Primary synovial osteochondromatosis of the shoulder: a rare cause of shoulder pain

Abstract

Synovial osteochondromatosis is a benign neoplastic condition which manifests as multiple cartilaginous or osteocartilaginous nodules within a joint, bursa and tendon sheath. It typically results in pain and stiffness of the affected joint, and is thought to arise as a result of synovial membrane proliferation and metaplasia. ¹ We report the diagnosis and management of a 36-year-old man who presented with a long history of shoulder pain, which had been managed conservatively prior to referral to orthopaedics. Following investigation and subsequent diagnosis, he underwent successful surgical treatment of primary synovial osteochondromatosis, in the form of open synovial debridement and excision of nodules, with no recurrence demonstrated at 1-year follow-up. This case illustrates the diagnosis and management of primary synovial osteochondromatosis, and emphasises the importance of serial imaging and specialist referral for cases of diagnostic uncertainty or failure to respond to treatment as expected.

Background

Synovial osteochondromatosis is a rare cause of shoulder pain. This case demonstrates the challenges in diagnosis of this condition, illustrating the importance of serial imaging and review of the differential diagnosis when patients are not responding to treatment as expected. In this case, and 25%–30% of cases overall, initial plain radiographs were unremarkable, thus highlighting the need to consider specialist orthopaedic and radiology advice when symptoms persist despite seemingly appropriate treatment.

Case presentation

A 36-year-old, right-hand-dominant man presented to the orthopaedic department with right shoulder pain. He reported a 15-year history of pain of unknown origin, with no previous trauma. He had a history of manual work as a delivery driver, which involved regular lifting and carrying. There were no symptoms of instability or locking. Initial plain radiography, undertaken soon after the development of symptoms, was unremarkable. Conservative treatment, in the form of steroid injections and physiotherapy, had been undertaken without success.

Physical examination showed no obvious deformity. Reduced active range of movement was demonstrated in comparison to the unaffected side, with flexion of 140°, abduction of 140°, internal rotation to the posterior superior iliac spine and external rotation of 50°. Testing of rotator cuff integrity suggested there was no full-thickness tear. Clinical testing for subacromial impingement, acromioclavicular joint pain and glenohumeral instability was negative. There was no distal neurovascular deficit.

Investigations

Plain radiography, obtained during this initial consultation, demonstrated multiple calcific densities over the glenohumeral joint suggestive of synovial osteochondromatosis (figure 1). Although the initial films from 2002 were unavailable, the radiology report of these images stated there was no abnormality.

Figure 1.

Plain radiography of the shoulder demonstrating multiple calcified intra-articular loose bodies.

Subsequent MRI demonstrated multiple calcified intra-articular loose bodies around the anterior and posterior joint and axillary recess. These were considered pathognomonic, and confirmed the diagnosis of synovial osteochondromatosis (figure 2).

Figure 2.

Axial MRI demonstrating location and morphology of calcified loose bodies within glenohumeral joint.

Differential diagnosis

The radiological findings at the time of presentation to orthopaedics were considered diagnostic. The plain radiograph (figure 1) clearly demonstrates multiple uniform calcified loose bodies located throughout the shoulder joint, which are considered pathognomonic.

Subsequent MRI and histology of the excised nodules confirmed the diagnosis, excluding secondary synovial osteochondromatosis, where fragments are often fewer, larger and associated with significant intra-articular degenerative change. Other differentials include chondrosarcoma, where the mass is more irregular, or pigmented villonodular synovitis which classically causes a blooming artefact on gradient echo imaging using MRI.

Treatment

The patient was managed with open surgical excision. After opening the shoulder via a deltopectoral approach, excision of multiple nodules was undertaken, as well as synovial biopsy. Over 70 loose bodies were excised (figure 3). Subsequent pathology report confirmed the diagnosis, with no chondroid fragments, inflammatory infiltrate or malignancy identified within the synovium.

Figure 3.

Loose bodies following open debridement.

Outcome and follow-up

Postoperative management consisted of a sling for comfort and graded mobilisation with physiotherapy supervision. At 1-year follow-up, plain radiography showed no sign of recurrence and the patient reported good functional recovery (figure 4). He was discharged from orthopaedic follow-up at this point.

Figure 4.

Plain radiography of the shoulder at 1-year follow-up demonstrating no recurrence of condition.

Discussion

Synovial osteochondromatosis can affect any synovial cavity. It is uncommon, most often seen in men between the third and fifth decade. It is usually monoarticular, most frequently affecting the knee and hip joints.^2–4 The exact incidence of osteochondromatosis affecting the shoulder is unclear, but it is thought to be very rare. In three reported case series of synovial osteochondromatosis involving almost 100 patients, the shoulder was affected in only five patients.^3–5

Synovial osteochondromatosis can be considered either primary (idiopathic) or secondary, occurring as a sequelae of intra-articular pathology, such as a traumatic osteochondral defect.⁶

The aetiology of primary synovial osteochondromatosis is unknown. Histological studies have shown that synovial cells undergo metaplastic change to chondrocytes, which then produce multiple clusters of cartilage, giving rise to the characteristic uniform loose bodies. Secondary osteochondromatosis is thought to arise from a central nidus, such as an osteochondral fragment in trauma, or degenerative disease such as osteoarthritis. Subsequent enlargement results from proliferation of connective tissue cells and cartilaginous metaplasia, and the characteristic loose bodies develop.^{7 8} The absence of trauma in our case suggests primary disease although the duration of symptoms makes the history unreliable.

Synovial osteochondromatosis is considered to fall under the umbrella of non-septic articular disorders, and symptoms are often non-specific, the clinical signs of pain, swelling and reduced range of movement overlap with many other disorders.¹ Lunn et al ⁹ reported on 18 patients with synovial osteochondromatosis, all of whom presented with pain and loss of function. Although locking and instability are commonly reported as a result of intra-articular loose bodies, only six patients in this series reported such symptoms.⁹

Diagnosis of synovial osteochondromatosis is usually made from the pathognomonic plain radiography features. Multiple intra-articular calcifications of a similar size and shape are distributed throughout the joint.³ CT and MRI will also optimally demonstrate bone or articular surface erosion and synovial involvement. Although osteochondromatosis can be reliably diagnosed by plain radiography in 70%–90% of cases,^{3 10} early primary osteochondromatosis results in non-ossified radiolucent cartilaginous loose bodies, which may significantly delay the diagnosis.¹¹ This is likely to have happened in this case, leading to a protracted period of unsuccessful conservative treatment.

Management of synovial osteochondromatosis is undertaken with the intention of resolving the symptoms arising from loose bodies, reducing the potential for further osteochondromatosis arising from the synovium and reducing articular surface damage from third body wear. Surgical excision of the loose bodies, and synovectomy is the usual treatment.⁹ Debate remains over whether open or arthroscopic surgery should be undertaken. While the disadvantage of arthroscopy is that synovectomy is more limited, there is no conclusive evidence that an open procedure confers any advantage with regard to recurrence. Some authors favour arthroscopic procedures due to the potential for reduced morbidity and earlier recovery^{12 13}; others favour an open procedure for the shoulder, in part for the ease of access to the bicipital groove.^{7 9} In the series described by Lunn et al,⁹ 9 of 18 patients had loose bodies in the bicipital groove, and failure to remove these at the time of surgery resulted in further surgery in three patients. In our case, this patient underwent open debridement of the biceps sheath as part of the procedure. Clearly, the optimal surgical intervention has yet to be established by the literature and further research is needed to establish whether an open or arthroscopic approach offers clinically superior outcomes.

Recurrence rates are quoted in the literature as 15%–25%.¹⁴ In our patient, there was no evidence of recurrence at 1 year postoperatively, and he regained full pain-free function. Malignant transformation into secondary synovial chondrosarcoma has been reported in 1%–10% of patients; in these cases, rapid symptom progression, early recurrence and infiltration into muscle are strong indicators of malignancy.⁸ In our case, the synovial biopsy showed no sinister features, and the patient made a rapid and complete recovery.

This case illustrates the diagnosis and surgical management of primary synovial osteochondromatosis in a patient who presented with shoulder pain and loss of function. Clinicians should maintain an index of suspicion for this condition when patients describe ongoing symptoms in the presence of normal initial imaging. Our case demonstrates the importance of serial imaging and referral for specialist opinion, when persistent symptoms do not respond to conservative treatment as expected.

Learning points.

• Synovial osteochondromatosis of the shoulder is a rare cause of pain but can present in a similar fashion to more common shoulder conditions.

• Radiological findings are pathognomonic, although in early stages, the typical nodules may not be seen on plain radiography, which can lead to a delay in diagnosis.

• Clinicians should maintain an index of suspicion for more unusual causes of shoulder pain and consider repeat imaging and/or specialist referral in cases that are not responding to treatment as expected.

• This case also highlights that significant shoulder pathology can be overlooked when the common clinical screening tests are unremarkable.

• Occasionally, the benign form can transform into secondary malignant synovial chondrosarcoma; therefore, histology of removed nodules is essential. Adequate duration of postoperative follow-up must also be ensured.