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

OBJECTIVES: 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. METHODS: 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 U 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). RESULTS: There was no difference in angular (P = .3) or shear displacement (P = .99) between either screw design after cyclical loading. Also, there was not statistical difference in load to failure testing between either construct (P = .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. CONCLUSIONS: 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.