Interossei

The Interossei are deep intrinsic muscles of the foot.

Anatomical Attachments:

• Origin: There are 4 dorsal interossei, each attaching to the 2 heads from the adjoining sides of the metatarsal bones; there are 3 plantar interossei each attaching to the bases and medial sides of the 3rd, 4th and 5th metatarsal bones.
• Insertion: The Dorsal Interossei attach into the medial side of the first phalanx of the 2nd toe, the 3rd and 4th toes attach to the lateral side of the first phalanx. The Plantar Interossei attach to the medial surfaces of the base of the proximal phalanges of the 3rd, 4th and 5th toes.

Action: The Dorsal Interossei abduct and flex the 2nd, 3rd and 4th toes. The Plantar Interossei adduct the 3rd, 4th, and 5th toes toward the 2nd toe, flex the first phalanges and extend the distal phalanges.

Synergist: Lumbricals.

Nerve Supply: Lateral plantar nerve (S1, S2).

Vascular supply: Dorsal Interossei - dorsal metatarsal artery, Plantar Interossei - plantar metatarsal artery.

• Primary: The pain refers to the side of the digit to where the tendon attaches and refers to the dorsum and the sole of the foot.
• Satellite or associated triggers: Deep Intrinsic muscles of the foot.

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Trigger Point Signs and Symptoms: There is difficulty in walking, paresthesia or edema of the foot, and deformity of the toes.

Trigger Point Activating and Perpetuating Factors: Wearing shoes that are too small, wearing a cast shoe for a long period of time, and injury to the foot or toes.

Differential Diagnosis: Plantar fasciitis, Plantar warts, Hallux valgus, Stress fractures, Charcot’s arthropathy, Frostbite, Diabetic neuropathy, Polyneuropathy, Hammer toe, Turf Toe, Nerve entrapment, Bunion/corns, Paronychia (ingrown toenail), (Segmental, Subluxation, Somatic dysfunction) L5 S1 or S2 radiculopathy, articular dysfunction, Osteoarthritis, Rheumatoid Arthritis, Gout, injured sesamoid bone, Foot trauma or Sprain/Strain injury, Hip or knee discomfort secondary to antalgic gait, Osteoporosis, Complex regional pain syndrome (Reflex sympathetic dystrophy), Systemic infections or inflammation, Nutritional inadequacy, Metabolic imbalance, Toxicity, Side effects of medication, With a positive Babinski’s toe sign suspect a Central nervous system (CNS) lesion.

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