Letter to the Editor regarding "Skin keratin correlates with bone and tendon collagen quality: a proof-of-concept clinical study using FTIR spectroscopy in shoulder arthroplasty patients"

To examine the statistical robustness and translational interpretation of reported associations between skin keratin signals and bone and tendon collagen quality in a proof-of-concept Fourier-transform infrared spectroscopy study of eight patients undergoing shoulder arthroplasty.

Correlation-specific denominators and unexplained asterisks in Table 2 were examined. Pearson coefficients and p values were recalculated from the rounded tabulated values using complete cases. Fisher 95% confidence intervals and Spearman rank-based sensitivity analyses were assessed; multiplicity and measurement reliability were also appraised.

If the asterisks indicate unavailable measurements, the skin keratin-bone collagen analysis includes seven complete pairs. Recalculation yields r = 0.719 and p = 0.068 rather than the reported r = 0.72 and p = 0.04. Skin keratin/lipid content versus bone mineralization yields r = 0.697 and p = 0.081 rather than p = 0.053, while bone versus tendon collagen yields r = 0.897 and p = 0.006 rather than p = 0.003. The skin-tendon Pearson correlation remains r = 0.76 and p = 0.03, but its approximate 95% confidence interval is 0.11-0.95; Spearman sensitivity analysis gives ρ = 0.55 and p = 0.16. Triplicate skin spectra were obtained, although within-subject repeatability was not reported.

Skin spectroscopy remains hypothesis-generating and cannot yet be considered a validated surrogate or predictive tool for deep-tissue quality. Clarification of missing-data handling, analytic denominators, multiplicity, and influence analyses, followed by standardized repeatability assessment and external clinical validation, is warranted.