Presentation
Pain and swelling knee.
Patient Data
Moderately large knee joint effusion with partly calcified intra-articular bodies.
Lateral subluxation of the patellar at least partly secondary to the effusion.
The joint fluid is filled with innumerable small (3 mm) T1 and T2 hypointense bodies filling and expanding the knee joint with an associated joint effusion. A larger lesion in the suprapatellar bursa likely represents a conglomerate lesion. The nodules bow the anterior cruciate ligament posteriorly. The posterior cruciate ligament has a normal appearance.
The cartilage covering the anterior aspect of the lateral femoral condyle is thinned and irregular. No underlying bone marrow abnormality. Small joint margin osteophytes noted.
Both menisci and collateral ligaments are intact.
The patella is subluxed laterally with an associated defect in the inferior cartilage and high T2 signal surrounding a subchondral cyst. Some of the medial retinacular fibers are avulsed from the patella. Patellar alta noted.
Conclusion:
Innumerable loose bodies with some ossification in the joint space, suspicious for synovial osteochondromatosis.
Degenerative changes with osteophyte formation and lateral femoral condyle cartilage thinning and irregularity.
Changes suggestive of previous lateral patella dislocation with degenerative changes in the patellofemoral compartment.
Histopathology
1. "Loose body Lt knee": Two fragments of firm to hard white tissue 35x30x15mm and 25x20x17mm. 2. "Synovial debris left knee": Multiple fragments of small firm white tissue measuring in aggregate 20x20x?2mm.
MICROSCOPIC DESCRIPTION: 1&2. Sections show multiple fragments of cartilaginous nodules composed of lobules of chondrocytes. The chondrocytes show mild atypia and focal binucleation. No mitosis is seen. There are foci of bland ossification. There is no evidence of malignancy.
DIAGNOSIS: Left knee biopsy: Chondromatosis.
Case Discussion
These small bodies in the knee joint as seen in this patient are often termed 'rice bodies'. The differential diagnosis for these includes synovial osteochondromatosis, inflammatory arthritis, and tuberculous infection.
Single joint involvement and the lack of any clinical suspicion of infection made the diagnosis of synovial osteochondromatosis more likely in this patient. The presence of larger calcified bodies on the plain films is pathognomonic for synovial osteochondromatosis.