Perionychium: Anatomy, Injuries, and Management

The perionychium is a vital part of our fingers and toes, encompassing the nail and its surrounding structures. Often taken for granted, it plays crucial roles in protection, peripheral circulation, and tactile sensation. Due to its prominent position on the fingertip, the perionychium is the most frequently injured part of the hand, commonly affected in older children and young adults.

Perionychium Anatomy: Understanding the Nail Structure

To effectively manage injuries, a thorough understanding of the perionychium's anatomy is essential. This complex structure includes several interconnected components:

• Nail Bed: The soft tissue beneath the nail, composed of the germinal matrix (proximally, producing 90% of the nail) and the sterile matrix (distally, adding cells for nail adherence).
• Nail Fold: The most proximal part of the perionychium, with a dorsal roof and a ventral floor (which is the germinal matrix).
• Eponychium: The skin proximal to the nail, covering the nail fold. It extends onto the nail as the nail vest or cuticle.
• Paronychium: The skin on each side of the nail.
• Hyponychium: The skin distal to the nail bed.
• Lunula: The white arc just distal to the eponychium, marking the distal extent of the germinal matrix.

Blood Supply and Sensation: The perionychium receives its blood supply from terminal branches of the radial and ulnar volar digital arteries. Sensation is provided by dorsal branches of the volar radial and ulnar digital nerves. The hyponychium, notably, has the highest density of lymphatics in the body, which helps prevent infection.

Common Injuries to the Perionychium

Perionychial injuries range from minor to severe, with doors, crushing objects, and tools being common culprits. The long finger is most often injured due to its exposure. Injuries are broadly classified as:

• Simple Lacerations
• Stellate Lacerations
• Severe Crush Injuries
• Avulsions
• Subungual Hematoma: This is bleeding beneath the nail, often challenging to assess due to hidden nail bed lacerations.

Managing Subungual Hematoma and Nail Bed Lacerations

Subungual hematomas can cause severe throbbing pain due to pressure. Drainage is often indicated. Surgical preparation of the finger, typically with povidone-iodine, is crucial to prevent bacterial inoculation. Trephination (creating a hole in the nail) is performed, ideally with a battery-powered microcautery to avoid injury to the nail bed. If nail edges are intact, drainage alone may suffice; however, if the nail is broken or edges are disrupted, nail removal and nail bed repair are recommended.

Nail bed repair involves:

• Anesthesia and Hemostasis: Digital block and tourniquet.
• Nail Removal: Using a periosteal elevator or iris scissors, carefully removing the nail to avoid further injury.
• Inspection and Débridement: Examination under loupe magnification. Conservative débridement is key, as the nail bed is difficult to mobilize. Contused edges are often left in place rather than risking a defect.
• Suturing: Repairing lacerations with fine 7-0 chromic sutures, using a micropoint spatula needle for precision.
• Nail as a Splint: The native nail, cleaned and with a drainage hole, is the best option for a splint and mold for the repaired nail bed. It's secured with a mattress suture (5-0 nylon) or a simple suture through the hyponychium. If unavailable, a 0.020-inch reinforced silicone sheet can be used.
• Post-Repair Protection: The finger is wrapped in nonadhesive gauze and a protective splint (four-prong or volar aluminum) for 2 to 3 weeks.

Addressing Avulsion Injuries and Nail Bed Defects

Avulsion injuries often involve a fragment of nail bed attached to the avulsed nail. In children, this may suggest a Salter I fracture, requiring radiographic evaluation. Repair often necessitates an eponychial incision for visualization. The avulsed nail bed is replaced as a graft, with the nail acting as an optimal bolster. Small fragments can survive on bare cortex.

Nail bed defects require specific approaches:

• Split-thickness loss regenerates without closure.
• Small full-thickness loss may heal by secondary intention, but often results in scarring and deformity.
• Lateral mobilization of the germinal matrix can close defects less than one-third of the nail width.
• Split-thickness nail bed grafts are preferred for larger sterile matrix defects, harvested from adjacent uninjured nail bed or, for larger defects (over 50%), from an adjacent finger or toe (the toe is often preferred to avoid donor site deformity).
• Full-thickness nail bed grafts are rarely used due to donor site deformity, except for replacing lost germinal matrix or when surrounding perionychium is also missing.

Managing Distal Phalanx Fractures and Amputations

Approximately 50% of nail bed injuries are associated with a distal phalanx fracture. Management varies based on the fracture type:

• Nondisplaced or distal tuft fractures are treated by nail bed repair and using the nail as a splint. A tension band suture can add stability.
• Displaced fractures, especially proximal to the nail fold, require accurate reduction and fixation with Kirschner wires. Avoiding crossing the DIP joint is ideal.
• Comminuted fractures with small fragments adherent to the nail bed are reduced by reapproximating the nail bed using the nail (or silicone if the nail is unavailable) as a splint. The goal is bony union and an even dorsal cortex to prevent nail deformity.
• Salter I fractures are often reduced with nail bed repair alone; pinning is avoided unless unstable.

Amputations are managed based on the remaining tissue and quality of the amputated piece. Options include revision amputation, closure with flaps and grafts, or replantation. For exposed distal phalanx, bone trimming or local/regional skin flaps (like V-Y advancement, cross-finger, or thenar flaps) can preserve length. Tension at closure must be avoided to prevent a