PubMed · 15643385
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Michael D Diodato, Sunil M Prosad, Mary E Klingensmith, Ralph J Damiano. 2004. Robotics in surgery.. https://doi.org/10.1067/j.cpsurg.2004.07.002
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Wear rate and wear direction vary considerably within total hip arthroplasty (THA) patient cohorts. Third body effects and wide-ranging differences in patient activity levels are two factors suspected of contributing to wear variability. A sliding-distance-coupled contact finite element formulation was used to test the hypothesis that nonidentical duty cycles (differing activities, or change of third body challenge) produce accelerations in polyethylene wear. Effects of nonidentical duty cycles, time-variant femoral head roughening, and outlier gait inputs were investigated. Without femoral head roughening, combination walk/stair-climb wear simulations did not result in appreciably higher volumetric wear than a walk-only simulation, but when a roughened zone was included, walk/stair-climb volumetric wear increased by approximately 57% above that of a similarly roughened walk-only simulation. To investigate time-variant femoral head roughening, wear simulations were begun with femoral head roughening at one location on the femoral head, switching to another location halfway through the simulation. Results varied depending on roughening sites, but cases of substantial increase in wear involved a transient jump in wear rate shortly after the change of head roughening location. Outlier duty cycles were simulated by increasing or decreasing the joint contact force and range of motion inputs, to levels at the 97.5th and 2.5th percentiles of a population of normal subjects. The resulting wear showed an increase or decrease closely proportional to the percentage by which each input (force or range of motion) was changed.
Bacterial infection primarily with Staphylococcus spp. and Propionibacterium acnes remains a significant complication following total hip replacement. In this in vitro study, we investigated the efficacy of gentamicin loading of bone cement and pre- and postoperative administration of cefuroxime in the prevention of biofilm formation by clinical isolates. High and low initial inocula, representative of the number of bacteria that may be present at the operative site as a result of overt infection and skin contamination, respectively, were used. When a high initial inoculum was used, gentamicin loading of the cement did not prevent biofilm formation by the 10 Staphylococcus spp. and the 10 P. acnes isolates tested. Similarly, the use of cefuroxime in the fluid phase with gentamicin-loaded cement did not prevent biofilm formation by four Staphylococcus spp. and four P. acnes isolates tested. However, when a low bacterial inoculum was used, a combination of both gentamicin-loaded cement and cefuroxime prevented biofilm formation by these eight isolates. Our results indicate that this antibiotic combination may protect against infection after intra-operative challenge with bacteria present in low numbers as a result of contamination from the skin but would not protect against bacteria present in high numbers as a result of overt infection of an existing implant.
In this paper an application of the boundary element method for simulating wear in total hip prosthesis is presented. Several examples including different update periods of the worn acetabular cup, various femoral head sizes and various materials for both the femoral head and the acetabular cup are simulated under the same variable loading conditions for up to 20 years of service. Moreover, two different femoral models are considered in order to investigate the influence of the femoral modelling. The analysis demonstrates that due to the boundary only modelling requirement, the computational time and storage remains low, allowing large service periods to be simulated. Generally, the results obtained are in good agreement with other researchers findings. Moreover, ignoring the bending of the femoral neck in the model, results in a small overestimation of the maximum wear depth, while the volumetric wear is slightly underestimated. However, these differences are trivial considering the reduction of the computational effort.