Individuals with primary osteoarthritis have different phenotypes depending on the affected joint - a case control study from southern sweden including 514 participants.

OBJECTIVE: The aim of this study was to evaluate whether primary osteoarthritis (OA), independent of affected joint, is associated with a phenotype that is different from the phenotype in a normative cohort. Material and.

METHODS: We included 274 patients with primary OA, 30 women and 32 men (mean age 66 years, range 42-84) with primary hip OA, 38 women and 74 men (mean age 61 years; range 34-85) with primary knee OA, 42 women and 19 men (men age 64 years, range 42-87) with primary ankle or foot OA and 20 women and 19 men (mean age 66 years, range 47-88) with primary hand or finger OA. Of all patients included with OA, 23% had hip OA, 41% knee OA, 22% ankle or foot OA and 14% hand or finger OA. Serving as references were 122 women and 118 men of the same ages who were population-based, included as a control cohort. We measured total body BMD (g/cm2) and proportion of fat and lean mass (%) with dual energy X-ray absorptiometry. Height, weight and BMI (kg/m2) were also assessed. We then calculated Z-scores (number of standard deviations difference from the mean value of the control cohort) in the OA patients and compared these between the groups.

RESULTS: Individuals with hand OA and controls had similar phenotype. Individuals with lower extremity OA, irrespective of the affected joint, had similar weight, BMI and BMD, but higher than in individuals with hand OA and controls (all p<0.05). Individuals with lower extremity OA had higher fat and lower lean mass than individuals with hand OA and controls (all p<0.001).

CONCLUSION: Individuals with primary OA in the lower extremity have a phenotype with higher BMD, higher BMI, proportionally higher fat content and lower lean body mass content. The different skeletal phenotypes in our patients with OA in the lower extremity and patients with hand OA indicate that separate pathophysiologic pathways may be responsible for primary OA in different joints.