Sesamoid bone

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Sesamoid bone_table_infobox_0

Sesamoid boneSesamoid bone_header_cell_0_0_0
DetailsSesamoid bone_header_cell_0_1_0
IdentifiersSesamoid bone_header_cell_0_2_0
LatinSesamoid bone_header_cell_0_3_0 os sesamoideum

pl. ossa sesamoideaSesamoid bone_cell_0_3_1

MeSHSesamoid bone_header_cell_0_4_0 Sesamoid bone_cell_0_4_1
TA98Sesamoid bone_header_cell_0_5_0 Sesamoid bone_cell_0_5_1
TA2Sesamoid bone_header_cell_0_6_0 Sesamoid bone_cell_0_6_1
FMASesamoid bone_header_cell_0_7_0 Sesamoid bone_cell_0_7_1

In anatomy, a sesamoid bone (/ˈsɛsəmɔɪd/) is a bone embedded within a tendon or a muscle. Sesamoid bone_sentence_0

It is derived from the Latin word sesamum ("sesame seed"), indicating the small size of most sesamoids. Sesamoid bone_sentence_1

Often, these bones form in response to strain, or can be present as a normal variant. Sesamoid bone_sentence_2

The kneecap is the largest sesamoid bone in the body. Sesamoid bone_sentence_3

Sesamoids act like pulleys, providing a smooth surface for tendons to slide over, increasing the tendon's ability to transmit muscular forces. Sesamoid bone_sentence_4

The sesamoid is a small nodular bone most often present embedded in tendons in the region of the thumb. Sesamoid bone_sentence_5

Calcification of sesamoid bone is one of the important features of pubertal growth spurt, which is earlier in females than in males. Sesamoid bone_sentence_6

Absence of sesamoid bone indicates delay in reaching puberty. Sesamoid bone_sentence_7

Structure Sesamoid bone_section_0

Sesamoid bones can be found on joints throughout the body, including: Sesamoid bone_sentence_8

Sesamoid bone_unordered_list_0

  • In the knee—the patella (within the quadriceps tendon). This is the largest sesamoid bone.Sesamoid bone_item_0_0
  • In the hand—two sesamoid bones are commonly found in the distal portions of the first metacarpal bone (within the tendons of adductor pollicis and flexor pollicis brevis). There is also commonly a sesamoid bone in distal portions of the second metacarpal bone.Sesamoid bone_item_0_1
  • In the wrist—The pisiform of the wrist is a sesamoid bone (within the tendon of flexor carpi ulnaris). It begins to ossify in children ages 9–12.Sesamoid bone_item_0_2
  • In the foot—the first metatarsal bone usually has two sesamoid bones at its connection to the big toe (both within the tendon of flexor hallucis brevis). One is found on the lateral side of the first metatarsal while the other is found on the medial side. In some people, only a single sesamoid is found on the first metatarsal bone.Sesamoid bone_item_0_3
  • In the neck—Although the hyoid bone is free-floating, it is not technically a sesamoid bone. All sesamoid bones form directly from the connective tissue found in tendons and ligaments. By contrast, the hyoid bone forms from a cartilaginous precursor like most other bones in the body.Sesamoid bone_item_0_4
  • In the ear—the lenticular process of the incus is a sesamoid bone and therefore is considered the fourth ossicle of the middle ear.Sesamoid bone_item_0_5

Common variants Sesamoid bone_section_1

Sesamoid bone_unordered_list_1

  • One or both of the sesamoid bones under the first metatarsophalangeal joint (of the great toe) can be multipartite – in two or three parts (mostly bipartite – in two parts). (See the X-ray photograph of the foot on the right.)Sesamoid bone_item_1_6
  • The fabella is a small sesamoid bone found in some mammals embedded in the tendon of the lateral head of the gastrocnemius muscle behind the lateral condyle of the femur. It is a variant of normal anatomy and present in humans in 10% to 30% of individuals. The fabella can also be mutipartite or bipartite.Sesamoid bone_item_1_7
  • The cyamella is a small sesamoid bone embedded in the tendon of the popliteus muscle. It is a variant of normal anatomy. It is rarely seen in humans, but has been described more often in other primates and certain other animals.Sesamoid bone_item_1_8

Sesamoid bone_unordered_list_2

  • Sesamoid bone_item_2_9
  • Sesamoid bone_item_2_10

Clinical significance Sesamoid bone_section_2

Sesamoid bone_unordered_list_3

  • A common foot ailment in dancers is sesamoiditis (an inflammation of the sesamoid bones under the first metatarsophalangeal joint of the big toe). This is a form of tendinitis which results from the tendons surrounding the sesamoid becoming inflamed or irritated.Sesamoid bone_item_3_11
  • Sesamoid bones generally have a very limited blood supply, rendering them prone to avascular necrosis (bone death from lack of blood supply), which is very difficult to treat.Sesamoid bone_item_3_12

Other animals Sesamoid bone_section_3

See also: The Panda's Thumb (book) Sesamoid bone_sentence_9

In equine anatomy, the term sesamoid bone usually refers to the two sesamoid bones found at the back of the fetlock or metacarpophalangeal and metatarsophalangeal joints in both hindlimbs and forelimbs. Sesamoid bone_sentence_10

Strictly these should be termed the proximal sesamoid bones whereas the navicular bone should be referred to as the distal sesamoid bone. Sesamoid bone_sentence_11

The patella is also a form of sesamoid bone in the horse. Sesamoid bone_sentence_12

Although many carnivores have radial sesamoid bones, the giant panda and red panda independently evolved to have an enlarged radial sesamoid bone. Sesamoid bone_sentence_13

This evolution has caused the two species to diverge from other carnivores. Sesamoid bone_sentence_14

The red panda likely originally evolved the "pseudo-thumb" in order to assist in arboreal locomotion. Sesamoid bone_sentence_15

When the red panda later evolved to consume a bamboo diet, the enlarged bone underwent exaptation to assist in grasping bamboo. Sesamoid bone_sentence_16

The giant panda, however, evolved the enlarged radial sesamoid bone around the same time as it evolved a bamboo diet. Sesamoid bone_sentence_17

In the giant panda, the bone allows for a pincer-like motion and is used in grasping the bamboo. Sesamoid bone_sentence_18

In these two panda species, DYNC2H1 gene and PCNT gene have been identified as possible causes for the pseudo-thumb development. Sesamoid bone_sentence_19

Recently, the enlarged radial sesamoid bone of cotton rats has been studied. Sesamoid bone_sentence_20

Their enlarged radial sesamoid bone and that of the giant panda have a similar morphology and size relative to the rest of the hand. Sesamoid bone_sentence_21

The reason for this evolutionary change is still unknown; however, it may be to assist in grasping small objects and thin branches. Sesamoid bone_sentence_22

See also Sesamoid bone_section_4

Sesamoid bone_unordered_list_4

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: bone.