LAUSR

I read with interest the article entitled “Disassociation of a coldwelded bimodular titanium femoral stem by intraoperative ice cooling” by Frandsen et al. [1], and I want to congratulate the authors on a report that deals with the challenging problems of stem, neck, and head modularity in contemporary total hip arthroplasty. Their unique technical solution should be remembered by all revision surgeons, and I agree with their logical approach to the difficult decision-making of when to remove a well-positioned, well-fixed, bimodular titanium femoral stem. I agree that current information about the Zimmer M/L taper prosthesis with Kinectiv Technology (Zimmer Biomet, Warsaw, IN) makes it a candidate for partial revision because (1) the neck is constructed of titanium (Ti) alloy, and although a Ti-Ti interface with the stem may coldweld [1] or even corrode [2,3], it will likely not lead to an adverse local tissue reaction as there is no cobalt (Co) alloy involved; (2) the design length of this particular modular titanium neck is relatively short and therefore unlikely to break, distinct from longer Ti modular necks that are apt to fracture [4,5]; and (3) usage of a ceramic femoral head at the obverse taper on the neck should diminish corrosion and metal loss [6], and again, without a Coalloy component in the mix, minimize the risk of adverse local tissue reactions. The decision to revise such a stem is complex [7], but the authors make a very logical argument for revising only the head and neck in their patient’s case. I would also like to add one observation to the authors’ case report that I think is very important. The case history and prerevision imaging (Figs. 1b and 3b, specifically) show conclusively that the patient had a long-standing gross trunnion failure (GTF) of his previous total hip replacement unrelated to his motorcycle crash. As Morlock et al have demonstrated, this is a very specific pattern (so-called “bird beak”) seen with end-stage mechanically assisted crevice corrosion (MACC) and is more commonly observed with less-stiff-material trunnions and smaller tapers [8]. Although GTF due to MACC has been noted rarely across many total hip arthroplasty designs and manufacturers [9], it is particularly common in a recalled Co-alloy femoral head and proprietary Ti-alloy trunnion (TMZF, Stryker, Mahwah, NJ) [8,10]. To my knowledge, the present case report by Frandsen et al. is the first such case noted in a Zimmer M/L taper prosthesis with Kinectiv Technology (Zimmer Biomet, Warsaw, IN). It is important to point out that the ZimmerM/L taper prosthesis (Zimmer Biomet, Warsaw, IN) has recently been described as having high revision for corrosion in a long-term analysis of the