Impaired Conditioned Pain Modulation in Young Female Adults with Long-Standing Patellofemoral Pain: A Single Blinded Cross-Sectional Study

Objective: Patellofemoral pain (PFP) is common among young individuals. Female adolescents with PFP present typically with localized mechanical hyperalgesia around the knee, but the effect of central pain mechanisms are unknown. This study aimed to compare temporal summation of pain, conditioned pain modulation (CPM), and widespread hyperalgesia in young female adults with PFP and age-matched pain-free controls.

Design: Cross-sectional study.

Setting and subjects: Twenty young female adults (19-21 years old) with long-standing PFP were compared with 20 pain-free controls from the same population-based cohort.

Methods: Cuff algometry was used to assess the pain detection threshold. Temporal summation of pain was assessed by recording the pain intensity on a visual analog scale during repeated cuff pressure stimulations at pain tolerance intensity on the lower leg. CPM was recorded as an increase in the cuff pain detection threshold in response to experimental conditioning pain imposed on the contralateral arm. Handheld pressure algometry was used to assess pressure pain thresholds (PPTs) on the knee, shin, and forearm. The examiner was blinded to the type of subject assessed.

Results: Compared with pain-free controls, young females with PFP showed no decrease in cuff pain thresholds (P < 0.40) or facilitated temporal summation (P < 0.15) but had a lower CPM response (P < 0.04) and lower PPTs (P < 0.005).

Conclusions: Young female adults with long-standing PFP demonstrated impaired CPM. This is important because PFP, a peripheral pathology, might have important central components that need to be studied in order to understand its extent and therapeutic implications.