PCNA and synovial chondromatosis: Although not used in this case, Saotome et al. reported that in immunological testing of PCNA in surgically removed loose bodies, 100% of primary cases (53/53) were PCNA positive, compared to 45.6% (15/37) of secondary cases, indicating that a negative result suggests secondary synovial osteochondromatosis [8].` Robinson et al. found that cells around primary chondroid nodules expressed PCNA and FGF9, with FGF9 playing a role in cell proliferation, differentiation, and movement necessary for normal cell development and tissue repair [6].