CORR Insights®: Revisions of Modular Metal-on-metal THA Have a High Risk of Early Complications

Where Are We Now?

Surgeons abandoned the first generation of metal-on-metal (MoM) THA components, introduced in the 1950s, because design-related flaws led to problems with frictional torque, wear, and premature loosening, resulting in revision for a high proportion of those implanted. But there was a notion that improvements in metallurgy would solve these problems. This belief led to the reintroduction of MoM THA components in the late 1990s. Unfortunately, orthopaedic surgeons performed thousands of MoM THA procedures before we realized that although some of the earlier problems with MoM bearings could be solved, doing so would unmask unexpected causes of premature revision including adverse local tissue reaction (ALTR) and elevated levels of systemic metal ion species [4]. Though the risk of revision after MoM THA varies depending on the specific device and patient factors [1], in general, the risk of revision of these devices is unacceptably high. Some of the adverse consequences resulting from the period of widespread MoM THA are known, while others are still being discovered. It has been established that elevated values of cobalt and chromium in the periarticular tissues can cause ALTR and other causes of premature revision [5]. Although some patients are more sensitive than others to these metal ions, the magnitude of the adverse reaction, in general, has been related to the levels of cobalt and chromium [3].

While patients with a MoM THA should be closely monitored, the majority of patients do not undergo revision hip arthroplasty. For those who undergo revision, the risk of surgical complications is high [6]. Therefore, determining the indications for revision and the optimal surgical technique for these patients is worthy of investigation.

Enter the investigation by Jennings and colleagues [2], which provides some insight into this issue and contributes to our knowledge of surgical management for ALTR. In their study, the authors confirm that MoM THA revision is associated with complications, specifically recurrent dislocation and periprosthetic joint infection. Their study also demonstrates a relationship between the preoperative values of serum cobalt and chromium and the risk of complications after surgery.

Where Do We Need To Go?

Jennings and colleagues [2] also suggest that revision MoM THA by isolated head-liner exchange may not be the best surgical method—but then what is? This question, and many others, still remain. For example, why are complications so common after revision of MoM THA? The most-common complications remain dislocation and infection. Is this because of severe soft-tissue compromise secondary to ALTR, or are there other important causes, such as leaving an imperfectly positioned acetabular component from the index arthroplasty? When patients do undergo a MoM THA revision, what is the best surgical technique? Should we rely on isolated head-liner exchange, revise to a dual mobility or constrained component, or revise of the components and debride the necrotic tissue?

Unfortunately, as MoM THA implants are in place for longer periods of time, the number of revisions will likely increase. Therefore, it is critical that we steadfastly continue to investigate this problem.

How Do We Get There?

Careful analysis of prerevision Metal Artifact Reduction Sequences MRI images may help assess the amount of soft-tissue damage, which could lead to a better understanding of the surgical methods surgeons should use when performing the revision. For example, simple head-liner exchange may be a good option for patients with well-positioned components and little soft-tissue damage.

Conversely, those with severe soft-tissue compromise may benefit from immediate use of a constrained component. Aggressive débridement of necrotic tissues, which are laden with metal ions, may reduce the high incidence of infection.

Registry data are unlikely to be detailed enough to provide firm guidance in terms of the management for these patients. Instead, multicenter investigations could generate a large amount of data on the specifics of surgical technique and resolve many unanswered questions. Specifically, the information obtained should identify patient profiles that do well with a simple head-liner exchange (many patients in the current study had no complications). Additionally, a future investigation has the potential to determine when well-fixed components are best removed and what they should be replaced with. The complications most-commonly associated with revision MoM THA, dislocation and infection, are devastating and frequently result in repeat revision surgery. Our efforts should focus on minimizing the risk of these complications through improvements to our surgical approaches. Until then, as Jennings and colleagues concluded: “Surgeons should be aware of the high complication risk associated in this seemingly straightforward procedure” [2].