June 15, 2007
The Patello-Femoral Joint
by Anne Kosacheff, YKHC Physical Therapist
The patello-femoral joint is made up of two bones: the patella (a.k.a. the “kneecap”) and the femur (your thigh bone). The patella is encapsulated (surrounded) by the patellar “tendon,” and rides in a groove at the far end of the femur. It acts like a pulley, improving the mechanical ability of the quadriceps muscles as they extend the knee. The back of the patella is covered with a layer of cartilage, as is the front of the groove on the femur. This allows the bones to glide smoothly and quietly as the knee bends and extends.
The patella is a sesamoid bone. This means it is not directly connected to another bone with ligaments. It is the largest sesamoid bone in the body. Many of us have smaller sesamoid bones in the flexor tendons of our toes (and sometimes our thumbs) which also function as pulleys to improve the mechanics of the tendons.
In a “normal” knee, the patella floats in the femoral groove, cushioned by a thick liquid called synovial fluid, and supported by the patellar tendon. If you recall from the previous article on the knee, the quadriceps are made up of four muscles which cover the entire front of your thigh. All four quadriceps muscles connect to the patellar tendon, and direct the movement of the joint. Remember the patella is not directly connected to another bone by ligaments, and is just floating in space.
If the quadriceps muscles are all flexible, and balanced in strength, the patella will ride in the femoral groove without any problems. If, however, the lateral (outside) quadriceps are tight or inflexible, this will pull the patella laterally (to the outside), and increase the pressure on the lateral patello-femoral joint. Over time, this can lead to a condition called “patello-femoral syndrome,” and progress to gradual degeneration of the cartilage, or chondromalacia. These conditions can be very painful and debilitating, and are very difficult problems to treat. The best treatment is prevention—keep your quads flexible and the VMO (vastus medialis obliqus) strong.
The VMO is just above your kneecap to the inside of your thigh. If you extend your knee all the way, it should pop out. If it doesn’t, get it stronger! One-legged mini squats with a concentrated effort to keep your knee strong and stable, and the VMO contracted throughout the movement, will improve the strength and co-ordination of your knee and your patello-femoral joint. Don’t forget to stretch after you exercise! Tight quadriceps cause increased pressure in the patello-femoral joint, and we all know what happens with increased pressure in the joints over time—degeneration! These simple stretches and exercises can prevent many of the problems associated with degenerative changes in the patello-femoral joint.
To see previous articles on the knee, go to www.ykhc.org and click on the Messenger link. Be sure to look for next month’s article on the ankle.