Biochemical Variation Among Normal Equine Carpal and Tarsocrural Joint Fluids are Detected by Infrared Spectral Characteristics and A Modified Approach to Linear Discriminant Analysis

Abstract

Research into osteoarthritis diagnostics has evolved from traditional methods that are only useful in more advanced clinical disease, towards the discovery of biomarkers that are predictive or reflective of preclinical joint disease. The potential of Fourier transform infrared spectroscopy (FTIR) coupled with chemometrics has been demonstrated as useful for the assessment of biomolecular responses to disease. Joint fluid was collected from 105 clinically normal antebrachiocarpal (AC), midcarpal (MC) and tarsocrural (TCRL) joints. Thin films were prepared and FTIR absorbance spectra in the mid-infrared region recorded. Interferograms were signal averaged and Fourier transformed to generate spectra with a nominal resolution of 4 cm-1. Comparisons among joints were made using a novel modified method similar to linear discriminant analysis, which maximized the difference of between-group variance minus within-group variance, followed by permutation testing. Differences within animal between contralateral pairs of joints were minimal. Significant differences among AC, MC and TCRL joint fluid spectra were found. The range of biomolecular differences among these normal joints as characterized by FTIR indicates that interarticular variation within the horse needs to be considered for ongoing research, especially when utilizing within-horse joints as controls.