Don't Swing A Hammer At This Nail!

HPI:
Right hand dominant middle aged female with history of HTN presents to the ED after accidentally hitting her left index finger with a hammer while working on a home improvement project.   Finger is painful and swollen but she has no other injuries and reports she is otherwise feeling well.

Physical Examination:
Erythematous, swollen, and tender left 2nd distal phalanx. There is a subungual hematoma present over approx. 75% of the nail but the nail is intact.  Motor and sensation intact, full ROM of PIP and DIP, 2+ radial pulse, no other injuries identified.

Radiology:
AP, lateral and oblique views of left 2nd phalanx – no fracture or dislocation identified

Management:
Nail removal and bedside repair of nail bed laceration, tetanus updated, discharged home with 48 hour follow up for reevaluation

Discussion:
Fingertip injuries = most common hand injuries seen in the ED
Most common mechanisms:

• Crush between two objects
  
• Catching finger in a door
  
• Power/home tools
  
• Direct blows (hammer injury)
  

Evaluate for:

• Subungual hematoma
  
• Laceration to the nail bed
  
• Avulsion of the nail bed
  
• DIP fractures or dislocations

Complications of injury:

• Nail loss
  
• Abnormal growth
  
• Nonadherence of new nail
  
• Splitting of the nail
  
• Soft tissue infection
  
• Osteomyelitis of the underlying distal tuft

Image obtained from Am Fam Physician. 2012 Apr 15;85(8):779-787.

Fingertip Anatomy:

• Nail = Desiccated, keratinized squamous cells

• Perionychium = Nailbed + paronychia
  
• Nailbed = Soft tissue beneath the nail that is bound to underlying periosteum of the distal phalanx, consists of the germinal and sterile matrix 
  
• Paronychia = Lateral nail folds 
  
• Hyponychium  = the skin distal and palmar to the nail – at the junction between the nailbed and fingertip. Contains a lot of PMNs and lymphocytes – helps protect subungal tissue from infection 
  
• Nail fold = Holds the proximal nail 
  
• Eponychium = aka the cuticle -- or the dorsal, distal portion of the nail fold where it attaches to the dorsum of the nail
  
• Lunula = The white part of the proximal nail just distal to the eponychium. Caused by nail cell nuclei in germinal matrix moving upwards and distally to create new nail
  
• Sterile Matrix = soft tissue deep to the nail and distal to the lunula, adheres to the nail
  
• Germinal Matrix = soft tissue deep to the nail and proximal to the sterile matrix, responsible for most of the nail development; the extensor tendon inserts <1.5mm proximally to this structure

Blood Supply and Innervation:

• Two volar arterial arches -- anastomoses between digital arteries just above the periosteum of distal phalanx
• Venous drainage coalesces in proximal nailbed and proximal to nail fold, drains over the dorsum of the finger

• Perionychium innervated by dorsal branches of the paired digital nerves

Nail Growth:

• Longitudinal nail growth = 70-160 days to cover entire length
  
• After an injury, growth may be stunted/absent for up to 21 days, then nail grows rapidly for approx. 50 days then resumes normal growth rate
  
• Results in a characteristic “lump” that often forms after traumatic injury

Treatment:
Obtain radiographs to rule out distal phalanx fracture
Evaluate for subunginal hematoma and nail bed lacerations

Drain hematoma if <50% nail involved 

• Puncture with sterile needle vs electrocautery 

Nail removal, I&D, repair of nail bed if >50% of nail involved

• Remove nail
  
• Repair nail bed with 6-0 absorbable suture or Dermabond
  
• Splint eponychial fold with original nail (if possible), aluminum splint, or non-adherent gauze to prevent scarring