Early changes in serum osteocalcin and body weight are predictive of implant fixation in a rat model of implant loosening

Authors: 
Wilson BM, Moran MM, Meagher MJ, Ross RD, Mashiatulla M, Virdi AS, Rick Sumner D
J Orthop Res. 2019 Dec 11. doi: 10.1002/jor.24563.

OBJECTIVE Biomarkers are of interest to identify patients at risk for peri-implant osteolysis and aseptic loosening. We used a rat model of particle-induced peri-implant osteolysis to investigate if early changes in biomarkers were associated with subsequent implant fixation strength.

METHODS Implants were placed in rat femora, which were then challenged with intra-articular knee injections of either clean-polyethylene, lipopolysaccharide-doped-polyethylene, or cobalt-chromium-alloy particles, with particle-free vehicle serving as control (n ≥ 8/group). Rats were weighed weekly, blood was collected at weeks 0, 3, 5, and 6, and locomotor behavior was assessed 4 days before study conclusion. Rats were euthanized 6 weeks post-surgery.

RESULTS Week 6 serum was analyzed for 5 bone-remodeling markers, while longitudinal serum was assessed for osteocalcin. Bone-implant contact, peri-implant trabecular architecture and implant fixation strength were measured. Rats challenged with cobalt-chromium particles had a significant reduction in implant fixation strength compared to the vehicle-control group (p=0.034). This group also had elevated serum osteocalcin (p=0.005), depressed weight gain (p = 0.001) and less frequent rearing behavior (p=0.029). Regardless of group, change in serum osteocalcin at week 3 (r=-0.368, p=0.046), change in weight at week 2 (r=0.586, p<0.001), as well as weight change at all other time intervals were associated with fixation strength.

CONCLUSION The finding that early alterations in serum osteocalcin and body weight were predictive of subsequent implant fixation strength supports continued investigation of biomarkers for early detection of peri-implant osteolysis and implant loosening. Further, change in biomarker levels was found to be more indicative of implant fixation status than any single measurement.