An intramedullary fixation device for use with a bone comprising a proximal end, is provided. The fixation device includes a nail sized and configured to be inserted into an intramedullary channel of the bone, the nail having a generally laterally extending bore, an arm sized and configured to be located so that at least a portion of the arm extends through the bore of the nail along the neck of the bone when the device is implanted in the bone, the arm having a threaded portion at one end for fixation into the head of the bone. The device also includes a locking mechanism to prevent rotation of the arm relative to the nail, the locking mechanism configured to allow sliding of the arm through the bore, the locking mechanism configured to be located on the lateral side of the nail and the distal side of the bone when the arm is disposed within the bore.