Unrecognized pin penetration in slipped capital femoral epiphysis.

There are at least nine different techniques recommended to lower the incidence of femoral head penetration by fixation pins in the pinning of slipped capital femoral epiphyses. The routine use of fluoroscopy and placement of the fixation pins no closer than 8 mm (or one-third the radius of the femoral head) from the subchondral bone will leave a safe, workable margin. Confirmation of subchondral location after the procedure can be done with fluoroscopy. With the leg in maximal internal rotation, the fluoroscopic unit is rotated from anteroposterior (AP) to lateral under continuous monitoring to detect anterolateral and posteromedial quadrant penetrations. With the fluoroscopic unit in the lateral position, the foot is externally rotated 90 degrees, again under continuous monitoring, to visualize the anteromedial and posterolateral quadrants. If the femoral head cannot be well-visualized in the lateral view, use of a lateral x-ray machine and AP fluoroscopy can be helpful. Another useful technique when the head cannot be well-visualized is the injection of contrast medium through a cannulated screw.