Kneecap pain is very common in football players and powerlifters because of the tremendous pressure put on the kneecaps when they do heavy barbell back squats and deadlifts. Early in my power-bodybuilding
career, during the days following a heavy squatting session, I would experience a condition called the "theater sign" that produced a dull ache around the knee joint, especially after I'd watched a long
movie or sat in a car for an extended period of time.
Through some investigative research I learned the dull ache was caused by abnormal tracking of the kneecap to the outside of the joint. I also learned there are numerous reasons why a kneecap doesn't track (or ride) correctly in the joint. The defect may be con-genital (present at birth). Another reason is pronated feet, where the foot rolls over excessively during walking and in turn causes excessive twisting forces in the legs. Take a look at the heels on your shoes and you will be surprised to see the amount of wear on the outer edges. Problems with pronated feet can be corrected by placing a pair of rigid orthotics (inserts) in a good pair of stable lifting shoes.
Since you are most likely a weight lifter or more specifically a football player / power-lifter, the above suggestions still may not minimize the kneecap pain you are experiencing because of a couple of other reasons. Imbalances in the various quad muscles (vastus lateralis, vastus inter-medius, vastus medialis and rectus femoris) occur during the squatting process. Depending on your squatting technique these muscles do not contract equally.
Yet another reason for kneecap pain is a lack of flexibility in the quads and ham-strings. When these muscles are tight, the kneecap has a tendency to press harder against the femur bones in the thighs as the knees flex and extend. This stress causes an erosion of the kneecap cartilage and pressure on the underlying bone and muscle tissue, which results in a dull ache or pain.
Also your squatting technique can aggravate kneecap pain. I rather suspect you are squatting in the accepted powerlifting style, using a 6-inches-beyond-shoulder-width stance and excessively rotating your feet out to the sides, more than 45 degrees from a forward position. Sure, you can probably lift a lot more weight that way, but at the cost of annihilating your knee joints, so don't be stupid.
To deal with kneecap pain, I suggest that before your squatting session you do 5 to 10 minutes of high-octane aerobic work to break a sweat, such as stationary cycling, Versaclimber, X-Country Skier (Nordic Track), stair stepper or rope skipping. Start slowly and work up to a relatively brisk pace the last minute or so. Then do 3 or 4 reps of PNF (proprioceptive neuromuscular facilitation) stretching for the quads and hamstrings. Hold each stretch for 6 to 8 seconds. The stretches will allow you to work through a greater range of motion when you squat.
Your squat stance should be at least shoulder width to a max of 4 to 6 inches wider than shoulder width. Rotate your feet outward but no more than 45 degrees. Make sure when you are doing back squats that you go slightly below parallel and thus increase quad flexibility.
You must address some questions as well. Did the kneecap pain you are experiencing come from a bigger weight jump and/ or volume increase in your squat sessions than you are accustomed to? Is the supposed kneecap pain in reality an anterior cruciate ligament (ACL) disruption? Finally, are the leg or knee extensions you have been doing the real culprit to your very real knee pain? Many sports-medicine experts say leg extensions are biomechanically dangerous to the knees. While that may be true, I have personally found full-range-of-movement leg extensions, using 260 pounds for 6 sets of 4 reps, resting 10 seconds between sets, to be very therapeutic. If I were going to suggest the use of leg extensions I would advise doing them in the top-half lockout position only and for 15 to 20 reps.
You can minimize kneecap pain through the use of nonsteroidal inflammation drugs such as ibuprofen (Motrin or Advil). Applying ice packs to your knees may alleviate the pain. You might further be kind to your knees by wearing a pair of TK (Tommy Kono) knee bands. Also consider going to an orthopedic specialist who deals with sports-specific injuries such as the one you have. Good luck!