By Dr. J. Halbrecht, MD, Othopaedic Surgeon, San Francisco, USA

Patella (Knee Cap)

The patella is a relatively small bone in the front of the knee that is embedded in the quadriceps (thigh muscle) tendon and acts to increase the biomechanical leverage of the quadriceps. The patella slides in a groove on the femur as the knee flexes and extends. Because the patella 'floats' within the substance of the quadriceps, proper tracking of this bone in the femoral groove is dependent on proper muscle balance to maintain a central position. Congenital anatomic factors such as the shape of the patella also influence this tracking. Also, because of the location of the patella, it is subject to higher stresses than other joint surfaces. So, despite having a thicker cartilage lining than any other bone, it often begins to wear out before other parts of the knee.

Chondromalacia Patella

What is it: This is a latin term meaning softening or break down of cartilage. Chondromalacia of the patella is one of the most common problems to affect the knee, and is particularly common in running and jumping athletes. Chondromalacia usually begins as softening of the otherwise very resilient cartilage and proceeds to cracking and eventually complete loss of the cartilage lining beneath the patella.

What are the symptoms: Pain in the front of the knee, crunching under the knee cap, swelling in the knee, symptoms increase with stair climbing, or prolonged sitting.

Early on, symptoms may simply be mild aching in the area of the patella due to the loss of integrity of the cartilage and a diminished ability for it to protect the underlying bone. Nerve fibers in the bone sense the increased stresses and pain occurs. In later stages of chondromalacia, the cartilage surface of the patella becomes roughened as pieces of cartilage begin to break off. This roughened surface causes a crunching sound under the patella and can lead to swelling of the knee. Symptoms will aggravate as small fragments of cartilage continue to break off and irritate the joint.

Treatment Options: Initial treatment focuses on physical therapy techniques for strengthening the muscles around the patella to balance the patella tracking and more evenly distribute forces on the patella. In severe cases, ice and antiinflammatory medicine will be necessary to calm down inflammation before exercises can be initiated. Occasionally, a patella tracking brace or special taping techniques will be utilized. Most patients will improve with non surgical management. In resistant cases arthroscopic surgery can be very helpful in smoothing out the roughened surface of the patella, removing any loose fragments of cartilage, and realigning the patella. Many cases of chondromalacia can be helped by a mini arthroscopy performed under local anesthesia in the office.

Patella Malalignment

The normal patella should track straight down the middle of the femoral groove. There are varying degrees of abnormal tracking, or patella malalignment. In mild cases of malalignment the patella is simply tilted in the groove, leading to increased pressure on the downward tilted side of the patella. Think of this as being like a tire out of alignment, where a subtle imbalance can quickly lead to uneven wear of the tire treads. In more severe cases, the patella will actually sublux, or slide partially out of the groove. In the most severe cases of malalignment, the patella will actually completely dislocate.

Proper tracking of the patella is influenced by many factors. Proper muscle balance is important and is one of the few factors that we can control. Usually the patella wants to sublux toward the outside of the knee (lateral). Strengthening the inside muscle (the VMO) can act to counter this tendency.

Tracking is also influenced by the anatomical shape of your patella, femoral groove, the angle your knee makes with your hip (knock knees) and even the position of your foot (pronation). The hip knee angle is important because the patella is embedded in the quadriceps tendon which originates at the hip and attaches at the knee. The more knock kneed someone is, the more of an angular pull occurs on the patella every time the quadriceps contracts. This angle is called the "Q" angle in medical terminology. In severe cases of angulation (a high "Q" angle) surgery can be performed to correct the "Q" angle. The shape of the patella and femoral groove cannot be easily modified.

Increased pronation of the foot (flat feet) can influence the tracking of the patella.This occurs because the rotation of the rest of the leg is affected by the way the foot contacts the ground. In patients with increased pronation, use of shoe orthotics (arch supports) may help patella tracking by modifying the rotation of the knee.

Surgical Treatment

For severe cases of patella malalignment surgery may be necessary. This is a new all arthroscopic method for realigning the patella (knee cap). Traditionally, patients with an unstable patella are subjected to an extensive operative procedure that involves making an incision to tighten the inner ligaments controlling the tracking of the patella.

An even newer technique for treatment of some types of patella instability is the use of a heated probe to shrink the stretched patella ligament or retinacullum. This method eliminates the need for any incisions or sutures in the knee. This method is currently being utilized for patients with less severe instability of the patella (called subluxation). With this method, rather than using sutures to tighten the ligaments and realign the patella, the stretched ligaments are heated which shrinks and tightens them.

Patella Dislocation

The patella is held in place by thin ligaments that act as check reins, keeping it from coming out of the femoral groove, while the muscles provide the fine tuning. With severe twisting maneuvers or direct trauma, the patella can dislocate, tearing these ligaments and coming completely out of place. Sometimes the patella will spontaneously reduce, sometimes a trip to the emergency room is necessary. Because the ligaments have torn, the patella usually will continue to be off balance even after the dislocation is reduced. This will lead to abnormal tracking and increased risk of redislocation in the future. In addition, small fragments of cartilage are often chipped off as the patella dislocates, and can cause damage to the joint as they float around.

Numerous studies have shown that patients who have dislocated their patella do not do well in the long term, and suffer either repeated dislocations or develop degeneration under the knee cap due to the now abnormal tracking. Recommended treatment is for immediate arthroscopic evaluation to remove the loose chips and to repair the torn ligaments and rebalance the patella tracking.