Femoral instrumentation using the anterosuperior iliac spine as a landmark in total knee arthroplasty. An anatomic study

Twenty-six adult cadavers were utilized in an anatomic study designed to measure intramedullary femoral alignment in relation to the anterosuperior iliac spine. Fifty femurs were measured to determine the reliability of the anterosuperior iliac spine as an accurate landmark for distal femoral resection in total knee arthroplasty (TKA). A precision machined stainless steel U-shaped parallel alignment guide was fabricated and inserted into the femoral canals of intact adult cadavers. The guide's relationship to the anterosuperior iliac spine was measured and recorded. All hips were maintained in neutral alignment. Independent variables recorded included gender, knee alignment, and side of lower extremity. The range for medial deviation was 1-28 mm for the right femur and 2-25 mm for the left femur (average, 8.5 mm). The range for lateral deviation was 3-14 mm for the right femur and 2-17 mm for the left femur (average, 10.3 mm). There was no statistical correlation between the independent variables of side measured, gender, and measured offset at the anterosuperior iliac spine. Based on this highly variable pattern of alignment, utilizing simulated intraoperative technique, use of the anterosuperior iliac spine does not provide a landmark accurate enough to repeatedly produce a distal femoral resection within 2 degrees-3 degrees of ideal. Use of the anterosuperior iliac spine may lead to less than ideal femoral resection and malpositioning of total knee components.