A confident diagnosis of knee osteoarthritis can be made without radiographic examination in adults older than 40 years based on criteria described in evidence-based recommendations to be published by the European League Against Rheumatism.
The criteria include usage-related knee pain, short-lived morning stiffness, functional limitation, and one or more “typical” examination findings, such as crepitus, restricted movement, and bony enlargement.
Clinical signs, symptoms, risk factors, and plain radiography are the cornerstones of the recommendations, which have a focus on clinical diagnosis that distinguishes them from the American College of Rheumatology criteria, said Weiya Zhang, Ph.D., of the University of Nottingham (England). He is lead author of the recommendations, which were presented at the annual European Congress of Rheumatology in Copenhagen and are slated for publication in an upcoming issue of the Annals of Rheumatic Disease.
The recommendations were developed by a task force of 17 osteoarthritis experts from 12 European countries. A systematic literature search was undertaken to identify the best available evidence, which was combined with clinical expertise in gauging the strength of each recommendation. Diagnostic accuracy was tested using multiple predictive models in two populations, including one from the Netherlands and one from the United Kingdom, Dr. Zhang explained.
The risk factors found to be strongly associated with knee OA in patients with knee pain include age older than 50 years, female sex, high body mass index, previous knee injury or malalignment, joint laxity, occupational or recreational usage, family history, and the presence of Heberden's nodes, the task force concluded.
Although plain radiography of the knee (including a weight-bearing view, a semiflexed view, and lateral and skyline views) remains the standard imaging modality for morphologic assessment of knee OA, imaging is an adjunct for diagnostic purposes. Other imaging modalities, such as MRI, sonography, and scintigraphy, are “seldom indicated for diagnosis of OA,” according to the authors. Classic radiographic features “are focal joint space narrowing, osteophyte, subchondral bone sclerosis, and subchondral cysts.”
Other recommendations cover the definition of knee OA, subsets of the disease, typical symptoms and signs, the use of laboratory tests, and differential diagnosis:
▸ Knee OA is a common, complex joint disorder that is characterized clinically by usage-related pain and functional limitation. The disorder entails focal cartilage loss, new bone formation, and involvement of all joint tissues—changes that are mirrored radiographically.
▸ Subsets of knee OA are associated with different risk factors and outcomes, and can be defined by compartmental involvement, bone response, the global pattern of OA, crystal presence, and the degree of inflammation. However, “the ability to discriminate subsets and the relevance for routine practice are unclear,” the task force noted.
▸ The typical symptoms of knee OA are often episodic, variable in severity, and slow to change. Night pain and more persistent pain at rest may indicate advanced OA.
▸ In addition to the key findings indicative of knee OA (crepitus, restricted movement, and bony enlargement), additional features may include deformity, instability, periarticular or joint-line tenderness, and pain on patellofemoral compression.
▸ Such features as severe local inflammation, erythema, and progressive pain unrelated to usage should raise red flags, as they suggest sepsis, crystals, or serious bone pathology.
▸ Laboratory tests on blood, urine, or synovial fluid are not required for the diagnosis of knee OA, but they may be used to confirm or exclude other inflammatory conditions.
▸ Synovial fluid should be aspirated and analyzed if a palpable effusion is present, in order to confirm or exclude inflammatory disease and identify urate and calcium pyrophosphate crystals.
The authors acknowledged that the recommendations are limited because they were derived from literature based on different studies; the likelihood ratios pooled from the literature may be affected by multiple factors, including the number of studies, the populations considered, and the cutoff values selected; and there was no universally applicable reference standard for knee OA. Also, the recommendations could be different for “less typical” patients younger than age 40 years.
Dr. Zhang reported having no relevant financial relationships to disclose.