Bumps at the root of middle finger in infants can be caused by osteochondroma, tendon sheath cyst, stenosing tenosynovitis, seed bone and other factors. 1. Osteochondroma: small bone-like bump at the root of the middle finger may be osteochondroma, which is a bony swelling protruding outward from the bone, and the local inflammatory reaction may occur and cause pain symptoms. 2. Tendon sheath cyst: due to the abnormal development of the tendon sheath at the root of the middle finger, it can lead to the increase of local synovial fluid, which can stimulate the surrounding tissues to appear the peritendinous membrane, leading to the appearance of the middle finger root bulge. 3. Stenosing tenosynovitis: stenosing tenosynovitis can be present at birth, and the inflammation stimulates the tendon to form a hard knot, which leads to a bulge at the root of the finger. 4. Seed bone: the bone at the root of the middle finger in infants can develop a seed bone, which is mostly located in the tendon and can strengthen the stability of the tendon, and a bump-like mass can be detected at the root of the middle finger. When there is a bump at the root of the middle finger in infants, they should consult a doctor in time. Under the guidance of specialists, they should actively carry out appropriate treatments, which can help to alleviate the uncomfortable symptoms as soon as possible.