New concepts in revision total knee arthroplasty.

Revision knee arthroplasty should be regarded as a discipline separate from primary surgery. A disciplined approach to diagnosis is mandatory in which the following categories for failure are useful: (a) sepsis, (b) extensor mechanism rupture, (c) stiffness, (d) instability, (e) periprosthetic fracture, (f) aseptic loosening and osteolysis, (g) patellar complications and malrotation, (h) component breakage, and (i) no diagnosis. In the event of no coherent explanation for pain and disability, the possibilities of chronic regional pain syndrome, hip or spine pathology, and inability of current technology to meet patient expectations should be considered and revision surgery should be avoided. Revision arthroplasty cannot be performed as if it were a primary procedure and indeed will be eight (or more) different surgeries depending on the cause of failure. Though perhaps counterintuitive, there is a logical rationale and empirical evidence to support complete revision in virtually every case. In general, revision implant systems are required. The early dependence on the "joint line" is inadequate, failing as it does to recognize that the level of the articulation is a three-dimensional concept and not simply a "line." The key to revision surgery technique is that the flexion gap is determined by femoral component size and the extension gap by proximal distal component position. Accordingly, a general technical pathway of three steps can be recommended: 1) tibial platform; 2) stabilization of the knee in flexion with (a) femoral component rotation and (b) size selected with evaluation of (c) patellar height as an indication of "joint line" in flexion only; and 3) stabilization of the knee in extension, an automatic step. Stem extensions improve fixation and, if they engage the diaphysis, may be used as a guide for positioning. Porous metals designed as augments for bone defects may prove more important as "modular fixation interfaces." It is postulated that with the exception of septic and extensor mechanism complications, first revision knee arthroplasty may exceed the durability of primary knee arthroplasty.