Safe Retractor Placement during Direct Anterior THA

One of my residency mentors always stressed that orthopaedic surgeons should be “masters of musculoskeletal anatomy.” During his first lecture each July, he would grill the junior residents on muscle origins and insertions, along with innervations. Knowing safe surgical planes helps us avoid complications from neural or vascular injury and increases the likelihood of a successful orthopaedic procedure. With the increased popularity of the direct anterior approach (DAA) for total hip arthroplasty (THA), it is crucial that orthopaedists understand the anatomical implications of that technique.

One key to a successful DAA hip replacement is adequate visualization, which is aided by retractors. However, malpositioned retractors can cause femoral nerve palsy, a potentially serious neurological complication that can delay postoperative rehabilitation. In the January 15, 2020 issue of The Journal, Yoshino et al. report on a cadaveric study that quantifies the distance between the femoral nerve and the acetabular rim at varying points along the rim. Knowing these precise distances could help surgeons make safer decisions about where—and where not—to place retractors.

The authors dissected 84 cadaveric hips from 44 formalin-embalmed cadavers and measured the distance from the femoral nerve to various points along the acetabular rim by using a reference line drawn from the anterior superior iliac spine (ASIS) to the center of the acetabulum. They found the femoral nerve was closest to the rim (only 16.6 mm away) at the 90° point.

In addition, at 90°, the thickness of the iliopsoas muscle and the femoral length (a probable proxy for size of the patient) were positively associated with increased distance to the nerve. Other anatomic factors such as inguinal ligament length, femoral head diameter, and thickness of the capsule were not associated with the nerve-rim distance.

The degree nomenclature used by Yoshino et al. can be correlated to a clock-face representation of the acetabulum, with the 60° point at the 3 o’clock (anterior) position; the 30° point represents a relatively safe  location for placement of the anterior inferior iliac spine retractor (see Figure above).

This important anatomic study can help us improve our mastery of musculoskeletal anatomy—and avoid, if possible, placement of retractors at 90° relative to a line drawn from the ASIS to the center of the acetabulum.

Matthew R. Schmitz, MD
JBJS Deputy Editor for Social Media

Tags: , , , , ,

2 responses to “Safe Retractor Placement during Direct Anterior THA”

  1. Klaue says :

    No comment about the nervus femoris cutaneus lateralis?

    Like

  2. Shyan Goh says :

    Yoshino et al. contribute to an increasing body of study on the positions of neurovascular structures relative to the acetabular landmarks. The perspective of various other authors (references happily supplied upon request) is interesting.The perception that the positioning of the soft tissue retractors on the anterior column of the acetabulum is the main reason for the high prevalence of femoral nerve injury relative to posterior or posterolateral approaches may not make complete sense, since the placement of retractors to expose the acetabulum in posterior approach may not be that much different than those described in the DAA papers. Given the similarities of the retractor placement, the true key to the causation of femoral nerve injury may be the amount of retraction and reliance of the anterior retractor to achieve adequate exposure.

    I am not well-versed in DAA hip surgery, but my limited knowledge suggests that anterior acetabular retraction is vital to adequate surgical exposure and that significant levering forces may be required to maintain safe access. If this is true, then the superior placement of the anterior retractors may not be adequate to prevent femoral nerve injury, and worse, could result in poor and even unsafe surgical exposure for DAA.

    Thus a recommendation of a safe zone for anterior acetabular retraction should be coupled with an appropriately designed retractor instrument to go with it.

    Like

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: