The impact of femoral flexion angle and tibial slope on knee gap in total knee arthroplasty

Abstract

Background: Inadequate gap balance during total knee arthroplasty (TKA) can result in postoperative pain, restricted range of motion, and suboptimal long-term outcomes. The sagittal alignment of the femoral and tibial components plays a pivotal role in determining both the flexion and extension gaps. This study systematically investigates how variations in femoral and tibial sagittal alignment affect knee gap dynamics during TKA, utilizing intraoperative data from a robotic-assisted surgical system. Method: This retrospective study analyzed data from 40 robotic-assisted TKA procedures. Surgical planning data were obtained using the landmark registration process. The tibial posterior slope was fixed at 3°, while the femoral flexion angle was adjusted incrementally from 3° to 8° in 1° intervals. Medial and lateral flexion gaps were measured at each increment. To examine the effect of tibial posterior slope on knee gap dynamics, the femoral flexion angle was maintained at 3°, and the tibial posterior slope was varied from 3° to 7° in 1° increments. Medial and lateral extension and flexion gaps were recorded for each configuration. Results: Both medial and lateral flexion gaps progressively increased as the femoral flexion angle was adjusted from 3° to 8°. Similarly, both flexion and extension gaps demonstrated a corresponding increase as the tibial posterior slope was elevated from 3° to 7°. Spearman correlation analysis showed that increasing femoral flexion and tibial slope significantly increased medial and lateral gaps (ρ > 0.99). Conclusion: Increasing femoral flexion results in a larger flexion gap, while a higher tibial slope leads to proportional increases in both flexion and extension gaps. Future studies incorporating intraoperative validation will be crucial for refining surgical techniques and improving outcomes in TKA.