Patellofemoral pain syndrome
|Patellofemoral pain syndrome|
|Synonyms||Patellar overload syndrome, runner's knee|
|Diagram of the bones of the lower extremity. Rough distribution of areas affected by PFPS highlighted in red: patella and distal femur.|
|Specialty||Orthopedics, sports medicine|
Patellofemoral pain syndrome (PFPS), also known as runner's knee, is a condition characterized by knee pain ranging from severe to mild discomfort seemingly originating from the contact of the posterior surface of the patella (back of the kneecap) with the femur (thigh bone). It is "anterior knee pain involving the patella and retinaculum that excludes other intra-articular and peri-patellar pathology".
The population most at risk from PFPS are runners, cyclists, basketball players and other sports participants. Onset can be gradual or the result of a single incident and is often caused by a change in training regimen that includes dramatic increases in training time, distance or intensity, it can be compounded by worn or the wrong type of footwear. Symptoms include discomfort while sitting with bent knees or descending stairs and generalised knee pain. Treatment involves resting and physical therapy that includes stretching and strengthening exercises for the legs.
- 1 Signs and symptoms
- 2 Causes
- 3 Diagnosis
- 4 Treatment
- 5 Epidemiology
- 6 See also
- 7 References
- 8 External links
Signs and symptoms
- Knee pain - the most common symptom is diffuse peripatellar pain (vague pain around the kneecap) and localized retropatellar pain (pain focused behind the kneecap). Affected individuals typically have difficulty describing the location of the pain, and may place their hands over the anterior patella or describe a circle around the patella (the "circle sign"). Pain is usually initiated when load is put on the knee extensor mechanism, e.g. ascending or descending stairs or slopes, squatting, kneeling, cycling, running or prolonged sitting with flexed (bent) knees. The latter feature 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 with occasional sharp pains.
- Crepitus (joint noises) may be present (but not have relation with pain and function) 
- Giving-way of the knee may be reported
In most patients with PFPS 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 medical cause of PFPS is thought to be increased pressure 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 as it moves through the femoral groove
- Quadriceps muscle imbalance
- Tight anatomical structures, e.g. retinaculum or iliotibial band.
Causes can also be a result of excessive genu valgum and the above mentioned repetitive motions leading to abnormal lateral patellar tracking. Individuals 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.
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 PF subluxation/dislocation) or prolonged repetitive compressive or shearing forces (running or jumping) on the PF joint. The result is synovial irritation and inflammation and subchondral bony changes in the distal femur or patella known as "bone bruises". Secondary causes of PF Syndrome are fractures, internal knee derangement, osteoarthritis of the knee and bony tumors in or around the knee.
Patients can be observed standing and walking to determine patellar alignment. The Q-angle, lateral hypermobility, and J-sign are commonly used determined 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.
Chondromalacia patellae is a term sometimes treated 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 characterized by softening of the patellar articular cartilage. Despite this academic distinction, the diagnosis of PFPS is typically made clinically, 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.
As patellofemoral pain syndrome is the most common cause of anterior knee pain in the outpatient, a variety of treatments for patellofemoral pain syndrome are implemented. Most patients with patellofemoral pain syndrome respond well to conservative therapy.
There is consistent but very low quality evidence that exercise therapy for PFPS reduces pain, improves function and aids long-term recovery. However, there is insufficient evidence to compare the effectiveness of different types of exercises with each other, and exercises with other forms of treatment.
- Type of muscle activity (concentric, eccentric or isometric)
- Type of joint movement (dynamic, isometric or static)
- Reaction forces (closed or open kinetic chain)
The majority of exercise programs intended to treat PFPS are designed to strengthen the quadriceps muscles. Quadriceps strengthening is considered to be the "gold" standard treatment for PFPS. Quadriceps strengthening is commonly suggested because the quadriceps muscles help to stabilize the patella. Quadriceps weakness and muscle imbalance may contribute to abnormal patellar tracking.
If the strength of the vastus medialis muscle is inadequate, the usually larger and stronger vastus lateralis muscle will pull sideways (laterally) on the kneecap. Strengthening the vastus medialis to prevent or counter the lateral force of the vastus lateralis is one way of relieving PFPS. However, there is growing evidence that support more proximal factors play a much larger role than vastus medialis (VMO) strength deficits or quadriceps imbalance. Hip Abductor, Extensor, and External Rotator weakness (particularly gluteus Maximus and Medius) appear to be prevalent in PPS and strengthening in these areas has demonstrated significant symptom reduction in many patients with PPS as well as helped prevent future more serious injuries such as non contact ACL tears in athletes. <Reference: The Influence of Abnormal Hip Mechanics on Knee Injury: A Biomechanical Perspective. Christopher M. Powers. Journal of Orthopaedic and Sports Physical Therapy 40(2), 42-51, 2010.>. <Anterior Cruciate Ligament Injury Prevention Training in Female Athletes: A Systematic Review of Injury Reduction and Results of Athletic Performance Tests. Frank R Noyes, Sue D Barber Westin. Sports Health 4 (1), 36-46, 2012.
Emphasis during exercise may be placed on coordinated contraction of the medial and lateral parts of the quadriceps as well as of the hip adductor, hip abductor and gluteal muscles. Many exercise programs include stretches designed to improve lower limb flexibility. Electromyographic biofeedback allows visualization of specific muscle contractions and may help individuals performing the exercises to target the intended muscles during the exercise. Electrostimulation may be used to apply external stimuli resulting in contraction of specific muscles and thus exercise.
Inflexibility has often been cited as a source of patellofemoral pain syndrome. Stretching of the laterial knee has been suggested to help.
Non-steroidal anti-inflammatory drugs (NSAIDs) are widely used to treat PFPS, however there is only very limited evidence that they are effective. NSAIDs may reduce pain in the short term, overall however, after three months pain is not improved. There is no evidence that one type of NSAID is superior to another in PFPS, and therefore some authors have recommended that the NSAID with fewest side effects and which is cheapest should be used.
Glycosaminoglycan polysulfate (GAGPS) inhibits proteolytic enzymes and increases synthesis and degree of polymerization of hyaluronic acid in synovial fluid. There is contradictory evidence that it is effective in PFPS.
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.
Braces and taping
Knee braces are ineffective in treating PFPS. The technique of McConnell taping involves pulling the patella medially with tape (medial glide). Findings from some studies suggest that there is limited benefit with patella taping or bracing when compared to quadriceps exercises alone.
Low arches can cause overpronation or the feet to roll inward too much increasing load on the patellofemoral joint. Poor lower extremity biomechanics may cause stress on the knees and can be related to the development of patellofemoral pain syndrome, although the exact mechanism linking joint loading to the development of the condition is not clear. Foot orthoses can help to improve lower extremity biomechanics and may be used as a component of overall treatment. Foot orthoses may be useful for reducing knee pain in the short term, and may be combined with exercise programs or physical therapy.
The scientific consensus is that surgery should be avoided except in very severe cases in which conservative treatments fail. The majority of individuals with PFPS receive nonsurgical treatment.
There is no evidence to support the use of acupuncture or low-level laser therapy to treat PFPS. Most studies touting the benefits of alternative therapies for PFPS were conducted with flawed experimental design, and therefore did not produce reliable results.
Specific populations at high risk of primary PFPS include runners, bicyclists, basketball players, young athletes and females.
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