficulties in comparison to ‘Normal’ will be discussed.

Results: There was no incidence of metalware failure, and no bone/screw interface problems. There was no loss of correction in those cases where follow-up was possible. Union was slow compared to some previously published series. Despite a tendency for a relative loss of lordosis across the fusion, overall lumbar lordosis was maintained within accepted values, and the fusion construct angle was within accepted limits. There was minimal change in Cobb angle of the fusion construct with time.

There have been four cases of < 25% retro-listhesis at the upper end of the constructs. These have not produced neurological symptoms, but as yet the significance clinically is unknown.

Conclusion: At this stage the authors feel that routine use of interbody spacers is not justified, as complications without their use have not been forthcoming.