Who’s at risk?
Anterior knee pain or Patello-femoral Pain Syndrome (PFPS) is the most commonly diagnosed knee condition seen in patients under the age of 50 (Lankhorst et al 2012). The incidence of presentation has been reported as being between 2-30% at sports medicine practices, with incidences as high as 43% in athletes (Crossley et al 2002). Women are typically reported to have a higher incidence than men (Taunton et al 2002).
Why does it occur?
Lankhorst et al (2012) presented a critical review looking at risk factors for PFPS. Using seven articles that met the stringent inclusion criteria, from an initial 3845, 135 variables of potential risk factors were evaluated. Risk factors included:
- physical fitness
- joint moments
- peak torques
- onset timing of Quadriceps muscles (Vastus Medialis Obliquus (VMO) and Vastus Lateralis (VL))
- general joint laxity
- patella mobility
- joint angles
- vertical ground reaction force
- plantar pressure
- psychological parameters
Where possible, results were pooled for more thorough meta-analysis. This revealed two prominent risk factors for the development of PFPS:
- decreased knee extension strength
- being female
Limitations exist however, primarily that many of the risk factors were described in single studies preventing pooling of data and deeper analysis. The risk factors identified may therefore be significant but require further evidence. It seems likely that there are many significant risk factors for the condition. For example another paper by Witvrouw et al (2000) revealed shortened quadriceps muscles, altered VMO muscle reflex response time, decreased explosive strength, and hyper-mobility of the patella as having significant correlations with the incidence of PFPS.
What does this mean?
The lack of definitive risk factors for PFPS belies the lack of understanding of the aetiology and pathology associated with the condition. PFPS is an umbrella term used to encompass retro-patellar and anterior knee pain, when other pathologies such as bursitis, tendinopathies, osteoarthritis and cartilage lesions, have been ruled out.
What causes the pain?
Studies looking at the distribution of nerves which carry signals that may produce pain have suggested the structures involved may be:
- anterior synovium
- subchondral bone
- medial and lateral retinaculae
- infrapatellar fat pad (Bierdert et al 2000, Dye et al 1998, Witonski & Wagrowska-Danielewicz 1999).
Physiotherapy is the most common treatment pathway used for this condition (Crossley et al 2001). Assessment may focus on five broad areas for objective assessment:
- symptoms (pain location and type)
- alignment of the lower extremity
- patellar position, tightness
- weakness and muscle loss
- knee function during dynamic activities (Witvrouw et al 2005)
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Crossley K, Bennell K, Green S, Cowan S, McConnell J. Physical therapy for patellofemoral pain: a randomised, double blinded, placebo-controlled trial. American Journal of Sports Medicine 2002;30(6):857-865
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