Friday, September 28, 2018 10:30 AM–12:00 PM abstracts: deformity: technical factors: 165. Sagittal imbalance in degenerative scoliosis can be corrected by addressing only the symptomatic levels in carefully selected patients: a retrospective radiographic study

Abstract

BACKGROUND CONTEXT The optimal method of addressing the positive sagittal imbalance often present in degenerative scoliosis (DS) is controversial. An important distinction is whether or not the etiology of the loss of lumbar lordosis (LL) and positive sagittal imbalance often seen on preoperative radiographs, is truly structural, or whether it is more positional in nature given that spinal stenosis is almost always present in DS patients who require surgery. This distinction directly affects the decision about whether or not, in addition to decompression, the entire curve needs to be addressed (regional or global fusion), or if a lesser local fusion of only the symptomatic levels can be performed with a satisfactory radiographic result. PURPOSE This study aims to determine (1) if the loss of LL often associated with DS is structural or rather largely due to positional factors secondary to spinal stenosis, and (2) if the entire DS curve or a lesser local fusion of only the neurologically symptomatic levels need to be addressed. STUDY DESIGN/SETTING Retrospective case series. PATIENT SAMPLE We obtained radiographic and clinical data on 114 consecutive patients. We included patients if they had loss of normal LL (positive sagittal imbalance) observed on preoperative radiographs and underwent a decompression and instrumented posterolateral inter-transverse process arthrodesis of only their neurologically symptomatic levels in the setting of DS. We excluded patients if they had undergone a previous fusion, concomitant osteotomy procedure, or any type of interbody arthrodesis, or had less than 6 months follow-up. Of the original 114 patients identified, 68 fulfilled the above criteria. OUTCOME MEASURES Pre- and postoperative radiographs were reviewed to measure lumbar lordosis, pelvic incidence, pelvic tilt, and sacral slope. Postoperative radiographs were also measured against preoperative extension lumbar radiographs and lumbar magnetic resonance imaging (MRI) to compare changes in radiographic pelvic parameters. METHODS Three independent members of the research team performed all measurements. Inter-rater reliability was calculated using a Pearson coefficient test and a strong correlation was considered if R>0.8. The three sets of measurements were then averaged for final statistical analysis. Relationships were considered significant at p RESULTS Average follow-up was 22 months. In addition to decompression, instrumented fusion was most commonly performed from L4 to S1 (N=17), followed by L3-S1 (N=12). The average PI found preop and postop was 52° and 53°, respectively. The average PT found preop and postop was 24° and 27°, respectively. Preoperative LL had a mean Cobb angle of 32° (range 2°–60°). Preop MRIs and lumbar extension radiographs revealed an average LL of 42° (range 10°–66°) and 48° (range 20°–74°), respectively. Initial postop radiographs (average 3 weeks) revealed that LL was corrected to a mean of 44° (range 14°–68°, p CONCLUSIONS We were able to correct LL to within 10° of the PI in this cohort of symptomatic DS patients with decompression and local instrumented fusion of symptomatic levels only. Loss of LL in symptomatic DS patients has a large positional component likely due to stenosis. Preoperative MRI and extension radiographs can be used to predict achievable postoperative LL correction.