The accessory obturator nerve is a relatively infrequent anatomical variant that is present in about 10-30% of individuals. When it exists, it usually arises from the ventral divisions of the L3 and L4 spinal nerves, which are part of the lumbar plexus.
Structure
- Type: The accessory obturator nerve is a mixed nerve, which means it carries both sensory and motor fibers, although its primary function is motor innervation.
- Branches: The nerve usually doesn’t have significant branching; instead, it generally proceeds to the target muscles directly.
Location
- Origination: The nerve originates from the lumbar plexus, generally from the ventral divisions of the L3 and L4 spinal nerves.
- Course: After originating from the lumbar plexus, the accessory obturator nerve descends along the medial border of the psoas major muscle, exiting the pelvis usually by passing over the superior pubic ramus.
- Innervation Targets: The accessory obturator nerve typically supplies the pectineus muscle, and occasionally, it may also supply the hip joint. In some cases, it may contribute to the cutaneous innervation of the medial thigh, although this is less common.
Functions of Accessory obturator nerve
The accessory obturator nerve is primarily involved in motor innervation, with limited or rare sensory functions. Its presence is variable, and it is not found in every individual. Here are its primary functions:
Motor Functions
- Pectineus Muscle: The most common target for the accessory obturator nerve is the pectineus muscle. The pectineus is one of the muscles that adduct the thigh, bringing it toward the midline of the body. This muscle also assists in flexing the thigh at the hip joint.
- Hip Joint: In some instances, the accessory obturator nerve may also provide minor innervation to the hip joint.
Sensory Functions
Limited Role: The accessory obturator nerve may occasionally have a sensory role, contributing to the cutaneous innervation of the medial thigh. However, this is relatively rare and not its primary function.
Integrated Functions
- Adduction and Flexion: Through its motor innervation of the pectineus muscle, the accessory obturator nerve contributes to the coordinated movements of adduction and flexion at the hip joint.
- Gait and Posture: Although its role is minor compared to the main obturator nerve, the accessory obturator nerve helps in maintaining proper gait and posture by facilitating adequate muscle tone and function in the pectineus muscle.
The accessory obturator nerve, while not present in all individuals, can have specific clinical significance when it does exist. Here’s a brief note on its clinical relevance:
Surgical Implications
- Pelvic and Lower Abdominal Surgeries: Awareness of the potential presence of the accessory obturator nerve is crucial during surgeries involving the pelvis and lower abdomen, such as gynecological procedures or hernia repairs, to avoid inadvertent injury.
- Hip Surgery: In hip surgeries or hip joint replacements, the accessory obturator nerve, if present, could potentially be at risk. Surgeons should be cautious to identify and preserve it.
Diagnostic Considerations
- Motor Function: Weakness in the pectineus muscle or issues with hip adduction might suggest an issue with the accessory obturator nerve, if present. This could be evaluated with electrophysiological studies like EMG (Electromyography).
- Pain or Sensory Disturbances: Though it’s rare, if there are unexplained sensory symptoms in the medial thigh region or the hip joint, the accessory obturator nerve could be considered as part of the differential diagnosis.
Anesthetic Implications
Regional Anesthesia: In procedures requiring regional anesthesia of the adductor muscles of the thigh or the hip joint, awareness of the accessory obturator nerve’s presence may be important for complete anesthesia.
