Background: Osteoarthritis (OA) is a common phenomena in the population. About 80% of the patients more than 55 years of age have reontgenographic signs of OA, while 25% have clinical signs. Eventually OA leads to joint destruction, which may necessitate joint replacement.

Aims: Our goal was to evaluate the synovial reaction in 10 patients who suffered from arthritis and thus underwent total knee replacement operation.

Methods: Ten patients with arthritis of the knee joint (8 with OA and 2 with rheumatoid arthritis (RA) who underwent total knee replacement were evaluated.

Age ranged between 66 and 79 years (mean 71 years). A control group consisted of 6 cadaver knees (mean age 31 years) with no previous history of knee problems.

All the patients in the research group were graded functionally for their knee score by the system of Hospital for Special Surgery Functional Score.

Additional plain X-ray score on a three point scale was performed. During surgery macroscopic changes on the articular surface of all three compartments were recorded on a four point scale. Synovial specimens were taken from each compartment for microscopic examination.

Results: In the research group the average knee score was 54. The macroscopic changes were found predominantly in the medial compartment. No correlation was found between microscopic and histological changes in the synovia. However, a statistically significant correlation between radiological changes in the medial and lateral compartments and macroscopic changes was noted. In the OA patients the ratio of T to B cells was 60% in favor of the B cells, in contrast to RA which was 75% in favor of T cells. In the control group the common find-ing was a thickened sub-synovial fat layer in the patello-femoral (PF) compartment.

Conclusions: Inflammatory reaction in the synovia is graded by the lymphocytic infiltration into the synovia. In OA this is usually mild. However, the predominant reaction is fibrosis. There is no correlation between this fibrotic reaction and overt radiological or macroscopic findings. The thick subsynovial fat layer found in the PF compartment in the control group has not been described previously in the literature and should be the focus of further investigations.