Convert to ICD-10-CM: 
991.1 converts approximately to:
- 2015/16 ICD-10-CM T33.529A Superficial frostbite of unspecified hand, initial encounterOr: 
- 2015/16 ICD-10-CM T34.529A Frostbite with tissue necrosis of unspecified hand, initial encounter
 ICD-9-CM Volume 2 Index entries containing back-references to 
991.1:
- Frostbite 991.3  hand 991.1 hand 991.1