The effects of kinematically aligned total knee arthroplasty on stress at the medial tibia: A case study for varus knee

Abstract

Objectives: Little biomechanical information is available about kinematically aligned (KA) total knee arthroplasty (TKA). The purpose of this study was to simulate the kinematics and kinetics after KA TKA and mechanically aligned (MA) TKA with four different limb alignments.

Materials and methods: Bone models were constructed from one volunteer (normal) and three patients with three different knee deformities (slight, moderate and severe varus). A dynamic musculoskeletal modelling system was used to analyse the kinematics and the tibiofemoral contact force. The contact stress on the tibial insert, and the stress to the resection surface and medial tibial cortex were examined by using finite element analysis.

Results: In all bone models, posterior translation on the lateral side and external rotation in the KA TKA models were greater than in the MA TKA models. The tibiofemoral force at the medial side was increased in the moderate and severe varus models with KA TKA. In the severe varus model with KA TKA, the contact stress on the tibial insert and the stress to the resection surface and to the medial tibial cortex were increased by 41.5%, 32.2% and 53.7%, respectively, compared with MA TKA, and the bone strain at the medial side was highest among all models.

Conclusion: Near normal kinematics was observed in KA TKA. However, KA TKA increased the contact force, stress and bone strain at the medial side for moderate and severe varus knee models. The application of KA TKA for severe varus knees may be inadequate.Cite this article: S. Nakamura, Y. Tian, Y. Tanaka, S. Kuriyama, H. Ito, M. Furu, S. Matsuda. The effects of kinematically aligned total knee arthroplasty on stress at the medial tibia: A case study for varus knee. Bone Joint Res 2017;6:43-51. DOI: 10.1302/2046-3758.61.BJR-2016-0090.R1.

Keywords: Computer simulation; Contact stress; Finite element analysis; Kinematic alignment; Total knee arthroplasty.

Fig. 1

Bone models constructed from CT data. The limb alignment was 0°, 6° varus, 10° varus, and 15° varus for the normal, slight varus, moderate varus, and severe varus models, respectively.

Fig. 2

Bone models after implantation with the mechanically aligned (MA) and kinematically aligned (KA) techniques.

Fig. 3

Contact position relative to the tibial component and the axial rotation for each model. Red and blue dots indicate the medial and lateral facet centre positions, respectively (MA, mechanically aligned; KA, kinematically aligned).

Fig. 4

Contact forces for each model. Red and blue lines indicate the medial and lateral contact forces, respectively (MA, mechanically aligned; KA, kinematically aligned).

Fig. 5

Contact stress on the tibial insert with the mechanically aligned (MA) and kinematically aligned (KA) techniques. Right side on the figure indicates medial condyles.

Fig. 6

Stress on the resected surface of the tibia with the mechanically aligned (MA) and kinematically aligned (KA) techniques. Right side on the figure indicates medial condyles.

Fig. 7

Stress to the medial tibial cortex with the mechanically aligned (MA) and kinematically aligned (KA) techniques.

Fig. 8

Strain to the medial tibial cortical bone with the mechanically aligned (MA) and kinematically aligned (KA) techniques.

Fig. 9

Strain to the medial tibial cancellous bone with the mechanically aligned (MA) and kinematically aligned (KA) techniques.