Prophylaxis of infection and effects on osseointegration using a tobramycin-periapatite coating on titanium implants--an experimental study in the rabbit.

No options are available for local antibiotic delivery from uncemented implants. By loading a porous titanium implant with a biomimetic HA-coating (PeriApatite, PA) with antibiotics, we could obtain adequate local antibiotic concentrations and reduce infection susceptibility. This study investigated the efficacy of a tobramycin-loaded PA-coated titanium foam implant in preventing infection, as well as the effects on osseointegration. In 72 New Zealand White rabbits, an uncoated (Ti), PA-coated (PA), or Tobramycin-PA-coated (PA-tobra) titanium foam rod was implanted intramedullary in the left tibiae after contamination of the implant bed with none (control), 10(3), 10(4) or 10(5) CFU Staphylococcus aureus. PA-tobra implants were loaded with 2.4 mg tobramycin. After 28 days analysis was done by bacteriology, histopathology and histomorphometry. Six percent of the contaminated PA-tobra rabbits were infected, whereas this was 53 and 67% for PA and Ti, respectively (p < 0.001). Quantitative cultures were also significantly lower in the PA-tobra group (p = 0.003). None of the control rabbits were infected. Histopathological and histomorphometrical scores were both better for the PA-tobra group, although only significant compared to Ti. No significant differences were observed between PA and Ti rabbits. We conclude that the application of tobramycin to PA-coated titanium foam implants appears to be an effective local antibiotic strategy for uncemented implants for infection prophylaxis and has a beneficial effect on implant fixation, which will result in improved long-term implant survival.

The role of cement viscosity on cement-bone apposition and strength: an in vitro model with medullary bleeding.

We compared the mechanical and morphological characteristics of cement-bone structures created with either standard- or low-viscosity cement using a human cadaver model that simulated intramedullary bleeding. The goal is to determine if the viscosity of the cement would affect the strength of the cement-bone interface and the degree of apposition between the cement and bone. The tensile strength of cement-bone constructs with standard-viscosity cement (2.42 +/- 1.55 MPa) was 21% stronger than with low-viscosity cement (2.00 +/- 1.51 MPa, P = .034). Cement-bone apposition was positively correlated (r2 = 0.29, P <. 0001) with the strength of the interface. There was 15% greater apposition between cement and bone (P = .036) for standard-viscosity cement. Low-viscosity cement may be less effective in displacing bone marrow and in preventing hemodynamic backflow, resulting in less apposition and a weaker interface.

The effect of low-viscosity cement on mantle morphology and femoral stem micromotion: a cadaver model with simulated blood flow.

BACKGROUND: Limited data exist on the performance of low-viscosity cement in clinically realistic cadaver models. METHODS: Paired stem/cement/femur constructs were generated with low-viscosity and standard-viscosity cements. The constructs were created and tested under simulated in vivo conditions, for which novel techniques were developed during this study. Mantle function was quantified by stem/cortex micromotions over 105cycles of "stair-climbing". Mantle morphology was determined from transverse sections. RESULTS: Penetration of low-viscosity cement was greater proximally but less distally (p = 0.02). Low-viscosity cement resulted in more stem retroversion (p = 0.04), but there was no difference in subsidence (p = 0.4). Low-viscosity cement mantles had greater fractions of non-apposed interface (p = 0.006). Fraction of non-apposed interface predicted stem retroversion (R2 = 0.64, p = 0.002). INTERPRETATION: Low-viscosity cement resulted in inferior cement mantles. Early micromotion was reduced by better interface apposition. The greater stem retroversion of low-viscosity cement would probably lead to higher revision rates. Early stem migration is due to interface non-apposition. Techniques should be developed to reduce non-apposition of cemented interfaces.

Preclinical evaluation of a poly (vinyl alcohol) hydrogel implant as a replacement for the nucleus pulposus.

STUDY DESIGN: An in vivo investigation into the safety of a novel hydrogel implant designed to replace the diseased nucleus pulposus. OBJECTIVES: To determine the local and systemic safety of this new implant in a nonhuman primate model. SUMMARY OF BACKGROUND DATA: A poly (vinyl alcohol) (PVA) hydrogel has been developed as a prosthetic replacement for the diseased nucleus pulposus. METHODS: PVA implants were inserted into discectomy defects created in the L3-L4 or L4-L5 intervertebral disc in 20 male baboons. Empty discectomy defects served as a surgical control in 8 additional animals. Routine follow-up evaluations included radiography, magnetic resonance imaging, gross pathology, and histopathology of both local and remote tissues. RESULTS: Insertion of the PVA hydrogel from an anterior direction produced extrusions in 5 animals from the first series of 15 surgeries (33%). A modified surgical technique, involving an anterolateral rather than anterior approach, was used in 5 animals, but the extrusion rate remained high (20%). Despite these surgical complications, the PVA implants were well tolerated over 24 months in vivo, with no evidence of device-related pathology in the adjacent disc tissue, spinal cord, or remote tissues. CONCLUSION: Implantation of the PVA implant for periods of up to 24 months produced no evidence of local or systemic toxicity. Additional studies are now needed to determine the efficacy of the device in its intended application.

The strength of acrylic bone cement cured under thumb pressure.

In this investigation, the static tensile strength of bone cement was quantified after mixing it in an open bowl or in a commercially available vacuum mixer and molding it under pressures consistent with values obtained by finger/digital application, as it is used in surgery. Pressure, held for a brief time span on cement in its lower viscosity state, has been demonstrated to increase penetration of the cement into bone. Clinically, bone cement is pressurized by digital pressure, specialized instruments, or by implant design. Specimens were cured under constant pressures of up to 100kPa, which is in the range reported for thumb pressurization of plugged proximal femurs and instrumented pressurization of acetabular sockets. The results showed that application of constant pressure during the polymerization of open bowl mixed bone cement significantly improved its mechanical properties. Application of 100kPa constant pressure to the open bowl mixed bone cement while it cured increased its ultimate strength to a value similar to vacuum mixed cement. Curing under pressure showed no significant effect on the tensile properties of vacuum mixed cement. Curing under pressure did not significantly reduce the size of the largest pores in the tensile specimens.

Mixing of acrylic bone cement: effect of oxygen on setting properties.

The present study investigates the effect of different mixing methods on the setting properties of bone cement. It was found that vacuum mixing decreased the setting time of the bone cement by nearly 2 min (10%), compared to mixing in air. Two additional experiments, in which the bone cement powders were purged with argon or oxygen, and mixed with the methyl methacrylate monomer, revealed that oxygen concentrations in the bone cement had a great effect on the setting time. The setting time increases significantly as the oxygen concentration increases, which suggests that the decrease in the setting time by vacuum mixing may be attributed to the lower oxygen levels present in the mixer. No significant effect was observed on dough time or maximum exothermic temperature by varying oxygen concentrations in the bone cement mixer.

Antibiotic bone cement for the treatment of Pseudomonas aeruginosa in joint arthroplasty: comparison of tobramycin and gentamicin-loaded cements.

One hundred clinical isolates of Pseudomonas aeruginosa were collected from 22 medical centers throughout Europe and were challenged with two aminoglycoside-loaded bone cements, employing a modified in vitro Kirby-Bauer susceptibility model. The results of this study show that Simplex P with tobramycin exhibits antibacterial activity against 98% of the strains tested, compared to 93% for Palacos with gentamicin. Additionally, for strains that were susceptible to the antibiotic bone cement formulations, the average zone of inhibition produced around the tobramycin-loaded cement disks was approximately 25% greater than that seen around the gentamicin-loaded cement disks. This difference was statistically significant (p << 0.01). Tobramycin-loaded bone cement is therefore the preferred formulation when addressing Pseudomonas aeruginosa in septic joint arthroplasty.

Effect of choice of surgical gloves on dough time measurements of acrylic bone cement.

In this study we investigated the effect of the brand of surgical gloves on the dough time determination for acrylic bone cements. Four different brands of powder-free latex surgical gloves were tested. Two commercial bone cements, Surgical Simplex P and Palacos R, were used for dough time measurement following standard test methods for acrylic bone cements (ASTM F-451 and ISO 5833). The results show that the measured dough time depended largely on the brand of gloves used, and could vary by nearly 250%. The surface morphological structures of gloves, determined by SEM, probably contribute to the differences in the measured dough time. This study provides experimental evidence that supports the need to describe the type of gloves used, in detail, when dough time is reported. It also illustrates the importance of the glove brand, when bone cement is to be handled as a dough in the clinical setting.