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 review of surgically treated adolescent idiopathic scoliosis. Objectives. To evaluate the spontaneous correction of the noninstrumented proximal thoracic (PT) curve after isolated correction of the main thoracic (MT) curve by either an anterior (ASF) or posterior (PSF) instrumentation and fusion. Summary of Background Data. There are no studies comparing the structural PT 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 scoliosis 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, range 3-42 degrees) and were evaluated for preoperative PT curve flexibility and postoperative curve correction after PSF with the PT curve not instrumented (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 postoperative, and latest follow-up (minimum 2-year) full-length radiographs were evaluated for the PT, MT, and thoracolumbar-lumbar coronal, side-bending, and sagittal Cobb measurements, as well as T1 tilt, clavicle angle, radiographic shoulder height, and the PT, MT, and thoracolumbar-lumbar apical vertical translation. A patient outcome questionnaire was also completed to correlate 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 the 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 over time. However, the spontaneous PT curve correction was significantly greater after an ASF versus PSF correction of the MT curve on both the immediate postoperative (P = 0.017) and minimum 2-year (P = 0.0024) evaluations, whereas the MT curve correction was the same in both groups (P = 0.45). There 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 radiographic shoulder height (P = 0.5883). Patient Outcome. Both groups reported improvement in shoulder balance and clinical appearance, but there was no statistical difference between the two groups (P = 0.24). Additionally, no patients reported deterioration in either parameter. Conclusions. Spontaneous proximal thoracic curve correction consistently occurs 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 curve flexibility) positively correlate with the postoperative spontaneous PT curve correction.