Insertion of the distal screws in interlocking nail fixation of femoral shaft fractures. Technical note.

The introduction of interlocking nails has greatly expanded the indications for intramedullary fixation of femoral shaft fractures, and several authors have reported good results with this method7. However, on occasion it may be difficult to insert the distal interlocking screw. Distal locking is presently accomplished using either mounted or handheld guides, and both techniques can result in excessive radiation exposure to the surgeon. The free-hand technique described herein uses the camera of the image intensifier as an alignment guide and overcomes several potential sources of error in placement of the distal screw. With this technique, the alignment axis of a distal screw-hole is determined with the image intensifier, as follows. The radiologic technician positions the image intensifier so that it is brought along a direction perpendicular to the long axis ofthe thigh, and the c-arm is then positioned to center the nail halfway between the source and the camera of the image intensifier. Translational displacements of the c-arm are then made so that the distal screw-hole is positioned as close to the center of the screen as possible. Limiting adjustments of the c-arm to one plane at a time, centering first in an anterior-posterior direction, followed by translational movements in a proximal-distal direction, is usually the most effective technique for centering the distal hole on the screen. The appropriate controls of the image intensifier are then locked. The distal screw-hole usually appears as an ellipse on the screen because the alignment axis of the roentgen beam is usually not exactly parallel to the alignment axis of the distal screwhole. The image intensifier is then rotated in the coronal plane until the elliptical hole on the screen widens to a maximum and the latch for coronal rotation is locked (Figs. I-A and I-B). The c-arm is then rotated in the transverse plane until the ellipse widens to a full circle, and then the c-arm is completely locked (Figs. 2-A and 2-B). The surgeon places the tip of a long-handled awl or of a pointed guide-wire on the lateral part of the femoral cortex near the center of the roentgen beam, and while the image intensifier is pulsed he or she moves the tip so as to place