Review Question - QID 220093

This patient developed a gluteus maximus lurch gait postoperatively which is indicative of weak hip extension secondary to iatrogenic injury to the inferior gluteal nerve which innervates the gluteus maximus and is at risk with screw placement in the posterior inferior quadrant of the acetabulum (Answer 1).

Transacetabular screws can be used to enhance cup fixation during total hip arthroplasty. The acetabulum is divided into quadrants by two intersecting lines. The first line extends from the anterior superior iliac spine through the center of the acetabulum to the posterior fovea. The second line is drawn perpendicular to the first line at the center of the acetabulum. The intersection of these two lines creates four quadrants, each containing specific anatomical structures. Screw placement within the "safe zone," or posterior-superior quadrant, carries a risk to the sciatic nerve and the superior gluteal nerve and vessels. Placement in the posterior-inferior quadrant, the "caution zone," poses a risk to the sciatic nerve, inferior gluteal nerve and vessels, as well as the internal pudendal nerve and vessels. The anterior-superior quadrant is referred to as a "danger zone," where screw placement can jeopardize the external iliac artery and vein. Similarly, the anterior-inferior quadrant, also known as a "danger zone," is associated with potential injury to the obturator nerve and vessel.

Wasielewski et al. conducted a review on acetabular anatomy and the application of transacetabular screw fixation in THA. They utilized cadaveric models to define four acetabular quadrants based on anatomical landmarks to guide screw placement. The posterior superior and posterior inferior quadrants were identified as the safest options due to their abundant bone stock and minimal risk to intrapelvic structures. The authors concluded that the anterior superior and inferior quadrants should be avoided to prevent injury to critical blood vessels and nerves, such as the external iliac artery and vein, as well as the obturator nerve, artery, and vein.

DeHart et al. review nerve injuries associated with THA. They report that nerve injuries occur in 1-2% of THA cases and are more prevalent in patients undergoing acetabular reconstruction for dysplasia or revision surgery. The peroneal division of the sciatic nerve is the most frequently affected, but other nerves, including the superior gluteal, obturator, and femoral nerves, may also be injured. The authors conclude that prevention is critical; however, treatments such as ankle-foot orthoses and pain management can support recovery. Furthermore, the utilization of electrodiagnostic studies intraoperatively can help guide surgical management in complex cases, although further prospective data is required before its use is standardized.

Illgen et al. review the optimal fixation methods for cementless primary THA. The authors point out that there is ongoing debate regarding the best fixation technique for the acetabular component in primary THA. However, it is well established that cementless components rely on biological fixation and demonstrate lower rates of radiographic loosening at 10 years compared to cemented components, even though their revision rates are similar. The authors conclude that cementless fixation may provide more durable long-term outcomes due to enhanced osseous ingrowth.

Figure A demonstrates the four quadrants of the acetabulum with the anterior-superior, anterior-inferior, posterior-superior, and posterior-inferior quadrants being labeled.

Incorrect Answers:
Answer 2 & 5: The sciatic nerve and superior gluteal nerve/vessels are at risk with transacetabular screw placement in the posterior-superior quadrant of the acetabulum.
Answer 3: The obturator nerve/vessels are at risk with screw placement in the anterior-inferior acetabular quadrant.
Answer 4: The external iliac artery and vein are at risk with screw placement in the anterior-superior acetabular quadrant.