The quadratus plantae (flexor accessorius) muscle is one of the central plantar muscles of the foot comprising the second layer of plantar foot muscles, together with the lumbricals.
The Quadratus plantae muscle is a deep muscle located in the foot. It is part of the intrinsic muscles of the foot, meaning that it originates and inserts entirely within the foot itself. The word “quadratus” comes from Latin and means “square,” which describes the roughly quadrilateral shape of this muscle.
Anatomically, the Quadratus plantae muscle originates from the medial (inner) side of the calcaneus, which is the heel bone of the foot. It then runs horizontally across the sole of the foot and inserts into the flexor digitorum tendon. The flexor digitorum tendon is a long tendon that connects to the flexor muscles of the toes (flexor digitorum longus) and allows for flexion of the toes.
Functionally, the Quadratus plantae muscle plays a crucial role in toe movement and stability during gait. It works together with other intrinsic muscles of the foot to control the alignment of the toes and helps maintain proper arch support, which is essential for distributing the body’s weight efficiently while walking, running, or standing.
The Quadratus plantae muscle also contributes to the flexion of the toes, assisting in the act of gripping or curling the toes downward. This function is especially important during activities that require strong toe flexion, such as pushing off the ground while walking or running.