Skin thickness alterations in pressure injury tissue: insights from high-frequency ultrasound and mixed-design analysis of variance

Purpose/aim To quantify skin thickness alterations in pressure injury (PI) tissue and evaluate the influence of PI risk factors using high-frequency ultrasound. Background Early PI detection remains challenging due to limitations of visual assessment. High-frequency ultrasound (HFUS) offers high-resolution skin imaging but lacks validation in PI tissues. Design Prospective comparative study. Methods In this cross-sectional study, we assessed skin thickness in 42 bedridden patients with pressure injuries (PIs). For each patient, measurements were taken at the PI site and an adjacent normal site using high-frequency ultrasound (18 MHz). A mixed-design ANOVA tested the effects of tissue type (within-subject: PI vs. normal), PI risk status (between-subject: high vs. low), and body mass index (BMI: ≥24 vs.<24 kg/m²), including all main and two-way interaction effects. Post-hoc tests were Bonferroni-corrected, and effect sizes were quantified using generalized eta-squared (η²G). Results Skin at pressure injury (PI) sites was substantially thicker than at adjacent normal sites (3.26 ± 0.63 mm vs. 2.11 ± 0.52 mm). A mixed-design ANOVA confirmed a large, significant main effect for tissue type (F (1, 38) = 57.980, p< 0.001, η g 2 = 0.500 ). Additionally, the model revealed a significant main effect for PI risk status, with high-risk patients exhibiting greater overall skin thickness (F (1, 38) = 11.150, p = 0.002, η g 2 = 0.090 ). The main effect of body mass index was not significant (p = .510). While no interactions reached statistical significance, the interaction between tissue type and PI risk status trended towards significance (F (1, 38) = 3.20, p = .082, η g 2 = 0.050 ). This trend reflected a pattern wherein the difference in skin thickness between PI and normal sites was more pronounced in high-risk patients compared to low-risk patients. No other interactions were significant (all p > 0.050). All model assumptions were met. Conclusions HFUS-detected skin thickening is a hallmark of PI tissue, primarily driven by local pathology and modulated by systemic risk factors. HFUS shows potential for objective PI assessment.