The influence of surgical malalignment on the contact pressures of fixed and mobile bearing knee prostheses––a biomechanical study
Introduction
Polyethylene wear of articular surface is a well-recognized complication of total knee arthroplasty. Factors related to failure of bearing surface of knee prosthesis include material properties of polyethylene, sterilization method, soft tissues balance, the patient’s daily activity and the contact pressures on the articular surfaces (Bartel et al., 1986; Collier et al., 1991; McNamara et al., 1994). An asymmetrical wear of the polyethylene component was the common pattern in many retrieval analyses (Wasielewski et al., 1994). Therefore, implant alignment and soft tissues balance and the wear of tibial polyethylene component has produced a lot of publications related to these areas (Liau et al., 1999; Liau et al., 2002).
The tibial component in total knee prostheses can be either a fixed or a mobile bearing. The long-term result between fixed bearings and mobile bearings is still a controversial issue (Lewis et al., 1982; Bert et al., 1998; Sanchez-Sotelo et al., 1999). From the biomechanical point of view, mobile bearing design can reduce polyethylene wear and minimize loosening by providing both congruity and mobility in the tibiofemoral joint (Goodfellow et al., 1986). In addition, another advantage of mobile bearing design is to accommodate any surgical malalignment of tibial baseplate and to allow intraoperative adjustment of joint space (Buechel and Pappas, 1989; Buechel and Pappas, 1987).
Many biomechanical studies have demonstrated that contact pressure on the tibial polyethylene component is closely related to polyethylene wear (Rose et al., 1980; Wright and Bartel, 1986). However, most studies in biomechanical tests, finite element analyses and analytical approaches assumed the femoral and tibial components were under an ideal contact alignment. The malalignment of knee prostheses was thought to accelerate polyethylene wear (Rose et al., 1980). Only a few researchers focused on the contact pressures on the tibial polyethylene components under malaligned conditions. Liau et al. (1999) used Fuji pressure sensitive film to study the influence of contact alignment of the tibiofemoral joint of knee prostheses in in vitro biomechanical test. They also used finite element analysis to investigate the effects of malalignment on the stresses in three different conformity designs of the tibiofemoral joint (Liau et al., 2002). Matsuda et al. (1999) utilized the digital electronic pressure sensor to investigate the effect of varus tilt on contact pressures in total knee prostheses. These studies focused on fixed bearing design with different articular curvatures. Matsuda et al. (1998) also measured the contact pressures on the upper- and under-surface of the tibial polyethylene components with a neutral and malrotated tibial tray of three mobile bearing designs and one fixed bearing design. They demonstrated that mobile bearing designs appear to offer advantages over the fixed bearing design when moderate rotational malalignment of the tibial component occurs. However, only the effect of rotational malalignment was considered in their study. To investigate the advantages of mobile bearing designs for accommodating surgical malalignments in the medial–lateral (ML) and anterior–posterior (AP) translations and internal–external (IE) rotation more clearly, this study was undertaken to compare the contact pressures on the tibial component in fixed bearing and mobile bearing knee prostheses under malaligned conditions.
Section snippets
Methods
A commercial knee system (U-knee system, United Orthopedic Co., Taipei, Taiwan) with a flat-on-flat design in the coronal plane and a semi-conformity design in the sagittal plane and 5 degrees of posterior slope in the tibial insert was used. The current design in the tibial component of U-knee system is a fixed bearing. The locking mechanism of the tibial component was modified to become a mobile bearing system. The mobile bearing knee prosthesis allows 1 mm translation in both ML and AP
Results
The typical results of the contact pressure distribution of the neutral and malalignment positions measured by Fuji prescale sensitive film were shown in Fig. 3. The maximum contact pressure (MCP) of fixed bearing design was 23.6 MPa, which was significantly higher than the mobile bearing design (22.3 MPa) (P<0.05) under the normal contact alignment. The MCP of fixed bearing design was also significantly higher than the mobile bearing design when the femoral component was translated posteriorly
Discussion
Mobile bearing knee prosthesis was designed to decrease the prevalence of prosthesis loosening and polyethylene wear (Goodfellow et al., 1986). It can also accommodate to surgical malalignment because of high mobility of the bearing element. When malalignment of prosthesis occurred, the loading distribution in the tibiofemoral joint would change, which may further alter stress distribution on the contact surface and soft tissues tension at knee joint. Therefore, to approach the actual
Conclusion
The mobile bearing design has lower MCPs than the fixed bearing design when malalignment of the tibiofemoral joint of knee prosthesis occurs. The mobile bearing design offers the advantage of self-adjusting over the fixed bearing design to accommodate surgical malalignment.
References (19)
- et al.
The incidence of modular tibial polyethylene insert exchange in total knee arthroplasty when polyethylene failure occurs
J. Arthroplasty
(1998) - et al.
The influence of contact alignment of the tibiofemoral joint of the prostheses in in vitro biomechanical testing
Clin. Biomech.
(1999) - et al.
The effect of malalignment on stresses in polyethylene component of total knee prostheses––a finite element analysis
Clin. Biomech.
(2002) - et al.
The influence of inserting a Fuji pressure sensitive film between the tibiofemoral joint of knee prosthesis on actual contact characteristics
Clin. Biomech.
(2001) - et al.
Contact stress analysis in meniscal bearing total knee arthroplasty
J. Arthroplasty
(1998) - et al.
Results and complications of the low contact stress knee prosthesis
J. Arthroplasty
(1999) - et al.
Contact area and pressure in the subtalar joint
J. Biomech.
(1995) - et al.
The effect of conformity, thickness and material on stresses in ultra-high molecular weight components for total joint replacement
J. Bone Joint Surg.
(1986) - et al.
The New Jersey LCS knee replacement system––biomechanical rational and comparison of cemented and noncemented results
Contemp. Orthop.
(1987)
Cited by (50)
The influence of cross shear and contact pressure on the wear of UHMWPE-on-PEEK-OPTIMA™ for use in total knee replacement
2023, Journal of the Mechanical Behavior of Biomedical MaterialsModern Total Knee Arthroplasty Bearing Designs and the Role of the Posterior Cruciate Ligament
2023, Arthroplasty TodayOptimal surgical component alignment minimizes TKR wear – An in silico study with nine alignment parameters
2022, Journal of the Mechanical Behavior of Biomedical MaterialsCitation Excerpt :Both force and displacement versions of the ISO standard are available, and it is left to the investigator to decide which version to use. In addition, there is a large range of variability in wear rates during mechanical wear testing (Knight et al., 2007; Cottrell et al., 2006; Strickland and Taylor, 2009; Popoola et al., 2010; Johnson et al., 2003; Muratoglu et al., 2007; Mell et al., 2018), mainly due to differences in control regime, testing setup, and experimental error (Brandt et al., 2010; Schwenke et al., 2005, 2009; Wang et al., 2004; Cheng et al., 2003; Zietz et al., 2015). This variability makes it difficult to compare results across studies and may mask changes in wear rate due to a change in input conditions, such as a misaligned component.
Challenges of pre-clinical testing in orthopedic implant development
2019, Medical Engineering and PhysicsCitation Excerpt :In this case, improper alignment led to increased loading of the medial side which caused full thickness wearing of the tibial insert (Fig. 4). Cheng et al. [35,36] demonstrated that malalignment also has a considerable influence on the biomechanics of the knee joint and the improper loading patterns can lead to implant failure, but mobile tibial bearings had a relatively better outcome than fixed bearings. Therefore, achieving correct frontal alignment and soft tissue balance is crucial for long-term success.
The choice of the femoral center of rotation affects material loss in total knee replacement wear testing – A parametric finite element study of ISO 14243-3
2019, Journal of BiomechanicsCitation Excerpt :During mechanical testing, experimental error and variations in testing methodology can lead to variability in wear outcome. Some of the sources of experimental variability include the choice of displacement vs force control (Schwenke et al., 2009), differences in the lubricant (Brandt et al., 2010; Schwenke et al., 2005; Wang et al., 2004), the component starting position (Cheng et al., 2003; Zietz et al., 2015), and the effect of fluid absorption by the polyethylene, which can mask low wear rates (Schwenke et al., 2005). Another source of variability within TKR wear tests that has been identified is the definition of the femoral flexion/extension center of rotation (CoR) (Brockett et al., 2016; DesJardins and Rusly, 2011; Jennings et al., 2007; McEwen et al., 2005; Zietz et al., 2015).