Abstract
Instability after total hip arthroplasty is the primary cause for revision surgery and is a frequent complication following revision surgery for any reason (Bozic et al, JBJS 2009). Surgical management of the unstable hip has not been uniformly successful with the best results occurring in those hips in which an identifiable cause of instability can be determined (Daly & Morrey, JBJS 1992). It was these sobering findings that led to the development of and increased use of constrained acetabular components.
While the results of revision surgery for instability using constrained components have been encouraging (Shapiro, Padgett, Sculco J Arthroplasty 2003) with a re-dislocation rate of less than 3%, reoperation for other reasons have noted to increase with time. The commonly used tripolar configuration has been susceptible to bearing damage at both the inner and outer bearing surface by the nature of the constrained mechanism (Shah, Padgett, Wright, J Arthroplasty 2009). In addition, we have noted instances of fixation failure directly related to the constrained acetabular device either from loss of implant fixation to the pelvis with or without cement (Yun, Padgett, Dorr, J Arthroplasty 2005).
The observation of these failure modes ranging from either fixation failures to overt biomaterial failure have led us to be extremely cautious in the “routine” use of constrained liners in revision THR.
Stratification of the recurrent dislocator has been nicely described by Wera et al (J Arthroplasty, 2012). The etiology of dislocation includes: acetabular malposition, femoral malposition, abductor deficiency, impingement, late bearing wear and unknown causes.
Implant instability due to malposition, impingement, and poly wear should be revised as appropriate to correct the underlying problem in addition to the use of either larger diameter heads. The emerging use of dual mobility articulations remains to be determined. However, the indiscriminate use of constrained liners should be avoided as the risk of problems outweighs their benefits.
