Abstract
Introduction: The cement mantle is a critical factor in the longevity of cemented total hip arthroplasty (THA). Concern has been raised about the reliability of plain radiographs for its assessment. A new high-definition, three-dimensional (3-D), in vitro method of cement mantle evaluation has been developed.
Aim: To compare cement mantle quality in six contemporary stem designs.
Methods: Exact resin replicas of six contemporary stem designs were implanted into cadaver femora using third generation techniques. The specimens were imaged with a high-speed, helical, computerised, tomographic scanner. Computer-assisted, 3-D analysis of the cement mantle thickness was made. Comparisons were made between different stem designs and also with plain film assessments of the mantles.
Results: Standard radiographs overestimated mantle thickness (p< 0.05) and underestimated the deficiencies. The percentage area of cement mantle that was thinner than 2mm ranged from 9% to 28%. Slight malrotation or malalignment of the stem with respect to the broach envelope produced deficient mantles. Characteristic patterns of deficiencies were seen for different stem designs.
Conclusions: Plain x-rays overestimated the cement thickness, frequently missed areas of substandard cement, and should, therefore, be interpreted cautiously. The cement mantle varies widely depending on the stem design and surgical technique, and commonly used designs have significant deficiencies in their mantles by standard criteria despite proper surgical technique. Surgeons should be familiar with the stem that they use and its instrumentation to maximise outcomes. This is a valuable technique for the study of the cement mantle as it relates to implant design, surgical technique and patient anatomy.
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
