Nerve Injury

Introduction

Welcome to the QBankMD MCCQE1 preparation guide on Nerve Injury. This comprehensive resource is tailored for Canadian medical students preparing for the Medical Council of Canada Qualifying Examination Part I (MCCQE1). Understanding nerve injuries is crucial for success in the MCCQE1 and for your future practice in the Canadian healthcare system.

Classification of Nerve Injuries

Understanding the classification of nerve injuries is essential for MCCQE1 preparation. The Seddon and Sunderland classifications are widely used in Canadian neurosurgery practice.

Seddon Classification

Sunderland Classification

This classification provides a more detailed breakdown of nerve injuries:

1. First-degree: Equivalent to neurapraxia
2. Second-degree: Axon disruption with intact endoneurium
3. Third-degree: Disruption of axon and endoneurium, intact perineurium
4. Fourth-degree: Disruption of axon, endoneurium, and perineurium, intact epineurium
5. Fifth-degree: Complete nerve transection

Pathophysiology of Nerve Injury

Understanding the pathophysiology is crucial for MCCQE1 success. Here's a step-by-step breakdown:

Clinical Presentation

Recognizing the clinical presentation of nerve injuries is essential for the MCCQE1 exam and Canadian medical practice. Key features include:

• Sensory deficits: Numbness, paresthesia, or pain in the affected nerve distribution
• Motor deficits: Weakness or paralysis of muscles innervated by the affected nerve
• Autonomic dysfunction: Changes in sweating, temperature regulation, or blood flow in the affected area

Diagnostic Approach

For MCCQE1 preparation, focus on the following diagnostic steps commonly used in Canadian healthcare:

1. Detailed history: Mechanism of injury, timing, associated symptoms
2. Physical examination:
   • Sensory testing (light touch, pinprick, temperature)
   • Motor testing (muscle strength grading)
   • Reflex testing
3. Electrodiagnostic studies:
   • Nerve conduction studies (NCS)
   • Electromyography (EMG)
4. Imaging:
   • Ultrasound: First-line imaging in many Canadian centers
   • MRI: For detailed soft tissue evaluation
   • CT: If bony involvement is suspected

Management

Management of nerve injuries in Canada follows a stepwise approach:

1. Initial management:

   • Protect the affected limb
   • Pain control (following Canadian pain management guidelines)
   • Prevent complications (e.g., contractures, pressure sores)

2. Conservative management:

   • Physical therapy and occupational therapy
   • Splinting or bracing
   • Electrical stimulation (where appropriate)

3. Surgical management:

   • Indicated for severe injuries or lack of improvement with conservative measures
   • Timing is crucial: early repair (within 72 hours) for sharp transections, delayed repair for other injuries

Prognosis and Rehabilitation

Prognosis varies depending on the injury severity, location, and timing of intervention. Key points for MCCQE1:

• Neurapraxia has the best prognosis, often with full recovery
• Proximal injuries have a poorer prognosis than distal injuries
• Age is a factor: younger patients generally have better outcomes
• Rehabilitation is crucial for optimal recovery

Canadian healthcare emphasizes a multidisciplinary approach to rehabilitation, involving:

• Physiotherapists
• Occupational therapists
• Pain specialists
• Mental health professionals

Canadian Guidelines and Considerations

While there are no specific Canadian guidelines for nerve injury management, the Canadian Association of Physical Medicine and Rehabilitation provides resources for rehabilitation approaches. Key considerations in the Canadian context include:

• Emphasis on early referral to specialized nerve injury clinics where available
• Integration of telehealth for follow-up in remote areas
• Consideration of socioeconomic factors in treatment planning, aligning with Canada's universal healthcare principles

Key Points to Remember for MCCQE1

• Know the Seddon and Sunderland classifications of nerve injury
• Understand the pathophysiology of Wallerian degeneration and nerve regeneration
• Recognize clinical presentations of common nerve injuries (e.g., radial, ulnar, median nerves)
• Be familiar with the diagnostic approach, including appropriate use of electrodiagnostic studies and imaging
• Understand the principles of conservative and surgical management
• Know the factors affecting prognosis and the importance of rehabilitation
• Be aware of Canadian-specific healthcare delivery considerations for nerve injury management

Sample Question

# Sample Question

A 28-year-old woman presents to a Canadian emergency department with weakness in her left hand following a fall onto her outstretched arm. She reports difficulty extending her wrist and fingers. Physical examination reveals weakness in wrist and finger extension, with preserved finger flexion and normal sensation. Which one of the following nerves is most likely injured?

- [ ] A. Median nerve
- [ ] B. Ulnar nerve
- [ ] C. Radial nerve
- [ ] D. Musculocutaneous nerve
- [ ] E. Axillary nerve

Explanation

The correct answer is:

• C. Radial nerve

Explanation: This scenario describes a classic presentation of radial nerve injury, commonly seen in the "Saturday night palsy" or "honeymoon palsy." The radial nerve innervates the extensor muscles of the wrist and fingers. Injury to this nerve results in weakness of wrist and finger extension, leading to wrist drop. The preservation of finger flexion and normal sensation helps differentiate this from median or ulnar nerve injuries.

In the Canadian healthcare context, this patient would typically be managed initially in the emergency department, with referral to a nerve specialist or physiatrist for follow-up and rehabilitation planning. Early initiation of hand therapy would be recommended to prevent complications such as contractures.

References

1. Campbell, W. W. (2008). Evaluation and management of peripheral nerve injury. Clinical Neurophysiology, 119(9), 1951-1965.

2. Grinsell, D., & Keating, C. P. (2014). Peripheral nerve reconstruction after injury: a review of clinical and experimental therapies. BioMed Research International, 2014.

3. Menorca, R. M., Fussell, T. S., & Elfar, J. C. (2013). Nerve physiology: mechanisms of injury and recovery. Hand Clinics, 29(3), 317-330.

4. Canadian Association of Physical Medicine and Rehabilitation. (2021). Clinical Practice Guidelines. Retrieved from https://capmr.ca/resources/clinical-practice-guidelines (opens in a new tab)

5. Doherty, C., & Forbes, R. (2014). Diagnostic Nerve Blocks. Continuing Education in Anaesthesia Critical Care & Pain, 14(6), 285-289.