Review Question - QID 217489

Moving the fascial incision more lateral to be over the muscle belly of the tensor fascia latae muscle belly decreases rates of injury to the lateral femoral cutaneous nerve.

The direct anterior approach for hip arthroplasty utilizes the superficial interval between the tensor fascia latae and the sartorius. Postoperatively many patients have numbness over the anterolateral thigh caused by injury or neuropraxia to the lateral femoral cutaneous nerve. This nerve originates from contributions from the L2 and L3 nerve roots and then travels through the iliacus muscle before gaining access to the thigh after passing under the inguinal ligament and then piercing the fascia latae; most variants pass either in the sartorius fascia or take an early posterior branching position and head towards the posterior thigh before traveling distally. Making the fascial incision lateral to the interval and directly over the tensor fascia latae muscle belly helps avoid the common paths of the lateral femoral cutaneous nerve and minimizes risk of injury to this structure.

Rudin et al review the anatomic course of the lateral femoral cutaneous nerve as it relates to direct anterior total hip arthroplasty. They report finding 3 different branching patterns: sartorius-type (in 36% of the specimens), characterized by a dominant anterior nerve branch coursing along the lateral border of the sartorius muscle with no, or only a thin, posterior branch; posterior-type (in 32%), characterized by a strong posterior nerve branch; and fan-type (in 32%), characterized by multiple spreading nerve branches of equal thickness. They conclude that injury is unavoidable in 30% of patients and that the incision should be kept as lateral as possible to minimize chance of injury.

Patton et al review clinical outcomes of patients with lateral femoral cutaneous nerve injury following direct anterior THA. They report that "numbness" occurred in 37% percent of patients following direct anterior total hip arthroplasty. They conclude that these symptoms improved over time and that at final follow up of 6-8 years only 11% of patients report continued symptoms.

Illustration A is a cadaveric dissection highlighting the path of the lateral femoral cutaneous nerve.

Incorrect Answers:
Answer 1: The femoral neurovascular bundle is medial to the rectus and should not be encountered during dissection utilizing this approach.
Answer 3 & 4: Improving trajectory for acetabular and femoral preparation is achieved with adequate and purposeful releases. Moving the fascial incision laterally rather than directly over the interval does not significantly influence exposure.
Answer 5: No change in prosthetic joint infection rates have been reported by moving the fascial incision laterally.