Ultrasound Diagnosis of Intermittent Flexor Hallucis Longus Dislocation

This case highlights an instance of intermittent dislocation of the flexor hallucis longus (FHL) tendon in the retro-malleolar area, which was triggered by a post-traumatic detachment of the retrotalar pulley from the medial tubercle of the talus. The detachment led to instability, allowing the tendon to dislocate during certain movements, causing pain and discomfort. High-resolution ultrasound imaging proved to be a valuable diagnostic tool in this case, as it allowed real-time visualization of the tendon displacement under dynamic stress conditions. During the examination, the patient was instructed to flex the hallux (big toe) against resistance provided by the examiner while the ankle remained in slight dorsiflexion. Under these conditions, the ultrasound captured the anterior displacement of the FHL tendon, which confirmed the diagnosis of tendon dislocation. Notably, following this maneuver, the tendon would return to its normal anatomical position, providing evidence of its intermittent nature. This condition was also associated with a noticeable and painful snapping sensation, which is often a key symptom in similar cases of tendon dislocation. The use of dynamic ultrasound in diagnosing FHL tendon dislocation was crucial, as it enabled visualization of the tendon’s movement and highlighted the relationship between physical stress and tendon displacement. Early diagnosis through this approach can help to inform potential treatment options, particularly for post-traumatic tendon instability. Such findings underscore the importance of dynamic imaging in identifying subtle soft-tissue injuries that might be missed with static imaging techniques.