The obturator nerve is a peripheral nerve of the lower limb, primarily recognized for controlling movement in the thigh. It originates from the lumbar plexus, a network of nerves formed by the spinal segments L2, L3, and L4. This nerve is responsible for a large portion of the thigh’s muscle mass. Weakness or loss of feeling related to this nerve can be a clue for diagnosing conditions involving the pelvis or upper leg. It ensures the proper movement and stability of the hip and leg.
Anatomical Journey of the Obturator Nerve
The obturator nerve begins its course deep within the abdomen, emerging from the medial border of the psoas major muscle. From this origin, the nerve descends through the pelvic cavity, running along the side wall. It passes behind the common iliac arteries and travels toward a bony opening in the pelvis known as the obturator foramen.
The nerve exits the pelvis by passing through the obturator canal. This narrow passage is where the nerve is susceptible to compression or injury. Upon exiting the canal and entering the medial thigh, the nerve divides into two main branches: the anterior division and the posterior division.
The anterior division travels between the adductor longus and adductor brevis muscles. The posterior division travels deeper, passing behind the adductor brevis and lying on the front surface of the adductor magnus muscle.
Motor Innervation: Controlling the Adductor Muscles
The primary function of the obturator nerve is to provide motor control to the muscles that make up the medial compartment of the thigh, often referred to as the adductor group. These muscles are responsible for adduction, the action of pulling the leg back toward the midline of the body. The adductor muscles are also important for stabilizing the pelvis while standing and walking.
The anterior division innervates the adductor longus, the adductor brevis, and the gracilis muscle. This branch may also supply the pectineus muscle, though this is variable. The gracilis assists in flexing the knee and rotating the leg inward.
The posterior division innervates the obturator externus muscle and a large portion of the adductor magnus muscle. The obturator externus is a deep muscle that externally rotates the thigh at the hip joint. The obturator nerve supplies the adductor part of the adductor magnus, while the hamstring part is supplied by the sciatic nerve.
Sensory Innervation: Skin Supply
The sensory function of the obturator nerve is limited compared to its motor role. It provides sensation to a small area of skin on the medial side of the thigh. This cutaneous branch typically emerges from the anterior division and supplies the skin closer to the knee.
The nerve also sends articular branches, supplying sensation to the hip and knee joints. The sensory input from these branches helps the brain monitor the position and movement of the joints. The nerve’s contribution to joint sensation is an important aspect of its function.
Causes and Symptoms of Obturator Nerve Damage
Damage to the obturator nerve, known as obturator neuropathy, is uncommon but can have consequences for movement and sensation. The nerve’s deep location protects it, but it can be injured by trauma to the pelvis, such as a fracture or during difficult childbirth. Compression can also occur from tumors, swollen ligaments, or an obturator hernia, where abdominal tissue pushes into the canal.
A patient experiencing obturator neuropathy typically feels pain radiating down the medial thigh and into the groin area. This pain is often accompanied by numbness or a tingling sensation (paresthesia) in the small patch of skin the nerve supplies. The most noticeable symptom is muscle weakness, specifically the inability to adduct the thigh effectively.
This weakness leads to a characteristic “waddling gait” because the person cannot stabilize their pelvis or pull the leg toward the midline during walking. Loss of adduction strength makes movements like crossing the legs or quickly changing direction difficult. Diagnosis often involves a physical exam to test adductor strength and may be confirmed with nerve conduction tests.