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.