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Lubricants Muscle are four small skeletal muscles, accessory to the tendons of the flexor digitorum longus, and numbered from the medial side of the foot; they arise from these tendons, as far back as their angles of division, each springing from two tendons, except the first. So the first lumbrical is unipenate and second, third, and fourth are bipinnate.
The muscles end in tendons, which pass forward on the medial sides of the four lesser toes, and are inserted into the expansions of the tendons of the Extensor digitorum longus on the dorsal surfaces of the proximal phalanges. All four lumbricals insert into extensor hoods of the phalanges, thus creating extension at the inter-phalangeal (PIP and DIP) joints. However, as the tendons also pass inferior to the metatarsal phalangeal (MTP) joints it creates flexion at this joint.
Origin and Insertion of Lubricants Muscle
The lumbricals originate from the tendons of flexor digitorum longus muscle, which is why they are sometimes referred to as the accessory muscles of the flexor digitorum longus. From medial to lateral, they are numbered I-IV.
The first lumbrical muscle originates from the medial side of the first flexor digitorum longus tendon, i.e. the one intended for the second toe. The rest of lumbricals have two origin points, arising from the facing surfaces of two adjacent tendons of the flexor digitorum longus, respectively.
From the point of origin, each lumbrical muscle passes anteriorly, plantar to the deep transverse metatarsal ligaments. The muscles bellies then turn obliquely upwards to attach on the base of the proximal phalanges of second to fifth digits and their extensor expansions.
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There are four muscles referred to as lumbricals in the foot
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Origin: Flexor digitorum longus tendon
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Insertion: Extensor digitorum longus tendon
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Action: Flex the metatarsophalangeal joints and extend the interphalangeal joints
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Blood Supply: Medial and lateral plantar arteries
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Innervation: Medial and lateral plantar nerve
Nerve Supply of Lubricants Muscle
The most medial lumbrical is innervated by the medial plantar nerve while the remaining three lubricants are supplied by the lateral plantar nerve.
Lumbrical muscles are supplied by the two terminal branches of the tibial nerve;
- The first lumbrical muscle is supplied by the medial plantar nerve (S1, S2).
- The lateral three lumbricals are innervated by the lateral plantar nerve (S2, S3).
Blood Supply
Lumbrical muscles are supplied by branches of an anastomotic network between the lateral plantar and dorsalis pedis arteries called the plantar arch. The convexity of the plantar arch gives off the lateral plantar artery and four plantar metatarsal arteries that supply the lumbrical muscles.
Function
By pulling the medial base of the proximal phalanx, the lumbrical muscles flex and adduct the toes at the metatarsophalangeal (MTP) joints. Conversely, by pulling the extensor expansions of the phalanges, the lumbricals extend the toes at the interphalangeal (IP) joints.
These actions of the lumbrical muscles provide a balancing function to the foot. Flexion and adduction at the MTP joints oppose the extension of the long and short extensor of the toes and prevent hyperextension of the toes during the propulsive phase of gait. The extension at IP joints prevents clawing during gait as it opposes to the flexion produced by the long and short flexors of the toes.
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