Abstract
[Introduction]
One of the modern design total knee arthroplasty (TKA) system, the NexGen Legacy posterior-stabilized (LPS) Flex prosthesis, has been in use at our hospital since 2001. Between 2006 and 2011, NexGen LPS-Flex primary TKA were mainly performed in combination with a cemented short-keeled minimally invasive version tibial tray (MIS tibial component) instead of the traditional NexGen stemmed tibial tray. We observed some cases required early revision of isolated tibial component in primary TKA performed in this period. Therefore, our objectives were to report the series of this revision cases and to consider this failure mechanism.
[Patients & Methods]
A total of 526 primary TKAs were performed using a NexGen LPS-Flex prosthesis and MIS tibial component during five-year period at our hospital. The mean age was 74 years at the time of the index procedure. We assessed revision rate of this tibial tray in this study and described clinical course of the revision cases. We also examined the clinical and radiographic features which could be associated with the failure.
[Results]
The mean duration of follow-up was 2.5 years and there were 13 knees received tibial component revision during this period. Twelve knees were diagnosed with osteoarthritis and one knee with rheumatoid arthritis. The duration between primary TKA and revision averaged at 3.3 years, and the mean age at the second procedure was 67 years. TKAs were performed without applying the tibial central extension stem in all 13 knees, and thick polyethylene insert like 17 or 20 mm were selected for seven and 14 mm for five of 13 knees, that were the typical features on the primary TKA. Postoperative course of all 13 cases was uneventful and 10 of 13 knees achieved deep knee flexion over at 125 degrees. Prerevision radiographs showed characteristic pattern with tibial tray debonding at the cement-implant interface and subsidence into varus and flexion in all 13 knees. In all cases, intraoperative findings revealed a grossly loose tibial component with most of the cement mantle still attached to the bone. No case exhibited signs of macroscopic polyethylene wear and femoral component loosening.
[Discussion]
The most common reason for failure of TKA is infection followed by implant loosening, polyethylene wear, and instability. Several studies document survival rates of over 90% up to 20 years with modern TKA designs using a cemented stemmed tibial component. Although failure of the tibial component was more prevalent in some early TKA designs, in recent years, failure of tibial fixation has been a rare cause of revision. Our experience with early aseptic loosening of this tibial component has suggested the low-profile design with no central stem as a cause for accelerated failure. Furthermore, other factors associated with increased this failure could include a thicker insert and postoperative achievement of high flexion.
