Abstract
Introduction: Stem alignment and cement mantle thickness influence stress distribution on the cement-bone and the bone-cement interfaces. Malposition of the implant and an incomplete cement mantle can lead to suboptimal long-term results. The proximal and distal centralisers that are currently available have shown severe limitations in their clinical application and do not centralise the stem in the lateral plane.
Aim: To evaluate a new stem-positioning system.
Method: One hundred Friendly (Lima LTO) stems implanted between October 1999 and October 2000 have been evaluated radiographically for stem centralisation and cement mantle thickness in both projections. One surgeon used the same technique in all patients and employed a newly designed set of proximal and distal centralisers.
Results: All cases had an acceptable and complete cement mantle. In only seven cases cement thickness was below 2mm in Gruen zone 14. Stem-bone contact was never observed. No patient had migration of the distal plug during pressurisation or complete cement defects. In eight cases mild (2 degrees to 4 degrees) valgus deviation of the stem was found. None of the distal centralisers failed whilst one of the proximal centralisers broke during insertion of the stem without influencing the final result.
Discussion: Cementing the stem is the most delicate phase of cemented total hip replacement. The use of proximal and distal centralisers is mandatory to prevent malposition which in turn results in incomplete cement mantle. The system employed in this series appears accurate and reproducible for stem alignment.
The abstracts were prepared by Professor A. J. Thurston. Correspondence should be addressed to him at the Department of Surgery, Wellington School of Medicine, PO Box 7343, Wellington South, New Zealand
