P144. Proximal lordosis compensation following lumbar fusion surgery

BACKGROUND CONTEXT Sagittal balance of the lumbar spine involves a distribution of lordosis favoring the lower segments. Patients with a normal lumbar lordosis distribution are well described as having favorable outcomes with regards to postoperative mechanical symptoms. However, the impact of altering lower lumbar segmental lordosis through fusion surgery on the sagittal alignment of the proximal lumbar segment has not been defined. PURPOSE To assess the relationship between changes in L4-S1 lordosis by fusion surgery on the change in L1-L3 lordosis. STUDY DESIGN/SETTING Retrospective review of radiographic sagittal balance. PATIENT SAMPLE Patients with degenerative spine disease receiving a 1- to 2-level lower segment (L4-S1) lumbar fusion surgery with preoperative and one-year postoperative standing lateral lumbar spine radiographs. OUTCOME MEASURES Changes in total and segmental lumbar lordosis, pelvic incidence, and lumbar distribution index. METHODS Patient demographics, comorbidities, surgical indications, and surgical procedures were obtained from review of the electronic medical record. Preoperative and 1-year postoperative radiographs were reviewed for lumbar sagittal balance measurements. Delta values were calculated by subtracting the preoperative data from the postoperative data. Groups were formed based on delta L4-S1 values: <10°, -10° to -6°, -5° to -1°, 0 to 5°, 6° to 10°, and >10°. Bivariate analysis was performed to detect changes in L1-L3 segmental lordosis between groups. Multivariate analyses identified variables independently associated with changes in L1-L3 segmental lordosis and L1-S1 lordosis. RESULTS We identified 251 patients receiving a 1- to 2-level fusion between L4-S1. No differences were detected between the groups with regards to BMI (median: 30.6; p=0.314), Elixhauser Comorbidity Index (median: 1.00; p=0.323), or sex (54.2% female; p=0.065). Patients in the >10° group were more likely to be younger (58 vs 66; p=0.007) and patients in the -5° to -1° group were less likely to be current smokers (0% vs 9.2%; p=0.036). Preoperative diagnosis was similar between groups with exception to the >10° group having fewer patients with stenosis (72.0% vs 87.6%; p=0.019). In addition, patients in the >10° group were more likely to receive an anterior lumbar interbody fusion (ALIF) (52% vs 17.1%; p10° group was more likely to have a 1-level L5-S1 fusion. Delta L1-L3 segmental lordosis was similar between the groups (median: 1; p=0.963). Multivariate regression analysis identified former smoking status as an independent predictor of delta L1-L3, and receiving an ALIF as independently associated with an increased delta L1-S1. CONCLUSIONS Regardless of the degree of change in L4-S1 segmental lordosis by the fusion operation, L1-L3 segmental lordosis was static. These data suggest that any change in lordosis that is achieved by surgery for lower lumbar fusions is likely to be realized as a change in overall lumbar lordosis without significant compensation by the proximal segment at 1-year. In addition, there does not appear to be any factor reasonably associated with a change in L1-L3 lordosis from surgery below this segment. Consistent with previous literature, receiving an ALIF is associated with the greatest degree of change in total lumbar lordosis. FDA Device/Drug Status This abstract does not discuss or include any applicable devices or drugs. Sagittal balance of the lumbar spine involves a distribution of lordosis favoring the lower segments. Patients with a normal lumbar lordosis distribution are well described as having favorable outcomes with regards to postoperative mechanical symptoms. However, the impact of altering lower lumbar segmental lordosis through fusion surgery on the sagittal alignment of the proximal lumbar segment has not been defined. To assess the relationship between changes in L4-S1 lordosis by fusion surgery on the change in L1-L3 lordosis. Retrospective review of radiographic sagittal balance. Patients with degenerative spine disease receiving a 1- to 2-level lower segment (L4-S1) lumbar fusion surgery with preoperative and one-year postoperative standing lateral lumbar spine radiographs. Changes in total and segmental lumbar lordosis, pelvic incidence, and lumbar distribution index. Patient demographics, comorbidities, surgical indications, and surgical procedures were obtained from review of the electronic medical record. Preoperative and 1-year postoperative radiographs were reviewed for lumbar sagittal balance measurements. Delta values were calculated by subtracting the preoperative data from the postoperative data. Groups were formed based on delta L4-S1 values: <10°, -10° to -6°, -5° to -1°, 0 to 5°, 6° to 10°, and >10°. Bivariate analysis was performed to detect changes in L1-L3 segmental lordosis between groups. Multivariate analyses identified variables independently associated with changes in L1-L3 segmental lordosis and L1-S1 lordosis. We identified 251 patients receiving a 1- to 2-level fusion between L4-S1. No differences were detected between the groups with regards to BMI (median: 30.6; p=0.314), Elixhauser Comorbidity Index (median: 1.00; p=0.323), or sex (54.2% female; p=0.065). Patients in the >10° group were more likely to be younger (58 vs 66; p=0.007) and patients in the -5° to -1° group were less likely to be current smokers (0% vs 9.2%; p=0.036). Preoperative diagnosis was similar between groups with exception to the >10° group having fewer patients with stenosis (72.0% vs 87.6%; p=0.019). In addition, patients in the >10° group were more likely to receive an anterior lumbar interbody fusion (ALIF) (52% vs 17.1%; p10° group was more likely to have a 1-level L5-S1 fusion. Delta L1-L3 segmental lordosis was similar between the groups (median: 1; p=0.963). Multivariate regression analysis identified former smoking status as an independent predictor of delta L1-L3, and receiving an ALIF as independently associated with an increased delta L1-S1. Regardless of the degree of change in L4-S1 segmental lordosis by the fusion operation, L1-L3 segmental lordosis was static. These data suggest that any change in lordosis that is achieved by surgery for lower lumbar fusions is likely to be realized as a change in overall lumbar lordosis without significant compensation by the proximal segment at 1-year. In addition, there does not appear to be any factor reasonably associated with a change in L1-L3 lordosis from surgery below this segment. Consistent with previous literature, receiving an ALIF is associated with the greatest degree of change in total lumbar lordosis.