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 inter -observer agreements using shear wave elastography (SWE).
Methods: 98 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 < 0.01), and weak negative correlation in suprapatellar (ρ, -0.31, p < 0.01), and left Achilles (ρ, -0.29, p < 0.01). 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 < 0.05). Kruskal Wallis showed significant differences in SWV for quadriceps (p = 0.01), suprapatellar (p = 0.03), and left Achilles (p = 0.01) among different age groups. Good interobserver [0.79-0.86 (95% CI, 0.32-0.94)] and inter-observer agreement [0.78-0.89 (95% CI , 0.62-0.95)] was 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.
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