Pain Processing May Be Altered in Women With Patellofemoral Pain

Young women with patellofemoral pain may have altered pain processing compared with healthy controls.

Young women with patellofemoral pain (PFP), both long-standing (>5 years) current and resolved postadolescent PFP (recovered-PFP), may have altered pain processing compared with healthy control patients, according to a study published in Pain.

Recurrent PFP is common in young women who display lowered pain inhibitory control and widespread pressure hyperalgesia. The mechanisms underlying recurrence of pain are not well understood, and it is unclear whether central pain mechanisms return to normal during pain-free periods or retain some level of sensitization despite symptomatic recovery. Investigators sought to explore differences in widespread and localized pain sensitivity, conditioned pain modulation, and temporal summation of pain in women with current PFP or recovered PFP and in pain-free women.

For this assessor-blinded cross-sectional study, a total of 87 women (<25 years) were enrolled and had current-PFP (n=36; mean age, 22.8 years; mean pain duration, 8 years) or recovered PFP (n=22; mean age, 23.2 years; mean pain duration, 5 years; mean time since knee pain, 2 years), or were pain-free (n=29; mean age, 23.1 years). Pronociceptive and antinociceptive profiles were examined, with conditioning pain modulation evaluated using increases in thresholds for cuff pain (primary endpoint), and pressure pain thresholds and temporal summation of pain assessed during repeated leg cuff pressure pain stimulations, using a visual analogue scale (secondary endpoints).

Participants in the current-PFP group had lower pressure pain thresholds at the shin, knee, and forearm (mean difference, 85-225 kPa; P <.05) and impaired conditioning pain modulation (mean difference, 11.6%, P =.004) compared with women in the recovered-PFP group. Conditioning pain modulation was comparable in the control and current-PFP groups. Participants in the recovered-PFP and current-PFP groups had facilitated temporal summation of pain compared with control participants (mean difference, 0.7-0.8 in visual analogue scale change; P <.05). Knee pressure pain thresholds were lowest in women with current PFP and highest in control participants (mean difference, 110-225 kPa; P <.05).

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Study strengths include using a population-based cohort to increase generalizability and limiting detection bias with blinded assessor. Study limitations include the cross-sectional design, which prevented meaningful inference regarding causality; not accounting for alternate pain locations in the recovered-PFP group; and a small sample size.

“Despite being recovered for a median of 2 years, those with a history of adolescent knee-pain continue to demonstrate altered pain processing. These findings are particularly interesting due to the potential effects of such maintained effects on central pain mechanisms for recurrence of pain symptoms, despite reporting no current pain,” concluded the study authors

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Holden S, Straszek C, Rathleff M, Petersen K, Roos E, Graven-Nielsen T. Young females with long standing patellofemoral pain display impaired conditioned pain modulation, increased temporal summation of pain and widespread hyperalgesiaPain. August 1, 2018. doi: 10.1097/j.pain.0000000000001356