Histologically based analyses of the nature and origin of loose bodies occurring in osteoarthrosis have been few, and further study is warranted.
We histologically examined 84 loose bodies and 9 related lesions (synovial membrane nodules) surgically removed from 24 joints of 24 patients with osteoarthrosis.
The 84 loose bodies included 48 chondral loose bodies (type I), 26 osteochondral loose bodies (type II), and 10 osseous loose bodies (type III). The 26 osteochondral loose bodies (type II) could be subdivided into 8 composed of cartilage with enchondral ossification (type IIa), 11 consisting of mature bone covered by cartilage without enchondral ossification (type IIb), and 7 made up of mature bone and partially articular cartilage or hyaline cartilage (type IIc). Synovial membrane nodules could be also divided into three types in the same manner as loose bodies. Many type IIa, type IIc and type III loose bodies and all synovial membrane nodules showed blood vessels containing red blood cells, as well as osteoclasts. The type I and type IIb loose bodies, however, did not show them.
It is well known that loose bodies grow from proliferation of cartilage without blood supply in the joint cavity, and that enchondral ossification is able to develop only under the condition of having a blood supply. As synovial membrane nodules were also classified to the same types as loose bodies and more than half of osteochondral and osseous loose bodies contained blood vessels with red blood cells, the loose bodies were thought to be caught in the synovial membrane and to be modified as the result of a blood supply. Considering the results of this study, the various histologic characteristics of loose bodies in osteoarthrosis resulted from modifications including cartilage proliferation in the joint cavity and enchondral ossification in the synovial membrane.