Abstract
Modular necks arrived in North America in the late 1970s. The purpose was to allow ceramic balls to be attached to metal stems. The advantages of modularity were so obvious that it was universally adopted with almost no untoward consequences.
A double-taper neck was developed in Italy by the Cremascoli Company and was used extensively with few reports of problems.
Recently, problems have been reported not only with double-taper necks, but also with head-neck junction tapers. Something would appear to have changed recently.
Some of these changes were shortening of the taper, lengthening of the neck, version angles were increased, and head sizes bigger than 32mm were introduced. Surface finish on some of the tapers was changed and they were ridged. This produces a better fit for a ceramic ball, but facilitates crevice corrosion with a metal ball.
The author used the original OTI cemented stem with a double-taper neck between 2002 and 2005. It was a cobalt chrome construct. The Cremascoli was a titanium hip. The OTI used the classic Morse taper with cogs for increased rotational resistance.
One hundred forty five stems were inserted. The neck stem taper broke in two cases and dislocated in one. All of these cases had a long neck and long heads and thus produced maximum moment arm. The stem was withdrawn from the market, the taper lengthened and the strength doubled. It was reintroduced in 2007. From 2007 to 2011, the author has done 188 cases, all cemented stems. No taper problems have occurred.
The conclusion is that a properly designed double taper neck does not appear to have a downside. The upside is the ability to change neck length and especially version after head insertion. Leg length and hip centering can, therefore, be fine-tuned as never before. The author continues to use this stem enthusiastically for all cemented cases.
