The patella (knee cap)is a small bone located in front of the knee. It protects the knee and connects the muscles in the front of the thigh to the tibia (shinbone).
The patella lies in a groove on the front of the femur called the trochlear groove. As you bend and straighten the knee, the patella will move back and forth inside this groove. This gliding movement is smooth and painless, because of the slippery articular cartilage covering both bones.
Patellofemoral arthritis occurs due to wearing of this cartilage exposing the underlying bone.
This may be due to abnormal movement which occurs when the patella does not fit properly in the trochlear groove of the femur. This leads increased stresses on the cartilage.
Factors increasing the risk of patellofemoral arthritis include obesity, excessive running or weight lifting, previous knee injury, and previous patellar dislocation or subluxation.
Patellofemoral arthritis causes pain in the front of the knee, making it difficult to kneel, get up from a low chair and climb stairs. In advanced cases there is pain even at rest.
Most patients are treated without surgery. This includes:
- Non-steroidal anti-inflammatory drugs like naproxen, and ibuprofen to reduce the pain.
- Strengthening of the quadriceps muscle is useful in patients with maltracking of the patella and weakness of these muscles.
- Avoid prolonged flexion (as with squatting and kneeling) and stair climbing.
- Weight loss is important in overweight or obese patients.
If non surgical treatment fails, several types of surgeries can be used:
Chondroplasty. It is a surgery done through arthroscopy in which the surgeon trims and smooths roughened arthritic joint surfaces. This can be used in mild to moderate cartilage wear.
Realignment. The tissues on either side of the patella are tightened or released to improve the position of the patella in the trochlear groove.
Patellofemoral replacement. The worn down cartilage surfaces are removed and replaced with metal and polyethylene (plastic) implants. The trochlear groove is covered by a metallic surface and a plastic implant is used on the patella. Both parts are held in place by bone cement.