Abstract
Patellofemoral Pain (PFP) is highly prevalent among adults and adolescents. Localized mechanical hyperalgesia around the knee and tibialis anterior have been observed in people with PFP, but limited knowledge of potential manifestations of central sensitisation exists. The aims of this study were to study conditioned pain modulation (CPM) and wide-spread hyperalgesia in adults with PFP. This assessor-blinded cross-sectional study design compared CPM and mechanical pressure pain thresholds (PPT) between 33 adults (23 females) diagnosed with PFP and 32 age and sex matched pain-free controls. The investigator taking the PPT measurements was blinded to which participants had PFP. PPTs were reliably measured using a Somedic hand-held pressure algometer at three sites: 1) The centre of the patella, 2) the tibialis anterior muscle and 3) a remote site on the lateral epicondyle. For the assessment of CPM, experimental pain was induced to the contralateral hand by immersion into a cold water bath (conditioning stimulus), and assessment of PPTs (the test stimulus) was performed before and immediately after the conditioning stimulation. On average, the CPM paradigm induced a significant increase in PPTs across the three sites (6.3–13.5%, P<0.05), however there was no difference in CPM between young adults with PFP compared to the control group, (F(1,189) = 0.39, P = 0.89). There was no difference in mechanical PPTs between the two groups (F(1,189) = 0.03, P = 0.86). Contrary to our a-priori hypothesis, we found no difference in CPM or PPT between young adults with PFP and age and sex matched pain-free controls.
Highlights
One of the most long-lasting and troublesome knee conditions among adolescents and adults is patellofemoral pain (PFP)
The knee pain map showed that most participants with PFP reported retropatellar pain (n = 18) or combined peripatellar and retropatellar pain (n = 12), with only one reporting peripatellar pain
The Conditioned pain modulation (CPM) testing induced a significant increase in PTTs across the three sites, but there was no difference in CPM between the PFP and control groups, (F(1,189) = 0.39, P = 0.89, Fig 1, mean values presented in S1 File) nor when adjusting for sex using an ANCOVA
Summary
One of the most long-lasting and troublesome knee conditions among adolescents and adults is patellofemoral pain (PFP). The underlying aetiology is largely unknown, it is often considered a loading related condition [6] This is because PFP often presents in highly active populations such as runners and military recruits, and has been associated with altered knee joint loading [7]. Boudreau et al noted that a longer symptom duration was associated with a greater distribution or spreading of the area of pain [8]. Together, these observation have led recent studies to investigate the role of other potential contributors to the pain experience, including psychological factors [10] and pain sensitivity [11]. Studies of pain sensitivity have demonstrated local mechanical hyperalgesia around the patella in adolescent [12] and adult females with PFP [13], while widespread mechanical hyperalgesia has only been reported in young female adults [13,14]
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