Pain thresholds, temporal summation and conditioned pain modulation in obese and non-obese individuals with knee Osteoarthritis: a transversal and longitudinal study

Abstract

Knee osteoarthritis (KOA) is a chronic degenerative joint disease, with pain being the main manifestation of the disease, generating a great impact on the quality of life of patients. Obesity is an important risk factor for the development and worsening of osteoarthritis symptoms. Changes in body composition, especially fat mass and lean mass, would be pain modifying factors, contributing to the development of pain sensitization. Considering the inflammatory and metabolic factors associated with excess adipose tissue, it is estimated that the amount of body fat can influence pain sensitization, through pain thresholds, temporal summation and conditioned pain modulation, as well as changes in functionality of the lower limb. Therefore, the project aims to evaluate the differences in pressure pain threshold, temporal summation and conditioned pain modulation in obese and non-obese KOA subjects, and subsequently relate it to body composition and functionality, physical activity level and quality of life. . The same measurements will be carried out after 8 months. 100 participants with KOA will be evaluated, with grades II, III and IV (Kellgren & Lawrence), divided into 2 groups: obese (BMI e30) and non-obese (BMI <30). All subjects will be submitted to bilateral knee radiography exams and blood collection from the antecubital vein, for analysis of the lipid and glycemic profile. The body composition of all participants will be evaluated by the Dual Energy X-ray Absorptiometry (DXA) exam. All subjects will respond to questionnaires to assess depression, quality of life and sleep, pain catastrophizing, kinesiophobia and KOA symptoms by WOMAC. For quantitative pain analysis, participants will locate body pain points through the figure of a homunculus and Quantitative Sensory Tests (TSQ) will be performed in a standardized sequence: 1- pressure pain threshold 2- temporal summation of pain; 3- conditioned pain modulation. Pressure pain thresholds will be evaluated by a pressure algometer, temporal summation will be evaluated by the Pinprick Stimulator equipment (MRC, Germany) and conditioned pain modulation with Algomed and Q-sense pressure algometers. Pain threshold test stimuli will be performed on the most symptomatic knee, in randomized order at the following points: lateral knee joint line, medial knee joint line, belly of the tibialis anterior muscle ipslateral to the ipslateral thenar eminence knee. Conditioned pain modulation will be performed on the joint lines of the most symptomatic knee and temporal summation on the back of the left hand. Conditioned pain modulation will compare the pain provoked by the test stimuli (pressure and heat) before and immediately after the application of conditioning tonic pain stimulus (4°C water). Subsequently, functional performance and Dynamic weight-bearing Assessment of Pain will be performed to assess pain related to physical activity. Finally, participants will wear an accelerometer (activPAL) attached to the right leg for 7 consecutive days to assess the level of physical activity. During the follow-up period, the subjects will receive an online form monthly, so that they can indicate changes in dietary changes and physical activities. For data analysis, a descriptive analysis will be carried out and the normality and homogeneity of variances will be verified. According to the data distribution, the corresponding independent or non-parametric t-test will be applied, especially for cross-sectional analyses. For the analysis of prospective data, mixed model ANOVA will be applied if the data are parametric and repeated measures ANOVA for non-parametric data. Finally, a linear regression model will be applied to the dependent variable pain, including the other variables as independent (significance level of 5%). (AU)