Flexor Digitorum Longus

The Flexor Digitorum Longus is a deep posterior muscle of the leg.

Anatomical Attachments:

• Origin: Attaches to the posterior surface of the tibia.
• Insertion: Attaches to the base of the distal phalanges of the 2nd, 3rd, 4th and 5th toes.

Action: Flexes the phalanges of the lateral 4 toes at the DIP joint, plantar flexes and supinates the foot.

Synergist: Gastrocnemius, Flexor hallucis longus, Peroneus longus and brevis, Tibialis posterior, Soleus, Plantaris.

Antagonist: Extensor hallucis longus, Extensor digitorum longus, Tibialis anterior, Peroneus tertius.

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Nerve Supply: Tibial Nerve (L5, S1).

Nerve Entrapment: According to Travell and Simons, in concert with the Flexor Hallucis Longus, a tarsal tunnel syndrome can develop.

Vascular supply: Posterior tibial artery

• Primary: The pain refers over the plantar surface of the foot with the spill over pain referring upward into the lateral tibia and down into the proximal four lesser toes.
• Satellite or associated triggers: Tibialis posterior, the long and short extensors of the toes, short flexors of the toes.

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Trigger Point Signs and Symptoms: Pain is experienced in the sole or the instep of the foot, as well as the plantar surface of the toes and is exacerbated during walking.

Trigger Point Activating and Perpetuating Factors: Running or jogging on a sloped or uneven surface, rigid shoe soles, dysfunctional or immobilized phalangeal joints.

Differential Diagnosis: Tarsal tunnel syndrome, (Segmental, Subluxation, Somatic dysfunction) L5 or S1 radiculopathy, Hammer or claw toes, Plantar fasciitis, Plantar wart, Pes cavus, Pes Planus, Osteoarthritis, Rheumatoid arthritis, Gout, Bursitis, Frostbite, Diabetic neuropathy, Neurogenic arthropathy (Charcot’s Joint), Metatarsal stress fracture, Bone cancer, Sprain/strain of the ankle, Peripheral vascular disease (PVD)-Intermittent claudication, Deep Vascular Thrombosis (DVT), TrPs or strain of Gastrocnemius or Soleus, Systemic infections or inflammation, Nutritional inadequacy, Metabolic imbalance, Toxicity, Side effects of medication.

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