Structural optimization of patient-specific temporomandibular joint replacement implants for additive manufacturing:novel metrics for safety evaluation and biomechanical performance

Total temporomandibular joint(TMJ)replacement is recommended only when there is irreversible damage to the joint and no conservative treatment can provide functional improvements.Several stock and custom-made TMJ implants have been made available;however,retrospective and comparative studies were unable to find significant differences between the two types of solutions.The introduction of additive manufacturing(AM)techniques in medical practice allows for a greater freedom of design and a higher degree of device customisation.The combination of AM with structural optimisation may streamline development and provide the key for fabricating biomechanic ally enhanced TMJ implants.In this study,structural optimis ation techniques were applied to develop and numerically validate a patient-specific TMJ implant.The biomechanical behaviour of each intermediate TMJ design was assessed under four different nominal and maximum biting tasks using finite element analyses.In addition,a new set of metrics were proposed to compare each design regarding biomechanical performance and implant safety.The results suggest that 55-82%of the natural/intact strain patterns can be recovered with the finally selected TMJ implant.This represents an increase of 15%in biomechanical performance for incisor biting,15%for right molar biting,17%for left molar biting and a decrease of 2%for left group biting compared with the initial design.The results also suggest that load transfer at the proximal ramus reduces the implant’s impact on the mandible’s strain patterns.Finally,structural optimisation allows for a volume reduction of up to 44%with a minimum loss of implant safety and biomechanical performance.

Comparison of the biomechanical performance of three spinal implants for treating the wedge-shaped burst fractures

Spinal fracture is a serious problem impairing life quality,associating with low back pain and many other chronic diseases.Among all the spinal fractures,the rate of thoracolumbar fractures is the highest and accounts for approximately 90%.Although surgical treatment is an effective approach,it is still unclear which treatment method performs the best.The aim of the present study was to investigate the biomechanical performance of three spinal implants for treating the thoracolumbar wedge-shaped burst fractures using the finite element(FE)method.FE model of the T12/L1/L2 spinal segment was created from CT images and the thoracolumbar wedge-shaped burst fractures were created by removing some elements in the anterior part of L1.The FE models of the traditional system,the universal spine system(USS)and the cortical bone trajectory(CBT)system were created and their biomechanical performances were evaluated.The results revealed that among the three fixation systems,the highest von-Mises stress occurred in the CBT system.Under all the loading scenarios except for the lateral bending,the maximal von-Mises stress was higher when the USS system rather than the traditional system was applied.The average displacement around the fracture site was the highest in the CBT system.Except for the lateral bending,the average displacement around the fracture site was higher when the USS system rather than the traditional system was applied.For all the fixation approaches,the highest von-Mises stress always occurred at the screw junctions.The present study provided important data for the treatment of thoracolumbar wedge-shaped burst fractures.For example,the traditional spinal system is preferentially selected for the thoracolumbar wedgeshaped burst fracture of L1.

A critical review on the biomechanical study of cervical interbody fusion cage

Anterior Cervical Discectomy and Fusion(ACDF)is the preferred surgical method for the treatment of severe cervical degenerative disc disease with radiculopathy or myelopathy,of which the objectives are to restore the normal height of intervertebral space and cervical lordosis through the implantation of cervical interbody fusion cage.The biomechanical performance of a cervical interbody fusion cage,which plays a significant role in achieving the goals of ACDF,is influenced by multiple factors.In this paper,various studies focusing on the biomechanical performance of cervical interbody fusion cage are reviewed.Furthermore,the research methods,biomechanical evaluation parameters and data analysis methods of these research are analyzed in order to obtain a comprehensive understanding of the progress and limitations of research in this field.Although great progress has been made to clarify the biomechanical behaviors of cervical interbody fusion cage,there is still controversy regarding the issues such as the relative contribution of multiple factors to the performance of cage,the interactions among these factors,as well as whether the effects of factors change with the process of intervertebral osseointegration and so on.Thus,investigations are still needed to improve the comprehension of cervical interbody fusion cage biomechanically.