The dorsal interossei muscles of the foot are a group of four muscles located between the metatarsal bones. These muscles play a crucial role in the mechanics of the foot, contributing to toe movement and the maintenance of the foot's arches. While their primary action of abduction in the foot is considered to be of limited importance, they work in conjunction with other muscles to ensure proper foot function, especially during dynamic activities.
These muscles are bipenniform, meaning their muscle fibers are arranged on both sides of a central tendon, giving them a feather-like appearance. Each of the four dorsal interossei muscles originates from two heads, specifically from the proximal half of the sides of adjacent metatarsal bones. This dual origin allows for a broad attachment and contributes to their power despite their relatively small size.
Origin and Insertion Points
The origin of the dorsal interossei muscles is quite specific. Each muscle arises from the proximal half of the sides of two adjacent metatarsal bones. This arrangement positions them strategically within the foot to exert their influence on the toes.
From their dual origins, the two heads of each dorsal interosseus muscle converge to form a central tendon. This tendon then extends forward, passing deep to the deep transverse metatarsal ligament. The insertion points for these tendons are primarily on the bases of the second, third, and fourth proximal phalanges. Additionally, they insert into the aponeurosis of the tendons of the extensor digitorum longus. It is important to note that these muscles do not attach to the extensor hoods of the toes. The first dorsal interosseus muscle inserts into the medial side of the second toe, while the other three insert into the lateral sides of the second, third, and fourth toes.
Actions and Innervation
The primary action attributed to the dorsal interossei of the foot is abduction at the metatarsophalangeal joints of the third and fourth toes. Abduction refers to moving the toes away from the midline of the foot. Interestingly, because the second toe has a pair of dorsal interossei muscles attached to both its medial and lateral sides, simultaneous contraction of these muscles results in no net movement of the second toe. This unique arrangement establishes the second toe as the functional midline of the foot, a contrast to the hand where the third finger serves as the midline.
Beyond abduction, the dorsal interossei, in collaboration with the plantar interossei, also contribute to flexion at the metatarsophalangeal joints. Despite their small size, these muscles are powerful and, alongside their plantar counterparts, are crucial for controlling the direction of the toes during vigorous activities. This control enables the longer and shorter flexor muscles to perform their actions effectively. Furthermore, due to their relationship with the metatarsophalangeal joints, the interossei muscles play a role in maintaining the anterior metatarsal arch of the foot, and to a lesser extent, the medial and lateral longitudinal arches of the foot.
All dorsal interossei muscles are innervated by the lateral plantar nerve, specifically from segments S2-3. The muscles located in the fourth interosseous space receive innervation from the superficial branch of this nerve, while the others are supplied by its deep branch. The first and second dorsal interossei muscles also receive additional innervation from the lateral branch of the deep fibular nerve, highlighting a dual nerve supply for some of these muscles.
