Mechanical evaluation of soft tissue and ligament implant fixation devices

The purpose of this study was to define a new mechanical measure of soft tissue fixation device performance and to use the method to assess the fixation performance of three fixation systems. The commonly used screw and spiked washer (SSW, Synthes) was tested as a method to fix both tendon and Ligament Augmentation Device (LAD, 3M Co.). Also tested was fixation of an LAD with a custom designed ligament implant fixation tab (LIFT). Specimens, goat tendons or LADs, were fixed under 44.5 N of tension to two flat segments of goat bone. Five specimens were tested for each group. After specimen fixation, increasing loads were applied to the specimen. One bone block was cyclically moved an incrementally increasing distance away from the other, along the axis of the specimen. Between applied loads the bone blocks were returned to their original positions. Two measurements were made at each level of applied load. The first was the force remaining in the specimen with the bone segments in their original positions. The second was the elongation required to return the fixed specimen to its original tension. The second measure was termed slippage, and includes effects of viscoelastic and plastic deformation of the tendon/LAD at both fixation points and within the tendon/LAD. Cyclic loading was continued until failure. The results are quantified in Table 1. This study demonstrates that soft tissue fixation devices may be characterized by loss of tension, and elongation required to regain original tension, as a function of applied loads. Such information may be useful to evaluate devices that are designed to reduce slippage.