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Patellofemoral Pain Syndrome

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Other Names

  • Patellofemoral Pain Syndrome (PFPS)
  • Patellofemoral Pain (PFP)
  • Anterior knee pain
  • Idiopathic knee pain

Background

  • This page refers to patellofemoral pain, a spectrum of anterior knee pain originating at the Patellofemoral Joint
  • The term 'patellofemoral pain' is not well defined
    • It generally refers to anterior knee pain
    • It covers all conditions related to anterior knee

History

Epidemiology

  • PFPS is the most common cause of knee pain in individuals under the age of 50[1]
    • 2 to 10 times more common in women than men[2]
    • Most common cause of anterior knee pain in pediatric, adolescent patients[3]
  • Prevalence
    • Reported as high as 25% in sports[4]
    • Up to 43% in military trainees (need citation)
    • 11-17% of patients who present to general practitioners[5]
    • 30% of adolescents will develop PFPS[6]
  • Incidence
    • 22 per 1000 person years among naval academy recruits[7]
  • Sports
    • Among adolescent basketball players: overall prevalence is 25%, with ~26% of female and 18% of male players affected[8]

Pathophysiology

  • General
    • PFPS is a common cause of anterior knee pain
    • It is most commonly seen in young women without any structural or pathological changes to the articular cartilage
    • The underlying etiology is often considered to be multifactorial
  • Patellar Tracking/ Malalignment
    • Patella maltracking has long been implicated as a caause
    • Witvrou et al: hypermobile patella had a significant correlation with the incidence of PFPS[9]
    • Draper et al: patients with PFPS squat with increased lateralization, increased lateral tilt of patella[10]
  • Vastus Lateralis and Vastus Medialis (VMO)
    • Cowan et al demonstrated by EMG delayed onset of VMO activation relative to vastus lateralis[11]
    • Patients with PFP tend to exhibit atrophy of the VMO as well[12]
  • Quadriceps Dysfunction
    • Several studies have shown that quadriceps muscle size, strength, and force are impaired in patients with patellofemoral OA[13]
  • Dynamic Valgus/ Q angle
    • The role of the Q-angle as a cause or predictor of PFPS is controversial
    • Some authors have demonstrated a relationship between the Q-angle and development of PFPS[14]
    • Other authors have not recreated that relationship[15]
    • Likely related to dynamic or functional malalignment than a structural problem
    • Multiple studies have demonstrated increased knee abduction, dynamic valgus stressors on the knee joint in PFPS among athletes[16]
  • Hip Stability, abductor strength
    • Multiple studies have shown weakness of hip external rotators, abductors lead to functional malalignment at the patellofemoral joint
    • Prins et al systematic review: strong evidence that females with PFPS have a decreased hip abduction, external rotation and extension strength[17]
    • Note that this is in female athletes, the evidence for male athletes is not strong
  • Disorders of the foot
    • Barton et al: PFPS associated with delayed timing of peak rear-foot eversion, increased rear-foot eversion at heel strike and reduced rear-foot eversion range[18]
    • Early rear-foot eversion appears to increase risk of developing PFPS[19]
    • Abnormalties with navicular bone, such as increased navicular drop, navicular drift and dorsiflexion also seem to contribute[20]
  • Hamstring imbalance, tightness
    • Several studies have identified a significant association between PFPS, hamstring tightness[21]
    • Besier et al: patients with PFPS have greater co-contraction of the quadriceps and hamstrings compared to controls[22]
  • Iliotibial Band
    • The IT band may have an influence on patellar tracking[23]
    • Kaplans fibers connect the IT band to the patella
  • "Knee-Spine Syndrome"
    • Significant difference in sacral inclination between subjects with and without anterior knee pain[24]
    • Otherwise not well described or understood
  • Psychological factors
    • Jensen et al: patients with PFPS have higher level of mental distress compared to healthy controls[25]
    • Coping mechanism of patients with PFPS similar to other groups of patients with chronic pain, PFPS more likely to catastrophize their pain[26]
    • Fear avoidance belief about physical activity associated with pain, function in PFPS patients[27]
    • Domenech et al: high incidence of psychological distress such as anxiety and depression[28]
  • Triggers for PFPS
    • Overload of the patellofemoral joint (e.g. highintensity training)
    • Dynamic valgus and functional lateralization of the patella may lead to overuse
  • Neurological etiology of pain in patients with PFPS
    • Most pain probably develops in the insertions of the extensor mechanism or within the subchondral bone
    • Increased expression of neurofilament protein, S-100 protein, neural growth factor and substance P in the lateral retinacula of PFPS[29]
    • Draper demonstrated increased metabolic bone activity in patients with PFPS using PET/CT[10]
  • Implicated pain sources
    • The medial retinaculum and MPFL[30]
    • Patellar compression of subchondral bone[31]
    • Fat pad

Etiology

  • Overuse
    • Including tendinitis, insertional tendonosis
  • Patellar instability
  • Osteochondral damage
  • Trauma

Associated Conditions

Anatomy of the patellofemoral mechanism[32]

Pathoanatomy

  • Knee Extensor Mechanism
  • Patellofemoral Joint
    • Characterized by the articulation of the patella within the condylar groove of the femur
    • Stabilized by the medial and lateral retinaculae
  • Patella
    • Functions as a lever, increasing the moment arm of the extensor mechanism[33]
    • Acts as a pulley, controlling the direction of the quadriceps
    • Articular cartilage, which is the thickest in the body, provides a smooth sliding surface with the femoral trochlea[34]
    • Acts as a shock absorber

Risk Factors

  • Non-modifiable
    • Female gender
    • Poor shock absorption (i.e. footwear, surface, muscles)
  • Sports
    • Running, Jumping sports
    • Endurance athletes
    • Basketball
    • Soccer
    • Lacrosse
  • Training
    • Training errors or overuse
    • Increased running mileage
    • Increased jumping
  • Muscular
    • Weak knee extension strength, especially VMO[35]
    • Weak hip abduction strength[36]
    • Weak hip external rotation strength
    • Poor flexibility of quadriceps, hamstring, iliotibial band
    • Poor core muscle endurance[37]
    • Foot pronation
  • Biomechanical/ Anatomic
  • Other
    • Trauma
  • Not associated
    • Foot arch height index[38]

Differential Diagnosis


Clinical Features

Clinical demonstration of the patellar grind test

History

  • Pain is universally anterior
  • They may describe it as “behind,” “underneath,” or “around” the patella
  • Usually insidious, but can be acute in nature
  • Pain is typically worse after prolonged sitting, squatting, kneeling, and stair climbing[43]
  • Patients often report clicking, popping, snapping and cracking
  • May report buckling, which is typically transient inhibition of quadriceps due to pain or deconditioning[44]
  • Theatre sign: Pain in the patellofemoral joint after prolonged period of sitting with knee flexed
  • Pain is often bilateral

Physical Exam: Physical Exam Knee

  • Absence of joint effusion; if present consider other etiology
  • Patellar J Sign: lateral tracking of patella shifts medially as knee brought into flexion
  • Compare quadriceps muscle tone, bulk of VMO to contralateral limb
  • On palpation, crepitus may be present
  • Palpate medial/lateral and superior/inferior patellar poles
  • May be ttp to medial or lateral retinaculum
  • May be ttp medial or lateral facets

Special Tests


Evaluation

  • Note: Diagnosis is primarily clinical and imaging is not generally required to make the diagnosis

Radiographs

Ultrasound

  • Can be used to evaluate extensor mechanism

MRI

  • Not routinely indicated in the diagnosis of PFPS
  • May be helpful to evaluate for:
    • Malalignment
    • Trochlear dysplasia
    • Patella tilt
    • Articular chondral injuries
  • Potential findings
    • Enlarged fat pad
    • Subchondral bone edema

Classification

  • Proposed clinical classification[45]
    • Patellofemoral instability, ie., subluxation or dislocation
    • Patellofemoral pain with malalignment but no episodes of instability
    • Patellofemoral pain without malalignment

Management

Nonoperative

  • Indications
    • Vast majority of cases
  • General goals
    • Reduce total patellofemoral compressive forces
    • Alter the distribution of stress forces on the patella
  • Relative rest and activity modification
    • Patients may need to temporarily discontinue offending activity
    • They may need to alter their sport or training habits
    • This could include avoiding/ limiting stairs, running, jumping, squats
  • Physical Therapy
    • Quadriceps strengthening is the gold standard treatment[46]
    • Increased quadricep strength has been show to reduce PFPS pain[47]
    • Bolga et al systematic review: Targeting hip abductors, external rotators generated a modest reduction in pain[48]
    • Harvie et al: 2008 meta-analysis showed positive effects on pain reduction[49]
    • Exercises should address hip muscles, trunk stability, quadriceps, hamstrings and the iliotibial tract

Pharmacotherapy

  • NSAIDS
    • A Cochrane review found limited evidence for the effectiveness of short term pain reduction in PFPS[50]
  • Topical NSAIDS
    • Cochrane review found topical NSAIDS are as effective as oral NSAIDS for chronic musculoskeletal pain[51]
  • Vitamin D
    • Anecdotal evidence that patients with PFPS have low vitamin D and osteopenia by DEXA[52]
    • It is unknown whether supplementation with vitamin D is beneficial

Bracing and Taping

  • Patellar Taping or McConnel Taping
    • Goal: modify patella tracking with adhesive tape, typically a medially directed force
    • When combined with physical therapy and daily home exercises, patellar taping was superior to the control group[53]
    • Warden et al: 2008 meta-analysis showed functional improvement, decreaesed pain when combined with exercise[54]
  • Patellar Brace
    • Goal: apply an external, medially directed force to counteract patella maltracking
    • Lun et al found patellar bracing non-superior to home exercise program with or without a patellar brace or knee sleeve[55]
    • D’hondt et al: 2002 meta-analysis showed patellar brace had positive effects on pain, function, patellofemoral congruence angle[56]
    • Overall, literature is weak and better designed studies are needed.
  • Knee Brace
    • Standard hinged knee brace
  • Foot Orthosis
    • Goal: insoles could improve rear-foot eversion or pes pronatus
    • Collins et al reported moderate improvement in pain in patients who used a corrective orthosis and participated in physical therapy[57]
    • Other studies have shown mixed results
    • Overall, literature is weak for PFPS and better designed studies are needed

Other Modalities

Operative

  • Indications
    • Unknown
    • Likely reserved for refractory cases
  • Technique
    • Arthroscopy
    • Percutaneous
    • Lateral reticular release
    • MPFL repair or reconstruction
    • Anteromedialization of the tibial tubercle
  • Research
    • Kettunen compared arthroscopy plus exercise to exercise alone in patients with chronic PFPS and found no difference[61]

Rehab and Return to Play

Rehabilitation

  • Needs to be updated

Return to Play

  • The athlete can return to sport when the following criteria are met[62]
    • No swelling
    • No pain in squatting and in ascending or descending stairs • Good quadriceps strength (especially vastus medialis obliques)
    • Proper hamstring flexibility
    • Normal gait biomechanics
    • Proper core stability strength
    • Good performance in challenging functional tests (vertical jumping, anteromedial lunge, step-down, single-leg press, and balance and reach tests)
    • The patient feeling that he/she is ready and has confidence in the injured knee

Complications and Prognosis

Prognosis

  • Kannus et al studied chronic PFPS over 7 years[63]
    • 2/3 of patients had complete recovery at 7 years
    • Approximately 30% of the non-recovery PFPS patients had persistent complaints
  • Predictor of poor long term prognosis[64]
    • PFP > 2 months duration
    • Anterior knee pain score < 70
    • Higher levels of usual/resting
    • High worst/activity-related pain

Complications

  • Knee Osteoarthritis
    • Proposed, although not well described, that PFPS increases likelihood of developing patellofemoral OA[65]
  • Patellofemoral Arthritis
  • Inability to return to sport
    • Up to 25% of recreational athletes diagnosed with PFP will stop participating in sports because of knee pain[66]

See Also


References

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Created by:
Jesse Fodero on 7 July 2019 14:34:05
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