Frostbite Grading System
Frostbite is classified into four degrees of severity based on the extent of tissue involvement and predicted outcomes: first-degree (recovery without tissue loss), second-degree (soft tissue amputation), third-degree (bone amputation), and fourth-degree (large amputation with systemic effects). 1
Classification System
The modern grading system predicts final outcomes based on the topography of lesions at initial presentation (day 0) and correlates strongly with the probability of amputation 1:
First-Degree Frostbite
- Complete recovery expected without permanent tissue loss 1
- Superficial injury affecting only the epidermis 2
- Patients achieve complete cure with conservative treatment alone, typically within 8-16 days 3
Second-Degree Frostbite
- Leads to soft tissue amputation without bone involvement 1
- Blisters and edema develop after rewarming 2
- When initial lesions involve the distal phalanx, probability of bone amputation is approximately 1% 1
- Complete cure achievable with conservative management in many cases 3
Third-Degree Frostbite
- Results in bone amputation of affected digits 1
- When lesions extend to the middle phalanx, amputation probability increases to 31%; for proximal phalanx involvement, 67% 1
- May require skin grafting following debridement, though some cases respond to conservative treatment over 29-39 days 3
- Hard eschar may form with potentially viable tissue beneath 2
Fourth-Degree Frostbite
- Causes large amputation with systemic effects 1
- When lesions involve metacarpal/metatarsal level, amputation probability reaches 98%; at carpal/tarsal level, 100% 1
- Requires surgical amputation procedures 3
- This grade should prompt consideration of thrombolytic therapy (rt-PA) within 24 hours of rewarming, as amputation is inevitable 4
Clinical Assessment Challenges
Estimating severity is difficult at initial presentation, especially in first aid settings 5. The extent of tissue loss is often less than initial appearances suggest 2, making early prediction challenging 1. Definitive assessment requires correlation with bone scan results, which are more accurate for predicting final outcomes 1.
Key Clinical Features by Severity
- Skin color progression: Pale → hardened → dark as severity increases 5
- Sensation: Complete inability to sense touch is a hallmark of acute frostbite 5
- Post-rewarming changes: Hyperemia develops and is often painful; blisters and edema appear after thawing 2
Common Pitfall
Do not attempt early surgical intervention based solely on initial appearance. Surgeons should wait for sufficient time until wound demarcation occurs before deciding on definitive surgical procedures 3. The amount of tissue loss at presentation does not reliably predict final outcomes 2.