What is Patellofemoral Pain Syndrome?

Patellofemoral pain syndrome (PFPS) is a condition where the kneecap (patella) doesn’t track properly over the thigh bone (femur). It causes excess friction and pain, usually in the inner margin of the knee, behind or below the kneecap.

Anatomy of the Patellofemoral Joint

The kneecap (patella) normally rides within a groove on the thigh bone (femur) called a ‘femoral condyle’, which forms the patellofemoral joint. As the knee bends and straightens the patella slides within a slot or groove on the femur. The patella moves in many directions within this groove to provide efficient movement up and down, side-to-side, rotation, and tilting without much friction. The bone surfaces are covered with cartilage to make joint movement smooth. It therefore can be said that the patella acts as a fulcrum, or a lever to the big muscles at the front of the thigh called the quadriceps that come down to attach to the knee. These thigh muscles are called ‘the quads’ because they consist of four muscles. With PFPS an imbalance in these muscles exists, usually the lateral muscle (vastus lateralis) over power the inner medial muscle (vastus medialis). This therefore pulls the patella out of the groove and there is more than normal contact and friction with the thigh bone (femoral condyle).

Differential Diagnosis

PFPS is often misdiagnosed for Chondromalacia patella and therefore correct diagnosis is critical. Chondromalacia patella is a chronic, degenerative condition that affects the underside of the kneecap (patella). The underside starts to soften (‘malacia’ means ‘soften’) and when it rubs on the femur it causes pain. It is thought that Chondromalacia patella is the sequelae of long term PFPS, i.e. PFPS may progress to Chondromalacia over time. Misdiagnosis occurs when a complete examination is not performed. As the two conditions present with almost identical signs and symptoms, an x-ray is necessary to differentiate between the two. A special view of the knee will show the underside of the patella that allows a look at the softening of the cartilage. A classis presentation on x-ray called the ‘crab meat’ sign (the cartilage looks like crab meat!) is indicative of Chondromalacia patella, and is only truly diagnosed when this sign is positive on x-ray.

Causes

Overuse – The repetitive bending and straightening of the knee that occurs in running, hills or stair use, may lead to the disorder because of the increased pressure points between the patella and femur when the knee is bent. Constant bending motion, especially on the weighted leg can irritate the patella.

Alignment – The quadriceps’ alignment between the hip and the knee (the Q angle) is thought to affect patella tracking. Patients with a larger than normal Q angle (greater than 20 degrees) may be more susceptible to patellofemoral pain because the patella has a tendency to track more laterally (to the outside). The Q angle of growing female athletes enlarges as the pelvis widens during the maturing process, increasing the risk for patellofemoral pain.

Muscular weakness – A weakness or strength imbalance of the quadriceps muscles may alter the tracking of the patella.

Muscular tightness – Tight muscles and tendons may also affect patellar tracking. The muscular structures that cause movement in the knee and hip must be flexible. If any one muscle or muscle group is tighter than the rest, patellar instability can occur.

Flat feet (excessive foot pronation) – Patients with little or no arch in the foot (see picture right) are also likely candidates for patellofemoral pain. As the foot rolls inward, the normal mechanics of the patellofemoral joint are altered causing this excess friction.

Signs and Symptoms

• Anterior pain or pain under or around the kneecap
• Worse with activities that load the joint (knee bending) – i.e. walking up stairs, running, squatting
• Knee cracks or needs to be cracked to decrease the pain
• Mild swelling especially post exercise
• Tender patella (kneecap) margins
• Wasting of the muscle on the inside of the front of the thigh (VMO)
• Patient cannot sit for long periods of time without straightening out the knees to make it crack. This is called the “Theatre Sign” – patients must sit in the aisle seat at the theatre so that they can straighten out the knee

Treatment

Treatment of PFPS involves several steps to correct the positioning and tracking of the kneecap and biomechanics of the lower leg. Physiotherapists since the 1980’s have been utilizing a proven method for treatment of PFPS based around the specific retraining of the VMO  (vastus medialis, a quadriceps muscle), with patella taping and correction of other biomechanical factors.

During your physiotherapy sessions, treatment may include ice, ultrasound, TENS, iontophoresis, patella taping, patella mobilisations, and stretching and massaging of the tight outer thigh muscles. Correction of biomechanics by improving muscle length, strength of thigh muscles, and correction of foot placement on walking through gait re-education and/or prescription orthotics will also be highly important. As part of all rehabilitation programs a specific home exercise program with exercises and stretches will be given.

Treatment for PFPS usually follows an active rehabilitation program, meaning the athletes can often continue to participate in their sports/activities provided they dedicated to the exercise program and are able to either tape or brace the knee during activity. Bracing/taping usually involves manually positioning the kneecap in its correct position until the strength of the muscles has regain proper function.

This is the most common presenting knee condition to physiotherapy practice that can affect one or both knees. It responds well to treatment but requires adherence and persistence. Left untreated, or unresponsive to treatment, arthritis with eventually result.