Elsevier

The Journal of Arthroplasty

Volume 31, Issue 12, December 2016, Pages 2685-2691
The Journal of Arthroplasty

Selected Papers from the 2015 European Knee Society Meeting
Biomechanical Effects of Different Varus and Valgus Alignments in Medial Unicompartmental Knee Arthroplasty

https://doi.org/10.1016/j.arth.2016.07.006Get rights and content

Abstract

Background

Medial unicompartmental tibial components are not always positioned following neutral mechanical alignment and a tibial varus alignment of 3° has been suggested based on several clinical follow-up studies. However, no biomechanical justification is currently available to confirm the suitability of different alignment positions.

Methods

This study aims at quantifying the effects on bone stresses, load distribution, ligament strains, and polyethylene insert stress distribution induced by a possible varus/valgus alignment in medial unicompartmental knee arthroplasty, ranging from 6° of varus to 6° of valgus, developing and using a validated patient-specific finite element model.

Results

Results demonstrate that both neutral mechanical and 3° of varus alignment induce lower stress distributions than valgus or a higher varus alignment for which higher values, up to 40%, are achieved for the polyethylene stress. When a unicompartmental knee arthroplasty is implanted, a mismatch in the stiffness of the joint is introduced, changing the load distribution from medial to lateral for all configurations with respect to the native configuration. However, slight differences are noticeable among the different configurations with a maximum of 190 N and 90 N for the lateral and the medial side, respectively.

Conclusion

Neutral mechanical or 3° of varus alignment present similar biomechanical outputs in the bone, collateral ligament strain, and on the polyethylene insert. A 6° varus alignment or changes in valgus alignment were always associated with more detrimental effects.

Section snippets

Native Knee Model Definition

A right leg from a 43-year-old woman was considered to represent the geometric native knee model. The anatomic structures were reconstructed from the patient's scans obtained both by magnetic resonance imaging and by computed tomography. Before reconstruction, medical records of the subject showed no case of musculoskeletal disorder nor problems of limb alignment; thus, the investigated knee was considered healthy.

The images were imported in an image processing software (Mimics 17.0;

Results

The load distribution between the medial and lateral compartments of the tibiofemoral joint was measured for the native knee first and then for all the models with a UKA in the different alignment configurations by using the average contact pressure. The average percentages of the load are shown in Figure 3.

The transferred load (in N) in the lateral and medial compartments for all of the analyzed knee models is reported in Table 2. In particular, it is possible to notice the load distribution

Discussion

This study aimed at analyzing, until now uncovered topic, about the optimal tibial alignment for UKA and potential aberrant performances due to malpositioning of the components. To investigate this question, a FE model was used to analyze and compare different configurations for several biomechanical outputs.

This numerical study comes with several assumptions, that is, only 1 patient's anatomy has been considered and only 1 UKA design has been virtually implanted. Additionally, potential

Conclusion

Neutral tibial alignment or a slight varus alignment (3°) in the coronal plane can effectively extend the life expectancy of a UKA being also compatible with soft tissue strains. Overcorrections could lead to higher stresses in the lateral compartment and to stress shielding under the implant.

Acknowledgments

This work was supported by FNRS (Fonds National de la Recherche Scientifique, CDR 19545501) and by FER ULB (Fonds d'Encouragement à la Recherche, FER 2014). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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    One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2016.07.006.

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