Synovial chondromatosis of the flexor hallucis longus tendon sheath

Background

Synovial chrondomatosis is a rare, benign proliferative cartilaginous lesion arising from the synovial tissue or bursal lining of or near joints. When it is extra-articular, it is considered tenosynovial chondromatosis. The lesions can often be ossified depending on their chronicity. Synovial chondromatosis is found all over the body, with the most common joint being the elbow, although many others have been described.1 2 This article describes a relatively rare case of secondary tenosynovial chondromatosis of the flexor hallucis longus (FHL) tendon in a male patient who was successfully treated with open excision, as well as a review of the literature. The authors received the patient’s informed consent for publication.

Case presentation

A male patient in his 40s presented to the foot and ankle clinic after sustaining an inversion injury to the left ankle 2 weeks prior. Since that time, he had been in a controlled-ankle motion (CAM) boot. He complained of pain primarily around the lateral malleolus. He had a prior history of ankle trauma, to include two ankle dislocations, one 24 years prior and one 11 years prior. He had ankle surgery 11 years ago, which was aborted intraoperatively secondary to an intact anterior talofibular ligament (ATFL) and loose bodies that were unobtainable. He was otherwise healthy with no contributory medical, surgical or family history.

On examination, he had both anterior and posterior impingement signs as well as a positive anterior drawer and inversion test, which suggested an incompetent ATFL and calcaneofibular ligament. He was point tender behind the malleoli bilaterally and anterior to the Achilles tendon.

Differential diagnosis

Plain radiographs demonstrated significant anterior tibiotalar and anterior syndesmotic osteophytes as well as four ossified loose bodies in the posterior ankle (figure 1). CT scan demonstrated similar findings plus additional non-ossified loose bodies likely within the sheath or substance of the FHL (figure 2).

Treatment

Given his injury pattern, long-standing instability and likely post-traumatic osteoarthritis including loose bodies recalcitrant to non-operative management, the patient was indicated for operative treatment. In the operating room, we made a 4-cm incision over the pre-existing posteromedial surgical scar from his prior debridement attempt and dissected down to the FHL. We noted six palpable nodules just beneath the outer layer of the tendon sheath just proximal to the musculotendinous junction. Using tenotomy scissors to open the sheath, we extracted the loose bodies, which were round and about 1–1.5 cm in size. They were sent to histopathological examination. Next, we made a lateral approach to the ankle and performed both an anterior cheilectomy and Brostrom repair of the lateral ankle ligaments to restore lateral ankle stability without complication.

Outcome and follow-up

Postoperatively, he was placed in a plaster splint and made non-weight bearing for 2 weeks. We then converted to a CAM boot with heal lifts, allowed weight bearing and began physical therapy. His surgical specimens from the FHL were sent for histopathological examination, where they were interpreted as benign trabecular bone and soft tissue with degenerative changes, consistent with a final diagnosis of osteochondral loose bodies. At 6-month follow-up, he was active without limitations. His radiographs demonstrate interval removal of the loose bodies (figure 3). To assess his overall function, the American Orthopaedic Foot and Ankle Society (AOFAS) Ankle-Hindfoot scale was used. This tool measures the overall function of the ankle in terms of pain, function and alignment.3 Scores range from 0 to 100, with healthy ankles scoring 100 points. The patient’s 6-month AOFAS score was 86, which was an improvement from 42 at initial presentation. At 24-month follow-up, his AOFAS improved to 90. He is back to high-intensity workouts and running multiple miles without pain.