Background Conventional radiography is the most commonly used imaging modality for assessing osteoarthritis (OA) in daily practice. However, the sensitivity of conventional radiography for detecting early changes of cartilage damage may be relatively low. Ultrasonography (US) is able to visualize large portions of femoral hyaline cartilage directly and to assess osteophytes [1-3].
Objectives The main aim of this study was to compare US with conventional radiography for the assessment of joint damage in knee OA.
Methods One hundred sixty-six knees of 84 patients (59 women and 25 men) with primary knee OA were included in this study. The femoral hyaline cartilage of the medial para-patellar aspect and osteophytes of both medial and lateral femoral condyle were scanned. The cartilage involvement and the osteophytes were both quantitatively (grade 0-3) and qualitatively assessed. An US global grade for knee joint damage was developed merging the US cartilage damage and osteophyte grades (grade 0-3). The US findings were compared with those obtained by conventional radiography using the Kellgren and Lawrence (K/L) grading system (grade 0-3).
Results There was a moderate agreement between US cartilage damage grade and K/L grade assessments (weighted κ=0.466: 95% CI 0.361-0.572) and fair agreement between US osteophyte grade and K/L grade assessments (weighted κ =0.306: 95% CI 0.208-0.405). A fair agreement was found also between the US global grade and K/L grade assessments (weighted κ =0.396: 95% CI 0.289-0.504). In 31 knees with K/L grade 1, US grade higher than 1 were found in 6 knees for cartilage damage and 14 knees for osteophytes. Ninety-two percent of knees that had less than 1 mm cartilage thickness were classified as severe OA in radiographs.
Conclusions The present study provides evidence supporting the concurrent validity of US in the assessment of knee joint damage due to OA through its agreement with conventional radiography. However, such a correlation was moderate. A possible reason explaining the discrepancy between radiographic and US assessment may be related to the fact that US allows a direct visualization of femoral cartilage while joint space width assessed by conventional radiography is the result of cartilage thinning and/or meniscal degeneration and protrusion.
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Disclosure of Interest None declared
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