Practice Variations Among Alternative Alignment Strategies in Total Knee Arthroplasty: A Systematic Review.

Restoration of limb alignment and joint stability across the functional range of motion is a primary goal of total knee arthroplasty (TKA). Multiple alignment strategies have evolved to achieve these objectives, yet a single optimal strategy remains controversial. This study evaluates practice variation among kinematic (KA), functional (FA), and mechanical alignment (MA) strategies in TKA with respect to tibial insert selection, posterior cruciate ligament (PCL) preservation, and deformity tolerance. A systematic PubMed review identified English-language studies of primary TKA published between 2006 and 2025 that reported alignment strategy, tibial insert type, PCL status, and mean deformity. Unicompartmental, revision/complex arthroplasty, and review or editorial studies were excluded. Of 1,099 identified articles, 152 met inclusion criteria for final analysis. Fifty studies (4,672 cases) evaluated KA, 10 studies (2,021 cases) evaluated FA, and 103 studies (11,446 cases) evaluated MA, contributing 242 analytic cohorts. In KA, tibial inserts included 54.5% cruciate-retaining (CR), 0.3% bicruciate retaining (BCR), 7.5% bicruciate stabilized (BCS), 4.3% condylar-stabilized (CS), 11.9% posterior stabilized (PS), 13.2% medial congruent/medial stabilized (MC/MS), 0.7% medial pivot (MP), 2.5% ball-in-socket medial conforming (B-in-S MC), 0.5% ball-in-socket condylar-stabilized (B-in-S CS), 3.9% ultra-congruent (UC), 0.2% constrained posterior-stabilized (CPS), and 0.4% constrained condylar knee (CCK). FA utilized 47.9% CR, 1.0% BCR, 6.0% CS, 36.9% PS, and 8.2% MC/MS, with no BCS, MP, B-in-S MC, B-in-S CS, UC, CPS, or CCK reported. MA demonstrated 34.6% CR, 1.3% BCR, 4.6% BCS, 3.0% CS, 45.4% PS, 0.7% MC/MS, 2.4% MP, 2.3% UC, 3.6% CPS, and 2.1% CCK. The PCL was preserved in 63.1% of KA, 58.9% of FA, and 38.4% of MA cases. Tibial insert distribution, PCL preservation, and instrumentation technique differed significantly across alignment strategies (all p < 0.001). Using a signed coronal deformity convention in which negative values indicate varus and positive values indicate valgus, mean preoperative coronal deformity was - 2.9, - 4.1, and - 4.7 degrees for KA, FA, and MA, respectively, with the most varus reported cohort-level mean deformities of - 13.4, - 17.6, and - 21.0 degrees; mean deformity did not significantly differ across alignment strategies (p = 0.124). Manual instrumentation predominated in KA (62.6%) and MA (74.5%), whereas FA was primarily robotic (90.8%). Significant heterogeneity exists in implant selection, PCL management, and instrumentation technique across alignment strategies, while mean preoperative coronal deformity did not significantly differ. Within the included literature, alignment philosophy alone does not dictate surgical practice and highlights the need for standardized definitions and reporting.