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, proximal extent of infection or chronic ulceration if present, and color of the limb). The level of amputation will not be altered by participation in the study. Two biosensors will be inserted into the subcutaneous tissue of each anatomic angiosome via a sterile 19 Gauge needle 1 cm caudad to the planned incision. Tissue oxygen tension will be recorded from each sensor immediately prior to the start of the surgical procedure and again immediately after inflation of the tourniquet. The surgical amputation procedure will proceed routinely with no alteration in the surgical plan from standard of care. Study follow-up will continue for 3 months after surgery; clinical endpoints at 3 months will be correlated with tissue oxygen tension measured intra-operatively just below the level of amputation.

Over 70,000 major amputations of the lower extremity are performed annually. The vast majority of these procedures are required secondary to vascular complications from medical conditions such as diabetes, arterial blockages, and smoking. Complications after amputation are common and often cause significant delays in healing and the need for additional surgery thereby resulting in a lower probability of future prosthetic fitting and use, decreased quality of life, and increased health care expenditure. Oxygen perfusion of the limb is a critical component of wound healing, however no existing method of measuring tissue perfusion can reliably predict the level of amputation likely to afford healing without significant complication. This project aims to enhance amputation level decision making by introducing a novel injectable sensor that can accurately quantify tissue oxygenation, thereby reducing the need for reoperation and prolonged wound care, and maximizing functional recovery.