The purpose of this study is to assess the overall effect of KeryFlex study intervention on quality of life and functionality for patients with retronychia or nail lichen planus.

Retronychia is the growth of the proximal nail plate into the proximal nail fold which was first described in 1999 by De Berker and Rendall. The disorder is common and most frequently affects women (~82%); the estimated average age is 39 years. The unilateral hallux is the most commonly diagnosed site, though nails of the hand (especially thumb and index finger) may also be affected. Common triggers of retronychia include minor trauma (e.g., wearing poorly fitting shoes, jogging,) and systemic illness (e.g., arthritis, thrombophlebitis), which cause disruption of the longitudinal nail bed growth and ultimately lead to the new plate growing vertically into the proximal nail fold. The most frequent cause is trauma. Clinical symptoms include pain, inflammation of the proximal nail fold, granulation tissue under the proximal nail fold, and changes in the proximal nail plate such as thickening or yellowing. Diagnosis is confirmed by clinical presentation and ultrasound. Treatment is particularly challenging. Topical corticosteroids have been used with favorable results; however, recurrences are frequent. Complete nail avulsion is used for severe and/or recalcitrant cases, but this is also associated with frequent relapse rates.

Lichen planus is a chronic inflammatory dermatosis involving mucocutaneous surfaces, scalp, and nails. Nail involvement is observed in around 10% of patient and typically affects the fingernails more than toenails. Nail lichen planus can cause extensive scarring and nail loss. Permanent dystrophy in the forms of anonychia and dorsal pterygium has both functional and psychological consequences. Diagnosis is typically clinical, but a punch biopsy of the nail matrix or nail bed may be utilized if a diagnosis is questionable. There is no evidence-based management for nail lichen planus to date, though expert consensus recommends intralesional steroid injections or systemic corticosteroids as first-line treatment. Outcomes are inconsistent with steroid treatment.

KeryFlex nail is defined as a cosmetic by the Food and Drug Administration (FDA). KeryFlex is a painless, in-office aesthetic application of acrylic nails which improves the appearance of nails damaged by various nail disorders. The composite resin creates a flexible, nonporous nail that allows the remaining natural nail to grow. KeryFlex is composed of a resin material which is applied on the affected nails following the next steps: debridement of the nail, application of bond, application of the resin in the desired color, shape, and size, and curing of the resin by an ultraviolet light. The typical interval between KeryFlex applications is 6 to 8 weeks.

Application of an artificial resin nail to the affected digit may help counter burdensome effects of retronychia or nail lichen planus, including impaired social interactions and loss of functionality. There are no other options for symptom management of retronychia or nail lichen planus in the literature to our knowledge. Attachment of an artificial nail to the newly growing nail may also prevent distal embedding caused by dorsal expansion of the distal pulp, a possible complication of the loss of counterpressure induced by the loss of the nail plate after total nail avulsion.6 Nail resin will be applied as part of the study. Importantly, patients with retronychia very often report that their nail does not grow as quickly as the non-affected ones. Therefore, Keryflex application may be particularly useful if these patients, considering that they would not need to replace the Keryflex as often.

KeryFlex, Pod-Advance, Inc. will provide necessary equipment, but it does not pay Weill Cornell Medicine to conduct this study.

At the screening visit, potential participants will be screened by inclusion and exclusion criteria. History will be obtained including review of medications. Nail clipping sample for histopathology will be taken to rule out onychomycosis if a diagnosis of retronychia is unclear.

Patients will be consented and at baseline visit, during which patients will also be asked to take a quality of life survey to assess baseline impact of retronychia on quality of life. Pre-treatment photographs of patient toenails will be taken. KeryFlex will then be applied to patients' affected nails.

Patients will come to clinic eight weeks after baseline visit, at which point patients will be asked to take a repeat quality of life and satisfaction survey. Post-treatment photographs of patient resin nails will be taken. KeryFlex will then be removed, and photographs post-removal will be taken. The typical interval between KeryFlex application is 6 to 8 weeks.

At two-month follow up visit after KeryFlex treatment, patients will be asked to take a repeat quality of life and satisfaction survey. Post-treatment photographs of patient toenails will be taken. KeryFlex resin will be removed, and photographs post-removal will be taken.

Inclusion criteria:

• Diagnosis of retronychia or nail lichen planus
• Able to understand and voluntarily sign an informed consent form
• 18-95 years old at time of consent
• Able to adhere to the study visit schedule and other protocol requirements

Exclusion criteria:

• Unable to provide written informed consent for any reason
• Diagnosis of peripheral vascular disease, arterial insufficiency, peripheral neuropathy, suspicious pigmented lesions on the nail or in-grown nails
• Sensitive or allergic to any KeryFlex ingredients
• Unable to abstain from using nail polishes, nail gels, or any other nail products 2 days prior to KeryFlex procedure and during the study period
• Pregnant, planning pregnancy, or nursing