Injury to the femoral nerve is a recognized complication during abdominal, pelvic
, inguinal and hip operations. The most common surgical cause associated with femoral nerve injury has been abdominal hysterectomy, (7.5-10% incidence quoted). I don't have the number for appendectomy but I'm sure the figure is lower.
The nerve usually is inadvertently damaged (either cut, snared by suture, stretch or pressure from retractors) during the procedure.