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Patellofemoral Arthritis
DESCRIPTION
Patellofemoral arthritis occurs when the articular cartilage along the trochlear groove and on the underside of the patella wears down and becomes inflamed. When cartilage wears away, it becomes frayed, and when the wear is severe, the underlying bone may become exposed. Moving the bones along this rough surface is painful.
CAUSES
The patella is a small bone located in front of your knee joint — where the thighbone (femur) and shinbone (tibia) meet. It protects your knee and connects the muscles in the front of your thigh to your tibia.
The patella rests in a groove on top of the femur called the trochlear groove. When you bend and straighten your knee, the patella moves back and forth inside the groove.
The ends of the femur, trochlear groove, and the undersides of the patella are covered with a slippery substance called articular cartilage. This helps the bones glide smoothly along each other as you move your leg.
Dysplasia occurs when the patella does not fit properly in the trochlear groove of the femur. Because of this, when the knee moves, there are increased stresses on the cartilage. This begins to wear the cartilage down.
Maltracking/Dislocation
When the kneecap does not run correctly in its groove the cartilage gets damaged leading to early arthritis. Patients with multiple kneecap dislocations are at risk of developing early patellofemoral arthritis
Kneecap Fracture
Patellar (kneecap) fractures often damage the articular cartilage that covers and protects the underside of the bone. Even though the broken bone heals, the joint surface may no longer be smooth. There is friction when the patella moves against the joint surface of the femur. Over time, this can lead to arthritis.
Dysplasia
Dysplasia occurs when the patella does not fit properly in the trochlear groove of the femur. Because of this, when the knee moves, there are increased stresses on the cartilage. This begins to wear the cartilage down.
This x-ray taken from above the knee shows dysplasia that has developed into severe arthritis. There is no joint space remaining in the knee on the left. On the right, the trochlear groove has become deformed.
SYMPTOMS
The main symptom of patellofemoral arthritis is pain. Because the patellofemoral joint is in front of the knee, you may have pain in this area. The pain can be present at rest or with no activity at all. Most of the time, however, it is brought on by activities which put pressure on the kneecap, such as kneeling, squatting, climbing stairs, and getting up from a low chair.
In addition, you may experience a crackling sensation called crepitus when you move your knee. Crepitus is sometimes painful and can be loud enough for other people to hear. When the disease is advanced, your kneecap may get stuck or “catch” when you straighten your knee.