Medically Reviewed | Dr. Tom Biernacki, DPM | Board-Certified Podiatric Surgeon | Balance Foot & Ankle, Michigan
Quick Answer:
Quick Answer: Flexor hallucis longus (FHL) tendinopathy and tenosynovitis cause posterior ankle and plantar first ray pain in dancers, gymnasts, and distance runners. The FHL runs through a fibro-osseous tunnel at the posterior talus where it is susceptible to impingement between the os trigonum (posterior talar process) and the calcaneus during forceful ankle plantarflexion. Chronic tendon inflammation in this tunnel produces the characteristic ‘trigger hallux’ — the great toe locks in flexion during ankle motion and snaps free as the tendon releases from the stenotic tunnel. Mild cases respond to rest, physical therapy, and ultrasound-guided injection. Refractory cases and trigger hallux require surgical FHL tendon sheath release, with excellent outcomes and quick return to dance and sport.
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The flexor hallucis longus (FHL) tendon — the critical flexor of the great toe and a powerful plantarflexor of the ankle — passes through a narrow fibro-osseous tunnel at the posterior ankle just behind the medial malleolus before continuing along the plantar surface of the foot to insert on the distal phalanx of the hallux. This anatomical bottleneck makes the FHL uniquely vulnerable to a condition that has ended the careers of professional dancers and haunted distance runners with mysterious posterior ankle pain: FHL tenosynovitis with functional stenosing — “trigger hallux.”
Why Dancers and Runners Are at Risk
The FHL tendon experiences extraordinary tensile loads during activities requiring maximal ankle plantarflexion and great toe push-off. In ballet dancers, the en pointe position subjects the FHL to repetitive high-load stress within the posterior ankle tunnel with each demi-pointe and pointe movement. Distance runners accumulate millions of push-off cycles that chronically load the FHL at its most vulnerable anatomical location. The result is tendon thickening, peritendinous adhesions, and eventually functional stenosis where the thickened tendon can no longer glide freely through the tunnel.
Trigger Hallux: The Hallmark Sign
The defining clinical finding of advanced FHL tenosynovitis is trigger hallux — the great toe locks in a flexed position during passive or active ankle range of motion testing. As the ankle dorsiflexes, the thickened FHL tendon attempts to slide through the stenotic posterior ankle tunnel and catches — trapping the toe in flexion. When sufficient force is applied, the tendon releases suddenly, producing a snapping or popping sensation and an audible click that can be heard in a quiet examination room. This pathognomonic finding immediately localizes the problem to the FHL within the posterior ankle tunnel.
Clinical Presentation
Patients report posterior and medial ankle pain that worsens during push-off activities, rising on tiptoe, and the downward phase of stairs. Swelling may be present along the medial ankle behind the medial malleolus. Tenderness on direct palpation of the posterior medial ankle at the level of the FHL tunnel is characteristic. Some patients also report pain along the plantar first ray — where the FHL courses beneath the sustentaculum tali and through the master knot of Henry — reflecting distal extension of the tendinopathy.
Concurrent Os Trigonum Syndrome
FHL tenosynovitis frequently coexists with os trigonum syndrome — impingement of the posterior talar process (or an accessory os trigonum ossicle) between the posterior talus and calcaneus during maximum plantarflexion. The os trigonum lies directly adjacent to the FHL tunnel and can contribute to tendon compression. When both conditions are present simultaneously, surgical treatment typically addresses both — FHL sheath release and os trigonum excision — in a single procedure.
Treatment
Conservative management includes relative rest from ballet, running, or provocative activities, physical therapy with eccentric FHL strengthening and posterior ankle flexibility, anti-inflammatory medication, and ultrasound-guided corticosteroid injection into the FHL tendon sheath (not into the tendon itself) to reduce tenosynovitis.
When conservative measures fail after 3–6 months, or when trigger hallux is present, surgical FHL tendon sheath release is performed. An endoscopic or mini-open approach opens the FHL retinacular tunnel, relieving the stenosis and restoring full tendon gliding. Concurrent os trigonum excision is performed when indicated. Return to dance and sport averages 3–4 months post-operatively. Outcomes are excellent — over 90% of patients achieve full symptom resolution and return to full activity.
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Best for: ballet dancers with FHL tenosynovitis managing symptoms during modified training
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Elastic kinesiology tape applied by a physical therapist or podiatrist to support the FHL tendon course and reduce posterior ankle compression during athletic activity.
Dr. Tom says: “My PT tapes my posterior ankle before practice sessions — the support reduces the snapping sensation significantly.”
Best for: FHL tenosynovitis activity modification; posterior ankle taping to reduce FHL impingement during sport
Not ideal for: trigger hallux with complete stenosis requiring surgical sheath release
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✅ Pros / Benefits
- Ultrasound-guided FHL sheath injection provides excellent temporary relief and may resolve early-stage tenosynovitis completely
- Surgical FHL sheath release is highly effective with over 90% of patients returning to dance and sport at full activity levels
- Concurrent os trigonum excision and FHL release in a single procedure reduces total recovery time for combined pathology
❌ Cons / Risks
- FHL tenosynovitis is frequently misdiagnosed as posterior ankle impingement, Achilles pathology, or tarsal tunnel syndrome
- Dancers often continue training through early symptoms until trigger hallux develops, delaying diagnosis to a more advanced stage
- Return to pointe work after surgical sheath release requires structured rehabilitation that may last 3–6 months
Dr. Tom Biernacki’s Recommendation
FHL tenosynovitis is the classic dancer’s ankle injury — and it’s also one of my favorite diagnoses because once you know to look for trigger hallux, the diagnosis is immediate and satisfying. Flex the ankle, watch the great toe lock — that’s it. Conservative treatment works well for mild cases, and the sheath release surgery is one of the most predictably successful operations I do. Dancers are particularly motivated rehabilitators, and the outcomes are almost uniformly excellent.
— Dr. Tom Biernacki, DPM | Board-Certified Podiatric Surgeon | Balance Foot & Ankle
Frequently Asked Questions
How do I know if I have FHL tenosynovitis?
Posterior medial ankle pain during push-off, running, or ballet that is worsened by great toe flexion, combined with a great toe that locks or snaps during ankle movement, is classic for FHL tenosynovitis with trigger hallux.
Can FHL tenosynovitis heal without surgery?
Mild cases without trigger hallux often respond to conservative management with rest, injection, and physical therapy. Established trigger hallux with functional stenosis typically requires surgical sheath release.
Is FHL tenosynovitis the same as Achilles tendinopathy?
No — both cause posterior ankle pain, but FHL tendinopathy causes pain medially and with great toe flexion, while Achilles tendinopathy causes pain centrally and with dorsiflexion. Both can coexist.
How long is recovery after FHL sheath release surgery?
Most patients begin walking within 2 weeks of surgery and return to athletic training at 6–8 weeks. Dancers typically return to full pointe work at 3–4 months.
Do all dancers eventually get FHL problems?
Not all — but professional dancers who perform en pointe work heavily are at significantly elevated risk due to the repetitive FHL loading involved in pointe and demi-pointe positions.
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Dr. Tom Biernacki, DPM is a double board-certified podiatrist and foot & ankle surgeon at Balance Foot & Ankle Specialists in Southeast Michigan. With over a decade of clinical experience, he specializes in heel pain, bunions, diabetic foot care, sports injuries, and minimally invasive surgery. Dr. Biernacki is a member of the APMA and ACFAS, and his patient education content on MichiganFootDoctors.com and YouTube has reached over one million views.
- Diagnosis and Treatment of Plantar Fasciitis (PubMed / AAFP)
- Heel Pain (APMA)
- Hallux Valgus (Bunions): Evaluation and Management (PubMed)
- Bunions (Mayo Clinic)
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