Minimum 5-year radiographic results of long scoliosis fusion in juvenile spinal muscular atrophy patients: Major curve progression after instrumented fusion

BACKGROUND: Previous studies reported on spinal muscular atrophy (SMA) scoliosis surgery outcomes without focus on major curve progression (MCP). The purpose of this study was to assess minimum 5-year radiographic outcomes, MCP, and factors for MCP after spinal surgery in juvenile SMA patients with open triradiate cartilage at the time of surgery. METHODS: Retrospective review of radiographic and clinical data of 22 SMA patients treated surgically at 3 institutions over 20 years was performed. Major curve Cobb angle, apical vertebral translation, pelvic obliquity, coronal balance, and sagittal Cobb angles (T5-T12 and T12-sacrum) were measured at preoperative, initial, and ultimate follow-up. MCP was defined as an increase in Cobb angle of ≥10 degrees between initial and ultimate follow-up. RESULTS: Overall, SMA patients had significant improvement in radiographic measurements at follow-up. Eight patients (36%) developed MCP and were similar in age (7.8 vs. 8.8 y, P=0.09) to non-MCP patients. Initial major curve Cobb angle correction was greater for MCP patients than for non-MCP patients (19 vs. 36 degrees, P=0.004). MCP patients lost 26 degrees (P=0.001) and non-MCP patients lost 2 degrees of major curve Cobb angle correction during follow-up. Both groups had similar ultimate follow-up radiographic outcomes and remained improved from preoperative deformity. All 14 non-MCP patients had long posterior instrumentation (T4 or higher to sacrum/pelvis), whereas all 4 patients with short posterior instrumentation developed MCP. Six patients underwent anterior-posterior spinal fusion (ASF-PSF) and had greater preoperative deformity than PSF-only patients, but ultimate major curve Cobb angle (38 vs. 44 degrees, P=0.4) was similar for both the groups. Two ASF-PSF patients developed MCP. CONCLUSIONS: Overall, SMA patients maintained scoliosis correction with nonpedicle screw-based (predominantly Luque-Galveston instrumentation) long spinal instrumentation at minimum 5-year follow-up. MCP >10 degrees developed in 36%, contrary to our expectation of 100% in these young juvenile SMA patients. All non-MCP patients had instrumentation from the upper thoracic spine (T1 to T4) to the sacrum, whereas all 4 patients with short instrumentation developed MCP. MCP and non-MCP patients had similar ultimate correction and remained improved from preoperative deformity. Skeletal immaturity and length of posterior instrumentation may influence MCP in SMA scoliosis surgery and should be considered during preoperative planning. LEVEL OF EVIDENCE: Case Series; Level IV.