Common Fibular Nerve Injury Case File

Common Fibular Nerve Injury Case File

Eugene C. Toy, MD, Lawrence M. Ross, MD, PhD, Han Zhang, MD, Cristo Papasakelariou, MD, FACOG

CASE 8

A 23-year-old female is seen on the postpartum floor the day after delivering a 9-lb baby boy. She is concerned about her right foot, which has become numb and weak since delivering the baby. Walking has been difficult for her because her right foot tends to drop, and her toes drag. When asked about her labor course, she reports that she had an epidural with satisfactory pain relief but a difficult and prolonged pushing stage of labor (3 h) in stirrups. She denies any back pain or problems with the other leg. On exam, she has decreased sensation on the top of the right foot and lateral side of the lower leg along with an inability to dorsiflex the right foot, resulting in a foot drop. Minimal peripheral edema is seen in both lower extremities.

⯈ What is the most likely diagnosis?

⯈ What factors likely led to this condition?

ANSWER TO CASE 8:

Common Fibular Nerve Injury

Summary: A 23-year-old female postpartum day 1 with right foot weakness, numbness, and foot drop after a difficult vaginal delivery.

• Most likely diagnosis: Common fibular nerve injury (compression)

• Factors leading to injury: Prolonged compression of common fibular nerve by stirrups and flexion at the knee

CLINICAL CORRELATION

Compression of the common fibular nerve during labor is the most common postpartum nerve injury of the lower extremity. Compression of the common fibular nerve occurs from both the flexion of the knees and compression from stirrup on lateral aspect of knee. The common fibular nerve may also be injured during knee surgery, trauma, or prolonged periods of compression (coma, deep sleep, lower-extremity cast). Because of the epidural anesthesia, the patient likely felt no pain from the prolonged compression. Injury to the common fibular nerve causes numbness, weakness to the lower leg and foot, and foot drop (inability to dorsiflex the foot). The majority of compression injuries after delivery are self-limiting and improve with supportive care. Proper positioning of the patient requires a good understanding of anatomy to avoid periods of prolonged nerve compression.

APPROACH TO:

Lower Limb

OBJECTIVES

1. Be able to describe the origin, course, muscles innervated, and distal cutaneous regions supplied by the sciatic nerve and its tibial and common fibular branches

2. Be able to describe the origin, course, muscles innervated, and distal cutaneous regions supplied by the femoral and obturator nerves

DEFINITIONS

Epidural: The space external to the spinal cord’s dura mater; anesthetic agents are injected into this space for epidural anesthesia

Nerve compression: Pressure on a nerve such that neural transmission is temporarily blocked

Dorsiflexion: Decrease in the angle between the lower leg and foot, as with walking on one’s heels; the opposite of plantarflexion, as standing on tiptoe

DISCUSSION

The sciatic nerve (L4−S3) is the largest nerve in the body, arising from the lumbosacral plexus. It exits the pelvis through the greater sciatic foramen, inferior to the piriformis muscle (see Figure 8-1). The sciatic nerve is actually two nerves, the tibial (medial) and common fibula (lateral) nerves, loosely bound together by connective tissue. The tibial nerve is derived from the anterior division of the anterior rami, while the common fibular is derived from the posterior division of the anterior rami. No muscles of the gluteal region are innervated by the sciatic nerve. It descends in the posterior compartment of the thigh, where its tibial nerve innervates all the muscles (hip extensors and knee flexors) of the posterior thigh except the short head of the biceps femoris (innervated by the common fibular nerve). At approximately superior angle of the popliteal fossa, the tibial and common fibular portions separate.

The common fibular nerve passes laterally, superficially, and courses around the neck of the fibula subcutaneously, where it risks injury or compression (Figure 8-2). It then divides into its superficial fibular nerve, which innervates the fibular muscles (evertors) of the lateral compartment of the leg, and the skin of the lateral leg and dorsum of the foot. The deep fibular nerve enters the anterior compartment of the leg, and innervates the muscles of this compartment (dorsiflexors), intrinsic dorsal foot muscles, and skin between the great and second toe. Severing the deep fibular nerve results in a foot drop.

The tibial nerve descends through the popliteal fossa and enters the posterior compartment of the leg to innervate the posterior compartment muscles (plantarflexors and invertors). It also gives off a medial sural branch which joins the communicating sural branch of the common fibular to form the sural nerve, which is sensory to the posterior aspect of the leg and lateral foot. At the level of the posterior malleolus, the tibial nerve divides into the lateral and medial plantar nerves, which innervate the intrinsic muscles and skin of the sole of the foot. Severing the tibial nerve in the leg results in an inability to stand on tiptoe.

The femoral nerve (L2−L4) arises from the lumbar plexus. It exits the abdomen posterior to the inguinal ligament and lies lateral to and outside the femoral sheath and its contents. It innervates the muscles (hip flexors and knee extensors) of the anterior compartment of the thigh and the skin of the anterior thigh and medial leg. The obturator nerve (L2−L4) exits the abdomen through the obturator canal and enters the medial compartment of the thigh to innervate these muscles (adductors) and a patch of skin on the medial side of the thigh.

Figure 8-1. Innervation of the thigh. (Reproduced, with permission, from Lindner HH. Clinical Anatomy. Norwalk, CT: Appleton & Lange, 1989.)

Figure 8-2. Innervation of the lower leg. (Reproduced, with permission, from Lindner HH. Clinical Anatomy. Norwalk, CT: Appleton & Lange, 1989:50.)

COMPREHENSION QUESTIONS

8.1 During an abdominal hysterectomy for a cancerous uterus, the obturator nerve was accidentally severed. This resulted in the patient losing which of the following actions?

A. Extension of the leg at the knee

B. Extension of the thigh at the hip

C. Adduction of the thigh at the hip

D. Flexion of the leg at the knee

E. Dorsiflexion of the foot at the ankle

8.2 A patient comes to you complaining of his inability to stand on tiptoe. Which of the following nerve injuries is most likely to be involved?

A. Femoral nerve

B. Tibial nerve

C. Common fibular nerve

D. Deep fibular nerve

E. Superficial fibular nerve

8.3 A 32-year-old woman is brought into the emergency department because she is unable to evert her foot at the ankle. Which of the following nerve injuries is most likely to be involved?

A. Femoral nerve

B. Obturator nerve

C. Tibial nerve

D. Deep fibular nerve

E. Superficial fibular nerve

8.4 A 14-year-old male is placed in a left lower leg cast after a skateboarding accident. After he has been in the cast for 3 weeks, he complains of some numbness of the “top of the left foot.” On exam, he is noted to be unable to dorsiflex his left foot. What is the most likely location of the nerve compression in this patient?

A. Lateral malleolus

B. Medial malleolus

C. Tarsal canal

D. Fibular head

E. Popliteal fossa

ANSWERS

8.1 C. The obturator nerve innervates the muscles of the medial compartment of the thigh which adduct the thigh at the hip.

8.2 B. The plantarflexors are located in the posterior compartment of the leg and innervated by the tibial nerve.

8.3 E. The muscles of the lateral compartment of the leg evert the foot and are innervated by the superficial fibular nerve.

8.4 D. This young man likely has compression of the common peroneal nerve as the nerve traverses laterally around the fibular head, where it is relatively superficial and not well protected. Injury to the common peroneal nerve leads to “foot drop” and inability to dorsiflex.

ANATOMY PEARLS

⯈ The muscles of the posterior thigh, leg, and sole of the foot are all innervated by the tibial nerve (except the short head of the biceps femoris).

⯈ The dorsiflexor muscles are innervated by the deep fibular nerve.

References

Gilroy AM, MacPherson BR, Ross LM. Atlas of Anatomy, 2nd ed. New York, NY: Thieme Medical Publishers; 2012:446−448. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy, 7th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2014:574−575, 586−587, 592, 596. Netter FH. Atlas of Human Anatomy, 6th ed. Philadelphia, PA: Saunders; 2014: plates 525−529.

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