Relationship between areas of popliteal cysts and radiological damage in rheumatoid arthritis and in osteoarthritis.

Fifty-five patients, (30 Rheumatoid Arthritis (RA) and 25 Osteoarthritis (OA], with knee synovial effusion and popliteal cysts, visualized through arthrograms, were studied. A relationship was sought between radiological findings and area of the cysts, measured through a millimeter grid. Ten radiological parameters were graded and summed up to obtain a "total knee score". A "total geode score" was also obtained by scoring, separately, the geodes. In addition two specific indexes were used--for comparison--the erosive index, modified after Berens and Lin, in RA and the Kelligren's index in OA. In RA a statistically significant, inverse correlation was found between the x-ray scores and the area of the cysts, while such a relationship was not observed in OA. However, only a third of the cysts accounted for the inverse relationship in RA. Furthermore, two control groups of RA and OA patients revealed a striking association between degree of radiological damage and frequency of popliteal cysts. Therefore, the hypothesis that popliteal cysts might have a protective effect against the articular-bone damage in RA, can be held only in few cases.