Spontaneous proximal thoracic curve correction after isolated fusion of the main thoracic curve in adolescent idiopathic scoliosis

Study Design. Retrospective clinical, radiographic, and patient outcome rev iew of surgically treated adolescent idiopathic scoliosis. Objectives. To evaluate the spontaneous correction of the noninstrumented p roximal thoracic (PT) curve after isolated correction of the main thoracic (MT) curve by either an anterior (ASF) or posterior (PSF) instrumentation a nd fusion. Summary of Background Data. There are no studies comparing the structural P T curve response after anterior versus posterior instrumented fusion of the MT curve in adolescent idiopathic scoliosis. Methods. Eighty-five patients (single surgeon) with adolescent idiopathic s coliosis underwent operative instrumentation and fusion of their MT curve. All patients had a PT curve greater than or equal to 20 degrees (average 29 degrees, range 20-49 degrees; average residual side-bending 18 degrees, ra nge 3-42 degrees) and were evaluated for preoperative PT curve flexibility and postoperative curve correction after PSF with the PT curve not instrume nted (n = 44) and ASF with the PT curve not instrumented (n = 41). Minimum follow-up was 2 years (average, 3.6 years). Preoperative, 1 week postoperat ive, and latest follow-up (minimum 2-year) full-length radiographs were eva luated for the PT, MT, and thoracolumbar-lumbar coronal, side-bending, and sagittal Cobb measurements, as well as T1 tilt, clavicle angle, radiographi c shoulder height, and the PT, MT, and thoracolumbar-lumbar apical vertical translation. A patient outcome questionnaire was also completed to correla te patient satisfaction with respect to their shoulder balance and overall appearance. Results. The two groups were found to be statistically equivalent (P = 0.66 ) in terms of preoperative PT curve, MT curve, and MT side-bending curves, with the PT side benders slightly more flexible for the ASF (43%) versus th e PSF group (31%) (P = 0.02). Radiographic. The spontaneous improvement in the PT curve was significant ( P < 0.0001) in both groups. Additionally, this correction was maintained ov er time. However, the spontaneous PT curve correction was significantly gre ater after an ASF versus PSF correction of the MT curve on both the immedia te postoperative (P = 0.017) and minimum 2-year (P = 0.0024) evaluations, w hereas the MT curve correction was the same in both groups (P = 0.45). Ther e was no difference in the postoperative sagittal change in the PT curve (P = 0.12) between the two groups, and there was no difference in radiographi c shoulder height (P = 0.5883). Patient Outcome. Both groups reported improvement in shoulder balance and c linical appearance, but there was no statistical difference between the two groups (P = 0.24). Additionally, no patients reported deterioration in eit her parameter. Conclusions. Spontaneous proximal thoracic curve correction consistently oc curs after instrumented correction of the main thoracic curve. Furthermore, this spontaneous correction is as good as or slightly better after an ASF versus PSF of the MT curve. The preoperative side bender radiographs (PT cu rve flexibility) positively correlate with the postoperative spontaneous PT curve correction.