Correlation of cervical endplate strength with CT measured subchondral bone density

Abstract

Cervical interbody device subsidence can result in screw breakage, plate dislodgement, and/or kyphosis. Preoperative bone density measurement may be helpful in predicting the complications associated with anterior cervical surgery. This is especially important when a motion preserving device is implanted given the detrimental effect of subsidence on the postoperative segmental motion following disc replacement. To evaluate the structural properties of the cervical endplate and examine the correlation with CT measured trabecular bone density. Eight fresh human cadaver cervical spines (C2-T1) were CT scanned and the average trabecular bone densities of the vertebral bodies (C3-C7) were measured. Each endplate surface was biomechanically tested for regional yield load and stiffness using an indentation test method. Overall average density of the cervical vertebral body trabecular bone was 270 +/- 74 mg/cm3. There was no significant difference between levels. The yield load and stiffness from the indentation test of the endplate averaged 139 +/- 99 N and 156 +/- 52 N/mm across all cervical levels, endplate surfaces, and regional locations. The posterior aspect of the endplate had significantly higher yield load and stiffness in comparison to the anterior aspect and the lateral aspect had significantly higher yield load in comparison to the midline aspect. There was a significant correlation between the average yield load and stiffness of the cervical endplate and the trabecular bone density on regression analysis. Although there are significant regional variations in the endplate structural properties, the average of the endplate yield loads and stiffnesses correlated with the trabecular bone density. Given the morbidity associated with subsidence of interbody devices, a reliable and predictive method of measuring endplate strength in the cervical spine is required. Bone density measures may be used preoperatively to assist in the prediction of the strength of the vertebral endplate. A threshold density measure has yet to be established where the probability of endplate fracture outweighs the benefit of anterior cervical procedure.

Cage Subsidence after Anterior Cervical Discectomy and Fusion Using a Cage Alone or Combined with Anterior Plate Fixation

“…However, biomechanical studies have shown that load to failure/yield load is associated with bone mineral density but not end plate thickness. 18,19 In our study, the inferior part of the cage sank significantly more than the superior part. This finding was also observed in another study.…”

“…12 Nonetheless, in biomechanical testing, the yield load was comparable between the superior and inferior end plate. 18 There were limitations to our study. It was retrospective and the number of patients was small.…”

“…9,14 The latter may be due to the higher contact stress from the smaller cage surface area and the lower yield load of the central part of the end plate compared with the periphery. 18 Larger intraoperative distraction may also lead to subsidence, 9 although this is not a universal finding.…”

Anterior cervical interbody constructs: effect of a repetitive compressive force on the endplate

“…The average trabecular bone density for each vertebral centrum was measured by averaging the scans between (not including) the endplates of the vertebral body. 41,42 Biomechanical Testing Six cervical levels (C3 to T1) from the five specimens were dissected and cleaned of soft tissue (N ¼ 30). The cartilaginous endplates were removed; the uncinate processes were left undisturbed.…”

Cervical Spine Anthropometric and Finite Element Biomechanical Analysis

“…Locations of thicker endplate bone are indicative of other factors that affect the biomechanical quality of the endplate. Density scans of the endplate, as measured by peripheral quantitative computed tomography (pQCT) scans, reveal that the endplate bone is denser in thicker regions (Ordway et al, 2007). Results show that an increase in bone density from 150 to 375 mg/mm 3 equates to an approximate stiffness increase from 100 to 200 N/mm.…”