In vitro assessment of prophylactic knee brace function

Abstract

In an attempt to evaluate the effectiveness of prophylactic knee bracing and to determine the influence of brace design and material characteristics on the protection of knee ligaments, a series of biomechanical studies were completed. The first series of tests were preliminary parametric tests of brace function utilizing cadaver limbs to understand the failure biomechanics of the medial restraints during low- and high-rate valgus-producing knee trauma. Static and dynamic mechanical properties of the braces were also studied. Finally, a limited series of brace/cadaver knee low-rate loading response tests were performed. With the information obtained from preliminary testing, an instrumented surrogate knee was developed and validated for lateral impact responses. The surrogate allowed for the measurement of ligament force time response during a controlled impact. Special impact facilities were constructed to allow the measurement and control of impact momentum. The effectiveness of six different prophylactic braces in preventing MCL and ACL injury was evaluated using the surrogate and impact facility. Impact parameters of mass, velocity, knee flexion angle, and limb restraint were varied to simulate different direct lateral impact conditions of game play. Testing results were normalized and expressed as an impact safety factor to allow for comparison of braces. An ISF of 1.5 (representing a ligament force reduction of 30%) was arbitrarily chosen as the minimum standard for brace performance. The majority of prophylactic knee braces tested proved to be biomechanically inadequate for protecting the MCl from a direct lateral impact. A few, however, appear to protect the ACL preferentially. In the case of a controlled, direct lateral blow, all but a few braces tested provided some beneficial protection to the MCL and ACL, but performed well below the standard 1.5 ISF level. Therefore, based on the biomechanical research, it is our opinion that the concept of prophylactic lateral knee bracing can be effective. We recommend that prophylactic braces not be abandoned, but rather improved, biomechanically validated, and further evaluated through well-controlled prospective clinical studies.