Professor Emeritus Mechanical and Aerospace Engineering, University of Missouri-Columbia, Columbia, Missouri
The University of Kansas Medical Center, Kansas City, Kansas
The Hospital for Special Surgery, New York, New York
San Diego Center for Spinal Disorders, La Jolla, California
Pages: 18 Published: Jan 2003
The clinical objectives for using transverse connectors (TCs) on different implant constructs are compiled. Results from a survey of 2499 clinical cases, hand held-loaded models, linkage analysis, and finite element analysis were used to identify the important biomechanical characteristics and parameters of constructs affecting the need for a TC and of the TC itself that are involved in achieving the clinical objectives. These were compared to those tested in ASTM standards to evaluate existing and needed TC tests. Axial and torsional gripping characteristics of TC interconnections are adequately tested with ASTM F 1798-97. ASTM F 1717-01 axial test protocol can reveal the effect of TCs on the flexion fatigue life of longitudinal members, however the torsional test protocol results have questionable clinical relevance due to fixtures constraining 3 of 6 construct relative degrees-of-freedom. A substitute gimbal-gimbal or gimbal- pushrod fixture is proposed. The following are proposed to test TC characteristics that are not tested with current ASTM standards: an H construct for testing TC lateral bending characteristics, an unconstrained 3D test for transfixed thoracolumbar constructs having different combinations of hook-claw-wire and screw foundations, and a fixture to test torsional characteristics of constructs having sacroiliac foundations.
Transverse connectors, spine implants, clinical objectives, biomechanical parameters, in vitro tests
Paper ID: STP11144S