- Phase 4- Tissue and Data Processing. Assays will be performed on the tissue samples to measure specific metabolic markers of the diabetic Achilles tendon. Tendon collagen concentrations will be determined via quantification of the collagen specific amino acid, hydroxyproline by high performance liquid chromatography (HPLC) and fluorometric detection. The extent of collagen cross-linking will be determined by measuring the amount of pyridinium cross-link hydroxylysylpyridinoline will also be assessed though HPLC. RT-PCR will also be performed to determine the expression of various MMPs and TIMPs. The blood markers will be processed at Georgetown University Hospital. The Department of Vascular Surgery at Georgetown University will perform the noninvasive and invasive studies and the results of their findings will be reported to the investigators.