Patellofemoral pain

INTRODUCTION — Patellofemoral pain (PFP) is a frequently encountered overuse disorder that involves the patellofemoral region and often presents as anterior knee pain. PFP is characterized by pain around or behind the patella that is aggravated by one or more activities that involve loading the patellofemoral joint during weight bearing on a flexed knee, and that cannot be attributed to another discrete intra-articular (eg, meniscus tear) or peripatellar (eg, patellar tendinopathy) pathology.

The pathophysiology, diagnosis, and management of PFP are reviewed below. Knee pain and its many other causes are discussed separately, including the following topics:

●Assessment of knee pain in adults (see "Approach to the adult with knee pain likely of musculoskeletal origin" and "Approach to the adult with unspecified knee pain")

●Assessment of knee pain in children (see "Approach to acute knee pain and injury in children and skeletally immature adolescents" and "Approach to chronic knee pain or injury in children or skeletally immature adolescents")

●Peripatellar conditions (see "Patella fractures" and "Recognition and initial management of patellar dislocations" and "Knee bursitis" and "Osgood-Schlatter disease (tibial tuberosity avulsion)" and "Plica syndrome of the knee")

●Knee ligament injuries (see "Anterior cruciate ligament injury" and "Posterior cruciate ligament injury" and "Medial (tibial) collateral ligament injury of the knee" and "Lateral collateral ligament injury and related posterolateral corner injuries of the knee")

●Knee meniscus and cartilage related conditions (see "Meniscal injury of the knee" and "Management of knee osteoarthritis")

●Conditions affecting muscles, tendons, and other soft tissues (see "Quadriceps muscle and tendon injuries" and "Hamstring muscle and tendon injuries" and "Iliotibial band syndrome")

TERMINOLOGY — PFP can be defined as anterior knee pain involving the patella and retinaculum that excludes other intraarticular and peripatellar pathology. PFP describes a symptom complex and is a diagnosis of exclusion.

The terminology used to describe PFP is used inconsistently and can be confusing. Common synonymous terms include retropatellar pain syndrome, runner's knee, lateral facet compression syndrome, and idiopathic anterior knee pain. The term chondromalacia patella is used to describe pathologic changes in the articular cartilage of the patella, such as softening, erosion, and fragmentation. While frequently confused with PFP, chondromalacia patella is a pathologic diagnosis and constitutes a distinct cause of knee pain [1].

EPIDEMIOLOGY — PFP is among the most common knee conditions seen by primary care physicians, orthopedic surgeons, and sports medicine specialists [2,3]. Although PFP is often seen in active individuals and may account for 25 to 40 percent of all knee problems seen in a sports injury clinic, the true incidence is not known [4]. PFP affects many running athletes and constitutes nearly 25 percent of all identified knee injuries [5-7]. (See "Running injuries of the lower extremities: Risk factors and prevention".)

PFP more commonly affects women [8]. In a seven year review of patients diagnosed with PFP at a sports medicine clinic, the ratio of women to men was nearly 2:1 (33.2 versus 18.1 percent) [9]. Another retrospective review found similar results [6].

PFP occurs disproportionately in active adolescents and adults in the second and third decades of life [9]. One observational study found a prevalence of over 20 percent among adolescents [10].

ANATOMY — Knee anatomy is discussed in detail separately; below, aspects of knee anatomy of particular relevance to patellofemoral pain (PFP) are described briefly. (See "Physical examination of the knee", section on 'Anatomy'.)

Knowledge of the knee's extensor mechanism and the complexity of the articulation between the patella and the femoral trochlea are fundamental to understanding PFP.

The patella is a sesamoid bone that lies within the quadriceps tendon and rides in the trochlear groove of the distal femur. Its primary function is to improve leverage for knee extension. Articular cartilage on both the underside of the patella and the trochlear groove interface at the patellofemoral articulation. Proper tracking within the trochlear groove requires a balance of the forces acting on the patella [11]. Key landmarks for the evaluation of PFP relate to this balance of forces at the patella and include (figure 1 and picture 1 and picture 2) [3]:

●Proximal knee: quadriceps tendon (picture 3 and picture 1)

●Lateral knee: lateral retinaculum, attachment of the vastus lateralis, iliotibial band (picture 4 and figure 2)

●Medial knee: medial retinaculum, attachment of the vastus medialis (picture 5 and figure 3)

●Distal knee: patellar tendon and its attachment at the tibial tubercle (tuberosity) (picture 6 and picture 1)

Other structures surrounding the patella that should be examined as part of the evaluation for PFP include the fat pads dorsal to and along alongside the patellar tendon (the fat pad of Hoffa) and the subcutaneous and deep infrapatellar bursae of the patellar tendon.

ETIOLOGY AND RISK FACTORS

Overview — PFP appears to be multifactorial, resulting from a complex interaction among intrinsic anatomic and extrinsic training factors. Although clinicians frequently make the diagnosis of PFP, no consensus exists about its etiology or the factors most responsible for causing pain [2,7,11,12]. Overuse, malalignment, and trauma are commonly cited causative factors [13]. Of these, overuse (ie, training overload) is most common (see 'Overload' below and 'Malalignment' below and 'Trauma' below). Early sports specialization has been identified as a risk factor for the development of PFP [14].

The concept of overloading the knee's extensor mechanism is fundamental to all theories of the pathophysiology underlying PFP. The overload may or may not involve malalignment. Overload likely leads to such injuries as subchondral bone degeneration, retinacular strain, and damage to small nerves, which culminate in PFP. (See 'Overload' below.)

One theory, commonly referred to as "patellar tracking," suggests that anterior knee pain arises from abnormal force generation and distribution during movement of the patella within the femoral trochlea. Articular cartilage is poorly innervated and pain correlates poorly with the extent of articular cartilage lesions [15]. Therefore, the most likely sources of pain are subchondral bone, synovium, retinaculum, skin, muscle, and nerve [13].

In contrast to traditional structural and biomechanical mechanisms, one alternative explanation emphasizes abnormal tissue homeostasis [12]. According to this theory, a number of interrelated pathophysiologic processes, including inflamed synovial lining and fat pad tissues, retinacular neuromas, increased intraosseous pressure, and increased osseous metabolic activity of the patella, create pain and dysfunction.

Overload — The majority of patients with PFP has no history of trauma and do not demonstrate malalignment during physical or radiographic examinations. In contrast, a careful history often identifies activities that overload the patellofemoral joint potentially leading to injury, and possibly disturbances in tissue homeostasis, culminating in PFP [12].

Several studies note that runners' total mileage (or volume) correlates with the development of PFP [16,17]. Furthermore, patients with PFP often report that symptoms began during a period of increased physical activity [2]. PFP occurs more often in patients participating in competitive sports than age matched controls, and correlates with increasing levels of physical activity [18].

Studies among military recruits have identified a number of risk factors that consistently correlate with overuse lower extremity injuries [19,20]. These include fitness level upon entry into the service, prior exercise behavior, body mass index (BMI) over 25, and training load. A high BMI is associated with increased risk for PFP generally [21]. In a study comparing 41 patients symptomatic with PFP and 79 controls using three-dimensional patellofemoral kinematics quantified from dynamic magnetic resonance images (MRIs), a statistically significant association was noted between BMI and patellar shift [22].

Malalignment — Proper function of the patellofemoral joint requires interplay among numerous static and dynamic structures involving the entire lower extremity as the patella tracks along the trochlea. Multiple authors postulate that patellar malalignment, resulting in abnormal patellar tracking, is the primary cause of PFP. The many studies of malalignment generally subdivide it into static and dynamic components.

Static biomechanical abnormalities include:

●Leg length discrepancy [23]

●Abnormal foot morphology [24]

●Hamstring and hip musculature tightness [25-28]

●Abnormal patellar mobility [29,30]

●Angular and rotational deformities of the lower extremity [18,31]

●Hallux valgus [32]

●Trochlear morphology [33]

Dynamic biomechanical abnormalities include:

●Muscle weakness or imbalance (eg, vastus medialis and hip abductors) [26,34-37]

●Knee abduction impulses [26,38,39]

●Hip weakness and adduction [40-43]

●Ground reaction forces [26]

●Excessive foot pronation [26,40,44,45]

●Insufficient foot pronation [41]

Studies of the biomechanical factors that potentially contribute to PFP demonstrate conflicting results, a lack of reproducibility, and no firm conclusions. Authors consistently cite the difficulty of research due to PFP’s likely multifactorial nature. However, new research tools and studies continue to emerge. As an example, a study using functional MRI found that patients with PFP did not demonstrate differences in quadriceps muscle recruitment when compared with controls [46].

Several studies have concluded that dynamic forces play a major role in the development of PFP, particularly hip abductor weakness [4,42,47,48]. One prospective observational study in female runners assessed the role of hip biomechanics and reported that greater hip adduction angles were strongly associated with an increased risk for developing PFP [43]. A systematic review of ten case-control studies reported that dynamic malalignment related to weakness of the gluteus medius may stem from delayed and briefer activation of this muscle, as demonstrated by electromyography [36]. Subsequently, a prospective study of military cadets identified unique sex-specific dynamic profiles of altered kinematics associated with increased risk of PFP [49]. Using three-dimensional motion analysis, researchers found that in males, landing with decreased knee flexion and increased hip external rotation increased the risk of PFP; while in females, landing with decreased hip abduction and increased knee internal rotation increased the risk of PFP.

Despite these findings, the role of hip abductor weakness in patients who develop PFP remains unclear and is a subject of active research. The authors of another systematic review noted that while multiple cross sectional studies have demonstrated hip abductor weakness in patients with PFP, the few prospective studies performed have not found an association between hip weakness and increased risk for developing the condition [50]. Moreover, in one prospective study involving 255 adolescent female athletes, those who developed PFP demonstrated greater hip abduction strength [51].

Faulty biomechanics with foot pronation or supination may play a role in PFP. In a prospective trial involving military recruits, under-pronation best predicted PFP [41]. The authors postulate that both excessive and insufficient pronation may play an important role [41]. In our clinical experience, seemingly innocent biomechanical abnormalities, when unmasked through overload, can lead to PFP.

Of the many static abnormalities that may contribute to PFP, the role of the Q angle has been the subject of numerous studies (figure 4) [52,53]. According to a systematic review of prospective studies, Q angle is not a risk factor for PFP [54].

Trauma — Direct and indirect injuries can damage structures around the patellofemoral joint. Direct blows sustained during falls, contact sports, or motor vehicle collisions (eg, knee striking dashboard) can injure the patella and trochlea, including articular surfaces, and surrounding structures. Indirect injuries from falls may include patellar dislocation or subluxations, retinacular strain, or damage to the articular cartilage.

CLINICAL PRESENTATION AND EXAMINATION

History — The diagnosis of PFP is based primarily upon history [52]. The onset of anterior knee pain may be gradual or acute, and may be precipitated by trauma. Pain may occur in one or both knees. Typically knee pain worsens with squatting, running, prolonged sitting, or when ascending or descending steps [52]. Pain is often poorly localized "under" or "around" the patella, and is usually described as "achy" but may be "sharp". Some patients may describe the affected knee as "giving way" or "buckling". In PFP, this perceived instability may be due to pain inhibiting proper contraction of the quadriceps, but it must be distinguished from instability arising from a patellar dislocation or subluxation, or from ligamentous injury of the knee.

Although some patients may describe a "catching" sensation under the patella, true locking of the knee or effusion are signs of intraarticular pathology NOT explained by the diagnosis of PFP. Such findings require further evaluation (see "Approach to the adult with unspecified knee pain"). Patients may describe an audible "popping" or "creaking" often after standing following prolonged sitting, or when ascending or descending stairs.

Overload and trauma are important risk factors for PFP. The clinician should inquire about exercise history to identify changes in training load. It is also important to ask about any prior knee surgery or knee injuries, especially to the patella.

Physical examination

Knee examination — A detailed description of a complete knee examination is presented separately (see "Approach to the adult with unspecified knee pain"). Key features relating to PFP include:

●Observation: Look for obesity, vastus medialis atrophy, angular and rotational deformities of the lower extremity, localized erythema

●Palpation: Determine if the quadriceps or patellar tendons are tender, check for the presence of localized warmth or an effusion

●Strength: Determine whether quadriceps strength is limited, look for hip abductor and external rotator weakness, note strength discrepancies between affected and unaffected lower extremities

●Range of motion of the knee (crepitus with range of motion is a nonspecific finding)

Examine the ipsilateral hip, as knee pain can be referred from the hip. Evaluate for a leg length discrepancy of ≥1.0 cm, which may have adverse effects on the lower extremity while running [55]. A small leg length difference (≤0.5 cm) is not uncommon and under most conditions does not contribute to PFP [56]. Evaluate the feet and arches. There is an association with cavus foot and lower extremity injuries (picture 7) [57].

Special tests — Tests of patellofemoral function have not been rigorously studied. Despite the dearth of evidence, the tests described below are commonly performed and may help to determine the diagnosis when considered in the context of the history and general examination findings. According to one small observational study, combinations of functional signs and tests, such as pain with resisted quadriceps contraction and pain with squatting, may be more diagnostic of PFP than any one examination maneuver [29].

●Squatting – 80 percent of patients with PFP experience pain with squatting [14].

●Patellar tendon palpation – Tenderness directly ventral or dorsal to the patellar tendon is associated with patellar bursitis and tendinopathy, while tenderness along either side of the patellar tendon is associated with inflammation of the fat pad of Hoffa. In an adolescent, tenderness at the inferior pole of the patella may be an apophysitis. These findings are not consistent with the diagnosis of PFP [14].

●Patella facet/retinaculum tenderness – With the patient's knee in full extension and the quadriceps relaxed, displace the patella laterally and palpate its lateral facet (undersurface) through the retinaculum and synovium. Repeat on the medial side. Tenderness is a positive finding.

●Patellar glide – With the knee extended and the quadriceps relaxed, manually displace the patella laterally and medially. Translation less than one-quarter of the patella's width signifies a tight retinaculum, while translation of three-quarters of the patella's width signifies a hypermobile patella [30].

●Apprehension test – With the quadriceps relaxed and the knee flexed to 30 degrees, apply pressure to the medial patella to push the patella laterally while looking at the patient's face. Apprehension as the patella reaches maximum passive displacement and the patient attempts to straighten the knee are a positive sign for patellar subluxation. The test has a reported sensitivity of 39 percent [58].

●Popliteal angle – The popliteal angle is a measure of hamstring flexibility. Tight hamstrings contribute to compressive forces across the patellofemoral joint and are associated with PFP [28].

With the patient relaxed and supine and their knee bent, flex the hip to 90 degrees, then gently extend the knee by lifting the lower leg until you appreciate resistance (felt as tension in the hamstring) (picture 8). The hip remains at 90 degrees of flexion while the knee is extended. The angle of the leg at the point of resistance is the popliteal angle, which is a relatively objective measure of hamstring flexibility. At 0 degrees the entire lower extremity is perpendicular to the exam table. Measurements greater than 20 degrees are consistent with hamstring inflexibility.

●Evaluation for dynamic malalignment:

While the patient is barefoot and in shorts, observe their gait for excessive varus (picture 9) or valgus knee (picture 10) movement. Then, while the patient is walking or running, observe their foot strike for excess supination or pronation. (See "Clinical assessment of walking and running gait".)

Have the patient perform a single leg squat or step down while looking for excessive contralateral pelvic drop, hip adduction and internal rotation, knee abduction, and excessive or insufficient foot pronation (picture 11) [11,59]. Perform a Trendelenburg test to assess for gluteus medius weakness. The test is performed by having the patient stand on one leg and observing the pelvis. The ipsilateral iliac crest should remain level or rise slightly; a drop of the iliac crest indicates gluteus medius weakness. Because fatigability of the hip abductors may be a component of dynamic instability, excessive knee valgus motion may not be apparent in the office setting.

Static testing of hip abductor and external rotator strength may help identify weakness and confirm observations noted on dynamic assessment [34,42,47,48].

●Other tests:

Patellar grind – We believe this test is unnecessarily painful and unhelpful and suggest it not be performed. Neither its sensitivity nor its specificity are well studied [58].

Medial plica – Palpation of a tender medial plica, a fold of synovium along the medial joint line at the medial femoral condyle, is not associated with the diagnosis of PFP.

Q angle – The Q angle does not correlate to PFP, and despite extensive study the clinical utility of this measurement remains uncertain [52,53].

DIAGNOSTIC IMAGING — PFP is a clinical diagnosis; plain films are unnecessary for initial management. In the absence of a history of trauma, overt instability, effusion, prior surgery, or pain at rest, imaging is not performed until the patient's symptoms fail to improve after one to two months of appropriate conservative therapy. Radiographic findings do not correlate well with clinical complaints and frequently the injured side is difficult to differentiate from the uninjured side [60].

When imaging is indicated, plain films of the knee (weight bearing PA, weight bearing lateral, and sunrise view (image 1)) are useful to rule out other sources of anterior knee pain, including bipartite patella (image 2 and image 3 and image 4), osteoarthritis (image 5), loose bodies, and occult fractures.

Advanced imaging, including magnetic resonance imaging (MRI), computed tomography (CT), musculoskeletal ultrasound (MSK US), and radionuclide scanning, is not indicated in the initial evaluation of the patient with PFP, but may help identify other pathology. MRI can detect chondromalacia patella, articular cartilage injuries, osteochondritis dissecans, and injuries to the patellar retinaculum and patellofemoral ligament. CT scanning with serial flexion views can identify patellofemoral malalignment and instability. MSK US may show enhanced echogenicity suggestive of patellar tendinopathy. Bone scans can reveal increased bone activity associated with subchondral stress. Even advanced imaging is limited in that there is often poor correlation between radiographic and clinical findings.

In one study correlating clinical exam to MRI and ultrasound findings in PFP, slight effusion or increased signal intensity at the attachment site of the medial retinaculum were present on MRI in two out of five severe cases of PFP [61]. The synovium, retinaculum, joint capsule, fat pad of Hoffa, and subchondral bone appeared normal in all cases. MSK US revealed a slight to moderate effusion and enlargement of the synovium in two of five severe cases.

DIAGNOSIS AND DIFFERENTIAL DIAGNOSIS — Patellofemoral pain (PFP) is a clinical diagnosis, with no pathognomonic sign or symptom. For most patients a careful history and physical examination establish the diagnosis, but the clinician must first exclude other conditions that mimic PFP. Typically, knee pain from PFP worsens with squatting, running, prolonged sitting, or when ascending or descending steps. Pain is often poorly localized "under" or "around" the patella, and is usually described as "achy" but may be "sharp". Examination findings consistent with PFP are described below; the broad differential diagnosis of anterior knee pain is reviewed separately. (See 'Physical examination' above and "Approach to the adult with knee pain likely of musculoskeletal origin" and "Approach to the adult with unspecified knee pain".)

Six anatomic areas are thought to contribute to PFP: subchondral bone, synovium, retinaculum, skin, nerve, and muscle [13]. The differential diagnosis of anterior knee pain involves these structures (table 1). (See 'Etiology and risk factors' above.)

The clinician must distinguish PFP from patellofemoral osteoarthritis, patellofemoral instability, and similar conditions that cause anterior knee pain. Patellofemoral osteoarthritis (PF OA) generally occurs in patients who are older than those who develop PFP and has characteristic radiographic findings. There is no known link between PFP and PF OA [4]. The patient with patellofemoral instability may have a history of patellar dislocation or describe a sensation of instability or movement of the patella. Both of these disorders, while related to PFP, require specific treatments distinct from those used to treat PFP. (See "Clinical manifestations and diagnosis of osteoarthritis" and "Recognition and initial management of patellar dislocations".)

INITIAL TREATMENT — The goals of treatment for PFP are to reduce pain, improve patellofemoral tracking and alignment, and return the patient to as a high a level of function as possible. The acute phase of treatment during the first week focuses on pain control; the subsequent recovery phase focuses on modification of risk factors and biomechanical deficits.

Acute phase

●Activity modification – Most experts believe that overload plays an important role in the development of PFP. Patients need to avoid activities that cause pain during rehabilitation. Most runners need to reduce their running volume and those with severe signs or symptoms (eg, limping) should curtail all running activities. Patients with less severe symptoms may need to stop only more extreme training, such as hill running and stadium step running. Athletes can maintain aerobic fitness by using a stationary bicycle (recumbent or upright), an upper body cycle, or by swimming, water running, or other activities, provided they do not cause pain.

●Nonsteroidal antiinflammatory drugs (NSAIDs) – There is no evidence to support the long-term use of NSAIDs for the treatment of PFP. According to one systematic review, limited evidence supports their use in the short term (two to three weeks) [62]. In this review, naproxen produced more significant pain reduction compared with placebo, but aspirin did not.

●Other modalities – Although formal studies are lacking, applying ice to the anterior knee is reasonable to relieve pain associated with PFP. There is no empiric evidence to support the use of ultrasound, iontophoresis, phonophoresis, or electrical stimulation in the treatment of PFP [62-66].

Recovery phase

Approach — Although many randomized clinical trials assessing treatments for PFP have been performed, quality is often limited, and the results do not support any specific rehabilitation protocol [67-70]. A relatively large proportion of patients (about 40 percent) diagnosed with PFP continue to have symptoms one year following typical conservative care [4,14]. Evidence summarized in a consensus statement from the 5^th International Patellofemoral Pain Research Retreat suggests that the combination of knee and hip exercises to increase lower extremity strength, mobility, and overall function represents the most effective intervention for these patients [68,69,71]. In addition, the consensus statement from this retreat endorsed combined interventions such as exercise therapy plus foot orthoses, patellar taping, and manual therapy. According to one randomized trial, supervised physical therapy may be superior to a home exercise program [72]. We have included a sample rehabilitation program suitable for uncomplicated cases of PFP (table 2).

A comprehensive approach to treatment should systematically address potential deficiencies in the interrelated group of muscles and other structures involved in moving the lower body (ie, the lower body kinetic chain). These structures include:

●Hip abductors

●Iliotibial band

●Knee extensors (quadriceps)

●Knee flexors (hamstrings)

●Feet – Excessive or insufficient pronation

●Core (ie, trunk) muscles

As PFP appears to be multifactorial, as yet unspecified subtypes of PFP may respond better to specific therapies [61].

Ideally, patients should begin physical therapy under the guidance of a knowledgeable physical therapist or comparable professional. For those unable to do so, general exercises for the treatment of PFP can be found at several websites, including the American Academy of Family Practice and the Lennox Hill Hospital Nicholas Institute. These exercises should not cause pain. Patients experiencing anything more than mild soreness should reduce the intensity of the inciting exercise. Patients with persistent or severe pain from rehabilitation exercises should be reevaluated by their clinician.

Stretching — Although an association between inflexibility and injury remains unproven, the decrease in stress at the patellofemoral joint provided by increased quadriceps, hamstring, and iliotibial band flexibility seems a reasonable therapeutic goal. Observational studies suggest an association exists between decreased quadriceps flexibility and PFP [25,73]. In a prospective case control study, a regime of quadriceps stretching decreased pain and improved function among patients with PFP, although these improvements did not correlate closely with the gains in quadriceps flexibility [74].

Hip strengthening — Several observational studies implicate hip abductor weakness in the development of PFP [34,36,42,47,48]. In response, many therapists incorporate hip abductor strengthening into their rehabilitation programs.

Although published evidence is limited, it suggests that strengthening of the hip musculature reduces pain, improves function, and is better than knee strengthening alone [75,76]. In one small single-blinded randomized trial, improvements in pain and function were noted in patients with PFP whose rehabilitation program emphasized hip strengthening exercises [77]. In an observational study, a six week program of closed kinetic chain hip strengthening and stretching resulted in significant improvements in pain and function [78]. Closed kinetic chain exercises are performed with the feet planted in a fixed position throughout the exercise (eg, squat, leg press). Case reports describe similar rehabilitation programs focused on improving core and hip stability and strength that allowed athletes to return to their previous level of activity [79,80].

Quadriceps strengthening — Quadriceps muscle weakness is a common problem among patients with PFP [81,82]. Treatment plans for PFP should include general quadriceps strengthening exercises using closed or open kinetic chain movements, depending upon the severity of symptoms and biomechanical dysfunction. Closed kinetic chain (CKC) exercises are performed with the feet planted in a fixed position throughout the exercise (eg, squat (picture 12 and picture 13), leg press (picture 14)) and thus provide greater stability. With open kinetic chain (OKC) exercises the feet change position.

Some researchers believe CKC exercises are better tolerated and produce less patellofemoral joint stress than OKC exercises [83] and may preferentially activate the vastus medialis [80]. In one small randomized controlled trial, the selected CKC exercise (semisquat) was more effective than the OKC exercise (straight leg raise) in treating "patellar chondromalacia" [84]. The diagnostic criteria described in the study were consistent with PFP.

Core stability — Deficiencies in core (ie, torso) strength, which affect pelvic stability, are a risk factor for lower extremity injuries, including PFP, according to one prospective observational study in college athletes [85]. Many experts suggest that exercises to improve core strength be included in rehabilitation programs for PFP [86]. Such exercises generally involve multiple joints and incorporate trunk rotation and flexion of the knee and hip.

Adjunctive therapy

Foot orthoses — Limited evidence suggests that foot orthoses may be useful for symptom relief in some patients with PFP [11,69,71,87,88]. Semirigid full length foot orthotics can help control excessive foot overpronation or supination, which are associated with dynamic instability, and reduce impact. (See "Running injuries of the lower extremities: Risk factors and prevention", section on 'Orthotics'.)

Two systematic reviews of studies of limited quality suggest that orthotics and physical therapy are more effective than physical therapy alone in reducing symptoms of PFP [71,89]. However, two other systematic reviews with more stringent inclusion criteria report that, although the available evidence is weak, there does not appear to be a clear benefit from treatment with foot orthoses [90,91]. The highest quality trial included in both these systematic reviews included 179 patients with symptoms of PFP of at least six weeks duration without prior treatment who were randomly assigned to treatment with orthotics, flat inserts, physical therapy, or orthotics plus physical therapy [88]. Although there was a trend towards greater short-term improvement among patients treated with orthotics (relative risk [RR] 0.66; 99% CI 0.05-1.17), no significant difference in long-term outcomes were noted.

An important unresolved clinical issue with foot orthoses is determining which subset of patients may benefit. According to a few observational studies, foot orthoses may be most effective in individuals with increased dynamic foot pronation and midfoot flexibility [45,69,92].

Bracing and patellar taping — Although the foundation of treatment for PFP remains exercise and strengthening, if a patient cannot participate fully in rehabilitation exercises due to pain or does not make progress, it is reasonable to perform taping or patellofemoral bracing if this improves symptoms.

A meta-analysis of 20 studies of patellar taping concluded that there is moderate evidence in support of this therapy for both reducing pain and improving functional capacity [93]. The review found that tailored taping (versus untailored or non-customized taping) that controlled the lateral tilt, glide, and spin (ie, rotation) of the patella was important for efficacy and provided immediate pain relief, although benefits appear to fade in long-term follow up. In addition, taping plus exercise provided greater pain relief than exercise alone at four weeks. A systematic review of five trials (235 patients) found that knee taping is helpful when used as an adjunct to traditional exercise therapy for PFP, but not when performed in isolation [94]. Taping may be less effective in patients with higher body mass indices [95].

According to two systematic reviews of controlled clinical trials involving patients with PFP, the available evidence is of limited quality but there does not appear to be a clear benefit from bracing for either reducing symptoms or improving function compared with physical therapy alone [91,96]. Some researchers believe there is a subgroup of patients that benefit from patellofemoral bracing [97].

Barefoot running, minimalist shoes, and gait retraining — Enthusiasts promote running barefoot or in minimalist running shoes as a means for reducing running injuries, including PFP, but evidence is limited. In a systematic review and meta-analysis of 22 studies of running footwear, researchers found weak evidence that minimalist running shoes may slightly reduce the loads placed on the patellofemoral joint compared with standard running shoes [98]. Minimalist running is reviewed in greater detail separately. (See "Running injuries of the lower extremities: Risk factors and prevention", section on 'Running shoe design'.)

The impact of a change in shoe type may be secondary to modifications in gait prompted by the change (eg, non-rearfoot strike pattern). Studies of gait retraining in subjects with PFP report reductions in pain and improvements in function through the introduction of one or more changes in running technique, including decreased hip adduction, increased forward trunk lean, and use of a non-rearfoot strike [99].

Injectable agents — A number of injectable medications, agents, and related techniques are used for a number of conditions, including osteoarthritis. However, there is no high-quality evidence supporting such therapies for the treatment of PFP. Such proposed interventions include intra-articular glucocorticoid, hyaluronic acid, platelet-rich plasma, glycosaminoglycan polysulfate, and botulinum toxin [62,100,101]. The use of biologic therapies for the treatment of tendon and muscle conditions is reviewed in detail separately. (See "Biologic therapies for tendon and muscle injury".)

Although evidence is scant, hyaluronic acid injection is used by some clinicians to treat refractory PFP. In a randomized trial, 45 patients received a single hyaluronic acid injection and 41 a sham injection, while all were prescribed a home exercise program [102]. No clinically significant difference was noted in the patients treated with hyaluronic acid.

In a trial of glycosaminoglycan polysulfate, 53 patients with chronic PFP were randomly assigned to receive five weekly intra-articular injections, five weekly sham injections (intraarticular isotonic saline), or no injections [100]. All groups received conservative therapy consisting of quadriceps-strengthening exercises, activity modification, and oral NSAIDs. Although both injection groups had better function at six weeks compared with the no-injection group, this difference was lost at six months. Symptoms resolved completely in over two-thirds of the patients in each group.

Botulinum toxin may have a role in treating some cases of PFP by facilitating lateral musculature and tensor fascia latae relaxation, essentially performing a nonsurgical lateral retinacular release. A few case reports describe such use, but this intervention remains preliminary and requires further study [103-106].

Lumbar, knee, or hip mobilization — Based on the literature review included in the 2018 PFP consensus statement, mobilization therapies have not been substantiated by controlled studies and are not recommended [69].

Dry needling — As gluteus medius dysfunction and weakness are commonly identified in PFP, research into the treatment of trigger points that may contribute to such weakness is being performed. As an example, in a study of 29 young non-athlete females with unilateral PFP, those treated with dry needling in addition to conventional physical therapy experienced greater reductions in pain and improvements in function compared with those treated with physical therapy alone [107].

FOLLOW-UP CARE — Treatments for PFP show varying degrees of success. Some patients have successful short-term outcomes but poor long-term outcomes after they return to their preinjury level of activity [108,109]. If the patient reports recurrence or persistence of knee pain, assess the patient's compliance with and response to the prescribed therapy.

Have the patient explain in detail the exercises they have been doing. When did they first see the physical therapist? How many times a week do they go to physical therapy? How often do they do their home program? Have the patient demonstrate some of the exercises. Ask about their tolerance of the therapy and quantify their cardiovascular workouts (eg, "I can ride the stationary bike for 10 minutes until my knee hurts," or "I'm still running 25 miles per week").

Because overuse is a significant risk factor for PFP, activity levels need to be quantified. Ask about previously aggravating activities and assess improvement (eg, "I can walk down stairs without pain now").

If there is improvement, continue physical therapy until the patient can perform all exercises without pain, and then slowly reintroduce activities which previously caused pain (eg, running). Increase activity levels in a gradual, step-wise progression, until the patient achieves the desired level. If symptoms are unchanged and the patient appears to be compliant with both therapy and activity modification, re-examine the patient to confirm the original diagnosis. Imaging with plain radiographs may be useful, as may orthotics, taping, or bracing if not previously done. If the compliant patient has not improved in three to six months of therapy, obtain an MRI or orthopedic consultation.

In patients with persistent symptoms, clinicians should consider the nature and role of the pain itself. Pain catastrophizing, pain self-efficacy, and fear-avoidance beliefs may be significant clinical factors in the assessment, treatment, and prognostication of PFP [110]. (See "Evaluation of chronic non-cancer pain in adults".)

INDICATIONS FOR ORTHOPEDIC REFERRAL — Evidence supporting surgical intervention for the treatment of PFP is lacking, and is not recommended in the 2018 PFP consensus statement [69]. In rare cases, it may be considered when an extensive trial of nonoperative therapies have failed, but it is a treatment of last resort. Nonoperative therapy should be pursued for 24 months prior to considering operative intervention [3].

Before surgery, other causes of anterior knee pain should be carefully excluded and a clearly identified structural abnormality amenable to surgery (eg, tight lateral retinaculum) should exist. Any surgery for PFP must address the patient's specific characteristics of abnormal patellar tracking; inappropriate and overzealous surgery can lead to significant patient disability [13].

Patellar alignment, patellar resurfacing, and patellar arthroplasty comprise the three principal categories of operative intervention for PFP. Most studies evaluating such surgery are uncontrolled case series, so the effectiveness of operative intervention remains unclear. In one randomized controlled trial involving 56 patients with chronic PFP, no difference in outcome was found in patients treated with arthroscopy and a home exercise program compared with those treated with exercise alone [111,112]. According to a case series of 34 athletes, patients with demonstrated lateral patellar instability are more likely to benefit from surgical repair [113].

COMPLICATIONS — While few long-term studies document the natural history or treatment of PFP, the general prognosis is favorable. Long-term observational studies suggest that at two to eight years most patients with PFP patients report only mild occasional symptoms. In a seven year follow-up of patients from a randomized, controlled trial, nearly 85 percent treated with a home exercise program reported successful outcomes [114].

Not all patients with PFP successfully complete nonoperative therapy and return to sporting activity [108]. Some must retire prematurely from sports that aggravate PFP. Persistent abnormal tracking of the patella or patellar instability can lead to patellofemoral osteoarthritis or chronic pain. Risk factors associated with a poor long-term prognosis include a hypermobile patella, older age, and bilateral symptoms [3,114]. One predictor of a poor functional outcome is fear avoidance behavior; addressing psychological comorbidities may be an important intervention for individuals who are failing to progress [115].

The failure of nonoperative therapy does not imply successful surgical treatment. A significant number of patients do not improve or are made worse by PFP surgery, at times requiring a salvage procedure [13]. (See 'Indications for orthopedic referral' above.)

RETURN TO SPORT OR WORK — Return to sport for the patient with PFP follows basic guidelines applicable for all overuse injuries. The patient should demonstrate motion equal to that of the uninvolved extremity, and strength at least 80 percent that of the opposite side. The presence of significant quadriceps atrophy or an effusion precludes a return to full activity. The patient should have no complaints of nocturnal pain or pain with activities of daily living prior to beginning sports. In general, mild pain that diminishes with activity is not concerning. Increased pain should prompt termination of the activity and reassessment by the clinician.

PREVENTION — There is little high quality evidence pertaining to the prevention of PFP [116]. According to a randomized controlled trial conducted among army recruits in the United Kingdom, an exercise program much like that used to treat PFP may be effective at preventing the development of anterior knee pain [117]. In this trial, 36 new cases of PFP (described as "overuse anterior knee pain") developed in the control group of 743 recruits compared to 10 new cases among the 759 recruits who participated in the preventative exercise program (HR 0.25; 95% CI 0.13-0.52).

With the exception of the prevention exercises, recruits participated in the exact same training activities over the 14-week trial period. Physicians assessing the recruits were blinded to which groups participated in the intervention. The prevention program consisted of the following exercises:

●Isometric hip abduction against a wall

●Forward lunges (movie 1)

●Single leg step downs

●Single leg squats (movie 2)

●Stretches for the quadriceps, iliotibial band, hamstrings, and calves

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Patellofemoral pain" and "Society guideline links: Knee pain".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topics (see "Patient education: Patellofemoral pain (The Basics)" and "Patient education: Knee pain (The Basics)" and "Patient education: Chondromalacia patella (The Basics)")

●Beyond the Basics topic (see "Patient education: Knee pain (Beyond the Basics)")

SUMMARY AND RECOMMENDATIONS

●Definition, epidemiology, and mechanism – Patellofemoral pain (PFP) is among the most common etiologies of anterior knee pain in the general population. PFP is characterized by pain around or behind the patella that is aggravated by one or more activities that involve loading the patellofemoral joint during weight bearing on a flexed knee, and that cannot be attributed to another discrete intra-articular (eg, meniscus tear) or peripatellar (eg, patellar tendinopathy) pathology. There is no consensus about its pathophysiology. Overuse is common among patients with PFP. (See 'Epidemiology' above and 'Etiology and risk factors' above.)

●Clinical presentation and diagnosis – PFP has no pathognomonic sign or symptom. PFP is a clinical diagnosis made based upon the history, examination, and the exclusion of alternative diagnoses; plain films are not required for initial management. (See 'Clinical presentation and examination' above.)

●Management – Physical therapy focused upon improving the strength of the musculature supporting the knee, hip, and torso, including the hip abductors and quadriceps, is generally effective as the sole treatment for PFP (table 2). (See 'Recovery phase' above.)

There is no evidence to support the long-term use of nonsteroidal antiinflammatory drugs (NSAIDs) for the treatment of PFP; limited evidence supports their use for short-term pain relief. (See 'Acute phase' above.)

●Indications for surgical referral – Surgical interventions for PFP lack compelling evidence but may be considered in rare cases when nonoperative therapies have failed. Nonoperative therapy should be pursued for 24 months prior to considering operative intervention and a clearly identified structural abnormality amenable to surgery (eg, tight lateral retinaculum) should exist. (See 'Indications for orthopedic referral' above.)

●Prognosis – The majority of PFP patients experience a resolution of symptoms following conservative treatment, although the condition can be recalcitrant to treatment and symptoms may persist for years in some cases.