KEELE, UK—Radiographic evidence of osteoarthritis (OA) is not always accompanied by knee pain in the general population, but patients who report knee pain are quite likely to have joint damage detectable by x-ray, Rachel Duncan, MSC, MRCP, reports in Annals of the Rheumatic Diseases.1
"Whether based on persistence of knee pain within a given period of time, the severity of pain and stiffness, or the degree of difficulty with locomotor activities attributed to the knee problem, there is a clear increase in the prevalence of definite radiographic osteoarthritis across categories of these characteristics," says Dr. Duncan, who is a Clinical Research Fellow at the Primary Care Sciences Research Centre, Keele University, Keele, UK. She notes, "Older people reporting knee pain will, more likely than not, have definite evidence of radiographic osteoarthritis irrespective of the nature, frequency, and severity of their symptoms and disability."
The data for this analysis were drawn from the Knee Clinical Assessment Study [CAS(K)], a prospective observational cohort study of persons with knee pain from the general population. Radiography for all subjects included three views: weight-bearing posteroanterior semiflexed/metatarsophalangeal according to the Buckland-Write protocol, skyline, and lateral. The latter two were obtained in a supine position with the knee flexed to 45 degrees. Radiographic arthritis was defined as a Kellgren and Lawrence (K&L) score >e;2 on the posterioranteroanter view and/or >e;2 on the skyline view, and/or the presence of definite superior or inferior patellar osteophytes on the lateral view, and/or the presence of posterior tibial osteophytes on the lateral view. The posterioranterior view and the posterior compartment of the lateral view were used to assess the tibiofemoral joint. The skyline and lateral views were used to assess the patellofemoral joint.
Pain persistence was assessed by questionnaire items on episode duration, days of knee pain in the last 2 months, days of knee pain in the last 6 months, and days of pain or aching or stiffness in the last month. Severity of knee pain, stiffness, and disability were assessed using the Western Ontario and McMaster Universities (WOMAC) Osteoarthritis Index. The Graded Chronic Pain Status was used to measure the combination of pain intensity and disability.
Dr. Duncan notes that this methodology differs from that in previous studies, which either selected patients according to radiographic stage and then looked at pain and disability, or used restricted radiographic views of the knee, often excluding the patellofemoral joint.
"This approach addresses the question, 'Does radiographic osteoarthritis occur more frequently in those with severe or persistent pain compared to those with mild or intermittent pain?'" she says.
As might be expected, but had not been previously well documented, the answer is "yes." The population-based study of 819 adults aged 50 years and older with knee pain found that radiographic osteoarthritis was more common in patients with a longer history of osteoarthritis and more persistent symptoms. Patients with higher WOMAC scores for pain severity, stiffness, and disability were more likely to have radiographic osteoarthritis. Individual WOMAC items for pain and disability regarding weight-bearing mobility were the most strongly associated with radiographic osteoarthritis. Persistent severe pain was associated with a significant increase in the occurrence of radiographic osteoarthritis. The new study did not include patients without pain and so did not address the question of whether radiographic osteoarthritis actually causes knee pain.
New Study Helps Quantify Relationship Between Pain and X-Ray OA
"The relationship between pain and structural damage in osteoarthritis has been difficult to quantify," explained Paul Emery, MA, MD, FRCP, lead clinician in the rheumatology division at Leeds Teaching Hospitals, UK. "Structural damage is fixed, whereas pain and dysfunction may well vary from time to time [and] a particular problem is with early disease where x-rays are very insensitive; in late disease there is a much better correlation."
The new study offers "better x-ray assessment and good clinical observation in a large number of patients," Dr. Emery told CIAOMED. "Their findings are of no surprise to people involved in the management of patients with OA, but they do represent a step forward in avoiding the more negative arguments."
Reference
1. Duncan R, Peat G, Thomas E. et al. Symptoms and radiographic osteoarthritis: Not as discordant as they are made out to be? Ann Rheum Dis. 2006 July 28; [Epub ahead of print].