Abstract: BACKGROUND: Total knee arthroplasty is one of the effective treatments for end-stage knee osteoarthritis. The design of prosthetic joints to match the national population is particularly urgent because of the serious complications that often arise when replacement prostheses designed according to foreign population standards are applied to the domestic population. Nevertheless, knowledge of the normal values of the anatomical parameters of the knee joint and sex, age, and side differences in them can provide a reference for the design of replacement prostheses.  
OBJECTIVE: To explore the normal anatomical parameters of bilateral normal knee joints and the age and sex differences in Guiyang.
METHODS: We conducted a retrospective observational cohort study of 2 978 patients with normal knee joints in Guiyang from 13 666 patients who underwent knee X-ray examination in Guizhou Provincial People’s Hospital from January 2015 to January 2021. Anatomical parameters, including the line parameters (knee space width, femoral condyle diameter, tibial plateau diameter, and Insall-Salvati index), and the angle parameters (femoral angle, femoral tibial angle, tibial angle, and posterior tibial slope) were measured on anteroposterior and lateral radiographs of the knee joint. Age, sex and side differences were compared.  
RESULTS AND CONCLUSION: (1) Sex differences in the femoral angle, femoral tibial angle, tibial angle, knee joint space, transverse diameter of femoral condyle, transverse diameter of tibial plateau, and Insall-Salvati index were found (P < 0.05). The femoral angle and Insall-Salvati index were higher in women than in men, while other parameters were lower in women than in men. There was no significant difference in posterior tibial slope (t=-0.64, P=0.523). (2) There were significant age differences in femoral tibial angle, lateral knee joint space in men and femoral tibial angle, tibial angle tibial plateau diameter in women (P < 0.05). (3) The femoral tibial angle in men and women aged 36-45 years and the tibial angle in women was the largest. The lateral knee joint gap of man aged 27-35 years (7.78±0.72) mm was larger than that in other groups. The transverse diameter of tibial plateau in women aged 18-26 years (72.08±5.81) mm was greater than that in other groups. There was no significant difference in other parameters (P > 0.05). (4) There were significant differences in the femoral angle, femoral tibial angle, tibial angle, posterior tibial slope, knee space, femoral condyle diameter, and Insall-Salvati index between bilateral knees (P < 0.05). Parameters were increased at the right side compared with the left side with the exception of femoral angle. There was no significant difference in the transverse diameter of tibial angle and tibial plateau (P > 0.05). (5) The results confirm that sex and side differences in the anatomical parameters of normal knee joints exist in subjects from Guiyang; however, the age differences are hardly detected. This study can provide normal knee values for prosthesis design in Guiyang.

Key words: normal population, knee joint, knee osteoarthritis, anatomical parameter, X-ray, normal value