My Boston had this. There is no way to fix this without surgery. The groove that the knee tendon runs in is too shallow and the tendon pops in and out of place. There is no way to deepend that groove to correct it without surgery. Also, as the tendon pops in and out and tends to wear the groove down even more. No to mention they may stop using that leg and the muscles will grow week. The only real option is surgery unless it isn't severe.