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".

PURPOSE: 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.

METHODS

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.

RESULTS

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.

CONCLUSION

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.