Review Question - QID 219536

Effective and safe retractor placement is essential while performing the direct anterior approach for total hip arthroplasty. As the anterior retractor moves anteriorly along the acetabular rim, the femoral nerve and external iliac vessels become closer in proximity.

The direct anterior approach allows an ideal visualization of the acetabulum. However, understanding anatomy and appropriate retractor placement is key to obtaining this visualization. The femoral nerve is the closest major neurovascular structure that runs adjacent to the anterior acetabular rim. To standardize placement of retractors, the acetabulum is often described as a clock face. A line drawn from the anterior superior iliac spine (ASIS) to the center of the acetabulum can be labeled 12 o'clock. As retractor placement moves clockwise, the retractor tip moves closer to neurovascular structures. A retractor placed at the 3 o'clock position will be closest to the femoral nerve. If the retractor tip is superficial to the rectus femoris, it could bluntly injure the femoral nerve. Even if placed deep to the rectus femoris, the femoral nerve can suffer a traction injury with prolonged tension. The anterior retractor should be carefully placed and traction should only be applied when needed.

Yoshino et al performed a cadaveric study investigating the relationship between the acetabular rim and the femoral nerve. 84 cadaveric hips were dissected while in the supine position. A straight line was drawn from ASIS to the center of the acetabulum and marked as 0 degrees. The distance to the femoral nerve was then measured at 0, 30, 60, 90, 120, and 150 degrees. At 0 degrees, the nerve was 33.2 mm medial, while at 90 degrees, the nerve was 16.6 mm medial (p<0.001). They conclude that retractor placement at 90 degrees over the acetabular rim should be avoided to reduce the risk to the femoral nerve.

Sullivan et al performed a cadaver study involving 22 hips to evaluate the distance from the anterior retractor tip to the femoral nerve and external iliac vessels. They placed the anterior retractor in three separate locations deep to the indirect head of the rectus femoris and then dissected the neurovascular structures to measure the distance. As the retractor was moved anteriorly and down the acetabular rim, the tip of the retractor moved from lateral to medial of the femoral nerve. They conclude that the anterior retractor should be placed in a superior position to avoid damage to neurovascular structures.

Figure A shows an illustration of the acetabulum with lines indicating retractor placement options.

Incorrect Answers:
Answer 2- The retractor should be placed deep to the indirect head of the rectus femoris.
Answers 3,4,5- Increasing anterior placement along the acetabular rim moves the retractor closer to the femoral nerve.