From the Research
The safe zone for component positioning in total hip arthroplasty is generally considered to be 15-25° of anteversion for the acetabular component and 35-45° of inclination (abduction), with the most recent and highest quality study suggesting a posterior approach specific safe zone of 10-25° anteversion and 30-50° abduction 1.
Key Considerations
- The combined anteversion (sum of femoral and acetabular anteversion) should ideally fall between 25-45° to achieve optimal stability.
- Proper component positioning is crucial because excessive anteversion can lead to anterior impingement and posterior dislocation, while retroversion increases the risk of posterior impingement and anterior dislocation.
- Excessive inclination can cause edge loading, accelerated wear, and instability, while insufficient inclination may result in impingement and limited range of motion.
Patient-Specific Factors
- Surgeons should consider patient-specific factors such as native femoral anteversion, acetabular version, spinopelvic mobility, and soft tissue tension when determining the optimal component positioning for each individual.
- The head/neck ratio and femoral antetorsion can also influence the safe-zone of operative acetabular orientations, with larger head/neck ratios increasing the size of safe-zones 2.
Clinical Implications
- The historical target values for cup inclination and anteversion may not be a safe zone given that the majority of contemporary THAs that dislocated were within those target values 3.
- The proposed safe zone in supine position may not be a useful measure in the assessment of standing radiographs of patients with significant anterior or posterior pelvic tilt 4.
- An anatomically well-placed acetabular cup does not guarantee a well-functional orientation during daily activities, and the in vivo mechanical performance and loading conditions of the THA component during other weight-bearing activities should be investigated in further studies 5.