Total Hip Modular Necks – Is this the next phase of Hip Failures?
Stryker Hip Stem Recall Raises Warnings (Orthopedics This Week)
While a blue ribbon FDA panel was wrestling with problems associated with metal-on-metal hips, Stryker Corporation was voluntarily recalling its Rejuvenate and ABG II modular-neck stems used during hip replacement surgery. The recall was announced July 6.
Is this the next phase of hip failures?
Only July 9, OTW‘s Elizabeth Hofheinz reported that Ryan Nunley, M.D., an assistant professor of orthopedics at Washington University in St. Louis, said, “…the next line of metal related issues that we’re beginning to see is with modular metal necks. Traditional total hips were all one piece (monoblock), but more recently some companies have jumped on the modular neck bandwagon. We are seeing corrosion at the location where the modular metal neck snaps into the body of the femoral stem, which is leading to a significant amount of metal ion release.”
“Companies are saying that these necks have been tested and are stable—and yes, they are likely not overly susceptible to fracture anymore. But there is clearly micro motion rubbing at the junction generating the metal debris and causing tissue necrosis and pseudotumor formation. The use of larger diameter heads on these modular necks with the same size trunion might also be causing more micro motion. While a bigger head may be a good thing in some respects for reducing dislocations, the downside is that the larger you make the head the more you increase the torque on the trunion taper, which causes the metal to shear and flake. This could be our next wave of failures with use of modular femoral necks in total hip replacement surgery.”
Fretting and Corrosion Risks
Stuart Simpson, Stryker’s Vice President and General Manager, Hip Reconstruction, said on July 6, “While modular-neck stems provide surgeons with an option to correct certain aspects of a patient’s anatomy and hip biomechanics, given the potential risks associated with fretting and corrosion at the modular neck junction, Stryker Orthopaedics decided to take this voluntary action.”
Stryker has notified healthcare professionals and regulatory bodies of this voluntary recall. Patients who received a Rejuvenate Modular or ABG II modular-neck stem are encouraged to contact their surgeon.
When Stryker released the “personalized” Rejuvenate Modular Primary Hip system back in February 2010, the company told OTW that the system was developed to optimize anatomic restoration by providing options that offer enhanced stability, proven modularity and intra-operative flexibility. With a wide range of femoral stem and neck combinations and an extensive range of length, version and offset, the company said surgeons would be better able to personalize the implant to a patient’s unique anatomy.
The system is comprised of separate femoral stem and neck components made of TMZF alley, a proprietary Stryker material with a plasma sprayed coating of commercially pure titanium and PureFix HA. The necks are made of CoCr alleoy.
Due to minimal sales to date, analysts do not expect this to have a material impact on Stryker’s results. However, the potential problem may not be limited to Stryker.
Mizuho Securities USA Inc. analyst Mike Matson, says a white paper on Stryker’s website seems to indicate that the problems can occur with most modular hip stem designs.
Wrote Matson in an investor note; “It’s unknown if these issues are specific to Stryker’s stem designs or an issue for the entire product class. If it’s the latter, we could see additional product recalls and/or product liability litigation at other companies as well.
While Stryker’s sales of modular hip stems is very small, other companies have more exposure. We estimate that Zimmer Holdings Inc.’s M/L Taper with Kinectiv modular hip stem has annual sales of less than 1% of Zimmer’s total annual sales and we believe that a significant portion of Wright Medical’s hip stems are modular.
A dedicated patient call center can be reached at 1-888-317-0200 and additional information can be found at www.AboutStryker.com/ModularNeckStems.