Abstract
There are numerous factors that influence total hip arthroplasty (THA) stability including surgical approach, soft-tissue tensioning, impingement, abductor status, and component positioning. A long-held tenet regarding acetabular component positioning is that cup inclination and anteversion of 40 degrees ± 10 degrees and 15 degrees ± 10 degrees, respectively, represents a “safe zone” as to minimise dislocation after primary THA. However, several studies have recently challenged that notion for individual patients. A study completed by Abdel et al identified a cohort of 9784 primary THAs performed at a single institution with 206 THAs (2%) that subsequently dislocated. The authors determined that 58% of the dislocated THAs had their acetabular component within the safe zone for both acetabular inclination and anteversion. When looked at separately, 84% had their inclination within the safe zone (mean value of 44 degrees ± 8 degrees), and 69% had their anteversion within the safe zone (mean value of 15 degrees ± 9 degrees). As such, surgeons should take into account that cup positioning alone does not determine the risk of instability following THA, as there are a multitude of other factors that can contribute to dislocation. Hip stability is multifactorial and likely patient-specific, and must take into account bony and muscular anatomy, static and dynamic soft tissue balance and intra-operative tensioning, and the functional demand and rehabilitative efforts of the patient.
