A resorbable, antibiotic-eluting bone void filler (AEBVF) was developed to address device-related infections. The AEBVF provides two functions: osteoconductive matrix for bone restoration, and local antibiotic delivery to treat device-related infections. In vitro evaluations of this AEBVF demonstrated antimicrobial activity to 7 weeks against Staphylococcus aureus (S. aureus).1 Subsequent rabbit studies demonstrated bactericidal capacity2 of the AEBVF against 105 CFU S. aureus and osteoconductivity.1 We hypothesized that the AEBVF would restore bone volume while eliminating 105 CFU S. aureus in a pilot sheep femoral condyle defect model.

Four groups (n=2/group) were utilized to assess osteoconductivity (Group A-commercial ProOsteon & B-AEBVF) and antimicrobial activity (Group C-ProOsteon with 105 CFU S. aureus & D-AEBVF with 105 CFU S. aureus). AEBVF devices comprised degradable polymers (PCL, PEG, PLGA), ProOsteon (Biomet, USA), CaCl2, and tobramycin.3 Devices (1.5cc ProOsteon or 6 AEBVF croutons) were implanted into rectangular defects in the medial face of each sheep femoral condyle. Defects were evaluated using backscatter electron microscopy, mineral apposition rate (MAR) analysis, and light microscopy with Sanderson's Rapid Bone Stain (SRBS).

All animals in Groups A, B, and D survived to the 12-week endpoint. In contrast, Group C animals were euthanized 11 days post-op. MAR and SRBS demonstrated comparable bone remodeling and defect restoration after 12 weeks in Groups A, B, and D. Notably, implant volumes of Groups A and D were greatly diminished (0.16±0.1%; 0.35%) after 12 weeks, compared to Group A (13.23±3.2%) and Time “0” (16.8%).

These data show the AEBVF device's ability to: eliminate 105 CFU S. aureus, promote bone remodeling comparable to known bone void filler, and degrade at rates that do not interfere with bone remodeling.

We have studied the relationship between metal ion levels and lymphocyte counts in patients with metal-on-metal hip resurfacings. Peripheral blood samples were analysed for lymphocyte subtypes and whole blood cobalt and chromium ion levels in 68 patients (34 with metal-on-metal hip resurfacings and 34 with standard metal-on-polyethylene total hip replacements). All hip components were radiologically well-fixed and the patients were asymptomatic. Cobalt and chromium levels were significantly elevated in the patients with metal-on-metal hip resurfacings, compared with the patients with standard metal-on-polyethylene designs (p < 0.0001). There was a statistically significant decrease in the level of CD8⁺ cells (T-cytotoxic/suppressor) (p = 0.005) in the metal-on-metal hip resurfacing group. A threshold level of blood cobalt and chromium ions was associated with reduced CD8⁺ T-cell counts. We have no evidence that our patients suffered as a result of this reduced level of CD8⁺ T-cells.