A 30-year-old female presented following a distortion injury of the left knee during swimming. Physical examination revealed swelling of the medial compartment and a slight positive anterior drawer test. The patient was referred for Magnetic Resonance Imaging (MRI) of the left knee.
T1-weighted image (WI) revealed a synovial-based mass, adjacent to the medial retinaculum of the patellar surface with a signal isointense to muscle (Fig. 1). On fat-suppressed T2-WI the lesion was heterogeneous with overall high signal intensity and multiple intralesional foci of low intensity (Fig. 2 A-B). A similar lesion was seen adjacent to the anterior intermeniscal transverse ligament (not shown). There was slightly increased fluid present in the suprapatellar recessus (Fig. 2 A-B). After administration of Gadolinium contrast, heterogeneous enhancement of both lesions was seen (Fig. 3 A-B). Gradient-echo images showed subtle blooming artefact of the low signal intensity foci on T2 WI (Fig. 4). On conventional radiograph, a focal increased attenuation of the mass adjacent to the inferomedial aspect of the patella was seen (Fig. 5). Arthroscopy revealed a synovial-based mass with some subtle area of bleeding at the surface (Fig. 6). Subsequently, biopsy was performed.
Primary synovial chondromatosis (PSC) is a benign neoplastic process of the synovium of joints, tendon sheaths or bursa. The disease follows three stages. First, a non-specific synovitis is seen with no loose bodies. In the transitional stage, loose bodies develop in addition to synovitis. Finally, synovial disease fades out and loose bodies detach, calcify and ultimately ossify [1-4]. PSC affects males 2-4 times more frequently than women in the third to fifth decade [1,2]. The knee and the hip joints are most affected, accounting for 80-90% [1,2]. Secondary SC is a nonneoplastic disorder due to underlying cartilage damage and mostly affects elderly patients [1,2].
Patients with PSC mostly presents with pain, swelling, restricted motion, articular crepitus, locking and rarely palpable nodules[1,2]. PSC is usually monoarticular. Polyarticular involvement may be associated with familial history and associated syndromes [2]. Malignant degeneration into chondrosarcoma is rare6].
Radiographs are negative in the initial stage. In the third stage, multiple small intraarticular calcified or ossified nodules of uniform shape are present. Other findings are ring-and-arc pattern and target appearance, consisting of a central focus and a single peripheral rim of calcification [2,3,5].
Ultrasound shows a heterogeneous mass containing hyperechogenic foci sometimes accompanied by acoustic shadowing in case of mineralization or enchondral ossification. The position of the (osteo)chondral nodules may change. On Power doppler ultrasound, the lesion is avascular [2,7].
Computed tomography may reveal nonmineralized nodules as low attenuation foci [2].
MRI findings differs along the disease stage. In the first stage non-specific lobulated synovial thickening is seen. Uncalcified nodules are isointense to muscle on T1 WI and hypointense to synovial fluid. On T2-WI calcified loose bodies show multiple signal voids on both sequences. Ossified loose bodies show a central area of bone marrow signal and a perilesional hypointense rim of cortical bone.
PSC should be differentiated from PVNS which may involve the same structures.
In contrast to PVNS, there is no blooming on gradient echo imaging, unless there is some bleeding like in our patient [2,3,5].
Although pressure erosion on the adjacent bone may occur, marrow infiltration is absent in PSC but occur in PVNS. Calcifications are absent in PVNS.
Preferred treatment is arthroscopic or open removal of the chondral fragments with or without synovial resection. The recurrence rate of intraarticular SC is very low but is higher in extraarticular lesions [1,2]. Biopsy is indicated in case of rapid increase in size, aggravating symptoms or diagnostic uncertainty.
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Primary synovial chondromatosis
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This case involves a 30-year-old female who injured her left knee during swimming, resulting in medial knee swelling and a mildly positive anterior drawer test. MRI images reveal:
X-ray shows focal calcification in the soft tissue shadow above the left patellofemoral joint. Arthroscopy demonstrates multiple solid, nodule-like structures in the joint cavity, suggesting cartilaginous or ossified tissue.
Characterized by synovial thickening, multiple small nodules in the joint, and the presence of calcification or ossification changes. Commonly affects the knee and hip joints and often shows “ring-like or arc-like” calcification patterns. These findings are consistent with the imaging features and the patient’s age in this case.
Usually presents as diffuse low signal lesions on MRI, especially on gradient echo sequences where a marked susceptibility effect (the “rust” or “blooming” sign) is often seen. Calcification is rare in PVNS, making this diagnosis less likely here.
Often found in older adults with preexisting osteoarthritis or cartilage damage. It is non-tumorous in nature. Given the patient’s relatively young age (30 years) and lack of evident joint degeneration, this is less probable.
Consider these if the lesion exhibits rapid expansion or clear signs of bone destruction or invasive behavior. In this case, there is no apparent bone marrow involvement or aggressiveness on imaging, so it is not the leading consideration.
Combining the patient’s age, clinical symptoms, imaging findings (particularly multiple cartilaginous nodules within the joint, along with calcification and ossification), and arthroscopic observations, the most likely diagnosis is Primary Synovial Chondromatosis (PSC).
If uncertainty about the nature of the lesion remains, or if there is rapid enlargement or worsening pain, arthroscopic biopsy is recommended to exclude malignant transformation.
According to current consensus, either arthroscopic or open surgical intervention to remove the cartilaginous fragments and perform partial synovectomy is the primary treatment choice. Postoperative rehabilitation can effectively improve joint function, alleviate pain, and reduce the likelihood of recurrence.
Throughout rehabilitation, closely monitor swelling, pain, and range of motion. If significant pain or increased swelling occurs, promptly modify the training plan and consult a healthcare professional.
Disclaimer: This report is for informational purposes only and does not replace clinical diagnosis or professional medical advice. If you experience any discomfort or have concerns, please consult an orthopedic or rehabilitation specialist for an individualized treatment plan.
Primary synovial chondromatosis
