Embodiments of a corpectomy method, comprising the steps of: providing a distractor unit comprising at least a first hydraulic cylinder configured to removably receive a piston of a predetermined length during a surgical procedure; providing the piston; providing a plurality of bone screws; affixing a first bone screw of the plurality of bone screws to a first vertebrae of a spine and a second bone screw of the plurality of bone screws to a second vertebrae of the spine; mounting the distractor unit onto the first bone screw and the second bone screw; and extending the hydraulic piston of the distractor unit to cause the first vertebrae and the second vertebrae to move away from each other are disclosed.