Can the acetabular position be derived from a pelvic frame of reference?

Area of Science:

• Orthopedic surgery
• Radiographic imaging
• Biomechanical analysis

Background:

• Acetabular center positioning significantly impacts hip function.
• Current clinical and radiographic methods for determining acetabular implant location lack accuracy and reliability.

Purpose of the Study:

• To investigate if normal acetabular position can be determined using simple, radiographically measurable pelvic dimensions.
• To establish a reliable method for preoperative planning of acetabular implant placement.

Main Methods:

• Computed tomographic (CT) scans of 37 normal hips were analyzed.
• A pelvic frame of reference was established, centered on the anterior-superior iliac spine.
• Hip center coordinates (C(x), C(y), C(z)) were expressed as percentages of corresponding pelvic dimensions (D(x), D(y), D(z)).

Main Results:

• The ratios C(x)/D(x), C(y)/D(y), and C(z)/D(z) averaged 9%, 34%, and 37%, respectively.
• These ratios demonstrated narrow distributions and high interobserver agreement (intraclass correlation coefficient = 0.95).
• Observed gender differences in ratios corresponded to up to 9 mm variations in hip center position.

Conclusions:

• The derived ratios offer a simple and dependable method for determining normal hip center position from pelvic dimensions alone.
• This approach provides surgeons with a straightforward tool for planning hip center placement.
• The method is particularly beneficial for revision hip arthroplasty and cases with significant osteophytes, dysplasia, or protrusio.