A 16 y. o. man complained of deep right ankle pain, followed by limitation of motion, that had lasted from several months. There was history of direct trauma. Radiographic findings were negative
The patient, a soccer player, arrived with a 2-month history of mild pain localized in the posterior and medial ankle, in the dorsiflexion and eversion positions. There was history of tendon contusions secondary to direct trauma, with the joint in eversion position during soccer games. The MRI study was performed using an MR scanner (0.2T) with a dedicated coil. The examination consisted of T1-weighted spin-echo (SE), PD-weighted turbo-spin-echo (TSE), T2*-weighted gradient-echo (GE) and GE-STIR sequences, performed in the axial, coronal and sagittal planes.
The flexor hallucis longus tendon is located postero-lateral to the posterior tibialis and the flexor digitorum longus tendons at the postero-medial aspect of the ankle joint. The tendon courses through the tunnel between the medial and lateral talar tubercles of the posterior talus, which is lined by a synovial sheath. The tendon enters the foot by crossing the posterior subtalar joint and passing under the inferior aspect of the sustentaculum tali. This is analogous to a "rope through a pulley." The usual location for tendon entrapment is the fibro-osseous tunnel where the tendon changes direction from a vertical course dorsal to the talus to a horizontal course beneath the calcaneus. Tendon injuries commonly occur as the result of overuse, and in athletes they typically occur in sports with repetitive cutting manoeuvres, such as running, or jogging . The injuries occur as a continuum from chronic degeneration to partial tears to full-thickness tears (overuse and rupture). The terminology used in describing tendon pathology has not bee standardized and variation is often encountered. In general , tenosynovitis is restricted to describe inflammation of the tendon sheath. Tendinosis relates to degeneration of the inner fibres of the tendon itself. Peritendonitis (or paratenonitis) describes inflammation of the paratenon, myotendonous juction, and the adjacent muscle. Partial tears describe discontinuity of the tendon fibres without complete loss of tendon integrity. Partial tears are often quantified as low or high grade depending on the suspected amount of tendon involvement. Complete tear or rupture is reserved for full-thickness tears with a loss of tendon function and often retraction of the myotendonous junction caused by contraction of the tendon injury accurately relative to the osseous insertion site and myotendonous junction and the size of the gap present between the tendon edges. MRI is the primary modality used to assess tendon injury. The presence of excessive fluid located in the tendon sheath, around a normal-appearing tendon is characteristic of diagnoses of tenosynovitis. Up to 20% of individuals have a normal communication between the flexor hallucis longus tendon synovial sheath and the ankle joint, but it is important not to mistake physiologic synovial fluid within the tendon sheath with an abnormality. The presence of a large amount of fluid within the flexor hallucis longus tendon sheath, in absence of fluid in the ankle joint in the aforementioned soccer player with previous trauma, brought us to diagnose tenosynovitis. Where a large amount of liquid was found in the ankle joint and in the tendon sheath, it would have been necessary to complete the investigation with intravenous contrast or with surgery in order to confirm the diagnosis. The patient was treated non-operatively with aggressive physical therapy, and he returned to normal physical activity and is now in good physical condition.
Tenosynovitis of the Flexor Hallucis Longus Tendon
In this case of a 16-year-old male patient’s ankle MRI sequences, the following features are observed:
Combining the patient’s symptoms (deep ankle pain, restricted motion) with the evidence of peritendinous effusion and local inflammatory changes indicated by imaging, the following should be considered first:
Based on the patient’s youth, sports-related trauma history, ankle pain and limited range of motion, and the MRI findings of significant fluid accumulation in the FHL tendon sheath without clear signs of tendon fiber rupture or bone fracture, the most likely diagnosis is FHL Tenosynovitis.
Following the confirmed diagnosis of FHL Tenosynovitis, the following comprehensive treatment and rehabilitation plan is recommended:
Rehabilitation exercises should be gradual, aiming to restore ankle joint range of motion (ROM) and muscle strength, and to prevent recurrence. The FITT-VP principle (Frequency, Intensity, Time, Type, Progression) can be used:
If severe pain or functional impairment persists despite long-term conservative treatment, advanced MRI or surgical exploration should be considered for further evaluation.
Note: If the patient has other systemic conditions (e.g., osteoporosis or cardiopulmonary issues), exercise intensity and methods should be individualized to ensure safety.
This report is intended for medical information purposes only and does not replace face-to-face clinical consultation or professional medical advice. If you have any questions or if your condition changes, please seek medical attention promptly.
Tenosynovitis of the Flexor Hallucis Longus Tendon
