The possible causes of hard lumps at the joints of the little finger include subcutaneous foreign bodies, keratosis, osteomalacia, tendon sheath cysts, viral infections, joint inflammation, and so on. 1. Subcutaneous foreign body: such as wooden thorns, hair, etc. into the subcutaneous, not timely treatment of the formation of hard lumps, generally painful when pressed, accompanied by redness, swelling. 2. Keratosis pilaris: it can be caused by long-term wear and tear, chronic skin diseases, etc., manifested as dry, cracked hard lumps. 3. Osteomalacia: commonly found in degenerative diseases of fingers, overstrain, bruises, etc. Typical manifestations are hard lumps in joints, pain, stiffness and rattling sound when moving fingers. 4. Tendon sheath cysts: joint lumps caused by chronic strain, arthritis, etc. Typically characterized by elasticity, clear boundaries, smooth surface, which may be accompanied by pressure pain, finger weakness and other symptoms. 5. Viral infections: most commonly seen in human papilloma virus caused by warts, mainly manifested as hard, rough protrusions and scattered black dots. 6. Joint inflammation: such as gouty arthritis, rheumatoid arthritis, etc., due to the inflammation caused by calcification phenomenon, so that the joints appear hard bumps, accompanied by obvious pain, redness and swelling, decreased mobility of the finger joints and so on. In addition, synovial lesions and cysts may also form bumps in the finger joints. This symptom alone cannot determine the cause of the disease. If the bumps continue to grow or are accompanied by obvious pain, it is recommended to go to the hospital as soon as possible to complete the relevant examinations and under the guidance of the doctor to carry out targeted treatment.