Synovial chondromatosis

Definition

Synovial chondromatosis (also known as synovial chondro-metaplasia) is a rare condition of unclear etiology in which foci of cartilage develop in the synovial membrane of joints, bursae, or tendon sheaths as a result of metaplasia of the subsynovial connective tissue. These nodules can detach and become loose bodies within the joint, which may undergo secondary calcification and ossification. Extra-articular involvement may occur if proliferating loose bodies break through the joint capsule or if synovial structures outside the joint (eg, tendon sheaths, bursae) are involved. Synovial chondromatosis is generally a primary condition, but it may occur secondary to osteoarthritis (OA).  Most common sites of involvement are the knee > hip > elbow > shoulder.  This condition is relatively uncommon: no well-defined reports of incidence are available.

Metaplasia

(Greek: "change in form") is the reversible replacement of one differentiated cell typewith another mature differentiated cell type. The change from one type of cell to another is generally caused by some sort of abnormal stimulus. In simplistic terms, it is as if the original cells are not robust enough to withstand the new environment, and so they change into another type more suited to the new environment. If the stimulus that caused metaplasia is removed or ceases, tissues return to their normal pattern of differentiation. Metaplasia is not synonymous with dysplasia and is not directly considered carcinogenic. It is also contrasted with heteroplasia, which is the abnormal growth of cytologic and histologic elements without a stimulus. (wikipedia)

Age

Usually appear during 3rd-5th decade of life

Gender

M>F 2:1

Presentation

Most often arises in the weight bearing joints of the lower extremity, particulary the hip and knee, usually monoarticular involvement.  In the upper extremity, the shoulder, elbow, wrist, and small joints of the hand may be affected as well.  Symptoms are similar to those of loose body formation.  Patients usually have a several year history of slowly progressing symptoms such as clicking, locking, or catching sensation during joint range of motion.  Baseline dull, aching discomfort is exacerbated by motion causing sharp pain.

Physical findings

Visible inspection of joint will likely be unremarkable.  Comparison to the contralateral side should be performed noting fullness, effusion, palpable loose bodies in synvovial recesses, and medial/lateral joint line tenderness. Patients may have limited range of motion (10-15 degree loss of flexion/extension), present with effusion, or inflammatory signs depending on the stage/extent of involvement/location.

Plain films

Findings are frequently normal. Approximately 1/3 cases may not have matrix mineralization.  Loose bodies that have ossified may be visible in the joint space.  Small round/oval nodules (1-3mm) with faint ring of peripheral calcification may be present.  Occasional involvement of the joint ligamentous structures (i.e. ACL/PCL).  Stigmata of degenerative joint disease often present as well.

A large popliteal mass with a calcific pattern that would suggest a cartilaginous tumor	Classic multiple radiodense loose bodies	Secondary osteoarthritis
Widening of the joint and expansion of the joint capsule that contains a large number of

CT Scan

A CT scan can demonstrate, an, effusion, a mass effect with radiolucent loose bodies or multiple calcified and or ossified loose bodied.

Synovial thickening, an effusion and multiple osetocartilagenous loose bodies

MRI

Variable findings depending on the relative amounts of synovial proliferation and calcified nodule formation.  Loose bodies tend to have low signal on T1-weighted images and high signal on T2-weighted images: with extensive calcification may have low signal on all images.

An effusion with numerous "rice bodies"	T2 MRI shows an effustion sheath with deposition of low signal pellets of osteocartilaginous material.

Differential Diagnosis

Synovial Chondrosarcoma, Myositis Ossificans, PVNS, Osteoarthritis, Septic Joint, Calcific Tendonitis (Shoulder), Soft Tissue Chondroma (Hand), Saponification of Patellar Fat Pad (anterior knee), Osteogenic Sarcoma or Myxoid Chondrosarcoma (posterior knee)

Natural history

Generally a benign, self limiting disease, however can be quite diasbling resulting in secondary degenerative osteoarthritis.  Simpler forms can be managed by arthroscopic debridement, repeated if necessary, more aggressive disease may require open synovectomy or joint replacement combined with a more complete synovectomy.

Pathology

Synovial chondromatosis is widely recognized as a metaplasia of the synovial membrane, the etiology of which remains unclear. The most common theory suggests that pluripotent mesenchymal cells located within the subintimal layer at the juncture of the synovium and the articular cartilage undergo a transformation to chondrocytes, resulting in nests of cartilage embedded within the synovial membrane, which become pedunculated and eventually extrude into the joint as loose bodies. Over a course of time, these bodies become calcified or even ossified, allowing for their identification on plain radiographs.

Low power showing a large hypertrophic villus projecting into the joint with a central focus of metaplastic immature-appearing cartilage.

Diagnosis and treatment

Again, patients often present with pain, swelling, and limited motion.  Effusion, diffuse tenderness, crepitus, decreased ROM, and, less commonly, palpable nodules or loose bodies are found on physical examination. The presentation may mimic that of OA; however, the two can usually be differentiated radiographically.  While various staging systems exist, there is some thought that the staging of synovial chondromatosis is a matter of timing and that the process is in fact self-limiting, as the cartilage nodules resorb over the course of years, leaving many cases undiagnosed.  Nevertheless, surgical removal combined with partial synovectomy has demonstrated decreased recurrence rates and remains the current standard of care. The treatment protocol is somewhat controversial. Many authors advocate surgical intervention as early as possible to relieve symptoms and prevent complications associated with disease progression. Removal of the loose bodies is necessary to alleviate symptoms and prevent secondary joint changes. The importance of complete synovectomy has been debated as well. Synovectomy is more extensive than simple removal of loose bodies, and it may be associated with increased morbidity (eg, arthrofibrosis).  However, some authors report a higher recurrence rate associated with simple removal of lose bodies versus partial or complete synovectomy.

Surgical Findings

Multiple, loose osteocartilaginous pellets lying within the shoulder joint.	Multiple loose bodies removed from the joint along with a portion of the resected synovial lining.	Multiple loose bodies with some synovial tissue

Complications

Recurrence (0-31%), Loss of ROM, arthrofibrosis, arthritis, transtion to synovial chondrosarcoma (rare/associated with multiple recurrences)

Recommended Reading

-OKU Musculoskeletal Tumors AAOS 2nd Edition 2007, Ch 28 pg 265-266.

-Adelani et al. Benign Synovial Disorders. JAAOS, Vol 16, No 5, May 2008, 268-275

-Sperling et al. Synovial chondromatosis and chondrosarcoma: a diagnostic dilemma. Sarcoma. 2003;7(2):69-73.

-Maurice et al.  Synvovial Chondromatosis JBJS Br 1988; 70(5): 807-11.

-Sah et al. Malignant Transformation of Synovial Chondromatosis of the Shoulder to Chondrosarcoma*.* A Case Report. JBJS Jun 2007;89:1321-1328.