Acetabular Component Retroversion in Hip Implants
Acetabular component retroversion means the artificial hip socket is oriented too far posteriorly (backward), causing the opening of the cup to face more posterolaterally instead of the normal anterolateral direction, which significantly increases the risk of hip dislocation and impingement. 1, 2
Definition and Orientation
Retroversion refers to the posterior (backward) tilt or rotation of the acetabular component relative to the pelvis. 2
- In a properly positioned acetabular component, the opening should face anterolaterally with approximately 15° of radiological anteversion 1
- A retroverted component has reduced or negative anteversion, meaning the cup opening faces more posteriorly than intended 2, 3
- This malposition can occur when the surgeon implants the component following the native acetabular anatomy in patients with congenital acetabular retroversion, or due to technical error during implantation 3
Clinical Significance and Complications
Retroversion dramatically increases dislocation risk, particularly posterior dislocations which are the most common type after total hip arthroplasty. 1
Dislocation Risk
- Patients with posterior dislocation after primary THA showed significantly reduced mean anteversion angles (11° compared to 15° in controls) 1
- After revision surgery, patients with posterior dislocation demonstrated even more pronounced retroversion (mean 12° anteversion, 40° abduction) 1
- The optimal safe zone for acetabular positioning is 15° anteversion and 45° abduction to minimize dislocation risk 1
Range of Motion Limitations
- Retroverted acetabular components cause significant ROM deficiencies, averaging 25-29% reduction in multiple movement planes 3
- Anterior impingement occurs between the femoral neck and the anterior acetabular rim during hip flexion and internal rotation 2, 3
- Surface replacement arthroplasty (SRA) is particularly problematic in retroverted acetabula, showing ROM deficits in 4 of 6 movement maneuvers 3
Assessment on Imaging
Radiographs are the first-line imaging modality for evaluating acetabular component position and detecting retroversion. 4, 5
- Component position can be assessed on standard AP pelvis and lateral hip radiographs 4
- CT with metal artifact reduction (MAR) provides superior detailed assessment of component positioning when radiographs are equivocal 4, 5, 6
- Serial radiographs allow comparison but may be affected by differences in hip flexion or rotation 5
Management Considerations
Prevention through accurate intraoperative positioning is critical, as malposition is a primary risk factor for revision surgery. 1, 7
Surgical Technique
- Surgeons must not blindly follow native acetabular anatomy in patients with congenital acetabular retroversion 3
- Intraoperative navigation reduces malposition risk by 5-fold compared to freehand techniques (85% accuracy vs 25% in freehand placement) 7
- In retroverted acetabula, increasing femoral stem anteversion by 10° can partially compensate for acetabular retroversion and restore ROM in most positions 3
Revision Surgery
- Retroverted components contributing to instability or impingement require revision with proper reorientation to the safe zone 1, 8
- Large hemispherical or "jumbo" cups with porous ingrowth surfaces can be used for most revisions 8
- Achieving component stability with sufficient host bone contact is mandatory during revision 8
Key Clinical Pitfalls
The most common error is placing the acetabular component in the anatomic position when the native acetabulum is retroverted, perpetuating the malposition. 3
- Always assess preoperative imaging for native acetabular version, particularly in younger patients or those with hip dysplasia 2
- Do not assume that matching native anatomy will provide optimal component positioning 3
- Consider using navigation or computer-assisted techniques for complex cases or revision surgery to ensure accurate component placement 7