Knee Pain Expansion in Early Osteoarthritis: Findings from Iwaki Cohort Study

Abstract

Purpose: In advanced knee osteoarthritis (KOA), chronic pain contributes to central sensitization, amplifying pain perception. Few studies have evaluated pain expansion in early-phase KOA. Here, we investigated how the pain area expands with KOA severity and its association with other knee symptoms.

Patients and methods: Among 737 community-dwelling volunteers, 658 were enrolled. Early KOA was defined according to Luyten's classification, and progressive KOA was defined as Kellgren-Lawrence ≥grade 2. A knee diagram, divided into 12 sections corresponding to the knee anatomy, was marked by patients to indicate areas of pain. The number of sections with reported pain was scored for analysis. Knee symptoms were evaluated using the Knee injury and Osteoarthritis Outcome Scales (KOOS), and their relationship with the number of pain-positive sections was analyzed.

Results: Of 658 subjects, 38 had early KOA and 233 had progressive KOA. The mean number of pain-positive sections was significantly higher in early KOA and progressive KOA groups than in normal knee (1.5, 1.0, and 0.3, respectively; p< 0.001). The anterior medial section (medial joint line and medial collateral ligament) was most frequently affected, followed by the pes anserinus and anterolateral region (lateral joint line and lateral collateral ligament) in overall participants. The number of indicated pain-positive sections correlated negatively with the KOOS scores. ROC analysis to estimate the KOOS total score cutoff for detecting the presence of two or more positive sections revealed a cutoff of 475 points for pain expansion, with a sensitivity of 0.310, a specificity of 0.846, and an [OR] of 12.21. (p ≤ 0.001, AUC: 0.828).

Conclusion: Individuals with early KOA perceived more expansive pain areas than those with normal knees or progressive KOA. Expansion of the pain area was associated with knee symptom. Investigating the expansion of the pain sections may be useful in diagnosis for early KOA.

Keywords: early knee osteoarthritis; knee osteoarthritis; pain drawing.

Figure 1

Flow of the participant enrollment process.

Figure 2

Diagram of pain drawing system.

Figure 3

Percentage of positives per section for each group Positive rates for each group (non-OA, early OA, and progressive OA) are shown. The positive rate in section 4 was the highest in all groups.

Figure 4

Heatmap illustrating the positivity rates for each compartment across the Non-OA, Early KOA, and Progressive KOA groups. Increased positivity rates were observed in the Early KOA and Progressive KOA groups, especially in the section 4 and section 8, and were accompanied by a higher incidence of medial knee joint pain.

Figure 5

ROC curve of KOOS total score for detecting pain expansion Receiver operating characteristic (ROC) analysis was performed to detect the cut-off point of KOOS total score for detecting pain expansion. The area under the curve was 0.828 (95% confidence interval: 0.786–0.870, p<0.001). The cut-off point was defined as the nearest point to the true positive, and estimated as 475 points with Odds ratio 12.21.