Prevalence and Topography of the Peroneus tertius Muscle: a Study of Human Cadavers

Introduction The peroneus tertius muscle, also known as fibularis tertius, is classified as an anatomic variation and has been described as inconstant in a wide variety of contemporaneous studies and in the classical medical literature. Its fibers are sometimes mistaken for those of the extensor digitorum longus muscle. In fact, peroneus tertius is detached from the extensor digitorum longus muscle through a tendon inserted into the base of the fifth metatarsal bone, after passing through the frondiform ligament of the extensor retinaculum. Objectives The present study evaluated the prevalence, origin and insertion point of the peroneus tertius muscle in human cadavers. Methods and Results Thirty-two lower limbs, 18.75% of which came from female cadavers, were obtained from two different anatomy laboratories at two separate institutes. The cadaver parts were dissected and photographed. Overall, the muscle was present in 93.75% of the samples and in 100% of the samples from female cadavers. The fibers of the muscle originated in the proximal third of the fibula in 6.68% of cases, in the middle third in 46.66% and in the distal third in 46.66% of cases. Insertion of the tendon was at the base of the fifth metatarsal in 70% of cases and in the space between the fourth and the fifth metatarsal in 30%. Conclusion Therefore, the peroneus tertius muscle was present in the majority of the cadaver parts analyzed; however, the sites of origin and insertion varied. These results contradict data in the classical literature and in contemporaneous studies.