Purpose: Ultrasound can be performed to evaluate the degree of osteophytes and synovitis in persons with knee OA bedside to patients, without any side effects or contraindications. Few studies have looked at the associations between ultrasound findings and pain, and there is limited knowledge regarding ultrasound as a valid examination to assess OA pathology of the knee. Hence, we aimed to compare the degree of OA changes by ultrasound among people with and without knee OA according to established classification criteria and study the associations between ultrasound findings and pain.
Methods: The Nor-Hand study is an observational cohort in which 300 patients with hand OA (89% women, median (IQR) 61 (57-66) years old) were recruited. The current analyses include cross-sectional data from the baseline examination. We included 286 participants in the present analyses after excluding participants with knee prostheses or arthrodesis. The participants reported the levels of knee/hip pain using the Western/Ontario McMaster University index (WOMAC) and marked their painful joints (including the bilateral knees) during the last 24 hours and last 6 weeks on two separate homunculi. An experienced rheumatologist (BSC) examined whether the participants fulfilled the clinical ACR criteria for knee OA or not (n=7 missing). A trained medical student performed the ultrasound examination of the knees using a General Electric (GE) Logic E9 ultrasound machine with a 6-15Mz probe. Both knees were scored for 1) the severity of osteophytes in the medial and lateral tibia and femur on 0-3 semi-quantitative scales (0=no, 1=small, 2=medium, and 3=large; sum range = 0-12 per knee), and 2) grey-scale synovitis on 0-3 semi-quantitative scales (0=no, 1=mild, 2=moderate, and 3=severe pathology). The highest score of osteophytes and grey-scale synovitis (range: 0-3) and the sum scores of both knees together (range: 0-24 for osteophytes and 0-6 for synovitis) were calculated.
We compared the degree of ultrasound pathologies in persons with vs. without clinical knee OA according to the ACR criteria using Chi-square tests for categorical data and Mann-Whitney U test or T-test for continuous data as appropriate. The associations between ultrasound pathologies and pain scores were explored by linear and logistic regression analyses, adjusted for age, sex, and body mass index. Generalized Estimating Equations were applied to account for two knees belonging to the same person.
Results: Knee osteophytes on ultrasound, but not grey-scale synovitis, were significantly more common in persons with knee OA compared with persons without knee OA (p<0.001) (Table 1). Osteophytes were associated with higher levels of WOMAC pain, while no association was found between grey-scale synovitis and WOMAC pain (Table 2). However, in analyses on joint level, both osteophytes (OR=1.8-8.2) and grey-scale synovitis (OR=1.2-8.2) were associated with pain in the same joint in both a short (24 hours) and long term (6 weeks) and with a stronger association for more severe ultrasound scores (Table 3).
Conclusions: People with knee OA had significantly more osteophytes by ultrasound than people without knee OA, while they had no differences in the degree of synovitis, which may be due to the definition of knee OA and a control group that was not entirely “healthy”. Both osteophytes and grey-scale synovitis were associated with pain in the same joint, supporting the validity of ultrasound in knee OA.
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