Anterior Knee Pain

Anterior knee pain, or pain in the front of the knee, is a very tough problem for patients to live with and orthopedic surgeons to treat.  There can be a number of different sources for anterior knee pain.  Patellar tendinitis, prepatellar bursitis, Osgood Schlatter, plica syndrome, fat pad syndrome, cysts and benign tumors are just a handful of different causes of the pain.  For most people, however, their pain is related to the patella, or knee cap, and the femur, or thigh bone, and the articulation of the patellofemoral joint.

The patella is a sesamoid bone, meaning it develops in a tendon.  It essentially is the transition between the quadriceps tendon and the patella tendon.  As a part of the quadriceps muscle, the patella, increases the mechanical advantage of the muscle to help  straighten out, or extend, the knee.  At least 30% of your strength to extend your knee can be lost if your patella is removed.

The patella courses over the cartilaginous portion of the end of the femur called the trochlea.  As your knee straightens and bends, the patella articulates at different positions along the trochlea.  Ideally, the trochlea is rather grooved essentially creating a V-shape.  The patella, ideally, is similarly shaped to sit in that groove.  Variations in the groove of trochlea and matching surface of the patella can lead to abnormalities and pain.  The abnormalities can result in abnormal motion, sometimes so extreme, the patella dislocates.  Also, since our hips are wider than our knees, the quadriceps muscles come down to the knee at an angle.  At the knee, the direction of the muscle changes as the patellar tendon goes to the tibia to insert on the tibial tubercle.  We call this angle the Quadriceps angle, or Q angle.  Since muscles usually want to pull in a straight line, this angle naturally makes the knee want to slide out to the side.

These factors can lead to abnormal or excessive pressures involving the patellofemoral joint.  This can lead to pain and eventually arthritis.  To add insult to injury, the patellofemoral joint can experience about 6 times your body weight with bending.  This only aggravates the situation.

Written by  Dr. Brimacombe, MD 

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