I haven't had that issue, but found this info after a quick google search (the "I" in the following is a doc responding to a quesion):
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). The nerve usually is inadvertently damaged (either cut, snared by suture, stretch or pressure from retractors) during the procedure. Post op complication such as a large blood clot (iliacus hematoma) can also injure the nerve. Infection (abscess) my develop post op and cause injury.
Other causes of femoral nerve injury/problem include:lithotomy position,
trauma(bullet and stab wound, hip and pelvic fractures), tumors, diabetes.
In your case it is important to know when the weakness occur, right away, soon after surgery or delayed (such as hematoma or abscess formation)
The most useful test is an EMG of not only your quadriceps muscles but also other muscles in the area in search of involvement outside the femoral nerve territory. A nerve conduction study may be helpful too.
If you have not been evaluated by a neurologist and EMG/NCS, then you should talk to your doctor. The prognosis is dependent on the cause and the extent of the injury.
If a complete laceration of the nerve is suspected, exploration and suturing of the nerve are indicated. In lesser injuries, it is best to await spontaneous recovery for a few weeks.
The EMG should be done after at least 3 weeks after the surgery/onset of the weakness.