Decreasing endplate porosity has been proposed as a risk factor for intervertebral disc degeneration, because it interferes with disc metabolite transport. However, endplate porosity has recently been shown to Nineteen cadaver motion segments (61–98 yrs) were compressed to 1kN while a pressure-transducer was pulled across the mid-sagittal diameter of the disc. Stress profiles indicated nucleus (intradiscal) pressure (IDP) and maximum stress in the anterior and posterior annulus. Subsequently, micro-CT was used to evaluate endplate porosity along the antero-posterior diameter of the adjacent endplates. Data were analysed using ANOVA and linear regression.Introduction
Methods
Dual energy X-ray absorptiometry (DEXA) is the gold standard for assessing bone mineral density (BMD) and fracture risk in vivo. However, it has limitations in the spine because vertebrae show marked regional variations in BMD that are difficult to detect clinically. This study investigated whether micro-CT can provide improved estimates of BMD that better predict vertebral strength. Ten cadaveric vertebral bodies (mean age: 83.7 +/− 10.8 yrs) were scanned using lateral-projection DEXA and Micro-CT. Standardised protocols were used to determine BMD of the whole vertebral body and of anterior/posterior and superior/inferior regions. Vertebral body volume was assessed by water displacement after which specimens were compressed to failure to determine their compressive strength. Specimens were then ashed to determine their bone mineral content (BMC). Parameters were compared using ANOVA and linear regression.Introduction
Methods
To investigate whether restoration of mechanical function and spinal load-sharing following vertebroplasty depends upon cement distribution. Fifteen pairs of cadaver motion segments (51-91 yr) were loaded to induce fracture. One from each pair underwent vertebroplasty with PMMA, the other with a resin (Cortoss). Various mechanical parameters were measured before and after vertebroplasty. Micro-CT was used to determine volumetric cement fill, and plane radiographs (sagittal, frontal, and axial) to determine areal fill, for the whole vertebral body and for several specific regions. Correlations between volumetric fill and areal fill for the whole vertebral body, and between regional volumetric fill and changes in mechanical parameters following vertebroplasty, were assessed using linear regression. For Cortoss, areal and volumetric fills were significantly correlated (R=0.58-0.84) but cement distribution had no significant effect on any mechanical parameters following vertebroplasty. For PMMA, areal fills showed no correlation with volumetric fill, suggesting a non-uniform distribution of cement that influenced mechanical outcome. Increased filling of the vertebral body adjacent to the disc was associated with increased intradiscal pressure (R=0.56, p<0.05) in flexed posture, and reduced neural arch load bearing (FN) in extended posture (R=0.76, p<0.01). Increased filling of the anterior vertebral body was associated with increased bending stiffness (R=0.55, p<0.05). Cortoss tends to spread evenly within the vertebral body, and its distribution has little influence on the mechanical outcome of vertebroplasty. PMMA spreads less evenly, and its mechanical benefits are increased when cement is concentrated in the anterior vertebral body and adjacent to the intervertebral disc.
