No description available.

The present thesis investigates the friction properties of total knee replacement components using lubricating fluids of different composition and rheology. The first stage of the thesis involves characterization of the rheological properties of hyaluronic acid (HA)/bovine calf serum (BCS) solutions. With increased concentration and molecular weight of HA, higher viscosities and more pronounced shear thinning in steady shear flow was observed. In dynamic oscillatory flow, the elastic character of the solutions became more pronounced and the cross-over frequency decreased upon increasing concentration and molecular weight of HA. The second part of the thesis involves the determination of a method by which the coefficient of friction is estimated using a linear reciprocating wear testing machine with spherical metal indenters articulating on flat UHMWPE samples and deionised (D.I.) water lubrication. A characteristic periodic pattern in the friction behaviour was observed and the coefficient of friction was computed by calculating the average of 30 points about the midpoint between reversals and using the average of three cycles. The third part of the thesis involves the investigation of the effect of fluid composition on the coefficient of friction in knee replacement components. With increased concentration of HA in solution (0-1mg/mL), the coefficient of friction of HA/BCS solutions decreased. However, with HA/BCS solutions of higher HA concentrations (above 1mg/mL), no significant difference in the coefficient of friction was observed. Similar behavior was observed with HA/Albumin solutions. With HA/ D.I. water solutions, the coefficient of friction was almost identical irrespective of the concentration of HA in solution. Significant difference in the rheological properties of HA/D.I. water solutions did not affect the coefficient of friction. The Stribeck analysis revealed that the coefficient of friction with HA/BCS and HA/D.I. water lubrication was not governed by hydrodynamic conditions. The fourth part of this thesis involved characterization of lubricating fluids before and after friction testing. Absorbance and dynamic light scattering measurements of HA/BCS solutions and of HA/Albumin solutions indicate a rise in turbidity and the presence of larger size particles in these solutions after friction testing. The ninhydrin test confirmed the presence of protein in the precipitates obtained following testing. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2010-09-24 14:06:41.437

Wear particle-induced inflammation leading to periprosthetic osteolysis remains a major cause of hip implant failure. As polyethylene particles from conventional metal-on-polyethylene implants have been associated with these failures, an interest in lower wear metal-on-metal (MM) bearings has emerged. However, the biological effects of nanometer-size chromium oxide particles, predominant type of wear particles produced by MM implants, remain mostly unknown. Therefore, this study aimed to determine the cytotoxicity of nanometer-size Cr2O3 particles on macrophages in vitro, by analyzing their effects on cell mortality and cytokine release and comparing them with those of similarly-sized alumina (Al2O3) particles (known to be relatively bioinert). Results showed that at high concentrations, nanometer-size Cr2O3 particles can be cytotoxic to macrophages, inducing significant decreases in total cell numbers and increases in necrosis. Results also showed that, at high concentrations, the cytotoxicity of Cr2O3 particles was overall higher than that of Al2O3 particles, even though Cr2O3 and Al2O3 are both stable forms of ceramic materials. However, it appeared to be lower than that of previously reported conventional polyethylene and CoCrMo particles. Therefore, chromium oxide particles may not be the main culprit in initiating the inflammatory reaction in MM periprosthetic tissues.

Die periprothetische Fraktur ist eine schwerwiegende Komplikation nach Implantation einer Hüftendoprothese und stellt hohe Anforderungen an das Therapieregime, den Operateur und das Material. Die Wahl des Therapieverfahrenes ist vom Frakturtyp, der Knochenqualität, der Prothesenstabilität und vom Allgemeinzustand des Patienten abhängig. Die Vergleichbarkeit der Ergebnisse zwischen verschiedenen Studien wird einerseits durch die individuellen Therapiestrategien und andererseits durch die Vielzahl an unterschiedlichen Klassifikationen erschwert. Das in der vorliegenden Arbeit anhand einer Vergleichsgruppen-Analyse nachuntersuchte Studienkollektiv bestand aus n = 23 Patienten in der Hauptgruppe und n = 19 Patienten in der Kontrollgruppe, deren klinische Behandlung zwischen 2002 und 2008 am Uniklinikum Leipzig durchgeführt wurde. Hierbei handelte es sich hauptsächlich um geriatrische Patienten mit einem erhöhten Frauenanteil. Die Analyse erfolgte mit einer medianen Follow-Up Zeit der Nachuntersuchung von zwei Jahren. Im Vergleich zu in Literaturdaten angegebenen Ursachen für die Implantation einer Hüftendoprothese zeigte sich in der Hauptgruppe eine höhere Rate an Patienten mit ursprünglicher proximaler Femurfraktur im Vergleich zu Coxarthrose. Die Studie ergab darüber hinaus, dass ein hohes Patientenalter bei der Primärimplantation zu einer kürzeren Standzeit der Prothese führte (p = 0,01++). Zur periprothetischen Fraktur war häufig unterhalb der Prothesenspitze lokalisiert und in den überwiegenden Fällen durch ein Niedrig-EnergieTrauma in Verbindung mit prädisponierenden Faktoren bedingt. Im Widerspruch mit der Literatur ereignete sich die periprothetische Fraktur in unserer Untersuchung häufiger und zeitlich eher bei Patienten mit zementierter Hüftendoprothese als bei denjenigen mit nicht zementierter Endoprothese (Beals and Tower, 1996). Die operative Frakturversorgung erfolgt bei gelockerter Endoprothese durch einen Prothesenwechsel und bei fester Endoprothese durch eine Osteosynthese. Die unterschiedlichen Frakturtypen und Versorgungsarten führten nicht zu einem signifikant unterschiedlichen funktionellen Ergebnis der Patienten, wobei im Vergleich der Frakturtypen vom Trend her Patienten mit Johansson I Fraktur das beste funktionelle Resultat erreichten. Bezüglich der Komplikationsrate zeigte sich in der plattenosteosynthetisch versorgten Patientengruppe im Vergleich zu der durch einen Prothesenwechsel versorgten Gruppe eine signifikant erhöhte Rate an Revisionseingriffen. Im Unterschied zur Kontrollgruppe war die postoperative Komplikationsrate in der Hauptgruppe erhöht und das funktionelle Endergebnis in den Scoresystemen signifikant schlechter. Bei der Therapie der periprothetischen Fraktur traten trotz der guten objektiven Beweglichkeit, Schmerzen und Einschränkungen in der Gehfähigkeit auf, die zu einer deutlichen Reduktion der Alltagskompetenzen führten. Aus diesem Grund sollten die Ziele der Therapie periprothetischer Frakturen in der Frakturprävention, Therapieoptimierung und Nachsorgeverbesserung liegen. Zu achten ist dabei auf eine individuell ausreichende postoperative Schmerztherapie und intensive frühfunktionelle physiotherapeutische Behandlung mit Förderung der Selbstständigkeit, wobei eine weitere wissenschaftliche Begleitung und Analyse der Behandlungsergebnisse zukünftig wünschenswert wäre.

Wear particle-induced inflammation leading to periprosthetic osteolysis remains a major cause of hip implant failure. As polyethylene particles from conventional metal-on-polyethylene implants have been associated with these failures, an interest in lower wear metal-on-metal (MM) bearings has emerged. However, the biological effects of nanometer-size chromium oxide particles, predominant type of wear particles produced by MM implants, remain mostly unknown. Therefore, this study aimed to determine the cytotoxicity of nanometer-size Cr2O3 particles on macrophages in vitro, by analyzing their effects on cell mortality and cytokine release and comparing them with those of similarly-sized alumina (Al2O3) particles (known to be relatively bioinert). Results showed that at high concentrations, nanometer-size Cr2O3 particles can be cytotoxic to macrophages, inducing significant decreases in total cell numbers and increases in necrosis. Results also showed that, at high concentrations, the cytotoxicity of Cr2O3 particles was overall higher than that of Al2O3 particles, even though Cr2O3 and Al2O3 are both stable forms of ceramic materials. However, it appeared to be lower than that of previously reported conventional polyethylene and CoCrMo particles. Therefore, chromium oxide particles may not be the main culprit in initiating the inflammatory reaction in MM periprosthetic tissues.

Wear particle-induced inflammation leading to periprosthetic osteolysis remains a major cause of hip implant failure. As polyethylene particles from conventional metal-on-polyethylene implants have been associated with these failures, an interest in lower wear metal-on-metal (MM) bearings has emerged. However, the biological effects of nanometer-size chromium oxide particles, predominant type of wear particles produced by MM implants, remain mostly unknown. Therefore, this study aimed to determine the cytotoxicity of nanometer-size Cr2O3 particles on macrophages in vitro, by analyzing their effects on cell mortality and cytokine release and comparing them with those of similarly-sized alumina (Al2O3) particles (known to be relatively bioinert). Results showed that at high concentrations, nanometer-size Cr2O3 particles can be cytotoxic to macrophages, inducing significant decreases in total cell numbers and increases in necrosis. Results also showed that, at high concentrations, the cytotoxicity of Cr2O3 particles was overall higher than that of Al2O3 particles, even though Cr2O3 and Al2O3 are both stable forms of ceramic materials. However, it appeared to be lower than that of previously reported conventional polyethylene and CoCrMo particles. Therefore, chromium oxide particles may not be the main culprit in initiating the inflammatory reaction in MM periprosthetic tissues.

Wear particle-induced inflammation leading to periprosthetic osteolysis remains a major cause of hip implant failure. As polyethylene particles from conventional metal-on-polyethylene implants have been associated with these failures, an interest in lower wear metal-on-metal (MM) bearings has emerged. However, the biological effects of nanometer-size chromium oxide particles, predominant type of wear particles produced by MM implants, remain mostly unknown. Therefore, this study aimed to determine the cytotoxicity of nanometer-size Cr2O3 particles on macrophages in vitro, by analyzing their effects on cell mortality and cytokine release and comparing them with those of similarly-sized alumina (Al2O3) particles (known to be relatively bioinert). Results showed that at high concentrations, nanometer-size Cr2O3 particles can be cytotoxic to macrophages, inducing significant decreases in total cell numbers and increases in necrosis. Results also showed that, at high concentrations, the cytotoxicity of Cr2O3 particles was overall higher than that of Al2O3 particles, even though Cr2O3 and Al2O3 are both stable forms of ceramic materials. However, it appeared to be lower than that of previously reported conventional polyethylene and CoCrMo particles. Therefore, chromium oxide particles may not be the main culprit in initiating the inflammatory reaction in MM periprosthetic tissues.

No description available.

The composition of orthopaedic wear testing lubricants used to mimic synovial fluid (SF) is known to significantly affect in vitro polyethylene (PE) wear; however, some wear testing standards may be promoting the use of lubricants that are not clinically relevant. The present thesis evaluated the biochemical composition of human osteoarthritic and periprosthetic SF in order to propose changes to lubricant specifications in current wear testing standards. Using this data, pin-on-disc wear tests were conducted to explore the effects of more clinically relevant lubricants on PE wear. Results showed that wear decreased using a more clinically relevant lubricant. Samples of these lubricants were biochemically evaluated and compared to the SF results previously obtained, which showed that current standards for wear testing lubricants are biochemically different from SF. The findings from the present thesis encourage the modification of standardized lubricant specifications to improve wear testing protocols and guarantee clinically relevant wear testing.

The composition of orthopaedic wear testing lubricants used to mimic synovial fluid (SF) is known to significantly affect in vitro polyethylene (PE) wear; however, some wear testing standards may be promoting the use of lubricants that are not clinically relevant. The present thesis evaluated the biochemical composition of human osteoarthritic and periprosthetic SF in order to propose changes to lubricant specifications in current wear testing standards. Using this data, pin-on-disc wear tests were conducted to explore the effects of more clinically relevant lubricants on PE wear. Results showed that wear decreased using a more clinically relevant lubricant. Samples of these lubricants were biochemically evaluated and compared to the SF results previously obtained, which showed that current standards for wear testing lubricants are biochemically different from SF. The findings from the present thesis encourage the modification of standardized lubricant specifications to improve wear testing protocols and guarantee clinically relevant wear testing.