Is the Cranial and Posterior Screw of the "Inverted Triangle" Configuration for Femoral Neck Fractures Safe?

OBJECTIVES: To determine the frequency where a posterior and cranial screw in a femoral neck that appeared contained on fluoroscopy violates the cortex.

METHODS: Ten specimens including the hemipelves with the proximal femur were obtained from unidentified embalmed specimens that were to be cremated after an institutional review board waiver was granted. Under fluoroscopy, the posterior and cranial screw of the inverted triangle configuration for the femoral neck was placed using standard technique with a cannulated 6.5 mm screw. AP and lateral images of the final screw placement were blinded to two orthopedic traumatologists and one musculoskeletal radiologist who were asked to determine if the screw radiographically breached the posterior and cranial cortex. Cadavers were stripped of soft tissues and inspected for screw perforation. Screws were grouped as contained, thread extrusion, or core extrusion.

RESULTS: Reviewers classified all ten screws as radiographically contained within the femoral neck. Cadavers were inspected and found to show: four of ten with core extrusion, three of ten with thread extrusion, and three of ten screws contained within the femoral neck.

CONCLUSIONS: 70% of screws that were judged to be radiographically contained had cortical breach near the area where the lateral epiphyseal vessels enter the femoral neck. We urge caution against placement of posterior-cranial implants with fluoroscopy alone even if they appear radiographically contained.