Mechanical Testing of Ligament Fixation Devices

The fixation of soft tissue grafts used in anterior cruciate ligament reconstruction (ACL) is a determining factor for the long-term success of the ACL reconstruction. This article provides an overview of the mechanical test methods used in our laboratory and the biomechanics literature to compare methods of soft tissue fixation that are available to the practicing orthopaedic surgeon. The basics of uniaxial tensile testing are reviewed with particular attention to the differences between the structural properties of the reconstructed graft and the material properties of the graft itself. The effects of the stiffness of individual components on the overall structural response of the system are studied in the context of a simple series spring model. Techniques used to measure graft cross-sectional area, overall elongation, and graft strain are reviewed. The importance of controlling temperature and hydration during and between tests is emphasized. Failure testing, cyclic loading, and in vitro evaluation of joint kinematics are reviewed with specific attention to factors that affect the overall test results. The final section provides a brief overview of the factors that contribute to a well-designed experiment and statistical analysis. It is hoped that the information in this article will provide the reader with the information necessary to critically evaluate the multitude of experimental studies that compare the mechanical characteristics of different ligament fixation techniques. Key'Words: Anterior cruciate ligament-Soft tissue fixation-Cyclic loading.