Differences in Pain Sensitivity in Young Females With Longstanding Patellofemoral Pain, Recovered Females With a History of PFP, and Healthy Controls.

Recently it has been demonstrated that females with longstanding PFP demonstrate increased pain sensitivity, or hyperalgesia in the peripheral nervous system and impaired conditioned pain modulation, which is representative of decreased descending control of pain in the central nervous system. This is commonly seen in older adults with chronic longstanding pain, such as knee OA.

Understanding the evolution of pain mechanisms during recovery may yield important insights into the highly recurrent nature of this condition. Self-reported recovery appears to be associated with increased pressure pain thresholds, in comparison to those with current PFP. However, it is unknown whether these characteristics, along with centrally mediated pain processing, ever return to 'normal', or to the same levels of those with no history of pain.

To examine this, the investigation will compare the three groups (PFP versus Recovered versus Control), on measures of pain sensitivity (as defined in the primary and secondary outcomes), to determine differences between groups.

Demographic data, regarding age, height and weight will be collected, as well as pain frequency (almost daily, several times per week, weekly, monthly, rarely, never), pain intensity (measured on numeric rating scale), Knee Injury and Osteoarthritis Outcome score, and spatial distribution of pain (using the Navigate pain application). The group that self report as recovered, will be asked to report when their symptoms resolved.

A subgroup analysis will be undertaken in the recovered group, to examine the relationship between the time since last knee pain was experienced, (duration they self- report being symptom-free), and pain sensitivity, as assessed by the primary and secondary outcome measures.