Obturator nerve lesions

Obturator nerve lesions are uncommon. They manifest as:

• Inability to adduct the leg
• Variable loss of sensation on the inner aspect of the thigh

Anatomy

Course of the obturator nerve

• Derived from L2, L3, L4 nerve roots
• Arises from the lumbar plexus
• Travels down the medial border of the psoas muscle (femoral nerve travels lateral)
• Enters the obturator foramen, dividing into anterior and posterior branches

Anterior division:

• Passes through the adductor canal with obturator vessels
• Runs behind pectineus and adductor longus, in front of adductor brevis
• Terminates as a sensory nerve to the medial thigh

Posterior division:

• Pierces obturator externus
• Passes behind adductor brevis and in front of adductor magnus
• Enters adductor canal and ends as a sensory branch to the knee joint

Obturator nerve innervations

Anterior division:

• Gracilis – adducts thigh, flexes knee
• Adductor brevis – adducts thigh
• Adductor longus – adducts thigh
• Sensory branch to medial thigh

Posterior division:

• Obturator externus – laterally rotates thigh
• Adductor magnus (adductor part) – adducts thigh
• Sensory branch to knee joint

Pathology

Causes of obturator nerve lesions

1. Trauma
   • Typically associated with pelvic fractures
2. Neuropraxias
   • Compression between fetal head and bony pelvis
   • Malposition of lower limb
   • Entrapment in adductor magnus (athletes)
   • Compartment syndrome of medial thigh
3. Mass lesions
   • Tumours
   • Abscesses
4. Neuropathies
   • Rarely affect obturator nerve
   • Consider diabetes, malignancy, infections, autoimmune causes if part of mononeuritis multiplex

Clinical assessment

In severe injuries:

• Loss of adduction and internal rotation
• Gait disturbance: externally rotated foot

Investigations

Blood tests (based on clinical suspicion):

1. FBC
2. U&Es / glucose
3. CRP
4. ESR
5. Others as indicated (e.g., lead levels)

CT scan – to assess for mass lesions
MRI – can visualise mass lesions and nerve involvement

Management

1. Treat underlying cause
2. Neuropraxias
   • Fasciotomy for compartment syndrome
3. Occupational therapy
   • Splinting and support
4. Physiotherapy
   • Recovery support or prevent secondary complications

Disposition

Disposition depends on:

• Cause of lesion
• Severity of symptoms
• Acuteness of onset

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References

Publications

• Brazis PW, Masdeu JC, Biller J. Localization in Clinical Neurology. 8e 2021
• Fuller G. Neurological Examination Made Easy. 6e 2019
• O’Brien M. Aids to the Examination of the Peripheral Nervous System. 6e 2023

FOAMed

• Coni R. Neuro 101: Peripheral Nervous System. LITFL
• Nickson C. Myotomes and Differentiating Nerve Lesions. LITFL