A new morphological classification for the fibularis quartus muscle

The fibularis quartus muscle (FQ) is an accessory fibular muscle that can be found in humans, reportedly in up to 22%. The aim of this study was to classify morphological patterns of the FQ and its anatomical variations.

Eighty lower limbs of 40 formalin-fixed adult Korean cadavers were used in this study.

The FQ was present in 13 of 80 specimens (16.3%). In two specimens, each specimen had two FQs with different origins and insertion sites. Thus, 15 cases of FQ were found in 13 specimens. The FQ originated from the fibularis brevis muscle (FB) in 12 cases (15%). In these cases, the FQ arose either as a muscle or as a tendon. The muscle fibers of the FQ merged into a tendon (8 of 12 cases) that inserted variously into (1) the tendon of the FB (three cases, 3.8%), (2) the lateral surface of calcaneus (two cases, 2.5%), (3) the inferior peroneal retinaculum (two cases, 2.5%), or (4) the dorsal surface of the base of fifth metatarsal bone (one case, 1.3%). The FQ arose as a tendon from the FB in 4 of 12 cases. In three of the four cases, the FQ inserted into the lateral surface of calcaneus. The FQ arose from structures other than the FB (three cases, 3.8%).

The present study has demonstrated a new classification for the FQ and its anatomical variations, and provided detailed data for its accurate identification of a muscle and relevant surgical procedures.