Choosing the Distal Fusion Level for Anterior Instrumentation and Fusion in Thoracic Adolescent Idiopathic Scoliosis

• a - Medtronic/Sofamor Danek

Introduction: Anterior spinal fusion and instrumentation (ASFI) for thoracic adolescent idiopathic scoliosis (AIS) has proposed advantages over posterior instrumentation, including improved sagittal plane reconstruction, the ability to save fusion levels, and improved coronal balance. Traditionally fusion levels for ASFI have included the end vertebrae (EV), although inclusion of the most distal vertebra in cases where the last two vertebrae tilting into the curve are parallel may be unnecessary.

Objective: To determine when ASFI one level proximal to the EV results in satisfactory correction and maintenance of correction.

Methods: Following IRB approval, a retrospective review from a single institution was performed of all patients who underwent ASFI for thoracic AIS with minimum 2 year follow-up. The medical record was reviewed and the PA and lateral radiographs were analyzed preoperatively, postoperatively and at 2 years. The tilt of the upper and lowest instrumented vertebrae (UIV and LIV) were measured on the preoperative PA radiographs, as well as the distal EV, defined as the vertebra just proximal to the disc which opened into the lumbar curve. Patients were divided into 2 groups: Group I (n=20): patients in whom the LIV was one level proximal to the EV. In these cases the disc below the LIV was either parallel or slightly open into the thoracic curve. Group II (n=14): patients in whom the LIV was the same as the EV. For this group, the disc below the EV was always open into the lumbar curve.

Results: S: Patients in group I were younger (12.6 vs 13.9 years) and preoperative curve magnitude was smaller (53.1 vs 60.3º) than in group II (p<0 .05). There were no preoperative differences in thoracic curve flexibility (54.9 vs 52.7%), apical vertebral translation (TAVT) (46.2 49.4mm) or the UIV/LIV ratio (1.03 0.95) between groups I and II. At 2 years follow-up, coronal correction (63.8 69.3%), AVT (12.4 12.6 mm) trunk shift (3.2 -2.1 similar groups. Five criteria selected to define a “good outcome”: (1) Cobb <30 degrees (2) LIV tilt < 15 (3) 20 mm (4) (5) TAVT <20 mm. 12 patients (60%) Group 1 7 (50%) that met all five (p="0.5)." A good outcome was more likely group when <25º, of> 1.0 and postoperative correction >65%.

Conclusions: ASFI one level proximal to the EV can be performed with a preoperative UIV/LIV tilt ratio of greater than 1.0 and when correction >65% can be anticipated from preoperative bending films. Fusion to the more proximal level will potentially decrease operative time and morbidity especially when choosing between T12 and L1 and when performing ASFI thoracoscopically.

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