eMedicine Specialties > Radiology > Musculoskeletal

Ankle, Flexor Hallucis Longus Tendon Injuries

Author: Stacy E Smith, MD, Associate Professor of Radiology, Division of Musculoskeletal Imaging, University of Maryland School of Medicine
Coauthor(s): Christopher W Flye, MD, Consulting Staff, Coastal Radiology Associates PLLC
Contributor Information and Disclosures

Updated: Jul 31, 2007

Introduction

Background

Injuries to the flexor hallucis longus (FHL) tendon have classically been described in ballet dancers secondary to their constant repetitive plantar flexion. Hence, the injury is often called dancer's tendinitis. Such injuries have also been described in association with climbing, soccer, and running in relation to frequent push-off maneuvers of the forefoot in these activities. FHL tenosynovitis is infrequently seen in association with other conditions, such as diabetes, rheumatoid arthritis, lupus, and seronegative spondyloarthropathies.

Pathophysiology

Pathology of the FHL tendon is commonly related to overuse. Direct trauma and, less commonly, inflammatory disease are other causes. Types of injuries with associated definitions include the following:

• Tendinopathy: This is a degenerative lesion in tendon tissue without alteration of the tendon sheath.
• Tenosynovitis: This is inflammation or infection in the vascular peritendinous tissue.
• Partial or complete tendon tears: Partial tears can be central or intrasubstance, or they can occur at the external margins of the tendon. Complete tears may occur with or without tendon retraction.
• Tendon entrapment or checkrein deformity: This is fixed tethering of the FHL tendon under or just proximal to the flexor retinaculum, which can be secondary to fracture.
• Tendon dislocation: This can be complete or incomplete.

Particularly in ballet dancers, repetitive and prolonged plantar flexion leads to tenosynovitis or tendinopathy. With further overuse, progression to frank longitudinal tears can occur.

Inflammation of the FHL tendon generally occurs in 1 of 3 areas: (1) at the fibro - osseous tunnel along the posteromedial ankle, (2) under the base of the first metatarsal where the flexor digitorum longus (FDL) tendon crosses the FHL tendon (known as the knot of Henry), or (3) where the FHL tendon passes between the great toe sesamoids beneath the metatarsal head.

When the tendon becomes nodular, triggering of the great toe (hallux saltans) may develop, and progression to hallux rigidus may occur.

Complete tears of the FHL tendon are rare, with fewer than 4 cases of acute rupture reported in the literature. Two were reported in athletes with acute trauma within 1 cm of the tendon insertion: 1 at the distal border of the tarsal tunnel in a high-level athlete with continued overuse and 1 in a patient with history of rheumatoid arthritis with spontaneous atraumatic rupture under the sustentaculum tali.

Entrapment of the flexor hallucis tendon may be due to an enlarged os trigonum, an associated calcaneal fracture or fracture dislocation (first reported in 1960 in Barcelona byJimeno-Vidal), or soft-tissue scar after injury or surgery. Entrapment of the musculotendinous junction secondary to callus has also been reported after fibular fracture fixation. One case report of intermittent dislocation is noted in the literature. The 2 hypotheses provided for such an event include hypoplasia of the posteromedial process of the talus and weakness of the fibrous retinaculum.

Frequency

United States

Unlike the posterior tibialis and Achilles tendons, the FHL tendon is among the tendons least commonly injured. Numeric details in the United States are not available, though these injuries are most frequently seen in ballet dancers and athletes (eg, downhill runners) who require repetitive push-off of the forefoot.

Mortality/Morbidity

Unrecognized injuries to the FHL tendon can lead to chronic pain, early arthritis, and fibrosis with resultant decreased range of motion over time. In elite athletes, particularly in athletes who repeatedly used plantar flexion maneuvers, determination of the degree of injury to the FHL or its surrounding structures is paramount because loss of their livelihood is at stake.

Race

No particular race predilection has been noted.

Sex

No particular sex delineation is noted.

Age

Injuries to the FHL tendon and its surrounding structures tend to most commonly occur in young athletes. However, recreational athletes ("weekend warriors") may have chronic tendinopathy and, in rare cases, acute tears. Abnormalities of and injuries to the FHL tendon without seemingly extreme exertion may occur over a larger age range in predisposed individuals, such as those with diabetes, rheumatoid arthritis, seronegative arthropathies, or lupus.

Anatomy

The FHL muscle is the most lateral muscle of the deep compartment of the calf originating from the lower two thirds of the posterior surface of the shaft of the fibula, with its distal tendinous insertion on the distal phalanx of the great toe. The FHL tendon itself begins just above the level of the medial malleolus and lies posterolateral to the posterior tibialis and FDL tendons in the posterior medial aspect of the ankle.

All 3 tendons course in the fibro - osseous tunnel behind the medial malleolus and beneath the flexor retinaculum; they then pass through the tunnel between the medial and lateral talar tubercles of the posterior talus, which is lined by a synovial sheath.

The FHL then enters the foot by crossing the posterior subtalar joint and passing under the inferior aspect of the sustentaculum tali, analogous to a rope through a pulley. The tendon then converges medially, crossing the FDL tendon in the middle plantar compartment with the FDL tendon positioned plantarly. This area where the FHL and the FDL tendon cross over in the foot is called the knot of Henry; this is located approximately 1 thumb breadth lateral to the tuberosity of the navicular.

A tendinous slip of the lateral portion of the FHL tendon joins with the FDL tendon in the sole of the foot, providing a tethering mechanism. This prevents excessive retraction of a proximal FHL tendon fragment after rupture.

In its distal aspect, the FHL tendon crosses the lateral belly of the flexor hallucis brevis muscle and lies superficial to and between the 2 heads of the flexor hallucis brevis muscle at the intersesamoid interval of the great toe, inserting into the base of the distal phalanx.

The tibial nerve innervates the FHL muscle and tendon.

Presentation

Dancers usually present with an insidious onset of posteromedial ankle pain, which is occasionally associated with localized swelling. Initial treatment is conservative with physical therapy, use of nonsteroidal anti-inflammatory drugs (NSAIDs), and alteration of exercise and activity. When medical therapy fails and symptoms persist unimproved after 3-6 months, surgical exploration and treatment may be required to repair any tears, excise nodules, and perform fibroosseous tunnel release, among other indications.

Preferred Examination

Physical examination is the initial evaluation for the patient with posteromedial ankle pain. To allow complete dorsiflexion at the ankle, the knee is flexed 90° to relax the gastrocnemius. The knee is then extended with plantar flexion of the ankle and great toe, with the clinician palpating behind the medial malleolus. These maneuvers can allow differentiation of tendinitis (diffuse tenderness or crepitation) from causes of trigger toe and hallux rigidus. Triggering occurs when a nodular thickening of the tendon snaps through the fibro-osseous tunnel. This is generally palpable. Hypertrophy of the FHL at the musculotendinous junction may produce hallux rigidus, with restriction of dorsiflexion of the hallux.

Computed tomography (CT) is best for precisely depicting the ossific anatomy and the gross size and location of the tendon. However, because of its multiplanar and multisequence capabilities, MRI helps in clarifying tendinous findings, such as coexistent tenosynovitis, tendinopathy, partial or complete tears, and associated fluid. In addition, magnetic resonance imaging (MRI) permits characterization of the anatomy of the fibrous retinaculum. Bone marrow edema is best evaluated with MRI and may help in identifying an os trigonum syndrome or contusions of adjacent bones.

Differential Diagnoses

Ankle, Tibialis Posterior Tendon Injuries

Other Problems to Be Considered

Posterior impingement syndrome
Achilles tendinitis
Os trigonum syndrome
Tarsal tunnel syndrome
Subtalar coalition
Fractured Stieda process
Calcaneal fractures with impingement

• Search for CME/CE on This Topic »

• Fracture, Ankle (Emergency Medicine)
• Dislocation, Ankle (Emergency Medicine)
• Acute Ankle Sprains (Orthopedic Surgery)
• Joint Reduction, Ankle Dislocation (Clinical Procedures)

• Reinjury Common After Low-Grade Ankle Sprain in Athletes
• Ultrasound Tops Clinical Exam for Ankle Assessment in Childhood Arthritis
• FDA Approves First Mobile-Bearing Total Ankle Replacement System

• Effect of unsupervised home based proprioceptive training on recurrences of ankle sprain: randomised controlled trial
• Diagnosis of Peripheral Arterial Disease in General Practice: Can the Ankle-Brachial Index Be Measured Either by Pulse Palpation or an Automatic Blood Pressure Device?
• Prevalence of Peripheral Arterial Disease In High-risk Patients Using Ankle-Brachial Index In General Practice: A Cross-Sectional Study