Teaching Case

A 40-year-old male patient presented to the GP in March 2008 with a history of recurrent left shoulder dislocations over the past four years.

Physical examination was unremarkable. Outpatient plain radiograph and an MRI was performed, but the patient did not attend follow-up appointments.

Initial plain radiography (Fig. 1) showed calcification in the region of the supraspinatus and a slightly loose body inferior to the glenoid but no fracture or osteoarthritis. During the follow-up appointment in August 2008, MRI was performed and showed subcortical cystic degeneration in the humeral head and features of synovial chondromatosis (Figs. 2, 3) and small loose bodies along the biceps tendon and supraspinatus tendon.

The patient did not attend the follow-up appointments and returned eight years later when a repeated plain radiography (Fig. 4) showed multiple intra-articular loose bodies around the humeral head. A subsequent MRI in June 2016 demonstrated progression, with multiple large loose bodies, supraspinatus tear and partial thickness infraspinatus tear (Fig. 5) that were visible along with multiple loose bodies within the suprapinatus tendon and the biceps tendon sheath (Figs. 6a, 6b, 7a, 7b).

Primary synovial chondromatosis (PSC) is an uncommon condition characterised by metaplasia of the chondroid along with multinodular proliferation of the synovial lining which can be of a diarthrodial joint, tendon sheath or bursa. The definite aetiology is unknown, although it was proposed that it is due to the reactivation of residual embryonal cells [3] present in the related area and, in some literature, trauma has been reported as the cause [2].

It is generally believed that PSC is not a neoplastic process, but a metaplastic process initiated by trauma or chronic irritation [6, 7, 8]. An animal study showed that synovial chondromatosis has a relationship with osteoarthritis secondary to trauma [8]. It has a male predominance with an incidence of 1:100000 and it mostly occurs afresh in a healthy joint [4]. The most common joint involved is the knee joint, followed by the hip joint. Involvement of the shoulder joint is uncommon and extra articular involvement is rare [5]. Generally, these patients have chronic pain and stiffness in the affected joint [1].

Diagnosis is usually straightforward with plain radiographs which show osteochondral loose bodies distributed within the joint capsule, but which rarely involve the bursae or tendon sheath [9]. Additional imaging aids the diagnosis in atypical cases and also identifies any associated abnormalities.
In this case, MRI was crucial in demonstrating the location of the loose bodies within the supraspinatus tendon which could have been mistaken for calcific tendinitis.

This was an unusual case of PSC effecting the shoulder joint along with tendon involvement and a causal relationship due to trauma and repeated irritation was hypothesised. Treatment is mainly aimed at symptomatic relief and, in complicated cases, surgical intervention may be necessary.

A combination of imaging techniques is required to reach the diagnosis and this particular case also highlights the importance of plain radiographs, particularly in musculoskeletal pathology. In this case, the diagnosis was made based on the radiological findings and the clinical history. The patient refused any surgical intervention and histological confirmation was not possible.