Laxity, Balance, and Alignment of a Simulated Kinematic Alignment Total Knee Arthroplasty

Abstract

Background: Kinematic alignment (KA) and related personalized alignment strategies in total knee arthroplasty (TKA) target restoration of native joint line obliquity and alignment. In practice, deviations from exact restoration of the prearthritic joint surface are tolerated for either the femur or tibia to achieve ligamentous balance. It remains unknown what laxity, balance, and alignment would result if a pure resurfacing of both femur and tibia were performed in a KA TKA technique.

Methods: We used data from 382 robot-assisted TKA performed with a digital joint tensioner to simulate TKA with a pure resurfacing KA technique for both femur and tibia. All knees had the posterior cruciate ligament retained. Knees were subdivided into 4 groups based on preoperative coronal alignment: valgus, neutral, varus, and high varus. Medial and lateral laxity in extension and flexion, balance in extension and flexion, and coronal plane alignment were compared between groups using analysis of variance testing.

Results: In simulated pure resurfacing KA TKA across a range of preoperative coronal plane deformities, only 11%-31% of knees would have mediolateral extension ligament balance within ±1 mm, and 20%-41% would have a medial flexion gap that is looser than the lateral flexion gap. Over 45% of knees would have coronal hip-knee-ankle angle >3 degrees from mechanical neutral.

Conclusions: In simulations of pure resurfacing KA TKA, there was wide variability in the resulting laxity and alignment outcomes. Most knees had alignment and balance outcomes outside of normally accepted ranges. Techniques that deviate from pure resurfacing in order to achieve balance appear favorable.

Keywords: Alignment; Balance; Kinematic alignment; Simulation; Total knee arthroplasty.

Figure 1

Distribution of hip-knee-ankle (HKA) angle across cohort. Knees are subdivided into 4 cohorts shown in different colors.

Figure 2

Comparison of (a) medial and (b) lateral extension laxity and (c) medial and (d) lateral flexion laxity across HKA groups. Data labels indicate mean values.

Figure 3

Comparison of extension balance in (a) extension and (b) flexion across HKA groups.

Figure 4

Resulting (a) femoral, (b) tibial, and (c) tibio-femoral coronal component alignment from a KA approach.