Iatrogenic fractures of the femoral neck during closed nailing of the femoral shaft.

We have reviewed our experience of four iatrogenic femoral neck fractures in 315 consecutive closed intramedullary nailings with the AO/ASIF universal femoral nail. The average neck-shaft angle in the bones that fractured was 139.3 degrees +/- 1.2 degrees SD (136 to 141); in the whole series the average neck-shaft angle was 125.3 degrees +/- 8.6 degrees and only 11 had angles of more than 135 degrees. The upper ends of the nails in the four which fractured were 17 mm, 5 mm, 3 mm, and 1 mm below the tip of the greater trochanter. In the seven patients with neck-shaft angles greater than 135 degrees but with no fracture, none of the nails had been inserted beyond the tip of the greater trochanter. We nailed six cadaver femora to simulate the forces produced by intramedullary nailing. Despite deep insertion, only one of the six sustained a neck fracture. This specimen had a radiographic neck-shaft angle of 140 degrees against an average of 127.3 degrees +/- 4.0 degrees for the other five. We believe that the medial prong of the AO insertion jig, with its medial overhang of 2 to 3 mm, may impinge on the superior aspect of a valgus femoral neck during final impaction, causing a neck fracture. This may be avoided by leaving the end of the nail above the tip of the trochanter in such cases.