Flexor Hallucis Longus Tendinopathy 2026: Causes, Diagnosis & Treatment | Podiatrist

You bend your big toe to push off during a run or a ballet relevé — and a sharp pain shoots behind your ankle. You may even feel a pop or a catch, as if the tendon is grabbing. That sensation belongs to the flexor hallucis longus tendon, one of the most mechanically loaded tendons in the foot, and one that goes underdiagnosed because it hides behind the ankle where plantar fasciitis and Achilles problems get all the attention.

In our Howell and Bloomfield Hills clinics, FHL tendinopathy accounts for a meaningful portion of the “my ankle has been bothering me for months and nobody figured it out” cases we see. Once it’s correctly identified, treatment is straightforward — but getting the diagnosis right is the critical first step.

What Is Flexor Hallucis Longus Tendinopathy

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The flexor hallucis longus (FHL) tendon originates in the deep posterior compartment of the lower leg, passes behind the medial ankle through a fibro-osseous tunnel at the back of the talus, travels under the foot through the tarsal tunnel and a second constriction point called the “knot of Henry,” and attaches to the base of the distal phalanx of the great toe. Its job is to flex the big toe — critical for push-off in running, jumping, and dance.

Tendinopathy refers to a spectrum of pathology within the tendon itself: acute inflammatory tendinitis, chronic degenerative tendinosis, or stenosing tenosynovitis — a thickening of the tendon sheath that causes triggering or locking of the big toe. All three can occur along the FHL, and all three require slightly different management approaches.

Ballet dancers earn the unofficial title of highest-risk group. The en pointe and demi-pointe positions load the FHL at extreme angles repetitively, and the tendon rubs against the posterior talar process with every relevé. Runners are the second most common group we treat — particularly those who have increased mileage rapidly or switched to minimalist footwear that demands more great toe flexion.

Symptoms of FHL Tendinopathy

The location of pain shifts depending on which part of the tendon is affected, which is one reason this condition is often misdiagnosed. Pain at the posterior ankle points to the tarsal tunnel segment. Pain along the plantar midfoot or at the great toe MTP joint suggests involvement at the knot of Henry or the distal tendon sheath.

• Posterior ankle pain — deep ache or sharp pain behind the medial ankle, worse with push-off
• Big toe triggering or locking — the hallmark of stenosing tenosynovitis; the toe clicks, catches, or temporarily locks when you try to flex or extend it
• Pain with resisted big toe flexion — pressing your big toe downward against resistance reproduces the pain
• Plantar midfoot aching — when the knot of Henry is involved, pain sits in the arch rather than the heel or ankle
• Night cramps — cramping in the great toe or arch at rest is a less-known but classic FHL sign
• Swelling behind the medial ankle — visible or palpable fullness in the tarsal tunnel region
• Weakness in great toe push-off — reduced power when standing on tiptoe or during late-stance phase of gait

Importantly, FHL symptoms are usually unilateral (one side) and activity-dependent at first, progressing to pain at rest in more advanced cases. If both feet are affected simultaneously, consider a systemic inflammatory condition rather than mechanical tendinopathy.

Causes and Risk Factors

FHL tendinopathy is almost always a cumulative overuse injury, but several anatomical and training factors stack the deck. Understanding the mechanism helps explain why certain treatments work and others don’t.

Risk Factor	Mechanism	Who It Affects
Ballet / dance (en pointe)	Posterior talar compression on FHL tendon	Dancers at all levels
Rapid mileage increase	Repetitive eccentric loading exceeds tendon repair rate	Recreational and competitive runners
Minimalist / zero-drop footwear	Increased great toe dorsiflexion demand amplifies FHL load	Transition runners
Os trigonum (accessory bone)	Osseous impingement on FHL at posterior talus	~7–14% of population
Hallux rigidus / stiff big toe	Altered push-off mechanics overload FHL	Middle-aged adults
Cavus (high-arch) foot type	Increased plantar fascial and flexor tendon tension	Any age

The presence of an os trigonum — a small accessory bone behind the talus present in roughly 10% of the population — dramatically increases FHL impingement risk. When plantarflexion compresses the os trigonum against the calcaneus, the FHL tendon gets pinched between them. We use weight-bearing lateral X-rays and MRI to identify this in patients who fail conservative care.

How FHL Tendinopathy Is Diagnosed

Diagnosis begins with a careful history — specifically asking about activity type, pain location, triggering sensation in the big toe, and whether symptoms started after a training change. The physical examination includes several targeted tests that are highly specific for FHL involvement.

The FHL stretch test: With the ankle in neutral, passively extend the great toe. Pain behind the medial ankle or a click in the toe reproduces the diagnosis with good sensitivity. Adding ankle dorsiflexion increases tension on the tendon and sharpens the reproduction of pain.

Resisted great toe flexion: Ask the patient to press their big toe downward against your resistance. Pain or weakness in this test strongly implicates the FHL, while a normal result shifts suspicion toward plantar fascia or intrinsic muscle pathology.

Triggering test: Passively move the great toe from flexion to extension while palpating the medial ankle tendon sheath. A palpable pop or audible click confirms stenosing tenosynovitis — the tendinopathy subtype most likely to need procedural intervention.

Imaging: Weight-bearing X-rays screen for os trigonum and arthritic changes. Ultrasound performed dynamically — watching the tendon glide in real time as you flex and extend the toe — reveals tendon thickening, sheath fluid, and the triggering phenomenon. MRI provides superior detail of tendon fiber disruption, partial tears, and bone marrow edema at the posterior talus.

In our clinic, we typically start with ultrasound because it’s fast, dynamic, and allows same-visit diagnosis. MRI is reserved for cases where os trigonum syndrome or partial tendon tear is suspected, or when the patient isn’t responding to initial treatment as expected.

Differential Diagnosis

FHL tendinopathy overlaps significantly with several other posterior ankle and hindfoot conditions. Getting the differential right before initiating treatment prevents weeks of misdirected therapy. These are the conditions we most commonly need to rule out in clinic.

Condition	Key Differentiating Feature	Diagnostic Test
Posterior ankle impingement	Pain on plantarflexion, not big toe flexion; no triggering	Posterior impingement test (forced plantarflexion)
Os trigonum syndrome	Often co-exists with FHL; bony posterior tenderness	Lateral X-ray, MRI bone edema
Tarsal tunnel syndrome	Burning/tingling distribution; positive Tinel’s at medial ankle	Tinel’s test, nerve conduction study
Achilles tendinopathy	Pain 2–6 cm above calcaneal insertion; no big toe involvement	Palpation, Royal London Hospital test
Posterior tibial tendon dysfunction	Progressive flatfoot deformity; pain along medial arch	Single-leg heel rise test, MRI
Plantar fasciitis	Morning start-up pain at medial heel; no ankle or toe symptoms	Windlass test, point tenderness at fascial origin

One nuance worth noting: FHL tendinopathy and os trigonum syndrome frequently coexist. If MRI shows os trigonum bone edema AND FHL tenosynovitis, treatment must address both — treating only one typically results in incomplete resolution.

Treatment Options for FHL Tendinopathy

Treatment follows a logical ladder from activity modification and load management through physical therapy, orthotic support, and procedural options — with surgery reserved for the minority who fail conservative care over 3–6 months.

Stage 1: Load Management (Weeks 1–3)

The FHL tendon cannot heal while it is being repeatedly overloaded. For dancers, this means a temporary modification of pointe work — not complete cessation, but replacing relevés with demi-pointe and eliminating forced turnout until pain resolves. For runners, reduce weekly mileage by 40–50% and eliminate hill work and speed intervals temporarily.

Footwear matters immediately. A shoe with a slight heel-to-toe drop (8–10mm) reduces the dorsiflexion demand on the FHL and provides passive offloading. Switching from zero-drop or minimalist shoes to a structured trainer during the recovery period accelerates healing in most patients we see.

Stage 2: Physical Therapy (Weeks 2–8)

The evidence base for FHL tendinopathy rehabilitation is extrapolated from Achilles and posterior tibial tendon data, but the principles are the same: progressive eccentric and isometric loading to stimulate tendon remodeling. Key exercises include:

• Isometric great toe flexion holds — press the big toe down against the floor for 30–45 seconds; isometric loads reduce pain quickly in the acute phase
• Eccentric heel lowering off a step — loads the entire posterior chain including FHL; 3 sets of 15 daily
• Towel scrunches and marble pickups — intrinsic strengthening reduces compensatory FHL overload
• Calf stretching (both straight-leg and bent-knee) — gastrocnemius and soleus tightness amplifies FHL tension; must be addressed
• Single-leg balance progression — restore proprioceptive control before returning to full activity

Stage 3: Orthotic Support

A full-length orthotic with a Morton’s extension (a rigid extension under the great toe) offloads the FHL by limiting great toe dorsiflexion during push-off. This is particularly effective for runners and patients with hallux rigidus contributing to FHL overload. We frequently pair this with a PowerStep Pinnacle as an over-the-counter bridge while custom orthotics are being fabricated.

For pain management alongside orthotics, Doctor Hoy’s Natural Pain Relief Gel — formulated with arnica and camphor — provides topical anti-inflammatory effect without the systemic risks of oral NSAIDs. Apply to the posterior ankle and plantar arch twice daily. Unlike Biofreeze (which we no longer recommend), Doctor Hoy’s works on the inflammatory cascade rather than just masking sensation with menthol.

Stage 4: Ultrasound-Guided Procedures

For cases not responding after 8 weeks of conservative care, ultrasound-guided corticosteroid injection into the FHL tendon sheath — not the tendon itself — can break the inflammatory cycle and restore gliding function. The sheath injection is safe and effective; injecting into the tendon substance carries rupture risk and should be avoided.

Platelet-rich plasma (PRP) injection is an emerging option for tendinopathy that has failed cortisone or for patients who prefer to avoid steroids. Evidence in FHL specifically is limited, but the broader tendinopathy PRP data supports its use as a second-line procedural option.

Stage 5: Surgery (Refractory Cases)

Surgery is needed in less than 15% of FHL tendinopathy cases in our experience. When it is needed, the procedure depends on the pathology: tarsal tunnel release decompresses the fibro-osseous tunnel at the medial ankle, while a knot of Henry release addresses the distal constriction point. Os trigonum excision is performed arthroscopically in most centers and dramatically improves outcomes when an impinging accessory bone is confirmed on MRI.

Recovery after surgery is typically 6–10 weeks non-weight-bearing followed by 6–8 weeks of rehabilitation. Return to dance or competitive running averages 4–6 months post-operatively.

Red Flags — See a Podiatrist Promptly

Most Common Mistake with FHL Tendinopathy

The most common mistake we see is treating FHL tendinopathy as plantar fasciitis. Both conditions affect the foot’s plantar and medial structures, both worsen with activity, and both are common in runners — so they get conflated constantly. The critical difference is that plantar fasciitis produces its worst pain in the first few steps in the morning at the medial heel, while FHL tendinopathy causes pain behind the ankle or at the ball of the foot during push-off, with no notable morning start-up component.

The fix: before prescribing plantar fasciitis stretches or cortisone, perform the FHL stretch test and resisted great toe flexion test. If either is positive, you’re dealing with the FHL. Plantar fasciitis stretches won’t hurt the FHL tendon, but they won’t help it either — and six weeks of the wrong treatment delays correct diagnosis and frustrates the patient.

Recommended Products for FHL Tendinopathy Recovery

In-Office Treatment at Balance Foot & Ankle

At Balance Foot & Ankle, we diagnose FHL tendinopathy in a single visit using in-office diagnostic ultrasound. Dr. Tom Biernacki performs dynamic tendon assessment — watching the FHL glide in real time — to identify the exact segment involved and whether stenosing tenosynovitis, tendinosis, or partial tearing is present. This precision allows us to target treatment exactly where it’s needed rather than applying a generic protocol.

For patients requiring ultrasound-guided sheath injection or PRP, those procedures are also available in-office at both our Howell and Bloomfield Hills locations. We accept most major Michigan insurance plans for diagnostic visits and conservative treatment. Same-day appointments are available — call (810) 206-1402 or book online. Learn more about our full tendon treatment options at our treatments page.

Frequently Asked Questions

How long does flexor hallucis longus tendinopathy take to heal?

Most patients see significant improvement within 6–8 weeks of consistent conservative care — load modification, physical therapy, and orthotic support. Complete resolution to full activity typically takes 10–14 weeks. Cases involving stenosing tenosynovitis or os trigonum impingement often take longer and may require a procedure. Starting treatment early is the strongest predictor of a faster recovery.

Can I keep running with FHL tendinopathy?

Modified running — reduced mileage, no hills, no speed work — is generally acceptable in mild to moderate cases if pain stays below a 4/10 during and after runs. Pain that climbs above a 5/10 during a run, or significant soreness lasting more than 24 hours after running, indicates you are overloading the tendon and need a longer rest period. Running through severe FHL pain risks progression to partial tendon tear.

What is triggering of the big toe, and is it serious?

Triggering — a clicking, catching, or temporary locking when you flex or extend the great toe — occurs when a thickened segment of the FHL tendon catches at the fibro-osseous tunnel entrance at the medial ankle. It is not immediately dangerous, but it indicates stenosing tenosynovitis that typically requires intervention beyond basic stretching. Left untreated, progressive thickening can lead to permanent restricted motion and the need for surgical tendon sheath release.

When should I see a podiatrist for FHL tendinopathy?

See a podiatrist if posterior ankle or big toe pain has persisted longer than 3 weeks despite rest and anti-inflammatory treatment, if you notice triggering or locking of the great toe, if you are a dancer unable to perform relevé without pain, or if symptoms are worsening rather than improving. Early evaluation with ultrasound diagnosis typically shortens total recovery time significantly. Call us at (810) 206-1402 for same-day appointments in Howell and Bloomfield Hills.

Does insurance cover FHL tendinopathy treatment?

Office visits, ultrasound imaging, physical therapy, and standard cortisone injections are typically covered by major Michigan insurance plans. Custom orthotics may require a copay or deductible. PRP injections are generally not covered. We verify benefits before your first visit — call (810) 206-1402 to confirm your coverage.

Sources

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2. Ribbans WJ, Ribbans HA, Cruickshank JA. “The management of posterior ankle impingement syndrome in sport: a review.” Foot Ankle Surg. 2015;21(1):1–10.
3. Dombek MF et al. “Peroneus brevis tendon tears: a retrospective review.” J Foot Ankle Surg. 2003;42(5):250–258.
4. Abramowitz Y et al. “Outcome of resection of a symptomatic os trigonum.” J Bone Joint Surg Br. 2003;85(7):1051–1054.
5. Murphy GA. “Disorders of tendons and fascia.” Campbell’s Operative Orthopaedics, 13th ed. 2017:4205–4290.
6. Maffulli N, Wong J, Almekinders LC. “Types and epidemiology of tendinopathy.” Clin Sports Med. 2003;22(4):675–692.

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