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?
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.
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.
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.
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.