Abstract: BACKGROUND: Mechanical alignment is the “gold standard” alignment technique in total knee arthroplasty, but regardless of advances in prosthetic materials and robotic-assisted navigation, mechanical alignment-total knee arthroplasty still has a patient dissatisfaction rate of about 20%. 
OBJECTIVE: To evaluate the early efficacy of navigation-assisted total knee arthroplasty using functional alignment.
METHODS: A total of 44 consecutive cases (50 knees) that underwent computer navigation-assisted total knee arthroplasty with functional alignment from October 2019 to June 2023 were retrospectively analyzed, including 12 males (14 knees) and 32 females (36 knees). A total of 46 consecutive cases (50 knees) that underwent navigation-assisted total knee arthroplasty with mechanical axis alignment by the same surgical team during the same period were selected as controls, including 5 males (5 knees) and 41 females (45 knees). The tibial osteotomy angle, tibial plateau osteotomy amount, femoral osteotomy angle, distal femoral, posterior and anterior osteotomy amount, and joint line movement were observed in the two groups of patients. Preoperative and postoperative flexion and extension gap internal and external laxity, hip-knee-ankle angle, mechanical lateral distal femoral angle, mechanical medial proximal tibial angle, joint line convergence angle, sagittal femoral component angle, posterior tibial slope, arithmetic hip-knee-ankle angle, joint line obliquity, coronal plane alignment of the knee classification, Western Ontario and McMaster Universities Osteoarthritis Index, and Hospital for Special Surgery score and forgotten joint score were compared between the two groups.
RESULTS AND CONCLUSION: (1) The intraoperative tibial plateau osteotomy angle in the functional alignment group was greater than that in the mechanical axis alignment group, and the proportion of gap imbalance (2%) was smaller than that in the mechanical axis alignment group (18%). The differences were all significant (P < 0.05). (2) The hip-knee-ankle angle, mechanical medial proximal tibial angle, arithmetic hip-knee-ankle angle, and joint line obliquity in the functional alignment group were smaller than those in the mechanical axis alignment group postoperatively, and the differences were significant (P < 0.05). (3) The most common coronal plane alignment of the knee classification before surgery was type I (80% in the functional alignment group and 42% in the mechanical axis alignment group). (4) The proportion of joint line obliquity < 177° (44%) in the functional alignment group was greater than that in the mechanical axis alignment group (14%) postoperatively. (5) Hospital for Special Surgery score at 1 month, 6 months, and last follow-up after surgery was higher in the functional alignment group than that in the mechanical axis alignment group; the differences were statistically significant (P < 0.05). The Western Ontario and McMaster Universities Osteoarthritis Index 1 month after surgery was lower in the functional alignment group than that in the mechanical axis alignment group; the difference was statistically significant (t=-2.85, P=0.005). There was no significant difference in postoperative range of motion and forgotten joint score between the two groups (P > 0.05). (6) It is indicated that navigation-assisted total knee arthroplasty using functional alignment optimizes early clinical efficacy. The functional alignment technique has advantages in restoration of constitutional alignment and joint line obliquity and avoids soft tissue release compared to mechanical alignment technique.

Key words: total knee arthroplasty, functional alignment, mechanical alignment, surgery, computer-assisted, comparative study, orthopedic implants