Abstract
Periprosthetic bone loss is an important factor in tibial implant failure mechanisms in total knee arthroplasty (TKA). The purpose of this study was to determine the effect of postoperative knee alignment and population variation on tibial bone remodeling, to assess long-term stability of a knee replacement. Strain-adaptive finite element (FE) remodeling simulations were conducted following kinematic and mechanical alignment of a cemented fixed-bearing implant after TKA; kinematic TKA alignment was assumed to be more consistent with the preoperative varus alignment, while mechanical alignment was defined according to the neutral mechanical axes. To account for the effect of tibial variation on the outcome, bone remodeling was considered over a population of 47 subjects. Bone mineral density (BMD) was analyzed over three regions of interest (ROIs); medial, lateral and distal. The two proximal ROIs showed an average decrease in BMD in both alignments after two years. Greater overall proximal bone loss was found in the mechanical postoperative knees in comparison with kinematically aligned implants. Bone resorption was also concentrated more medially in mechanical alignment: increased medial ROI bone loss was found in every subject compared to kinematic alignment; while in the lateral ROI, higher regional two-year BMD was found in 39 of the 47 cases (82.9%) following mechanical alignment. Two distinct remodeling pathways were identified over both alignments, based on the variance in density change over the population; displaying predominant bone apposition either around the distal tip of the keel or at the lateral cortex. This study demonstrates that correction of native varus alignment to neutral mechanical alignment leads to an increase in medial bone resorption. Large variation between specimens illustrates the benefit of population-based FE analyses over single model studies.
Highlights
Total knee arthroplasty (TKA) is one of the most successful surgical interventions, but despite reduced revision rates, the number of primary TKA failures is increasing as a result of the aging population and the acceptance of TKA in younger patients (Sharkey et al, 2013)
Medial bone loss has been observed in the vast majority of failed cases (Martin et al, 2018), and increased medial bone resorption has been found to be related to the mechanical correction of anatomical varus knees towards neutral or valgus alignment following TKA (Jaroma et al, 2016; Martin et al, 2017; Yoon et al, 2018), indicating extensive bone remodeling could increase the risk of catastrophic varus collapse
In 39 cases (82.9%), a reduction of bone loss in the lateral regions of interest (ROIs) was found for me chanical TKA alignment; total bone loss over the two proximal ROIs together was greater in mechanical alignment for 93.6% of the subjects
Summary
Total knee arthroplasty (TKA) is one of the most successful surgical interventions, but despite reduced revision rates, the number of primary TKA failures is increasing as a result of the aging population and the acceptance of TKA in younger patients (Sharkey et al, 2013). Medial bone loss has been observed in the vast majority of failed cases (Martin et al, 2018), and increased medial bone resorption has been found to be related to the mechanical correction of anatomical varus knees towards neutral or valgus alignment following TKA (Jaroma et al, 2016; Martin et al, 2017; Yoon et al, 2018), indicating extensive bone remodeling could increase the risk of catastrophic varus collapse These clinical findings are in line with Wolff’s law and the strain-adaptive bone remodeling theories (Huiskes et al, 1987), since all indicated factors are related to greater stress reduction in the medial proximal tibia. This technique has been challenged in recent years by the kinematic alignment (Riviere et al, 2017; Cherian et al, 2014), which would result in alignment more consistent to the preop erative knee
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