Patellofemoral Pain Syndrome (PFPS), is commonly referred to as runner’s knee, and is a common cause of anterior knee pain.
Patellofemoral pain syndrome is a broad term to describe painful conditions around or behind the patella, and is one of the most common types of knee pain in people under 60 [Dixit et al, 2007; Gaitonde et al, 2019].
What causes Patellofemoral Pain Syndrome?
The cause for patellofemoral pain syndrome is multifactorial, and thought to be due to altered biomechanics of the knee during dynamic movements. These biomechanical changes are often a result of muscle weakness and poor neuromuscular control leading to an imbalance in the forces controlling patellar tracking during knee movements.
Additional factors that may influence patellofemoral pain syndrome, include overuse, trauma, muscle dysfunction, tight lateral restraints, patellar hypermobility, and poor quadriceps flexibility [Dixit et al, 2007; Collado & Fredericson, 2010].
Muscular imbalance or weakness: One systematic review showed that decreased strength in the quadricep muscles may cause an increased risk of patellofemoral pain as it can lead to instability of the patella [Lankhorst et al, 2022]. Weakness in the hip abductors, particularly the gluteus medius and external rotators can contribute to malalignment and stress along the lateral patella [Boling et al, 2009; Earl et al, 2011].
Neuromuscular Control: Impaired neuromuscular control, including delayed muscle activation and/or reduced strength around the knee, can contribute to patellar maltracking [Alsaleh et al, 2021; Barton et al, 2013].
How do you know if you have Patellofemoral Pain Syndrome?
Patellofemoral Pain Syndrome (PFPS) is characterized by several key symptoms. The most common symptom is pain around or behind the patella that is exacerbated by activities.
Activities that can increase patellofemoral joint stress include: running, squatting, kneeling, ascending or descending stairs, and prolonged sitting with the knees flexed (often referred to as the "theater sign") [Dixit et al, 2007; Thomee et al, 1999; Gaitonde et al, 2019].
Patients often report a nagging dull and achy pain or an occasional sharp twinge of pain. The pain is typically insidious in onset, meaning it develops gradually without a specific injury or event. The pain may be associated with a sensation of knee instability or giving way [Dixit et al, 2007; Gaitonde et al, 2019; Dutton et al, 2016; Collado & Fredericson, 2010].
How is Patellofemoral Pain Syndrome Diagnosed?
Diagnosis is based on a combination of a detailed history, physical examination, and imaging. During the physical examination, a series of provocative tests may be utilized to further determine presence of injury.
Imaging, such as X-rays, is generally not required unless there is a history of trauma, effusion, or failure to respond to conservative treatment.
Advanced imaging may be required to confirm diagnosis and determine injury severity, and a recent study showed both magnetic resonance imaging (MRI) and ultrasound can help effectively identify and assess surrounding structures to aid in the diagnosis of patellofemoral pain syndrome [Pacini et al, 2023].
What are the potential misdiagnoses when evaluating Patellofemoral Pain Syndrome symptoms?
When evaluating symptoms of patellofemoral pain syndrome several potential misdiagnoses should be considered:
Meniscal Tears: Meniscal tears can present with knee pain and a sensation of instability. They are often associated with joint line tenderness [Hunter et al, 2022; Duong et al, 2023].
Patellar Tendinitis: Also known as "jumper's knee," this condition involves pain localized to the patellar tendon, typically exacerbated by jumping or running activities [Calmbach & Hutchens, 2003; Slotkin et al, 2018].
Osteoarthritis (OA): OA of the knee, particularly in older adults, can cause anterior knee pain. It is often associated with joint stiffness and crepitus [Duong et al, 2023].
Chondromalacia Patella: This condition involves the softening and degeneration of the cartilage on the underside of the patella, leading to anterior knee pain similar to PFPS [Welsh, 1985; Elias & Whilte, 2004].
Patellar Subluxation or Dislocation: Partial or complete displacement of the patella from its normal position can cause pain and a sensation of instability [Elias & Whilte, 2004; Lester et al, 2014].
Iliotibial Band Syndrome: This overuse injury causes lateral knee pain and can sometimes be confused with PFPS due to its proximity to the patella [Hunter et al, 2022].
Pes Anserine Tendonitis/Pes Anserine Bursitis: Inflammation of the pes anserine tendons or pes anserine bursa located at the medial aspect of the knee can mimic the symptoms of patellofemoral pain syndrome [Calmbach & Hutchens, 2003].
Hip Pathologies: Conditions in the hip can refer pain to the knee, potentially leading to misdiagnosis [Calmbach & Hutchens, 2003].
How is Patellofemoral Pain Syndrome Treated?
Conservative Treatments
Patellofemoral Pain Syndrome (PFPS) is primarily treated through conservative measures, focusing on a multimodal approach that includes exercise therapy, patient education, and adjunctive treatments.
Physical Therapy/Strengthening Exercises: Strengthening exercises targeting the quadriceps, hip muscles and core are the cornerstone of management. Both knee-targeted and hip-targeted exercises have been shown to be effective in reducing pain and improving function [Barton et al, 2015; Neal et al, 2024; Gaitonde et al, 2019; Neal et al, 2022].
Corticosteroid Injections:There is insufficient evidence to support the use of corticosteroid injections specifically for PFPS, and their use is not recommended based on current clinical guidelines and systematic reviews [Hunter et al, 2022; Hart, 2011; Everhart et al, 2017; Neal et al, 2022].
Viscosupplementation Injections:There
is limited evidence supporting the use of viscosupplementation
injections for treating Patellofemoral Pain Syndrome (PFPS).
Most of the available literature on viscosupplementation, specifically hyaluronic acid (HA) injections, focuses on its application in knee osteoarthritis, particularly tibiofemoral osteoarthritis. In a study by Clarke et al., the authors evaluated the use of intra-articular hyaluronic acid injections (Synvisc) in patients with patellofemoral osteoarthritis and found significant improvements in pain and function [Clarke et al, 2005]. However, this study targeted osteoarthritis rather than Patellofemoral Pain Syndrome, and the results cannot be directly extrapolated due to differences in the underlying pathology.
Platelet Rich Plasma (PRP): There
is currently no strong evidence supporting the use of Platelet-Rich
Plasma (PRP) injections for treating Patellofemoral Pain Syndrome
(PFPS). The available literature on PRP primarily focuses on its application in other knee-related pathologies, such as knee osteoarthritis and patellar tendinopathy, and there are no case reports or studies available on PRP for PFPS.
Prolotherapy: There is currently no strong evidence supporting the use of prolotherapy injections for treating Patellofemoral Pain Syndrome (PFPS), and there are no case reports or studies available on prolotherapy for PFPS.
Surgical Treatments
Surgical intervention is rare for these injuries, and is typically reserved for specific cases with identifiable structural abnormalities [Petersen et al, 2014; Fulkerson, 2002].
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