Note: If possible you should have the material from your bone box or that available in the model room with you when you use this pre-lab material.
The clavicle, commonly called the "collar bone", is a critical component of the shoulder girdle. The upper limb is indirectly attached to the axial skeleton through the clavicle. The clavicle is a strut-like bone in the shape of a shallow letter 'S' and lies transversely on the cranial end and ventral side of the rib cage. . The clavicle articulates with two bones, the sternum and the scapula. The medial end of the clavicle expands into an ovoid and articulates with the manubrium. The lateral end of the clavicle flattens craniocaudally and articulates with the acromion of the scapula. The clavicle has a synovial joint at each end. There is an articular disc at its sternoclavicular joint. At the articulation with the scapula it is bound tightly to the acromion with ligaments that cross the synovial joint. The cranial surface of the clavicle is relatively smooth. The caudal surface of the clavicle presents a conoid tubercle which is the attachment of the conoid ligament, which binds the clavicle to the coracoid process of the scapula.
- Identify the following landmarks on the clavicle:
1. sternal end
2. acromial end
3. conoid tubercle
The scapula is a spade-shaped bone comprised of a thin triangular body and a semi-ovoid cavity known as the glenoid fossa (glenoid cavity). The glenoid fossa faces lateral and slightly anterior and cranial. A bony spine runs across the dorsal surface of the scapular body and terminates in the acromion. The scapula articulates with two bones, the humerus and clavicle. The scapula does not directly contact the bony rib cage: the two structures are separated by muscle and other soft tissue.
- Identify the following landmarks on the scapula:
1. coracoid process
3. scapular spine
4. inferior angle
- Study the sternoclavicular and acromioclavicular joints on an articulated skeleton.
- Place your fingertips on your own sternoclavicular joint, and raise, lower, protract, and retract your shoulder.
Note the relatively great mobility of the sternoclavicular joint.
- Place your fingers on the spine of your scapula and the thumb of the same hand on your clavicle, and raise, lower, protract, and retract your shoulder.
The acromioclavicular joint permits only a little fore-and-aft sliding of the scapula on the clavicle. Mobility is greatly restricted by the powerful coracoclavicular ligament that passes upward from the coracoids to the clavicle. This ligament so strongly prevents the scapula from being driven medially that, if you fall on your shoulder, you are more likely to fracture your clavicle than to dislocate the acromioclavicular joint.
- Locate the following areas of major muscle attachment on a disarticulated scapula:
- the ventral subscapular fossa (for the subscapularis muscle)
- the dorsal supraspinous fossa (for the suprapinous muscle)
- the dorsal infraspinous fossa (for the infraspinatus and teres minor muscles)
The humerus is the large single bone of the upper arm. Proximally, it articulates with the glenoid fossa of the scapula forming the glenohumeral joint. The humeral head is large and globular. Just ventral to the articular surface is the lesser tubercle, where the subscapularis attaches. Lateral to the articular surface is the greater tubercle. The rotator cuff muscles of the shoulder insert on the proximal humerus.
- Examine a disarticulated humerus and identify the following:
- humeral head
- anatomical neck
- the greater tubercle where the supraspinatus, infraspinatus, and teres major insert
- the lesser tubercle where subscapularis and the more distal attachments of the rest of the latissimus group insert
- the deltoid tuberosity where the deltoid muscle inserts
- the intertubercular groove through which the tendon of the long head of biceps brachii runs on its way from the upper edge of the glenoid fossa to the radius
The distal humerus presents a number of osteological projections. Muscles which flex and extend the hand originate on the medial and lateral epicondyles of the distal humerus respectively. The trochlea and capitulum lie between the medial and lateral epicondyles. The spool-shaped trochlea is medial to the rounded capitulum. These processes comprise the distal articular surfaces where the humerus articulates with the radius and ulna.
- Examine a disarticulated humerus and identify the following:
- the lateral epicondyle from which the superficial extensors of the forearm originate
- the medial epicondyle from which the superficial flexors of the forearm originate
- the dorsal olecranon fossa
- Flex your wrist and fingers and feel the flexor muscle mass on the medial side of the elbow contract. You can extend the wrist and fingers and feel the extensor muscles contract on the lateral side of the elbow.
4. Radius and ulna
There are two primary bones of the forearm (remember the arm is the section between the shoulder and elbow and the forearm is the section between the elbow and wrist): The radius (on the lateral side that articulates with the wrist on the thumb side of the hand) and the ulna (on the medial side).
The radius lies on the lateral (thumb) side of the forearm. Proximally, the radial head articulates with the capitulum of the humerus. Distally, the radius articulates with the scaphoid and lunate (two carpal bones discussed later).The radius is distinctive in having a concave head at the proximal end that allows a wide angle of rotation at the humeroradial joint, where its fossa articulates with the capitulum.
- Identify the following features of the radius:
- radial head
- radial tuberosity
- styloid process
The ulna lies on the medial side of the forearm. Proximally, it articulates with the trochlea of the humerus. The proximal ulna is marked by the olecranon process (where the triceps muscles insert and what you use to "elbow" an opponent in basketball) and by the sigmoid notch (where the ulna articulates with the trochlea of the humerus in a hinge joint that, unlike the radius, allows almost no rotation). Therefore the elbow joint, which consists of the humeroradial and humeroulnar joints, flexes at its articulation with the ulna and rotates at its articulation with the radius, the latter providing the mechanism for pronation in which the hand is flipped palm downward. The pointed projection at the distal end is called the styloid process and is attached to the radius by a band of fibrocartilage.
- Identify the following features on an ulna:
- olecranon process
- sigmoid notch
- radial notch
- coronoid process
- styloid process
- Observe the medial (flexor) and lateral (extensor) epicondyles of your own humerus. Feel the stringy ulnar nerve as it passes superficially between the medial epicondyle and olecranon process. The tingly sensation of hitting your "funny bone" occurs as a result of banging your ulnar nerve here. At the wrist, palpate the ulnar styloid process and the distal end of the radius. Locate the pisiform bone, a sesamoid carpal bone protecting the ulnar artery and nerve as they enter the hand.
- When you rotate your hand from palm ventrally (as in anatomical position) to palm facing dorsally you have moved your hand from a supinated position to a pronated one. This movement of supination to pronation occurs when the distal head of the radius rotates on the capitulum , the bone rotates along its long axis, and the proximal head of the radius flips over the ulna. With the upper limb in anatomical position (i.e., forearm fully supinated), feel the positions of the shafts of the radius (along the lateral surface of the forearm) and the ulna (along its medial surface). Now pronate the forearm while following the movements of the radius. Notice how the radius rotates across the ulna (realize that this rotation takes place between the heads of the radius and ulna). Look at an articulated skeleton and examine the movements of the radius during supination and pronation.
- Surface anatomy: In your cubital fossa, attempt to locate the basilic vein, the cephalic vein, and the median cubital vein (commonly used for venipuncture). Realize that superficial veins are commonly variable - the median cubital vein may form a more direct connection between the cephalic and basilic veins.
The wrist joint is complex consists of 8 carpal bones (small irregular bones) arranged in two rows. The complex movements of the wrist joint are accomplished by the carpal bones. The eight carpal bones are arranged in two rows, a proximal row and a distal row, with four bones each, thus there is a radiocarpal and an ulnocarpal joint, midcarpal joints (between the carpals in each) , and carpometacarpal joints (between the carpals and the palm).
5a. Proximal Row: The carpal bones are named for their shapes. From lateral to medial, the bones which make up the proximal carpal row are:
- the scaphoid (resembles a boat),
- the lunate (resembles a crescent moon),
- the triquetral (with three articular facets),
- the pisiform (pea-shaped), a very unassuming little round bone which is unique in that it articulates with only one other carpal bone (the triquetral).
5b. Distal row: The bones of the distal carpal row are (again from lateral to medial):
- the trapezium (four-sided), which has a large saddle-shaped facet on its distal surface for articulation with the first metacarpal,
- the trapezoid (also four-sided), slightly smaller than the trapezium and basically irregular in shape,
- the capitate (with a rounded head), the largest carpal bone, which occupies a central position in the distal carpal row,
- the hamate (hook-shaped), with its distinctive hamulus process.
The palm of the hand is made up of 5 metacarpals. Each metacarpal bone consists of a base, a shaft, and a head. Proximally, each articulates with the distal carpal row. Distally, each articulates with a proximal phalanx. The proximal ends of the metacarpals tend to have a concave or flat articular surface, while the distal ends have a convex articular surface. They are numbered I through V, starting with the lateral bone.
There are five digits with two phalanges in the thumb and three phalanges in the remaining digits for a total of 14 phalanges on each hand.
7a. Proximal phalanges: The first row of five phalanges, the proximal row, articulates proximally with the distal ends of the metacarpals. The proximal articular surface of a proximal phalanx is concave, and fits with the convex head of the metacarpal. Distally, the proximal phalanges articulate with the middle phalanges (except in the thumb, where there is no middle phalanx). The distal articular surface is flattened mediolaterally, with a slight depression in the center. This gives the distal articular surface the appearance of having two "lobes".
7b. Middle phalanges: The middle four phalanges (the thumb has no middle phalanx) articulate proximally with the proximal phalanges, and distally with the distal phalanges. The proximal
articular surface is generally concave, with the concavity "divided" to articulate with the two lobed distal articular surface of the proximal phalanges. The distal articular surfaces are very similar in appearance to those of the proximal phalanges.
7c. Distal phalanges: The five distal phalanges articulate proximally with the middle phalanges.
The articular surface is similar to the proximal articular surfaces of the middle phalanges. Distally, the distal phalanges are marked by apical tufts.