6.7: Bones of the Upper Limb

By the end of this section, you will be able to:

• Identify the divisions of the upper limb and describe the bones in each region
• List the bones and bony landmarks that articulate at each joint of the upper limb

The upper limb is divided into three regions. These consist of the upper arm, located between the shoulder and elbow joints; the forearm, which is between the elbow and wrist joints; and the hand, which is located distal to the wrist. There are 30 bones in each upper limb (Figure \(\PageIndex{1}\)). The humerus is the single bone of the upper arm, and the ulna (medially) and the radius (laterally) are the paired bones of the forearm. The base of the hand contains eight bones, each called a carpal bone, and the palm of the hand is formed by five bones, each called a metacarpal bone. The fingers and thumb contain a total of 14 bones, each of which is a phalanx (plural = phalanges) bone of the hand.

Figure \(\PageIndex{1}\): Bones of the Upper Limb. Bones of the brachial, antebrachial, and manual regions. (Image credit: "Bones of the Upper Limb" by Jennifer Lange is licensed under CC BY-NC-SA 4.0, modification of image from Anatomy Standard.)

Humerus

The humerus is the single bone of the upper arm region (Figure \(\PageIndex{2}\)). At its proximal end is the head of the humerus. This is the large, round, smooth region that faces medially. The head articulates with the glenoid cavity of the scapula to form the glenohumeral (shoulder) joint. Located on the lateral side of the proximal humerus is an expanded bony area called the greater tubercle. The smaller lesser tubercle of the humerus is found on the anterior aspect of the humerus. Both the greater and lesser tubercles serve as attachment sites for muscles that act across the shoulder joint.  The deltoid tuberosity is a roughened, V-shaped region located on the lateral side in the middle of the humerus shaft. As its name indicates, it is the site of attachment for the deltoid muscle.

A. Anterior View

B. Posterior View

Figure \(\PageIndex{2}\): Humerus. The humerus is the single bone of the upper arm region. It articulates with the radius and ulna bones of the forearm to form the elbow joint and with the scapula to form the shoulder joint.  (Image credit: "Humerus - Anterior and Posterior" by Claire McGuire are licensed under CC BY-NC-SA 4.0, modification of image from Anatomy Standard.)

Distally, the humerus becomes flattened. The prominent bony projection on the medial side is the medial epicondyle of the humerus. The much smaller lateral epicondyle of the humerus is found on the lateral side of the distal humerus. All of these areas are attachment points for muscles that act on the forearm, wrist, and hand. The powerful grasping muscles of the anterior forearm arise from the medial epicondyle, which is thus larger and more robust than the lateral epicondyle that gives rise to the weaker posterior forearm muscles.

The distal end of the humerus has two articulation areas, which join the ulna and radius bones of the forearm to form the elbow joint. The more medial of these areas is the trochlea, a hour glass- or pulley-shaped region (trochlea = “pulley”), which articulates with the ulna bone. Immediately lateral to the trochlea is the capitulum (“small head”), a knob-like structure located on the anterior surface of the distal humerus. The capitulum articulates with the radius bone of the forearm. Just proximal to these bony areas are spaces that accommodate the forearm bones when the elbow is fully bent (flexed) and fully straightened (extended). Superior to the trochlea on the anterior surface is the coronoid fossa, which receives the coronoid process of the ulna when the elbow is flexed. Similarly, the posterior humerus has the olecranon fossa, a larger depression that receives the olecranon process of the ulna when the forearm is fully extended.

A. Anterior View

 

B. Posterior View

 

C. Lateral View

 

D. Proximal Radius and Ulna

 

Figure \(\PageIndex{3}\): Bones of the Elbow Joint.  At the elbow joint the "C" shaped trochlear notch pivots around the hourglass shaped trochlea. (Image credits: "Elbow- Anterior, Posterior, and Lateral" and "Proximal Radius and Ulna" by Claire McGuire are licensed under CC BY-NC-SA 4.0, modification of image from Anatomy Standard.)

Ulna

The ulna is the medial bone of the forearm. It runs parallel to the radius, which is the lateral bone of the forearm (Figure \(\PageIndex{4}\) and Figure \(\PageIndex{5}\)). The proximal end of the ulna resembles a crescent wrench with its large, C-shaped indentation called the trochlear notch. This smooth region articulates with the trochlea of the humerus at the elbow joint. The posterior and proximal portion of the ulna, containing the proximal part of the trochlear notch, is the olecranon process.  The olecranon process forms the bony tip of the elbow that contact the table.  The inferior portion of the trochlear notch is on a prominent lip of bone called the coronoid process of the ulna. To the lateral side and slightly inferior to the trochlear notch is a small, smooth area called the radial notch (this looks like a bite mark in the coronoid process).  This indented area is the site of articulation between the proximal radius and ulna, forming the proximal radioulnar joint.

More distal is the shaft of the ulna. The lateral side of the shaft forms a ridge called the interosseous border of the ulna. This is the line of attachment for the interosseous membrane of the forearm, also known as the antebrachial interosseous membrane, a sheet of dense connective tissue that unites the ulna and radius bones (Figure \(\PageIndex{6}\)). The small, rounded area that forms the distal end is the head of the ulna. Projecting from the posterior side of the ulnar head is the styloid process of the ulna, a short bony projection. This serves as an attachment point for a connective tissue structure that unites the distal ends of the ulna and radius.

In the anatomical position, with the elbow fully extended and the palms facing forward, the arm and forearm do not form a straight line. Instead, the forearm deviates laterally by 5–15 degrees from the line of the arm. This deviation is called the carrying angle. It allows the forearm and hand to swing freely or to carry an object without hitting the hip. The carrying angle is larger in females to accommodate their wider pelvis.

Figure \(\PageIndex{4}\): Bones of the Forearm - Anterior View.  The radius and the ulna run parallel when in anatomical position.  The radius is lateral (thumb side) and the ulna is medial (pinky side).  (Image credit: "Bones of the Forearm - Anterior View" by Jennifer Lange and Claire McGuire is licensed under CC BY-NC-SA 4.0, modification of image from Anatomy Standard.)

Figure \(\PageIndex{5}\): Bones of the Forearm - Posterior View.  The radius articulates with the carpals at the wrist joint while the ulna articulates with the trochlea at the elbow joint. (Image credit: "Bones of the Forearm" by Jennifer Lange and Claire McGuire is licensed under CC BY-NC-SA 4.0, modification of image from Anatomy Standard.)

Radius

The radius runs parallel to the ulna, on the lateral (thumb) side of the forearm (see Figure \(\PageIndex{4}\) and Figure \(\PageIndex{5}\)). The head of the radius is a disc-shaped structure that forms the proximal end. The small depression on the surface of the head articulates with the capitulum of the humerus as part of the elbow joint, whereas the smooth, outer margin of the head articulates with the radial notch of the ulna at the proximal radioulnar joint.  Inferior to this point on the medial side is the radial tuberosity, an oval-shaped, bony protuberance that serves as a muscle attachment point.

The shaft of the radius is slightly curved and has a small ridge along its medial side. This ridge forms the interosseous border of the radius, which, like the similar border of the ulna, is the line of attachment for the interosseous membrane that unites the two forearm bones (Figure \(\PageIndex{6}\)). The distal end of the radius has a smooth surface for articulation with two carpal bones to form the radiocarpal joint or wrist joint (Figure \(\PageIndex{7}\)). On the medial side of the distal radius is the ulnar notch of the radius. This shallow depression articulates with the head of the ulna, which together form the distal radioulnar joint. The lateral end of the radius has a pointed projection called the styloid process of the radius. This provides attachment for ligaments that support the lateral side of the wrist joint. Compared to the styloid process of the ulna, the styloid process of the radius projects more distally, thereby limiting the range of movement for lateral deviations of the hand at the wrist joint.

 

 

Figure \(\PageIndex{6}\): Radioulnar Joints Bone Landmarks.  The radius and ulna articulate at three places - the proximal and the distal ends as well as the shafts.  (Image credit: "Radioulnar Joints Bone Landmarks" by Jennifer Lange is licensed under CC BY-NC-SA 4.0, modification of image from Anatomy Standard.)

Figure \(\PageIndex{7}\): Bones of the Wrist Joint.  The wrist is the radiocarpal joint, with the primary joint surfaces on the radius, scaphoid, and lunate. (Image credit: "Wrist Joint - Anterior" by Claire McGuire is licensed under CC BY-NC-SA 4.0, modification of image from Anatomy Standard.)

Carpal Bones

The wrist and base of the hand are formed by a series of eight small carpal bones (see Figure \(\PageIndex{8}\)). The carpal bones are arranged in two rows, forming a proximal row of four carpal bones and a distal row of four carpal bones. The bones in the proximal row, running from the lateral (thumb) side to the medial side, are the scaphoid (“boat-shaped”), lunate (“moon-shaped”), triquetrum (“three-cornered”), and pisiform (“pea-shaped”) bones. The small, rounded pisiform bone articulates with the anterior surface of the triquetrum bone. The pisiform thus projects anteriorly, where it forms the bony bump that can be felt at the medial base of your hand. The distal bones (lateral to medial) are the trapezium (“table”), trapezoid (“resembles a table”), capitate (“head-shaped”), and hamate (“hooked bone”) bones. The hamate bone is characterized by a prominent bony extension on its anterior side called the hook of the hamate bone.

A helpful mnemonic for remembering the arrangement of the carpal bones is “So Long To Pinky, Here Comes The Thumb.” This mnemonic starts on the lateral side and names the proximal bones from lateral to medial (scaphoid, lunate, triquetrum, pisiform), then makes a U-turn to name the distal bones from medial to lateral (hamate, capitate, trapezoid, trapezium). Thus, it starts and finishes on the lateral side.

Figure \(\PageIndex{8}\): Bones of the Hand. The eight carpal bones form the base of the hand. These are arranged into proximal and distal rows of four bones each.  (Image credit: "Carpals" by Claire McGuire is licensed under CC BY-NC-SA 4.0, modification of image from Anatomy Standard.)

The carpal bones form the base of the hand. This can be seen in the radiograph (X-ray image) of the hand that shows the relationships of the hand bones to the skin creases of the hand (see Figure \(\PageIndex{9}\)). Within the carpal bones, the four proximal bones are united to each other by ligaments to form a unit. Only three of these bones, the scaphoid, lunate, and triquetrum, contribute to the radiocarpal joint. The scaphoid and lunate bones articulate directly with the distal end of the radius, whereas the triquetrum bone articulates with a fibrocartilaginous pad that spans the radius and styloid process of the ulna. The distal end of the ulna thus does not directly articulate with any of the carpal bones.  The four distal carpal bones are also held together as a group by ligaments.  The joints between each adjacent carpal is one of the intercarpal joints.  Together, the radiocarpal and intercarpal joints are responsible for all movements of the hand at the wrist. The distal carpal bones also articulate with the metacarpal bones of the hand.

Figure \(\PageIndex{9}\): Bones of the Hand. This radiograph shows the position of the bones within the hand. Can you identify each of the carpals in each view? (Image credit: Case courtesy of Jessica Hui Shi Ng, Radiopaedia.org. From the case rID: 70530.)

In the articulated hand, the carpal bones form a U-shaped grouping. A strong ligament called the flexor retinaculum spans the top of this U-shaped area to maintain this grouping of the carpal bones (Figure \(\PageIndex{10}\)). The flexor retinaculum is attached laterally to the trapezium and scaphoid bones, and medially to the hamate and pisiform bones. Together, the carpal bones and the flexor retinaculum form a passageway called the carpal tunnel, with the carpal bones forming the walls and floor, and the flexor retinaculum forming the roof of this space. The tendons of nine muscles of the anterior forearm and an important nerve pass through this narrow tunnel to enter the hand. Overuse of the muscle tendons or wrist injury can produce inflammation and swelling within this space. This produces compression of the nerve, resulting in carpal tunnel syndrome, which is characterized by pain or numbness, and muscle weakness in those areas of the hand supplied by this nerve.

Figure \(\PageIndex{10}\): Carpal Tunnel. The carpal tunnel is the passageway by which nine muscle tendons and a major nerve enter the hand from the anterior forearm. The walls and floor of the carpal tunnel are formed by the U-shaped grouping of the carpal bones, and the roof is formed by the flexor retinaculum, a strong ligament that anteriorly unites the bones. (Image credit: "The Carpal Tunnel" by OpenStax is licensed under CC BY 3.0.)

Metacarpal Bones

The palm of the hand contains five elongated metacarpal bones. These bones lie between the carpal bones of the wrist and the bones of the fingers and thumb (see Figure \(\PageIndex{11}\)). The proximal end, also known as the base, of each metacarpal bone articulates with one of the distal carpal bones. Each of these articulations is a carpometacarpal joint. The elongated portion of the metacarpal bone is the body, or shaft. The expanded distal end, also known as the head, of each metacarpal bone articulates at the metacarpophalangeal joint with the proximal phalanx bone of the thumb or one of the fingers. The distal end also forms the knuckles of the hand, at the base of the fingers. The metacarpal bones are numbered 1–5, beginning at the thumb (or moving lateral to medial).

Figure \(\PageIndex{11}\): Metacarpals and Phalanges.  The digits are numbered 1 to 5, with digit 1 being the thumb.  Both the metacarpals and phalanges are named according to which digit they belong to. (Image credit: "Metacarpals and Phalanges" by Claire McGuire is licensed under CC BY-NC-SA 4.0, modification of image from Anatomy Standard.)

The first metacarpal bone, at the base of the thumb, is separated from the other metacarpal bones. This allows it a freedom of motion that is independent of the other metacarpal bones, which is very important for thumb mobility. The remaining metacarpal bones are united together to form the palm of the hand. The second and third metacarpal bones are firmly anchored in place and are immobile. However, the fourth and fifth metacarpal bones have limited anterior-posterior mobility, a motion that is greater for the fifth bone. This mobility is important during power gripping with the hand (Figure \(\PageIndex{12}\)). The anterior movement of these bones, particularly the fifth metacarpal bone, increases the strength of contact for the medial hand during gripping actions.

Figure \(\PageIndex{12}\): Hand During Gripping. During tight gripping—compare (b) to (a)—the fourth and, particularly, the fifth metatarsal bones are pulled anteriorly. This increases the contact between the object and the medial side of the hand, thus improving the firmness of the grip. (Image credit: "Hand Gripping" by OpenStax is licensed under CC BY 3.0.)

Phalanx Bones

The fingers and thumb are composed of 14 bones, each of which is called a phalanx bone (plural = phalanges), named after the ancient Greek phalanx (a rectangular block of soldiers). The thumb (pollex) is digit number 1 and has two phalanges, a proximal phalanx, and a distal phalanx bone (see Figure \(\PageIndex{11}\)). Digits 2 (index finger), 3 (middle finger), 4 (ring finger), and 5 (little finger) have three phalanges each, called the proximal, middle, and distal phalanx bones. An interphalangeal joint is one of the articulations between adjacent phalanges of the digits. Each phalanx bone has a base (proximal end), body (shaft), and a head (distal end).

DISORDERS OF THE...

Appendicular System: Fractures of Upper Limb Bones

Due to our constant use of the hands and the rest of our upper limbs, an injury to any of these areas will cause a significant loss of functional ability. Many fractures result from a hard fall onto an outstretched hand. The resulting transmission of force up the limb may result in a fracture of the humerus, radius, or scaphoid bones. These injuries are especially common in elderly people whose bones are weakened due to osteoporosis.

Another frequent injury following a fall onto an outstretched hand is a Colles fracture (“col-lees”) of the distal radius (see Figure \(\PageIndex{13}\)). This involves a complete transverse fracture across the distal radius that drives the separated distal fragment of the radius posteriorly and superiorly. This injury results in a characteristic “dinner fork” bend of the forearm just above the wrist due to the posterior displacement of the hand. This is the most frequent forearm fracture and is a common injury in persons over the age of 50, particularly in older women with osteoporosis. It also commonly occurs following a high-speed fall onto the hand during activities such as snowboarding or skating.

Figure \(\PageIndex{13}\): Fractures of the Upper Limb.  A Colles fracture of the distal radius is the most common forearm fracture. The scaphoid is the most commonly fractured carpal. (Image credits: Colles fracture case courtesy of Pir Abdul Ahad Aziz Qureshi, Radiopaedia.org. From the case rID: 47908.  Scaphoid fracture case courtesy of David Cuete, Radiopaedia.org. From the case rID: 27557.)

The most commonly fractured carpal bone is the scaphoid (see Figure \(\PageIndex{13}\)), often resulting from a fall onto the hand. Deep pain at the lateral wrist may yield an initial diagnosis of a wrist sprain, but a radiograph taken several weeks after the injury, after tissue swelling has subsided, will reveal the fracture. Due to the poor blood supply to the scaphoid bone, healing will be slow and there is the danger of bone necrosis and subsequent degenerative joint disease of the wrist.

Interactive Element

Explore the structure of the bones of the upper limb in these 3D models:

Human Humerus by UBC Faculty of Medicine on Sketchfab
Human Radius by UBC Faculty of Medicine on Sketchfab
Human Ulna by UBC Faculty of Medicine on Sketchfab
Human Hand Bones by UBC Faculty of Medicine on Sketchfab

 

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Concept Review

Each upper limb is divided into three regions and contains a total of 30 bones. The upper arm is the region located between the shoulder and elbow joints. This area contains the humerus. The proximal humerus consists of the head, which articulates with the scapula at the glenohumeral joint, the greater and lesser tubercles separated by the intertubercular (bicipital) groove, and the anatomical and surgical necks. The humeral shaft has the roughened area of the deltoid tuberosity on its lateral side. The distal humerus is flattened, forming a lateral supracondylar ridge that terminates at the small lateral epicondyle. The medial side of the distal humerus has the large, medial epicondyle. The articulating surfaces of the distal humerus consist of the trochlea medially and the capitulum laterally. Depressions on the humerus that accommodate the forearm bones during bending (flexing) and straightening (extending) of the elbow include the coronoid fossa, the radial fossa, and the olecranon fossa.

The forearm is the region of the upper limb located between the elbow and wrist joints. This region contains two bones, the ulna medially and the radius on the lateral (thumb) side. The elbow joint is formed by the articulation between the trochlea of the humerus and the trochlear notch of the ulna, plus the articulation between the capitulum of the humerus and the head of the radius. The proximal radioulnar joint is the articulation between the head of the radius and the radial notch of the ulna. The proximal ulna also has the olecranon process, forming an expanded posterior region, and the coronoid process and ulnar tuberosity on its anterior aspect. On the proximal radius, the narrowed region below the head is the neck; distal to this is the radial tuberosity. The shaft portions of both the ulna and radius have an interosseous border, whereas the distal ends of each bone have a pointed styloid process. The distal radioulnar joint is found between the head of the ulna and the ulnar notch of the radius. The distal end of the radius articulates with the proximal carpal bones, but the ulna does not.

The base of the hand is formed by eight carpal bones. The carpal bones are united into two rows of bones. The proximal row contains (from lateral to medial) the scaphoid, lunate, triquetrum, and pisiform bones. The scaphoid, lunate, and triquetrum bones contribute to the formation of the radiocarpal joint. The distal row of carpal bones contains (from medial to lateral) the hamate, capitate, trapezoid, and trapezium bones (“So Long To Pinky, Here Comes The Thumb”). The anterior hamate has a prominent bony hook. The proximal and distal carpal rows articulate with each other at the midcarpal joint. The carpal bones, together with the flexor retinaculum, also form the carpal tunnel of the wrist.

The five metacarpal bones form the palm of the hand. The metacarpal bones are numbered 1–5, starting with the thumb side. The first metacarpal bone is freely mobile, but the other bones are united as a group. The digits are also numbered 1–5, with the thumb being number 1. The fingers and thumb contain a total of 14 phalanges (phalanx bones). The thumb contains a proximal and a distal phalanx, whereas the remaining digits each contain proximal, middle, and distal phalanges.

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Review Questions

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Critical Thinking Questions

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Glossary

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Contributors and Attributions

• OpenStax Anatomy & Physiology (CC BY 4.0). Access for free at https://openstax.org/books/anatomy-and-physiology