Metal Heads and Accolade, Meridian and Citation Stems
Most modern hip implants are what is called “modular.” That means that several parts are assembled to work as one unit. Unfortunately, the parts are man-made and typically consist of a metal stem, a head and a two-piece cup. After the end of your femur is cut off the stem is impacted into a canal drilled in the femur and the head is impacted onto the stem. On the hip side the cup is usually two pieces; a metal cup and a plastic liner. The cup is placed in your acetabulum or hip bone and the plastic liner fits inside the cup. After the parts are assembled and implanted the metal head goes inside the plastic liner and the implants take the place of the hip God gave us.
The problem with Stryker’s modular hip stem/metal head combination is that the man-made metal stem and head do not work well together. Unlike all other manufacturers, Stryker chose to use its own titanium allow for the stems. Most companies use commercially pure Ti-6AI-4V titanium. Stryker instead started making stems out of TMZF titanium back in 2000. The sales pitch was that TMZF was stronger but more flexible than Ti-6 titanium. In addition, the part of the stem where the head connects to it is much smaller in Stryker hip stems than those of other manufacturers. But, it’s turned out that when you connect the head to a small stem made of “more flexible” metal you get movement at the connection. Movement at a metal on metal connection is bad. It causes the two metals to wear away and then corrode.
Symptoms of Failed LFIT V40 Femoral Heads
Stryker’s metal heads are made of chromium and cobalt. Once motion and corrosion start chromium and cobalt are released into the tissue surrounding the hip. It is widely accepted in the scientific and orthopedic community these days that chromium and cobalt are toxic to human tissue, bone and muscle. Release of chromium and cobalt into the tissue can also result in those metals being taken up and circulated throughout the body in the blood stream. The particles of chromium and cobalt are so small that they can cross the blood-brain and fetal-placental barriers. Patients suffering from cobalt and chromium poisoning can experience the following:
- Pain around the hip
- Loss of mobility
- Ringing in the ears
- Deteriorating vision
- Muscle death
- Bone death
- Large fluid collections around the hip joint
- Growth of odd, non-native tissue around the hip also called a pseudotumor
All of the above can lead to the need for an unnecessary and risky revision surgery to remove and replace the defective parts. Of course this results in major expense, time away from work, extended rehab and serious inconvenience. Revision surgeries are very risky and often result in complication such as infection, fracture, blood clots and prolonged pain. So much for the promise most doctors make that, “This will be the last hip you will ever need.”
Rejuvenate and ABG II Failures
The recalled Rejuvenate and ABG II hip implants were also “modular.” The difference between these two implants and the Accolade, Meridian and Citation is that the stem was actually two pieces as opposed to one. Sometimes they are referred to as dual-modular. In the Rejuvenate and ABG II a modular neck is inserted into the stem to form one piece. The head is then impacted onto the neck. What the Rejuvenate and ABG II have in common with the one piece Accolade, Meridian and Citation is that the stems are all made of TMZF titanium. The Rejuvenate an ABG II neck is made of chromium and cobalt. So, when a Rejuvenate or ABG II neck is inserted into the TMZF stem you have the exact same combination of metals you have when a metal head is used on the Accolade, Meridian or Citation. Since the TMZF stem is much softer than chromium cobalt neck you get motion at the connection between the two. As discussed above, motion at a modular connection is bad. Motion leads to material loss which leads to corrosion. Once the corrosion starts you have the exact same problem discussed above with exactly the same symptoms and consequences.
Stryker Abandoned TMZF
Just before Stryker recalled the Rejuvenate and ABG II it redesigned the Accolade and changed the titanium to the Ti-6AI-4V alloy. So, once Stryker recalled the Rejuvenate and ABG II it essentially eliminated TMZF titanium from its entire product line. This does not appear to be a coincidence.