Medically reviewed by Dr. Tom Biernacki, DPM — Board-Certified Podiatric Surgeon — Balance Foot & Ankle, Howell & Bloomfield Hills, MI. Last updated April 2026.

What Is Flexor Hallucis Longus Tendinopathy?

The flexor hallucis longus (FHL) is the tendon responsible for plantarflexing (curling down) the big toe and contributing to ankle push-off force. It originates in the posterior leg, passes through a fibro-osseous tunnel behind the medial ankle (the sustentaculum tali), and inserts at the base of the distal phalanx of the hallux. FHL tendinopathy is inflammation and degeneration of this tendon, most commonly at the fibro-osseous tunnel where it courses behind the medial ankle. It is particularly common in ballet dancers, gymnasts, and push-off athletes (sprinters, basketball players) who generate high FHL loading during repeated toe plantarflexion. At Balance Foot & Ankle in Howell and Bloomfield Hills, Michigan, Dr. Tom Biernacki, DPM evaluates FHL tendinopathy. Call (810) 206-1402.

Symptoms and Clinical Presentation

FHL tendinopathy causes deep posteromedial ankle pain — pain at the back and inside of the ankle, distinct from Achilles tendinopathy (posterior midline) and posterior tibial tendinopathy (medial ankle with arch collapse). Characteristic finding: “hallux saltans” or trigger toe — the big toe locks or catches during active flexion/extension at specific range positions as the thickened FHL tendon catches at the fibro-osseous tunnel. Palpation tenderness is located posterior to the medial malleolus along the FHL tunnel. Pain increases with active big toe plantarflexion resistance testing. In ballet dancers, the classic presentation is posterior ankle pain that increases en pointe and with relévé (rising onto toes).

Diagnosis

MRI with the ankle in plantar flexion position best visualizes FHL tendon signal change, thickening, and tunnel stenosis. Dynamic musculoskeletal ultrasound can demonstrate the trigger toe mechanism in real time — the tendon can be seen catching at the tunnel during active toe motion. Standard X-rays are typically normal but may show an os trigonum (accessory bone at the posterior talus) that can create additional posterior ankle impingement concurrent with FHL stenosis — posterior ankle impingement is an important differential. Diagnostic ultrasound-guided local anesthetic injection into the FHL sheath provides both diagnostic confirmation and temporary therapeutic relief.

Conservative Treatment

Conservative management for FHL tendinopathy: relative rest and activity modification, particularly eliminating the specific activities that load the FHL maximally (en pointe, bounding, toe-off sprinting); a cam boot or walking cast for 4–6 weeks for acute high-grade inflammation; physical therapy focusing on eccentric FHL strengthening and progressive return-to-activity protocol; and ultrasound-guided corticosteroid injection into the FHL sheath — provides significant temporary relief but carries risk of tendon weakening with repeated injections (limit to 1–2 per year). Custom orthotics with metatarsal padding to reduce terminal push-off force through the FHL. PRP injection is emerging as an alternative to corticosteroid for FHL tendinosis with early supporting evidence.

Surgical Treatment — FHL Release

When conservative management fails after 3–6 months, surgical FHL release (tunnel release) decompresses the fibro-osseous tunnel at the sustentaculum tali, eliminating the stenosis that causes the trigger toe and tendon impingement. The procedure can be performed endoscopically or through a small open incision. If a concurrent os trigonum is identified, it is typically removed at the same time. Recovery: 4–6 weeks in a cam boot, 3–4 months to full athletic activity. Outcomes are excellent in appropriately selected patients — 85–90% return to pre-injury activity level after FHL release.

FHL Tendinopathy Management in Howell & Bloomfield Hills Michigan

Dr. Tom Biernacki, DPM provides FHL tendinopathy evaluation with in-office diagnostic ultrasound and comprehensive conservative and surgical management at Balance Foot & Ankle. Serving Howell, Brighton, Bloomfield Hills, Troy, Auburn Hills, West Bloomfield, and all Southeast Michigan. Book your evaluation or call (810) 206-1402.

FHL Tendinopathy & Big Toe Tendon Pain Treatment in Michigan

Flexor hallucis longus (FHL) tendinopathy causes pain behind the inner ankle and under the big toe, especially in dancers and runners. Our podiatrists diagnose FHL problems with ultrasound and create targeted rehabilitation and treatment plans.

Explore Our Tendon Treatment Options → | Book Your Appointment | Call (810) 206-1402

Clinical References

1. Hamilton WG. Stenosing tenosynovitis of the flexor hallucis longus tendon and posterior impingement upon the os trigonum in ballet dancers. Foot Ankle. 1982;3(2):74-80.
2. Michelson J, Dunn L. Tenosynovitis of the flexor hallucis longus: a clinical study of the spectrum of presentation and treatment. Foot Ankle Int. 2005;26(4):291-303.
3. Gould N. Stenosing tenosynovitis of the flexor hallucis longus tendon at the great toe. Foot Ankle. 1981;2(1):46-48.

Dr. Tom Biernacki, DPM

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.