Study design: Biomechanical analysis and retrospective chart review.
Objectives: To determine the mechanical properties of cobalt chromium alloy wires and review the clinical application of the wires as sublaminar implants to correct spinal deformity.
Summary of background data: Sublaminar wires are commonly used as anchors in spinal deformity surgery. In stainless steel instrumentation systems, single strand wires (Luque wires) may be retightened over time to take advantage of stress relaxation while correcting spinal deformity. Because of the mechanical properties of titanium, solid titanium wires are not used as sublaminar wires. Cobalt chromium alloy is a titanium compatible alloy that can be twisted in a similar fashion to stainless steel sublaminar wires.
Methods: Comparative tensile tests were performed using cobalt chromium alloy wires and Luque stainless steel wires. In addition, 22 consecutive posterior spinal fusions for idiopathic scoliosis were performed using cobalt chromium alloy wires as sublaminar implants.
Results: Yield and ultimate tensile loads for the cobalt chromium alloy wires are on average 66% (P < 0.001) and 60% (P < 0.001) higher, respectively, than those for the steel wires. Mean preoperative thoracic curve for patients with idiopathic scoliosis was 56 degrees +/- 15 degrees , which corrected to 19 degrees +/- 11 degrees (67% correction, P < 0.001) when cobalt chromium alloy wires were used as sublaminar implants. Mean preoperative lumbar curve was 52 degrees +/- 14 degrees , which corrected to 17 degrees +/- 8 degrees (68% correction, P < 0.001). There were no instrumentation failures, neurologic complications, or infections.
Conclusions: The advantages of cobalt chromium alloy wire over steel wire include greater tensile strength and titanium compatibility. Cobalt chromium alloy solid wires may be used as sublaminar implants with titanium spinal instrumentation with excellent clinical results.