ARTICLE IN PRESS JID: JINJ [m5G;November 27, 2020;18:14] Injury xxx (xxxx) xxx Contents lists available at ScienceDirect Injury journal homepage: www.elsevier.com/locate/injury The safety and accuracy of the fluoroscopic imaging during proximal femoral fixation: A computerized 3D reappraisal of the joint penetration risk Lercan Aslan b,1 , Omer Subasi a,1 , Mehmet Demirhan b , Aksel Seyahi b , Ismail Lazoglu a,∗ a Manufacturing and Automation Research Center, Koc University, Istanbul 34450, Turkey b Koc University, School of Medicine, Department of Orthopaedics and Traumatology, Istanbul 34365, Turkey a r t i c l e i n f o Article history: Accepted 23 November 2020 Available online xxx Keywords: Proximal nailing Trochanteric fracture Tip-Surface Distance Fluoroscopy a b s t r a c t Background: To assess the success of proximal cephalomedullary nailing operations for treating trochanteric fractures, surgeons utilize 2D fluoroscopy to observe the relative positions of the femoral head and the implant. One distance-based risk parameter, observed from the AP and Lateral projections, is the Tip-Surface Distance(TSD) that dictates how close to the outer cortex should the implant tip be residing to avoid post-surgical complications such as cut-out or joint penetration. In this study, the safety and the accuracy of the orthogonal fluoroscopic imaging were evaluated. Methods: A femoral head model was created and the risk zone was defined as a hemispherical shell of 5 mm thickness beneath the subchondral cortex, which should not be violated during screw insertion. The remaining hemisphere beneath the risk zone was designated as the safe zone. To assess the effect of head size, each simulation was conducted for 34, 47, and 60 mm diameter(D femur ) femoral heads. The rate of safe zone violation was calculated for all possible screw endpoints with a TSD of at least 5 mm on fluoroscopic orthogonal views (TSD AP and TSD Lat ). Results: The minimum risk of joint penetration was achieved when the TSD AP /TSD Lat ratio was 1. For D femur of 34 mm there was a risk of 91.7% of the safe zone violation when each TSD AP and TSD Lat were 5 mm and 0% for 9 mm. For D femur of 47 mm, the risk was 92.2% for 5 mm and 0% for 11 mm. For D femur of 60 mm, the risk was 92.3% for 5 mm and 0% for 13 mm. Safety maps were constructed for all possible TSD combinations for 34, 47, and 60 mm femoral heads. Conclusions: Depending solely on the orthogonal fluoroscopic images is not a safe and accurate tech- nique for assessing joint penetration risk during proximal femoral fixation due to the spherical geometry of the femoral head. The screw tip can lie completely outside of the femoral head even when it appears inside, in both orthogonal fluoroscopic views. Evidently, when using TSD, more stringent distance limits should be chosen, contrary to the recommended 5 mm limit. Our safety maps for TSD combinations may be used to check the security of the implantation. © 2020 Elsevier Ltd. All rights reserved. Introduction Cut out of the femoral head screw, and joint penetration are two catastrophic complications in proximal femoral fracture fixa- tion. Insufficient penetration of the screw into the femoral head will decrease its stability resulting in fixation failure [1,2]. On the other hand, the insertion of the screw too close to the joint line will increase the risk of screw migration and joint penetration[3]. ∗ Corresponding author. E-mail address: ilazoglu@ku.edu.tr (I. Lazoglu). 1 These authors contributed equally to this work In the literature, cut out is reported as one of the most common mechanical failure modes with a complication risk as high as 12% for intertrochanteric fracture fixation[15]. A critical factor in avoid- ing cut out is the optimal positioning of the implants inside the femoral head [4,5]. A strong correlation is recorded in the litera- ture between the non-optimal placement of the lag screw and an enhanced risk of cut out [15–18]. During surgery, the conventional method to control the 3D po- sition of the screw is to assess the screw tip-joint surface distance (TSD) on 2D orthogonal (anteroposterior and lateral) fluoroscopic images. This subjective appraisal of the joint penetration risk is an inherently flawed method [6,7]. The inconsistent views of the https://doi.org/10.1016/j.injury.2020.11.064 0020-1383/© 2020 Elsevier Ltd. All rights reserved. Please cite this article as: L. Aslan, O. Subasi, M. Demirhan et al., The safety and accuracy of the fluoroscopic imaging during proximal femoral fixation: A computerized 3D reappraisal of the joint penetration risk, Injury, https://doi.org/10.1016/j.injury.2020.11.064