Ulna
Encyclopedia
The ulna is one of the two long bones in the forearm
, the other being the radius
. It is prism
atic in form and runs parallel to the radius, which is shorter and smaller. In anatomical position (i.e. when the arms are down at the sides of the body and the palms of the hands face forward) the ulna is located at the side of the forearm closest to the body (the medial side), the side of the little finger
. The corresponding bone in the leg
is the fibula.
Proximally, the ulna has a bony process
, the olecranon process, a hook-like structure that fits into the olecranon fossa
of the humerus. This prevents hyperextension and forms a hinge joint with the trochlea of the humerus.
There is also a radial notch
for the head of the radius, and the ulnar tuberosity to which muscles attach.
At the distal end of the ulna is a styloid process
.
http://www.innerbody.com/image_skelfov/skel21_new.html
types of the ulna include:
s, the olecranon process is still present, albeit as a projection from the upper radius.
Forearm
-See also:*Forearm flexors*Forearm muscles...
, the other being the radius
Radius (bone)
The radius is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna, which exceeds it in length and size. It is a long bone, prism-shaped and slightly curved longitudinally...
. It is prism
Prism (geometry)
In geometry, a prism is a polyhedron with an n-sided polygonal base, a translated copy , and n other faces joining corresponding sides of the two bases. All cross-sections parallel to the base faces are the same. Prisms are named for their base, so a prism with a pentagonal base is called a...
atic in form and runs parallel to the radius, which is shorter and smaller. In anatomical position (i.e. when the arms are down at the sides of the body and the palms of the hands face forward) the ulna is located at the side of the forearm closest to the body (the medial side), the side of the little finger
Little finger
The little finger, often called the pinky in American English, pinkie in Scottish English , or small finger in medicine, is the most ulnar and usually smallest finger of the human hand, opposite the thumb, next to the ring finger.-Muscles:There are four muscles that...
. The corresponding bone in the leg
Human leg
The human leg is the entire lower extremity or limb of the human body, including the foot, thigh and even the hip or gluteal region; however, the precise definition in human anatomy refers only to the section of the lower limb extending from the knee to the ankle.Legs are used for standing,...
is the fibula.
Articulations
The ulna articulates with:- trochlea of the humerusHumerusThe humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
, at the right side elbow as a hinge jointHinge jointA hinge joint is a bone joint in which the articular surfaces are molded to each other in such a manner as to permit motion only in one plane—backward and forward—the extent of motion at the same time being considerable....
with semilunar trochlear notch of the ulna. - the radiusRadius (bone)The radius is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna, which exceeds it in length and size. It is a long bone, prism-shaped and slightly curved longitudinally...
, near the elbow as a pivot jointPivot jointA Pivot joint is a type of diarthrosis, or synovial joint. In pivot joints, the axis of a convex articular surface is parallel with the longitudinal axis of the bone.-Movements:...
, this allows the radius to cross over the ulna in pronationPronationIn anatomy, pronation is a rotational movement of the forearm at the radioulnar joint, or of the foot at the subtalar and talocalcaneonavicular joints. For the forearm, when standing in the anatomical position, pronation will move the palm of the hand from an anterior-facing position to a...
. - the distal radius, where it fits into the ulna notch.
- the radius along its length via the interosseous membraneInterosseous membraneAn interosseous membrane is a broad and thin plane of fibrous tissue that separates many of the bones of the body. It is an important component of many joints.Interosseous membranes in the human body:* Interosseous membrane of the forearm...
that forms a syndesmoses joint - it is also called the poisidion
Proximal and distal aspects
The ulna is broader proximally, and narrower distally.Proximally, the ulna has a bony process
Process (anatomy)
In anatomy, a process is a projection or outgrowth of tissue from a larger body. The vertebra has several kinds of processes,such as: transverse process, prezygapophysis, postzygapophysis.-Examples:Examples of processes include:...
, the olecranon process, a hook-like structure that fits into the olecranon fossa
Olecranon fossa
The olecranon fossa is a deep triangular depression on the posterior side of the humerus, superior to the trochlea, in which the summit of the olecranon is received during extension of the forearm.-External links: *...
of the humerus. This prevents hyperextension and forms a hinge joint with the trochlea of the humerus.
There is also a radial notch
Radial notch
The radial notch of the ulna is a narrow, oblong, articular depression on the lateral side of the coronoid process; it receives the circumferential articular surface of the head of the radius....
for the head of the radius, and the ulnar tuberosity to which muscles attach.
At the distal end of the ulna is a styloid process
Ulnar styloid process
The styloid process of the ulna projects from the medial and back part of the bone; it descends a little lower than the head, and its rounded end affords attachment to the ulnar collateral ligament of the wrist-joint....
.
Structure
The long, narrow medullary cavity is enclosed in a strong wall of compact tissue which is thickest along the interosseous border and dorsal surface. At the extremities the compact layer thins. The compact layer is continued onto the back of the olecranon as a plate of close spongy bone with lamellæ parallel. From the inner surface of this plate and the compact layer below it trabeculæ arch forward toward the olecranon and coronoid and cross other trabeculæ, passing backward over the medullary cavity from the upper part of the shaft below the coronoid. Below the coronoid process there is a small area of compact bone from which trabeculæ curve upward to end obliquely to the surface of the semilunar notch which is coated with a thin layer of compact bone. The trabeculæ at the lower end have a more longitudinal direction.http://www.innerbody.com/image_skelfov/skel21_new.html
Muscle attachments
| Muscle | Direction | Attachment |
| Insertion | >- | Insertion | >- | Insertion | Coronoid process of the ulna Coronoid process of the ulna The coronoid process is a triangular eminence projecting forward from the upper and front part of the ulna.Its base is continuous with the body of the bone, and of considerable strength.... >- | Pronator teres muscle Pronator teres muscle The pronator teres is a muscle of the human body that, along with the pronator quadratus muscle, serves to pronate the forearm .-Structure:... |
Origin | medial epicondyle of the humerus Medial epicondyle of the humerus The medial epicondyle of the humerus, larger and more prominent than the lateral epicondyle, is directed a little backward. In birds, where the arm is somewhat rotated compared to other tetrapods, it is called ventral epicondyle of the humerus.... ) >- | Flexor carpi ulnaris muscle Flexor carpi ulnaris muscle The flexor carpi ulnaris muscle is a muscle of the human forearm that acts to flex and adduct the hand.-Origin and insertion:Flexor carpi ulnaris muscle arises by two heads - humeral and ulnar, connected by a tendinous arch beneath which the ulnar nerve and ulnar artery pass.* The humeral head... |
Origin | >- | Origin | radius Radius In classical geometry, a radius of a circle or sphere is any line segment from its center to its perimeter. By extension, the radius of a circle or sphere is the length of any such segment, which is half the diameter. If the object does not have an obvious center, the term may refer to its... ) >- | Flexor digitorum profundus muscle Flexor digitorum profundus muscle - References :... |
Origin | interosseous membrane Interosseous membrane An interosseous membrane is a broad and thin plane of fibrous tissue that separates many of the bones of the body. It is an important component of many joints.Interosseous membranes in the human body:* Interosseous membrane of the forearm... ) >- | Pronator quadratus muscle |
Origin | >- | Origin | lateral epicondyle of the humerus Lateral epicondyle of the humerus The lateral epicondyle of the humerus is a small, tuberculated eminence, curved a little forward, and giving attachment to the radial collateral ligament of the elbow-joint, and to a tendon common to the origin of the Supinator and some of the Extensor muscles. In birds, where the arm is somewhat... ) >- | Supinator muscle Supinator muscle In human anatomy, the supinator is a broad muscle in the posterior compartment of the forearm, curved around the upper third of the radius. Its function is to supinate the forearm.-Terminology:... |
Origin | >- | Origin | >- | Origin | dorsal Dorsum (biology) In anatomy, the dorsum is the upper side of animals that typically run, fly, or swim in a horizontal position, and the back side of animals that walk upright. In vertebrates the dorsum contains the backbone. The term dorsal refers to anatomical structures that are either situated toward or grow... shaft of ulna (also shares origin with the dorsal shaft of the radius and the interosseous membrane) >- | Extensor pollicis brevis muscle Extensor pollicis brevis muscle In human anatomy, the extensor pollicis brevis is a skeletal muscle on the dorsal side of the forearm. It lies on the medial side of, and is closely connected with, the abductor pollicis longus.-Origin and insertion:... |
Origin | >- | Origin | Posterior surface of distal ulna (also shares origin with the interosseous membrane) |
Fracture
Specific fractureBone fracture
A bone fracture is a medical condition in which there is a break in the continuity of the bone...
types of the ulna include:
- Monteggia fractureMonteggia fractureThe Monteggia fracture is a fracture of the ulna that affects the joint with the radius. More precisely, it is a fracture of the proximal third of the ulna with dislocation of the head of the radius...
- a fracture of the proximal third of the ulna with the dislocation of the head of the radius - Hume fractureHume fractureThe Hume fracture is an injury of the elbow comprising a fracture of the olecranon with an associated anterior dislocation of the radial head which occurs in children. It was originally described as an undisplaced olecranon fracture, but more recently includes displaced fractures and can be...
- a fracture of the olecranonOlecranonThe olecranon is a large, thick, curved bony eminence of the forearm that projects behind the elbow.It is situated at the upper end of the ulna, one of the two bones in the forearm...
with an associated anterior dislocation of the radial headHead of radiusThe head of the radius has a cylindrical form, and on its upper surface is a shallow cup or fovea for articulation with the capitulum of the humerus....
In other animals
In four-legged animals, the radius is the main load-bearing bone of the lower forelimb, and the ulna is important primarily for muscular attachment. In many mammals, the ulna is partially or wholly fused with the radius, and may therefore not exist as a separate bone. However, even in extreme cases of fusion, such as in horseHorse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
s, the olecranon process is still present, albeit as a projection from the upper radius.
See also
- Bone terminology
- Terms for anatomical location
- Ossification of ulnaOssification of ulnaThe ulna is ossified from three centers: one each for the body, the inferior extremity, and the top of the olecranon.Ossification begins near the middle of the body, about the eighth week of fetal life, and soon extends through the greater part of the bone....