Similar joint line convergence angle correction with mechanical and patient-specific alignment in robotic-assisted TKA

Introduction

In total knee arthroplasty (TKA), positioning implants closer to the patient's constitutional alignment improves joint line obliquity (JLO), replicating normal biomechanics and gait patterns. As a result, the joint line convergence angle (JLCA) has gained recognition as a key parameter for assessing intra-articular deformity and lateral soft tissue laxity. This study aimed to evaluate JLCA changes following robotic-assisted TKA (RA-TKA) using two alignment strategies. We hypothesized that a patient-specific alignment (PSA) strategy would result in greater JLCA correction and improved outcomes.

Methods

A retrospective review of 98 patients (100 knees) undergoing RA-TKA was performed. Group I (50 knees) underwent mechanical alignment (MA), while Group II (50 knees) underwent PSA. JLCA was measured preoperatively and postoperatively by two independent observers. Demographic and functional data, including KOOS JR scores were collected, and statistical analyses were performed using STATA v.18.5.

Results

Both groups showed significant postoperative improvement in JLCA: from 2.34° to 0.35° in the MA group, and from 2.43° to 0.29° in the PSA group. However, the degree of JLCA correction did not differ significantly between groups (p = 0.285). KOOS JR scores improved similarly in both groups, with no significant differences at 1-year follow-up.

Conclusions

Robotic-assisted TKA significantly improved JLCA regardless of alignment strategy. Patient-specific and mechanical alignment approaches yielded comparable radiographic and functional outcomes.

Level of evidence

Level IV.