The Flexor Hallucis Longus (FHL) tendon is a robust structure running through the lower leg and into the foot. It functions as a powerful engine for movement, particularly during activities that require lifting the heel off the ground. The FHL is deeply involved in the mechanics of walking, running, and jumping, providing the necessary leverage for a strong push-off. When pain develops in this area, it can severely limit daily activities and athletic performance, making understanding its role essential for managing discomfort and restoring function.
The Role of the FHL Tendon in Foot Movement
The FHL muscle originates on the posterior surface of the fibula in the lower leg. Its long tendon travels distally, passing through a fibro-osseous tunnel situated just behind the medial malleolus (the prominent bony bump on the inside of the ankle). The tendon continues along the sole of the foot, inserting into the base of the farthest bone of the big toe.
The primary action of the FHL is to powerfully flex the big toe, pulling it downward. This movement is integral to the propulsion phase of the gait cycle. During walking or running, the FHL provides the final, forceful push-off that transitions the body from the stance phase to the swing phase. This capability is particularly important for athletes who rely on powerful toe-off, such as sprinters and dancers.
Causes and Symptoms of FHL Tendinopathy
When the FHL tendon becomes irritated, it is diagnosed as FHL tendinopathy, involving the degradation or inflammation of the tendon fibers. A closely related issue is tenosynovitis, which is inflammation of the protective synovial sheath that lubricates the tendon as it moves through the ankle tunnel. Both conditions result from the tendon’s inability to adapt to cumulative mechanical stress.
The main cause of FHL issues is repetitive microtrauma, where small, repeated stresses accumulate faster than the body can repair the tissue. This is prevalent in athletes who perform repeated forceful plantarflexion, such as dancers, leading to the common diagnosis of “dancer’s tendinitis.” Runners who rapidly increase their training load also place excessive strain on the tendon structure.
Structural foot issues, including excessive overpronation or flat feet, can alter the angle of the tendon pull, increasing friction as it passes behind the ankle bone. The most common symptom is a deep, aching pain located specifically behind or slightly below the medial malleolus. Pain typically worsens when pushing off the ground, standing on the toes, or during activities that require heel lift.
In chronic cases, the tendon sheath can thicken or scar tissue can accumulate, leading to a catching or locking sensation in the big toe known as “trigger toe.” This mechanical block occurs as the enlarged tendon attempts to pass through the narrow fibro-osseous tunnel.
Conservative Management and Rehabilitation
Initial management of FHL tendinopathy focuses on reducing inflammation and removing the mechanical stressor. This involves a period of rest, meaning a temporary cessation or modification of activities that reproduce the pain, particularly running or dancing. Applying ice and utilizing non-steroidal anti-inflammatory drugs (NSAIDs) can help manage acute discomfort and swelling in the early stages.
Once acute pain subsides, physical therapy becomes the primary intervention to restore tendon strength and resilience. A specific focus is placed on stretching the calf complex, particularly the gastrocnemius and soleus muscles, as tightness in these areas increases the load placed on the FHL tendon. Improving ankle dorsiflexion mobility is also a goal to reduce compensatory strain.
The hallmark of tendon rehabilitation is the implementation of eccentric loading protocols. These controlled exercises involve strengthening the muscle while it is lengthening under tension, which helps reorganize the collagen fibers within the tendon. Therapeutic modalities like ultrasound or dry needling may be employed to stimulate healing and improve blood flow to the affected area.
Supportive measures often complement the physical therapy program. Custom or over-the-counter orthotics can be used to control excessive foot pronation, reducing friction on the tendon’s path behind the medial malleolus. For cases that remain refractory to initial treatment, a corticosteroid injection into the tendon sheath may be considered to reduce localized inflammation.
Surgical Options for Chronic FHL Issues
Surgery is reserved for FHL issues that have failed to respond to a minimum of six to twelve months of consistent conservative management. It is also indicated for chronic cases of mechanical trigger toe where the tendon is physically blocked and movement is severely restricted. The primary goal of surgical intervention is to create more space for the tendon and remove damaged tissue.
The two main procedures are tenosynovectomy and debridement. Tenosynovectomy involves surgically releasing and removing the inflamed, thickened tendon sheath. Debridement clears away scar tissue or degenerative nodules from the tendon itself. These procedures are often performed using minimally invasive endoscopic techniques. Post-operative recovery involves immobilization followed by physical therapy, with a return to full activity often taking three to six months.