Impact of obesity, structural severity and their combination on the efficacy of viscosupplementation in patients with knee osteoarthritis.

Background: Obesity and radiological severity have been identified to be independent predictors of a low rate of response to viscosupplementation (VS), in patients with knee osteoarthritis (OA). Is that enough to formally refute VS in such patients in whom surgery is sometimes contraindicated?

Objectives: To compare pain and function scores before and 6 months after knee VS, according to the weight status (obese versus non obese), the radiological severity (mild/moderate versus severe) and both combined.

Methods: Post-hoc analysis of a prospective, double blind, randomized, multicentre trial, comparing 2 viscosupplements, in patients with symptomatic knee OA. Patients were classified according to body mass index (BMI < or ≥ 30 kg.), OARSI radiological grade (1-2 versus 3) and OMERACT-OARSI response criteria (Yes/No). WOMAC between-group comparisons (obese versus non-obese, OARSI 1-2 versus 3, and both combined) in all patients and in OMERACT-OARSI Responders, were achieved using Mannn-Whitney U test.

Results: One-hundred and sixty-six patients were analyzed: 28.3% were obese, 44% were OARSI grade 3, 42,2% were neither obese nor OARSI 3, whereas 14.5% were obese and OARSI 3. At baseline WOMAC pain score did not differ according to the patients sub-groups (p > 0.05). Six months after VS, WOMAC pain decreased significantly in all patient sub-groups (all p < 0.01). At month 6, WOMAC pain sub-score was significantly lower in non-obese than in obese patients (4.9 ± 4.1 versus 7.1 ± 4.9; p = 0.008) and in patients OARSI 1-2 versus 3 (4.8 ± 4.3 versus 6.4 ± 4.5; p = 0.009). However, in responder patients there was no difference in pain score and pain decrease related to the weight status and the radiological score.

Conclusion: These results do not confirm our previous conclusions that recommended not performing VS in obese patients with severe knee OA. Although the chances of being a responder were much reduced in these patients, the benefit of patients who respond to treatment was similar to that of subjects with normal weight and mild/moderate OA. Different pain phenotypes, more than overweight and advanced disease, might be the main reason for the success or failure of VS.