New growths taking origin in the synovial membrane are rare, and are not usually diagnosed before operation. They are attended with exudation into the joint, and in the case of sarcoma the fluid is usually blood-stained. If the tumour projects in a polypoidal manner into the joint, it may cause symptoms of loose body. One or two cases have been recorded in which a cartilaginous tumour growing from the synovial membrane has erupted through the joint capsule and infiltrated the adjoining muscles. Multiple cartilaginous tumours forming loose bodies are described on p. 544.
Cysts of joints constitute an ill-defined group which includes ganglia formed in relation to the capsular ligament. Cystic distension of bursę which communicate with the joint is most often met with in the region of the knee in cases of long-standing hydrops. It was suggested by Morrant Baker that cystic swellings may result from the hernial protrusion of the synovial membrane between the stretched fibres of the capsular ligament, and the name “Baker's cysts” has been applied to these.
In the majority of cases, cysts in relation to joints give rise to little inconvenience and may be left alone. If interfered with at all, they should be excised.