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.

Materials & method: From July 1990 to July 1997, we reviewed 58 hips in 47 patients receiving primary cemented hip arthroplasty with porous-coated prosthesis. There were 31men and 16 women. The diagnoses included AVN of femoral head in 18, OA in 4, femoral neck fracture in 33 and RA in 3 patients. The prosthesis included PCA 17, Osteonics in 18, United in 21 and Richard in 1.

Initially, all the femoral canals were prepared with the routine cementless fixation technique modified by the author (rasp-ream-rasp technique). With insertion of the final-size rasp, reliable fixation was not obtained possibly due to poor bone quality or inherent canal geometry. To avoid fracture with insertion of the next-sized stem, bone cement was added as gap-filler to augment fixation of the final-sized stems.

Result: The average age of the patients at operation was 51.1 years old (range, 34 to 88). The mean follow-up was 5.8 years (range, 2 to 10). No patients were lost to follow-up. The mean Harris hip score at final F/U was 92 points. The X-rays taken postoperatively, 3months, 6months, 1 year, 2 years and the last F/U were checked carefully. Radiographically, there was no stem loosening, no measurable subsidence or demarcation line both in bone-cement and implant–cement interfaces. Even in the thinnest area of cement layer, no breakage or fracture was detected. Load transfer predominantly occurred at proximal 1/3 in 38 stems, at middle 1/3 in 20 stems (i.e. junction of porous coating and uncoated surface of the stem). No load transfer was noted at distal 1/3.

Conclusion: When reliable cementless stem fixation is not obtained intraoperatively, cement can be added to function as “gap-filler” for augmenting the initial fixation. The clinical and radiological result is quite favorable. Thin (< 2mm) cement mantle between bone and porous-coated stem will not result in early cement mantle break and implant failure.

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.