Lock, Pop, grind and no it's not a dance move
Knee problems associated with locking, grinding, and popping
Since u are not a firecracker or a soda can you can be forgiven to think that popping sounds in the knee is an indication that something is wrong. The truth though is that popping sounds occurs naturally when movement occurs in the joints. A slight misalignment in the knee cap (Patella) or the movement of different ligaments across the joint can give a popping sound. If it is a case however where this sounds is accompanied by pain then one has reason for concern. Grinding and locking are better indicators of a physiological disorder in the knee, but the pain factor is also very important in these cases.
As stated earlier unless accompanied by pain then a popping sound is perfectly normal, however if there is pain then it is often an indication that the anterior cruciate ligament (ACL) has been torn. ACL maybe torn in two pieces or there might just be a partial rip, the extent of damage will determine treatment implemented. If ACL is ripped apart then surgery followed by rehab will be necessary, however for partial tears one just need to stay away from physical activities for awhile as the injury will self heal. A popping sound in conjunction with pain may also be an indication of another condition known as Discoid Lateral Meniscus or "popping-knee syndrome". This occurs when there is an abnormal shaped meniscus in the knee joint. This can usually be treated by conservative methods such as stretching, however if pain persist arthroscopic surgery though optional might be required.
When cartilage degeneration occur the bones of the knee joint tends to grind together causing immense pain and producing a grinding sound. This is usually caused by rheumatoid arthritis which rarely occurs in individuals under 50. The degeneration caused by rheumatoid arthritis is irreversible. Patella tendonitis (runner's knee) can also cause degeneration of cartilage and thus the pain and grinding sound. Runner's knee is the most likely cause of the grinding sound in the knees of young individuals particularly athletes. Fortunately in this case the degeneration is reversible, as resting the knee and doing exercises that strengthen the quadriceps muscles will see the knee return to normal over time.
You may find yourself playing a game of basketball and suddenly being unable to flex a leg or you may be kneeling then find that you are unable to straighten your leg to get up; when this happens you are experiencing a phenomenon known as locking which can be quite painful. There are generally two type of locking, pseudo-locking and true locking. Pseudo locking is a reaction to pain and functions like a kill switch where the knee locks into position when tension in the area becomes excessive. True locking results from physiological problems in the knee, causing the knee become rigid, unable to bend or extend. True locking usually occurs when torn cartilage or bone fragment (resulting from a bone disorder known as Osteochondritis Dissecans) becomes jammed between joints surfaces restricting movement of the knee joint. When a muscle on the inside of the thigh becomes weak and fragile or the outer muscles tighten they can throw off alignment of the knee cap, which also lead to locking.
Locking can easily be corrected by resting as movement will eventually return to joints. In the case of true locking the problem can only be completely nullified by orthopaedic surgery to remove loose bone or cartilage.