Popliteal cysts, femoral erosion and degenerative changes in the knee joint.

Positive correlations obtained between the presence of anterior femoral erosion, enlargement of the gastrocnemius-semimembranous bursa and osteoarthritis in the knee suggests that these are all manifestations of a degenerative process developing with increasing age. Popliteal cysts are considered to act as a decompressing factor for raised intraarticular knee pressure. The association of popliteal cysts with femoral erosions suggests that both conditions may be attributed to similar mechanisms, namely, hydrarthrosis and raised joint pressure secondary to degenerative articular disease. The double contrast arthrograms did not reveal the presence of detectable synovial hypertrophy in these cases, suggesting that anterior femoral erosions do not usually result from such a process. The LT/LP ratio (patellar tendon length to length of the patella) did not prove to have any correlative value with the presence of popliteal cysts, femoral erosions or degenerative osteoarthritis.