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Nail with a lesser radius of curvature
28%
659/2370
Nail with a greater radius of curvature
66%
1565/2370
Piriformis entry portal
3%
70/2370
Trochanteric entry portal
2%
50/2370
Lateral decubitus patient position
1%
17/2370
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The image in Figure A shows an unstable intertrochanteric fracture and the image in Figure B shows perforation of the anterior cortex of the femur by the intramedullary implant. This complication is due to a mismatch of the curvature of the nail with the anterior bow of the femur, and was likely caused by a nail of a greater radius of curvature (eg, straighter than the femur). Egol et al measured the radius of curvature for 474 matched cadaveric femurs and found the average anterior radius of curvature to be 120cm (+/- 36cm). In contrast, the radii of curvature for the measured intramedullary nails ranged from 186cm to 300cm, demonstrating that the nails were straighter than the femurs. The authors advocate for a decreased radius of curvature (more curve) for intramedullary nails, especially larger diameter implants designed for fractures about the hip Ostrum and Levy present a case series of 3 patients with subtrochanteric fractures who had anterior penetration of the femoral cortex. They state that the mismatch in femoral bow between the bone and the implant is a contributing factor to distal femoral anterior cortex penetration in intramedullary nailing of subtrochanteric fractures. Simonian et al present 4 iatrogenic femoral neck fractures that occured during a series of 315 femoral nails. The authors attempted to reproduce the iatrogenic fractures with cadaveric femurs and felt that the iatrogenic fractures may be due to a combination of a valgus femoral neck and impingement from the AO insertion jig used at the time. Harper and Carson examined 14 cadaveric femurs and intramedullary implants at the time. Similar to Egol et al, they found a mismatch between the radius of curvature of the femurs and the intramedullary nails. Illustration A shows the difference between a lesser and greater radius of curvature. Illustration B demonstrates how to calculate radius of curvature based on an implant with an exaggerated bow. Illustration C shows the anterior bow of a synthetic femoral model compared with several intramedullary implants.
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