Surgical Outcomes for Drop Body Syndrome in Adult Spinal Deformity

Study Design.A multicenter retrospective case series of patients treated surgically for adult spinal deformity (ASD).Objective.The aim of this study was to compare clinical outcomes between propensity score matched ASD patients with or without drop body syndrome (DBS).Summary of Background Data.DBS is an extreme primary sagittal-plane deformity often seen in Asian countries. Although the importance of sagittal alignment is widely recognized, surgical outcomes for deformities purely in the sagittal plane are poorly understood.Methods.This study included 243 consecutive patients (age 66±17 years; range 22-78) who were treated surgically for ASD and were followed at least 2 years (mean follow-up 3.7±2.3 years). DBS was defined as a primary lumbar kyphosis with PI-LL >40°, Cobb angle <30°, and multifidus cross-sectional area <300mm². DBS patients were matched with non-DBS patients by propensity scores for age, gender, lowest instrumented vertebra (LIV) level, and number of levels fused. Demographics, radiographic findings, and clinical outcomes were compared between DBS and non-DBS patients.Results.Of 243 patients with ASD, 34 had DBS (14%); 28 of these were propensity-matched with ASD patients without DBS. Baseline bone mineral density (BMD), body mass index (BMI), and frailty were similar in DBS and non-DBS patients. Baseline sagittal alignment was worse in DBS than in non-DBS patients [C7SVA 14±5 vs. 8±5cm; pelvic incidence (PI)-lumbar lordosis (LL) 60±14 vs. 36±20°], and scoliosis research society (SRS)22 scores were also worse for DBS patients (2.5±0.6 vs. 2.9±0.8). Although DBS patients had more complications (20 DBS vs. 16 non-DBS), the clinical outcomes were similarly improved in both groups after surgery. At the 2-year follow-up, the spinopelvic malalignment was worse in DBS than non-DBS patients (PI-LL 17±16° vs. 8±13°, P<0.05).Conclusion.DBS affected 14% of 234 ASD patients. Although DBS patients had inferior baseline SRS22 scores than non-DBS patients, ASD surgery resulted in similar clinical improvement in both groups. Future studies should examine the influence of lifestyle and genetics on clinical outcomes after surgery for DBS.Level of Evidence: 3.