Static and dynamic analysis of five anterior instrumentation systems for thoracolumbar scoliosis.

STUDY DESIGN A nondestructive biomechanical investigation among five anterior spinal instrumentation systems for scoliosis. OBJECTIVES The purpose of this study is to analyze the static and dynamic biomechanical stability of five different systems. SUMMARY OF BACKGROUND DATA Although a variety of anterior spinal instrumentation systems for scoliosis are available, very few attempts have been made at comparative biomechanical studies. METHODS Thirty calf spines were underwent static biomechanical tests, including flexion-extension, axial rotation, and lateral bending loading modes in the multisegmental spinal model. Five anterior instrumentation systems included: 1) Texas Scottish Rite Hospital system; 2) Bad Wildungen Metz; 3) anterior ISOLA; 4) Cotrel-Dubousset Hoph; and 5) Kaneda Anterior Scoliosis System. The initial and postfatigue stability after a cyclic loading test were analyzed by measuring the range of motion at instrumented segments compared to the intact within the same specimen (% to intact). RESULTS Two-rod systems showed a significant decrease in range of motion compared to one-rod systems in flexion-extension (P < 0.001) and axial rotation (P < 0.05). In lateral bending, all systems demonstrated a significant decrease in range of motion of less than 40% to the intact (P < 0.001). After cyclical loading test, all systems increased in range of motion. In flexion-extension, one-rod systems depicted a significant increase in range of motion, compared to two-rod systems (P < 0.05). CONCLUSIONS In the initial stability analysis, two-rod systems are superior to one-rod systems. For one-rod systems, repeated physiologic loading may result in reduced stability in flexion-extension.