Ninety-five patients with knee osteoarthritis were randomized to receive either kinematic alignment total knee arthroplasty (TKA) (n=46) or mechanical alignment TKA (n=49). The primary outcome was the mean difference in tibial joint line angle (TJLA) in single-leg stance between the two groups. Secondary outcomes included TJLA differences based on constitutional joint line obliquity (JLO), the proportion of patients achieving a TJLA within approximately 2° of parallel, and the changes from constitutional to postoperative JLO. Outcomes were assessed postoperatively. Overall, the results revealed that KA achieved a significantly closer to parallel TJLA in single-leg stance and restored constitutional JLO more accurately, particularly in patients with apex distal JLO. The study concludes that KA more reliably achieves a TJLA parallel to the floor in single-leg stance than MA, depending on the patient’s constitutional JLO.