Comparison Between 4.0-mm Stainless Steel and 4.75-mm Titanium Alloy Single-Rod Spinal Instrumentation for Anterior Thoracoscopic Scoliosis Surgery

Abstract

Retrospective review of a consecutive, single surgeon case series. To compare minimum 2-year postoperative outcomes between 4.0-mm stainless steel and 4.75-mm titanium alloy single-rod anterior thoracoscopic instrumentation for the treatment of thoracic idiopathic scoliosis. Advances in anterior thoracoscopic spinal instrumentation for scoliosis have attempted to mitigate the postoperative complications of rod failure, pseudarthrosis, and deformity progression. Biomechanical data suggest that the 4.75-mm titanium construct has a lower risk of fatigue failure compared to the 4.0-mm stainless steel construct. Sixty-four consecutive anterior thoracoscopic spinal instrumentation cases in patients with thoracic scoliosis performed by a single surgeon and with minimum 2-year follow-up were retrospectively reviewed. The first 34 cases used a 4.0-mm stainless steel (SS) construct, whereas the subsequent 30 cases used a 4.75-mm titanium (Ti) alloy instrumentation system. The first 10 SS cases and the first 5 Ti cases were excluded from the statistical comparison to account for a potential learning curve effect. A multivariate analysis of variance (P < 0.05) was used to compare radiographic, perioperative, and postoperative complication data between patients surgically treated with the 2 different instrumentation systems. Patients in the SS group (n = 24) underwent surgery from 2000 to 2001, whereas patients in the Ti group (n = 25) underwent surgery from 2002 to 2004. The mean age at surgery, gender ratio, length of hospitalization, estimated blood loss, and operative time were not statistically different between the 2 patient groups (P > 0.13). The average follow-up in the SS group was, however, significantly longer than in the Ti group (4.0 +/- 1.4 years vs. 2.3 +/- 1.0 years; P = 0.001). Preop main thoracic Cobb angles were similar between the 2 groups (P = 0.62); however, the 2-year main thoracic Cobb was significantly smaller (P = 0.03) and the 2-year percent correction was significantly greater in the Ti group (P = 0.03). Five patients (21%) in the SS group had a pseudarthrosis, 3 (13%) experienced rod failure, and 2 (8%) required a revision posterior spinal fusion. In the Ti group, 2 patients (8%) had a pseudarthrosis, and no patient experienced rod failure or required a revision procedure. Although the average follow-up in the Ti group was significantly shorter than in the SS group, the 4.75-mm titanium alloy construct resulted in improved maintenance of deformity correction at 2-years postop and a lower incidence of instrumentation-related complications (pseudarthrosis, rod breakage, and surgical revisions) compared to the 4.0-mm stainless steel construct. Improved outcomes with the titanium alloy construct are likely because of the mechanical properties of the implant, refined patient selection criteria, and greater surgical experience gained with time.