Selection of internal fixation method for femoral intertrochanteric fractures using a finite element method

BACKGROUND Failure to fix unstable intertrochanteric fractures impairs return to daily activities.AIM To simulate five different internal fixation methods for unstable proximal femoral fractures.METHODS A three-dimensional model of the femur was established from sectional computed tomography images,and an internal fixation model was established.Finite element analysis of the femur model was established,and three intertrochanteric fracture models,medial defect,lateral defect,and medial-lateral defects,were simulated.Displacement and stress distribution after fixation with a proximal femoral anti-rotation intramedullary nail(PFNA),integrated dual-screw fixation(ITN),PFNA+wire,PFNA+plate,and PFNA+wire+plate were compared during daily activities.RESULTS The maximum displacement and stress of PFNA and ITN were 3.51 mm/473 MPa and 2.80 mm/588 MPa for medial defects;2.55 mm/288 MPa and 2.10 mm/307 MPa for lateral defects;and 3.84 mm/653 MPa and 3.44 mm/641 MPa for mediallateral defects,respectively.For medial-lateral defects,reconstructing the medial side alone changed the maximum displacement and stress to 2.79 mm/515 MPa;reconstructing the lateral side changed them to 3.72 mm/608 MPa,when both sides were reconstructed,they changed to 2.42 mm/309 MPa.CONCLUSION For medial defects,intramedullary fixation would allow early low-intensity rehabilitation exercise,and ITN rather than PFNA reduces the risk of varus and cut-out;for lateral wall defects or weakness,intram-edullary fixation allows higher-intensity rehabilitation exercise,and ITN reduces the risk of varus.For both medial and lateral defects,intramedullary fixation alone will not allow early functional exercise,but locating lateral or medial reconstruction will.For defects in both the inner and outer sides,if reconstruction cannot be completed,ITN is more stable.

A segmental defect adaptation of the mouse closed femur fracture model for the analysis of severely impaired bone healing

Objective: To better characterize nonunion endochondral bone healing and evaluate novel therapeutic approaches for critical size defect healing in clinically challenging bone repair, a segmental defect model of bone injury was adapted from the threepoint bending closed fracture technique in the murine femur.Methods: The mouse femur was surgically stabilized with an intramedullary threaded rod with plastic spacers and the defect adjusted to different sizes. Healing of the different defects was analyzed by radiology and histology to 8 weeks postsurgery. To determine whether this model was effective for evaluating the benefits of molecular therapy, BMP-2 was applied to the defect and healing then examined.Results: Intramedullary spacers were effective in maintaining the defect. Callus bone formation was initiated but was arrested at defect sizes of 2.5 mm and above, with no more progress in callus bone development evident to 8 weeks healing. Cartilage development in a critical size defect attenuated very early in healing without bone development, in contrast to the closed femur fracture healing, where callus cartilage was replaced by bone. BMP-2 therapy promoted osteogenesis of the resident cells of the defect, but there was no further callus development to indicate that healing to pre-surgery bone structure was successful.Conclusions: This segmental defect adaptation of the closed femur fracture model of murine bone repair severely impairs callus development and bone healing, reflecting a challenging bone injury. It is adjustable and can be compared to the closed fracture model to ascertain healing deficiencies and the efficacy of therapeutic approaches.