Insall–Salvati Ratio and Femoral Cartilage Thickness: Ultrasonographic and Clinical Evaluation in Knee Osteoarthritis

Background/Aims: This study aimed to evaluate the relationship between the Insall–Salvati ratio (ISR) and femoral cartilage thickness (FCT) in patients with knee osteoarthritis (KOA), and to examine their associations with radiographic disease stage, clinical findings, and functional capacity, including the ability of mean FCT to discriminate late-stage KOA.

Materials and Methods: This cross-sectional study included 104 patients (52/group) diagnosed with KOA via American College of Rheumatology criteria: early stage (Kellgren–Lawrence [K–L] 1-2) and late stage (K–L 3-4). One index knee per participant was analyzed. The ISR was measured on radiographs, and FCT on ultrasonography. Visual Analog Scale (VAS), Knee Injury and Osteoarthritis Outcome Score (KOOS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and 100-m walking time were recorded. Data were analyzed using age- and body mass index (BMI)-adjusted ANCOVA. Stage-specific Pearson correlations were adjusted via the Benjamini–Hochberg false discovery rate (FDR) procedure. Multivariable regression and receiver-operating characteristic curve analyses were also conducted.

Results: After FDR correction, mean ISR correlated with FCT in late-stage KOA (r = 0.527, q < 0.001) but not in early-stage KOA (r = 0.331, q = 0.058). Age- and BMI-adjusted ANCOVA confirmed between-stage differences in mean FCT, VAS, KOOS, WOMAC, and 100-m walking time (all P < .001); however, mean ISR did not differ by stage (P = .419). In multivariable regression, late-stage KOA (B = −0.411 mm) and mean ISR (B = 0.829 mm per 1-unit increase) were independently associated with mean FCT (R2 = 0.463). Mean FCT discriminated late-stage KOA (area under the curve = 0.845, 95% CI: 0.771-0.919); a cutoff of ≤1.82 mm yielded 63.5% sensitivity and 88.5% specificity.

Conclusion: Ultrasonographic FCT is strongly associated with radiographic stage, pain, functional scores, and walking performance, showing good discrimination of late-stage KOA. While ISR was not stage discriminative, it was independently associated with FCT. These findings should be viewed as exploratory; causal inferences cannot be drawn from this cross-sectional design.

Cite this article as: Yesilmen N, Elbastı MŞ, Korkmaz M. Insall–Salvati ratio and femoral cartilage thickness: Ultrasonographic and clinical evaluation in knee osteoarthritis. ArchRheumatol. Published online April 27, 2026. doi:10.5152/ArchRheumatol.2026.26308.