Effect of Posterior Tibial Slope on Knee Kinematics After Bicruciate-Retaining Total Knee Arthroplasty.

Background: Following total knee arthroplasty (TKA), normal knee kinematics are rarely replicated. Retention of both cruciate ligaments (bicruciate retaining TKA) has helped this. Postoperative posterior tibial slope (PPTS) may further affect ligament tension and kinematics. The objective of this study is to determine how changes between the preoperative posterior tibial slope (PTS) and PPTS affect knee kinematics.

Methods: Twenty bicruciate retaining TKAs were performed using standard instrumentation. Fluoroscopic kinematic data were obtained during gait and a single knee bend. Differences (Δ) between radiographic measurements of preoperative and PPTS were correlated with in-vivo knee kinematics. Patients were separated into 2 groups based on their Δ values. Group I consisted of Δ values less than 0.7, indicating either a similar PPTS compared to preoperative PTS or a slightly flatter PPTS. Group II consisted of Δ values above 0.7, indicating a steepened PPTS.

Results: Preoperative PTS values ranged from -0.5° to 11.2°, with an average of 5.0° ± 3.4°. PPTS values ranged from 3.0° to 12.1°, with an average of 7.1° ± 3.1°. Weight-bearing range of motion (WBROM) measured from 94° to 139°, and femorotibial axial rotation ranged from -2.9° to 17.3°. A -test revealed average values for WBROM in Group I (Δ < 0.7) to be significantly greater than those for Group II (Δ > 0.7) ( = .01).

Conclusions: These findings indicate that either a PPTS approximating the preoperative PTS or a slightly flattened PPTS in comparison (Δ < 0.7) is associated with WBROM greater than 130°. Values for axial rotation and anterior sliding were not significantly associated with changes to the PTS.