Constraint in Total Knee Replacement and Catastrophic Polyfailure
DNB Orthopaedics • October 2024 • Paper IV • 10 Marks
Introduction
Constraint in total knee arthroplasty (TKA) refers to the degree to which the prosthetic design mechanically restricts abnormal translation and rotation of the femur relative to the tibia.
The ideal implant provides sufficient stability while preserving as much normal knee kinematics as possible.
Golden principle:
Use the least amount of constraint necessary to obtain a stable, balanced knee.
Increasing constraint improves stability, but transfers greater stress to the implant–bone interface and may increase the risk of loosening or mechanical failure.
Normal Sources of Knee Stability
Stability after TKA depends on a combination of:
- Collateral ligaments — MCL and LCL
- Posterior cruciate ligament when retained
- Joint-line and component positioning
- Flexion and extension gap balance
- Extensor mechanism
- Articular geometry of the implant
As ligamentous competence decreases, increasing prosthetic constraint may be required.
A. Spectrum of Constraint in TKA
Least constraint
↓
Cruciate-retaining (CR)
↓
Posterior-stabilized (PS)
↓
Ultracongruent / deep-dish
↓
Varus-Valgus Constrained (VVC) /
Constrained Condylar Knee (CCK)
↓
Rotating hinge
↓
Fixed hinge
↓
Maximum constraint
1. Cruciate-Retaining TKA
In a CR knee, the posterior cruciate ligament (PCL) is…