Major lower extremity amputation procedures secondary to compromised vascularity demonstrate extremely high rates of infection, wound complication, mortality, and reoperation, resulting in reduced mobility, cardiovascular deconditioning, and muscle weakness, decreasing the probability of future prosthetic fitting. This in turn results in a compromise in quality of life and increased health care expenditures by the Veterans Health Administration. While multiple factors contribute to delayed or failed wound healing, limb perfusion is a known critical component in stump healing. While ankle-brachial index (ABI) and transcutaneous oxygen pressure (TCPO2) measurements can be used to quantify limb perfusion and can assist in determining the need for an amputation, the literature is conflicted as to the utility of these values in predicting amputation stump healing, with no clear association established. Without reliable objective means of predicting the likelihood of healing, the level of amputation is determined clinically by the operating surgeon based on subjective (i.e. visual) assessment of skin and tissue integrity, quality, and perfusion. This study introduces an injectable subcutaneous bio-sensing technology used with an optical analysis data acquisition system that will immediately detect clinically relevant tissue oxygenation tension in a specific anatomic plane. The overarching hypothesis of this study is that accurate real-time measurement of tissue oxygen tension obtained by use of a novel implantable biosensor is a vital component in determining the appropriate level of amputation, promoting fast primary healing of the residual limb thereby providing a path for the veteran to earlier mobility, increased likelihood of prosthetic fitting, and improved function. This study aims to 1) correlate tissue oxygen tension measured by the biosensor 1 cm below the clinically determined amputation level with established clinical endpoints of primary healing of surgical incision/wound, secondary healing of surgical incision/wound requiring local wound care without reoperation, reoperation for wound revision, and reoperation for revision amputation at a more proximal level; 2) establish the reliability and responsiveness of the biosensor in obtaining accurate readings of the tissue oxygen tension when implanted subcutaneously in the lower extremity of human subjects and 3) establish preliminary guidelines for use of tissue oxygen tension in conjunction with covariate risk score for reamputation to preoperatively guide the determination of the most appropriate level of amputation to best predict primary healing of lower extremity amputation stumps, expediting prosthetic fitting and mobility, minimizing complication rates, and decreasing associated costs. Per current standard of care, the amputation level will be determined by the operating surgeon based on clinical judgement of the appearance of the surrounding tissue (skin integrity, amount of edema, pr...