Sciatic Nerve Palsy After Total Hip Arthroplasty

COPYRIGHT © 2023 BY THE JOURNAL OF BONE AND JOINT SURGERY, INCORPORATED. Sciatic nerve (SN) injuries are well-known and potentially devastating postoperative injuries. Nerve injuries can involve compression, traction, transection, and/or ischemia. The prevalence of SNpalsies in the literature ranges between 0.08% and 3.7%. Some studies state that the posterior approach is the most commonly involved, whereas other studies do not favor one approach over the other as being a higher risk. In revision cases, it could increase between 0% to 8%. This number can be even higher because electromyographic (EMG) studies performed after a routine total hip replacementhavedemonstrated thata subclinical injury could occur in up to 70% of the cases. Although there are multiple causes described in the literature that can cause a SN palsy, in 50% of cases the reason remains unknown. Studies have shown revision surgery, surgeon inexperience, female gender, underlying spinal stenosis, and hip dysplasia as some risk factors for SN palsies. Potential intraoperative causes include patient positioning, draping, forceful dislocation of the femoral head dislocation, leg lengthening, placement of retractors with subsequent compression of the nerve, involvement of the nerve due to the use of cerclage wires, and the combination movements (hip flexion, adduction, and internal or external rotation) during femoral preparation. Multiple reduction maneuvers of a dislocated total hip arthroplasty should be limited. Multiple attempts can injure the adjacent soft tissue and/or cause a hematoma, which can either displace the nerve anteriorly into a more vulnerable position or cause compression on the nerve leading to a palsy. There are also case reports of the nerve being entrapped around the femoral neck after a reduction maneuver. The absolute lengthening threshold is controversial. Hasija et al. noted an increased risk for nerve injuries with less lengthening of “fixed” nerves (peroneal branch) compared with more “free-moving” nerves (tibial branch). Dehart and Riley demonstrated that SN injuries occurred in animal models with lengthening more than 25%. Others have demonstrated an increased risk of SN neuropraxia, after a hip replacement, with lengthening more than 2 to 3 cm. There is, however, no known maximum leg lengthening that may be performed to prevent nerve palsy. Although positioning was a contributing factor for SN injury, Takada et al. did not see a difference in the distance between the SN and the posterior acetabular edge, when patients transitioned between supine and lateral decubitus positions. Dellon included preoperative neuropathy as a risk factor that can cause nerve injuries. They concluded that surgeons should keep this inmindduring the surgery to avoid using excessive force during arthroplasty. In a retrospective study by O’Brien et al. looking at 10,624 patients who underwent a primary total hip arthroplasty, a mere 0.09% had a permanent SN palsybutdemonstrated improved sensory motor deficits. They identified female gender (reduced muscle mass; altered blood supply of the nerve after pregnancy), acetabular protrusion (nerve is closer to the acetabulum), and junior surgeonsas risk factors forSNpalsies.One