Minimally invasive total knee arthroplasty has gained popularity in recent years as a surgical procedure that should produce a shorter recovery period for the patient and to improve pain relief immediately following operation. To facilitate this surgical procedure, manufacturers of knee implants have launched a number of products that surgeons can use. One of these implant products is the Zimmer NexGen MIS Tibial component, which is used in conjunction with the NexGen CR/CR-Flex and the Next Gen LPS/LPS-Flex knee implants. Recently, researchers conducted a study involving precisely this product, and concluded by recommending the discontinued use of the product in total knee arthroscopy surgeries.
The study was based on 529 minimally invasive surgeries performed on 460 patients between March 2007 and 2008, all of which utilized the Zimmer NexGen MIS Tibial Component. From this pool of patients, the researchers identified all patients who required a revision surgery as a result of aseptic loosening, or the weakening of the bond that connects the implant to the patient’s bone. For those patients, the researchers reviewed all the clinical, radiographic and surgical observations during the revision procedure. Patients were also assessed for signs or symptoms of pain, instability and infection. Radiographs from the initial procedure were reviewed to assess alignment of the implant. As a result of this review, the researchers observed a trend that shows early failure of the NexGen MIS Tibial Component that involves aseptic loosening, despite appropriate sizing, position and cementing.
Specifically, eight knees in eight patients, out of the total of 529 surgeries performed, or 1.5%, required a revision surgery to address early aseptic loosening. These revision surgeries, on average, occurred approximately 17 months after the initial knee replacement surgery. In all of these cases, the patients experienced pain that worsened when they put more weight on the knee. These symptoms generally began appearing in patients approximately 11 months after the initial operation. In addition to pain, some patients reported knee instability.
While the 1.5% rate may seem low, the researchers note that studies conducted on minimally invasive implant products other than the Zimmer NexGen MIS Tibial Component had significantly lower failure rates. For example, the researchers point out encouraging studies that show only a 0.33% failure rate on two other minimally invasive products. In addition, another study that involved the NexGen MIS Tibial Component as well as another, similar product, showed a 5.6% failure rate—far above the rates being reported for other products.
The researchers do not offer a concrete conclusion as to what causes the early failures in the NexGen component, indicating that future research studies need to examine that question. One hypothesis is that the problem is actually with the surgical techniques used in the minimally invasive procedure. Another suggested reason for failure was related to the cementing of the device during the procedure. The researchers also indicate that the design features of the NexGen Component itself are the problem.
The researchers involved with the study continue to monitor patients who have received the NexGen Component as part of a minimally invasive procedure in order to determine the root cause of the failures. In the meantime, the researchers found premature loosening of the tibial component at a rate high enough to cause concern and to cause them to discontinue its use.
Product Identification Notice: In any of our web pages referring to Zimmer NexGen products, these pages are intended to provide information about and are referring to the same Zimmer products that were identified by Dr. Berger in his presentation and study entitled "The High Failure Rate of a High-Flex Total Knee Arthroplasty Design," and were written about in the NY Times article titled "Surgeon vs. Knee Maker: Who’s Rejecting Whom?," and that are reported in the FDA MAUDE database, where reports involving the Zimmer NexGen CR Flex Cementless or Porous Femoral component can be found and also those products associated with aseptic loosening of the Zimmer MIS Tibial Component that led certain doctors to discontinue its use, and to recommend discontinued use of this product in primary TKA until the etiology of the high early failure rate of this implant is determined. See prospective studies comparing the results of the Zimmer MIS Tibial Component using conventional and minimally invasive exposures as well as comparing fixation with different types of bone cement as described in Early Aseptic Loosening With a Precoated Low-Profile Tibial Component A Case Series. Not all Zimmer NexGen products are involved in our investigations and lawsuits.