Comparison of the effect of metabolic, inflammatory and neuropathic phenotypes on osteoarthritic pain and disability between genders

Abstract

Purpose: Osteoarthritis (OA) has been usually defined as a painful joint disease that predominantly affects elderly. However, the degree of pain that patients with OA experiment vary considerably and do not always correspond with the severity of structural changes. This is in part explained by multiple mechanisms that might contribute to pain perception in OA . Comorbidity is considered one of those mechanisms. However, in the search for OA-phenotypes, comorbidity has been used in general as an index or sum of different diseases that do not always contribute to modify pain perception. Different phenotypes have been previously explored to understand the genesis of pain in OA. Metabolic, neuropathic and Inflammatory, are some of the most studied. We hypothesized that these phenotypes may be constituted by associated comorbidities that might have a fundamental effect on pain severity and disability (clinically relevant). The purpose of this study was to classify a cohort of patients with knee/hip osteoarthritis according with their comorbidities in these three phenotypes. The resulting groups were compared on the following clinical factors: pain severity, number of pain sites and disability. Methods: This is a cohort study of patients with knee or hip osteoarthritis, who received or are candidates to receive a joint replacement. All patients in this cohort presented advanced OA at hip and/or knee joints with radiographic evidence of the disease. We interviewed 862 patients. Patients with other pathologies, rheumatoid arthritis, lupus, avascular necrosis or fractures were excluded (n¼135). On top of medical records, questionnaires included: Gender and age, joint(s) affected with pain. Weight and height were measured and body mass index (BMI) was calculated. Patients were asked about the difficulty of walking and climbing stairs and it was scored from 0-3 as follows: without difficulty (0), with some (1), great difficulty (2) or unable to do (3). Pain at each joint was determined by the patients using a numerical rating scale (NRS). Comorbidities were identified, classified, or converted to the ICD-10 codes. Logistic regression and Analysis of variance (ANOVA) with mean values (m) were used to verify the degree of association of the comorbidities grouped in three phenotypes