Hyaluronic Acid-Based Hydrogel Coating Does Not Affect Bone Apposition at the Implant Surface in a Rabbit Model

Background Uncemented orthopaedic implants rely on the bone-implant interface to provide stability, therefore it is essential that a coating does not interfere with the bone-forming processes occurring at the implant interface. In addition, local application of high concentrations of antibiotics for prophylaxis or treatment of infection may be toxic for osteoblasts and could impair bone growth. Questions/Purposes In this animal study, we investigated the effect of a commercially available hydrogel, either unloaded or loaded with 2% vancomycin. We asked, does unloaded hydrogel or hydrogel with vancomycin (1) interfere with bone apposition and timing of bone deposition near the implant surface; and (2) induce a local or systemic inflammatory reaction as determined by inflammation around the implant and hematologic parameters. Methods In 18 New Zealand White rabbits, an uncoated titanium rod (n = 6), a rod coated with unloaded hydrogel (n = 6), or a rod coated with 2% vancomycin-loaded hydrogel (n = 6) was implanted in the intramedullary canal of the left tibia. After 28 days, the bone volume fraction near the implant was measured with microCT analysis, inflammation was semiquantitatively scored on histologic sections, and timing of bone apposition was followed by semiquantitative scoring of fluorochrome incorporation on histologic sections. Two observers, blinded to the treatment, scored the sections and reconciled their scores if there was a disagreement. The hematologic inflammatory reaction was analyzed by measuring total and differential leukocyte counts and erythrocyte sedimentation rates in blood. With group sizes of six animals per group, we had 79% power to detect a difference of 25% in histologic scoring for infection and inflammation. Results No differences were found in the amount of bone apposition near the implant in the No Gel group (48.65% ± 14.95%) compared with the Gel group (59.97% ± 5.02%; mean difference [MD], 11.32%; 95% CI, −3.89% to 26.53%; p = 0.16) or for the Van2 group (56.12% ± 10.06%; MD, 7.46; 95% CI, −7.75 to 22.67; p = 0.40), with the numbers available. In addition, the scores for timing of bone apposition did not differ between the No Gel group (0.50 ± 0.55) compared with the Gel group (0.33 ± 0.52; MD, −0.17; 95% CI, −0.86 to 0.53; p = 0.78) or the Van2 group (0.83 ± 0.41; MD, 0.33; 95% CI, −0.36 to 1.03; p = 0.42). Furthermore, we detected no differences in the histopathology scores for inflammation in the No Gel group (2.33