Abstract
BackgroundImplant surface integrity and cement bonding are assumed to be sufficient in primary total knee replacements to stabilize implants for extended wear without concerns over delamination and loosening. Yet there exists a significant rate of aseptic loosening where failure at implant cement interface occurs. The aim of this study is to look at specific aspects leading to aseptic loosening of the total knee replacement, where cement adhesion to the implant results in the lowest pull off strength.MethodsVirgin ceramic coated and uncoated chrome cobalt tibial trays were used in a pull off study using differing viscosities of cement at varied time intervals to compare which combination is strongest compared to which is least resistant to pull off testing.ResultsLow viscosity cement had a 44% (5.9 kg verses 3.3 kg, p < 0.001) higher pull-off strength compared to high viscosity cement. Coated implants had a 30% (3.9 kg verses 5.5 kg, p = 0.037) lower pull-off strength compared to non-coated. Testing measures were limited to cement utilization less than 5 minutes due to the poor adhesion of the dowels beyond this time. Finally, there was a significant difference in adhesion properties between brand names when utilizing low viscosity cement on the non-coated trays (10.34 kg for Simplex verses 4.87 for Palacos, p = 0.021).ConclusionThere are differences in adhesion properties between cement vendors, prompting significant concerns over the use of coated implants with particular cement types. Use of low viscosity cement on non-coated surfaces in the early liquid phase of cement curing was found to produce the best chance for adequate adhesion. This study demonstrates that there is variation in the adhesive properties of implants utilized in total knee replacements, and that the orthopedic community should consider not only the implant, cement, and curing time individually, but the overall integrity conferred from the combination of all of these variables.
Highlights
Implant surface integrity and cement bonding are assumed to be sufficient in primary total knee replacements to stabilize implants for extended wear without concerns over delamination and loosening
If the dowel was not placed within 15 s of its assigned interval, it was moved to a subsequent time interval. This rather abbreviated application time range was strictly adhered to during testing to encompass the best “workable phase” wisdom defined by vendors, as we found during the pre-testing that a delay in application of cement beyond 5 min created such a poor adhesion that it eliminated any useful surface bonding and as a result would skew data to such a low adhesion level that comparison differences would not be apparent
Averaged pull off strength for Simplex low viscosity (SLV) and Palacos low viscosity (PLV) together was 5.9 kg, versus that of high viscosity at 3.3 kg, implicating cement bonding strength is reduced by 44% when utilizing high viscosity cement over low viscosity cement
Summary
Implant surface integrity and cement bonding are assumed to be sufficient in primary total knee replacements to stabilize implants for extended wear without concerns over delamination and loosening. There exists a significant rate of aseptic loosening where failure at implant cement interface occurs. The aim of this study is to look at specific aspects leading to aseptic loosening of the total knee replacement, where cement adhesion to the implant results in the lowest pull off strength. Worldwide registry data show failure of total knee replacements on the order of less than 1% per year [17,18,19]. A series of failures occurred in a cohort of coated implants using the same traditional cement technique and conditions that had been used for the proceeding 30 years [17,18,19]. We found a 3% gross loss and the 6% at-risk of failure, noted by progressive cement loosening, implants over a 6-month period, rather than the expected 0.5% failure per year rate seen in the past
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