Soft tissue elasticity in total knee arthroplasty: An in vivo quantitative analysis.

Background: Soft tissue balance is essential for total knee arthroplasty success. The elastic properties of soft tissues affect knee-joint stability and flexibility. This study proposed a novel methodology for in vivo quantitative analysis of soft tissue elasticity during total knee arthroplasty. In this study, we aimed to (1) establish a mathematical model to depict medial and lateral soft tissue elasticity, (2) report the individual differences and interindividual commonalities in soft tissue elasticity.

Methods: A specifically designed knee tensor was used to evaluate soft tissue elasticity by dynamically applying sequential tensions to medial and lateral compartments while measuring knee joint gaps in both compartments. Measurements were performed on ten knees of six cadavers. Bivariate polynomial regression was used for analysis, and the equivalent elastic coefficient (N/mm) was calculated.

Findings: Soft-tissue elasticity showed high individual differences. The equivalent elastic coefficient was larger in the medial compartment than in the lateral compartment, and the equivalent elastic coefficient of the lateral compartment gradually decreased while the medial equivalent elastic coefficient remained constant when the knee was flexed. The lateral gaps increased from 0.1 to 3.9 mm, and the medial gaps increased from 0 to 1.5 mm when the tension increased from 60 to 90 N. The shapes and distributions of the silkworm-like lattices in elasticity and balance evaluations are clinically relevant to knee balance.

Interpretation: Soft-tissue balance in total knee arthroplasty is significantly affected by soft-tissue elasticity. An intraoperative quantitative analysis of elasticity helps to tail an individualized balancing target for total knee arthroplasty.