Bunions - Hallus Abductor Valgus – Part 3

Specific Anatomy: There are four layers of muscle in the foot, with each muscle layer performing a specific action and function. If any of these four areas has been injured, the overall stability of the foot can be compromised, further accelerating the formation of the bunion.

A practitioner who is trained in biomechanics can identify, through gait analysis, just which muscles are creating an abnormal motion pattern. They can then confirm their analysis through hands-on palpation, locate just where the restriction is located, and use soft-tissue treatments to remove those restrictions.

Consider how the following four layers of muscles act to keep your foot aligned.

First Layer of Foot Muscles (Superficial layer)

o Flexor digitorum brevis: Flexes the toe joints (MP & PIP joints).

o Abductor hallucis: Balances out the adductor hallucis. This muscle acts to moves the big toe (hallucis) away from the second toe (abduction), and assists in flexing the big toe.

o Abductor digiti minimi: Moves the little toe away (abduction) from the fourth toe, and assists in flexing the little toe.

Second Layer of Foot Muscles

o Quadratus plantae (QP): This muscle assists with flexion of the four lateral toes. This is an interesting muscle since it attaches to the tendon of the flexor digitorum longus (FDL) which originates under your calf muscles. The tendons of the FDL extend all the way down to insert under your foot at the four lateral toes. A tight FDL affects the function of the QP. This is great example of how the entire kinetic chain must be considered. In this case, a muscle under your calf muscle is affecting the stability of your foot.

o Lumbricals: These muscles help to flex and extend the toes. This set of four muscles has no bony attachment, and attaches from the tendons of the FDL to the tendons of the EDL (extensor digitorum longus). 

Note: The lumbricals are partially controlled by a balance of tension between the FDL and EDL – which act like “guy wires” on the mast of a sailboat. In layman’s terms - the interaction between the muscles of your shins and the deep muscles of your calf directly affect the stability of your foot.

Third Layer of Foot Muscles

o Flexor hallucis brevis: Flexes the big toe at the MTP joint.

o Adductor hallucis: This two headed muscle moves the big toe inward (adduction). This muscle is often overlooked in the treatment of bunions. It is very important to treat this muscle in order to resolve Bunions.

o Flexor digiti minimi brevis: Flexes the little toe at the MTP joint.

Fourth Layer of Muscles

o Dorsal interossei: Four muscles that cause outward motion (abduction) of the third and fourth toes.

o Plantar interossei: Three muscles that cause inward motion (adduction) of the third, fourth and fifth toes at the MP joints.

Remember, a restriction in any one of these muscles will result in an overall decrease in foot stability.

In part four of Bunions – Hallus Abductor Valgus I will provide some specific treatment exercises and discuss the use of supportive aids for the treatment of bunions.

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