Kneecap (Patellar) Problems
Introduction
Several problems can affect the kneecap (patella). These include a condition called chondromalacia patellae--in which cartilage under the kneecap softens--and kneecap dislocation. Although kneecap problems can affect anyone of any age, chondromalacia patellae occurs most often in young adults.
Anatomy
Normally, the kneecap glides in a groove formed by the upper leg bone (femur). This natural guideway is called the patellofemoral groove.
If the cartilage that lies underneath the kneecap softens, the kneecap may rub against the lower end of the femur instead of gliding smoothly across it. Bone misalignment or muscle imbalance can also cause problems. The thigh muscle (quadriceps) controls knee motion and keeps the patella on track in the patellofemoral groove. If bones that meet in the knee aren't lined up just right or the quadriceps muscle is imbalanced, the patella may be pulled to one side as it moves along the patellofemoral groove. Such an "off-track" patella can eventually damage the underlying cartilage.
The shape of the patellofemoral groove can be a problem too. If one side is shallower than normal, the kneecap may slip out of the groove, resulting in a dislocation.
Causes
Osteoarthritis or just the wear and tear of normal aging can soften cartilage under the kneecap. In addition, some people are born with slightly misaligned bones, imbalanced quadriceps muscles, or shallow patellofemoral grooves that increase the chances of cartilage damage or knee dislocation. A patellar dislocation can also occur when a person twists his knee, changes direction, or suffers a direct blow to the knee while playing sports.
Symptoms
A dislocated knee may be signaled by a popping noise or feeling when the injury occurs. The knee may buckle or "give way" when you walk. You may experience tenderness, swelling, and bruising around the joint.
Diagnosis
Arthritis and other Joint Problems, a history and physical exam will help your doctor make the diagnosis. An x-ray will detect signs of underlying arthritis and show if your kneecap is sitting properly in the patellofemoral groove. An MRI scan can detect cartilage breakdown.
Treatment
Chondomalacia patellae: To relieve pain, your doctor may recommend an ice massage.
Your doctor may recommend low-impact exercises that strengthen the thigh muscle (quadriceps).
If these treatments fail to alleviate symptoms, you'll need arthroscopic surgery. During the operation, the surgeon may "shave" the patella (removing damaged pieces of cartilage) or cut ligaments so the kneecap can move more easily. For more information on this type of surgery, see the section on Arthroscopy.
If you're one of the few people who have severe chondromalacia patellae, you may need more extensive surgery to fix misaligned bones. For this operation, you may need to spend a night or two in the hospital.
Patellar dislocation: This problem is corrected by physical manipulation of the patella from the outside, or by surgery. In either case, you may need a cast or brace for 6 to 8 weeks.
