Abstract
Instability remains a common reason for revision after primary TKA. Careful preoperative examination is necessary to determine the exact direction of and reason for the instability. Radiographs and CT can be useful to evaluate component alignment and rotation. Obviously, ruling out concurrent infection should be a part of the routine preoperative workup. PCL insufficiency can be treated by conversion to a more “dished” insert if available, and all other component issues are acceptable. If dished inserts are not available, then revision to a posterior stabilised component can be effective. Flexion instability can occur with PCL substituting designs, and may require revision as well. Up-sizing, and posteriorising the femoral component (often requiring posterior augmentation) to tighten the flexion gap can be an effective strategy. With collateral ligament problems, so called CCK or “constrained” implants can be effective. While ligament advancement or augmentation techniques have been described, few surgeons are familiar with these techniques, and most “back up” such reconstructions with constrained implants. With more severe collateral ligament deficiencies, multi-directional instabilities, or massive flexion-extension gap mismatches, the use of so-called “hinged” implants can be effective. It is wise to have various levels of constraint available preoperatively when undertaking these challenging revisions.
