Atlas of Anatomy

19 Shoulder & Arm

Bones of the Upper Limb

Fig. 19.1   Skeleton of the upper limb
Right limb. The upper limb is subdivided into three regions: arm, forearm, and hand. The shoulder girdle (clavicle and scapula) joins the upper limb to the thorax at the sternoclavicular joint.

images
images

Fig. 19.2   Palpable bony prominences
Except forthe lunate and trapezoid bones, all of the bones in the upper limb are palpable to some degree through the skin and soft tissues.

images

Clavicle & Scapula

images The shoulder girdle (clavicle and scapula) connects the bones of the upper limb to the thoracic cage. Whereas the pelvic girdle (paired hip bones) is firmly integrated into the axial skeleton (see p. 358), the shoulder girdle is extremely mobile.

Fig. 19.3   Clavicle
Right clavicle. The S-shaped clavicle is visible and palpable along its entire length (generally 12 to 15 cm). Its medial end articulates with the sternum at the sternoclavicular joint (see p. 258). Its lateral end articulates with the scapula attheacromioclavicular joint (see p. 259).

images

images Clinical

Scapular foramen
The superior transverse ligament of the scapula (see p. 259) may become ossified, transforming the scapular notch into an anomalous bony canal, the scapular foramen. This can lead to compression of the suprascapular nerve as it passes through the canal (see p. 333).

images

Fig. 19.4   Scapula
Right scapula. In its normal anatomical position, the scapula extends from the 2nd to the 7th rib.

images

Humerus

Fig. 19.5   Humerus
Right humerus. The head of the humerus articulates with the scapula at theglenohumeral joint (see p. 258). Thecapitellum and trochlea of the humerus articulate with the radius and ulna, respectively, at the elbow (cubital) joint (see p. 282).

images images

images Clinical

Fractures of the humerus
Anterior view. Fractures of the proximal humerus are very common and occur predominantly in older patients who sustain a fall onto the outstretched arm or directly onto the shoulder. Three main types are distinguished.

images

Extra-articular fractures and intra-articular fractures are often accompanied by injuries of the blood vessels that supply the humeral head (anterior and posterior circumflex humeral arteries), with an associated risk of post-traumatic avascular necrosis.

Fractures of the humeral shaft and distal humerus are frequently associated with damage to the radial nerve.

Joints of the Shoulder

Fig. 19.6   Joints of the shoulder: Overview
Right shoulder, anterior view.

images

Fig. 19.7   Joints of the shoulder girdle
Right side, superior view.

images

Fig. 19.8   Scapulothoracic joint
Right side, superior view. In all movements of the shoulder girdle, the scapula glides on a curved surface of loose connective tissue between the serratus anterior and the subscapu-laris muscles. This surface can be considered a scapulothoracic joint.

images

Fig. 19.9   Sternoclavicular joint
Anterior view with sternum coronally sectioned (left). Note: A fibrocartilaginous articular disk compensates for the mismatch of surfaces between the two saddle-shaped articular facets of the clavicle and manubrium sterni.

images

Fig. 19.10   Acromioclavicular joint
Anterior view. The acromioclavicular joint is a plane joint. Because the articulating surfaces are flat, they must be held in place by strong ligaments, greatly limiting the mobility of the joint.

images

images Clinical

Injuries of the acromioclavicular joint
A fall onto the outstretched arm or shoulder frequently causes dislocation of the acromioclavicular joint and damage to the coracoclavicular ligaments.

images

Joints of the Shoulder: Glenohumeral Joint

Fig. 19.11   Glenohumeral joint: Bony elements
Right shoulder.

images

Fig. 19.12   Radiograph of the shoulder
Anteroposterior view.

images

Fig. 19.13   Glenohumeral joint: Capsule and ligaments
Right shoulder.

images

Fig. 19.14   Glenohumeral joint cavity
Anterior view.

images

Fig. 19.15   MRI of the shoulder
Coronal section, anterior view.

images

Subacromial Space & Bursae

Fig. 19.16   Subacromial space
Right shoulder.

images

Fig. 19.17   Subacromial bursa and glenoid cavity
Right shoulder, lateral view of sagittal section with humerus removed.

images

Fig. 19.18   Subacromial and subdeltoid bursae
Right shoulder, anterior view.

images

Anterior Muscles of the Shoulder & Arm (I)

Fig. 19.19   Anterior muscles
Right side, anterior view. Muscle origins (O) are shown in red, insertions (I) in blue.

images images

Anterior Muscles of the Shoulder & Arm (II)

Fig. 19.20   Anterior dissection
Right arm, anterior view. Muscle origins (O) are shown in red, insertions (I) in blue.

images images

Posterior Muscles of the Shoulder & Arm (I)

Fig. 19.21   Posterior muscles
Right side, posterior view.

images images

Posterior Muscles of the Shoulder & Arm (II)

Fig. 19.22   Posterior dissection
Right arm, posterior view. Muscle origins (0) are shown in red, insertions (I) in blue.

images images

Muscle Facts (I)

images The actions of the three parts of the deltoid muscle depend on their relationship to the position of the humerus and its axis of motion. At less than 60 degrees, the muscles act as adductors, but at greater than 60 degrees, they act as abductors. As a result, the parts of the deltoid can act antagonistically as well as synergistically.

Fig. 19.23   Deltoid
Right shoulder.

images

images

Fig. 19.24   Rotator cuff
Right shoulder. The rotator cuff consists of four muscles: supraspinatus, infraspinatus, teres minor, and subscapularis.

images

images

Muscle Facts (II)

Fig. 19.25   Pectoralis major and coracobrachialis
Anterior view.

images

images

Fig. 19.26   Subclavius an pectoralis minor
Right side, anterior view.

images

Fig. 19.27   Serratus anterior
Right lateral view.

images

images

Muscle Facts (III)

Fig. 19.28   Trapezius
Posterior view.

images

Fig. 19.29   Levator scapulae with rhomboids major and minor
Right side, posterior view.

images

images

Fig. 19.30   Latissimus dorsi and teres major
Posterior view.

images

images

Muscle Facts (IV)

images The anterior and posterior muscles of the arm may be classified respectively as flexors and extensors relative to the movement of the elbow joint. Although the coracobrachialis is topographically part of the anterior compartment, it is functionally grouped with the muscles of the shoulder (see p. 274).

Fig. 19.31   Biceps brachii and brachialis
Right arm, anterior view.

images

images

Fig. 19.32   Triceps brachii and anconeus
Right arm, posterior view.

images

images