Background/Purpose: Peripheral and central sensitization (alterations in pain signaling) are related to heightened pain severity and can be present in knee osteoarthritis (OA). Sensory input plays an integral role in motor function, and the pain adaptation theory recognizes the impact of pain on motor function. However, it is unknown if sensitization independently contributes to alterations in physical function beyond the effect of pain severity. We examined the relation of sensitization to low physical function in older individuals with or at risk for knee OA independent of pain severity.

Methods: The MOST Study is a NIH-funded cohort of persons with or at risk of knee OA. Two sensitization measures were assessed: 1) Temporal summation (a marker of central sensitization) was defined as being present when, after touching the skin of the right wrist with a 60g monofilament repeatedly at 1Hz for 30s, the participant reported new or increased pain at the wrist. 2) Pressure pain threshold (PPT) is a marker of peripheral +/- central sensitization at sites of disease/inflammation, or of central sensitization when assessed at an otherwise normal area. PPT was assessed with an algometer (1 centimeter (cm)² tip) as the point at which the participants indicated that the pressure first changed to slight pain. Three trials (0.5 kilograms (kg)/s) at each anatomic site were averaged. PPT was assessed at the right wrist and index patella (i.e., knee with the worst knee pain). PPT was divided into sex-specific tertiles. Low physical function was assessed by gait speed and WOMAC function (0-68 scale). Gait speed was calculated from the 20-meter walk test (meters (m)/second(s)). Gait speed and WOMAC function were dichotomized at 1.0 m/s and >28/68, respectively, which are standard definitions of low physical function. Logistic regression models were used to determine the relation of temporal summation and PPT to physical function while adjusting for age, sex, BMI, clinic site, depressive symptoms, catastrophizing, and knee pain severity.

Results:

2171 participants were included: mean±SD age and BMI were 67.9±7.8 and 30.7±5.9, respectively; 60% were female. Temporal summation was present at the wrist in 42.2% of participants. The mean PPT at the wrist and index patella were 3.4±1.5 and 5.0±2.2 kg/cm², respectively. 53.3% and 10.9% of participants had low physical function as defined by slow walking and WOMAC, respectively. In general, participants with temporal summation at the wrist and low PPTs at the wrist and index patella were more likely to have slow walking (Table). Participants with low PPTs at the patella were more likely to have low WOMAC physical function.

Conclusion: Measures of pain sensitization are related to physical function. The relation is independent of knee pain severity and provides support that peripheral and central nervous system alterations may not only affect pain severity, but also physical function.