Femoral nerve

The femoral nerve is the largest branch of the lumbar plexus, originating from the L2, L3, and L4 spinal nerves. It is responsible for providing motor and sensory innervation to the anterior thigh, part of the lower leg, and parts of the pelvic region. This nerve plays a key role in the movement of the thigh and leg, as well as sensory perception in these areas.

Location

The femoral nerve originates in the lumbar region, specifically from the lumbar plexus, and travels down the posterior abdominal wall. It passes beneath the inguinal ligament and enters the thigh through the femoral triangle, where it lies lateral to the femoral artery. Once in the thigh, it divides into several branches, innervating the quadriceps muscle group and providing sensory innervation to the skin of the anterior and medial thigh, and part of the lower leg through its branches like the saphenous nerve.

Anatomy

Origin

The femoral nerve arises from the lumbar plexus, specifically from the ventral rami of L2, L3, and L4 spinal nerves. These spinal nerve roots converge within the psoas major muscle in the posterior abdominal wall, forming the femoral nerve, which then emerges along the lateral border of the psoas major.

Course

The femoral nerve follows a distinct pathway from its origin in the lumbar region to its terminal branches in the thigh and lower leg.

Lumbar Region

In the lumbar region, the femoral nerve runs along the lateral edge of the psoas major muscle, staying within the posterior abdominal wall. It courses deep to the iliacus muscle, which it partially innervates. Here, it is positioned between the psoas major and iliacus muscles as it continues to descend toward the pelvis.

Pelvic Region

The femoral nerve exits the pelvic cavity by passing beneath the inguinal ligament, a fibrous band running from the anterior superior iliac spine (ASIS) to the pubic tubercle. This ligament forms the boundary between the pelvis and thigh, and the femoral nerve travels through the sub-inguinal space, alongside important structures like the femoral artery and femoral vein.

Femoral Triangle

Once the femoral nerve passes beneath the inguinal ligament, it enters the femoral triangle in the upper thigh. The femoral triangle is a wedge-shaped space bounded by the inguinal ligament (superiorly), the sartorius muscle (laterally), and the adductor longus muscle (medially). Within this region, the femoral nerve is located lateral to the femoral artery and femoral vein. The nerve remains outside the femoral sheath, which encloses the artery and vein.

Branches in the Thigh

After entering the femoral triangle, the femoral nerve divides into several branches, both motor and sensory, that innervate various structures of the thigh and lower leg.

• Anterior Division: This division contains sensory and motor branches.
  • Intermediate cutaneous nerve of the thigh: Provides sensory innervation to the anterior aspect of the thigh.
  • Medial cutaneous nerve of the thigh: Provides sensory innervation to the medial thigh.
  • Motor branches: Innervate the sartorius muscle.
• Posterior Division: This division primarily supplies motor branches to the quadriceps muscle group and a sensory branch.
• • Nerve to quadriceps femoris: Innervates the quadriceps muscle group, including the rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius.
  • Saphenous nerve: The largest sensory branch of the femoral nerve, it provides sensory innervation to the medial leg and foot. It travels down the thigh, enters the adductor canal, and continues its path along the medial leg and foot.

Branches of the Femoral Nerve

The femoral nerve divides into several branches that provide both motor and sensory innervation to the thigh and lower leg. These branches can be grouped into motor and sensory branches.

Motor Branches

The motor branches of the femoral nerve primarily supply the muscles of the anterior compartment of the thigh, including:

• Iliacus muscle: The femoral nerve provides innervation to the iliacus muscle as it runs along the lateral side of the psoas major muscle.
• Pectineus muscle: The femoral nerve innervates the pectineus muscle, which is located in the upper part of the medial compartment of the thigh.
• Sartorius muscle: The longest muscle in the body, the sartorius receives motor innervation from the femoral nerve.
• Quadriceps femoris: This powerful group of muscles, including the rectus femoris, vastus medialis, vastus intermedius, and vastus lateralis, is innervated by the posterior division of the femoral nerve.

Sensory Branches

The sensory branches of the femoral nerve supply the skin of the anterior thigh and medial leg, as well as portions of the medial knee and foot.

• Anterior cutaneous branches: These branches include the intermediate and medial cutaneous nerves of the thigh, which supply the skin over the anterior and medial aspects of the thigh, respectively.
• Saphenous nerve: As the terminal branch of the femoral nerve, the saphenous nerve is a key sensory nerve providing innervation to the skin over the medial side of the leg and foot. It travels down the thigh within the adductor canal and becomes superficial near the knee, continuing along the medial aspect of the leg and ankle.

Anatomical Relations

The femoral nerve has important anatomical relationships with several structures during its course:

• Psoas Major Muscle: The femoral nerve emerges from the lateral border of the psoas major, which forms part of the posterior abdominal wall.
• Iliacus Muscle: The femoral nerve runs between the iliacus and psoas major muscles and innervates the iliacus muscle before passing under the inguinal ligament.
• Inguinal Ligament: The nerve passes beneath this ligament, entering the thigh through the sub-inguinal space.
• Femoral Artery and Vein: In the femoral triangle, the femoral nerve is located lateral to the femoral artery and vein. The nerve remains outside the femoral sheath, which encloses these vessels.

Variations

Anatomical variations of the femoral nerve are uncommon but may occur. Some individuals may exhibit:

• Variations in branching patterns: The branches of the femoral nerve may differ slightly in terms of their origin or course.
• Additional or absent branches: In rare cases, individuals may have extra or missing branches, particularly in the cutaneous branches that supply the skin of the thigh.

Vascular Supply

The femoral nerve receives blood supply from the branches of the iliac arteries, particularly from the external iliac artery as it descends through the pelvis, and from the femoral artery in the thigh. These vessels provide nutrients and oxygen to the nerve along its course.

Termination

The femoral nerve terminates primarily as the saphenous nerve after giving off its motor and sensory branches. The saphenous nerve continues to provide sensory innervation to the medial aspect of the leg and foot, extending down toward the ankle and the medial arch of the foot.

Function

The femoral nerve plays a critical role in both motor and sensory innervation, primarily supplying the anterior thigh muscles and the skin of the anterior and medial thigh, as well as the medial leg and foot. Its functions are essential for lower limb movement, particularly in activities like walking, running, and maintaining posture. Below is a detailed description of its key functions.

Motor Function

The femoral nerve provides motor innervation to several muscles of the anterior thigh. These muscles are primarily responsible for movements at the hip and knee joints, enabling flexion of the hip and extension of the knee.

Hip Flexion

The femoral nerve innervates muscles that allow the thigh to be flexed at the hip joint, a movement that is crucial for walking, climbing stairs, and other leg movements.

• Iliacus Muscle: The femoral nerve supplies the iliacus muscle, which, along with the psoas major (innervated by lumbar plexus), forms the iliopsoas muscle group. This muscle group is the primary hip flexor, responsible for lifting the thigh towards the body during activities like walking, running, or kicking.
• Pectineus Muscle: Another muscle innervated by the femoral nerve, the pectineus contributes to hip flexion and also assists in adduction of the thigh. It plays a role in bringing the thigh closer to the body, particularly during walking or squatting motions.
• Sartorius Muscle: The sartorius is the longest muscle in the body and is responsible for flexing, abducting, and externally rotating the hip. It also helps in knee flexion. The femoral nerve innervates this muscle, allowing it to function in complex movements such as sitting cross-legged (tailor’s position).

Knee Extension

The femoral nerve is critical for extending the knee, a movement required for standing, walking, and running. It innervates the quadriceps femoris muscle group, which is the primary extensor of the knee.

Quadriceps Femoris Muscle Group: The quadriceps muscle consists of four parts: the rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. All four muscles are innervated by the femoral nerve and work together to extend the knee joint. The rectus femoris also contributes to hip flexion, as it spans both the hip and knee joints. Knee extension is essential for movements like standing up from a seated position, walking, running, and jumping.

Sensory Function

The femoral nerve also provides sensory innervation to the skin of the anterior and medial thigh, as well as the medial aspect of the leg and foot via its terminal branches. Sensory fibers from the femoral nerve transmit signals related to touch, pain, temperature, and proprioception to the central nervous system.

Anterior Thigh Sensation

The anterior cutaneous branches of the femoral nerve supply sensory innervation to the skin over the anterior aspect of the thigh. These branches include:

• Intermediate cutaneous nerve of the thigh: Provides sensory innervation to the middle portion of the anterior thigh.
• Medial cutaneous nerve of the thigh: Supplies the medial portion of the anterior thigh, ensuring the sensation of the skin in this area.

These branches allow the body to detect sensations such as:

• Touch: The ability to feel light and deep touch over the anterior and medial aspects of the thigh.
• Pain: Transmission of pain signals from injuries or trauma to the skin of the thigh.
• Temperature: Detection of hot and cold stimuli affecting the skin.

Medial Leg and Foot Sensation

The saphenous nerve, the longest sensory branch of the femoral nerve, provides sensory innervation to the skin of the medial side of the leg, medial knee, medial malleolus, and medial foot. It is essential for the transmission of sensory information from these regions.

• Medial Knee and Leg: The saphenous nerve supplies sensation to the skin over the medial knee and leg, providing important feedback during walking and balance maintenance. This feedback includes:
  • Touch and Pressure: Sensing light touch, pressure from clothing or footwear, and environmental stimuli.
  • Proprioception: Sensing the position and movement of the leg, which is crucial for balance and coordination during walking or running.
• Medial Ankle and Foot: The saphenous nerve continues its course down to the medial malleolus and the arch of the foot, transmitting sensory signals such as:
  • Temperature: Detecting changes in temperature, such as from water or surfaces underfoot.
  • Pain and Injury: Allowing for the detection of cuts, abrasions, or other trauma to the medial foot and ankle.

Contribution to Reflexes

The femoral nerve also plays a role in the lower limb reflex arcs, especially those related to the knee joint.

Patellar Reflex (Knee Jerk Reflex)

The patellar reflex is one of the most commonly tested reflexes and involves the femoral nerve. When the patellar tendon is tapped, it causes a rapid contraction of the quadriceps muscle group, resulting in the extension of the knee. This reflex is a key test in neurological examinations to assess the integrity of the femoral nerve and the L2-L4 spinal segments.

Integration with the Lumbar Plexus

The femoral nerve functions as a major part of the lumbar plexus, where it receives contributions from the L2, L3, and L4 spinal nerves. This nerve network provides the femoral nerve with motor and sensory fibers that allow it to innervate the anterior compartment of the thigh, the skin of the thigh, and the medial leg.

The femoral nerve’s integration with the lumbar plexus ensures coordination with other lumbar and sacral nerves, contributing to the overall function of the lower limb.

Clinical Significance

The femoral nerve is vital for both motor and sensory functions in the lower limb. Damage to this nerve can lead to significant impairments in mobility and sensation, primarily affecting the anterior thigh, knee, and medial leg.

Common Causes of Injury

• Trauma: Direct injury to the femoral nerve, such as from pelvic fractures, penetrating injuries, or blunt trauma, can lead to nerve dysfunction.
• Surgical Complications: The femoral nerve may be inadvertently damaged during abdominal, pelvic, or hip surgeries, such as hernia repairs or hip replacements.
• Compression or Entrapment: Conditions such as retroperitoneal hematomas or tumors can compress the femoral nerve, leading to motor or sensory deficits.

Symptoms of Femoral Nerve Injury

• Motor Impairment: Weakness or paralysis of the quadriceps muscles leads to difficulty with knee extension, making walking, standing, or climbing stairs challenging.
• Sensory Loss: Numbness, tingling, or loss of sensation can occur in the anterior thigh, medial leg, or foot due to damage to the sensory branches, including the saphenous nerve.
• Patellar Reflex Loss: Injury to the femoral nerve can lead to loss of the patellar reflex (knee jerk), an important clinical sign of femoral nerve dysfunction.