Femoral Nerve Injuries

Allen H. Maniker

Case Presentation

Case 1

A 57-year-old male suffered a sports-related hip injury that was originally thought to be nonoperative. He subsequently developed aseptic necrosis of the right femoral head and eventually required a total hip replacement. Waking up immediately after surgery he noticed that he was having difficulty straightening his leg at the knee and lifting it up at the hip. He was also experiencing a significant amount of burning and sharp pain down the anterior surface of his leg with extreme hypersensitivity to touch. He was able to ambulate only with the use of a walker. He was first evaluated at 1 month postsurgery when strength at his iliopsoas and quadriceps femoris was 0/5. He also exhibited sensory changes in the femoral nerve distribution. Subsequent electromyography (EMG) confirmed an incomplete femoral nerve injury. At 2 months he was able to flex his leg at the hip with 4/5 strength, and the burning sensation had been replaced with nonpainful numbness. At 4 months postsurgery he had 5/5 strength in his iliopsoas and pins and needles type paresthesias into his thigh and medial leg. At 5 months postsurgery he exhibited 3/5 strength into this quadriceps muscle and was ambulating with a cane. At 7 months postsurgery his iliopsoas and quadriceps muscles were 5/5 and sensation had normalized into his leg and foot. With return to normal motor and sensory function he was discharged from care.

Diagnosis

Femoral neuropathy secondary to total hip arthroplasty

Figure 39–1 Illustration of patient’ s area of allodynia after vulvar and lymph node dissection surgery (with scar in groin outlined).

Case Presentation

Case 2

A 57-year-old female, 12 months prior, had undergone a vulvar resection and lymph node dissection for vulvar carcinoma. Postsurgically she recovered without complication. Approximately 3 months postsurgery she developed burning paresthesias along the distribution of a portion of the lateral femoral cutaneous nerve. She had been placed on gabapentin without relief. She presented to the office unable to sit due to pain and allodynia (light touch causing a painful sensation) in the noted distribution (Fig. 39–1). Multiple lidocaine injections into the area of the lateral femoral cutaneous nerve offered temporary relief and confirmed a diagnosis of lateral femoral cutaneous nerve entrapment. The nerve was exposed and found to be entrapped in dense scar tissue (Fig. 39–2). A neurolysis was performed and the patient’ s pain and allodynia resolved over the course of the next month.

Figure 39–2 Intraoperative photograph of lateral femoral cutaneous nerve entrapped in dense scar tissue

Diagnosis

Meralgia paresthetica; entrapment of the lateral femoral cutaneous nerve in postoperative scar

Anatomy

The femoral nerve takes its origin from the L2, L3, and L4 spinal nerve roots (Fig. 39–3). It is the largest branch of the lumbar plexus and goes on to supply the iliacus and psoas muscles (collectively termed iliopsoas), the pectineus, the sartorius, and the muscles that make up the quadriceps femoris (rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis). The iliopsoas muscle serves as the major flexor of the hip and the quadriceps muscles serve as the major extensor of the knee. The sartorius muscle serves to provide upward and rotatory motion of the thigh as the heel is raised to the opposite knee. The femoral nerve also supplies small articular branches to the hip and knee joint and to the adjacent vessels. Its sensory component supplies cutaneous branches to the anteromedial aspects of the thigh, leg, and medial foot down to the instep (the latter through its saphenous branch).

After the union of the anterior divisions of the second, third, and fourth lumbar spinal roots as the femoral nerve, the nerve passes inferolaterally in a retroperitoneal location, at first lying on top of the psoas muscle. It then pierces through the psoas muscle to move to the medial edge of the muscle and then travels in the groove between the psoas and the iliacus. Entering into the thigh behind the inguinal ligament it lies lateral to the femoral vascular sheath in the femoral triangle. Approximately 3.8 cm distal to the ligament it divides into multiple motor and sensory cutaneous branches. Motor branches are supplied to the muscles as already named.

Among the cutaneous sensory branches of the femoral nerve, the anterior femoral cutaneous nerves arise in the femoral triangle, pierce the fascia lata 8 to 10 cm distal to the inguinal ligament, and descend to knee level, supplying the skin and fascia over the front and medial sides of the thigh. Another branch, the saphenous nerve, is the largest and longest of the femoral branches. It arises at the femoral triangle and descends through it on the lateral side of the femoral vessels to enter the adductor canal. It crosses the vessels obliquely to lie on their medial side anterior to the lower end of the adductor magnus. In the canal, branches of the saphenous communicate with branches of the anterior femoral cutaneous nerves to form the sub-sartorial plexus. At the lower end of the canal the saphenous nerve gives off an infrapatellar branch that supplies sensation to the skin over the medial and anterior knee and the patellar ligament. The nerve continues down the medial aspect of the leg, pierces the fascia lata between the tendons of the sartorius and gracilis muscles, and gives off the sensory medial crural cutaneous branches to supply the skin of the medial leg. In the lower leg the saphenous nerve divides into its terminal branches, a smaller branch that follows the medial tibial border to the level of the ankle, and a larger branch that supplies sensation to the medial side of the foot.