Evaluation and management of mechanical and structural nail disorders: A clinical review

Physical trauma is the most common cause of toenail onychodystrophy, surpassing onychomycosis. Ill-fitting footwear and anatomical foot/toe abnormalities, including Morton's toe, hallux valgus/erectus/rigidus, and flat and splay foot, predispose the forefoot to nonphysiologic strain and toenail alterations, often resembling onychomycosis. Dystrophic toenails should therefore be assessed alongside foot and toe alignment while standing and walking, with close examination of footwear. Trauma-induced onychodystrophy predisposes to secondary onychomycosis, and histopathologic/mycologic confirmation is needed. Moreover, anatomic foot/toe abnormalities may worsen nail psoriasis through koebnerization. Thus, toenails may still appear dystrophic after treating comorbid conditions if the precipitating factor is not addressed or cannot be successfully treated. Additional nail disorders induced by mechanical trauma include subungual heloma, onychophosis, frictional onycholysis, leukonychia, melanonychia, Beau's lines/onychomadesis/retronychia, and disappearing nail bed. Additionally, arthritic conditions affecting the distal interphalangeal joint may theoretically impact the adjacent nail matrix and cause nail alterations. Hyperglycemia, neuropathy, and vasculopathy likely play a role in the pathogenesis of onychodystrophies in patients with diabetes mellitus. Diabetic patients are prone to developing structural foot/toe problems, onychomycosis, and ingrown toenails (onychocryptosis), which increase their risk of ulcer formation. Therefore, treating onychomycosis and onychocryptosis in diabetic patients is crucial to prevent complications, including ulcers, osteomyelitis, and amputations.