Avoiding the blood supply to the femoral head during cannulated screw fixation: A comparison of two techniques.

Abstract

To compare the strength of the inverted triangle (IT) versus the L-shaped cannulated screw fixation technique for stabilizing a Pauwels 2 femoral neck fracture. To demonstrate the risk to the blood supply to the femoral head from a posterior-superior screw. The IT construct was compared with the L-shaped design in 10 composite femurs. A Pauwels 2 fracture was made with a 5 mm gap. Each specimen was loaded over 5000 cycles, measuring angular/shear displacement then loaded to failure. The data were analyzed using Mann-Whitney <i>U</i> test. Three separate fresh frozen cadavers were injected with low-viscosity epoxy. The intraosseous bloody supply was inspected in each femoral head (no fixation, IT, L-shaped). There was no difference in angular (<i>P</i> = .3) or shear displacement (<i>P</i> = .99) between either screw design after cyclical loading. Also, there was not statistical difference in load to failure testing between either construct (<i>P</i> = .99). The average load to failure in the IT group was 3204.4 N. The average was 3180.2 N in the L-shaped design. We demonstrated the presence of the intraosseous portion of the lateral epiphyseal vessel in the specimen without screw fixation. This was preserved in the specimen with the L-shaped design but absent in the specimen following IT fixation. The strength of the L-shaped construct was not statistically different than the strength of the IT design. The posterior-superior screw may put the main blood supply to the femoral head at risk and should be avoided.