Patellofemoral Pain Syndrome (PFPS) is an overuse injury of the extensor mechanism of the knee, characterized by retropatellar or peripatellar pain.
The etiology of PFPS is multi-factorial and commonly related to biomechanical and tissue overload which lead to increased stress in the patellofemoral joint. Predisposing factors may be classified as those related to local joint impairments, altered lower extremity biomechanics and training errors or overuse¹¹.
Epidemiology including risk factors and primary prevention
The reported incidence in the clinical setting ranges from 21 to 40%, affecting females twice as often as males.1,2 It constitutes nearly 25% of all knee injuries in runners. Risk factors can be divided into intrinsic and extrinsic as well as those factors that are modifiable and those that are not. Modifiable intrinsic factors include weak muscles (hip abductor, external rotators, and vastus mediualis dysfunction); inflexibility of the iliotibial band, quadriceps, hamstring, and gastrocsoleus tendons; foot overpronation; and increased joint reactive forces with heel strike. Non-modifiable factors include patella alta, femoral anteversion, pes planus, age, gender and race. Extrinsic factors include training errors or overtraining, such as an overly rapid increase in training progression or intensity, inappropriate running shoes, uphill training and hard playing surfaces. Preventive strategies include identification and correction of modifiable risk factors11.
The anatomy and biomechanics of the patellofemoral joint play a major role on its function, stability, and pathology. Abnormalities to bony structures, dynamic and static stabilizers affect patellar tracking along the femoral trochlea, and lead to uneven distribution of patellofemoral compressive forces and joint stress.1
The pain generators include the subchondral bone of the patella, synovial capsular and retinacular soft tissues, and tendon insertions on the patella. The resulting pain can be associated with stimulation of free nerve endings, secretion of inflammatory mediators, and abnormal transmission of forces to the subchondral bone. Patellofemoral joint reaction forces increase with high degrees of knee flexion and this may trigger pain receptors in the subchondral bone.1
Disease progression including natural history, disease phases or stages, disease trajectory (clinical features and presentation over time)
In the early stage of PFPS, anterior knee pain occurs with jumping, running, and stair climbing, and improves with rest. As the clinical condition progresses, pain occurs with activity, may impair sports performance, and improves after a period of inactivity. If not diagnosed and treated appropriately, patellar pain will be present with less activity and even at rest, impairing activities of daily living. When exercise resumes following periods of rest, the pain may return if biomechanical, training, or footwear errors are not corrected. Over time, abnormal wear to the patella and associated femoral cartilage leads to chondromalacia and chronic pain.
Specific secondary or associated conditions and complications
Pain, arthrogenic muscle inhibition, abnormalities in lower limb biomechanics, reduced sports performance, and ultimately degenerative changes in articular cartilage and subchondral bone will occur leading to patellofemoral osteoarthritis (PFOA). PFOA is highly prevalent affecting both lateral and medial patellar facets13.
2. ESSENTIALS OF ASSESSMENT
Patients describe an ill-defined ache in the anterior knee with insidious onset. It worsens with activities involving knee flexion, such as squatting, sitting for prolonged periods (theater sign), descending stairs, or running hills. They may describe episodes of give-way, weakness/instability, buckling, patellar instability, clicking and knee swelling or stiffness.
Examination includes evaluation of static and dynamic factors that can alter patellofemoral mechanics, including apprehension testing, as well as evaluation of other knee pathology. Inspection of the patella for abnormal tilt, rotation, anterior-posterior position, and the thigh for muscle atrophy; assessment of patellar tracking evaluating for the J-sign (lateral tracking of the patella as the knee moves from flexion to extension); lower extremity alignment looking for femoral anteversion, increase in the dynamic Q angle, genu valgum or recurvatum, external tibial rotation, and foot over-pronation. Exam should include palpation of the patella, patellar tendon, and peripatellar soft tissues, as well as muscle strength testing of the hip, knee, and ankle musculature, and flexibility of the ITB, hamstrings, quadriceps, and gastrocsoleus tendons. Referred pain from the hip should also be evaluated.1,2,3
The step-down or single leg squat test and observational gait analysis of walking and running mechanics can be used to evaluate dynamic lower extremity kinematics. Biomechanical assessment includes looking for excessive contralateral pelvic drop, lateral trunk deviation, hip adduction and internal rotation, knee valgus, tibial external rotation, and foot pronation.
Erythrocyte sedimentation rate, or “sed rate” (ESR) and C-reactive protein test (CRP) screen for active systemic inflammatory arthritis or connective tissue disorder.
Plain films of the knee (weight-bearing A-P, lateral with 30°of flexion, and axial views) are useful to rule out other sources of anterior knee pain, including bipartite patella, degenerative changes, loose bodies, and occult fractures, and to assess for patellar position. If plain films are negative and diagnosis is not clear, then a magnetic resonance imaging (MRI) or a computed tomography (CT) scan should be used to further evaluate the knee. Musculoeskeletal ultrasound can be useful in evaluating soft tissues around the patella, the thickness the lateral retinaculum and individuals with patellar tendinopathy. A new method using real-time MRI allows measurement of patellofemoral joint kinematics during weight-bearing and non–weight- bearing dynamic tasks.4
Supplemental assessment tools
Instrumented biomechanical evaluation of specific tasks such as squats, step-down maneuvers and the drop jump, using dynamic electromyography and video analysis, can be used in athletes and active individuals. Patients should also have their gait assessed to examine for issues that could lead to PFPS, such as excessive or prolonged pronation, tibial internal rotation, or femoral internal rotation.
Early predictions of outcomes
The severity of symptoms on initial clinical presentation and persistent quadriceps weakness or pain may result in slow response to treatment. In one study, younger age at the time of presentation was predictive of success of exercise interventions while older age was associated with benefit from orthotic use14.
Training surface and uphill training are important factors to consider. These surfaces may increase the stress reaction forces that are applied to the extensor mechanism during running or jumping activities. The patient should be assessed to determine if they are wearing the appropriate shoes as well. Different foot and body types demand the correct type of running shoe as abnormal forces in the foot and ankle will translate to the knee.
Social role and social support system
Because of the multi-factorial nature of PFPS, psycho-social factors may play an important role in the treatment planning and education of the patient, family members, and coaching staff. Understanding the nature of the disease process and treatment interventions may lead to better outcomes.
PFPS is a condition best treated with a multi-disciplinary team approach. The team includes the primary and consulting physicians, athletic trainer, physical therapist, and other sports health specialists (psychology, exercise physiology). Adherence to treatment by the patient is directly influenced by the proper coordination of treatment care and communication within the treating team. An important issue to address is return to sport. Athletes should have normal motion, strength and lower extremity biomechanics. They should be free of pain at rest and with activity prior to returning to full exercise and participation.
3. REHABILITATION MANAGEMENT AND TREATMENTS
Available or current treatment guidelines
There are no standard treatment guidelines for PFPS. Treatment is based on identification and correction of suspected contributing factors. Early therapeutic interventions include relative rest, physical modalities, and/or oral medications. Exercise, particularly strength training with open kinetic chain (OKC) and closed kinetic chain (CKC) exercises involving the hip, knee, and ankle muscles may be effective in long-term management.
At different disease stages
Acute management includes modified rest, ice, and NSAIDs to control symptoms and allow participation in a treatment program. Patellar taping and braces to reduce abnormal patellar tracking, and ankle-foot orthoses may lead to short-term reduction in symptoms, treatment tolerance, and adherence to training regimen.5
Exercise therapy, specifically strength training with OKC and CKC exercises, is proven to be effective in the treatment of PFPS in the sub-acute phase. Strengthening of the hip abductors, hip external rotators, VMO, and lumbo-pelvic core muscles improves pelvic, hip, and knee dynamic stabilization during functional activities. Strengthening the quadriceps and hip muscles and stretching the iliotibial band reduces patellar lateralization. Soft tissue mobilization and stretching of tight retinacular structures improves patellar mobility; while ITB, hamstring, and quadriceps stretching improves patellar tracking. Foot pronation correction with Achilles tendon stretching and ankle strengthening is also beneficial.6,7,8,9
In later stages of the syndrome, gait and running retraining is essential for a complete rehabilitation and prevention of subsequent symptomatic episodes. Barefoot or forefoot running may be beneficial in decreasing anterior knee stress during activity. Furthermore, training errors should be identified, such as excessive training load, increasing intensity too fast, inadequate time to recovery, and excessive hill work. For patients with chondromalacia, visco-supplementation can be considered. In patients with chronic symptoms secondary to lateral pressure syndrome, an arthroscopic lateral release can relieve patellar tilt.
Coordination of care
Patient coordination of care will depend on response to initial treatment. Early intervention may lead to return to activity, however patients that do not respond to treatment may require further evaluation with advance imaging, interventional procedures, and in some instances, surgical evaluation.
Patient & family education
Education about the condition, diagnostic approach, and treatment plan is essential in all medical issues. This is especially true in the young athletic population since the parents play a leading role in the health-related decision-making process. An important consideration in the long-term management of PFPS is to strongly encourage the patient to maintain their home exercise program even after symptoms have resolved. If the PFPS was related to strength or flexibility deficit, those issues will likely return if the patient does not continue their home program.
Treatment outcomes can be measured according to symptom resolution, including pain, level of physical activity (including return to play), and patient satisfaction.
Translation into practice: practice “pearls”/performance improvement in practice (PIPs)/changes in clinical practice behaviors and skills
PFPS is a multifactorial problem; therefore an increased understanding of the pathoanatomy and etiology of the condition will improve treatment outcomes. With appropriate consideration, clinicians should consider foot orthoses for older patients and those with greater forefoot valgus, exercise for younger patients, and patellar taping for pain relief.14
4. CUTTING EDGE/EMERGING AND UNIQUE CONCEPTS AND PRACTICE
Cutting edge concepts and practice
The use of dynamic assessment of lower extremity alignment and biomechanics aids the clinician in further defining the etiology of PFPS and planning treatment. Dynamic MRI, instrumented biomechanical testing and gait analysis, including evaluation of running technique, should be considered in the management of athletes or patients not responding to treatment.
Emerging therapeutic interventions for musculoskeletal injuries include the use of prolotherapy, platelet rich plasma (PRP), and mesenchymal stem cell therapy (MSC). PRP and autologons stem cell therapies are being used in the knee for cartilage lesions; otherwise, there are currently no published studies about these therapies for PFPS.10
5. GAPS IN THE EVIDENCE-BASED KNOWLEDGE
Gaps in the evidence-based knowledge
There is no specific treatment protocol that will address all patients with PFPS. What constitutes the optimal combination of medications, therapeutic modalities, flexibility and strengthening exercise, as well as modification of equipment and sports technique for different subgroups of patients remains to be determined.
- Collado H, Fredericson M. Patellofemoral pain syndrome. Clin Sports Med. 2010;29: 370-398.
- Micheo WF. Concepts in sports medicine. In: Braddom RL. Physical Medicine and Rehabilitation. 2nd ed, Elsevier. Philadelphia, PA. 2006: 1021-1046.
- Fredericson M, Yoon K: Physical examination and patellofemoral pain syndrome. Am J Phys Med Rehabil. 2006;85: 234–243.
- Elias DA, White LM. Imaging of patellofemoral disorders. Clinical Radiology. 2004;59: 543–557.
- Heintjes E, Berger MY, Bierma-Zeinstra SM, et al. Pharmacotherapy for patellofemoral pain syndrome. Cochrane Database Syst. 2004;3: CD003470.
- Heintjes E, Berger MY, Bierma-Zeinstra SM, et al. Exercise therapy for patellofemoral pain syndrome. Cochrane Database Syst.Rev. 2003;4: CD003472.
- Nakagawa TH, Muniz TB, Baldon R M, et al. The effect of additional strengthening of hip abductor and lateral rotator muscles in patellofemoral pain syndrome: a randomized controlled pilot study. Clin Rehabil. 2008;22(12): 1051-60.
- Finnoff JT, Hall MM, Kyle K, et al. Hip strength and knee pain in high school runners: a prospective study. PM&R. 2011;3(9): 792-801.
- Earl JE, Hoch AZ. A proximal strengthening program improves pain, function, and biomechanics in women with patellofemoral pain syndrome. Am J Sports Med. 2011;39(1): 154-63.
- Koga H, Engebretsen L, Brinchmann JE, et al. Mesenchymal stem cell based therapy for cartilage repair: a review. Knee Surgery, Sports Traumatology, Arthroscopy. 2009;17(11): 1289-1297.
- Fredericson M, Khadavi M, Dutton R. Update on rehabilitation on patellofemoral pain. Curr Sports Med Reports. 2014;13(3): 172-178.
- Seif-Barghi T, Mazaheri R, Halabchi F. Patellofemoral pain syndrome and modifiable intrinsic factors. 2013 Jun;4(2): 85-100
- Witvrouw E, Callaghan M, Stefanik J, et al. Patellofemoral pain: consensus statement from the 3rd International Patellofemoral Pain Research. Br J Sports Med 2014;48: 411-414
- Lack S, Barton C, Vicenzino B. Outcome predictors for conservative patellofemoral pain management: A systematic review and meta analysis. Sports Med 2014;44: 1703-1716.
Original Version of the Topic:
William F. Micheo, MD, Gerardo Miranda, MD. Patellofemoral syndrome. Publication Date:2012/07/20.
William F. Micheo, MD
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Gerardo Miranda, MD
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Juan Carlos Perez, MD
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