Gunston describes a new concept of knee replacement designed to reproduce the polycentric (multiple instant-centre) motion of the normal knee rather than act as a hinge. Separate cemented metal femoral runners and polyethylene tibial tracks resurface each condyle and plateau while the collateral and cruciate ligaments are retained. He reports early results in 22 knees in patients with rheumatoid polyarthritis.
The core teaching point is kinematic: the normal knee is not a hinge. Its instant centre of rotation migrates posteriorly in a spiral as it flexes, combining rocking, gliding, and axial rotation. A resident should understand why early constrained hinge knees failed, they generated large torsional and shear stresses at the cement-bone interface that unconstrained designs avoid.
Gunston's answer was to resurface each condyle and plateau separately with metal-on-polyethylene bearings, retain the cruciate and collateral ligaments to guide and stabilize motion, and let the ligaments handle stability while the surfaces bear compression.
This directly applied Charnley's low-friction hip principles (metal-on-polyethylene, PMMA cement) to the knee and established the ligament-preserving resurfacing concept that underlies modern condylar knee arthroplasty. The practical adjustment pearl remains relevant: setting the relative levels of the components takes up collateral laxity and corrects deformity.
Gunston describes a new concept of knee replacement designed to reproduce the polycentric (multiple instant-centre) motion of the normal knee rather than act as a hinge. Separate cemented metal femoral runners and polyethylene tibial tracks resurface each condyle and plateau while the collateral and cruciate ligaments are retained. He reports early results in 22 knees in patients with rheumatoid polyarthritis.
The core teaching point is kinematic: the normal knee is not a hinge. Its instant centre of rotation migrates posteriorly in a spiral as it flexes, combining rocking, gliding, and axial rotation. A resident should understand why early constrained hinge knees failed, they generated large torsional and shear stresses at the cement-bone interface that unconstrained designs avoid.
Gunston's answer was to resurface each condyle and plateau separately with metal-on-polyethylene bearings, retain the cruciate and collateral ligaments to guide and stabilize motion, and let the ligaments handle stability while the surfaces bear compression.
This directly applied Charnley's low-friction hip principles (metal-on-polyethylene, PMMA cement) to the knee and established the ligament-preserving resurfacing concept that underlies modern condylar knee arthroplasty. The practical adjustment pearl remains relevant: setting the relative levels of the components takes up collateral laxity and corrects deformity.