None — Knee Function
The knee is a complex joint made of three bones: the lower end of the femur (thighbone), the upper end of the tibia (shinbone) and the patella (knee cap). The ends of the bones are covered in a layer of cartilage that protects the bones and provides lubrication. Four ligaments (tough bands of tissue) connect and hold the bones in place: the anterior cruciate ligament (ACL), posterior cruciate ligament, and two collateral ligaments.
The patella, located in the front of the knee, protects the joint. It is held in place by two tendons. The patellar tendon attaches the patella to the shin bone. The quadriceps tendon attaches the top of the knee cap to the thigh muscles. When the knee is bent or straightened, the underside of the kneecap glides over a V-shaped notch in the femur.
Patellofemoral Pain Syndrome
The American Academy of Orthopaedic Surgeons reports, in 2003, there were 19.4 million visits to physician's offices for knee pain, making it the most common complaint seen by orthopedic surgeons. One of the most common causes of knee pain is patellofemoral pain syndrome (PFPS), also known as anterior knee pain, or runner's knee. Researchers estimate 25 percent of physically active Americans have PFPS. Women are affected more often than men.
In PFPS, the kneecap doesn't move properly over the end of the femur, causing wear on the cartilage. Eventually, when a section of cartilage softens and erodes, the bones rub together. The problem can occur if the kneecap is out of alignment, the muscles that hold the kneecap in place are unbalanced or the knees are stressed from excessive movement (like jumping and twisting).
The main symptom associated with PFPS is pain in the front of the knee. The pain is especially prevalent when climbing or descending stairs, getting up from a seated position or sitting with knees bent for an extended period. Tracy Dierks, Ph.D., Physical Therapy Researcher with IU School of Health and Rehabilitation Services in Indianapolis, IN, says runners with PFPS often complain of knee pain that starts sometime during the run and intensifies until they stop running.
The Hip Connection
Dierks says one of the most common reasons for PFPS appears to be a weakness in the hip muscles. The muscles on the side of the hip are responsible for keeping the femur in place. When those muscles are weak, the femur may rotate inward, preventing the patella from gliding over the track.
The researchers are studying the role of hip muscle strengthening exercises for patients with PFPS. Ten patients so far have completed the pilot program. Dierks says, prior to the exercise intervention, all the participants were forced to stop during a run because of knee pain. After the exercise program, all the runners were able to continue running without pain.
Research compiled and edited by Barbara J. Fister
For general information on knee problems: