Slight undercorrection following total knee arthroplasty results in superior clinical outcomes in varus knees.

Purpose: Restoration of correct alignment is one of the main objectives of total knee arthroplasty (TKA). However, the influence of residual malalignment on clinical and functional outcomes is currently uncertain. This study was therefore undertaken to ascertain its influence in patients undergoing TKA for varus osteoarthritis of the knee.

Methods: A cohort of 132 consecutive patients (143 knees) with pre-operative varus alignment was evaluated with a mean follow-up period of 7.2 years. Based upon the post-operative alignment, patients were stratified into three groups: neutral, mild varus, and severe varus. These groups were compared with respect to clinical and functional outcomes.

Results: All patients had post-operative improvements in Knee Society Score (KSS). Knees that were left in mild varus scored significantly better for the KSS and the Western Ontario and McMaster Universities Arthritis Index, compared with knees that were corrected to neutral and knees that were left in severe varus exceeding 6°. No revisions occurred in any of the groups at midterm follow-up.

Conclusion: The results of this study contradict the conventional assumption that correction to neutral mechanical alignment leads to the best outcome following TKA. Patients with pre-operative varus had better clinical and functional outcome scores if the alignment was left in mild varus, as compared with patients with an alignment correction to neutral.

Level of evidence: Therapeutic study, Level III.