Patellofemoral pain syndrome (PFPS; not to be confused with jumper's knee) is knee pain as a result of problems between the kneecap and the femur. The pain is generally in the front of the knee and comes on gradually. Pain may worsen with sitting down with a bent knee for long periods of time, excessive use, or climbing and descending stairs. While the exact cause is unclear, it is believed to be due to overuse. Risk factors include trauma, increased training, and a weak quadriceps muscle. It is particularly common among runners. The diagnosis is generally based on the symptoms and examination. If pushing the kneecap into the femur increases the pain, the diagnosis is more likely. Treatment typically involves rest and rehabilitation with a physical therapist. Runners may need to switch to activities such as cycling or swimming. Insoles may help some people. Symptoms may last for years despite treatment. Patellofemoral pain syndrome is the most common cause of knee pain, affecting more than 20% of young adults. It occurs about 2.5 times more often in females than males.
Signs and symptoms The onset of the condition is usually gradual, although some cases may appear suddenly following trauma. The most common symptom is diffuse vague pain around the kneecap (peripatellar) and localized pain focused behind the kneecap (retropatellar). Affected individuals typically have difficulty describing the location of the pain. They may place their hands over the anterior patella or describe a circle around the patella. This is often called the "circle sign". Pain is usually initiated when weight is put on the knee extensor mechanism, such as when ascending or descending stairs or slopes, squatting, kneeling, cycling, or running. Pain during prolonged sitting is sometimes termed the "movie sign" or "theatre sign" because individuals might experience pain while sitting to watch a film or similar activity. The pain is typically aching and occasionally sharp. Pain may be worsened by activities. The knee joint may exhibit noises such as clicking. However, this has no relation to pain and function. Giving-way of the knee may be reported. Reduced knee flexion may be experienced during activities.
Causes In most people with patellofemoral pain syndrome an examination of their history will highlight a precipitating event that caused the injury. Changes in activity patterns such as excessive increases in running mileage, repetitions such as running up steps and the addition of strength exercises that affect the patellofemoral joint are commonly associated with symptom onset. Excessively worn or poorly fitted footwear may be a contributing factor. To prevent recurrence the causal behaviour should be identified and managed correctly. The cause of pain and dysfunction often results from either abnormal forces (e.g. increased pull of the lateral quadriceps retinaculum with acute or chronic lateral patellofemoral subluxation/dislocation) or prolonged repetitive compressive or shearing forces (running or jumping) on the patellofemoral joint. The result is synovial irritation and inflammation and subchondral bony changes in the distal femur or patella known as "bone bruises". The medical cause of PFPS is thought to be increased pressure or on the patellofemoral joint. There are several theorized mechanisms relating to how this increased pressure occurs:
Increased levels of physical activity Malalignment of the patella or abnormal patellar tracking as it moves through the femoral groove. People with genu valgum have larger than normal Q-angles causing the weight-bearing line to fall lateral to the centre of the knee causing overstretching of the MCL and stressing the lateral meniscus and cartilages. Quadriceps muscle imbalance Tight anatomical structures, e.g. retinaculum or iliotibial band Excessive genu valgum and repetitive motion Patellofemoral pain syndrome can also result from fractures/trauma, internal knee derangement, osteoarthritis of the knee, and bony tumors in or around the knee.
Diagnosis
Examination People can be observed standing and walking to determine patellar alignment. The Q-angle, lateral hypermobility, and J-sign are commonly used to determine patellar maltracking. The patellofemoral glide, tilt, and grind tests (Clarke's sign), when performed, can provide strong evidence for PFPS. Lastly, lateral instability can be assessed via the patellar apprehension test, which is deemed positive when there is pain or discomfort associated with lateral translation of the patella. Various clinical tests have been investigated for diagnostic accuracy. The Active Instability Test, knee pain during stair climbing, Clarke's test, pain with prolonged sitting, patellar inferior pole tilt, and pain during squatting have demonstrated the best accuracy. However, careful consideration is still needed when using these tests to make a differential diagnosis of PFPS. Individuals with PFP may be exhibit higher pain level and lower function. Magnetic resonance imaging rarely can give useful information for managing patellofemoral pain syndrome and treatment should focus on an appropriate rehabilitation program including correcting strength and flexibility concerns. In the uncommon cases where a patient has mechanical symptoms like a locked knee, knee effusion, or failure to improve following physical therapy, then an MRI may give more insight into diagnosis and treatment.
Classification PFPS is one of a handful of conditions sometimes referred to as runner's knee; the other conditions being chondromalacia patellae, iliotibial band syndrome, and plica syndrome. Chondromalacia patellae is a term sometimes used synonymously with PFPS. However, there is general consensus that PFPS applies only to individuals without cartilage damage, thereby distinguishing it from chondromalacia patellae, a condition with softening of the patellar articular cartilage. Despite this distinction, the diagnosis of PFPS is typically made based only on the history and physical examination rather than on the results of any medical imaging. Therefore, it is unknown whether most persons with a diagnosis of PFPS have cartilage damage or not, making the difference between PFPS and chondromalacia theoretical rather than practical. It is thought that only some individuals with anterior knee pain will have true chondromalacia patellae.
Differential diagnosis
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