A buffer (10) for placement in a human knee between the femur and tibia comprises an outer sack (14) formed of a pliable material and having a one-way valve (22), a generally circularly shaped inner ring (16) received within the outer sack (14), and a friction reducing fluid (18) received within the outer sack (14) via the one-way valve (22). The inner ring (16) includes top and bottom surfaces (38,40) angled inwardly with respect to each other, such that the ring (16) is generally concave. The buffer (10) is configured for insertion between the femur and tibia so as to at least partially prevent the bones from contacting each other, which reduces the pain and discomfort associated with a loss of articular cartilage (12). The buffer (10) is arthroscopically inserted in the knee using an especially designed sleeve (20) configured for support of the buffer (10) during insertion.