Joint Line Convergence Angle After Total Knee Arthroplasty: Comparison between Mechanical Alignment and Patient-Specific Alignment with Robotic-Assisted Surgery

Abstract

Introduction

Different alignment strategies have been used to restore the femoral and tibial surfaces to their pre-arthritic state after total knee arthroplasty (TKA), improving patient satisfaction. Due to this paradigm change, the knee joint line orientation (JLO), an essential component of knee kinematics, has recently garnered interest as a clinical parameter.

This study aimed to evaluate the JLO measured by the joint line convergence angle (JLCA) after TKA using two different alignment strategies and robotic-assisted surgery. We hypothesized that a patient-specific alignment strategy would lead to more JLCA values considered normal (0–2°).

Methods

A retrospective review of data from 98 patients (100 knees) who underwent robotic-assisted TKA was performed. Group I consisted of 50 knees that underwent TKA using a mechanical alignment strategy, and Group II consisted of 50 knees that underwent TKA using a patient-specific alignment strategy. The JLCA was measured by two different observers in pre-operative and post-operative radiographs. Statistical analysis was performed using the T-Student test, chi-square test, and linear regression for multivariate analysis.

Results

There were no statistically significant demographic differences between both groups regarding age, gender, side, body mass index, Kellgren Lawrence classification, pre-operative range of motion, and hip-knee-ankle (HKA) angle measurement. The mean age was 69 years and 61.2% of all patients were females. In Group I, the average pre-operative JLCA was 2.34° (1.49 SD), and the average post-operative JLCA was 0.35° (0.27 SD). In Group II, the average pre-operative JLCA was 2,43° (1.72 SD), and the post-operative average JLCA was 0.29° (0.24 SD). In Group I the mean difference between the pre and post-operative JLCA was 2.34 (1.48 SD), and in Group II the mean difference between the pre- and post-operative JLCA was 2.43 (1.72 SD). There was not a statistically significant difference between both groups regarding JLCA improvement (p = 0.285).

Conclusions

The JLCA improved post-operatively in both mechanical and patient-specific alignment strategies after robotic-assisted TKA without significant differences between strategies.

Keywords

total knee arthroplasty - patient-specific alignment - mechanical alignment - joint line convergence angle - joint line obliquity - robotic surgical

Publication History

Received: 20 November 2024

Accepted: 02 April 2025

Article published online:
20 May 2025

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