Synovial chondromatosis of the flexor hallucis longus tendon sheath

Abstract

This case report discusses a rare case of secondary tenosynovial chondromatosis of the flexor hallucis longus (FHL). 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 diagnosis is often delayed given the rarity of presentation and non-specific symptoms. The case was highly unusual in that hindfoot pain was caused by several centimetre-sized osteochondral bodies within the FHL tendon sheath. Anterior cheilectomy was performed. The patient returned to full activity following surgery without recurrence of the disease. The condition can be successfully treated operatively.

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).

Figure 1.

Preoperative AP and lateral radiographs four ossified loose bodies in the posterior ankle.

Figure 2.

Sagittal images from a preoperative CT scan again demonstrating ossified loose bodies with additional non-ossified loose bodies as well.

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.

Figure 3.

AP and lateral radiographs taken 6 months after surgery demonstrate interval removal of loose bodies without recurrence.

Discussion

We present a unique case of a highly physically active man with a long history of ankle trauma, pain and instability. He presented to our clinic with osteochondral loose bodies within the tendon sheath of his FHL. After surgical intervention to include removal of osteochondral loose bodies from his FHL tendon sheath, he reported significant improvement in his pain, stability and function of his ankle. His clinical presentation, imaging, intraoperative findings and pathological evaluation are consistent with tenosynovial chondromatosis.

Tenosynovial chondromatosis is a rare condition characterised by the formation of multiple cartilaginous nodules in the synovium of the tendon sheath. It is thought to be a benign chondrogenic metaplasia of extra-articular synovial tissue. Radiographs usually demonstrate multiple soft tissue nodules in the distribution of a tendon. Gross inspection demonstrates multilobulated synovium with multiple white/bluish nodules that are composed of hyaline cartilage. On histology, there is metaplastic synovium demonstrating cartilaginous nodules beneath the surface lining of the synovial membrane.

We hypothesise that this case is likely secondary tenosynovial chondromatosis, rather than primary, based on the patient’s long history of trauma. His trauma may have caused a metaplastic transformation of the tenosynovium, especially given the communication between the joint space and the FHL in about 20% of patients.⁴ This condition is rarely discussed in publicly available literature, with even fewer reports in the FHL.⁵ Lui reports a case from zone 2 FHL, which is different from our zone 1 case.⁶ Oakley et al were the first to report on tenosynovial osteochondromatosis in the FHL in 2010.⁷ Thomsen et al report on a similar case in 2015, the first of its kind in a collegiate athlete.⁸ Lui reports a case series of three patients treated by tendonoscopy.⁹ Otherwise, the discussion in the literature is sparse. This case adds to the growing body of evidence that tenosynovial osteochondromatosis should be considered as a rare but possible differential diagnosis for subacute or chronic posterior ankle pain.

Learning points.

• Tenosynovial chondromatosis is a rare condition characterised by the formation of multiple cartilaginous nodules in the synovium of the tendon sheath.

• Patient had a long history of ankle trauma which may have caused a metaplastic transformation of the tenosynovium.

• Significant improvement in pain, stability and function was reported after surgical intervention.

• Tenosynovial osteochondromatosis should be considered as a rare but possible differential diagnosis for subacute or chronic posterior ankle pain.

Ethics statements

Patient consent for publication

Consent obtained directly from patient(s).