Sesamoid bone

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Sesamoid bone

In anatomy

Anatomy

Anatomy is a branch of biology that is the consideration of the body plan. It is a general term that includes human anatomy, animal anatomy and plant anatomy ....
, a sesamoid bone is a bone

Bone

Bones are rigid organ that form part of the endoskeleton of vertebrates. They function to move, support, and protect the various organs of the body, produce red blood cell and white blood cells and store minerals....
embedded within a tendon

Tendon

A tendon is a tough band of fibrous connective tissue that usually connects muscle to bone and is capable of withstanding tension . Tendons are similar to ligaments except that ligaments join one bone to another....
. They usually resemble sesame

Sesame

Sesame is a flowering plant in the genus Sesamum. Numerous wild relatives occur in Africa and a smaller number in India. It is widely naturalization in tropical regions around the world and is cultivated for its edible seeds, which grow in pods....
seed, hence the name.

Sesamoid bones are typically found in locations where a tendon passes over a joint

Joint

A joint is the location at which two or more bones make contact. They are constructed to allow movement and provide mechanical support, and are classified structurally and functionally....
, such as the hand, knee, and foot. Functionally, they act to protect the tendon and to increase its mechanical effect. The presence of the sesamoid bone holds the tendon slightly farther away from the center of the joint and thus increases its moment arm

Moment (physics)

In physics, the term "moment" can refer to many different concepts:*Moment of force is a synonym for torque, an important basic concept in physics, civil engineering, and mechanical engineering....
.

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Human anatomy

Sesamoid bones can be found on joints throughout the body, including:

In the knee
Knee

----The knee is the lower extremity joint connecting the femur, patella, and the tibia and the surrounding anatomical region which includes the popliteal fossa, also known as "knee pit"....
- the patella
Patella

The patella, also known as the knee cap or kneepan, is a thick, triangular bone which articulates with the femur and covers and protects the knee joint....
In the hand
Hand

The hands are the two intricate, prehensile, multi-fingered body parts normally located at the end of each arm of a human or other primate. They are the chief organs for physically manipulating the environment, using anywhere from the roughest motor skills to the finest , and since the fingertips contain some of the densest areas of nerve e...
- two sesamoid bones are located in distal
Anatomical terms of location

Standard anatomical terms of location are employed in sciences dealing with the anatomy of animals to avoid ambiguities which might otherwise arise....
portions of the first metacarpal bone
First metacarpal bone

The first metacarpal bone which connects to the thumb is shorter and stouter than the others, diverges to a greater degree from the carpus, and its volar surface is directed toward the palm....
. There is also commonly a sesamoid bone in distal portions of the second metacarpal bone
Second metacarpal bone

The second metacarpal bone is the longest, and its base the largest, after the first metacarpal.Its base is prolonged upward and medialward, forming a prominent ridge....
. The pisiform of the wrist
Carpus

In tetrapods, the carpals is the sole cluster of the bones in the wrist between the radius and ulna and the metacarpus. The bones of the carpus do not belong to individual fingers , whereas those of the metacarpus do....
is a sesamoid bone as well.
In the foot
Foot

The foot is an anatomical structure found in many animals. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is a separate organ at the terminal part of the leg made up of one or more segments or bones, generally including claws or nails....
- the first metatarsal bone
First metatarsal bone

The first metatarsal bone is the bone in the body of the foot just behind the big toe.It is remarkable for its great thickness, and is the shortest of the metatarsal bones....
has two sesamoid bones at its connection to the big toe
Hallux

The hallux, commonly referred to as the big toe , although it may not be the longest toe on the foot of some people, is the innermost toe of the foot....
.

Injuries of the sesamoid bones

A common foot ailment in dancers is sesamoiditis
Sesamoiditis

Sesamoiditis is inflammation of the sesamoid bones. In humans it occurs on the bottom of the foot, just behind the large toe. There are normally two sesamoid bones on each foot; sometimes sesamoids can be bipartite, which means they each comprise two separate pieces....
.
A bi-partite sesamoid bone is when the sesamoids are in 2 separate entities - usually congenital, but may be related to a history of trauma.

Equine anatomy

In equine anatomy, the term sesamoid bone usually refers to the two sesamoid bones found at the back of the fetlock

Fetlock

Fetlock is the common name for the metacarpophalangeal and metatarsophalangeal joints of the horse. It is formed by the junction of the third metacarpal or metatarsal bones proximad and the proximal phalanx distad ....
or metacarpophalangeal/metatarsophalangeal joints in both hindlimbs and forelimbs

Equine forelimb anatomy

The equine forelimb is the front, or thoracic limb of the horse. It is attached to the trunk of the animal by purely muscular connections ....
. Strictly these should be termed the proximal sesamoid bones whereas the navicular bone

Navicular bone

The navicular bone occurs in human and horse anatomy....
should be referred to as the distal sesamoid bone. The patella is also a form of sesamoid bone in the horse.

Panda anatomy

In both the giant panda

Giant Panda

The Giant Panda is a mammal classified in the bear family , native to central-western and southwestern China. The Giant Panda was previously thought to be a member of the Procyonidae family....
and the red panda

Red Panda

The Red Panda, also called the Firefox or Lesser Panda , is a mostly herbivorous mammal, specialized as a bamboo feeder. It is slightly larger than a domestic cat ....
, the radial sesamoid is larger than the same bone in counterparts such as bear

Bear

Bears are mammals of the family Ursidae. Bears are classified as caniforms, or doglike carnivorans, with the pinnipeds being their closest living relatives....
s. It is primarily a bony support for the pad above it, allowing the panda's other digits to grasp bamboo

Bamboo

The bamboos are a group of woody perennial plant evergreen plants in the true grass family Poaceae, subfamily Bambusoideae, tribe Bambuseae....
while eating it. The panda's thumb is often cited as a classical example of exaptation

Exaptation

Exaptation, cooption, and preadaptation are related terms referring to shifts in the function of a trait during evolution. For example, a trait can evolve because it served one particular function, but subsequently it may come to serve another....
, where a trait evolved for one purpose is commandeered for another.

Sesamoid bone

Human anatomy

Injuries of the sesamoid bones

Equine anatomy

Panda anatomy

See also