The purpose of this prospective observational cohort study is to define the reliability and accuracy of Near Infrared Spectroscopy (NIRS) in the detection of intra-compartmental tissue perfusion in injured and noninjured extremities over time. Additionally, it will establish diagnostic perfusion value thresholds to be used in a subsequent interventional study confirming the efficacy of NIRS-based ACS monitoring. Through prospective measurements of NIRS values, vital signs, intracompartmental pressures and clinical examinations, guidelines and parameters will be established for the use of NIRS in diagnosing acute compartment syndrome (ACS), monitoring patients at risk for ACS and evaluating the adequacy of fasciotomy in patients treated for ACS.