A New Normative Zone for Acetabular Anteversion Positioning in ASD Patients

Area of Science:

• Orthopedic Surgery
• Biomedical Engineering
• Spine Surgery

Background:

• Adult spinal deformity (ASD) patients undergoing total hip arthroplasty (THA) have higher hip dislocation rates compared to those with normal spinal alignment.
• The traditional Lewinnek safe zone for acetabular implant placement is insufficient for ASD patients due to significant spinopelvic variations like pelvic retroversion.

Purpose of the Study:

• To define and validate patient-specific normative zones for acetabular anteversion in ASD patients.
• To develop a method for optimizing acetabular cup placement that accounts for individual spinopelvic alignment and surgical plans, aiming to reduce dislocation risk.

Main Methods:

• A multicenter retrospective analysis involving 146 ASD patients and 47 asymptomatic controls.
• Three-dimensional biplanar radiograph reconstructions were used to measure spinopelvic alignment and acetabular orientation.
• Three distinct normative zones for acetabular anteversion were defined based on pelvic tilt and pelvic incidence, considering different surgical scenarios (no spinal realignment, post-spinal realignment, uncertain plans).

Main Results:

• Normative Zone 1 (no spinal realignment) and Zone 2 (post-spinal realignment) were delineated using specific regression formulas based on pelvic tilt and incidence.
• Normative Zone 3, the intersection of Zones 1 and 2, provided a narrower target anteversion range for complex cases.
• These patient-specific zones enable tailored acetabular cup placement, considering individual spinopelvic parameters.

Conclusions:

• The study successfully defined patient-specific normative zones for acetabular anteversion, addressing limitations of traditional methods in ASD patients.
• Implementing these tailored zones has the potential to significantly reduce the risk of hip dislocation in patients with spinal malalignment undergoing THA.
• This approach offers a clinically significant advancement in optimizing acetabular component positioning for complex orthopedic cases.