Monitoring bacterial burden, inflammation and bone damage longitudinally using optical and μCT imaging in an orthopaedic implant infection in mice.
BACKGROUND
Recent advances in non-invasive optical, radiographic and μCT imaging provide an opportunity to monitor biological processes longitudinally in an anatomical context. One particularly relevant application for combining these modalities is to study orthopaedic implant infections. These infections are characterized by the formation of persistent bacterial biofilms on the implanted materials, causing inflammation, periprosthetic osteolysis, osteomyelitis, and bone damage, resulting in implant loosening and failure.


RESULTS
An orthopaedic implant infection model was used in which a titanium Kirshner-wire was surgically placed in femurs of LysEGFP mice, which possess EGFP-fluorescent neutrophils, and a bioluminescent S. aureus strain (Xen29; 1×10(3) CFUs) was inoculated in the knee joint before closure. In vivo bioluminescent, fluorescent, X-ray and μCT imaging were performed on various postoperative days. The bacterial bioluminescent signals of the S. aureus-infected mice peaked on day 19, before decreasing to a basal level of light, which remained measurable for the entire 48 day experiment. Neutrophil EGFP-fluorescent signals of the S. aureus-infected mice were statistically greater than uninfected mice on days 2 and 5, but afterwards the signals for both groups approached background levels of detection. To visualize the three-dimensional location of the bacterial infection and neutrophil infiltration, a diffuse optical tomography reconstruction algorithm was used to co-register the bioluminescent and fluorescent signals with μCT images. To quantify the anatomical bone changes on the μCT images, the outer bone volume of the distal femurs were measured using a semi-automated contour based segmentation process. The outer bone volume increased through day 48, indicating that bone damage continued during the implant infection.


CONCLUSIONS
Bioluminescent and fluorescent optical imaging was combined with X-ray and μCT imaging to provide noninvasive and longitudinal measurements of the dynamic changes in bacterial burden, neutrophil recruitment and bone damage in a mouse orthopaedic implant infection model.
Orthopaedic Hospital Research Center, Orthopaedic Hospital Department of Orthopaedic Surgery, David Geffen School of Medicine at University of California Los Angeles (UCLA), Los Angeles, California, USA.
Jared A
JA
Niska
Jeffrey A
JA
Meganck
Jonathan R
JR
Pribaz
Jonathan H
JH
Shahbazian
Ed
E
Lim
Ning
N
Zhang
Brad W
BW
Rice
Ali
A
Akin
Romela Irene
RI
Ramos
Nicholas M
NM
Bernthal
Kevin P
KP
Francis
Lloyd S
LS
Miller
D000818:Animals; D058491:Bacterial Load; D001842:Bone and Bones / Q000000981:diagnostic imaging* / Q000473:pathology; D005453:Fluorescence; D020007:Implants, Experimental / Q000009:adverse effects; D007249:Inflammation / Q000150:complications / Q000000981:diagnostic imaging / Q000473:pathology*; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000382:microbiology / Q000473:pathology / Q000601:surgery; D008297:Male; D051379:Mice; D020556:Neutrophil Infiltration; D061848:Optical Imaging; D009985:Orthopedics; D016459:Prosthesis-Related Infections / Q000150:complications / Q000000981:diagnostic imaging / Q000382:microbiology* / Q000473:pathology; D013211:Staphylococcus aureus / Q000254:growth & development*; D055114:X-Ray Microtomography