Radiologic Results of Posterior Lumbosacral Fixation according to Sacral Fixation Methods: Single Screw vs Double Screws

Shin, Byung Joon; Kim, Kyung Je; Cho, Yang Bum; Kim, Yon Il

Abstract

STUDY DESIGN: This is a retrospective study comparing the radiologic results of sacral fixation using anteromedially directedsingle screw and triangulated double sacral screws.
OBJECTIVES
To know whether the single screw fixation is enough for short level lumbosacral fusion. SUMMARY OF LITERATURE REVIEW: Method of sacral fixation is one of a hot issue in spinal instrumentation because of high complication rate. So, many kinds of sacral fixation methods were developed for long level spinal instrumentation. But, it is unclear whether we should use the special sacral fixation techniques instead of simple single screw fixation for the short level lumbosacral fusion.
MATERIALS AND METHODS
Inclusion criteria of this study were fixation down to sacrum or sacralized L5, less than three segments fixation and minimum radiologic follow-up for one year. Of those patients treated with lumbosacral fixation using pedicle screw instrumentation from March 1989 to June 1998, forty-four patients met these criteria. They were divided into two groups according to the method of sacral fixation, Group I for single screw fixation and Group II for double screw fixation. Number of patients were 37 in Group I and 7 in Group II. The mean follow-up was 36.5 and 66.6 months, respectively. The radiologic results were evaluated by metal failure, change of lumbar lordosis, change of lumbosacral angle and change of L5-S1 disc space height.
RESULTS
metal failure were identified in five patients(13.5%), all in sacral screws of Group I. There were 4 screw breakages and 1 screwrod dissociation. The change of lumbar lordosis was averaged 2.3 degrees(-17~38) in Group I and -4.0 degrees(-25~17) in Group II(p=0.194). The change of lumbosacral angle was averaged 2.3 degrees(-7~12) and 3.7 degrees(-1~12), respectively(p=0.596). The change of disc height was 5.6%(-13~33) and 8.8%(-5~16), respectively(p=0.381).
CONCLUSIONS
Group I has much higher rate of instrumentation failure than Group II and all the instrumentation failures were occured at sacral screws. Other radiologic measurements were not statistically significant between the two groups. Stable fixation of the sacrum is necessary to prevent instrumentation failure at the sacrum even though the fusion is less than three levels.