Effects of knee simulator loading and alignment variability on predicted implant mechanics: A probabilistic study

Abstract

Inherent variability in total knee arthroplasty loading and alignment, present in vivo and in simulator testing, may ultimately influence polyethylene tibial insert wear and long-term performance. The effect of this variability was quantified on implant kinematics and contact mechanics during simulated gait loading conditions using semi-constrained and unconstrained fixed bearing, cruciate retaining implants. A probabilistic finite element model of the Stanmore knee wear simulator was utilized to estimate the envelope of anterior-posterior (AP) and internal-external (IE) position and contact pressure and to evaluate the variability in corresponding ranges of motion (ROM). Variability levels were represented by standard deviations of up to 10% of the maximum value for load inputs and 0.25 mm and 0.58 for component alignment inputs. Model predictions compared well with experimental simulator results for the semi-constrained implant, with predicted positional envelopes of up to 1.8 mm (AP) an 3.48 (IE) for the semi-constrained and upto 2.6 mm (AP) and 3.78 (IE) for the unconstrained implant at the variability levels evaluated. ROM varied by up to 22%, while peak contact pressure variations averaged less than 2 MPa for both designs. For each implant, loading variability was more influential during the swing phase of gait, while alignment variability affected kinematics more during stance. The relative rank of sensitivities showed differences between the two designs, providing insight into critical parameters affecting kinematics and contact characteristics. ß

Contribution of geometric design parameters to knee implant performance: Conflicting impact of conformity on kinematics and contact mechanics

“…Overall, the general trends of finite element computations were well compared with the previously 177 published experimental and computational literature for the fixed-bearing cruciate retaining implants [38][39][40][41]. …”

“…Penalty based contact 61 condition was specified at the tibia insert and femoral component interface with a friction coefficient of 0.04 62 [37]. 63 Kinematics and contact mechanics were calculated based on a computational model of Stanmore knee 64 simulator [38][39][40][41]. Stanmore simulator is a well-established load-controlled knee simulator in which in vivo 65 environment of knee joint is replicated through applying forces and moments to femoral and tibial 66 components [42,43].…”

In vivo contact kinematics and contact forces of the knee after total knee arthroplasty during dynamic weight-bearing activities

“…Wear of tibial polyethylene component depends, among various other factors, on load distributions, component geometry and kinematics of the knee (Laz, et al, 2006, McEwen, et al, 2005. Increased sliding, particularly combined anteroposterior and mediolateral sliding, at the contact interface has been associated with increased wear (Blunn, et al, 1991, Fisher, et al, 2006, McEwen, et al, 2005, Todo, et al, 1999.…”

The anterior–posterior laxity after total knee arthroplasty inserted with a ligament tensor

“…This also makes the prosthesis more constrained. Laz et al [9] showed more AP laxity for an unconstrained prosthesis compared to a semi-constrained prosthesis. Since 1998 we started to use a ligament guided knee system (balanSys TM ) with a calibrated tensor and a relatively dished insert.…”