Flexor Hallucis Longus tendinitis is an overuse condition affecting the tendon that flexes the big toe. Repetitive stress can cause inflammation, irritation, thickening, or degeneration of the tendon and its surrounding sheath. FHL tendinitis most commonly affects dancers, runners, and athletes who repeatedly push off the big toe, but it can occur in anyone who places excessive or repetitive stress on the foot and ankle.
Pain is typically felt along the back or inner side of the ankle and may extend into the arch or underside of the foot. Early diagnosis and appropriate treatment can relieve symptoms, restore tendon function, and prevent chronic tendon damage.
Causes
FHL tendinitis usually develops from repetitive loading of the tendon. Activities that require frequent plantarflexion, toe-pointing, jumping, or forceful push-off can increase stress along the tendon and cause irritation over time.
Ballet dancers are particularly susceptible because movements such as pointe and relevé repeatedly load the FHL tendon. Runners, soccer players, gymnasts, and other athletes who frequently push off the toes are also at increased risk.
Additional factors that may contribute include:
- · Tight calf muscles
- · Flat feet or excessive pronation
- · Abnormal foot mechanics
- · Sudden increases in training intensity
- · Repetitive ankle and toe motion
- · Previous ankle or foot injury
- · Tendon adhesions or thickening within the tendon sheath
The FHL tendon travels through narrow anatomical spaces behind the ankle. Repetitive friction or compression can cause the tendon sheath to become inflamed and narrowed, resulting in stenosing tenosynovitis. In more advanced cases, adhesions or tendon thickening can interfere with normal tendon movement and produce clicking, catching, or locking of the big toe.
Anatomy
The FHL muscle is located deep in the back of the lower leg. Its tendon travels behind the ankle, passes through a groove in the talus, continues underneath the foot, and attaches to the base of the distal phalanx of the big toe.
The tendon helps bend the big toe downward and contributes to ankle plantarflexion. It also assists with maintaining the arch and provides important stability and power during push-off.
Because the tendon passes through a relatively narrow tunnel behind the ankle and changes direction as it enters the foot, it is particularly susceptible to irritation from repetitive motion. The tendon also crosses the flexor digitorum longus tendon in the midfoot, an area commonly referred to as the knot of Henry.
Symptoms
Symptoms generally develop gradually and are related to activities that repeatedly load the tendon.
Common symptoms include:
- · Pain along the back or inner side of the ankle
- · Tenderness along the FHL tendon
- · Pain with push-off or running
- · Pain when flexing the big toe
- · Pain when pointing the toes downward
- · Swelling around the inner or back portion of the ankle
- · Stiffness of the big toe or ankle
- · Clicking, catching, or snapping during movement
- · Weakness when pushing off
- · Difficulty standing on tiptoe
Pain may extend from behind the ankle into the arch or underside of the foot. Symptoms often worsen with running, dancing, jumping, climbing stairs, or other repetitive activities.
Diagnosis and Imaging
Diagnosis is primarily based on the patient’s symptoms and physical examination. We evaluate tenderness along the tendon and assess ankle and big toe motion. Pain may be reproduced by simultaneously dorsiflexing the ankle and extending the big toe, which places the FHL tendon under tension.
Ultrasound can demonstrate tendon thickening, inflammation, fluid around the tendon, and adhesions while also allowing the tendon to be evaluated dynamically during movement.
MRI provides more detailed information and may identify tenosynovitis, partial tendon tearing, tendon degeneration, or entrapment. Imaging is particularly useful when symptoms persist despite treatment or when another condition may be responsible for the pain.
Other conditions that can cause similar symptoms include posterior ankle impingement, tarsal tunnel syndrome, plantar fasciitis, sesamoid disorders, stress injuries, and posterior tibial tendon problems.
Severity and Progression
FHL tendinitis can range from mild inflammation to significant structural tendon damage.
- · Mild disease: Inflammation and irritation are present without significant structural damage. Pain is usually activity-related.
- · Moderate disease: Tendon thickening or narrowing of the surrounding sheath may restrict normal tendon movement.
- · Severe disease: Partial tearing, adhesions, or significant tendon degeneration can cause persistent pain and mechanical catching or locking.
Early treatment is important because continued repetitive loading can allow inflammation to progress to chronic tendinopathy and structural tendon damage.
Nonsurgical Treatment
Most cases of FHL tendinitis improve with nonsurgical treatment. The primary goals are to reduce tendon stress, control inflammation, restore normal tendon movement, and gradually return to activity.
Treatment may include:
- · Activity modification: Temporarily reducing running, jumping, pointe work, and other activities that repeatedly load the tendon allows it to recover.
- · Immobilization: A walking boot or brace may be used for a short period when symptoms are severe.
- · Physical therapy: Treatment focuses on restoring calf flexibility, improving ankle and big toe mobility, strengthening the foot and ankle, and correcting abnormal movement patterns.
- · Orthotics: Custom or prefabricated orthotics may help improve foot mechanics and reduce stress on the FHL tendon.
- · Heel lifts: In selected patients, a temporary heel lift can decrease tension on the tendon.
- · Medication: Anti-inflammatory medications may help control pain and inflammation when medically appropriate.
Corticosteroid injections are generally used cautiously around the FHL tendon because injections directly into or immediately around a tendon can increase the risk of tendon weakening or rupture.
Surgical Treatment
Surgery is considered when symptoms persist despite appropriate nonsurgical treatment or when mechanical tendon problems, significant adhesions, or structural tearing interfere with function.
FHL tenolysis or tendon release involves freeing the tendon from scar tissue or adhesions and releasing areas of narrowing that prevent normal tendon gliding. This may be performed through an open or minimally invasive approach depending on the location and severity of the problem.
In patients with substantial tendon degeneration or other reconstructive needs, the FHL tendon can sometimes be used as a tendon transfer, particularly during reconstruction of a chronically diseased Achilles tendon. The FHL provides additional plantarflexion strength while generally preserving useful big-toe function.
The specific procedure depends on the condition of the tendon, the location of the pathology, and the patient’s functional requirements.
Recovery and Rehab
Recovery depends on the severity of the condition and whether surgery is required. Many patients with mild to moderate FHL tendinitis improve within several weeks with activity modification, therapy, and appropriate support.
After surgery, patients may initially require a period of immobilization and restricted weight-bearing. Weight-bearing and activity are gradually increased as healing progresses. Physical therapy focuses on restoring range of motion, strength, balance, and controlled push-off.
Return to running, jumping, dancing, or other high-demand activities should occur gradually. Athletes and dancers may require additional rehabilitation to safely return to their previous level of performance.
Potential Complications
If symptoms are not appropriately treated, persistent tendon irritation can lead to chronic tendinopathy, adhesions, restricted tendon motion, or partial tearing. Rarely, continued degeneration can result in tendon rupture.
Following surgery, potential complications include infection, nerve irritation, stiffness, scar tissue, persistent pain, weakness, and recurrence of symptoms. Careful rehabilitation and gradual progression of activity can help minimize these risks.
Long-Term Outlook
The prognosis for FHL tendinitis is generally very good, particularly when the condition is recognized early and repetitive stress is reduced. Most patients can return to normal activities without persistent pain.
Athletes and dancers can often return to their previous level of performance following appropriate treatment and rehabilitation. Preventing recurrence requires attention to training volume, calf flexibility, foot mechanics, footwear, and proper technique.
Persistent symptoms should not be ignored because chronic tendon inflammation and degeneration can make treatment more difficult and prolong recovery.
When to See a Specialist
Persistent pain behind or along the inner side of the ankle, particularly pain that occurs with push-off or big-toe movement, should be evaluated by a foot and ankle specialist. Evaluation is especially important when symptoms interfere with walking, running, dancing, or athletic performance.
At Complete Orthopedics, our doctors evaluate the FHL tendon through a detailed physical examination and appropriate imaging. Treatment is tailored to the severity of tendon disease and the patient’s activity demands, with an emphasis on restoring comfortable movement and preventing recurrent injury.
The content on this page has been authored, edited, or approved by the doctors below, and was last reviewed for accuracy on September 15, 2026.
