Bones of the Upper Limb

Bones of the Upper Limb

• The upper limb (UL) bones include the pectoral girdle (clavicle and scapula), arm (humerus), forearm (radius and ulna), wrist (carpal bones), and hand (metacarpals and phalanges).
• The pectoral girdle is composed of the clavicle and the scapula. The clavicle is a light, doubly curved bone lying across the root of the neck that aids upper limb movement. The scapula is a triangular flat bone, extending between the 2nd-7th ribs. It has three processes: spine, acromion, and coracoid; the glenoid cavity provides articulation for the humerus.

Clavicle (Collar Bone)

• A doubly curved, long bone, lying horizontally across the root of the neck, and is subcutaneous throughout its length.
• Formed by membranous ossification, making it the first bone to ossify.
• Serves as a rigid support for the scapula and free upper limb, keeping them away from the trunk for maximum arm movement.
• Transmits forces from the upper limb to the axial skeleton.
• Provides attachment for muscles.
• Forms part of the cervicoaxillary canal, protecting its neurovascular bundle.
• Has two ends: medial (sternal) which is triangular and enlarged, and lateral (acromial) which is flattened.
• Its shaft has two surfaces (superior and inferior) and two borders (anterior and posterior).
• The inferior surface has impressions for the costoclavicular ligament, subclavian groove, conoid tubercle, and trapezoid ridge.
• Articulates with the manubrium (medially at the sternoclavicular joint), scapula (laterally at the acromioclavicular joint), and 1st rib (inferiorly at the costoclavicular joint).

Scapula (Shoulder Blade)

• A triangular flat bone, extending between the 2nd-7th ribs.
• Its three processes include a thick spine, the acromion (subcutaneous point), and the coracoid (beaklike process). It also has three borders (superior, medial/vertebral, and lateral/axillary) that terminate at the lateral angle.
• It has three angles: superior, lateral (with the glenoid cavity), and inferior.
• Two surfaces: convex posterior (divided by the spine into the supraspinous and infraspinous fossae), and concave anterior (subscapular fossa).
• Serves as an attachment to muscles, facilitating considerable arm movement on the thoracic wall.
• The glenoid cavity forms the socket of the shoulder.
• Well-protected by muscles and thoracic wall; stable fracture with minimal surgical intervention.
• Articulates with the clavicle (at the acromioclavicular joint), and humerus (at the glenohumeral joint).

Humerus (Arm Bone)

• The largest bone in the upper limb.
• Proximal end: head, neck, greater and lesser tubercles, with the intertubercular groove separating the greater and lesser tubercles. The head articulates with the glenoid cavity of the scapula.
• Shaft (body): deltoid tuberosity for deltoid muscle attachment; spiral (radial) groove for radial nerve and vessels.
• Distal end: trochlea for ulna articulation, capitulum for radius articulation, coronoid and radial fossae, olecranon fossa, and medial and lateral epicondyles.
• Articulates with scapula (glenohumeral joint) and radius and ulna (elbow joint).
• Fractures commonly occur at the surgical neck and are often osteoporosis-related in the elderly.

Forearm (Radius and Ulna)

• Formed by two bones: radius (lateral) and ulna (medial), located in the forearm.
• Proximal ends: ulna has an olecranon process (elbow prominence) and coronoid process that articulate with the trochlea of the humerus; the radius has a head that articulates with the capitulum of the humerus.
• Shaft: the radius and ulna are connected by the interosseous membrane.
• Distal ends: the ulna has a radial notch for articulation with the radius, while the radius possesses a distinct styloid process and ulnar notch.
• Articulate with each other, the humerus (elbow joint), and carpal bones (wrist joint).
• The radius is the shorter and lateral of the two bones that articulate with the scapula through the humerus; the ulna is the medial bone.

Hand Bones

• Carpals: eight small bones arranged in two rows (proximal and distal), providing wrist flexibility. Examples include scaphoid, lunate, triquetrum, pisiform, trapezoid, trapezium, capitate, and hamate.
• Metacarpals: five bones forming the palm, each with a base, shaft, and head. They articulate with the carpals proximally and phalanges distally (forming knuckles). The first metacarpal is the shortest and most mobile.
• Phalanges: form the fingers (except thumb, having only two). Each finger has a proximal, middle, and distal phalanx, with the proximal being the largest and the distal the smallest, ending in nail beds.

Articulations

• Refer to the specific articulations of each bone (e.g., acromioclavicular, glenohumeral, radioulnar, sternoclavicular, wrist joints).
• Joints and articulation locations are stated within the descriptions of each set of bones (e.g., carpals, radius, ulna, scapula).

Muscle Attachments

• Refer to muscle attachments lists for each bone (e.g., clavicle, scapula, humerus, radius, ulna, carpals, metacarpals, phalanges).

Fractures

• Specific fracture types for each bone (e.g., clavicle fractures, humerus fractures, Colle's fracture).
• Common locations of fractures, contributing factors including osteoporosis, and consequent complications are included with each respective bone description.

Nerves & Clinical Significance

• Include clinical significance statements regarding each bone. Specific nerve locations and implications related to bone fractures are also in the relevant sections.

This quiz focuses on the anatomy of the bones in the upper limb, including the pectoral girdle, humerus, radius, ulna, and the wrist and hand structure. Explore details about the clavicle, scapula, and their functionalities in supporting upper limb movement. Test your knowledge on the structural composition and significance of these bones.