The healing stages of an intramedullary implanted tibia: A stress strain comparative analysis of the calcification process

Abstract

Close tibial shaft fractureUnreamed intramedullary tibial nails a b s t r a c t Aims: The extended usage of unreamed tibial nailing resulted in reports of an increased rate of complications, especially for the distal portion of the tibia. Unreamed nailing favours biology at the expense of the achievable mechanical stability, it is therefore of interest to define the limits of the clinical indications for this method. Extra-articular fractures of the distal tibial metaphysis, meta-diaphyseal junction, and adjacent diaphysis are distinct in their management from impaction derived ''pilon'' type fractures and middiaphyseal fractures. The goals of this work were to gain a thorough understanding of the load-sharing mechanism between unreamed nail and bones in a fractured tibia. With this purpose a complete model of the human leg was realised, simulating a mid-diaphyseal fracture, classified as A2 type 1, according to the AO classification.The analysis of the entire chain allows to have a complete picture of the stress distribution and of the most stressed bones and soft tissues, but, more importantly can overcome problems connected with boundary conditions imposed at single bony components.Methods: Model consists of six bony structures: pelvis, femur, patella, fibula, tibia, and a simplified lump of the feet, configured in a standing up position. Their articular cartilage layers, were simulated by 3D membranes of opportune stiffness connecting the different segments. Moreover an unreamed intra-medullary nail Expert Tibial Nail (DePuy Synthes ® ) stabilized the fractured tibia. A load of 700 N has been applied at the top of pelvis and a part the feet, at the tip, was rigidly fixed. Five different contact interfaces have been imposed at the different bony surfaces in contact.Results: Three different conditions were analysed: the initially healthy tibia, the A2 type 1 fractured tibia with the Expert tibial nail implanted, and the follow up stage after complete healing of tibia. Non-linear finite element analysis of the models were performed with Abaqus version 5.4 (Hibbitt, Karlsson and Sorensen, Inc., Pawtucket, RI) using the geometric non linearity and automatic time stepping options. Conclusion:The obtained results reveal interesting consequences deriving by taking into account how the stress shielding can influence the integrity and resistance of bones, in order to identify the mechanical reasons for the unfavourable clinical results, and to *

Healing of tibial comminuted fractures by the meaning of an innovative intramedullary nail

“…Measurements The higher values must be considered as the effect of the holding pins anchoring to the bone and the load acting at the top of the tibia, see Table 2. In literature Filardi 11 obtained a value of 160 MPa, on the nail body of an Expert Tibial Nail (DePuy Synthes ® ) loading the entire lower bony chain with a vertical force of 700 N. Superior screws were subjected to receive a stress of 36 MPa and a significant concentration of stress was detected on the bony area around the holes, while the three inferior screws resulted unloaded. A finite element analysis by Gomez-Benito et al 12 compared the biomechanical performance of reamed and unreamed tibial nails.…”

Finite element analysis of the foot: Stress and displacement shielding

“…14,15 A vertical force of approximately 350 N is applied on the top of the talus corresponding to a BW of 70 kg. 16 The vertical upward force of the Achilles tendon, with magnitude of 175 N, was applied at the posterior extreme of the calcaneus, see Fig. 3.…”

Recent developments on intramedullary nailing: a biomechanical perspective

“…Several factors have been suggested to determine the mechanical environment at the fracture site: those that result from the stiffness of the implant, such as the rigidity of the nail and the screws, and those that result from movements between the different components that constitute the bone–implant structure construct . Strategies have been developed to try to guarantee an optimum implant stability and interfragmentary mechanical environment . Some authors have focused on experimenting with different biomaterials to evaluate the positive impact that they may have on the mechanical behavior of the bone–implant system and consequently on the healing process.…”

“…49 Strategies have been developed to try to guarantee an optimum implant stability and interfragmentary mechanical environment. [50][51][52][53][54] Some authors have focused on experimenting with different biomaterials to evaluate the positive impact that they may have on the mechanical behavior of the bone-implant system and consequently on the healing process. Other authors seem to be more concerned with increasing the structural stability.…”