Flexor Hallucis Longus Tendinopathy & Trigger Toe: Diagno…

Flexor hallucis longus (FHL) tendinopathy is one of the most misdiagnosed causes of posterior ankle and great toe pain, particularly in dancers, gymnasts, and runners. The FHL tendon travels through a tight fibro-osseous tunnel behind the ankle, making it uniquely vulnerable to stenosing tenosynovitis and triggering — problems that require a specific diagnosis to treat correctly.

FHL Tendon Conditions: Classification and Characteristics

Condition	Pathology	Key Symptom	Who Gets It	Conservative Success Rate
FHL tendinopathy (non-insertional)	Collagen degeneration in tendon body, typically at posterior ankle tunnel	Deep posterior ankle ache; worse going up stairs or on toes	Runners, dancers	60–75%
FHL tenosynovitis	Inflammation of synovial sheath surrounding tendon; fluid accumulation	Posterior ankle swelling; crepitus with passive great toe motion	Overuse athletes; posterior impingement	70–80%
Stenosing FHL tenosynovitis (“trigger toe”)	Nodule formation on tendon; catches at fibro-osseous tunnel entrance	Great toe locking or triggering; clicking; can’t fully flex/extend big toe	Ballet dancers (relevé position); gymnasts	40–60% — surgical release often needed
FHL partial tear	Longitudinal or transverse partial fiber disruption	Sharp pain at posterior ankle with great toe pushoff; weakness	Acute overload; forced plantar flexion	Moderate — depends on tear extent
FHL complete rupture	Full tendon discontinuity	Complete loss of great toe plantar flexion strength; may hear pop	Rare; forceful hyperextension	0% — surgical repair needed
Os trigonum syndrome with FHL involvement	Accessory bone pinches FHL at posterior talar process during plantar flexion	Posterior ankle pain in pointed-foot position; worsens in relevé or going downstairs	Dancers; soccer players (shooting motion)	50–65% with injection; surgical excision often needed

FHL vs. Other Causes of Posterior Ankle Pain

Condition	Pain Location	Aggravating Movement	Key Distinguishing Test
FHL tenosynovitis	Medial posterior ankle; posteromedial	Great toe flexion against resistance; going up on tiptoe	Passive great toe flexion/extension produces posteromedial ankle pain
Achilles tendinopathy	Posterior heel or tendon midportion	Running; first steps in morning	Royal London Hospital test; palpation along tendon body
Os trigonum impingement	Posterolateral ankle	Forced plantar flexion (pointe in ballet, downhill)	Nutcracker test: forced passive plantarflexion reproduces pain
Posterior tibial tendinopathy	Medial ankle below and behind medial malleolus	Single-leg heel raise; walking	Too many toes sign; single-leg heel rise failure
Tarsal tunnel syndrome (posterior)	Medial ankle; radiates to heel/sole	Standing; prolonged walking	Tinel’s sign behind medial malleolus; nerve conduction study
Peroneal tendinopathy	Posterior lateral ankle	Eversion against resistance; lateral ankle loading	Tenderness along peroneal groove behind lateral malleolus

Treatment Approach for FHL Tendinopathy and Trigger Toe

Conservative management of FHL tendinopathy begins with relative rest from the provocative activity, NSAIDs for 2–3 weeks (if tolerated), and physical therapy focused on eccentric strengthening and posterior ankle flexibility. Corticosteroid injection into the FHL sheath can reduce acute tenosynovitis but must be performed with ultrasound guidance to avoid intratendinous injection, which carries a small risk of tendon weakening.

Stenosing FHL tenosynovitis (trigger toe) responds poorly to conservative care in most patients. When triggering is mechanical — caused by a tendon nodule that catches at the fibro-osseous tunnel — surgical release of the tendon sheath and tunnel is often required. This is a relatively minor outpatient procedure with predictable outcomes and a return to dance or sport at 3–4 months post-operatively.

Os trigonum excision, when performed alongside FHL sheath decompression, resolves most cases of combined posterior impingement and FHL involvement. Endoscopic techniques reduce recovery time compared to traditional open surgery.

Balance Foot & Ankle evaluates FHL tendon conditions and posterior ankle pain at our Howell and Bloomfield Hills offices. If you’re a dancer or athlete with persistent posterior ankle pain that hasn’t responded to standard treatment, call (810) 206-1402 for a specialized evaluation.

For a complete clinical overview: Ankle Pain Conditions Guide — location-by-location ankle pain diagnosis and treatment