What is the Kanawel (Kanavel) sign?

Kanavel Signs: Diagnostic Criteria for Pyogenic Flexor Tenosynovitis

The Kanavel signs are four clinical findings used to diagnose pyogenic flexor tenosynovitis (PFT), consisting of: tenderness along the flexor tendon sheath, symmetric finger swelling, pain with passive extension, and a semi-flexed posture of the affected digit. 1

The Four Kanavel Signs

1. Tenderness along the flexor tendon sheath: Exquisite tenderness over the course of the flexor tendon sheath, particularly at the A1 pulley

   • Recent research shows that specifically focusing on A1 pulley tenderness increases diagnostic specificity 2
   • This sign has high sensitivity (91-97%) but moderate specificity (51-69%) 1

2. Symmetric finger swelling: Uniform swelling of the entire digit rather than localized swelling

   • This differs from other finger infections which often present with more localized swelling 1

3. Pain with passive extension: Significant pain when the examiner attempts to extend the affected finger

   • This sign reflects increased pressure within the tendon sheath and is highly sensitive for PFT 1
   • The pain is typically disproportionate to the degree of manipulation 1

4. Semi-flexed posture: The affected finger is held in slight flexion at rest

   • This position minimizes pain by reducing tension on the inflamed tendon sheath 1
   • The patient typically resists attempts to extend the finger due to pain 1

Diagnostic Value and Limitations

• Individual Kanavel signs have excellent sensitivity (91.4-97.1%) but poor specificity (51.3-69.2%) 1

• The most predictive combination includes:

  • Tenderness along the flexor tendon sheath
  • Pain with passive extension
  • Duration of symptoms less than 5 days 1

• When these three factors are combined in a prediction algorithm, the diagnostic accuracy is significantly improved (area under ROC curve of 0.91) 1

Recent Modifications and Improvements

• A1 pulley tenderness: A 2022 study found that specifically assessing tenderness at the A1 pulley (rather than the entire sheath) improves diagnostic specificity 2

  • When A1 pulley tenderness is added to the traditional Kanavel signs, there is increased specificity and diagnostic accuracy 2

• Imaging adjuncts: Contrast-enhanced CT can provide objective measurements to support diagnosis

  • Tendon sheath to tendon width ratios ≥1.3 in both coronal and sagittal planes have high sensitivity and specificity for PFT 3
  • Each additional Kanavel sign increases the likelihood of PFT by approximately 14% 3

Clinical Implications

• The number of positive Kanavel signs correlates with disease severity

  • Patients with surgically confirmed PFT typically present with more Kanavel signs (average 2.9) compared to those with simple cellulitis (average 0.5) 3

• Duration of symptoms is important for treatment decisions

  • Patients with shorter symptom duration and fewer Kanavel signs may be successfully treated with antibiotics alone 4
  • Those with more signs and acute presentations often require surgical intervention 4

• False positives can occur with other inflammatory conditions of the hand, so clinical context remains important 1, 4