Nail Diseases: Diseases of the nail plate and tissues surrounding it. The concept is limited to primates.Arthritis, Psoriatic: A type of inflammatory arthritis associated with PSORIASIS, often involving the axial joints and the peripheral terminal interphalangeal joints. It is characterized by the presence of HLA-B27-associated SPONDYLARTHROPATHY, and the absence of rheumatoid factor.Nails: The thin, horny plates that cover the dorsal surfaces of the distal phalanges of the fingers and toes of primates.Bone Nails: Rods of bone, metal, or other material used for fixation of the fragments or ends of fractured bones.Nails, Ingrown: Excessive lateral nail growth into the nail fold. Because the lateral margin of the nail acts as a foreign body, inflammation and granulation may result. It is caused by improperly fitting shoes and by improper trimming of the nail.