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Long-term biotribological evaluation of total hip and knee arthroplasty implants
Long-term biotribological evaluation of total hip and knee arthroplasty implants
Total joint arthroplasty (TJA) is one of the clinically most successful and cost-effective surgical procedures being performed as a treatment for end-stage osteoarthritis. However, complications may occur due to biological responses triggered by polyethylene wear particles and metal ions released from the implant components. Originally, TJA was conceived as a procedure for elderly patients with moderate activity levels. Nevertheless, this procedure has now expanded to younger and more active patients, who generate more wear products due to their higher activity level. The purpose of the following doctoral thesis was to perform a series of pre-clinical tests in the field of biotribology in order to better understand the mechanisms that generate wear and evaluate if the implants in question are able to fulfill the demanding requirements of a long-term clinical performance. Two main research topics were defined, each one addressing a certain aspect of the implants: 1) backside wear on acetabular polyethylene liners and 2) biotribological behavior and metal ion release barrier function of zirconium nitride (ZrN) multilayer coated knee implants, designed for patients with metal ion hypersensitivity. Backside wear due to micro-motion and poor conformity between the polyethylene liner and its acetabular shell may contribute to the overall amount of released wear particles and lead to aseptic loosening. Two research publications regarding this topic were performed with the purpose of understanding the wear process at the backside of polyethylene liners with a certain locking mechanism. As there are currently no studies nor standards to quantitatively measure the backside wear, a semi-quantitative optical analysis was developed in order to evaluate this type of wear. In the first research publication, a direct comparison between the backside wear of short-term in vitro wear simulated and retrieved acetabular liners with an equivalent life in service was done to obtain a first knowledge of the type of wear present at this non-articulating cup-insert fixation surface. In the second research publication, a long-term in vitro wear simulation was performed to analyze if this type of wear increases with time. The main finding of these two research publications was that most of the backside wear produced on the liners occurred during their insertion and removal from the acetabular shell rather than during their life in service and that there was no significant incremental progression of this type of wear through time (high cycle testing). Regarding metal ion release, metal hypersensitivity became an important topic of research due to the adverse clinical results seen in patients with elevated cobalt values in blood. An alternative for such patients is the use of implants with a ZrN multilayer coating, which prevents the release of metal ions from the CoCrMo substrate material. The second part of this doctoral thesis was focused in the pre-clinical evaluation of total knee implants with such a ZrN multilayer coating. For the third and final research publication of the present thesis, a highly demanding activities knee wear simulation was performed for the first time on a ZrN multilayer coated knee implant with the purpose of comparing its wear characteristics and metal ion release barrier function against its clinically established uncoated version made out of CoCrMo. The results demonstrated that the ZrN multilayer coating significantly reduced the polyethylene wear rate and metal ion release from the substrate material, even under such highly demanding conditions. Besides, the integrity of the ZrN multilayer coating was not impaired by failure modes such as delamination, surface disruption or flaking, resulting in a full functioning multilayer coating with long-term behavior. In conclusion, this doctoral thesis demonstrates that the analyzed implants are able to maintain their good biotribological performance at the long-term, even under highly demanding conditions. Long-term in vitro tests that account for high demanding activities, need to be applied in future pre-clinical testing in order to evaluate and ensure the performance at the long-term of total joint arthroplasty implants in younger patients. Regarding metal ion release, metal hypersensitivity became an important topic of research due to the adverse clinical results seen in patients with elevated cobalt values in blood. An alternative for such patients is the use of implants with a ZrN multilayer coating, which prevents the release of metal ions from the CoCrMo substrate material. The second part of this doctoral thesis was focused in the pre-clinical evaluation of total knee implants with such a ZrN multilayer coating. For the third and final research publication of the present thesis, a highly demanding activities knee wear simulation was performed for the first time on a ZrN multilayer coated knee implant with the purpose of comparing its wear characteristics and metal ion release barrier function against its clinically established uncoated version made out of CoCrMo. The results demonstrated that the ZrN multilayer coating significantly reduced the polyethylene wear rate and metal ion release from the substrate material, even under such highly demanding conditions. Besides, the integrity of the ZrN multilayer coating was not impaired by failure modes such as delamination, surface disruption or flaking, resulting in a full functioning multilayer coating with long-term behavior. In conclusion, this doctoral thesis demonstrates that the analyzed implants are able to maintain their good biotribological performance at the long-term, even under highly demanding conditions. Long-term in vitro tests that account for high demanding activities, need to be applied in future pre-clinical testing in order to evaluate and ensure the performance at the long-term of total joint arthroplasty implants in younger patients.
Total Joint Arthoplasty, backside wear, knee wear simulation, high demanding activities, metal ion release
Puente Reyna, Ana Laura
2019
English
Universitätsbibliothek der Ludwig-Maximilians-Universität München
Puente Reyna, Ana Laura (2019): Long-term biotribological evaluation of total hip and knee arthroplasty implants. Dissertation, LMU München: Faculty of Medicine
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Abstract

Total joint arthroplasty (TJA) is one of the clinically most successful and cost-effective surgical procedures being performed as a treatment for end-stage osteoarthritis. However, complications may occur due to biological responses triggered by polyethylene wear particles and metal ions released from the implant components. Originally, TJA was conceived as a procedure for elderly patients with moderate activity levels. Nevertheless, this procedure has now expanded to younger and more active patients, who generate more wear products due to their higher activity level. The purpose of the following doctoral thesis was to perform a series of pre-clinical tests in the field of biotribology in order to better understand the mechanisms that generate wear and evaluate if the implants in question are able to fulfill the demanding requirements of a long-term clinical performance. Two main research topics were defined, each one addressing a certain aspect of the implants: 1) backside wear on acetabular polyethylene liners and 2) biotribological behavior and metal ion release barrier function of zirconium nitride (ZrN) multilayer coated knee implants, designed for patients with metal ion hypersensitivity. Backside wear due to micro-motion and poor conformity between the polyethylene liner and its acetabular shell may contribute to the overall amount of released wear particles and lead to aseptic loosening. Two research publications regarding this topic were performed with the purpose of understanding the wear process at the backside of polyethylene liners with a certain locking mechanism. As there are currently no studies nor standards to quantitatively measure the backside wear, a semi-quantitative optical analysis was developed in order to evaluate this type of wear. In the first research publication, a direct comparison between the backside wear of short-term in vitro wear simulated and retrieved acetabular liners with an equivalent life in service was done to obtain a first knowledge of the type of wear present at this non-articulating cup-insert fixation surface. In the second research publication, a long-term in vitro wear simulation was performed to analyze if this type of wear increases with time. The main finding of these two research publications was that most of the backside wear produced on the liners occurred during their insertion and removal from the acetabular shell rather than during their life in service and that there was no significant incremental progression of this type of wear through time (high cycle testing). Regarding metal ion release, metal hypersensitivity became an important topic of research due to the adverse clinical results seen in patients with elevated cobalt values in blood. An alternative for such patients is the use of implants with a ZrN multilayer coating, which prevents the release of metal ions from the CoCrMo substrate material. The second part of this doctoral thesis was focused in the pre-clinical evaluation of total knee implants with such a ZrN multilayer coating. For the third and final research publication of the present thesis, a highly demanding activities knee wear simulation was performed for the first time on a ZrN multilayer coated knee implant with the purpose of comparing its wear characteristics and metal ion release barrier function against its clinically established uncoated version made out of CoCrMo. The results demonstrated that the ZrN multilayer coating significantly reduced the polyethylene wear rate and metal ion release from the substrate material, even under such highly demanding conditions. Besides, the integrity of the ZrN multilayer coating was not impaired by failure modes such as delamination, surface disruption or flaking, resulting in a full functioning multilayer coating with long-term behavior. In conclusion, this doctoral thesis demonstrates that the analyzed implants are able to maintain their good biotribological performance at the long-term, even under highly demanding conditions. Long-term in vitro tests that account for high demanding activities, need to be applied in future pre-clinical testing in order to evaluate and ensure the performance at the long-term of total joint arthroplasty implants in younger patients. Regarding metal ion release, metal hypersensitivity became an important topic of research due to the adverse clinical results seen in patients with elevated cobalt values in blood. An alternative for such patients is the use of implants with a ZrN multilayer coating, which prevents the release of metal ions from the CoCrMo substrate material. The second part of this doctoral thesis was focused in the pre-clinical evaluation of total knee implants with such a ZrN multilayer coating. For the third and final research publication of the present thesis, a highly demanding activities knee wear simulation was performed for the first time on a ZrN multilayer coated knee implant with the purpose of comparing its wear characteristics and metal ion release barrier function against its clinically established uncoated version made out of CoCrMo. The results demonstrated that the ZrN multilayer coating significantly reduced the polyethylene wear rate and metal ion release from the substrate material, even under such highly demanding conditions. Besides, the integrity of the ZrN multilayer coating was not impaired by failure modes such as delamination, surface disruption or flaking, resulting in a full functioning multilayer coating with long-term behavior. In conclusion, this doctoral thesis demonstrates that the analyzed implants are able to maintain their good biotribological performance at the long-term, even under highly demanding conditions. Long-term in vitro tests that account for high demanding activities, need to be applied in future pre-clinical testing in order to evaluate and ensure the performance at the long-term of total joint arthroplasty implants in younger patients.