The biomechanics of lateral knee bracing. Part II: Impact response of the braced knee.

In Part I of our study on lateral knee bracing, we evaluated brace effectiveness using cadaveric knees and two commercially available braces (McDavid and Omni). The results indicated that for low-rate dynamic valgus loading, neither brace provided significant protection against MCL injury. Also, four potentially adverse effects were noted. The goals in Part II were to: 1) determine the clinical significance of brace induced MCL preload; 2) define the functional character of an "ideal" brace; 3) design and validate a surrogate knee model for testing brace effectiveness; and 4) determine brace performance under impact loading using the surrogate knee and six commercially available brace types (manufactured by DonJoy, McDavid, Mueller, Omni Scientific, Stromgren-Scott, and Tru-Fit). Knee braces, modified to measure varus/valgus bending force, were used to determine MCL preload effects in 13 human volunteers. An anatomically correct surrogate knee model, instrumented to measure ligament/tendon tension and medial joint opening, was developed and validated using information from our previous cadaver studies and results of analyses on the effects of high strain rates (100% versus 1000% strain/sec) on MCL failure. Over 500 impact tests were performed on the surrogate knee in unbraced versus braced conditions. Tests were conducted for three impactor masses, two flexion angles, and free or constrained limb positions. Impact safety factors (ISF) were calculated for each test condition and brace type. An ISF of 1.50 (MCL load reduction of 30%) was considered significant.(ABSTRACT TRUNCATED AT 250 WORDS)