As epidemic of knee replacements looms, x-rays may provide predictive power

In the longest natural history study of radiographic knee osteoarthritis (OA) to date, researchers demonstrated the annual rate at which women develop the condition is low, though if x-rays demonstrate possible osteophyte at baseline, knee OA was more likely to worsen, according to a study published in the July issue of Arthritis & Rheumatism.

K. M. Leyland, MSc, of the University of Oxford, U.K., and colleagues noted the importance of establishing the history of OA as a way to better understand the condition during a time when its economic burden is increasing. They said there were 54 percent more knee replacements in 2004 compared to just four years earlier, and this number is estimated to increase to 1.4 million by 2015.

“Because of the increasing health burden due to the aging population and a projected 45 percent lifetime risk of symptomatic knee OA developing, there is an urgent need to understand the natural course of knee OA in order to target preventative therapies and reduce known risk factors for both the incidence and progression of knee OA,” wrote the authors.

Leyland et al examined women from the Chingford Women’s Study. From this community-based cohort, 1,003 subjects with a median age of 53 years were enrolled in the study. Of these, 561 had a complete radiography series available, featuring bilateral x-rays of the knees obtained at approximately five-year intervals. Images were scored for OA using Kellgren/Lawrence (K/L) grades, in which a score of 0 is normal, 1 indicates possible osteophyte, and scores of 2-4 indicate a more definite diagnosis with increasing deformities.

Results showed that at baseline, 13.7 percent of subjects had radiographic knee OA of K/L grade 2 or worse in at least one knee. Prevalence increased to 47.8 percent by year 15, with the annual cumulative incidence of the condition at 2.3 percent between baseline and the final year of the study.

Patients with a K/L grade of 1 at baseline were more likely to have their condition worsen by year 15 compared with subjects who had any other K/L grade at baseline—even those with worse grades at baseline—reported Leyland and colleagues. More than 51 percent of subjects with a K/L grade of 1 at baseline underwent OA progression, and those with a grade of 2 underwent progression in less than 48 percent of cases. Only 1.1 percent of knees with a baseline K/L grade of 0 progressed to total knee replacement.

Prevalence of radiographic knee OA was connected to various patient characteristics, including age. Of women older than 60 years at baseline, 42.2 percent developed OA by year 15, compared with 26 percent of women younger than 50 years at baseline. Obese patients had a cumulative incidence of the condition nearly 20 percent higher by year 15 than women in the normal or overweight categories.

The authors pointed out that the majority of patients who underwent knee replacement by year 15 did not have a K/L grade of 2 or above at baseline, suggesting radiographs are not the optimal tool for making long-term predictions about the possibility of total knee replacement. However, the clinical advantages offered by alternatives to plain film radiography, such as MRI, are uncertain and are still being researched, according to Leyland and colleagues.