Obesity is related to clinical pain severity and pressure pain sensitivity among older adults with and without knee osteoarthritis

Studies have shown that obesity is an important risk factor for knee osteoarthritis (KOA) incidence and associated pain sensitivity. However, less is known about whether obesity is also related to pain sensitivity among individuals without KOA. The purpose of this study was to examine whether obesity is related to reports of OA pain as well as mechanical pain sensitivity among older adults with and without KOA. The sample consisted of older (age 45-85), community-dwelling adults and included 168 participants (74% women) with KOA and 101 participants (66% women) without KOA. Weight and height measurements were collected from each participant in order to calculate Body Mass Index (BMI). Participants completed the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and underwent algometry to determine pressure pain thresholds (PPTs). PPTs were assessed at the medial and lateral joint lines of the most affected knee for participants with KOA; PPTs were assessed at a randomly selected knee for those without KOA. Additional testing sites included the quadriceps, forearm, and trapezius ipsilateral to the knee. Obese (BMI ≥ 30) KOA participants reported significantly greater symptoms (pain, stiffness, and dysfunction) on the WOMAC compared to non-obese (BMI < 30) KOA participants (p<.001). Similarly, obese KOA participants demonstrated significantly lower PPTs at the medial (p<.001) and lateral (p =.024) knee joint, but not at other testing sites. Interestingly, obese participants without KOA also demonstrated significantly lower PPTs at the medial (p=.015) and lateral (p =.04) knee joints compared to non-obese participants without KOA. Results suggest that obesity may be a risk factor for enhanced pain sensitivity localized at the knee irrespective of KOA status. Future research should focus on expanding knowledge about mechanisms of the relationship between obesity and pain in samples with and without KOA.