Cobalt Chromium Toxicity Resource Center

Influence of Femoral Stems with Modular Neck Designs on Health Consequences and Presence of Metal Ions





Metal on metal (MOM) prostheses have different designs. One such MOM stem design, Profemur Z, includes a femoral stem with a modular neck that enables adjustments which are separate from femoral fixation. There is concern with the potential for fracture of the modular neck in relation to the modular junction. Fracturing of this junction may potentially lead to the production and release of metal debris and ions causing adverse local tissue reactions, or ALTR.

The Profemur Z allows for a modular neck-body junction which can be inserted with a variety of orientations, angles, and directions. The neck has a taper where a modular head may attach. These models only used titanium alloy necks until cobalt chromium alloy necks were available. There are many cases of corrosion and modular neck fracture secondary to failure of the Profemur Z stem design. According to the Australian Orthopedic Association’s National Joint Replacement Registry, there is an 11% failure rate for patients with this device over a 5 year period. This is a significant failure rate compared to other femoral stems.

An increase in serum chromium and cobalt levels was indicated in patients with MOM hip prostheses. The modular head-neck junction, and bearing surface, is the main cause of the cobalt and chromium release in the blood stream. There was a significant elevation in cobalt and chromium serum levels as a result. Whereas titanium alloy prostheses, had low elevations of cobalt and chromium serums, the adverse local tissue reaction, results from the release of cobalt and chromium in those stem designs produced with a modular neck made from a cobalt-chromium alloy. The etiology of modular neck fractures stems from fatigue failure and crack formation from corrosion due to metalurgical reactions of the device with body chemistry. In addition, those stem designs with a modular neck-body junction made of both chromium-cobalt and titanium have the ability to cause even more detrimental local tissue reactions.

Crack formations on the neck-body interface are the result of oxide-formation and oxide-driven stress. Over time, pitting and formation of cracks are exacerbated by increased stress corrosion and oxidation surrounding the interface of the mechanism. Stress corrosion causes the dissolution process of metal ions. The consequences of elevated metal ion levels from the cobalt-chromium stems in patients include pseudotumor formation, severe pain, osteolysis, and taper corrosion.

Subsequently, there is an increased revision rate for prostheses with this femoral stem design. During revision surgeries, findings illustrated significant corrosion at the modular neck-body interface.

The Full Article can be read at:

http://www.arthroplastyjournal.org/article/S0883-5403(14)00297-6/abstract

Source: Silverton Craig D., Jacobs Joshua J., Devitt Jeffrey W.,
Cooper H. John, Midterm Results of a Femoral Stem with a Modular Neck Design:
Clinical Outcomes and Metal Ion Analysis, Journal of Arthroplasty (2014), doi:
10.1016/j.arth.2014.04.039


Leave a Reply

Your email address will not be published. Required fields are marked *

Real Time Web Analytics