Nail Bed Injury



Nail Bed Injury


Andrew D. Sobel



INTRODUCTION

Fingertip injuries, and injuries to the nail bed specifically, are common problems that vary widely in mechanism and severity. Injuries to the nail can involve any combination of the nail plate, nail bed, germinal matrix, eponychium, or bone of the distal phalanx. Nail bed injuries in the pediatric population may have different management than those in the adult population, depending on a variety of factors including involvement of the growth plate. Proper evaluation and identification of the injury and timely management is critical to preventing a painful, sensitive, or cosmetically unappealing outcome.



  • Anatomy (see Figure 52.1)1,2



    • Perionychium3—the nail and its surrounding structures



      • Nail plate



        • Made of onchyn, a keratin-like material


        • Protects the nail bed and distal tissue. Improves sensory feedback of the fingertip


      • Eponychium



        • Fold of tissue dorsally and proximally over nail


        • Serves to smooth the nail plate as it grows


      • Sterile matrix



        • Contains one to two layers of germinal cells that contribute to nail plate thickness as it grows and moves distally


      • Lunula



        • White arc on the proximal nail


        • Nail bed distal to the lunula is the sterile matrix; proximal to and including the lunula is the germinal matrix


      • Germinal matrix



        • Extends from ventral floor to lunula. Immediately superficial to distal phalanx periosteum



        • Ventral floor



          • ▲ Three to four germ cell layers thick. Produces 90% of the nail plate volume through “gradient parakeratosis”


      • Dorsal root/roof



        • Contributes to the nail plate formation. Source of shiny quality of nail plate


      • Hyponychium



        • Site at which the sterile matrix stops and epithelial skin starts at the distal tip. A keratin plug at this site acts as a barrier between the nail and sterile matrix to prevent contamination/infection


      • Paronychium



        • Folds of skin on sides of nail that can tear (“hangnail”) and become infected (“paronychia”)


    • Pulp4



      • Distributes force placed on the palmar finger


      • Contains sensory receptors such as Pacinian and Meissner corpuscles, Merkel cell-neurite complexes


    • Extensor tendon (terminal slip)



      • Inserts approximately 2 mm proximal to the germinal matrix on the distal phalanx


    • Flexor digitorum profundus (FDP) tendon



      • Inserts on the distal phalanx just proximal to the distal palmar digital arterial anastomosis


    • Vasculature5



      • Dorsal vein—overlies the distal phalanx and is important for anastomosis in amputations


      • Digital arteries—send major branches to the pulp, paronychium, and nail fold. Smaller branches go to the nail bed


    • Nerves



      • Digital nerves send branches to the paronychium, pulp, and fingertip


      • Located palmar to the digital arteries


    • Zones—see Classification



      • Tamai


      • Allen


      • Fassler


  • Mechanism of injury6



    • Crush



      • Most common mechanism for nail bed injuries


    • Sharp laceration



    • Avulsion



      • Nail bed avulsions with the loss of matrix tissue result in some of the worst outcomes as they often result in permanent deformity.


      • Fingertip avulsion (including the nail bed) may result in a more proximal injury as tension can be placed on the neurovascular structures.


    • Bite



      • May result in inoculation with flora from the mouth of the animal



        • Eikenella sp. (human bites)—adjunctively treat with amoxicillin-clavulanic acid7


        • Pasteurella sp. (dog or cat bites)—adjunctively treat with amoxicillin-clavulanic acid8



  • Epidemiology



    • Adult injuries6



      • Historically occur more commonly in men, likely due to occupational hazards



        • Powered hand tools or fixed powered machines are the top contributors to fingertip injuries in industries such as agriculture, manufacturing, and construction.9


        • Injuries at home in patients >15 years old are also typically caused by power tools (power saws, lawn mowers, snow blowers, etc.).10


      • The middle finger is most commonly injured as are the distal and middle portions of the nail bed because these are the most exposed/unprotected by the rest of the hand.


    • Pediatric injuries11,12



      • Nail bed injury present in 15% to 24% of fingertip injuries in children


      • Highest incidence in children <5 years old


      • Most commonly caused by jamming or crushing finger in a door


      • The middle finger and distal nail bed are most commonly injured.






FIGURE 52.1 Anatomy of the finger distal to the distal interphalangeal joint (DIPJ). Pertinent structures and classifications of zone anatomy (Tamai and Allen) are labeled. From Lee DH, Mignemi ME, Crosby SN. Fingertip injuries: an update on management. J Am Acad Orthop Surg. 2013;21(12):756-766.


EVALUATION

May 7, 2019 | Posted by in ORTHOPEDIC | Comments Off on Nail Bed Injury
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