IATROGENIC FRACTURES OF THE FEMORAL-NECK DURING CLOSED NAILING OF THEFEMORAL-SHAFT

We have reviewed our experience of four iatrogenic femoral neck fractu res in 315 consecutive closed intramedullary nailings with the AO/ASIF universal femoral nail. The average neck-shaft angle in the bones tha t fractured was 139.3 degrees +/- 1.2 degrees so (136 to 141); in the whole series the average neck-shaft angle was 125.3 degrees +/- 8.6 de grees 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 wit h neck-shaft angles greater than 135 degrees but with no fracture, non e of the nails had been inserted beyond the tip of the greater trochan ter. We nailed six cadaver femora to simulate the forces produced by i ntramedullary nailing. Despite deep insertion, only one of the six sus tained a neck fracture. This specimen had a radiographic neck-shaft an gle 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 insert ion jig, with its medial overhang of 2 to 3 mm, may impinge on the sup erior aspect of a valgus femoral neck during final impaction, causing a neck fracture. This may be avoided by leaving the end of the nail ab ove the tip of the trochanter in such cases.