Recommended Tibial Slope in Posterior-Stabilized Total Knee Replacement
For posterior-stabilized (PS) total knee replacement, aim for a posterior tibial slope of 3-7 degrees to optimize stability and prevent complications, with slopes greater than 7 degrees associated with increased instability and implant loosening.
Optimal Slope Range
Target a posterior tibial slope of 3-7 degrees in PS total knee arthroplasty to balance stability across the range of motion 1, 2.
Avoid posterior slopes greater than 7 degrees, as this threshold is associated with:
Biomechanical Considerations
A 7-degree posterior slope specifically loosens the knee to varus-valgus and anterior-posterior stress in flexion in rotationally unconstrained, ACL-sacrificing designs 1.
Eliminating posterior slope (0 degrees) improves varus-valgus stability in flexion but slightly increases anterior-posterior laxity in extension 1.
A 3-degree posterior slope provides intermediate stability values between 0 and 7 degrees, though not statistically different from either extreme 1.
Clinical Outcomes Data
In a 16-year follow-up study of unicompartmental arthroplasty (which shares biomechanical principles with PS TKA), knees without loosening had significantly lower mean posterior tibial slopes compared to those with loosening 2.
All seven knees revised for failure in ACL-deficient cases had tibial slopes greater than 8 degrees at implantation 2.
There is a significant linear relationship between anterior tibial translation and posterior tibial slope, with each degree of increased slope contributing to anterior translation 2.
Measurement Technique
Measure posterior tibial slope on long lateral or expanded lateral radiographs to ensure accuracy 3.
The functional tibial slope should be defined as the complement of the angle formed by the tangent to the tibial medial plateau and the lateral mechanical axis of the leg 4.
Standing lateral radiographs with the knee in full extension and true lateral positioning provide the most accurate measurements 4.
Common Pitfalls to Avoid
Do not use excessive posterior slope (>7 degrees) to address flexion tightness—instead, consider other soft tissue balancing techniques or implant selection 1, 2.
Recognize that while larger tibial slopes widen the flexion gap in PS designs, this comes at the cost of stability 3.
Be aware that posterior tibial slope parallel to the natural tibial slope (average 7 degrees) minimizes tibial component subsidence, but must be balanced against stability concerns in PS designs 3, 4.