Effects of coronal plane conformity on tibial loading in TKA: a comparison of AGC© flat versus conforming articulations
Conforming articulations potentially decrease polyethylene contact stresses in total knee arthroplasty (TKA); however, less is known about the effect of coronal geometry on tibial loading and clinical failure. This study examined the relationship between coronal plane geometry and loading patterns in the proximal tibia. Composite tibiae were implanted with modular, metal-backed tibial trays and were compressively loaded with conforming and nonconforming ultra-high molecular weight polyethylene (UHMWPE) tibial bearings and comparable femoral components. Changes in strain on the proximal tibia were quantified using a photoelastic strain analysis method. In balanced loading, coronally dished components created a strain increase in the anterior medial tibia while creating a significant strain decrease in the posterior tibia. Proximal tibial strains were decreased and centralized in conforming versus flat articulations. This centralization of loading may lead to a reduction in edge loading during gait. Lower strains were observed with coronally dished implants in key regions corresponding to the clinical overload of the tibia leading to aseptic loosening.
- [Show abstract] [Hide abstract] ABSTRACT: A prospective randomized study was conducted to determine if a design change in the articular surface geometry introduced in the Optetrak total knee to increase prosthetic joint conformity and further reduce polyethylene stress had any impact on implant survival, particularly when the all-polyethylene version of the implant was used. Forty-seven patients undergoing bilateral simultaneous total knee arthroplasties were randomized for the side, receiving an all-polyethylene tibial component and followed up for a mean 11.6 years. Survival rates for the all-polyethylene and metal-backed modular versions of the implant were both 98%, excluding a single case of deep infection. Survival rates with revision for aseptic loosening as an end point were 100%. The increase in tibial and femoral radii in the coronal plane of the Optetrak posterior stabilized knee did not result in a reduced implant survival rate in either the metal-backed modular or all-polyethylene versions of the implant.0Comments 15Citations
- [Show abstract] [Hide abstract] ABSTRACT: Clinical success of unicompartmental knee arthroplasty (UKA) is on the rise and is dependent on multiple patient, implant, and surgical factors. Tibial subsidence has been clinically reported as a cause of failure in UKA with an all-polyethylene tibial design in the absence of metal backing, yet the role of metal backing UKA tibial components on tibial loading is not fully understood. In this study, composite tibiae were implanted with medial all-polyethylene fixed-bearing or metal-backed UKA tibial components and a 1.5-kN load applied in 3 different contact positions simulating femoral translation during gait. All-polyethylene tibial components exhibited significantly higher strain measurements in each femoral position. This study demonstrates the role that metal backing plays on generating an even loading distribution while diminishing the development localized regions of excessive loading across the medial tibial cortex.0Comments 16Citations
- [Show abstract] [Hide abstract] ABSTRACT: Prosthetic alignment, patient characteristics and implant design are all factors in long-term survival of total knee arthroplasty (TKA), yet the level at which each of these factors contribute to implant loosening has not been fully described. Prior clinical and biomechanical studies have indicated tibial overload as a cause of early TKA revision. The purpose of this study was to determine the relationship between tibial component design and bone resection on tibial loading. Finite element analysis (FEA) was performed after simulated implantation of metal backed and all-polyethylene TKA components in 5 and 15 mm of tibial resection into a validated intact tibia model. Proximal tibial strains significantly increased between 13% and 199% when implanted with all-polyethylene components (p<0.05). Strain significantly increased between 12% and 209% in the posterior tibial compartment with increased bone resection (p<0.05). This study indicates elevated strains in all-polyethylene implanted tibiae across the entirety of the proximal tibial cortex, as well as a posterior shift in tibial loading in instances of increased resection depth. These results are consistent with trends observed in prior biomechanical studies and may associate the documented device history of tibial collapse in all-polyethylene components with increased bone strain and overload beneath the prosthesis.0Comments 0Citations