A surgical instrument is provided for cutting bone and other tissue. The surgical instrument is powered by a pressurized fluid and includes a rotatable shaft connected to a dissection tool. The instrument includes a housing member comprising a one-piece base. A rotor housing chamber is defined by the base, and the rotatable shaft is located in the rotor housing chamber. A first hearing housing is defined by the base, located adjacent the rotor housing chamber, and houses a first bearing that engages the rotatable shaft. A second bearing housing is defined by the base, located on an opposite side of the rotor housing chamber from the first bearing housing, and houses a second bearing that engages the rotatable shaft. A passage is defined by the base and operable to direct a pressurized fluid through the base to the rotor housing chamber in order to rotate the rotatable shaft.