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 and 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, and reduced CPM) compared with pain-free females. Design: Cross-sectional study. 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 +/- 5.9 cm, pain free 166 +/- 9.5 cm; mass: PFP 66.7 +/- 9.6 kg, pain free 69.3 +/- 7.5 kg). Main Outcome Measure(s): Temporal summation of pain was assessed with 10 punctate stimuli applied to the knee and calculated by the difference in pain intensity between beginning and end responses. Pressure pain thresholds were tested at 4 sites (3 for local hypersensitivity [knee] and 1 for widespread hypersensitivity [hand]). Conditioned pain modulation was conducted by comparing PPTs during 2 conditions (baseline and ice immersion). Conditioned pain modulation response was defined the percent difference between conditions. Between-groups differences in TSP response were analyzed with a Welch test. Separate Welch tests analyzed group comparisons of PPTs and CPM responses at 4 sites. Results: Females with PFP exhibited greater TSP response = .019) and lower CPM response at patella center (P = .010) and hand sites (P = .007) than pain-free females. Pressure pain thresholds group differences were not observed at any site (P > .0125). Conclusions: Females with PFP modulate pain differently than pain-free females. Clinicians should recognize signs of central sensitization and their potential effect on treatment options.