Re-operation for femoral shaft nonunion initially treated with intramedullary nailing: exchange n... скачать в хорошем качестве

Re-operation for femoral shaft nonunion initially treated with intramedullary nailing: exchange n...

Published in "Injury": https://doi.org/10.1016/j.injury.2023... ------------------------------------------- Re-operation for femoral shaft nonunion initially treated with intramedullary nailing: exchange nailing versus plate augmentation Hideyuki Mimata, Yusuke Matsuura, Sei Yano, Seiji Ohtori, Mitsugu Todo Introduction Intramedullary nailing for femoral shaft fractures has been reported to result in nonunion in 3.1-12.5% of patients. Although exchange nailing and plate augmentation are the main revision options for nonunion, the mechanical improvement of revision surgery, including callus at the fracture site, has not been adequately evaluated. Especially in femoral shaft fractures, hypertrophic nonunion is common, which is considered to be caused by mechanical instability. Therefore, mechanical evaluation is considered important in the selection of revision surgery. At the User Meeting 2021, we performed a quantitative CT-based finite element analysis (QCT/FEA) on a case after intramedullary nailing and showed that the mechanical response of the callus during the bone healing process can be quantitatively evaluated by the tensile failure ratio of the callus[1]. This study aimed to evaluate the mechanical improvement of revision surgery by creating exchange nailing models and plate augmentation models for a femoral shaft nonunion initially treated with intramedullary nailing and performing QCT/FEA. Material and Method A finite element model was constructed from CT images of a 6-months after intramedullary nailing with suspected nonunion. As revision surgery, models with the intramedullary nail exchanged and models with an augmentation plate added were created (Fig. 1), and QCT/FEA was performed using MECHANICAL FINDER version 11. The model consists of proximal and distal femoral fragments, callus, artifact region, intramedullary nail, plate, and screws. The material properties of bone and callus were based on the formulas of Matsuyama et al.[2] and Suzuki et al.[3] respectively, and those of intramedullary nails, plates, and screws were assigned as Ti6Al4V. Contact conditions were set on the interfaces of intramedullary nail to bone/callus, plate to bone/callus, and intramedullary nail to screw, with a friction coefficient of 0.0. The hip contact force and muscle forces at maximum load during gait cycle were given and analyzed. The volume ratio of the callus at the fracture site with a tensile failure risk of 1 or greater was evaluated as the tensile failure ratio. The relative displacement of the proximal and distal bone fragments at the fracture site was measured on the medial and lateral sides to evaluate the movement of the bone fragments. Results Tensile failure ratio decreased with increasing nail diameter compared to the model with 11-mm diameter and 360-mm length nail, but did not decrease with increasing length alone (Fig. 2). The plate augmentation reduced the tensile failure risk, especially on lateral side, and the tensile failure ratio decreased with decreasing screw fixation distance. Relative displacement between the bone fragments showed an opening of the lateral side and internal rotation of the proximal fragment relative to the distal fragment (Fig. 3). Increasing the diameter of the nail or the plate augmentation inhibited both the lateral opening and the internal rotation. Discussion Tensile failure ratio and bone fragment movement were both reduced when the diameter of the intramedullary nail was increased, which may be due to that the second moment of area acts in proportion to the fourth power of the diameter. On the other hand, simply lengthening with the same diameter did not show any mechanical improvement. This is because the rigidity against bending does not change only by lengthening, and that the screw position of the distal bone fragments becomes more distal with nail length. On the other hand, the plate augmentations were as effective as the exchange nailing to a 13 mm diameter. It is thought that direct fixation of the lateral side is more effective in reducing opening and rotation. Bone grafting is often applied at the same time in actual plate augmentation, which may enhance the benefit of the plate augmentation as bone healing progresses. There are some clinical reports that plate augmentation is equivalent or superior to exchange nailing in bone union rate, and from the results of this study, plate augmentation could be an option for revision surgery that can be expected to achieve bone union. In addition to invasiveness, blood loss, operative time, complications, and functional impairment, mechanical instability, which significantly affect bone union, should also be considered when selecting a revision surgery. QCT/FEA is expected to be applied to determine the optimal surgery method pre-operatively. MECHNANICAL FINDER User Meeting 2022 https://mechanical-finder.com/2022/us...