It is a well-known fact that babies have more bones than adults. Newborn babies have between 275 and 300 bones, and as they grow, smaller bones fuse and harden to form larger bones, whereas most adults have only 206 bones (smaller, softer bones give the baby more flexibility to curl up in the womb and navigate the birth canal).
But is it possible for adults to gain bone mass as well?
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However, there are often no obvious signs that someone has more than the typical number of bones.
“It’s very easy to not realize that someone has an accessory bone,” Dr. Vandan Patel, an orthopedic surgeon at Mercy Medical Center Foot and Ankle Reconstruction Institute in Baltimore, told Live Science. In most cases, accessory bones do not cause symptoms. “We often find out that there is an accessory bone when we do an X-ray for an unrelated matter and it happens to be found,” he explained.
Ellen Ogut, associate professor of anatomy at Istanbul’s Medeniyat University, said even when X-rays show accessory bones, they are often overlooked or misinterpreted as fracture fragments or age-related changes. Overall, “studies suggest it occurs in approximately 10-30% of the general population,” but “the true prevalence is likely higher than generally recognized,” Ogut told Live Science.
Patel said appendicular bones are commonly found in the foot and ankle. The most common accessory bone is known as the triquetrum, he said. “This occurs in up to 10 to 25 percent of people,” Patel points out. “It’s located at the back of the ankle joint. It can cause pain, especially when you point your toes and ankle down, such as when a ballet dancer is in an en pointe position.”
Another common accessory bone is called the external tibial ostium, also known as the accessory scaphoid. “It’s found in up to 12% of the population,” Patel said. “This is located on the inside of the foot, next to the normal navicular bone. The navicular bone may appear enlarged. It can cause pain in the arch and is common in flatfoot deformities.”
Doctors also learn about many unusual accessory bones, Ogut said, often through studying cadavers and medical images. One example, he noted, is the acetabulum, the accessory bone of the hip joint that can be associated with hip pain. This accessory bone is found in less than 5% of the general population, Ogut noted in a 2025 review article in the Bratislava Medical Journal.
In some cases, it is also possible to have accessory ribs. According to the Cleveland Clinic, up to 1% of people are born with one or two extra neck bones, known as cervical ribs. This unusual bone does not resemble a typical rib. They may be vertical or diagonal instead of horizontal like the ribs in the chest. In most cases, cervical ribs do not cause problems, but they can cause pain and weakness in the arm. Physical therapy and medicine can help in these cases. The clinic noted that it can also be removed by surgeons as it serves no purpose.
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