The effect of posterior tibial slope on knee flexion in posterior-stabilized total knee arthroplasty

To evaluate and quantify the effect of the tibial slope on the postoperative maximal knee flexion and stability in the posterior-stabilized total knee arthroplasty (TKA). Fifty-six patients (65 knees) who had undergone TKA with the posterior-stabilized prostheses were divided into the following 3 groups according to the measured tibial slopes: Group 1: a parts per thousand currency sign4A degrees, Group 2: 4A degrees aEuro"7A degrees and Group 3: > 7A degrees. The preoperative range of the motion, the change in the posterior condylar offset, the elevation of the joint line, the postoperative tibiofemoral angle and the preoperative and postoperative Hospital for Special Surgery (HSS) scores were recorded. The tibial anteroposterior translation was measured using the Kneelax 3 Arthrometer at both the 30A degrees and the 90A degrees flexion angles. The mean values of the postoperative maximal knee flexion were 101A degrees (SD 5), 106A degrees (SD 5) and 113A degrees (SD 9) in Groups 1, 2 and 3, respectively. A significant difference was found in the postoperative maximal flexion between the 3 groups (P < 0.001). However, no significant differences were found between the 3 groups in the postoperative HSS scores, the changes in the posterior condylar offset, the elevation of the joint line or the tibial anteroposterior translation at either the 30A degrees or the 90A degrees flexion angles. A 1A degrees increase in the tibial slope resulted in a 1.8A degrees flexion increment (r = 1.8, R (2) = 0.463, P < 0.001). An increase in the posterior tibial slope can significantly increase the postoperative maximal knee flexion. The tibial slope with an appropriate flexion and extension gap balance during the operation does not affect the joint stability. Retrospective comparative study, Level III.