Pain Is Modulated Differently Between Females with and without Patellofemoral Pain: Factors Related to Sensitization.

CONTEXT Patellofemoral pain (PFP) has poor long-term recovery outcomes. Central sensitization describes central nervous system changes altering pain modulation, which can complicate recovery (poorer prognosis, worse function). Signs of central sensitization include amplified pain facilitation, pain hypersensitivity, and impaired pain inhibition, which can be measured with temporal summation of pain (TSP), pressure pain thresholds (PPTs) and conditioned pain modulation (CPM), respectively. Sex differences exist for these test responses, but female-only PFP investigations of sensitization are uncommon. Understanding pain modulation in females with PFP could improve treatment protocols. OBJECTIVE To determine whether females with PFP exhibit signs of central sensitization (greater TSP, lower PPTs, reduced CPM) compared to pain-free females. DESIGN Cross-sectional Setting: Laboratory Patients or Other Participants: Thirty-three females [(20 PFP, 13 pain-free); Age: PFP 29.2 ± 7 years, pain-free 28 ± 7 years; Height: PFP 166.7 ± 5.9cm, pain-free 166 ± 9.5cm, Mass: PFP 66.7 ± 9.6kg, pain-free 69.3 ± 7.5kg). MAIN OUTCOME MEASURES TSP was assessed with ten punctate stimuli applied to the knee and calculated by the difference in pain intensity between beginning and end responses. PPTs were tested at four sites [3 for local hypersensitivity (knee), 1 for widespread hypersensitivity (hand)]. CPM was conducted by comparing PPTs during two conditions (baseline, ice immersion). CPM response was defined as the percent difference between conditions. Between-group differences in TSP response were analyzed with a Welch's test. Separate Welch's tests analyzed group comparisons of PPTs and CPM responses at four sites. RESULTS Females with PFP exhibited greater TSP response (P=0.019) and lower CPM response at patella center (P=0.010) and hand sites (P=0.007) than pain-free females. PPT group differences were not observed at any site (P>0.0125). CONCLUSIONS Females with PFP modulate pain differently than pain-free females. Clinicians should recognize signs of central sensitization and their potential impact on treatment options.