228. Does interbody fusion protect against rod failure in the lower lumbar spine after long fusions to the sacrum: a comparative analysis of adult spinal deformity patients

Abstract

BACKGROUND CONTEXT The incidence of pseudarthrosis and rod fracture after long spinal fusion to the sacrum for correction of adult spinal deformity ranges from 20% to 40%. Several strategies have been proposed to decrease pseudarthrosis rates across the lumbosacral junction including rigid sacropelvic fixation, BMP and the use of interbody fusions at the lower lumbar spine. However, rod failures in the lumbar spine after ASD correction remain high despite the use of BMP and sacropelvic fixation. The question whether Interbody fusion is needed with the combination of sacropelvic fixation and use of BMP after long PSF to the sacrum in ASD remains unanswered. PURPOSE To investigate the incidence of rod fractures in patients undergoing surgery for correction of adult spinal deformity with or without the use of interbody fusions in the caudal levels of the fusion construct at L3 and below. We compared the rate of RF in 256 ASD patients who underwent long spinal fusion using BMP and sacropelvic fixation with and without Interbody fusion in the lower lumbar spine. STUDY DESIGN/SETTING Single institution retrospective cohort study. PATIENT SAMPLE Adult spinal deformity patients who underwent PSF to the sacrum with use of bilateral pelvic fixation and BMP with or without interbody fusion performed in the lower lumbar spine L3-S1. OUTCOME MEASURES The primary outcome of interest was the incidence of rod fractures at the lower lumbar spine from L3 to the sacrum. METHODS We reviewed clinical records of patients that underwent surgery for correction of adult spinal deformity between 2008 and 2014. Patient demographics, comorbidities, indications for surgery, as well as intra- and postoperative variables were collected for each patient. Patients were dichotomized into one of two groups based on whether an interbody fusion was performed at the caudal levels of the fusion construct. All patients had a minimum two-year follow-up. 526 ASD patients was reviewed, only primary surgeries were included. Interbody fusions were performed in the lower lumbar spine L3-S1 most commonly at L5-S1. The primary outcome of interest was the rod failure rates from L3-S1. All patients had a minimum 2-year follow-up. RESULTS A total of 256 patients underwent long PSF for correction of ASD, 141 patients had interbody fusion (IF group) at any level L3-S1 with mean follow up of 59 ±29 months and 115 patients had no interbody fusion(NIF group) with 50±22 months mean f/u. At baseline, there were no significant differences between both groups in gender (p=0.97), BMI (p=0.62), smoking status (p=0.40), diabetes(p=0.34) or osteopenia p=0.73. The median number of levels fused in the IF group was 10(7-15) compared with 8 levels (7-15) in the NIF group. BMP and sacropelvic fixation (233 iliac screws and 23 patients had S2AI screws) were used in all patients. Pre-op sagittal plane deformity was not different between both groups. At last follow-up, there was no statistically significant difference in rate of Rod failure between IF n=29(21%) vs NIF n=17(15%) p=0.23. IF group had 19(13%) unilateral rod failures and 10 (7% ) bilateral rod failures. NIF group included 12(10%) unilateral rod failures and 5(4%) bilateral rod failures. The most common location of rod failures was different between the groups, L3-L4 was the most common location in the IF group with 6.5% followed by L5-S1 in 6.1% of patients. Interbody fusion was performed at L4-5 and L5-S1 in the majority of patients that failed at L3-4. In the NIF group L5-S1 was most common location in 6.4% followed by L4-L5 in 2.7% of patients. CONCLUSIONS This study suggests that interbody fusion of the lower lumbar spine in ASD patients may not be associated with a decrease in the incidence of rod failures at the Lubosacral junction. Interbody fusion does not protect against rod failure in the lower lumbar spine in long PSF to the sacrum and may encourage failure at L3-4, the level above the interbody fusion. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.