Article

Relative contributions of design, alignment, and loading variability in knee replacement mechanics

Computational Biomechanics Lab, University of Denver, 2390 S. York Street, Denver, Colorado 80208. .
Journal of Orthopaedic Research (Impact Factor: 2.97). 12/2012; 30(12):2015-24. DOI: 10.1002/jor.22169
Source: PubMed

ABSTRACT Substantial variation in total knee replacement (TKR) outcomes exists within the patient population. Some of this variability is due to differences in the design of the implanted components and variation in surgical alignment, while other variability is due to differences in the applied forces and torques due to anatomic and physiological differences within a patient population. We evaluated the relative contributions of implant design, surgical alignment, and patient-specific loading variability to overall tibiofemoral joint mechanics to provide insight into which measures can be influenced through design and surgical decisions, and which are inherently dependent on variation within the patient population and should be considered in the robustness of the implant design and surgical procedure. Design, surgical, and loading parameters were assessed using probabilistic finite element methods during simulated stance-phase gait and squat activities. Patient-specific loading was found to be the primary contributor to joint loading and kinematics during low flexion, particularly under conditions of high external loads (for instance, the gait cycle with high internal-external torque), while design and surgical factors, particularly femoral posterior radius and posterior slope of the tibial insert became increasingly important in TKR performance in deeper flexion. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:2015-2024, 2012.

3 Followers
 · 
131 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: A variety of design and patient parameters have been implicated in recent reports of fretting corrosion at modular connections in total hip arthroplasty. We sought to identify the relative sensitivity of mechanical fretting to a comprehensive set of parameters such that attention may be focused on key variables. Stochastic finite element simulation of the head-neck taper-trunnion junction was performed. Four-hundred parameters sets were simulated using realistic variations of design variables, material properties and loading parameters to predict contact pressures (P), micromotions (M) and fretting work (coefficient of friction⁎P⁎M) over cycles of gait. Results indicated that fretting work was correlated with only three parameters: angular mismatch, center offset and body weight (r=0.47, 0.53, 0.43, p<0.001). Maximum contact pressure increased by 85 MPa for every 0.1° of angular mismatch. Maximum micromotion increased by 5 µm per 10 mm additional head offset and 1 µm per 10 kg increased body weight. Uncorrelated parameters included trunnion diameter, trunnion length and impaction forces. It was concluded that appropriate limiting of angular mismatch and center offset could minimize fretting, and hence its contribution to corrosion, at modular connections.
    Journal of Biomechanics 05/2014; 47(7). DOI:10.1016/j.jbiomech.2014.02.035 · 2.50 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: For clinically predictive testing and design-phase evaluation of prospective total knee replacement (TKR) implants, devices should ideally be evaluated under physiological loading conditions which incorporate population-level variability. A challenge exists for experimental and computational researchers in determining appropriate loading conditions for wear and kinematic knee simulators which reflect in vivo joint loading conditions. There is a great deal of kinematic data available from fluoroscopy studies. The purpose of this work was to develop computational methods to derive anterior-posterior (A-P) and internal-external (I-E) tibiofemoral (TF) joint loading conditions from in vivo kinematic data. Two computational models were developed, a simple TF model, and a more complex lower limb model. These models were driven through external loads applied to the tibia and femur in the TF model, and applied to the hip, ankle and muscles in the lower limb model. A custom feedback controller was integrated with the finite element environment and used to determine the external loads required to reproduce target kinematics at the TF joint. The computational platform was evaluated using in vivo kinematic data from four fluoroscopy patients, and reproduced in vivo A-P and I-E motions and compressive force with a root-mean-square (RMS) accuracy of less than 1mm, 0.1°, and 40N in the TF model and in vivo A-P and I-E motions, TF flexion, and compressive loads with a RMS accuracy of less than 1mm, 0.1°, 1.4°, and 48N in the lower limb model. The external loading conditions derived from these models can ultimately be used to establish population variability in loading conditions, for eventual use in computational as well as experimental activity simulations.
    Journal of Biomechanics 04/2014; 47(10). DOI:10.1016/j.jbiomech.2014.04.024 · 2.50 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Few registry-based studies in the United States have compared the survivorship of different knee implant designs in total knee arthroplasty. The purpose of this study was to compare differences in survivorship of commonly used tibial implant designs in primary total knee arthroplasty.METHODS: A total of 16,584 primary total knee arthroplasties in 11,992 patients were performed at a single institution from 1985 to 2005. Patients were prospectively followed at regular intervals to ascertain details of subsequent revisions. Overall revision rates and revisions for aseptic loosening, wear, and osteolysis were compared across twenty-two tibial implant designs using Cox proportional hazards regression models adjusting for age, sex, calendar year, and body mass index.RESULTS: In comparison with metal-backed modular implants, all-polyethylene tibial components had a significantly lower risk of revision (hazard ratio, 0.3; 95% confidence intervals: 0.2, 0.5 [p < 0.0001]). The risk reduction with all-polyethylene tibial components was not affected by age, sex, or body mass index. With metal-backed modular tibial designs, cruciate-retaining knees performed better than the posterior-stabilized knees (p = 0.002), but this finding was limited to one specific metal-backed modular tibial component, the Press Fit Condylar design. With all-polyethylene tibial components, there was no survivorship difference between cruciate-retaining and posterior-stabilized designs.CONCLUSIONS: All-polyethylene tibial components were associated with better outcomes than metal-backed modular components. Cruciate-retaining and posterior-stabilized designs performed equally well, except with the Press Fit Condylar design. Obese patients may have superior results with all-polyethylene and posterior-stabilized components.LEVEL OF EVIDENCE: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.
    The Journal of Bone and Joint Surgery 07/2014; 96(14):e121. DOI:10.2106/JBJS.M.00820 · 4.31 Impact Factor