CT Osteoabsorptiometry Assessment of Subchondral Bone Density Predicts Intervertebral Implant Subsidence in a Human ACDF Cadaver Model

Abstract

Study Design: Cadaveric biomechanics study. Objective: Subchondral bone mineral density (sBMD) reflects the long-term mineralization and distribution of stress on joints. The use of 3-dimensional (3-D) methods to evaluate sBMD, including computed tomography osteoabsorptiometry (CT-OAM), enables the assessment of density distribution with emphasis on subchondral bone. This study sought to measure the sBMD of cervical endplates using CT-OAM and correlate it to mechanical implant subsidence in a cadaveric model. Methods: Fourteen fresh human cadaveric cervical spines were subjected to dynamic testing after single level discectomy and instrumentation using a PEEK interbody spacer. Specimens were imaged with CT 3 times: 1st) whole intact cervical spine, 2nd) after implantation, and 3 rd) after testing. These images were used to assess sBMD distributions using CT-OAM directly underneath the spacer. Subsidence was defined as the displacement of the device into the endplates. Results: The observed “failure mode” was consistently recorded as subsidence, with a mean of 0.45 ± 0.36 mm and 0.40 ± 0.18 mm for the C4-5 and C6-7 levels, respectively. There were no differences by level. The experimental cyclic test showed that denser endplates experienced less deformation under the same load. Conclusions: This study achieved its stated aim of validating the use of CT-OAM as a method to analyze the sBMD of the cervical endplates. Studies such as this are providing new information on available technology such as CT-OAM, providing new tools for clinicians treating spinal conditions in need of augmentation and stabilization via interbody devices.

Mapping Subchondral Bone Density Distribution in the Canine C6-C7 Vertebral Endplates: A CT-OAM Study

“…Therefore, non-destructive measurement of subchondral bone density provides a realistic estimate of the endplate's strength. Recent human studies have also shown that higher sBMD in the endplates is associated with a lower likelihood of subsidence compared to endplates with lower sBMD and vice versa [21,33]. This further validates the use of CT-OAM as a valuable tool for predicting cage subsidence and optimization of cage design based on CT-OAM bone density mapping like in human spinal surgery [34].…”

“…Typically, CT-OAM values are expressed in Hounsfield Units (HU). The distribution of bone mineral density in the vertebral endplates assessed using CT-OAM has been strongly correlated with the local mechanical strength of the endplates in humans, as determined by indentation testing [21][22][23][24][25]. Reversely, by mapping the subchondral bone density of the endplates, we gained direct insights into their mechanical strength and the potential implications for cage design.…”

Risk Factors for Subsidence Following Anterior Lumbar Interbody Fusion

“…Past studies have demonstrated that the central endplate represent the region of lowest subchondral BMD and is thus less resistant to compressive load than the peripheral endplate. [18][19][20][21] A biomechanical study evaluating the effect of cage width in a human cadaveric lateral lumbar interbody fusion (LLIF) model found that placement of a larger cage that spans the width of the ring apophysis increased the compressive strength of the construct, thus decreasing the risk of subsidence. 22 Few clinical studies have investigated the relationship between cage placement and subsidence in posterior approaches to lumbar fusion.…”

“…The relationship between BMD and endplate strength has been well established, with several biomechanical studies demonstrating a higher risk of endplate failure with lower BMD due to lower compressive strength under dynamic loading. [19][20][21]25 Clinical studies have also found low BMD and osteoporosis to significantly increase the risk for subsidence in the context of several fusion procedures, including LLIF, posterior lumbar interbody fusion (PLIF), and transforaminal lumbar interbody fusion (TLIF). 10,[26][27][28] Recently, a study by Jones et al used QCT technology to assess how the BMD of the cage footprint affected the risk for subsidence in LLIF, establishing a cutoff for volumetric trabecular BMD of 211.04 kg/m 2 , below which risk for subsidence was increased.…”

Computed tomography Osteoabsorptiometry: Review of bone density, mechanical strength of material and clinical application

“…High mechanical strength was substantially linked with high density regions of the acetabulum and femoral head (SBP correlation coefficients ranged from 0.77 to 0.97 for FL and 0.97 to 0.96 for CF) ( Hoechel et al, 2013 ). Several researchers have discovered a link between the density distribution and mechanical strength of the talar dome ( Leumann et al, 2015 ), cervical vertebral body ( Hara et al, 2021 ), and upper and lower cervical endplate ( Orías et al, 2021 ). Yet, we are aware that, while there is a strong association between the two in this sort of research, a quantitative comparison of bone density and mechanical strength is unachievable.…”