Agreement Between Knee Radiography and Knee Ultrasonography in the Detection of Osteophyte (Spur) Formation and Joint Space Narrowing in Knee Osteoarthritis: A Cross-Sectional Study at Gatot Soebroto Central Army Hospital, Indonesia, August-September 2026

Abstract

Background: Knee osteoarthritis (OA) is one of the most common degenerative joint diseases among adult and older populations, with osteophyte (spur) formation and joint space narrowing (JSN) as its two principal radiological hallmarks. Conventional radiography remains the standard imaging modality but is limited by its two-dimensional nature and inability to directly assess soft tissue, whereas ultrasonography (US) allows real-time visualization of bone margins and periarticular soft tissue without ionizing radiation. Reported agreement (kappa) between radiography and US for osteophyte detection varies widely across populations (0.18–0.58), underscoring the need for population-specific data. Objective: To determine the level of agreement between knee radiography and knee US in detecting osteophyte formation and joint space narrowing in patients with knee osteoarthritis. Methods: An analytic observational study with a cross-sectional design was conducted on 42 subjects with a clinical diagnosis of knee OA who underwent weight-bearing knee radiography and knee US of the same knee at the Radiology Installation of Gatot Soebroto Central Army Hospital (RSPAD Gatot Soebroto Puskesad), Jakarta, Indonesia, between August and September 2026. Subjects were enrolled by consecutive sampling. Radiographic (anteroposterior weight-bearing and lateral) and B-mode US (high-frequency linear transducer, weight-bearing position) examinations were interpreted independently by different radiologists. Agreement was analyzed using Cohen’s kappa (κ), with sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of radiography relative to US calculated as supplementary diagnostic parameters. Results: Of 42 subjects, the majority were female (35; 83.3%), with a mean age of 59.79 years (median 58; range 40–82 years). Osteophyte formation was detected in 38 subjects (90.5%) by radiography and 36 subjects (85.7%) by US, yielding κ = 0.774 (95% CI 0.469–1.000; p < 0.001; substantial agreement). All discordant pairs (n = 2) showed the pattern “radiography positive, US negative,” giving radiography a sensitivity of 100%, specificity of 66.7%, PPV of 94.7%, and NPV of 100% relative to US. Joint space narrowing was identically detected in 40 of 42 subjects (95.2%) by both modalities, yielding κ = 1.000 (95% CI 1.000–1.000; p < 0.001; almost perfect agreement). US additionally identified patellar cartilage thinning in 38 (90.5%), meniscal degeneration in 36 (85.7%), synovitis in 35 (83.3%), and knee joint effusion in 3 of 42 subjects (7.1%) — findings not assessable by radiography. Conclusion: Knee radiography and knee US show substantial-to-almost-perfect agreement in detecting osteophyte formation and joint space narrowing, supporting the use of knee US as a complementary, radiation-free modality in the evaluation of knee osteoarthritis, particularly given its additional capacity to characterize periarticular soft-tissue abnormalities not detectable by radiography.