Background: Restoration of correct coronal alignment is one of the main goals of total knee arthroplasty (TKA). Traditionally, TKA has been considered successful when a neutral mechanical hip-knee-ankle (HKA) axis within 3° is achieved. Recent studies have reported no differences or improved clinical outcomes following a slight under-correction of the HKA axis for a varus knee. However, the influence of under-correction of a valgus knee has not been reported. This study investigated the influence of post-operative HKA alignment in TKA patients with valgus deformity on clinical outcomes.
Methods: Ninety-three knees (93 patients) with pre-operative valgus alignment were evaluated with a mean follow-up period of 60 months. All patients were classified into three groups based on post-operative HKA alignment: neutral (0 ± 3°), mild valgus (3°-6°), and severe valgus (> 6°). These groups were compared using the Western Ontario and McMaster Universities osteoarthritis (WOMAC) index, the Knee Society (KS) knee score, KS function score, α-angle, β-angle, patella tilt angle, and the congruence angle.
Results: Sixty-nine knees were included in the neutral group, seventeen knees in the mild valgus group, and seven knees in the severe valgus group. In all cases, post-operative clinical and functional scores significantly improved compared to pre-operative scores. There were no differences between the three groups in post-operative clinical and functional scores. More post-operative patellar tilt angle outliers (> 10°) and congruence angle outliers (> 16°) were apparent in the severe valgus group (patellar tilt angle, 13 vs. 17 vs. 57.1%, p = 0.022; congruence angle, 32 vs. 47 vs. 71%, p = 0.035).
Conclusions: Slight under-correction following TKA for a valgus knee resulted in similar clinical outcomes. A residual valgus angle of more than 6° can induce patellar maltracking.
Level of evidence: III, Retrospective comparative study.
Keywords: Alignment; Knee valgus; Neutral alignment; Patellar maltracking; Total knee replacement.