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Objective: The aim of this study was to conduct a sonographic assessment of sciatic nerve thickness and stiffness following total hip arthroplasty (THA) and to determine the relationship between sonographic characteristics of the sciatic nerve and clinical outcomes., Methods: This prospective study included patients undergoing primary cementless THA due to hip osteoarthritis between January 2018 and January 2019 in a tertiary-level hospital. The thickness, strain elastography, strain ratio (SR), and shear wave elastography (SWE) of the sciatic nerve were measured. The clinical outcome measures included leg lengthening (LL), leg length discrepancy (LLD), Oxford Hip Score (OHS), Visual Analog Scale (VAS) at rest, VAS during activity, and the Leeds Neuropathic Symptoms and Signs Evaluation (LANSS) scale. The data of the patient group were assessed preoperatively and at 3, 6, and 12 months postoperatively., Results: The sciatic thickness and SR values of the operated side were significantly lower than those of the non-operated side (P < 0.05 for all). The sciatic SWE was significantly greater on the operated side compared with the non-operated side (P < 0.001 for all). Sciatic nerve thickness and SR were negatively correlated, and sciatic nerve SWE was positively correlated with OHS, VAS at rest, VAS during activity, and LANSS values. Sciatic nerve thickness and SR values were significantly lower, and SWE was significantly higher in the group with a change in LL > 20 mm. Clinical scores decreased during the following period in mild and moderate lengthening group (< 20 mm). In the severe lengthening group (≥ 20 mm), the clinical score increased over time. The VAS activity score was higher in the mild and moderate LL group (< 20 mm) than the VAS rest score (P < 0.001). However, the VAS rest score was significantly higher in the severe LL group (≥ 20 mm) than the VAS activity score (P < 0.001)., Conclusion: The results of this study have shown a significant relationship between thickness and stiffness of the sciatic nerve and LL after THA. The ultrasound parameters were significantly associated with functional outcomes., Level of Evidence: Level IV, Therapeutic Study.