Laboratory Studies
If the physical findings suggest possible infection, order the following studies:
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Erythrocyte sedimentation rate (ESR)
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C-reactive protein (CRP) level
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Complete blood count (CBC) with differential
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Lyme titer
Results of these tests are expected to be normal in persons with primary synovial chondromatosis, but they may be elevated in persons with secondary synovial chondromatosis due to systemic inflammation from a condition such as rheumatoid arthritis (RA).
Imaging Studies
Plain radiography
Plain radiography with orthogonal views of the affected joint [47, 22] frequently yields normal findings. Between 5% and 30% of patients do not have radiographically visible calcifications.
Typical plain radiograph of knee in patient with synovial chondromatosis. No abnormalities are noted.
If loose bodies undergo ossification, they may be visible in the joint space. The pattern of mineralization varies with size. Large nodules have large, stippled, or ringlike calcified areas. Small nodules have flecks of calcium. Secondary widening of the joint space may be noted, even if the nodules are not directly visible. In 30% of cases, no matrix mineralization is present, and loose bodies appear as foci with opacity similar to that of water.
In secondary synovial chondromatosis, changes consistent with the underlying disease process are evident.
Magnetic resonance imaging
Cartilaginous nodules have intermediate signal intensity on T1-weighted magnetic resonance imaging (MRI; see the first image below) and high signal intensity on T2-weighted images (see the second, third, fourth, and fifth images below), with decreasing intensity as the amount of calcium in the nodule decreases. [47] The addition of intra-articular gadolinium-based contrast material increases the sensitivity for detecting lesions.
Sagittal T2-weighted MRI through knee in adult with synovial chondromatosis demonstrates abnormal signal intensity in suprapatellar pouch. Also note hypertrophic synovium in intercondylar notch region and normal posterior cruciate ligament.
Sagittal T2-weighted MRI of patient with synovial chondromatosis. Note hypertrophic synovium and normal anterior cruciate ligament.
Coronal T2-weighted MRI of patient with synovial chondromatosis demonstrates punctate areas of low intensity within synovial fluid.
Computed tomography
Computed tomography (CT) is useful only for identifying calcified loose bodies. Unmineralized nodules typically cannot be visualized.
Procedures
Arthrocentesis is used to obtain a sample of synovial fluid if the physical findings suggest infection. The sample should be sent for a cell count, crystal examination, Gram staining, and cultures. All findings should be within normal limits in persons with primary synovial chondromatosis. Although interleukin (IL)-6 and vascular endothelial growth factor (VEGF)-A have been noted to be elevated in synovial fluid samples, these findings do not yet play a significant role in clinical practice. [21]
Image-guided synovial biopsy, using either ultrasonography (US) or CT, has been found to be safe and effective for establishing a definitive diagnosis of synovial lesions (eg, synovial chondromatosis or pigmented villonodular synovitis) before surgical or other intervention. [48]
Histologic Findings
Primary synovial chondromatosis
On hematoxylin-eosin staining, thick, villous formation to the synovial membrane with islands of clustered chondrocytes is seen. The chondrocytes in the nodules are usually arranged in loose clusters, though a nonclustered uniform distribution may occur. Discrete lobules of hyaline-type cartilage can be noted with mild cellularity and surrounded by a think fibrous layer. [22]
In two thirds of cases, the chondrocytes show mild-to-moderate nuclear atypia with pleomorphism, enlarged and open-faced nuclei, and frequent binucleation. Mitotic figures are rarely found. Osteoclastlike giant cells and chondroblasts with a dense, eosinophilic cytoplasm may rim the nodules.
If calcification occurs, it is distributed in a patchy, irregular pattern. In late stages, the nodules may undergo true ossification via vascular invasion and endochondral bone formation.
Secondary synovial chondromatosis
Foci of implanted articular cartilage with and without subchondral necrotic bone are found. The chondrocytes of implanted cartilage usually lack significant atypia or binucleation, and any calcification occurs in a zonal, ringlike fashion.
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Arthroscopic appearance of synovial chondromatosis loose bodies in shoulder.
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Arthroscopic shaver during attempted removal of loose bodies.
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Sagittal T2-weighted MRI through knee in adult with synovial chondromatosis demonstrates abnormal signal intensity in suprapatellar pouch. Also note hypertrophic synovium in intercondylar notch region and normal posterior cruciate ligament.
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Sagittal T2-weighted MRI of patient with synovial chondromatosis. Note hypertrophic synovium and normal anterior cruciate ligament.
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Sagittal T1-weighted MRI of knee in patient with synovial chondromatosis.
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Coronal T2-weighted MRI of patient with synovial chondromatosis demonstrates punctate areas of low intensity within synovial fluid.
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Coronal T2-weighted MRI of knee in patient with synovial chondromatosis.
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Typical plain radiograph of knee in patient with synovial chondromatosis. No abnormalities are noted.
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Arthroscopic image of pedunculated synovial chondromatosis in knee.
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Arthroscopic image of pedunculated synovial chondromatosis in knee.
