Letter to the editor on “Catastrophic failure of a dual mobility bearing in a revision total hip arthroplasty”

We read with interest the article “Catastrophic failure of a dual mobility bearing in a revision total hip arthroplasty” by Brazier et al., with this case report demanding attention due to its headline title. The authors present their personal use of a dual mobility (DM) system, which is found to be “off label” and not recommended by any manufacturer or by the French orthopedic community [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11]. Consequently, we would like to widen the discussion and raise numerous concerns.

The first concern is about the cup inclination. As explained by the authors, the acetabular component orientation might influence the wear vector and cause accelerated polyethylene wear. The wear rate of a DM system may decrease when the abduction angle is increased by up to 65 degrees as demonstrated in vitro by Loving et al [12], but it seems logical that with an extreme abduction (70-75 degrees), the risk of the liner wear will become greater. Reading this article shows that the authors were aware of this concern; however, they describe changing only the bearing couple without changing the cup inclination. Figure 1 demonstrates the previous cup to be in an incorrect position. Author’s case report figure 2 is annotated as “AP pelvis radiograph (a) completed 4 weeks after revision surgery. … demonstrating acceptable position of components”. How can the authors state that the position of the component is now acceptable if the previous incorrectly positioned cup has not been removed?