(a) This illustration shows the suggested position of the blocking screws for correction of a valgus deformity. The screws centered around the osteotomy are more typically used leaving the peripheral screws as an option. (b) The same planning can be used for correction of a varus deformity. The overlay of the hands is showing a principle called the “reverse rule of thumbs” whereby the bone is grabbed with the thumb and index fingers of both hands and a correction simulated. The blocking screws should be placed opposite the location of the thumb and index fingers. (c) In the sagittal plane, the blocking screws are inserted posterior to the ILN at the osteotomy site. The distal screw is the most important, but the proximal screw can also be used for a shorter nail. The peripheral screws are seldom needed. (d). This fluoroscopy shot shows ideal posterior blocking screw placement: close to the osteotomy site and lying against the ILN (arrow).