Stryker Accolade TMZF and LFIT V40 Chrome/Cobalt Hip Replacement Defects
Stryker hip stems made of TMZF are proving to be very problematic. The most commonly implanted Stryker hip stem has been the Stryker Accolade. When a Stryker LFIT V40 Chrome/Cobalt head is placed on a Stryker Accolade TMZF system, the same combination of mixed metals exists as the combination that caused such problems with the Stryker Rejuvenate and ABG II systems.
Accolade stems used in conjunction with LFIT V40 chome/cobalt heads have been failing at alarming rates due to fretting and corrosion at the head/stem connection.
Stryker LFIT V40 Recall
On August 29, 2016, Stryker initiated a Class 2 Device Recall of 44,000 Styker LFIT V40 Femoral Heads. This Strkyer recall is incomplete and possibly misleading. It only involves femoral heads that were manufactured from 2002 through 2011 even though the literature shows that heads implanted before and after 2011 fail just as frequently. There was no re-design of the V40 heads in 2011, so it makes no sense that a Stryker LFIT V40 femoral head manufactured in 2010 is subject to recall while one made in 2012 is not.
In addition, the recall is limited to femoral heads of 35mm and larger and with offsets of greater than or equal to +4. Offset describes where the head comes to rest on the stem. Adjusting the interior taper of the femoral head will cause the head to sit farther out from or closer to the stem. Plus offsets mean the head is farther from the stem, while negative offsets mean the head sits farther down the on the stem. Medical literature suggests that all Styker LFIT V40 heads fail, not just those offset at +4 or greater.
TMZF: The True Reason for the Recall
Large head LFIT V40s with +4 offsets were not suddenly safe after 2011. The design of LFIT V40s didn’t change after 2011. What did change in the 2011-2012 time period is that Stryker eliminated TMZF titanium from its product line. Rejuvenate and ABG II were recalled and the Accolade was redesigned to replace TMZF with Ti6 titanium.
The significance of TMZF was discussed in a 2014 article in Clinical Orthopaedics and Related Research, in which the authors studied corrosion at the modular head-neck junction as a cause for early failure in modern hip replacement systems. The authors analyzed a large revision retrieval database of femoral stems and, among other things, concluded that one of the strongest predictors of corrosion was the flexural rigidity of the femoral trunnion and that the three most flexible trunnions all shared the same alloy (TMZF) and taper geometry (V40). Porter et al. Modern Trunnions Are More Flexible: A Mechanical Analysis of THA Taper Designs, Clin. Orthop. Relat. Res. 2014:472(12):3963
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