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Randomized Controlled Trial
. 2017 Aug;88(4):377-382.
doi: 10.1080/17453674.2017.1315553. Epub 2017 Apr 18.

Is a hollow centralizer necessary when using a polished, tapered, cemented femoral stem?

Erik Weber  1 , Christer Olsson  2 , Uldis Kesteris  1 , Gunnar Flivik  1
Affiliations
Randomized Controlled Trial

Is a hollow centralizer necessary when using a polished, tapered, cemented femoral stem?

Erik Weber et al. Acta Orthop. 2017 Aug.

Abstract

Background and purpose - A tapered, polished and collarless stem is normally equipped with a hollow centralizer to prevent the stem from becoming end-bearing in the cement as the stem subsides. In a randomized clinical trial, we evaluated such a stem (MS-30), which was initially introduced with a solid centralizer but was later recommended to be fitted with a hollow centralizer. We hypothesized that while the stem would sink more, it would become rotationally stable and have less retroversion with a hollow centralizer than with a solid centralizer. Patients and methods - We randomized 60 patients with primary hip arthritis to receive either a hollow centralizer or a solid centralizer with the stem. The effect was evaluated over a 10-year follow-up period with repeated RSA examinations, conventional radiographs, and clinical follow-ups using the WOMAC and SF-12 questionnaires. Results - At 10-year follow-up, the group with hollow centralizers had subsided more than the group with solid centralizers (1.99 mm (hollow) as opposed to 0.57 mm (solid); p < 0.001). However, rotation was similar at 10-year follow-up (mean retroversion 1.34° (hollow) and 1.30° (solid)). Both groups showed excellent 10-year results, with similar clinical outcome, and none of the stems were radiographically loose or had been revised. Interpretation - As expected, there was more subsidence in the group with hollow centralizers, and with similar magnitude to that reported in earlier RSA studies on conceptually similar prostheses. Interestingly, there was no difference in the rotational behavior of the prostheses. This stem type appears to have a design that, regardless of the type of centralizer and the possibility of subsidence, withstands the rotational forces it is subjected to very well. This study does not support the need for a hollow centralizer for these types of stems.

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Figures

Figure 1.
Figure 1.
Left: MS-30 with hollow centralizer; right: MS-30 with solid centralizer. Both stems were fitted with tantalum marker towers at the tip and in the proximal section, supplied by the manufacturer.
Figure 2.
Figure 2.
Left: the solid, 3-winged, peg-fitted asymmetrical centralizer; right: the hollow, 4-winged open-ended centralizer. The centralizers were available in 2 sizes for each stem size (large and small) and were selected depending on the width of the femoral canal.
Figure 4.
Figure 4.
Graph showing mean retroversion (Y-rotation) measured with RSA technique, including confidence intervals (bars).
Figure 5.
Figure 5.
Graph showing mean stem subsidence (Y-translation) measured with RSA technique, including confidence intervals (bars).
See this image and copyright information in PMC

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