ABSTRACT
STUDY DESIGN: Experimental study. PURPOSE: The study aimed to develop a finite element (FE) model to determine the stress on the discs adjacent to the fused segment following different types of floating lumbar spinal fusions. OVERVIEW OF LITERATURE: The quantification of the adjacent disc stress following different types of floating lumbar fusions has not been reported. The magnitude of the stress on the discs above and below the floating fusion remains unknown. METHODS: A computer-aided engineering-based approach using implicit FE analysis was employed to assess the stress on the lumbar discs above and below the floating fusion segment (L4-L5) following anterior and posterior lumbar spine fusions at one, two, and three levels (with and without instrumentation). RESULTS: Both discs suprajacent and infrajacent to the floating fusion experienced increased stress, but the suprajacent disc experienced relatively high stress level. Instrumentation increased the stress on the discs suprajacent and infrajacent to the floating fusion, but the magnitude of stress on the suprajacent disc remained relatively high. CONCLUSIONS: The FE model was employed under similar loading and boundary conditions to provide quantitative data, which will be useful for clinicians to understand the probable long-term effects of floating fusions.
ABSTRACT
STUDY DESIGN: Experimental study. PURPOSE: The aim of the study was to develop a finite element (FE) model to study the long-term effects of various types of lumbar spinal interventions on the discs adjacent to the fused segment. OVERVIEW OF LITERATURE: Earlier FE studies have been limited to one particular type of fusion and comparative quantification of the adjacent disc stresses for different types of surgical interventions has not been reported. METHODS: A computer aided engineering (CAE) based approach using implicit FE analysis assessed the stresses in the lumbar discs adjacent to the fused segment following anterior and posterior lumbar spine fusions at one, two and three levels (with and without instrumentation). RESULTS: It was found that instrumentation and length of fusion were the most significant factors in increasing adjacent level stresses in the lumbar discs. CONCLUSIONS: In the present study, a calibrated FE model that examined spinal interventions under similar loading and boundary conditions was used to provide quantitative data which would be useful for clinicians to understand the probable long-term effect of their choice of surgical intervention.
ABSTRACT
Mobile-bearing total knee arthroplasty designs were thought to be associated with lesser stresses on the polyethylene (PE) insert as compared to fixed-bearing designs. The wear rate of the PE liner was felt to be less in the mobile-bearing knees due to the decrease in the stresses. However, a reevaluation of the biomechanics of the mobile-bearing design is necessary due to the recent clinical reports on the long-term outcome of mobile-bearing knees which have not demonstrated any significant benefit in terms of implant survival and polyethylene wear rate. In this explicit finite element analysis of mobile-bearing and fixed-bearing knee designs using LS-DYNA, no significant differences have been found in the maximal stresses in the superior (articulating) surface of the PE insert in mobile- and fixed-bearing designs. On the inferior surface of the PE insert, the peak stresses were nearly 30% higher in the mobile-bearing compared with the fixed-bearing design. Thus, contrary to earlier expectations, mobile-bearing designs may be associated with higher overall PE stresses and wear than the fixed-bearing designs. Further research is necessary to minimize the wear rate of the PE insert in mobile-bearing total knee arthroplasty.
