A concave groove on the nail cap of the middle finger is abnormal and may be caused by trauma, iron deficiency anemia, nail malnutrition and other conditions. 1. Trauma: usually the patient’s nails are hit by external forces, causing trauma to the middle finger nails, resulting in nail plate damage, which will appear in the middle finger nail cover has a concave down a groove. 2. Iron deficiency anemia: it is usually caused by insufficient iron intake and excessive iron loss. Patients often have pale skin, dizziness, shortness of breath and other symptoms, some patients also have pale, thin nails, or even spatulate nails, which can be manifested as a concave groove on the nail cover of the middle finger. 3. Nail dystrophy: This condition may be caused by congenital incomplete nail formation, acquired nail nutritional disorders, and is also related to psoriasis, lichen planus, syphilis, scleroderma and other factors. Patients often appear nail plate thinning or thickening, and may also be accompanied by superficial fine line longitudinal ridge, which can be manifested as a concave groove on the nail cover of the middle finger. It is recommended that when patients have a concave groove on the nail cover of the middle finger, the cause of the disease should be clarified in time, and active treatment should be carried out.