For each individual, the femoral nerve shows various shapes and locations. This is because the femoral nerve is located on top of the iliacus muscle, so the shape and location of the femoral nerve seems to be related to the patient's muscle mass. Ultrasound of the quadriceps femoris could represent a widely available, non-invasive, affordable, and reliable tool to evaluate skeletal muscle. We aim to investigate the relationship between muscle mass and the shape of the femoral nerve through this observational study.

Inclusion Criteria:

1. Patients aged 19 years old or older and scheduled for elective total knee arthroplasty

Exclusion Criteria:

1. Pre-existing neurologic or anatomic deficits in the lower extremities

patients undergoing total knee arthroplasty