Bones of the Upper Limb: Scapula Anatomy

The coracoid process in the scapula has an ossification center that appears in the first year of life and fuses at 15 years of age. Secondary centers appear between 14 and 20 years of age and fuse between 22 and 25 years of age.

The glenoid's oblique orientation from posterior to anterior and lateral to medial helps prevent posterior dislocation following a fall on an outstretched hand, but increases the likelihood of anterior dislocation following a direct fall on the shoulder.

The clavicle, a bone between the sternoclavicular and acromioclavicular joints, is attached to the first costal cartilage and is the first bone to begin ossification. It is also the site of the subclavian vessels and the brachial plexus trunks.

The humerus, the long bone in the upper limb, has a hemispherical head, bicipital groove, surgical neck, spiral groove, and deltoid tuberosity. It begins ossifying before any other bone and has multiple secondary centers.

The radius and ulna have cylindrical and hook-shaped heads, respectively, and are connected by the interosseous membrane. The radius has a radial tubercle and styloid process, while the ulna has a styloid process that is more proximal.

Chest radiographs require special views to adequately evaluate the clavicle and its relationship to the lungs. The rhomboid fossa, a small depression on the inferior surface of the clavicle, is seen in less than 1% of normal chest X-rays.

The primary center for the humerus appears in the eighth week of fetal life, and secondary centers appear in the head, greater and lesser tubercles, capitellum, radial head, internal epicondyle, trochlea, and olecranon. These fuse with one another and with the shaft at various ages.

The radial head has a single cortical line on its upper surface and is perpendicular to the neck in a normal radiograph. The ulnar styloid is proximal to the radial styloid and has a line joining them at an angle of 110° with the long axis of the radius. The pronator quadratus is a muscle that passes between the distal ulna and radius and is visible as a linear lucency on a lateral radiograph of the wrist.

The mandible is a bone that forms the lower jaw. It is unique in the skull as it is the only bone united to the skull through the mobile temporomandibular joint.

The inner surface of the mandible is attached to the muscles of the floor of the mouth and the muscles of mastication, while the outer surface is attached to the muscles of the jaw, including those involved in chewing.

The temporomandibular joint is a synovial joint located between the condyle of the mandible and the temporal bone. It is a complex joint that allows for the mandible to move during chewing and speaking.

The mandible is not part of the cranium nor the facial skeleton. It is composed of a single, horseshoe-shaped bone.

The skull consists of 22 bones, including the frontal, parietal, occipital, temporal, sphenoid, ethmoid, maxillae, zygomatic, nasal, and lacrimal bones.

The anterior view of the skull includes the forehead, orbits, nasal region, upper jaw, and lower jaw.

The mandible forms the visible part of the lower jaw.

The nasal cavities are elongated, wedge-shaped spaces within the skull, and are separated from each other by a midline nasal septum.

The anterior apertures of the nasal cavities are the nares, and the posterior apertures are the choanae, which open into the nasopharynx.

The skull is divided into several parts: the vault, consisting mainly of the temporal and parietal bones; the base of the skull, consisting mainly of the sphenoid, temporal, and occipital bones; and the facial skeleton, consisting of the paired nasal bones, palatine bones, lacrimal bones, zygomatic bones, maxillae, and the unpaired vomer.

Carpal tunnel views are taken by extending the wrist and focusing on the anterior part.

Supernumerary bones in the wrist include the oscentrale and osradiale externum.

The nutrient arteries of the scaphoid enter the bone exclusively in its distal half.

Scaphoid bones ossify in a clockwise order from capitate to trapezoid, with the capitate first and pisiform last.

The metacarpals and phalanges have distinct features, with each having a rounded head, a shaft, and a base.

The metacarpal sign is a radiological feature where the line tangential to the heads of the fourth and fifth metacarpals does not cross the third metacarpal head in normal hands.

The carpal angle is formed by lines tangential to the proximal ends of the scaphoid and lunate bones, with an average angle of 138° in normal hands.

Sesamoid bones are found in relation to the anterior surface of certain joints, with two sesamoids in the thumb's metacarpophalangeal joint being the most common.

Bones of the upper limb, including the metacarpals and phalanges, begin to ossify between the ninth and twelfth fetal weeks, with secondary ossification centers appearing later.

The muscles of the upper limb have distinct positions relative to one another in the upper arm and forearm.

The deltoid muscle covers the upper lateral aspect of the humerus, while the flexors and extensors of the shoulder and elbow have distinct positions.

The interosseous membrane separates the anterior and posterior compartments of the forearm, with the flexors and extensors of the wrist and fingers located anteriorly and posteriorly, respectively.

The interosseous nerves and arteries lie close to the interosseous membrane, while the radial and ulnar nerves and vessels lie anteriorly on each side.

The individual muscles may be difficult to distinguish on axial CT due to the lack of fat in the forearm.