Peroneus brevis is a more effective evertor than peroneus longus.

A primary function of the peroneus longus and peroneus brevis is to provide the eversion moment necessary to balance the opposing inversion moments. Surgeons often deal with the loss of or need to sacrifice one of these tendons. This study compares the evertor mechanisms of the peroneus brevis and peroneus longus muscle. This is accomplished in a cadaver model in which the performance of each of the muscle tendons during early heel rise of gait is assessed utilizing the same tendon loads in each so that force is not a variable. Six fresh-frozen cadaver foot-ankle specimens were studied during a simulated early heel rise phase of the gait cycle. The study compared the effect of the peroneus brevis and peroneus longus by separately applying the same load to the each of the tendons. At the talonavicular joint, the peroneus brevis loaded condition externally rotated the navicular 2.1 degrees more than when the peroneus longus was loaded. At the subtalar joint, the peroneus brevis loaded condition resulted in 0.9 degrees more calcaneus valgus relative to the talus than was present during the peroneus longus loaded condition. The experimental data support the hypothesis that the peroneus brevis tendon mechanism is more effective than is the peroneus longus mechanism in rotating the navicular externally and the calcaneus into valgus. This has clinical implications for assisting surgeons in trying to preserve evertor function.