Introduction
Background
Synovial osteochondromatosis (SOC) is a benign condition characterized by synovial membrane proliferation (demonstrated in the images below) and metaplasia. The entity also is termed synovial chondromatosis. The synovial lining of a joint, bursa, or tendon sheath undergoes nodular proliferation, and fragments may break off from the synovial surface into the joint. There, nourished by synovial fluid, the fragments may grow, calcify, or ossify. The intra-articular fragment may vary in size from a few millimeters to a few centimeters.
Sagittal T1-weighted and sagittal short-tau inversion recovery (STIR) images of the ankle show proliferating synovium, which is seen as foci of increased signal intensity on the STIR images.
Sagittal T1-weighted and sagittal short-tau inversion recovery (STIR) images of the ankle show proliferating synovium, which is seen as foci of increased signal intensity on the STIR images.
The degree of calcification varies, and calcification may be seen as a few calcific specks or as foci of frankly ossified bodies. The fragments may be found free within the joint cavity, or they may be embedded within the proliferating synovium, which may extend into the surrounding soft tissues. The natural history of SOC entails gradual progression of disease, joint deterioration, and secondary osteoarthritis. Essentially, the disease is a benign process, and although studies in the literature have reported malignant transformation, this finding is decidedly unusual.
The images below present a detailed view of SOC of the shoulder.
Plain radiograph of a 19-year-old man who initially presented with a history of shoulder pain of insidious onset. The patient was found to have synovial osteochondromatosis. Frontal radiograph of the shoulder shows multiple rounded, calcified bodies in the axillary recess and in the subscapularis bursa.
Magnetic resonance imaging (MRI) scan of a 19-year-old man who initially presented with a history of shoulder pain of insidious onset. The patient was found to have synovial osteochondromatosis. Coronal T1-weighted image of the shoulder shows multiple hypointense foci in the axillary recess and in the subacromial space. Note the hypointense foci deep to the deltoid in the subdeltoid bursa. The foci result from the presence of osteocartilaginous bodies in these areas. Cartilage bodies may be present in the sleeve of the biceps tendon.
Magnetic resonance imaging (MRI) scan of a 19-year-old man who initially presented with a history of shoulder pain of insidious onset. The patient was found to have synovial osteochondromatosis. Oblique sagittal proton density– and T2-weighted images show multiple, rounded, hypointense foci in the subscapularis bursa projecting underneath the coracoid process. Note the high signal intensity simulating the presence of surrounding fluid from the joint effusion. Some of the high signal intensity results from edematous proliferating synovium. The synovium is dissecting the body of the scapula and the infraspinatus. Note the solitary osteochondral body in that location.
Magnetic resonance imaging (MRI) scan of a 19-year-old man who initially presented with a history of shoulder pain of insidious onset. The patient was found to have synovial osteochondromatosis. Oblique sagittal proton density– and T2-weighted images show multiple, rounded, hypointense foci in the subscapularis bursa projecting underneath the coracoid process. Note the high signal intensity simulating the presence of surrounding fluid from the joint effusion. Some of the high signal intensity results from edematous proliferating synovium. The synovium is dissecting the body of the scapula and the infraspinatus. Note the solitary osteochondral body in that location.
Image from a 19-year-old man who initially presented with a history of shoulder pain of insidious onset. The patient was found to have synovial osteochondromatosis. Some of the multiple stones were removed from the patient's shoulder during surgery. Note the lamellate pattern to the chondral bodies.
Recent studies
Ackerman et al examined the outcome of total joint arthroplasty for severe arthritis in 11 patients with synovial chondromatosis who were treated with total hip arthroplasty (n = 7) or total knee arthroplasty (n = 4) and who returned for follow-up at a mean of 10.8 years after surgery. In all 11 patients, pain and functional scores showed significant improvement. All patients displayed improved range of motion, but synovial chondromatosis did return in 1 knee and in 1 hip.1
Urbach et al reported the results of arthroscopic treatment for synovial chondromatosis of the shoulder with loose body removal and partial synovectomy in 5 patients. According to the authors, clinical results were very good in all patients 4 to 9 years after surgery. Radiologic signs of chondroma were observed in 2 patients, but revision surgery was not necessary in either patient.2
Galat et al studied 8 patients with synovial chondromatosis of the foot (n = 2, midfoot) or ankle (n = 6), all of whom presented with pain, locking, or stiffness. Four patients underwent ankle synovectomy with loose body removal and were pain-free at last follow-up (avg, 9.5 y; range, 1-31 y). One patient underwent excision and midfoot arthrodesis for severe midfoot destruction. Ultimately, 3 patients underwent below-the-knee amputation, 1 patient for multiple recurrences and 2 patients for malignant transformation to low-grade chondrosarcoma.3
Pathophysiology
SOC is characterized by synovial membrane metaplasia, hyperplasia, and hyaline or myxoid change. The synovial lining of a joint, bursa, or tendon sheath undergoes nodular proliferation, and fragments may break off from the synovial surface into the joint. In this location, where they are nourished by synovial fluid, the fragments may grow, calcify, or ossify.4
Mortality/Morbidity
Generally, SOC is a monoarticular disease that has a benign course. Several reports in the literature describe malignant transformation. The transformations occurred after several recurrences following treatment.
Sex
SOC shows a predilection of 2- to 4-fold for males over females.
Age
Individuals of all ages can be affected, but the disease is often diagnosed in persons aged 20-50 years.
Presentation
Patients with SOC often relate a history of several years of joint pain with swelling. The affected joint frequently has an associated limitation in range of motion and/or a history of locking. SOC is almost always a monoarticular process, and the large joints are more commonly affected. These include the knee, hip, elbow (shown below), and shoulder. However, the disease process may affect any synovial surface, including the extra-articular bursa.
Lateral radiograph of the elbow of a 29-year-old man who presented with locking and reduced range of motion of the elbow. Soft-tissue fullness simulating effusion is noted. In addition, rounded, calcified bodies are seen anteriorly and posteriorly around the elbow.
Axial computed tomography (CT) images of the elbow at the level of the radial ulna joint. Note the presence of osteocartilaginous bodies in the radial ulna joint and also posteriorly.
Sagittal reconstruction from a spiral computed tomography (CT) scan series of the elbow shows the distribution of the calcified bodies in the olecranon fossa and around the posterior and anterior aspects of the joint.
SOC shows a predilection for males that is 2- to 4-fold greater than that for females; most patients with SOC present in the third to fifth decades of life.
If the intra-articular fragments are adequately calcified, the diagnosis is easily made with plain radiographic examination. With noncalcified fragments, MRI scans are required to show the nature and extent of SOC.
Purists differentiate primary, or idiopathic, SOC from the secondary form. In secondary SOC, the initial predisposing factor is an unrelated articular process leading to joint disintegration, production of intra-articular fragments, synovitis, and, eventually, synovial metaplasia. The cause of primary SOC is unknown.
Preferred Examination
Radiographic findings are frequently diagnostic. CT scans and CT arthrograms also may be used, especially for demonstrating noncalcified intra-articular bodies. MRI usually helps establish the diagnosis, and the images demonstrate the true extent of the disease. Ultrasonographic examination may be used to investigate accessible joints.
Radiographs should be obtained first. MRI scans should then be obtained preoperatively. When MRI is not readily available, CT arthrography may be performed.
Limitations of Techniques
Radiographs may not demonstrate noncalcified bodies. CT scans may not demonstrate the full extent of proliferating synovial disease. SOC may be confused with pigmented villonodular synovitis (PVNS) if only MRI scans are available, and plain radiographs may help in such cases.
Differential Diagnoses
Pigmented Villonodular Synovitis
Other Problems to Be Considered
Rice bodies of tuberculosis and rheumatoid arthritis
Synovial hemangioma
More on Synovial Osteochondromatosis |
 Overview: Synovial Osteochondromatosis |
| Imaging: Synovial Osteochondromatosis |
| Follow-up: Synovial Osteochondromatosis |
| Multimedia: Synovial Osteochondromatosis |
| References |
| Further Reading |
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Further Reading
Related eMedicine topics
Synovial Chondromatosis (Orthopedic Surgery)
Osteoarthritis
Osteochondroma and Osteochondromatosis
Solitary Osteochondroma
Osteochondroma (Pathology)
Keywords
synovial osteochondromatosis, synovial chondromatosis, synovial joint, synovectomy, osteochondromatosis, synovial membrane, chondromatosis, synovial membrane proliferation, synovial membrane metaplasia, synovial membrane hyperplasia
