Pincer nail deformity (PND), also known as trumpet or involuted nail, is a chronic, often painful, onychopathy characterized by an exaggerated transverse overcurvature of the nail plate. Unlike typical onychocryptosis (ingrown toenail), which usually involves soft tissue impingement at the lateral nail fold, PND involves the progressive, symmetrical or asymmetrical, involution of the nail plate edges, often into a “C” or “omega” shape. This extreme curvature leads to chronic compression of the underlying nail bed (dermis) and distal phalanx, resulting in significant pain, subungual hyperkeratosis, and, frequently, secondary ingrown nail development. The etiology is multifaceted, involving genetic predisposition, tight-fitting footwear, trauma, and underlying pathologies such as osteoarthritis of the distal phalanx (dorsal exostosis) or fungal infection (onychomycosis). Due to the chronic nature of the deformity and its detrimental impact on patient mobility and quality of life, treatment strategies must be comprehensive and follow a logical progression, escalating from conservative techniques for mild cases to definitive surgical correction for severe and recurrent deformities.

The initial management of pincer toenails focuses on conservative, non-invasive measures aimed at relieving immediate pressure and correcting the contributing factors. Patient education is paramount, emphasizing proper preventative nail care—specifically, trimming the nail plate straight across, ensuring the nail corners extend slightly beyond the soft tissue of the lateral nail folds, and avoiding the practice of “digging out” the corners. A crucial element of conservative care is addressing external mechanical forces and underlying diseases. Patients must transition to wearing appropriate footwear with a wide and deep toe box to eliminate external lateral pressure that exacerbates the nail curvature. Furthermore, if a fungal infection is diagnosed, concurrent use of topical or systemic antifungal medications is necessary, as onychomycosis often leads to nail thickening and increased rigidity, compounding the pincer effect. In early or mild cases, temporary relief can be achieved through non-invasive physical techniques, such as the strategic placement of cotton wicks or dental floss beneath the involuted nail edges to lift them away from the nail bed, or through the use of topical softening agents like high-concentration urea or acetylcysteine to temporarily increase nail plate flexibility.

When conservative measures fail or in cases presenting with moderate curvature and associated pain, non-invasive corrective bracing, known as orthonyxia, represents the next tier of treatment. Orthonyx devices function analogously to orthodontic braces, applying gentle, continuous, counter-tension to the curved nail plate to gradually flatten its transverse profile. These systems are highly favoured for patients with comorbidities, such as diabetes or peripheral vascular disease, where surgical intervention carries increased risks, or for patients with needle phobia. Two primary categories exist: tension-wire systems and composite resin systems. Tension-wire systems, often made from flexible nickel-titanium shape-memory alloys, utilize small hooks engaged under the nail edges, connected by a bar across the nail surface. The alloy exerts an expansive force as it warms to body temperature, slowly correcting the curve. The limitation of wire systems is their potential for dislodgement and the technical skill required for precise application.

Conversely, composite resin systems, such as the Onyfix® Nail Correction System, have gained recent prominence. This technique involves applying a hardened composite resin strip, cured via an LED light, across the base of the nail plate. As the composite cures, it establishes a permanent, tension-free corrective force. As the nail grows distally from the matrix, the hardened composite acts as a splint, guiding the new growth into a flatter, more anatomically correct shape. The treatment course is prolonged, often requiring three to four composite applications over a six-to-twelve-month period to allow the entire nail plate to grow out fully corrected. Clinical studies have shown these methods to be highly effective at providing long-term pain relief and morphological correction, often with immediate symptomatic relief and without the downtime or risks associated with surgery. However, patients must be aware that long-term adherence to preventative measures remains essential to prevent recurrence once the device is removed.

For severe, recalcitrant, or repeatedly recurring pincer nails that are unresponsive to non-invasive treatments, definitive surgical intervention is often necessary to achieve a permanent cure. Surgical strategies focus on permanently reducing the width of the nail plate and correcting any underlying anatomical abnormalities. The most commonly performed procedure is a Partial Nail Avulsion with Chemical Matrixectomy. This involves removing a narrow, offending strip of the lateral nail plate border, followed by chemical ablation (destruction) of the corresponding lateral horn of the germinal nail matrix. Phenol (usually 88%) is the traditional and gold-standard chemical agent, causing localized chemical destruction via coagulation necrosis, while sodium hydroxide (NaOH) is a common alternative. This procedure permanently narrows the nail plate, thereby preventing the severe transverse curvature from recurring.

In cases of severe PND, particularly those involving an underlying skeletal abnormality like a dorsal exostosis (a bony spur) on the distal phalanx, more complex Definitive Surgical Reconstruction may be required. These reconstructive procedures aim not just to narrow the nail but to physically widen the nail bed or re-establish a flatter foundation for nail growth. Techniques may include:

• Wedge Resection and Nail Bed Widening: This involves surgically excising the hypercurved lateral portions of the nail bed along with the lateral matrix horn, followed by meticulous suturing to reconstruct a flatter nail unit.
• Osteophyte Removal: If an exostosis is identified radiographically, the bony spur must be surgically rongeured away, as its presence mechanically forces the nail matrix dorsally, contributing directly to the pathological curvature.
• Dermal Grafting or Flap Procedures: For highly contracted nail beds, procedures like the Z-plasty technique or the insertion of a dermal or mucosal graft may be used to physically expand the nail bed width, preventing lateral compression.

These surgical methods, while more invasive, offer the highest likelihood of a permanent cure and are critical for restoring both function and cosmetic appearance in advanced PND. Long-term outcomes for surgical matricectomy show relatively low recurrence rates, typically between 5% and 15%, provided the entire lateral matrix is successfully ablated and any underlying skeletal pathology is addressed.

The treatment of pincer toenails is dictated by the severity of the deformity, the presence of concurrent symptoms, and patient-specific factors. The treatment pathway is a clinical ladder: starting with education and simple conservative care for mild cases; progressing to non-invasive orthonyx bracing for moderate, high-risk, or non-responsive cases; and culminating in definitive surgical matrixectomy or reconstructive procedures for severe, chronic, or recurrent disease. Effective management requires a careful differential diagnosis to address causative factors, such as footwear and infection, and a commitment to personalized care to ensure optimal long-term outcomes, minimizing pain, restoring nail function, and reducing the likelihood of recurrence.