How to Choose the Appropriate Posterior Slope Angle Can Lead to Good Knee Joint Function Recovery in Total Knee Arthroplasty?

Total knee arthroplasty (TKA) effectively alleviates pain and restores function in severe osteoarthritis, with high long-term prosthesis survival. Nevertheless, suboptimal limb function and prosthesis malposition can necessitate early revision. Prior studies indicate that malalignment (eg, varus), rotational malalignment of components, and deviations in coronal or axial alignment adversely affect outcomes and patellofemoral mechanics. Determining an appropriate posterior tibial slope (PTS) during tibial osteotomy remains contentious due to intraoperative errors, variability in soft tissues, and mixed biomechanical effects: increasing PTS may improve flexion but risk anterior tibial translation and polyethylene wear; reducing PTS may limit flexion but can mitigate paradoxical anterior translation in cruciate-retaining (CR) designs. Building on earlier small-sample, short follow-up work, this study investigates how changes in PTS influence 3-year postoperative pain and function after CR TKA and explores any relationship with postoperative complications.

Prior literature links postoperative alignment and range of motion to patient satisfaction and implant kinematics. Varus alignment decreases function, and rotational malalignment, particularly excessive internal femoral rotation, can cause patellofemoral tracking problems. Finite element and in vivo kinematic studies have shown that tibial slope changes alter femorotibial contact and patellar tracking. Instrumentation and navigation studies report notable osteotomy errors (>2° in over 30% of cases), highlighting technical challenges in achieving planned PTS. Several biomechanical and clinical investigations suggest that PTS influences flexion gaps, quadriceps mechanics, and midflexion kinematics, with CR prostheses being particularly sensitive. Measurement methods for tibial slope (eg, Utzschneider technique) have been validated for reproducibility. However, consensus on the optimal PTS range remains lacking, warranting larger clinical outcome studies.

Design: Retrospective cohort study of 240 consecutive CR TKA patients, all operated on by the same senior surgeon using a consistent technique with a CR prosthesis (Waldemar Link GmbH & Co. KG, Hamburg, Germany; Medium). Surgical period: September 2012 to September 2015; outcomes assessed 3 years postoperatively. Grouping by PTS change: Based on the change in posterior tibial slope (postoperative minus preoperative) measured on lateral radiographs using the Utzschneider method (proximal tibial anatomical axis; slope from metal-backed tibial component configuration): Group 1, >5°; Group 2, 3°–5°; Group 3, 0°–3°; Group 4, −3°–0°; Group 5, <−3°. Positive values indicate a larger postoperative decrease in PTS; negative values indicate an increase in PTS. Participants: 240 patients with knee osteoarthritis; mean age 62.5 years (range 57–68) at surgery. Outcomes: Assessed at 3 years post-op using Knee Society Score (KSS; pain, ROM, stability), WOMAC (pain, stiffness, function), and VAS pain. Postoperative complications recorded: periprosthetic femoral fracture, prosthetic loosening, and polyethylene insert wear. Statistics: SPSS 21.0; scale data expressed as median (QL, QU). Between-group comparisons via Kruskal–Wallis H-test; significance at P<0.05. Preoperative group comparability on WOMAC and KSS confirmed with non-significant H-tests.

- Preoperative comparability: No significant differences among groups in preoperative WOMAC (H=8.567, P=0.070; elsewhere reported H=1.632, P=0.825) or KSS (median 8.5; H=0.286, P=0.998). - Pain: VAS improved substantially to 1.0–3.0 at 3 years, with significant between-group differences (H=93.400, P<0.001). - Function (KSS): Increased significantly across groups (H=164.460, P<0.001); Group 2 (3°–5° decrease in PTS) had the highest median KSS (97.0), Group 5 (increase >3°) the lowest (78.0). - WOMAC: Reduced significantly with medians per group: Group 1=24.0; Group 2=11.0; Group 3=14.0; Group 4=20.0; Group 5=26.0 (H=164.223, P<0.001). Group 2 showed the best (lowest) WOMAC; Group 5 the worst (highest). - Complications: No periprosthetic femoral fractures, prosthetic loosening, or polyethylene wear detected at 3-year follow-up. Overall, a modest reduction in PTS (3°–5°) yielded superior pain and function, whereas both larger decreases (>5°) and increases (<−3°) in PTS were associated with inferior outcomes.

Findings demonstrate that altering posterior tibial slope meaningfully affects postoperative recovery after CR TKA. Excessive decreases in PTS may restrict flexion and contribute to anterior knee pain, while excessive increases can posteriorize the femur relative to the tibia, reduce the quadriceps moment arm, induce joint laxity, and worsen patient-reported outcomes. Group 2, with a small reduction (3°–5°) in PTS, achieved the best KSS and WOMAC scores and lowest VAS pain, supporting the hypothesis that modestly lowering PTS in CR designs may mitigate paradoxical anterior translation and optimize biomechanics. Groups approximating the preoperative slope (0° to slight decrease) performed worse than Group 2, possibly reflecting altered postoperative biomechanics in PCL-preserving constructs where restoring the native slope does not necessarily maximize function. No association with implant-related complications was observed, likely influenced by limited follow-up duration. These results emphasize careful intraoperative control of PTS to avoid extremes that impair recovery.

Osteotomy at different posterior tibial slope angles in TKA influences postoperative functional outcomes. Both excessive increases and excessive reductions in PTS adversely affect recovery, whereas a modest reduction appears to provide the most favorable knee function at 3 years after CR TKA.

- Retrospective single-surgeon study, subject to selection and measurement biases. - Multiple factors beyond PTS (eg, soft-tissue balance, component rotation, alignment) influence outcomes; PTS is only one contributor. - Follow-up limited to 3 years for complication assessment; longer-term events (loosening, wear) may be underrepresented. - Lack of detailed subgroup pairwise statistics and potential inconsistency in reported timelines.