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Brandt J.-M.,Concordia Hip and Knee Institute | Medley J.B.,University of Waterloo | MacDonald S.J.,London Health Sciences Center | Bourne R.B.,London Health Sciences Center
Knee | Year: 2011

Two self-aligning mobile bearing knee replacements (SAL-1) with gamma-in-nitrogen sterilized polyethylene inserts were revised due to instability after 6.3. years and after 14.2. years in vivo in two patients. The predominant damage features were burnishing, cracking, and delamination and were observed on the proximal bearing surface of the retrieved polyethylene inserts. This suggested an association with sub-surface fatigue, perhaps initiated by in vivo oxidative degradation which was confirmed by developing a sub-surface white band in one insert. The damage features observed on the distal bearing surface of the polyethylene inserts suggested both an adhesive wear mechanism and an abrasive wear mechanism. The titanium-nitrite coated, titanium-alloy tibial tray was severely worn in one case and possibly contributed to third-body abrasive wear at the distal surface interface. We suggest to carefully follow-up patients who received this type of mobile bearing knee system. © 2010 Elsevier B.V.

Austman R.L.,University of Western Ontario | Austman R.L.,Concordia Hip and Knee Institute | King G.J.W.,University of Western Ontario | Dunning C.E.,University of Western Ontario
Journal of Orthopaedic Research | Year: 2011

Distal ulnar arthroplasty is becoming a popular treatment option for disorders of the distal radioulnar joint; however, few studies have investigated how load transfer in the ulna is altered after insertion of an implant. The purpose of our study was to compare bone stresses before and after insertion of two commercially available cemented distal ulnar implants: an implant with a titanium stem and an implant with a cobalt chrome stem. Appropriately sized implants of both types were inserted into eight previously validated subject-specific finite element models, which were created by using information derived from computed tomography scans. The von Mises stresses were compared at eight different regions pre- and post-implantation. The bone stresses with the titanium stem were consistently closer to the pre-implantation stresses than with the cobalt chrome stem. For the loading situation and parameters investigated, results of these models show that insertion of the E-Centrix® ulnar Head may result in less stress shielding than the SBI uHead™ stem. Future studies are required to investigate other implant design parameters and loading conditions that may affect the predicted amount of stress shielding. © 2011 Orthopaedic Research Society.

Brandt J.-M.,Concordia Hip and Knee Institute | Charron K.,University of Western Ontario | Zhao L.,University of Western Ontario | MacDonald S.J.,University of Western Ontario | Medley J.B.,University of Waterloo
Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine | Year: 2012

Calf serum lubricants consisting of various polypeptide constituent fractions are routinely used in knee wear simulators as part of the standardized test protocol. Three calf sera (bovine, new-born and alpha) were diluted as per the recommendation of ISO-14243-3 and used in displacement-controlled knee wear simulators to investigate their effects on polyethylene wear. Biochemical analyses included measuring total polypeptide degradation, electrophoretic profiles and low-molecular weight polypeptide concentrations to elucidate their involvement in the wear process. The effects of the various calf sera constituent fractions on microbial growth were also explored. The polyethylene wear rates and the results from the biochemical analyses for the three calf serum lubricants were all found to be statistically significantly different from each other. The lubricant derived from the alpha-calf serum was closest in constituent fractions to human synovial fluid. It also showed the lowest polyethylene wear rate (14.38-±-0.85-mm3/million cycles) and the lowest amount of polypeptide degradation (7.77-±-3.87%). Furthermore, the alpha-calf serum lubricant was associated with the least amount of change in the electrophoretic profile, the least change in low-molecular weight polypeptide concentration, and the lowest microbial growth in the presence of sodium azide (a microbial inhibitor conventionally used in implant wear testing). Replacing sodium azide with a broad spectrum antibiotic-antimycotic eradicated the microbial growth. Some speculation was entertained regarding the effect of alpha-calf serum on colloid-mediated boundary lubrication. Based on the results, it was recommended that ISO-14243-3 be modified to include guidelines on calf serum constituent fractions that would favour using alpha-calf serum in order to improve the fidelity of the simulation in knee implant wear testing. © IMechE 2012.

Brandt J.-M.,Concordia Hip and Knee Institute | Haydon C.M.,London Health Sciences Center | Harvey E.P.,University of Waterloo | McCalden R.W.,London Health Sciences Center | Medley J.B.,University of Waterloo
Tribology International | Year: 2012

Two semi-quantitative grading methods (referred to as the Hood/Wasielewski-method and the Modified-method) were described and then applied to 52 retrieved tibial polyethylene inserts from modular total knee replacements. Their ability to assess backside surface damage was compared. The damage score correlation with the implantation period greater than 24 months was better using the Modified-method (R=0.524, p=0.006) than using the Hood/Wasielewski-method (R=0.328, p=0.102). Also, the Modified-method gave significantly higher damage scores for males with gamma-in-air irradiated polyethylene inserts whereas the Hood/Wasielewski-method did not. Thus, the damage score obtained using the Modified-method seemed to provide a better representation of clinical surface damage and possibly PE wear. © 2012 Published by Elsevier Ltd. All rights reserved.

Brandt J.-M.,Concordia Hip and Knee Institute | MacDonald S.J.,London Health Sciences Center | Bourne R.B.,London Health Sciences Center | Medley J.B.,University of Waterloo
Knee | Year: 2012

Retrieved knee implants were examined to investigate the influence of patient and implant related factors on backside damage. Fifty-two implants of three different models were examined that all had cemented tibial trays without screw holes. A semi-quantitative grading system supplied backside damage scores (BDS) for each polyethylene (PE) tibial insert. Evidence was obtained to support the use of a constraining partial-peripheral locking mechanism and polished tibial tray surface (particularly for male patients) to reduce backside damage. Overall, male patients in the present study were associated with higher body mass and higher BDS compared with female patients. Furthermore, PE inserts sterilized by gamma-in-air had higher BDS than PE inserts sterilized in inert environments (gas-plasma or ethylene-oxide). Also, the proximal surfaces of tibial trays that had been grit-blasted showed embedded particles that may have increased backside damage. While none of these overall findings was unexpected, the present study provided detailed supporting analysis based on data from clinical retrievals, which may further support the use of a polished tibial tray combined with partial-peripheral locking mechanism to reduce BDS. © 2011 Elsevier B.V.

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