To investigate the relationship between baseline radiographic severity of knee osteoarthritis (OA) and the importance of long-term joint space narrowing.
Sub-analysis from a three-year randomized, placebo-controlled, prospective study, of 212 patients with knee OA, recruited in an osteoarthritic outpatient clinic and having been part of a study evaluating the effect of glucosamine sulfate on symptom and structure modification in knee OA.
Measurements of mean joint space width (JSW), assessed by a computer-assisted method, were performed at baseline and after 3 years, on weightbearing anteroposterior knee radiographs.
In the placebo group, baseline JSW was significantly and negatively correlated with the joint space narrowing observed after 3 years (r=-0.34, P=0.003). In the lowest quartile of baseline mean JSW (<4.5mm), the JSW increased after 3 years by (mean (S.D.)) 3.8% (23.8) in the placebo group and 6.2% (17.5) in the glucosamine sulfate group. The difference between the two groups in these patients with the most severe OA at baseline was not statistically significant (P=0.70). In the highest quartile of baseline mean JSW (>6.2mm), a joint space narrowing of 14.9% (17.9) occurred in the placebo group after 3 years while patients from the glucosamine sulfate group only experienced a narrowing of 6.0% (15.1). Patients with the most severe OA at baseline had a RR of 0.42 (0.17-1.01) to experience a 0.5mm joint space narrowing over 3 years, compared to those with the less affected joint. In patients with mild OA, i.e. in the highest quartile of baseline mean JSW, glucosamine sulfate use was associated with a trend (P=0.10) towards a significant reduction in joint space narrowing.
These results suggest that patients with the less severe radiographic knee OA will experience, over 3 years, the most dramatic disease progression in terms of joint space narrowing. Such patients may be particularly responsive to structure-modifying drugs.