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Acetabular cup position and risk of dislocation in primary total hip arthroplasty
Kurt G Seagrave1,2, Anders Troelsen2, Henrik Malchau3,4
1a Faculty of Medicine , University of New South Wales , Sydney , Australia.
Insights
Hip dislocation after total hip arthroplasty (THA) is common. This review found the "Lewinnek safe zone" for acetabular cup positioning is not consistently justified, and optimal placement remains debated due to multifactorial causes.
Area of Science:
- Orthopedic Surgery
- Biomechanical Engineering
- Medical Imaging
Background:
- Hip dislocation is a frequent complication following total hip arthroplasty (THA).
- Acetabular cup positioning is a key factor influencing THA dislocation risk.
- Current optimal parameters for cup inclination and anteversion remain under investigation.
Purpose of the Study:
- To systematically review methods for measuring acetabular cup placement in THA.
- To identify target zones for optimal cup positioning.
- To assess the association between acetabular cup positioning and dislocation after primary THA.
Main Methods:
- Systematic literature search of the PubMed database (January-February 2016).
- Inclusion of articles comparing acetabular cup positioning and dislocation risk.
- Consideration of surgical approach and cup angle measurement techniques.
Main Results:
- 28 relevant articles were identified.
- Evidence linking cup positioning to dislocation risk was inconsistent across studies.
- No statistically significant difference in mean cup anteversion/inclination angles was found between dislocating and non-dislocating THA.
- The Lewinnek safe zone did not consistently reduce dislocation rates.
Conclusions:
- The established "Lewinnek safe zone" for acetabular cup positioning lacks consistent justification.
- Drawing definitive conclusions on optimal cup positioning is challenging due to study variability and the multifactorial nature of THA dislocation.
- Future research should standardize measurement tools and analyze surgical approach independently.
Abstract:
Background and purpose - Hip dislocation is one of the most common complications following total hip arthroplasty (THA). Several factors that affect dislocation have been identified, including acetabular cup positioning. Optimal values for cup inclination and anteversion are debatable. We performed a systematic review to describe the different methods for measuring cup placement, target zones for cup positioning, and the association between cup positioning and dislocation following primary THA. Methods - A systematic search of literature in the PubMed database was performed (January and February 2016) to identify articles that compared acetabular cup positioning and the risk of dislocation. Surgical approach and methods for measurement of cup angles were also considered. Results - 28 articles were determined to be relevant to our research question. Some articles demonstrated that cup positioning influenced postoperative dislocation whereas others did not. The majority of articles could not identify a statistically significant difference between dislocating and non-dislocating THA with regard to mean angles of cup anteversion and inclination. Most of the articles that assessed cup placement within the Lewinnek safe zone did not show a statistically significant reduction in dislocation rate. Alternative target ranges have been proposed by several authors. Interpretation - The Lewinnek safe zone could not be justified. It is difficult to draw broad conclusions regarding a definitive target zone for cup positioning in THA, due to variability between studies and the likely multifactorial nature of THA dislocation. Future studies comparing cup positioning and dislocation rate should investigate surgical approach separately. Standardized tools for measurement of cup positioning should be implemented to allow comparison between studies.
