A systematic review of radiological outcomes and implant positioning in robotic-assisted functionally aligned robotic total knee arthroplasty.

INTRODUCTION

Functional alignment (FA) or functional knee positioning is a patient-specific strategy for total knee arthroplasty (TKA) that utilizes robotics to balance coronal, sagittal, and axial planes while preserving joint-line orientation and soft-tissue tension within predefined guardrails. Although early clinical outcomes are encouraging, the radiographic profile and workflow consistency of robotic FA have not been clearly synthesized.

METHODS

In accordance with PRISMA guidelines, English-language studies of primary robotic FA-TKA with ≥2-year follow-up were searched. Eligible designs included RCTs, prospective/retrospective cohorts, and large case series (≥50 patients). Information on pre- and postoperative coronal alignment [hip-knee-ankle angle (HKA), lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA)], component positioning (femoral valgus/rotation/flexion; tibial varus/rotation/slope), and explicit FA workflow boundaries (guardrails) was extracted.

RESULTS

Twenty-one cohorts (5,360 knees) reported at least one radiographic or workflow endpoint. Preoperatively, the predominant deformity was varus. Postoperatively, limb alignment converged near neutral: HKA clustered around 178-179.5°, with LDFA ~89-91° and MPTA ~87-89°. Component positions were tightly distributed within FA targets: femoral valgus ≈ 0.5-1.5°, tibial varus ≈ ~3°, femoral flexion ~6-9°, and tibial slope ~0-3°; tibial rotation was overwhelmingly referenced to Akagi's line, and femoral rotation to the TEA in most series. Reported guardrails showed strong convergence: typical workflows included femoral valgus -3° to +6°, tibial varus 0-6°, tibial slope 0-3°, and femoral ER ~3-6° to TEA. Across cohorts, achieved radiographs closely tracked these limits, indicating high adherence and reproducibility. Most observational studies had a moderate risk of bias; the lone RCT was low risk.

DISCUSSION: Robotic FA-TKA delivers a radiographic profile with slight femoral valgus and modest tibial varus, while keeping components within narrow, pre-specified guardrails.

LEVEL OF EVIDENCE: Level III, systematic review and meta-analysis.