The knee is a highly complex joint, routinely experiencing extremely high forces. As a result, it is very prone to injury, especially to its soft tissue structures, such as the ligaments. Functional knee bracing has become a common method of augmenting ligament deficient knees. However, the scientific merit of functional knee bracing still remains in question with no known studies having provided a definitive conclusion as to their efficacy. Most studies have taken a case study approach whereby the mechanical characteristics, such as control of tibial displacement, of individual braces are examined and reported. This approach is limited in its applications as it can only aid new brace designs retroactively, in an iterative approach, and only on an individual design basis.

This study performed mechanical testing on four functional knee braces. Two were braces currently available, the CTi and the Generation II, and two were prototype designs, the NPcf and the NPsrp. Three mechanical stiffness were recorded for each brace:​ effective stiffness, the stiffness displayed by leg with the brace on;​ brace stiffness, the stiffness of the brace itself;​ and interface stiffness, the stiffness achieved at the interface between the brace and the leg. Each stiffness was determined under both varus and valgus loading conditions. The NPcf model proved to be the best in resisting varus and valgus loading, while the CTi and NPsrp models were extremely comparable in their performance and the Generation II was shown to be the least able to control varus and valgus displacements.

Using the parameters of effective, brace and interface stiffnesses a mathematical model was constructed to attempt to examine the relative contributions of the brace and interface stiffnesses to the effective stiffness of the brace. The predictive ability of the model was excellent when compared to observed results. Modelling indicates that, although a stiff brace is necessary to stabilizing a knee, a good interface must be created between the brace and the leg to transfer the stiffness of the brace to the knee itself. Several factors influencing the interface and brace stiffness were discussed. In vivo validation of the model and further elucidation of its components are necessary to draw more precise conclusions.