In total knee arthroplasty, posterior tibial slope is an important parameter. An excessively increased posterior tibial slope (>10°) in a posterior-stabilized TKR is most likely to result in:
- A Extension gap tightness and reduced flexion range
- B Flexion instability and increased risk of posterior dislocation of the polyethylene insert ✓
- C Increased compressive load on the patellofemoral joint
- D Valgus malalignment of the tibial component
Correct answer: B. Flexion instability and increased risk of posterior dislocation of the polyethylene insert
Explanation
Posterior tibial slope in TKR creates a tendency for the tibia to slide anteriorly under load in extension and posteriorly in flexion. An excessive posterior slope (>10°) in a posterior-stabilized design — where the PCL is already sacrificed — leads to an increased flexion gap relative to extension, causing flexion instability. In extreme cases this can result in posterior dislocation (cam-post dislocation) of the polyethylene insert during deep flexion. A reduced slope causes extension tightness and restricted ROM, not an increased one.
Reference: Maheshwari Essential Orthopaedics, 6th ed.
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Written and medically reviewed by the StethoPrep medical team.