In VivoMicroCT Monitoring of Osteomyelitis in a Rat Model

Abstract

Infection associated with orthopedic implants often results in bone loss and requires surgical removal of the implant. The aim of this study was to evaluate morphological changes of bone adjacent to a bacteria-colonized implant, with the aim of identifying temporal patterns that are characteristic of infection. In an in vivo study with rats, bone changes were assessed using in vivo microCT at 7 time points during a one-month postoperative period. The rats received either a sterile or Staphylococcus aureus-colonized polyetheretherketone screw in the tibia. Bone-implant contact, bone fraction, and bone changes (quiescent, resorbed, and new bone) were calculated from consecutive scans and validated against histomorphometry. The screw pullout strength was estimated from FE models and the results were validated against mechanical testing. In the sterile group, bone-implant contact, bone fraction, and mechanical fixation increased steadily until day 14 and then plateaued. In the infected group, they decreased rapidly. Bone formation was reduced while resorption was increased, with maximum effects observed within 6 days. In summary, the model presented is capable of evaluating the patterns of bone changes due to implant-related infections. The combined use of longitudinal in vivo microCT imaging and image-based finite element analysis provides characteristic signs of infection within 6 days.

Impact of Bacterial Infections on Osteogenesis: Evidence From In Vivo Studies

“…Bone resorption, cortical thickening, and periosteal new bone apposition are the key signs of osteomyelitis by plain radiography or computed tomography (CT) imaging . The osteomyelitis‐related bone changes are consistent among small or large animal models, and are similar to those seen in patients (Fig.…”

“…A reduced bone‐implant fixation may result into further mechanical instability of the bones. Osseointegration studies have shown that bacterial contamination promotes high osteoclast activity and fibrous capsule development directly around the implant, reducing the strength of implant fixation already in the first‐week …”

“…In the case of intramedullary fixation, bone apposition is observed in the periosteal region along the length of the implant . Studies that have incorporated micro‐CT algorithms to quantify bone formation and bone destruction separately from each other, have confirmed that significantly enhanced bone volume is measured more peripheral to the infected site …”

Relative effects of age on implant integration in a rat model: A longitudinal in vivo microct study

“…Our model enables longitudinal, time‐dependent measurements of bone distribution, changes and of the resulting implant fixation. Since this approach was first reported it was successfully used to describe bone dynamics around bisphosphonate‐releasing implants, around infected implants and in osteoporotic animals . But to acquire images with high enough quality, BaSO 4 loaded PEEK screws are used, instead of more standard stainless steel or titanium screws, which would generate metallic artifacts in tomographic reconstructions .…”

“…Bone‐implant contact (BIC) was computed by voxel‐counting of the segmented image within ROI 1. Given the quasiplanar nature of ROI 1, BIC can be expressed as volume fraction (%) within ROI 1, which correlates well against histology …”