Abstract
Materials and Methods: This study included careful analysis of 24 knees with polyethylene wear in which revision surgery was performed. Preoperative evaluations included (1) single-leg standing AP, lateral and stress view, (2) dynamic weight-bearing lateral radiographs, and (3) manual test under anesthesia. Intraoperatively, (1) morphologic change of the worn inserts, (2) rotational alignment of tibia-femoral articulation (3) motion behavior of the joint following trial insertion was observed. Based on the above evaluation, 20 knees were revised with 3-component revision by constrained PS knees. The remaining 3 knees received isolated insert exchange.
Results: During the follow-up of 2–6 years, good and excellent results were obtained in all 21 patients who received three-component revision with Osteonics series IV constrained PS prosthesis. The mean HSS score was 92 and the mean ROM was 112 degrees. In the three patients receiving exchange of a thicker polyethylene only, two failed with the same mechanism 15 months and 23 months later and received re-revision. The X-ray of the remaining patient at 5-year F/U revealed impending failure.
Discussion: Based on our preoperative plain/dynamic radiographs and intraoperative findings, we postulate that tibial polyethylene wear is attributed to retained PCL in the absence of ACL, excessive posterior slope of tibial cut, rotational mismatch of tibia-femoral rotation and abnormal condylar lift-off in weight-bearing phase. With passage of time and progression of wear, secondary ligamentous decompensation and multidirectional instability may develop as a result of abnormal kinematics. Therefore, by isolated exchange of insert, the failure mechanism remains unchanged and secondary ligamentous instability persists. Eventually the new insert will fail again.
Conclusion: In revision surgery of tibial polyethelene wear, both the primary cause of failure and the secondary ligamentous instability must be addressed. The author strongly advocate that, in addition to reversal of the primary failure mechanism by 3-component revision, the use of a constrained PS prosthesis is mandatory to overcome the secondary soft tissue decompensation.
The abstracts were prepared by Professor Jegan Krishnan. Correspondence should be addressed to him at the Flinders Medical Centre, Bedford Park 5047, Australia.
