Restoration of Stability, Maintaining Joint Line, Gap Balancing, and Constraint Selection in Revision Total Knee Arthroplasty

Stability means that a knee arthroplasty can maintain its structure and permit desired motion under physiologic load. Revision knee arthroplasty, when performed specifically for instability, cannot necessarily depend on healthy, intact ligaments. These revisions should be amongst the most successful, provided that the causes of instability are identified and corrected. Two sets of forces must be identified: those responsible for instability (e.g. malalignment, gait pathology, and spinal deformity) and those that provide stability (correct component size and position, ligament integrity, and mechanical constraint). Three types of knee arthroplasty instability may require attention: (a) varus–valgus, (b) Plane of motion and (c) Flexion instability. The importance of the level of the joint line is generally exaggerated. Other principal goals take priority: alignment, rotational position, fixation, motion, and stability for example. A simple sequence of three steps (a. Tibial platform b. Flexion gap and c. Extension gap) combined with mechanical constraint when indicated, reliably restores stability and motion to the failed TKA.