What is the reason for grating sound from the knee after an ACL reconstruction?

Q: I ruptured the anterior cruciate ligament (ACL) in my left knee 10 years back. A tendon from the same knee was put to replace the ligament using arthoscopy. I haven't had any major problems but at the same time I haven't worked a lot to bring the left thigh muscles back to its original shape. The left thigh muscle is still weaker than the right one. I have a desk job. I have bought a cross-trainer and have been using it for about 5 minutes everyday in the morning at a slow and steady pace. While, working on the cross trainer, I have noticed that I get a lot of the knuckle breaking sounds from my operated left knee. I guess the two bones are rubbing against each other. I do not have any swelling or pain in the knee. What is the reason for the sound? Are my thigh muscles weak? Will this sound reduce as I continue exercising? Should I continue the exercise or not? What exercises do you recommend for me to build the left thigh muscles back?

A:The grating sound emanates from the knee cap joint. A sizeable proportion of patients who have undergone ACL reconstruction with the patellar tendon (BTB) develop patello femoral pain and crepitus. You are lucky if you don't have pain. Again a sizeable portion of the normal population also develop arthritis in the same patello femoral joint from mal alignment related overload, age etc. This again settles down with the right kind of exercises. You should have a balance of stretching, isotonic exercises and avoid overdoing them.The sound may decrease as muscles build up due to perhaps a rebalancing of the muscles but may not be abolished given that arthrosis has probably developed under the knee cap. You need not stop them.