At revision total knee arthroplasty, gap balancing demonstrates severe instability in the coronal plane in both varus and valgus testing, while the flexion and extension gaps are symmetric and balanced. The most appropriate constraint level is:

• A Posterior-stabilized implant
• B Cruciate-retaining implant with a thicker insert
• C Rotating hinge with a linked mechanism
• D Varus-valgus constrained condylar implant ✓

Explanation

When collateral function is lost producing bidirectional coronal instability but the flexion-extension gaps remain balanced, a constrained condylar implant with a tall central box and cam controlling varus-valgus motion suffices. A rotating hinge is reserved for gross multidirectional instability, marked flexion-extension gap mismatch, extensor mechanism deficiency, or massive bone loss where unlinked constraint will fail. A posterior-stabilized design controls only posterior translation and cannot resist medial-lateral opening once collaterals are deficient.

Reference: Miller's Review of Orthopaedics, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.