Since Sawbones Biomechanical Materials have low variability and allow specific bone qualities to be selected, this study (see below) was able to rank various cage factors influencing subsidence. The results provide a strategy for surgeons planning cervical fusion.
Using Solid Rigid Polyurethane foams 10pcf (#1522-01) and 20pcf (#1522-03) in place of cadaver vertebrae, this study conducted dynamic loading on cervical interbody fusion cages to measure subsidence. Two different densities were selected to represent various bone qualities; a lower density to simulate total removal of the cortical endplate and a higher density to simulate an intact cortical endplate. In doing so, the authors found that bone quality has the largest impact on subsidence compared to cage footprint, cage material and plate surface texture.
The Effect of Cervical Interbody Cage Morphology, Material Composition, and Substrate Density on Cage Subsidence.
In cervical spine fusion surgery, vertebral interbody spacers preserve disk height and sagittal alignment, thereby avoiding neural compression and kyphotic collapse.1 Subsidence refers to an undesirable penetration of the interbody cage into adjacent vertebral bone, which, when severe enough, can lead to radicular pain and loss of sagittal plane alignment.2 …Although several factors have been shown to contribute to subsidence, the interactions between these factors is unclear.
Closed-cell, rigid polyurethane foam (Sawbones; Pacific Research Laboratory) was chosen in two densities to model two discrete scenarios of bone quality. The lower-density foam had a density of 160.19 kg/m3 and a compressive modulus of 58 MPa, whereas the higher-density foam had a density of 320.37 kg/m3 and a compressive modulus of 210 MPa.