Bones Variation
Accessory ossicles
Small extra bones, most often in the foot, that form when a growth centre never fuses with its main bone. They are usually harmless but can be mistaken for fractures on an X-ray.
About 2 in 5 feet
Bones and joints
Cracking, bending, extra bones, missing bones, and joint flexibility.
Showing 12 oddities.
Bones and joints set the shape and the range of movement of the whole skeleton. Small differences in how they form, or how far they bend, show up for life, usually with no effect on health.
Cervical ribs and accessory ossicles are extra bone, formed where none is expected. Hitchhiker's thumb and hypermobility are about how far a joint bends past the average. Knuckle cracking is neither of those: it is a sound made by gas forming in the fluid of a normal joint.
Most of these are simple variation, not damage. A joint that bends further, or a bone that grew an extra piece, is a structural fact about that person's skeleton. The entries here answer the question people ask when they notice something odd about their own bones: is this normal, and what does it mean.
Results narrow the list below as you type.
Bones Variation
Camptodactyly
A finger that stays bent forward at its middle joint and cannot fully straighten, usually the little finger. Under 1% of people have it. Mild cases rarely cause trouble, but the bend can get worse while a child grows.
Under 1% of people
Bones Variation
Cervical rib
An extra rib above the normal top rib, growing from the lowest bone in the neck. About 1 in 100 people have one, and most never know.
About 1% of people
Bones Variation
Clinodactyly
A finger that curves sideways toward its neighbours, most often the little finger leaning toward the ring finger. Between 1% and 20% of people have it, and on its own it is harmless.
1–20% of people
Bones Variation
Hitchhiker's thumb
A thumb whose top joint bends back past 50 degrees, once taught as a simple recessive gene. Thumb angle is really a smooth range, and the genetics are not that simple.
24–36% of people in the US
Bones Variation
Joint hypermobility
About 1 in 5 people have joints that bend further than usual, measured with a nine-point test called the Beighton score. For most people it causes no trouble.
10–25% of people
Bones Trick
Knuckle cracking
Pulling or bending a finger joint until it pops. Between 25% and 54% of people do it out of habit. The pop comes from a gas bubble in the joint fluid, and it does not cause arthritis.
25–54% crack habitually
Bones Trick
Midtarsal break
A foot that bends in the middle, between the heel and the ball, as well as at the toes. About 1 in 12 people have it. It looks like the midfoot bend of apes.
About 1 in 12 (8%)
Bones Variation
Morton's toe
A second toe that looks longer than the big toe because the first metatarsal bone in the foot is short. It is common, and it is the foot shape seen on classical Greek statues.
3–22% of people
Bones Variation
Torus palatinus
A hard bony lump along the midline of the roof of the mouth that grows slowly and is completely harmless. Many people find it by chance and worry that it is a tumour.
About 20% of people
Bones Trick
Voluntary joint dislocation
Pushing a joint partly or fully out of its socket on purpose, then back in. Between 10% and 25% of people have some joint hypermobility. One survey of students and their siblings found 0.5% to 2.6% could dislocate a shoulder at will.
0.5–2.6% (shoulder, one survey) Icky
Bones Variation
Webbed toes
Two toes joined by skin, most often the second and third, in about 1 in 2,000 to 2,500 babies. The toes usually work normally and many people leave them as they are.
About 1 in 2,000–2,500 births