How should transient paresthesia of the infrapatellar branch of the saphenous nerve after knee trauma or surgery be managed?

Management of Transient Paresthesia of the Infrapatellar Branch of the Saphenous Nerve

Transient paresthesia of the infrapatellar branch of the saphenous nerve after knee trauma or surgery typically resolves spontaneously and requires reassurance, monitoring, and symptomatic management rather than aggressive intervention.

Understanding the Clinical Context

The infrapatellar branch of the saphenous nerve (IPBSN) is a purely sensory nerve that innervates the anteromedial aspect of the knee and anteroinferior knee joint capsule 1, 2. Injury to this nerve is extremely common after knee surgeries and trauma, with sensory changes occurring in approximately 70% of patients following total knee arthroplasty 3. The nerve's anatomical course is highly variable with no definite safe zone, making iatrogenic injury nearly unavoidable during anterior knee approaches 4.

Initial Assessment and Monitoring

Key Clinical Features to Document

• Distribution of paresthesia: Specifically map the area of sensory change on the anteromedial knee 1
• Timing of onset: Document whether symptoms appeared immediately post-trauma/surgery or developed gradually 1
• Associated symptoms: Assess for pain, burning, or allodynia that might suggest neuralgia rather than simple neuropraxia 1
• Motor function: Confirm that quadriceps and other motor functions remain intact, as the IPBSN is purely sensory 1, 2

Critical Differential Diagnosis

Rule out acute compartment syndrome (ACS) if the injury occurred in the context of lower leg trauma, particularly with tibial fractures 5. Key distinguishing features include:

• ACS presents with severe, progressive pain disproportionate to the injury, not isolated paresthesia 5
• ACS involves deep compartment pain with passive stretch, not superficial sensory changes 5
• If any concern for ACS exists, measure intracompartmental pressures immediately (threshold: 30 mmHg absolute or within 30 mmHg of diastolic pressure) 5

Management Algorithm

For Transient Paresthesia (Expected to Resolve)

Weeks 0-6: Observation Phase

• Provide patient education that sensory changes are common and typically improve over 3-12 months 3
• Document baseline sensory deficit with dermatomal mapping 1
• Reassure that this does not affect functional outcomes in most cases 3
• No specific treatment is required during this period 1

Weeks 6-12: Reassessment

• Re-examine sensory distribution to document improvement or progression 1
• If symptoms are stable or improving, continue observation 1
• If symptoms are worsening or developing neuropathic pain features (burning, allodynia), proceed to diagnostic workup 1

For Persistent or Progressive Symptoms (>3 months)

Diagnostic Nerve Block

• Perform ultrasound-guided diagnostic block of the IPBSN 6
• Use low-volume local anesthetic (1-2 mL of 0.25% bupivacaine) 1
• Positive response (>50% pain relief) confirms IPBSN neuralgia as the source 1

Treatment Options for Confirmed IPBSN Neuralgia

1. Conservative management first-line 1:

   • Neuropathic pain medications (gabapentin 300-900 mg TID or pregabalin 75-150 mg BID)
   • Topical lidocaine patches to affected area
   • Physical therapy focusing on desensitization

2. Interventional options if conservative fails 1, 6:

   • Serial therapeutic nerve blocks (every 2-4 weeks for 3-6 sessions)
   • Pulsed radiofrequency ablation of the IPBSN
   • Cryoneurolysis as alternative neuroablative technique

3. Surgical neurectomy 1:

   • Reserved for refractory cases after failed conservative and interventional management
   • Consider only when diagnostic blocks provide consistent, reproducible relief

Patient Counseling and Expectations

Preoperative counseling is essential for any planned knee surgery, as patients should be informed that sensory changes occur in up to 70% of cases and can significantly affect satisfaction even when functional outcomes are excellent 3. Two critical points to emphasize:

• Most sensory deficits improve substantially within 6-12 months 3
• While common, sensory changes can be a significant source of dissatisfaction for some patients despite good functional results 3

Common Pitfalls to Avoid

• Do not confuse isolated IPBSN paresthesia with compartment syndrome: IPBSN injury causes superficial sensory changes without the severe, progressive deep pain characteristic of ACS 5, 1
• Do not rush to interventional treatment: Most cases resolve spontaneously and aggressive early intervention is not warranted 1
• Do not perform sympathetic blocks: Despite documented vasomotor instability, sympathetic blocks do not address the underlying peripheral nerve pathology and are ineffective 1
• Do not dismiss patient concerns: Even though sensory deficits may seem minor clinically, they can significantly impact patient satisfaction and quality of life 3
• Do not assume all anterior knee paresthesia is IPBSN-related: Consider other causes including patellofemoral pathology, referred pain from lumbar spine, or complex regional pain syndrome, particularly if symptoms are atypical 1