Practice Essentials
Patellofemoral syndrome (PFS) is characterized by a group of symptoms that contribute to anterior knee pain. The pain is associated with positions of the knee that result in increased or misdirected mechanical forces between the patella (kneecap) and femur. [1, 2, 3] While there are several factors associated with this syndrome, there is a lack of consensus regarding the cause. The basic exercise principles for the management of PFS include improving the range of motion of the iliotibial band, hip flexors, and quadriceps; strengthening the core, quadriceps, hip abductors, hip extensors, and hamstrings; and restricting the offending physical activity.
Symptoms of patellofemoral syndrome
Knee pain is the most common presentation of PFS. The pain characteristically is located behind the kneecap (ie, retropatellar) and most often manifests during activities that require knee flexion and forceful contraction of the quadriceps (ie, squats, ascending/descending stairs, running).
Diagnosis and management of patellofemoral syndrome
PFS is a clinical diagnosis based on history and physical examination. Clinicians should make the diagnosis of PFS using the following criteria [4] :
-
The existence of retropatellar or peripatellar pain
-
Retropatellar or peripatellar pain reproduced via squatting, stair ascension, prolonged sitting, or other functional activities in which the patellofemoral joint is loaded while in flexion
-
Exclusion of other disorders in which anterior knee pain may result
Plain film radiographs can be used to assess the patella's position. The anterior-posterior, lateral, and sunrise views can be
Background
In the patellofemoral joint, the patella, a large sesamoid bone, articulates with the trochlear groove of the femur. Embedded in the quadriceps extensor mechanism, the patella increases the moment arm of the quadriceps muscles, protects the distal joint surfaces of the femoral condyles during knee flexion, and guards the quadriceps tendon from damaging compressive forces during resisted knee extension. [4]
The patellofemoral joint's stabilizing structures consist of the quadriceps, patellar tendon, vastus medialis obliquus, medial patellofemoral ligament, medial patellotibial ligament, medial retinaculum, oblique lateral retinaculum, patellotibial band, epicondylopatellar bands, and lateral retinaculum. [6]
Pathophysiology
Overall, PFS is thought to be associated with a combination of anatomic, biomechanical, behavioral, and psychological factors.
While theories regarding the pathophysiology of PFS vary, the prevailing theory is that the syndrome is caused by abnormal tracking and alignment of the patella due to an imbalance of ligamentous and muscle forces as well as malalignment between the joint surfaces. Patellar maltracking leads to irritation of the richly innervated nerve endings within the retinaculum, subchondral bone, Hoffa (infrapatellar) fat pad, and peripatellar synovium. Moreover, load-bearing positions, as assumed in squatting and stair climbing, increase maltracking in patients with PFS. Excessive use of the joint with regard to either frequency or amount of loading also contributes to the symptoms. [6, 7]
Psychological stress, chronic pain, and central sensitization may play a role in PFS. A systematic review reported that catastrophizing and fear avoidance had strong and consistent associations with pain and function in persons with PFS. [8]
Epidemiology
Frequency
PFS is estimated to be the most common cause of anterior knee pain in athletic and nonathletic populations. [9] PFS is common in the United States; the incidence is 1.5-7.3%, [4]
Mortality/Morbidity
Morbidity associated with PFS is directly proportional to the activity level of the patient.
Race
No racial predilection has been identified for PFS.
Sex
PFS affects females more frequently than males.
Age
PFS occurs most frequently in adolescents and young adults.
Prognosis
PFS is often successfully treated with conservative measures. The most cited factors predicting poor outcomes are a longer symptom period prior to intervention, higher baseline pain severity, and poor function. [4]
Patient Education
Health-care professionals should provide education about load management, self-management of pain, and the nature and possible causes of PFS. There is low-credibility evidence from a 2020 systematic review that in patients with PFS who receive health professional–delivered education alone, outcomes with regard to pain and function may be similar to those derived from exercise therapy plus health professional–delivered education. [10]
Risk Factors
Risk factors for PFS include the following [11] :
-
Female sex
-
Activities that involve squatting, stair ambulation, and running
-
Delayed activation of the vastus medialis versus that of the vastus lateralis
-
Decreased muscle strength in knee extensors
-
Decreased flexibility of the iliotibial band, quadriceps, gastrocnemius
-
Overuse and training errors
There is limited evidence supporting variable foot plantar loading and kinematics as risk factors for PFS. [12]
There is a discrepancy in the literature on hip strength and the risk of developing PFS. Moderate to strong evidence from a limited number of prospective studies indicate that there may be no association between isometric hip strength and the risk of developing PFS. [13] However, in a 2011 prospective study of high school running athletes, stronger preinjury hip abductors and weaker preinjury hip external rotators were linked to PFS development, while a higher hip external-to-internal rotation strength ratio was found to possibly protect against PFS development. [14]
