Defining normal enthesis stiffness range in a healthy adult population.

Objectives: This study explores the correlation between volunteer demographics with enthesis stiffness and intra- and interobserver agreements using shear wave elastography (SWE).

Methods: Ninety-eight healthy volunteers were recruited. SWE was performed on quadriceps, suprapatellar, infrapatellar, and Achilles entheses. The stiffness measurements were measured in shear wave velocity (SWV).

Results: Mann-Whitney test revealed insignificant difference in SWV among gender. Wilcoxon signed-rank test showed significant difference in SWV between left and right Achilles entheses. Spearman correlation test revealed moderate negative correlation between SWV and age group in quadriceps (ρ, -0.45, P < .01), and weak negative correlation in suprapatellar (ρ, -0.31, P < .01), and left Achilles (ρ, -0.29, P < .01). Multiple linear regression analysis showed subjects' demographic significantly predicted quadriceps, suprapatellar, and left Achilles entheses stiffness with only age statistically significantly to the prediction (P < .05). Kruskal-Wallis showed significant differences in SWV for quadriceps (P = .01), suprapatellar (P = .03), and left Achilles (P = .01) among different age groups. Good interobserver [0.79-0.86 (95% CI, 0.32-0.94)] and interobserver agreement [0.78-0.89 (95% CI, 0.62-0.95)] were found in all the entheses.

Conclusion: SWE emerges as a reproducible method for entheses stiffness quantification, with the study highlighting age as a significant factor impacting SWV in quadriceps, suprapatellar, and left Achilles entheses. Among the studied entheses, SWV for Achilles enthesis is the highest in all age groups.

Advances in knowledge: The study significantly contributes to the understanding of enthesis stiffness by exploring the influence of gender, BMI, and age.