A small bone on the palm bone is considered to be a congenital developmental abnormality, osteophyte, bone tumor, tendon sheath cyst and so on. 1. Congenital developmental abnormality: developmental abnormality can appear in the palm of the hand finger parts of the polydactyly, due to the deformity of the finger is shorter than the normal finger, can be manifested in the palm of the bone on the growth of a small bone. 2. Bone hyperplasia: due to osteoarthritis, rheumatoid arthritis, etc., it can lead to the formation of spiny or labial bone spurs on the edge of the bone, or wear and tear of the articular cartilage, which can lead to the hyperplasia on the edge of the joints to form bone cumbersome. 3. Bone tumor: when there is bone tumor in the palm of hand or when bone metastatic cancer reaches the palm of hand, it can form a hard lump on the bones of palm of hand which grows gradually. 4. Tendon sheath cyst, due to the continuous flexion and extension activities of fingers, the flexor tendons of fingers are constantly rubbing inside the tendon sheath, which causes the tendon sheath to be swollen, forming a hard lump that looks like a small bone. Small bones on the bones of the palm of the hand is recommended to actively seek medical attention, physician guidance under the treatment.