Comparative Analysis of Pedicle Screw Versus Hook Instrumentation in Posterior Spinal Fusion of Adolescent Idiopathic Scoliosis: A Matched Cohort Analysis

Purpose: The purpose of this study is to compare the results of posterior correction and fusion with segmental hook instrumentation vs with pedicle screw instrumentation in AIS using a matched cohort study analysis with medical records and x-rays.

Methods: 40 AIS patients at a single institution underwent posterior fusion with segmental hook (20) or pedicle screw (20) instrumentation and were sorted and matched according to four criteria: similar patient age, curve type, fusion levels, and operative method. Patients were evaluated at a minimum 2-year follow-up according to radiographic changes, operative time, intraoperative blood loss, implant cost, pulmonary function test, and SRS 24 scores.

Results: The two cohorts were well matched. The preoperative Cobb angle averaged 61.7º in the hook group and 63.7º in the screw group. Average major curve correction was 51.6% in the hook group and 73.8% in the screw group (p=0.000). At 2-year follow-up, major curve correction was significantly greater in the screw group (70.8%) compared to the hook group (42.7%) (p=0.000). Apical vertebral translation was corrected by 41.2% in the hook group and 62.6% in the screw group. With pedicle screws, the lowest instrumented vertebra was 0.4 levels below the lower end vertebra, whereas in the hook group it was 1.3 levels below the lower end vertebra. Operative time and intraoperative blood loss was similar in both groups. Average implant cost in the hook group (12.4 fixation points; 6514 USD) was significantly lower than that of the screw group (18.2 fixation points; 12031 USD). Two years following surgery, the screw group had improved percent predicted pulmonary function values (13 thoracoplasties and 7 iliac crest bone graft patients, FVC: 74.1-77.4%; FEV1: 70.0-76.1%), while the hook group had decreased or near preoperative pulmonary function values (12 thoracoplasties and 8 iliac crest bone graft patients: FVC: 84.5- 82.6%, FEV1: 79.2-78.6%; FVC: p=0.043; FEV1: p=0.152. SRS 24 scores were similar in both groups at final follow-up. Hook group: 99.7 vs pedicle group: 94.5 (p=0.171). There were no neurologic complications related to hook or pedicle screw instrumentation.

Conclusion: Pedicle screw instrumentation, although more expensive, offers a significantly greater major curve correction without neurologic problems and improved pulmonary function values in the operative treatment of adolescent idiopathic scoliosis and enables a slightly shorter fusion length than segmental hook instrumentation.