Implications of three-dimensional modeling of tibia for intramedullary nail fixation: A virtual study on Asian cadaver tibia

Introduction: To determine the optimal entry point (EP) of intramedullary nail (IMN) fixation and introduce a consistent landmark for practical application by analyzing three-dimensional (3D) modeling and virtual implantation. Materials and methods: A total of 104 cadaveric femurs (50 males and 54 females) underwent continuous 1.0 mm slice computed tomography (CT) scans. CT images were imported into Mimics (R) software to reconstruct 3D model of tibiofibular bone with medullary canal. Expert Tibial Nail (ETN (R), empty set12mm/Length 315 mm) was processed into a 3D model at the actual size and optimally implanted in the tibia. After IMN was aligned in a neutral position, it was defined as a true AP projection. In the true AP projection, optimal EP and relationship with adjacent structures were assessed based on the degree of tibial rotation. Results: EP was placed eccentrically around the lateral tibial spine in cephalad view and in true AP projection in all models. In true AP projection, the overlapping point between fibular tip and cortical margin of lateral condyle was placed lateral to the fibular tip in 62 models, and exactly matched with fibular tip in 42 models. As tibia rotates, the position of EP in the AP view changes. When tibia was externally rotated, EP was located to the lateral, not the medial side of the lateraltibialspine. The obliquity of guide wire also changed withtibialrotation; the obliquity of guide wire aligned in a straight in true AP projection. Conclusion: Optimal determination of EP and guide wire direction should be performed by considering the overlapping point that should be placed to just or lateral side of fibular tip in AP projection. Compared with fibular bisector line, the overlapping point is also useful as a practical landmark for making true AP projection and determining optimal EP. (C) 2019 Elsevier Ltd. All rights reserved.