An injury to the Flexor Hallucis Longus (FHL) tendon causes medial ankle pain or pain on the bottom of the foot. FHL injury is a condition that is often overlooked or misdiagnosed. This injury affects dancers, runners, soccer players, and any other athlete who performs repeated, propulsive forces, or jumping. Injury of the Flexor Halicus Longus muscle is sometimes called “Dancer’s tendonitis” but it is not limited to just dancers.
The Flexor Hallucis Longus (FHL) muscle allows you to point your big toe (plantar-flexing your big toe) and stabilizes the Subtaler Joint. The Subtaler Joint is located between two bones in your ankle - the Talus and the Calcaneus. The Subtaler Joint allows movement of the heel toward the medial plane (inversion) as well as movement of the heel towards the lateral plane (eversion). (Dancer from Alvin Ailey)
Anatomy/Biomechanics of Medial Ankle Pain
The Flexor Hallucis Longus muscle is located deep under your calf muscles (the most lateral muscle of the deep compartment). The FHL originates on the lateral lower leg (distal 2/3 of Fibula). It then travels at an oblique angle (crosses the posterior surface of Tibia) down towards the medial ankle (posterior surface of Talus) and travels under a section of the heel bone (Sustentaculum Tali of Calcaneus). The FHL then passes under the sole of the foot (between the two heads of the FHB) and inserts into the base of the big toe (base of the Distal Phalanx of Hallax).
As mentioned the FHL Tendon curves around a structure called the Sustentaculum Tali. The Sustentaculum Tali is a bony section on the inside of the heel bone (Calcaneus). This is often a site of friction and irritation for the FHL tendon. The FHL tendon also travels between the two Sesamoid bones just behind the big toe (Metatarso-Phalangeal Joint). The sheath that surrounds the FHL tendon is often irritated.
Causes and Presentation of Medial Ankle Pain
The repetitive motion of pushing-off with your foot (plantar flexion) during dance, running, soccer, and jumping can cause injury to the FHL.
Injury to the FHL tendon and muscle can present in a variety of ways - sometimes involving inflammation and sometimes not. Injury to the tendon without inflammation is refer to as a “Tendinopathy”. Tendinopathy refers to a degenerative lesion in the tendon without affecting the tendon sheath that surrounds the tendon.
When FHL inflammation (tendonitis) is present in the foot, it usually occurs in one of the following three locations.
1. Inside of the ankle (fibro-osseous tunnel along the Posteromedial Ankle).
2. At the “Knot of Henry” – a section just behind the big toe (first metatarsal) where the FDL muscle crosses the FHL tendon.
3. Just behind the big toe by the Sesamoids bone.
o A Sesamoid bone holds its tendon away from the center of the joint and acts to increase mechanical force.
When the FHL tendon becomes nodular, a condition called Hallux Saltans can develop. Hallux Saltans is similar to trigger finger in the hand, except it occurs in the big toe. Triggering of the toe occurs when the nodular thickening of the tendon snaps through the fibro-osseous tunnel. This causes a jerking motion, much like a trigger finger.
If not addressed Hallux Saltans can contribute to the progression of an additional condition called Hallux Rigidus. Hallux Rigidus means "stiff great toe". Hallux Rigidus is the second most common disorder of the first MTP joint. The most common injury is a bunion - otherwise known as Hallux Valgus.
In part two of Medial Ankle Pain, we will discuss special considerations for dancers, diagnosis and imaging, and finally treatment.
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