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Knee Bracing

Although considerable controversy still surrounds the use of knee bracing in the sports medicine patient, several recent randomized controlled trials have shed new light on the subject. This entry reviews the current clinical and biomechanical evidence supporting the efficacy of four brace types: prophylactic, rehabilitative, functional, and offloader knee braces. Brace-fitting techniques and tips are also presented.

Knee Biomechanics

A keen understanding of the normal biomechanics of the knee is essential to brace design, selection, and fit. Forces that are applied to the knee are resisted by an interdependent combination of muscle, ligament, meniscocapsular components, surface shape, and loading factors. The anatomic description of the knee as a simple diarthrodial hinge joint belies the very complex kinematic reality of the joint. The knee moves on six different axes and planes (Figure 1). The anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) are critical to normal knee biomechanics as they constrain and guide the femur and tibia during the arc of motion.

Brace Design

The principles underlying the design of an ideal knee brace hold true for all the categories of braces. The brace should produce a synergistic effect with the normal soft tissue knee stabilizers through a normal range of motion and should not interfere with normal knee function. It should not increase the risk of injury to other parts of the athlete's lower extremity or other players the braced athlete may come into contact with. It should protect the knee from external forces causing excess varus (bow-legged position) or valgus (knock-knee position), rotation (twisting), or anterior-posterior translation (linear motion). Finally, it should adapt to various patient shapes and sizes as well as being cost-effective.

Prophylactic Knee Bracing

Prophylactic knee braces (PKBs) are commonly used during a variety of sporting activities, including football and soccer, in an attempt to decrease the frequency of both contact and noncontact knee ligament injuries. PKBs are commonly available in two designs. The traditional prophylactic brace has a single lateral upright with a single-axis, double-axis, or polycentric hinge at the level of the knee joint (Figure 2). A second prophylactic brace design has bilateral uprights with a polycentric hinge. The medial and lateral uprights in this latter brace have an interconnecting band (Figure 3). The results of basic biomechanical and functional studies demonstrate considerable inconsistency; however, we can still glean valuable knowledge from the results.

Figure 1 The Six Degrees of Knee Motion Freedom

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Prophylactic Knee-Bracing Evidence

Knee models with spring-loaded, remotely teetered steel cables have been developed to test the performance of PKBs. PKBs seem to be more effective when they allow adequate distance between the knee and its hinges and when the braces are sufficiently stiff to inhibit premature joint contact during loading. The brace ideally will disperse the force from the imparted blow away from the joint to the distal brace attachments at the thigh and calf. The PKB seems to have a more favorable protective effect for the ACL than for the medial collateral ligament (MCL) in braced patients during an impact on the outside of the knee. The brace has provided consistent protection against MCL strain in the range of 20% to 30% when compared with the unbraced knee.

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