THA Instability

One of the most frequent complications after total hip arthroplasty (THA) is instability. The risk of dislocation depends on patient-related factors (e.g., obesity, neurological disorders, and compliance) and surgical factors (experience of the surgeon, approach, and prior surgeries). The risk of THA instability increases with the number of revision surgeries performed on the hip arthroplasty. Initially, conservative treatment should be tried. A closed reduction should be attempted for all cases. For recurrent dislocations, revision surgery should be performed. Prior to the revision, a thorough analysis of the dislocation mechanism should be conducted. Major causes for instability are implant malpositioning, weakness of the abductor trochanteric complex, impingement of the components, and liner wear. Conventional X-rays for general implant assessment are usually used to evaluate major implant malpositionings. Further diagnostics like CT for the determination of the rotational position of the implants, especially for the femoral component, can also be performed. During revision surgery, prior to the removal of the implant, the cause for instability should be verified intraoperatively. The chosen revision strategy should correct the underlying etiology. Revision bearings like dual-mobility cups and constrained liners, and in some cases, larger femoral heads can reduce the risk of ongoing joint dislocation. Overall, the most frequent complication after revision for hip arthroplasty instability is still the recurrent dislocation. This should emphasize the importance of a correct diagnosis as part of the treatment strategy.