Functional alignment in robotic-assisted total knee arthroplasty for valgus deformity achieves safe coronal alignment and excellent short-term outcomes

Abstract

Purpose: Functional alignment (FA) in total knee arthroplasty (TKA) prioritizes soft tissue balancing and anatomical restoration without systematic correction to neutral alignment. Most studies have focused on varus deformity, with little evidence available about FA in valgus deformity. The hypothesis of the present study was that FA in robotic-assisted TKA for valgus deformity would demonstrate correction of the coronal alignment and yield satisfactory short-term outcomes.

Methods: This retrospective study included 58 patients with valgus coronal alignment (hip-knee-angle [HKA] ≥ 183°) who underwent robotic-assisted TKA using the FA technique with a minimum of 1-year follow-up. Outcomes were assessed through the Knee Society Score (KSS), Oxford Knee Score (OKS), Forgotten Joint Score (FJS) and radiographic measurements of alignment and phenotypes. Complication and revision rates were also analyzed.

Results: The cohort included 39 females and 19 males with a median age of 70. Post-operatively, 86.2% of cases achieved coronal alignment within the safe zone (HKA 177-183°). Significant improvements were observed in KSS (part 1: 69.5-95, part 2: 65-94, p < 0.001), while OKS and FJS exhibited optimal outcomes. Two complications were recorded: one aseptic loosening (1.7%) and one early infection (1.7%). Kaplan-Meier survival analysis indicated favourable implant survivorship at a median follow-up of 18 months.

Conclusion: FA in image-based robotic TKA is a safe and effective approach for patients with valgus deformity. This procedure resulted in a modest correction of the coronal alignment, where no soft tissue releases were needed. The majority of the cases fell within the target coronal alignment boundaries by only accommodating the individual laxities, suggesting the aim of FA to restore each knee's pre-pathological alignment.

Level of evidence: Level IV.

Keywords: functional alignment; knee phenotype; robotic knee replacement; valgus knee.

Figure 1

Flow chart of the enrolment process during the study period (April 2021 to October 2023). FA, functional alignment; HTO, high tibial osteotomy; MA, mechanical alignment; TKA, total knee arthroplasty.

Figure 2

(a) Variation in individual HKA before and after the surgery. The green area represents the goal boundaries of a final coronal alignment for a valgus phenotype. A trend in reducing the coronal deformity is shown. The post‐operative HKA of the aseptic loosening case is highlighted with a red circle. (b) Variation in individual Valgus deformity before and after the surgery according to the Mako System. The final valgus deformity of aseptic loosening case is highlighted with a red circle. (c) CPAK phenotypes variation before and after the surgery. The blue line represents patients categorized by their phenotype preoperatively, while the orange line indicates patients in the same groups who maintained the same phenotype post‐operatively. CPAK, Coronal Plane Alignment of the Knee; HKA, hip–knee–angle.

Figure 3

(a) Preoperative and post‐operative coronal alignment of a patient with the final HKA within the expected boundaries. (b) Preoperative and post‐operative coronal alignment of the patient reporting an aseptical loosening of the tibial plateau 7 months after the surgery. A slight out‐of‐the‐target final coronal HKA is shown.

Figure 4

Kaplan–Meyer survival analysis of the cohort.