Abstract
Introduction and Aims: The ‘Natural Knee’ (versions I and II-Zimmer) is a primary tri-compartmental device designed for either cemented or cementless application. The cementless option includes a metal backed patella component. We present a three to seven year analysis of survival of 156 knees.
Method: Data was collected at post-operative times of one year and five years or more, to derive HSS scores. Radiological assessments included full length standing radiographs in maximum knee extension and neutral rotation, Merchant views at 30 degrees and fluoroscopically screened AP and lateral views.
Results: Of the 152 patients, 12 had died and two were lost to follow-up. One hundred and thirty-eight patients (156 knees) were available for review. Mean HSS score pre-op was 59 and at five years 91.3. Twenty-two required manipulation under anaesthesia post-operatively. Fourteen of the 122 cementless knees were revised but none of the cemented implants have required revision. Mean time to revision was 40.3 months (range 9–80 months). There were no deep infections. Revisions were for malalignment (one), secondary patella resurfacing (one), late PCL rupture (one), early tibio-femoral poly wear (two), metal backed poly fracture (two), tibial osteolysis without loosening (two), established aseptic loosening (3), and pain without loosening but hot bone scan suggesting subtle aseptic loosening (2). These last two were well fixed at revision and conversion to cemented primary components gave excellent results. There was a tendency for screw track osteolysis that was particularly difficult to detect on plain radiographs. The overall survival of this knee system at seven years when applying the Kaplan-Meier analysis is 87.4%. There was statistical significance comparing failure of cementless and cemented fixation (p=0.035).
Conclusion: This study demonstrates a significant early failure in the Cementless Natural Total Knee replacement system. Screw tract osteolyis of the tibial component is of particular concern as it is diffcult to demonstrate this on routine radiographs. Early failure of the metal-backed patella component in the absence of significant axial or rotational alignment is unacceptable.
These abstracts were prepared by Editorial Secretary, George Sikorski. Correspondence should be addressed to Australian Orthopaedic Association, Ground Floor, The William Bland Centre, 229 Macquarie Street, Sydney, NSW 2000, Australia.
At least one of the authors is receiving or has received material benefits or support from a commercial source.
