Is numbness in the axillary nerve distribution normal after an anterior shoulder dislocation if the patient can still abduct and fire the deltoid muscle?

Axillary Nerve Numbness After Anterior Shoulder Dislocation

Yes, numbness in the axillary nerve distribution is a common finding following anterior shoulder dislocation, even when deltoid function remains intact. 1

Incidence and Pathophysiology

• Axillary nerve injury occurs in approximately 42% of anterior shoulder dislocations, making it the most frequently affected nerve in this type of trauma 1
• The mechanism typically involves a stretch injury to the nerve during the dislocation event 2
• The axillary nerve is particularly vulnerable due to its anatomical course around the surgical neck of the humerus 2

Clinical Presentation

• Sensory deficit in the lateral aspect of the shoulder (over the "regimental badge" area) is often the first sign of axillary nerve involvement 1
• Preservation of motor function (ability to abduct and fire deltoid) with isolated sensory deficit is a common presentation pattern 1, 3
• This dissociation between sensory and motor function occurs because:
  • Sensory fibers may be more susceptible to stretch injury than motor fibers 1
  • Partial nerve injuries can affect different components of the nerve unequally 2

Prognosis

• Most axillary nerve injuries following shoulder dislocation recover spontaneously 1
• Sensory recovery may lag behind motor recovery 1, 2
• Factors associated with poorer prognosis include:
  • Increasing age of the patient 1
  • Presence of hematoma 1
  • Blunt trauma mechanism (versus simple dislocation) 2

Evaluation

• Clinical examination should assess:

  • Sensory function in the axillary nerve distribution (lateral shoulder) 1
  • Deltoid muscle strength (abduction and anterior/middle/posterior fiber testing) 1
  • Signs of other associated nerve injuries (suprascapular, musculocutaneous) 1

• Electrodiagnostic studies:

  • Not routinely necessary when motor function is preserved 1
  • Should be considered if there is significant motor weakness after 3 weeks 1
  • Can help determine if the lesion is in continuity 2

Management

• For patients with preserved motor function (as in this case):

  • Reassurance that sensory symptoms often improve over time 1, 3
  • Appropriate rehabilitation program focusing on deltoid strengthening and shoulder stabilization 1
  • Regular follow-up to monitor for any deterioration in motor function 1

• For patients with significant motor deficits:

  • More intensive rehabilitation to prevent glenohumeral fixation, which can limit functional recovery 2
  • Electrodiagnostic studies after 3 weeks to assess nerve continuity 1
  • Consideration of nerve transfer procedures if no recovery by 5-12 months 4

Long-term Outcomes

• Even with permanent axillary nerve injury, good functional outcomes are possible, especially in younger patients 3
• The intact rotator cuff can compensate for deltoid weakness in many cases 4, 3
• Some patients maintain high levels of function despite persistent deltoid atrophy 3

Common Pitfalls

• Failing to assess for axillary nerve injury after shoulder dislocation 1
• Assuming poor prognosis based solely on sensory deficits when motor function is preserved 1, 3
• Overlooking the potential for good functional recovery despite persistent neurological deficits 3
• Neglecting rehabilitation, which can lead to glenohumeral fixation and poorer outcomes 2