An assembly of sterile devices designed to measure and display, periodically or continuously, the interstitial pressure in a closed fascial compartment of muscle. It typically consists of a battery-powered, hand-held, pressure-measuring instrument with a display and connected devices used to access the muscle compartment (e.g., a prefilled syringe, one-way valves, and a side ported noncoring needle and/or slit catheter). It is intended to assess chronic and/or acute compartmental syndrome, a condition of increased intra-compartmental pressures from swelling within muscle compartments and tendon sheaths due to trauma. This is a single-use device.