Time out, moratorium on use of MoM hip bearings should remain in place
It has been more than 4 years since the problems with metal-on-metal hip arthroplasty bearings first came to light and the subsequent recalls began. Orthopaedic surgeons worldwide have pondered the lessons learned from this catastrophe and now many are wondering when, and if, the use of metal-on-metal articulations can be resumed.
After the problems with implanting metal-on-metal (MoM) bearings surfaced, the use of this articulation was considered risky for patients due to reportedly high revision rates, pseudotumors, non-specific symptoms that developed elsewhere in some patients’ bodies, and high levels of chromium and cobalt ions in the blood. At the time, little was known about the consequences of those elevated levels of ions for patients.
Then orthopaedic companies, societies, organizations and national health authorities worldwide began to investigate what had occurred, which led to several guidelines being developed and published to assist surgeons as they followed up on their MoM cases. Most national orthopaedic societies recommended a complete moratorium or a temporary time out on MoM bearing use to allow for the resolution of all the issues and, most importantly, to keep patients safe. Today, many orthopaedic surgeons wonder whether MoM bearings can be safely used once again. Depending on who you talk to and which articles you read, the answers are different.
It has been determined the failure rates with MoM bearings are related to several issues, including the type and size of prosthesis and the gender of the patient. It also has become clear the rate of severe pseudotumors did not reach the level that was anticipated. In fact, some studies show those rates are about as low as those with other types of hip bearings. In addition, we have since learned that other total hip replacement implants have the potential to create pseudotumor-like changes in the soft tissue around the hip joint and some of those prostheses also may be associated with elevated levels of chromium and cobalt in the blood.
At the same time, we have realized that MoM bearings that are “silent” for a number of years may suddenly become problematic. In addition, time has shown it is difficult to revise patients who have severe pseudotumors and there is a high risk of poor outcomes following the surgery.
Therefore, I wonder if the dust has settled yet.
At my institution, we had performed 203 hip resurfacing procedures with MoM bearings and immediately discontinued doing those kinds of cases by the spring 2012, at which time the Danish Orthopaedic Society strongly recommended all orthopaedic departments stop surgeries with MoM bearings, take a time-out and perform detailed follow-up for all the resurfacing cases.
National guidelines were then created in Denmark, after which we followed each patient clinically via blood ion measurements, ultrasound and metal artifact reduction sequence-MRI. Because of this, the problems with MoM in Denmark never escalated to the level that was anticipated in early 2012. Undoubtedly, the patients were concerned, but, in actuality, few patients had any real symptoms related to problems with their hip prostheses.
The revision rates of MoM hips at 6 postoperative years remain low, at less than 3%. Although we have seen no severe pseudotumors, we identified several minor fluid-filled cysts in the area round the hip joint in patients. When we studied these cysts in association with other types of bearings and implants, we found these cysts occur in those cases, as well. On top of that, the patients with large head MoM bearings had good function scores. In fact, nearly all the patients with large-head metal bearings who were candidates for a contralateral hip replacement asked that we please use the same model of prosthesis for their second surgery.
Not time to proceed
My guess is, if you ask the patients, most of them would say “yes.” If you ask industry, all of the companies will probably say “no, that it is just too risky to proceed further.” If you ask the authorities, they will certainly say “no.”
If you ask me, as a surgeon, I would go with the majority and say “no.” This is mainly due to the fact that there are several good total hip systems available that are safe and work well. They have a low revision rate, as proven in several joint implant registries. Therefore, I do not think we should proceed with a bearing that has been associated with unpredictable outcomes in the past. If I needed to undergo hip replacement surgery, I would refuse a MoM bearing, even if it was the best one for me, because of the current knowledge surrounding hips treated with MoM arthroplasty. Secondly, it is still only 6 years to 8 years after the peak use of MoM bearings worldwide. It is possible we have only seen the tip of the iceberg.
Therefore, we should continue to permanently or temporarily discontinue the use of MoM hip articulations. During this time, I encourage orthopaedic surgeons to perform highly detailed follow-up of all their MoM patients. It is equally important, for the future, that they report the results of all their observations, whether positive or negative, accordingly and alert the national hip arthroplasty registries worldwide of the results of their findings.