Restricted kinematic alignment in primary total knee arthroplasty: A systematic review of radiographic and clinical data

Introduction: Kinematic alignment (KA) has increased in popularity in recent years, becoming a viable alternative to MA with encouraging short-and mid-term follow-up results. Recently, the concept of restricted kinematic alignment (rKA) has been developed to restore native knee kinematics better, avoiding failure of coronal alignment. This systematic review aims to examine whether rKA improves outcome scores (PROMs) compared with MA and to evaluate the radiographic analysis of the lower limb alignment and the causes of complications and reoperations with the rKA approach. Methods: A systematic literature search was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines on the Pubmed/Medline, Scopus, Cochrane Library, and Embase databases. The following key terms were used: "restricted kinematic alignment, rKA, kinematic align-ment, primary total knee arthroplasty, primary total knee replacement, TKA rKA, and TKR rKA." The initial screening identified 328 studies. Each eligible article was evaluated according to the inclusion criteria: studies with levels of evidence (LoE) 1 to 4, written in English, published through May 2022, and involving human subjects. Criteria from the Methodological Index for Non-Randomized Studies (MINORS) were used to assess the methodological quality of the articles.Results: Six clinical studies were included in this systematic review. The study was registered in the International Prospective Registry of Systematic Reviews (PROSPERO). A total of 574 knees were included. After excluding patients due to loss of follow-up or missing data, 475 knees were analyzed. The following rKA-related data were evaluated: patient-reported outcome scores (PROMs), radiographic analysis of the lower limb alignment, and causes of complications and reoperations.Conclusions: The rKA is an improved concept for restoring native knee kinematics, avoiding excessive coronal varus/valgus alignment. It provides equivalent or slightly better PROMs than MA without increasing the risk of short-middle-term implant failure. Clinical studies with extended follow-up are needed to confirm this trend.