This narrative review by Morgan et al. (JAAOS 2005) defines the spectrum of implant constraint in primary TKA — from cruciate-retaining to rotating-hinge — and provides a clinical decision framework for selecting the appropriate constraint level based on deformity severity, ligament status, and patient-specific factors.
When planning primary TKA, grade your constraint to the pathology: standard CR or PS for most knees, PS when deformity exceeds 15° varus or the PCL is unreliable (RA, patellectomy), VVC when coronal instability persists after soft-tissue balancing, and rotating-hinge only for salvage-level instability or severe bone loss — stepping up constraint unnecessarily increases interface stress and complicates future revision.
This narrative review by Morgan et al. (JAAOS 2005) defines the spectrum of implant constraint in primary TKA — from cruciate-retaining to rotating-hinge — and provides a clinical decision framework for selecting the appropriate constraint level based on deformity severity, ligament status, and patient-specific factors.
When planning primary TKA, grade your constraint to the pathology: standard CR or PS for most knees, PS when deformity exceeds 15° varus or the PCL is unreliable (RA, patellectomy), VVC when coronal instability persists after soft-tissue balancing, and rotating-hinge only for salvage-level instability or severe bone loss — stepping up constraint unnecessarily increases interface stress and complicates future revision.