What are the common neuropathies after total knee replacement and how are they managed?

Common Neuropathies After Total Knee Replacement: Diagnosis and Management

Peripheral nerve injury is an uncommon but significant complication after total knee arthroplasty (TKA), with the peroneal nerve being the most frequently affected nerve (0.37% incidence), followed by the sciatic nerve and the infrapatellar branch of the saphenous nerve. 1

Types of Neuropathies After TKA

1. Common Peroneal Nerve Neuropathy

• Presentation: Foot drop, lateral knee pain, weakness of foot dorsiflexion, numbness/paresthesia over dorsum of foot and lateral calf
• Incidence: Most common nerve injury (68.5% of post-TKA neuropathies) 1
• Mechanism: Direct compression, traction during surgery, tourniquet pressure, or postoperative swelling
• Management:
  • Conservative: Ankle-foot orthosis, physical therapy, nerve gliding exercises
  • Surgical: Nerve decompression for persistent symptoms (40.7% of nerve surgeries) 2

2. Sciatic Nerve Injury

• Presentation: Combined foot drop and plantar flexion weakness, posterior thigh pain
• Incidence: Second most common (20.4% of post-TKA neuropathies) 1
• Mechanism: Excessive leg manipulation, tourniquet pressure, or postoperative hematoma
• Management: Similar to peroneal nerve injury but with broader rehabilitation focus

3. Infrapatellar Branch of Saphenous Nerve Injury

• Presentation: Medial knee pain, numbness in medial aspect of knee
• Mechanism: Direct injury during surgical approach
• Management:
  • Ultrasound-guided hydrodissection with corticosteroid injection
  • Neurectomy with targeted muscle reinnervation (TMR) or regenerative peripheral nerve interface (RPNI) for persistent cases (48.1% of nerve surgeries) 2, 3

4. Less Common Neuropathies

• Tibial nerve: Plantar foot numbness, weakness of plantar flexion
• Sural nerve: Lateral foot numbness
• Lumbosacral plexus: More extensive leg weakness and sensory changes

Diagnostic Approach

1. Clinical Assessment:

   • Detailed neurological examination
   • Mapping of sensory deficits
   • Motor strength testing
   • Timing of symptom onset (immediate vs. delayed)

2. Imaging:

   • Radiographs: Initial imaging to assess prosthesis position and alignment 4
   • CT: For assessment of component rotation if mechanical impingement is suspected 4
   • MRI with metal artifact reduction: For soft tissue assessment around the knee 4

3. Electrodiagnostic Studies:

   • EMG/NCS to confirm neuropathy and assess severity
   • Helps differentiate axonotmesis from neurapraxia

Management Algorithm

Acute Phase (0-6 weeks)

1. Conservative Management:

   • Pain control: Multimodal analgesia including paracetamol, NSAIDs/COX-2 inhibitors, and opioids as needed 4
   • Reduce swelling: Cooling, compression, and elevation
   • Protect the affected nerve: Appropriate bracing/orthosis
   • Physical therapy: Maintain joint mobility while protecting nerve

2. Monitoring:

   • Serial neurological examinations
   • Document recovery progression

Subacute Phase (6 weeks-3 months)

1. Continue Conservative Management if improving
2. Consider Intervention if no improvement:
   • For medial knee pain: Ultrasound-guided hydrodissection and corticosteroid injection of saphenous nerve 3
   • For lateral knee pain/foot drop: Consider nerve decompression if compression is identified

Chronic Phase (>3 months)

1. Surgical Management for persistent symptoms:

   • Peroneal nerve: Decompression at fibular head
   • Saphenous nerve: Neurectomy with TMR or RPNI 2
   • Combined approaches: Based on clinical presentation (11.1% of cases) 2

2. Pain Management:

   • Assess for neuropathic pain using validated tools (e.g., painDETECT)
   • Consider gabapentinoids, SNRIs, or TCAs for neuropathic pain
   • Consider referral to pain specialist for refractory cases

Prognosis

• Most post-TKA neuropathies show significant improvement within 1 year 1
• Motor recovery is typically complete or near-complete in most cases with appropriate management 1
• Neuropathic pain may persist longer than motor deficits 5
• Surgical intervention for persistent neuropathic pain shows improvement in 95.5% of cases 2

Prevention Strategies

• Careful surgical technique with attention to nerve anatomy
• Appropriate tourniquet pressure and duration
• Proper positioning during surgery
• Early recognition and management of postoperative swelling
• Vigilant monitoring for vascular complications that may cause secondary nerve compression 6

Key Pitfalls to Avoid

1. Delayed diagnosis: Early identification improves outcomes
2. Attributing all knee pain to the prosthesis: Consider nerve injury as a differential diagnosis
3. Missing vascular complications: Pseudoaneurysms can cause secondary nerve compression 6
4. Inadequate follow-up: Neuropathic pain peaks between 6 weeks and 3 months postoperatively 5
5. Overlooking inflammatory causes: Though rare, consider inflammatory neuropathy in atypical presentations 1