Background Knee pain is the principal clinical symptom of knee osteoarthritis (OA). Although much effort has been devoted toward defining knee pain, the correlation between knee pain and radiographic severity of knee OA by categorical methods, such as the Kellgren Lawrence grade, was not as strong as expected. In this categorical system, joint space narrowing and osteophytosis are not assessed separately, while accumulating lines of evidence indicate that joint space narrowing and osteophytosis may have distinct etiologic mechanisms, and their progression may be neither constant nor proportional. Although osteophytosis also has some effect on activities of daily living and quality of life, joint space narrowing is the primary outcome in studies of OA. Therefore, to examine the association between knee OA and pain, joint space narrowing should be assessed separately. Thus, an automatic system that can quantify the joint space width of the knee in OA on standard radiographs and allow for objective, accurate, and simple assessment of the structural severity of knee OA was developed.

Objectives The objective of the present study was to clarify the association of joint space narrowing with knee pain in Japanese men and women using a large-scale, population-based cohort of the Research on Osteoarthritis/osteoporosis Against Disability (ROAD) study.

Methods This study examined the association between minimum joint space width (mJSW) in the medial compartment and pain in the knee. mJSW was measured in the medial and lateral compartments of the knee using a knee OA computer-aided diagnosis system.

Results From the 3,040 participants in the ROAD study, the present study analyzed the data from 2,733 participants who completed the radiographic examinations and questionnaires regarding knee pain (975 men and 1,758 women; mean age, 69.9 years). Subjects with lateral knee OA were excluded. mJSW in subjects with and without knee pain were 2.4 ± 1.2 mm and 3.3 ± 0.9 mm, respectively, in men (p<0.05) and 2.0 ± 1.1 mm and 2.8 ± 0.8 mm, respectively, in women (p<0.05). medial mJSW/lateral mJSW in subjects with and without knee pain were 57.2 ± 27.6% and 72.8 ± 20.8%, respectively, in men (p<0.05) and 52.2 ± 31.5% and 71.4 ± 33.0%, respectively, in women (p<0.05). After adjustment for age and BMI, medial mJSW and medial mJSW/lateral mJSW, were significantly associated with knee pain (p<0.05). The threshold of medial mJSW by ROC curve analysis was 2.87 mm (sensitivity 0.67, specificity 0.65, AUC 0.70) in men and 2.01 mm (sensitivity 0.43, specificity 0.689, AUC 0.69) in women, while that of medial mJSW/lateral mJSW was 55.2% (sensitivity 0.45, specificity 0.68, AUC 0.66) in men and 57.9% (sensitivity 0.57, specificity 0.75, AUC 0.69) in women.

Conclusions The present cross-sectional study, using a large-scale population from the ROAD study, showed that joint space narrowing was significantly associated with knee pain. The thresholds of joint space width for knee pain were approximately 3 mm in men and 2 mm in women.

Disclosure of Interest None declared