Perionychium: Anatomy, Injuries, and Surgery

The perionychium is a vital part of our fingers and toes, frequently injured due to its exposed position. Understanding its intricate anatomy, common injuries, and available surgical treatments is crucial for students in healthcare and anyone interested in hand and foot health. This guide provides a comprehensive overview of the perionychium, covering everything from its structure to advanced surgical techniques.

Perionychium: Anatomy Explained for Students

To truly grasp the impact of injuries, it's essential to first understand the normal anatomy of the perionychium. This complex structure includes several components that work together to produce and support the nail.

Components of the Perionychium

• Nail Bed: The soft tissue beneath the nail, comprising the germinal matrix proximally and the sterile matrix distally. The germinal matrix produces about 90% of the nail, while the sterile matrix adds a thin layer of cells to the nail's undersurface, ensuring it adheres to the nail bed.
• Nail Fold: The most proximal extent of the perionychium, consisting of a dorsal roof and a ventral floor. The ventral floor is the germinal matrix.
• Eponychium: The skin proximal to the nail, covering the nail fold. It extends distally onto the nail as the nail vest or cuticle, and its dorsal roof produces the nail's characteristic shine.
• 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 of the Perionychium

The perionychium has a rich blood supply from the terminal branches of the radial and ulnar volar digital arteries and capillary loops. Veins drain into the proximal nail bed and nail fold. Sensation is provided by dorsal branches of the volar radial and ulnar digital nerves, as well as the dorsal radial digital nerve branches. The hyponychium contains the highest density of lymphatics, aiding in infection deterrence.

Common Perionychial Injuries and Their Management

Given its prominence, the perionychium is the most frequently injured part of the hand. Injuries often involve the long finger and the most distal part of the nail bed, frequently including the hyponychium.

Preoperative Evaluation

When evaluating fingertip injuries, a patient history is vital. A radiograph of the affected finger is highly recommended due to a 50% chance of associated bone involvement. Common trauma sources include doors, smashing fingers between objects, and lacerations from tools. Injuries are categorized into simple lacerations, stellate lacerations, severe crush, avulsions, and subungual hematomas.

Subungual Hematoma Treatment

Subungual hematoma results from bleeding beneath the nail due to compression. If the nail is intact and causing severe throbbing pain, evacuation is indicated. Surgical preparation with povidone-iodine is essential to prevent infection. Trephination (creating a hole in the nail) is typically performed with a battery-powered microcautery unit, which cools on contact with the hematoma, preventing nail bed injury. Drainage is recommended if the nail edges are intact. If the nail is broken or disrupted, removal, exploration, and repair of the nail bed are advised.

Nail Bed Repair Techniques

Nail bed repair is performed under digital block anesthesia and a tourniquet for hemostasis. The nail is carefully removed, cleaned, and soaked in povidone-iodine. The nail bed is examined under magnification, with minimal trimming of irregular edges to avoid compromising the repair. Repair is done with 7-0 chromic sutures using a micropoint spatula, double-arm ophthalmic needle.

• Simple Lacerations: Repaired directly.
• Stellate Lacerations: Meticulous approximation of multiple segments yields good outcomes.
• Crush Injuries: Have a poorer prognosis due to greater contusion and complex lacerations.

After repair, the native nail (if available) is the best protection and mold for the nail bed. A hole is cut in the nail for drainage, and it's secured with a 5-0 nylon mattress suture. If the nail is unavailable or badly damaged, a 0.020-inch reinforced silicone sheet can be used, secured with a nail fold suture.

Avulsion Injuries

Nail bed avulsion often involves a fragment of the nail bed attached to the avulsed nail. In children, it may indicate a Salter I fracture. Adequate visualization for repair requires eponychial incisions made perpendicular to the lateral curved portion of the eponychial fold. The avulsed nail bed is replaced as a graft, with the nail acting as a bolster. Small fragments can be removed from the nail and regrafted. A 1 cm diameter graft usually survives by inosculation and vascular ingrowth.

Nail Bed Defect Management

• Split-thickness injury: Regenerates without closure.
• Small full-thickness loss: Traditionally left to heal, but often results in scarring and nail deformity. Lateral mobilization of the germinal matrix can be useful for defects 3 to 5 mm.
• Larger defects (>50%): Require split-thickness or full-thickness nail bed grafts. Split-thickness grafts are often harvested from an adjacent finger or toe (toe is preferred due to lower risk of donor site deformity). Full-thickness grafts are rare, except for lost germinal matrix or when surrounding perionychium is also missing.
• Harvesting a Graft: The donor site is anesthetized, exsanguinated, and a tourniquet applied. A split-thickness graft (approx. 0.010 inch thick) is harvested with a No. 15 scalpel, using a back-and-forth sawing motion, visualizing the blade for thinness. It is then sutured into the defect with 7-0 chromic sutures.

Associated Distal Phalanx Fractures

About 50% of nail bed injuries include a distal phalanx fracture. Nondisplaced or distal tuft fractures are treated with nail bed repair and nail replacement 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 (longitudinal or crossed). With crush injuries, comminuted bony fragments are reduced by reapproximating the nail bed using the nail as a splint (or silicone if the nail is unavailable). An even dorsal cortex is crucial for proper nail bed healing.

Amputation Management

Treatment depends on remaining tissue and the amputated piece. Options include revision amputation, closure with flaps/grafts, or replantation. For exposed distal phalanx, bone may be trimmed for primary closure, or local/regional skin flaps (e.g., “V-Y” advancement, cross-finger, thenar flaps) can preserve length. To avoid a "hook nail," tension should be avoided when suturing fingertip skin to the distal nail bed, and the nail bed should be shortened to the end of the remaining phalanx if bone is lost. Amputations through the eponychium may be replanted, but revision amputation is often performed if less than 25% of the nail bed distal to the eponychium remains.

Postoperative Care and Potential Complications

Postoperative care involves protecting the repair and managing potential issues. Patients are typically seen 5-7 days after surgery, with gentle dressing removal.

Postoperative Management Key Points

• Warm soapy soaks may be recommended for dressing removal.
• Sutures holding the nail/silicone in the nail fold are removed in 5-7 days to prevent sinus tract formation. Other sutures can remain 10-14 days.
• The old nail usually adheres for 1-3 months until pushed off by new growth.
• Splints are worn for 3-4 weeks for protection and fracture immobilization.
• Nail growth averages 0.1 mm/day (2-3 mm/month). New growth may be delayed 3-4 weeks after nail removal.

Common Perionychial Complications and Treatments

Scarring of the sterile matrix can lead to notching, splitting, elevation, or nonadherence of the nail. Germinal matrix scarring can cause complete absence of nail growth. Uneven dorsal cortex or scarring can also lead to issues.

• Nail Ridges: Caused by uneven dorsal cortex or scar. Correction involves elevating the nail bed, excising the scar, or leveling the bone.
• Split Nail: Caused by a longitudinal ridge or scar in the germinal or sterile matrix. For germinal matrix scars, excision and a full-thickness germinal matrix graft (often from the second toe) are needed. For sterile matrix scars, resection and a split-thickness sterile matrix graft are used.
• Nonadherence: Results from sterile matrix scars not producing nail cells. Resection of the scar and replacement with a split-thickness sterile matrix graft are preferred. Chronic nonadherence from repetitive trauma may also require graft replacement.
• Absence of Nail: Can be partial or complete. Distal absence is treated with scar removal and a split-thickness sterile matrix graft. Complete absence is more challenging; options include skin grafts to mimic a nail or complex microvascular toe transfers.
• Eponychial Deformities: Traumatic loss exposes the proximal nail, leading to loss of shine. Notching is often aesthetic, but can be functional. Pterygium (scarring of eponychium/nail fold to nail bed) causes absence or splitting of the nail. Treatment involves freeing the dorsal roof and inserting a silicone sheet or applying a thin split-thickness sterile matrix graft. Defects may be reconstructed with composite toe eponychial grafts or rotation flaps.
• Hyponychial Deformities: Pterygia can also occur here. Hooking of the nail results from tight closure of an amputation or loss of bony support. Acute treatment involves replacing lost bone or trimming the nail bed. Late correction may involve "V-Y" advancement flaps, cross-finger flaps, or bone grafts. A prosthesis is a simpler alternative. Hyponychial nonadherence (from chemical exposure or chronic moisture) may require nail removal and scraping of keratinous material.
• Dull Nail: A cosmetic issue caused by scar within the dorsal roof of the nail fold. No functional treatment is usually necessary.
• Pincer Nail (Trumpet Nail): Excess transverse curvature leading to pain and deformity. Treatment includes nail plate removal, elevation of the nail bed sides, flattening of the distal phalanx dorsal surface, widening of the hyponychium, and placement of autogenous dermal grafts or AlloDerm under the lateral nail bed between it and the periosteum.

Perionychial Infections and Tumors

Acute Infections

• Fungal: Most commonly onychomycosis. Initial treatment is topical or systemic antifungals. Surgical intervention (nail removal, application of antifungal cream) may be needed for resistant cases.
• Bacterial (Paronychia): Staphylococcus aureus is common. If infection is above the nail, drainage by lifting the paronychium is sufficient. If beneath the nail, partial nail removal is needed. Antibiotics are for cellulitis. Incisions into the eponychium are avoided.

Chronic Infections

Chronic paronychia, often caused by gram-negative organisms and fungus (Candida), typically occurs between the nail and the dorsal roof of the nail fold. Treatment includes topical/oral antifungals, avoiding moisture, and for resistant cases, Keyser-Eaton marsupialization (excising a crescent from the proximal nail fold).

Benign Tumors of the Perionychium

• Pyogenic Granuloma: Rapidly growing, red, elevated lesions usually from trauma. Treated with silver nitrate cauterization or excision. Biopsy is needed if persistent.
• Subungual Nevi: Pigmented moles in the nail bed. Often present from birth. Incisional biopsy is generally recommended due to potential for malignant degeneration. Hematomas can mimic nevi; monitoring pigment progression with nail growth helps differentiate.
• Verruca Vulgaris (Warts): Treated with laser therapy after shaving the keratin layer. Multiple treatments may be necessary. Resulting scars may require nail bed grafting.
• Ganglion (Mucous Cysts): Most common tumors deforming the nail bed, arising from DIP joint osteophytes. Pressure on the nail bed causes ridging or grooving. Treatment involves nail removal (if severe deformity), débridement of DIP osteophytes, and drainage of the cyst. Excision of the cyst wall is usually unnecessary.
• Glomus Tumor: Arises from glomus bodies regulating blood flow/temperature. 50% occur subungually, causing exquisite pain, bluish discoloration, and temperature sensitivity. Diagnosis aided by ultrasound/MRI. Treatment is surgical excision after nail removal.

Malignant Tumors of the Perionychium

• Basal Cell Carcinoma: Rare in the finger, often linked to radiation or chronic trauma. Complete resection with clear margins is required. Amputation is recommended if the distal phalanx is involved.
• Squamous Cell Carcinoma: The most common malignant tumor of the perionychium. Can be secondary to radiation exposure, repeated trauma, or HPV. Often misdiagnosed as paronychia, leading to delayed treatment. Requires complete lesion resection with adequate margins. Amputation is indicated for large lesions or bone involvement.
• Melanoma: Poor prognosis compared to other body sites. Frequently misdiagnosed, leading to delayed treatment. Any pigmented lesion not advancing with nail growth should raise suspicion. Melanoma in situ requires excision with 5-mm margins. Invasive melanoma may require conservative amputation. Sentinel node biopsies are used to detect lymph node metastases.

Frequently Asked Questions (FAQ) about the Perionychium

What is the primary function of the perionychium?

The perionychium primarily protects the fingertip, helps regulate peripheral circulation, and contributes to tactile sensation, which assists in picking up small objects. It is also responsible for producing and supporting the fingernail, which itself serves protective and functional roles.

How does an injury to the germinal matrix differ from an injury to the sterile matrix?

An injury to the germinal matrix (the proximal part of the nail bed) typically leads to the absence of nail growth or significant nail splitting, as it produces about 90% of the nail. In contrast, an injury to the sterile matrix (the distal part of the nail bed) leads to nail deformity, such as nonadherence or ridging, because its role is to add cells that keep the nail adherent to the nail bed.

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