Continuing Education Activity

Patellofemoral syndrome (PFS) is one of the most common causes of anterior knee pain. It is commonly known as runner's knee, patellofemoral pain syndrome, retropatellar pain syndrome, lateral facet compression syndrome, or idiopathic anterior knee pain. It is a diagnosis of exclusion once another intra-articular and peripatellar pathology has been ruled out. Pain is often located behind or around the patella and aggravated by loading a flexed knee joint. It is one of the most common causes of knee pain seen by clinicians. Studies have shown that up to two-thirds of patients can be successfully treated with a proper rehabilitation protocol. This activity will highlight the role of the interprofessional team in the evaluation and management of patients with patellofemoral syndrome.

Objectives:

• Identify the etiology of patellofemoral syndrome medical conditions and emergencies.
• Outline the appropriate evaluation of patellofemoral syndrome.
• Review the management options available for the patellofemoral syndrome.
• Describe interprofessional team strategies for improving care coordination and communication to advance patellofemoral syndrome and improve outcomes.

Introduction

Patellofemoral syndrome (PFS), also known as patellofemoral pain syndrome and runner's knee, is among the most common causes of anterior knee pain encountered by clinicians. Patients typically report generalized anterior knee pain that is aggravated by loading the flexed knee, such as running, climbing stairs, and squatting. PFS is considered a diagnosis of exclusion once intraarticular or peripatellar pathologies have been excluded. The majority of patients with PFS experience symptom resolution with conservative treatment. However, in some rare cases, they may be resistant to therapies and have persistent symptoms for years.

Etiology

The etiology of patellofemoral syndrome remains unclear; however, it is likely multifactorial and secondary to training practices. It is thought to involve 6 anatomic areas, including subchondral bone, synovium, retinaculum, skin, nerve, and muscle.[1] Studies point to 4 major contributing factors: malalignment of the lower extremity and/or patella, muscular imbalance of the lower extremity, overactivity/overload, and trauma.[2] Of the 4 contributing factors, overuse appears to be the most important. Additionally, early sport specialization has been shown to increase the relative risk of PFS by 1.5-fold compared with multisport athletes.[3]

Malalignment and Muscular Imbalance

The patellofemoral joint relies on complex interactions between static and dynamic structures throughout the lower extremity as the patella tracks within the trochlea. Static components include leg-length discrepancies, abnormal foot morphology, tightness of the hamstring and hip musculature, angular or rotational deformities, and trochlear morphology. Dynamic components include muscle weakness, ground reaction forces, and insufficient or excessive foot pronation. Studies on malalignment that may contribute to PFS are conflicting, with no clear consensus, likely due to its multifactorial nature. Multiple studies have concluded that hip abductor weakness may play a significant role.[4] Another study examining female runners identified hip biomechanics as a potential cause, finding that greater hip adduction angles were associated with an increased risk of PFS.[5] Although multiple studies have shown an association between hip abductor weakness, others have not been able to demonstrate a relationship and, in some cases, have shown that increased hip abduction strength is the cause.[6]

Overactivity and Overload

Many patients with PFS do not exhibit malalignment. Instead, during careful interviewing, overload of the patellofemoral joint is often described, which can lead to the development of PFS.[7] Studies have shown that increased joint workload, such as miles run/volume of work, correlates with the development of PFS, and patients typically report that pain began during a period of increased activity.[8][9] Risk factors that can lead to overload and thus increase the risk of PFS include prior fitness level, prior exercise regimen, and BMI >25.[10]

Trauma

Direct or indirect injuries to the patellar area can damage structures leading to PFS. Although studies have identified the above causes and risk factors for developing patellofemoral syndrome, most would agree that its development is rarely secondary to a single factor.

Epidemiology

Patellofemoral syndrome is among the most common knee conditions encountered by clinicians. In active individuals, it may account for 25% to 40% of all knee problems seen in a sports medicine clinic, although the true incidence is unknown.[4] PFS affects women more than men, with a ratio of approximately 2:1, according to studies.[11][12] The age of occurrence is typically observed in adolescents and adults in the second and third decades of life.[11] Its prevalence in adolescence was over 20%.[13]

History and Physical

The diagnosis of patellofemoral syndrome is heavily reliant on a detailed and accurate history and physical examination. Symptoms can be unilateral or bilateral and can be gradual or acute. Patients also report worsening symptoms with squatting, running, prolonged sitting, or stair climbing.[14] The pain is usually poorly localized. It is located behind or around the patella and is usually painful, but it can also be sharp. PFS is considered a diagnosis of exclusion; therefore, one must rule out other conditions that it may mimic. Some patients may describe a giving way or a catching sensation in the knee. Both of which could be signs of ligamentous or intraarticular pathology. When taking a patient's history, it is most important to ask the patient about trauma to the knee, including previous surgeries and activities of overuse.

On physical examination, begin with a general overview and observation of the patient and the affected joint. Are they obese? What is their age? Are there any muscular abnormalities, such as vastus medialis atrophy? Is there erythema on the joint suspicious of infection? Palpation can be useful for determining whether the quadriceps or patellar tendons are tender, while also assessing for effusion or warmth. Simple muscle strength testing can be beneficial, looking for weakness in the hip abductors or quadriceps. Record the differences between the affected and unaffected sides, as PFS can lead to weakness. Also, assess the range of motion of the affected knee. Lastly, examination of the ipsilateral hip should also be performed, as the pain could be referred.

Multiple special tests can be performed; however, many are nonspecific for PFS. One study comparing the validity of clinical features found that the sensitivity of the patellar tilt, active instability, patella alta, and apprehension tests was approximately 50%; specificity ranged from 72% to 100%.[15] In the same study, patellofemoral pain syndrome was characterized by increased quadriceps angle, lateral and medial retinacular tenderness, patellofemoral crepitus, a squinting patella, and reduced patellar mobility. Measurements of the popliteal angle have also been shown to be closely associated with the development of patellofemoral syndrome. Popliteal angle measurements are used to assess hamstring flexibility. Tight hamstrings add compressive forces across the patellofemoral joint, increasing the likelihood of developing PFS.[16]

Evaluation

Patellofemoral pain syndrome is typically diagnosed based on clinical evaluation. Further investigation with plain radiography is usually not performed until symptoms fail to improve after 1-2 months of conservative management. Radiographs typically do not correlate well with the complaint, and the affected versus unaffected side is often difficult to distinguish.[15] If the patient fails to respond to therapy, imaging is used to rule out other causes of similar pain, such as bipartite patella, osteoarthritis, loose bodies, and occult fracture. Advanced imaging, such as MRI, musculoskeletal ultrasound, and computed tomography, is usually not indicated and typically used again to evaluate other pathologies.

Treatment / Management

Treatment of PFS is usually conservative and aimed at reducing pain, improving patellar tracking, and returning to baseline function. The treatment of patellofemoral syndrome is divided into 2 main phases: the acute phase and the recovery phase. The acute phase involves activity modification, NSAID use, and other conservative modalities such as ice. NSAIDs, specifically naproxen, have been shown to decrease overall pain when compared to aspirin and placebo; however, they are usually not recommended as a long-term treatment.[17] Other modalities, such as the therapeutic ultrasound and electrical stimulation, have not been shown to improve symptoms.[18][19] After the acute phase of treatment, the patient enters the recovery phase, which aims to address the factor most likely responsible for the condition's development. Combining knee and hip exercises to increase lower-extremity strength, mobility, and function is the most effective intervention.[20] If the patient experiences pain during exercise, adjunct therapy may be indicated. This includes patellar taping. Patellar taping has been shown to decrease overall pain when used in conjunction with physical therapy when compared to physical therapy alone.[21] However, in patients with a larger BMI, taping is less effective.[22] Therapy should be patient-specific and tailored to address the identified dysfunction. Referral to orthopedic surgery is not recommended and is considered a treatment of last resort.[23] Non-operative therapy should be pursued for 24 months before operative interventions are considered.[24]

Differential Diagnosis

The differential diagnosis of PFS is broad and can be divided into 6 anatomic areas, as discussed earlier. These include patellofemoral osteoarthritis, Osgood Schlatter disease, plica, bursitis (prepatellar or Hoffa), Saphenous neuritis, quadriceps tendinopathy, patellar tendinopathy, or referred pain from the hip or back. Given the broad differential, the clinician must perform a thorough history and physical examination to identify relevant risk factors and effectively treat the patient.

Prognosis

The prognosis of patellofemoral syndrome is good; however, around 40% of patients diagnosed with PFS have continued symptoms 1 year following typical treatment.[25] At 7 years, a study reported that nearly 85% of patients treated with a home exercise regimen achieved self-reported successful outcomes. Predictors of poor long-term prognosis include a hypermobile patella, older age, and bilateral symptoms.[26]

Complications

One complication from PFS includes the development of patellofemoral osteoarthritis secondary to the inadequate tracking of the patella, which may lead to chronic pain. Another complication is that some patients must stop activities that they previously enjoyed due to that activity causing them pain.

Deterrence and Patient Education

Patients should receive education on the diagnosis, causes, and treatments. They should be given a list of home exercises or prescribed physical therapy to teach the patient how to perform the appropriate exercises. Patients are advised to rest, take NSAIDs, and ice as much as possible for the first 2 to 3 weeks.

Enhancing Healthcare Team Outcomes

Patellofemoral syndrome is a condition with a relatively good prognosis; however, it can limit a patient quite substantially secondary to pain. In patients with anterior knee pain, the history of present illness is key to determining the correct diagnosis. Once the diagnosis is established, the provider must counsel the patient on the treatment timeline and the need for rest. Physical therapy is important in the recovery phase of the condition and should be initiated as soon as the patient can tolerate activity. It is important to maintain clear communication with the physical therapist to improve patient outcomes. It is also important to obtain their input on when the patient is cleared to return to a sports or exercise regimen.

This research was supported (in whole or in part) by HCA Healthcare and/or an HCA Healthcare-affiliated entity. However, the views expressed in this publication represent those of the author(s) and do not necessarily represent the official views of HCA Healthcare or any of its affiliated entities.

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Disclosure: Jared Bump declares no relevant financial relationships with ineligible companies.

Disclosure: Lindsay Lewis declares no relevant financial relationships with ineligible companies.