Disease severity and knee extensor force in knee osteoarthritis: Data from the Osteoarthritis Initiative
Arthritis Care & Research , 05/01/2012
Berger MJ et al. – The method of disease severity stratification influences the magnitude of knee extensor force deficits because no difference in force between disease subgroups was observed when stratifying with Kellgren/Lawrence (K/L) grade. Furthermore, there was large variability in the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score within each radiographic subgroup, highlighting the limitations in using radiographic measures to reflect symptom severity.Methods
- Data from the Osteoarthritis Initiative (n = 659) were analyzed. Knee extensor force was assessed with isometric contractions.
- Clinical severity was measured with the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC).
- Patients were stratified into tertiles of severity (i.e., moderate, mild, and severe OA) based on the lowest, middle, and highest WOMAC scores, respectively.
- Kellgren/Lawrence (K/L) grading was used to assess radiographic severity of the tibiofemoral compartment and patients were again stratified into mild (K/L grade <2), moderate (K/L grade 2), and severe (K/L grade >2) knee OA.
- When stratifying with the WOMAC, force was significantly lower in the severe group compared to the mild (18% lower; P < 0.001) and moderate groups (9% lower; P = 0.03), and in the moderate group compared to the mild group (10% lower; P = 0.03).
- When stratifying with K/L grade, small nonsignificant differences were observed in the severe (7% lower; P = 0.19) and moderate groups (8% lower; P = 0.08) compared to the mild group.
- Large intragroup variability was observed when comparing WOMAC scores across radiographic severity (coefficients of variation were 79.3%, 74.6%, and 61.6% for K/L grade <2, K/L grade 2, and K/L grade >2, respectively).