Surgical tips of intramedullary nailing in severely bowed femurs in atypical femur fractures: Simulation with 3D printed model.
INTRODUCTION
The surgical management of atypical femoral fractures (AFFs) is complex in cases with severe bowing of the femur, being associated with a high rate of failure. Our first aim was to use preoperative templating and 3D printed model characterise the technical difficulties associated with use of current commercially available intramedullary nail (IMN) systems for the management of AFFs with severe bowing. Our second aim was to use outcomes of our 3D printing analysis to define technical criteria to overcome these problems.


MATERIAL AND METHODS
The modelled femur with 3D printing had an anterior bowing curvature radius of 772mm and an angle of lateral bowing of 15.4°. Nine commercially available IMN systems were evaluated in terms of position of the nail within the medullary canal, occurrence of perforation of femoral cortex by the distal tip of the nail, and location of the site of perforation relative to the knee joint. The following IMN systems were evaluated: unreamed femoral nail (UFN), cannulated femoral nail (CFN), Sirus nail, right and left expert Asian femoral nail (A2FN), right and left Zimmer Natural Nail (ZNN), proximal femoral nail anti-rotation (PFNA), and Zimmer Cephalomedullary Nail (CMN).


RESULTS
Along the sagittal plane, the UFN, CFN and Sirus systems were acceptably contained within the medullary canal, as well as the "opposite side" A2FN and ZNN. Only the Sirus IMN system was contained along the coronal plane. The distal part of the all other IMN systems perforated the anterior cortex of the femur, at distances ranging between 2.8 and 11.7cm above the distal end of the femoral condyles. Using simulated fracture reduction in the 3D printed model, none of the 9 IMN systems provided acceptable anatomical reduction of the fracture. A residual gap in fragment position and translation was provided by the "opposite side" ZNN, followed by the UFN and Sirus systems.


CONCLUSION
Commercially available IMN systems showed mismatch with severely bowed femurs. Our simulation supports that fit of these systems can be improved using an IMN system with a small radius of curvature and diameter, and by applying specific operative procedures.
['Park|Jai Hyung|JH|', 'Lee|Yongkoo|Y|', 'Shon|Oog-Jin|OJ|', 'Shon|Hyun Chul|HC|', 'Kim|Ji Wan|JW|']
D000369:Aged, 80 and over D001858:Bone Nails D005260:Female D005264:Femoral Fractures D005269:Femur D005594:Fracture Fixation, Intramedullary D017102:Fracture Healing D006801:Humans D021621:Imaging, Three-Dimensional D066330:Printing, Three-Dimensional D016896:Treatment Outcome
Intramedullary nailing Femur Atypical femur fracture 3D print Mismatch