A double patella-like condition secondary to synovial osteochondromatosis
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To our knowledge, this is the first case of synovial osteochondromatosis in a patient presenting with a double patella-like condition. The true duplication of the patella, which is called double patella, is extremely rare. In our case, the operative and histopathological findings showed that the double patella-like condition was secondarily induced by synovial osteochondromatosis. Synovial osteochondromatosis should be considered as a differential diagnosis for congenital double patella.
KeywordsOsteochondromatosis Synovial osteochondromatosis Chondromatosis Double patella Knee
True duplication of the patella, which is called double patella, is extremely rare . To our knowledge, the total number of reported cases is only 15. When a case with double patella is examined, bipartite patella, patella fractures, and postoperative morphological changes should be considered in differential diagnosis.
Congenital duplication of the patella is called double patella . To our knowledge, double patella is extremely rare, and the total number of reported cases is only 15.
When a case with double patella is examined, bipartite patella, patella fractures, and postoperative morphological changes should be considered in differential diagnosis. Bipartite patella is more common than double patella. It has been hypothesized that bipartite patella is due to the failure of the ossification nuclei to merge. The presence of 2 distinct and separate ossification centers may be the cause of double patella. Double patella is a congenital malformation involving 2 independent cartilaginous centers that each give rise to a patella, complete with its own aponeurotic expansion and patella tendon . MRI is very important to accurately evaluate the anatomical aspects and confirm the diagnosis of a double patella . The available literature showed that in the majority of cases with double patella, the position of the second patella is superior or inferior compared with that of the normal patella, although the position of the second patella in relation to the first is unimportant. In some cases with congenital double patella, an association between the formation of double-layer patella, which is the same type as ours, and multiple epiphyseal dysplasia was described [3, 4]. Only 1 isolated case of traumatic double patella has been reported . Furthermore, a case with unusual double patella, which had been formed despite surgical treatment of a patella sleeve fracture, has been reported . However, in these cases, the possibility of congenital double patella could be excluded on the basis of medical history and radiographic features.
In our case, the histological findings showed the features of synovial osteochondromatosis. In addition, the multifocality of small intraarticular loose bodies was consistent with this feature. We found the sites of active cartilaginous metaplasia in the synovial membrane on the patella-like loose body. Transitional lesions with both active intrasynovial proliferation and free loose bodies were confirmed, and, thus this case was diagnosed as second-phase synovial osteochondromatosis . However, it is extremely rare for synovial osteochondromatosis to grow to the size of the patella, as in this case. It has been recently reported that the expression of the fibroblast growth factor (FGF) receptor was observed specifically in synovial osteochondromatosis . FGFs may cause proliferative changes, such as osteophytes in osteoarthritis . Although the cause of synovial osteochondromatosis is still controversial, it could be speculated that the cytokines induced by osteoarthritis, such as FGFs, activated the matrix synthesis of synovial osteochondromatosis in the patellofemoral joint. Thus, synovial osteochondromatosis should be considered as a differential diagnosis for congenital double patella.
To our knowledge, this is the first case of synovial osteochondromatosis in a patient presenting with a double patella-like condition. Synovial osteochondromatosis should be considered as a differential diagnosis for congenital double patella.
Written informed consent was obtained from the parent of the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.
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