A biomechanical comparison of eight popular commercially available rehabilitative knee braces was undertaken using a specially designed mechanical surrogate and computerized data acquisition system. Tests conducted included passive extension, valgus rotation, and anterior-posterior tibial translation. Most of the braces tested significantly reduced both translations and rotations compared to the unbraced limb under static test conditions. Braced versus braced performance varied and was found to depend upon a number of mechanical and design factors.