1 Bones, Ligaments, and Joints
1.1 The Upper Limb as a Whole
A Skeleton of the right upper limb
a Anterior view, b posterior view.
The skeleton of the upper limb consists of the shoulder girdle, arm, forearm, wrist, and hand. The shoulder girdle (clavicle and scapula) is joined to the upper limb at the shoulder joint, and it joins the upper limb to the thorax at the sternoclavicular joint (see p. 261). The limb itself consists of the
• forearm, and
B Palpable bony prominences on the right upper limb
a Anterior view, b posterior view.
Except for the lunate and trapezoid bones, all of the bones in the upper limb are palpable to some degree through the skin and soft tissues. By consensus, standard reference points have been defined for use in measuring the lengths of the segments of the dependent limb (with the palm turned forward):
• Length of the arm = distance from the acromion to the lateral epicondyle.
• Length of the forearm = distance from the lateral epicondyle to the styloid process of the radius.
• Length of the hand = distance from the styloid process of the radius to the tip of the third finger.
The segment lengths of the limb may be measured, for example, to aid in the precise evaluation of isolated pediatric growth disturbances that are confined to a particular bone.
1.2 Integration of the Shoulder Girdle into the Skeleton of the Trunk
A Bones of the right shoulder girdle in relation to the trunk
a Anterior view, b posterior view, c lateral view.
The two bones of the shoulder girdle (the clavicle and scapula) are connected at the acromioclavicular joint (see p. 261). In its normal anatomic position, the scapula extends from the second to the seventh rib. The inferior angle of the scapula is level with the spinous process of the seventh thoracic vertebra, and the scapular spine is level with the spinous process of the third thoracic vertebra. When the scapula occupies a normal position, its long axis is angled slightly laterally, and its medial border forms a 3 to 5° angle with the midsagittal plane.
B Right shoulder girdle
Superior view. With the transition to a bipedal mode of locomotion, the human scapula moved from the more lateral placement in quadruped mammals to a more posterior position, and also a more frontal orientation, on the back of the thorax. Viewed from above, the scapula forms a 30° angle with the coronal plane. The scapula and clavicle subtend an angle of approximately 60°. Because of this arrangement, the two shoulder joints are angled slightly forward, shifting the range of arm movements forward into the field of vision and action. This reorientation in humans creates the opportunity for visual control of manual manipulations (hand–eye coordination).
C Comparison of the shoulder girdle and pelvic girdle in their relation to the skeleton of the trunk
Superior view. Unlike the very mobile shoulder girdle, the pelvic girdle, consisting of the paired hip (coxal) bones, is firmly integrated into the axial skeleton. As the trunk assumes an upright position, the pelvis moves over the weight-bearing surface of the feet, making it necessary for the pelvis to support the total weight of the trunk. This basically limits the lower limbs to functions of locomotion and support while freeing the upper limbs from these tasks and making them a versatile organ of movement and expression that is particularly useful for touching and grasping.
1.3 The Bones of the Shoulder Girdle
A Position and shape of the right clavicle
a Clavicle in its normal relation to the scapula, superior view.
b Isolated clavicle, superior view.
c Isolated clavicle, inferior view.
The clavicle is an S-shaped bone, approximately 12 to 15 cm long in adults, that is visible and palpable beneath the skin along its entire length. The medial or sternal end of the clavicle bears a saddle-shaped articular surface, while the lateral or acromial end has a flatter, more vertical articular surface. The clavicle is the only bone in the limbs that is not preformed in cartilage during embryonic development; instead, it ossifies directly from connective tissue (membranous ossification). A congenital failure or abnormality in the development of this connective tissue results in an anomaly called cleidocranial dysostosis. There may be associated ossification defects in the cranial vault, which are also formed by membranous ossification (craniofacial dysostosis). Besides fractures due to obstetric trauma (1–2% of all newborns), fractures of the middle third of the clavicle are one of the most common fractures that are sustained by children and adults (in children, some 50% of all clavicular fractures occur before 6 years of age).
C The right scapula. Anterior view
D The right scapula. Posterior view
E The scapular foramen
The superior transverse ligament of the scapula (see p. 269) can become ossified, transforming the scapular notch into an anomalous bony canal referred to as a scapular foramen. This can lead to compression of the suprascapular nerve as it passes through this canal (see p. 390). Active rotational movements of the shoulder aggravate the nerve, leading to significant symptoms (scapular notch syndrome). A common result is weakness and atrophy of the muscles—the supraspinatus and infraspinatus—that the suprascapular nerve innervates (see p. 305).
1.4 The Bones of the Upper Limb: The Humerus
A The right humerus
a Anterior view, b posterior view.
B Supracondylar process
An anomaly sometimes found on the distal humerus above the medial epicondyle is referred to as a supracondylar process. This bony outgrowth is a relatively rare atavistic feature in humans that corresponds to a normal structure in other vertebrates, in which it forms part of a supracondylar canal (see p. 395).
C The supratrochlear foramen
The presence of a supratrochlear foramen is another rare variant in which the two opposing olecranon and coronoid fossae communicate through an opening.
D Position of the intertubercular groove of the right humerus with the limb hanging downward
Anterosuperior view. With the upper limb in the neutral (0°) position (see p. 277), the greater tubercle faces laterally, and the lesser tubercle faces anteriorly. The intertubercular groove between them transmits the tendon of the long head of the biceps muscle. The glenoid cavity forms a 30° angle with the sagittal plane.
E The proximal right humerus. Superior view
F The distal right humerus. Inferior view
1.5 The Bones of the Upper Limb: Torsion of the Humerus
A The right humerus
a Lateral view, b medial view.
B Fractures of the proximal humerus
Anterior view. Fractures of the proximal humerus comprise approximately 4 to 5% of all fractures. They occur predominantly in older patients who sustain a fall onto the outstretched arm or directly onto the shoulder. Three main types are distinguished:
• Extra-articular fractures (a)
• Intra-articular fractures (b)
• Comminuted fractures (c)
Not infrequently, extra-articular fractures at the level of the surgical neck (site of predilection for extra-articular fractures of the proximal humerus) and intra-articular fractures at the level of the anatomic neck are accompanied by injuries of the blood vessels that supply the humeral head (anterior and posterior circumflex humeral arteries, see p. 357), with an associated risk of post-traumatic avascular necrosis. Besides proximal humeral fractures, other important injuries are fractures of the humeral shaft and fractures of the distal humerus (e.g., supracondylar fractures). Fractures of the humeral shaft are frequently associated with damage to the radial nerve in its groove (see p. 371 for neurologic deficits following a radial nerve lesion).
C Torsion of the humerus
Right humerus, superior view. The shaft of the adult humerus normally exhibits some degree of torsion, i. e., the proximal end of the humerus is rotated relative to its distal end. The degree of this torsion can be assessed by superimposing the axis of the humeral head (from the center of the greater tubercle to the center of the humeral head) over the epicondylar axis of the elbow joint. This torsion angle equals approximately 16° in an adult, compared to about 60° in a newborn. The decrease in the torsion angle with body growth correlates with the change in the position of the scapulae. Thus, while the glenoid cavity in the newborn still faces anteriorly, it is directed much more laterally in the adult (see p. 243). As the position of the scapula changes, there is a compensatory decrease in the torsion angle to ensure that hand movements will remain within the visual field of the adult.
D Comparison of the humeral head axis and epicondylar axis
Skeleton of the right arm, viewed from the medial view with the forearm pronated.
1.6 The Bones of the Upper Limb: The Radius and Ulna
A The radius and ulna of the right forearm
a Anterior view, b posterior view.
The radius and ulna are not shown in their normal relationship; they have been separated to demonstrate the articular surfaces of the proximal and distal radioulnar joints.
B The radius and ulna of the right arm in (a) supination and (b) pronation
The radius and ulna are parallel to each other in supination, whereas in pronation the radius crosses over the ulna. The movement of turning the palm upward or downward (supination/pronation) takes place at the proximal and distal radioulnar joints (see p. 282).
1.7 The Bones of the Upper Limb: The Articular Surfaces of the Radius and Ulna
A The right upper limb
Lateral view. The forearm is supinated (the radius and ulna are parallel).
B Right forearm
Lateral view. The radius and ulna are shown in a disarticulated position to demonstrate the articular surfaces of the ulna for the proximal and distal radioulnar joints (see C).
C The radius and ulna of the right forearm
Anterosuperior view. The proximal and distal radioulnar joints are functionally interlinked by the interosseous membrane between the radius and ulna. As a result, motion in one joint is invariably combined with motion in the other (see p. 284).
D The proximal articular surfaces of the radius and ulna of the right forearm. Proximal view
E Cross section through the right radius and ulna. Proximal view
F The distal articular surfaces of the radius and ulna of the right forearm. Distal view
1.8 The Bones of the Upper Limb: The Hand
A The bones of the right hand. Palmar view
The skeleton of the hand consists of
• the carpal bones,
• the metacarpal bones, and
• the phalanges.
The palm refers to the anterior (flexor) surface of the hand, the dorsum to the posterior (extensor) surface. The terms of anatomic orientation in the hand are palmar or volar (toward the anterior surface), dorsal (toward the posterior surface), ulnar (toward the ulna or small finger), and radial (toward the radius or thumb).
B The bones of the right hand. Dorsal view
The radiocarpal and midcarpal joints are indicated by blue lines.
1.9 The Bones of the Upper Limb: The Carpal Bones
A Carpal bones of the right hand
a After removal of radius and ulna, proximal view; b column model of the hand, dorsal view; c with the wrist in flexion, proximal view.
The carpal bones are arranged in two rows of four bones each—one proximal row and one distal row (see also B). From a biomechanical and clinical standpoint, the carpal bones do not form two transverse rows but are arranged in three longitudinal columns: a radial scaphoid column (consisting of the scaphoid, trapezium, and trapezoid bones), a central lunate column (consisting of the lunate and capitate), and an ulnar triquetral column (consisting of the triquetrum and hamate). In this functional classification, the pisiform is regarded as a sesamoid bone embedded in the tendon of the flexor carpi ulnaris muscle (see p. 406). The bones in each row are interconnected by tight joints, their surfaces exhibiting a palmar concavity and a dorsal convexity. This creates the carpal tunnel on the palmar surface (see p. 290), which is bounded by a bony eminence on the radial and ulnar sides.
B Articular surfaces of the midcarpal joint of the right hand
The distal row of carpal bones is shown from the proximal view. The proximal row is shown from the distal view.
C Articular surfaces of the radiocarpal joint of the right hand
The proximal row of carpal bones is shown from the proximal view. The articular surfaces of the radius and ulna and the articular disk (ulnocarpal disk) are shown from the distal view.
Clinically, the radiocarpal joint is subdivided into a radial compartment and an ulnar compartment. This takes into account the presence of the interposed ulnocarpal disk, which creates a second, ulnar half of the radiocarpal joint in addition to the radial half. Accordingly, the radius articulates with the proximal row of carpal bones in the radial compartment, while the head of the ulna and ulnocarpal disk articulate with the proximal row of carpal bones in the ulnar compartment.
1.10 Architecture of the Radiocarpal Junction and the Metacarpus; Distal Radius and Scaphoid Fractures
A Architecture of the metacarpus
The metacarpus is the key region for the architecture of the hand. It is where the five digital rays form and then develop into the thumb and fingers. While in neutral position, the longitudinal axis of each finger is parallel, and the longitudinal axis of the abducted thumb and the spread fingers converge to an intersection point in the capitate (a). However, when bending the finger joints, the axes converge to an intersection point in the scaphoid (b). Only the knowledge of these defined basic anatomic positions allows for the diagnosis of mal-alignments caused by injury (most notably rotational mal-alignments of the fingers, meaning “twisting” of phalanges as a result of a fracture (see inset). The five digital rays are connected by three functionally significant arches (c): a longitudinal arch along the third ray, a metacarpal arch, and a transverse carpal arch.
B Inclination angle of the articulating surfaces along the distal radius
a Radioulnar inclination angle, right hand, dorsal view.
b Dorsopalmar inclination angle, right hand, ulnar view.
c X-ray image of carpal region, dorsopalmar beam path and
d radioulnar beam path (c and d from Schmidt HM, Lanz U. Chirurgische Anatomie der Hand. 2nd ed. Stuttgart: Thieme; 2003).
The distal radius helps form the radiocarpal and distal radioulnar joints. In addition, it supports the ulnocarpal disk and the strong dorsal and palmar extrinsic ligaments (see p. 286). It is primarily responsible for carpal load transmission within the longitudinally arranged columns (scaphoid column, lunate column, and triquetrum, see p. 256) and thus is prone to injury (see C). For a harmonious relationship between the parts forming the radiocarpal joint in terms of optimal mobility of the hand, the position of the part of the socket formed by the radius is of importance. The carpal articulating surface of the ulna is not vertical to the longitudinal axis of the forearm, but in a radioulnar inclination angle of 20 to 25° (ulnar inclination) and a dorsopalmar inclination angle of 10 to 15° (palmar inclination). The distal radial length relative to the ulna (tip of the styloid process of the radius to the carpal articulating surface of the ulna) is approximately 9 to 12 mm (important for optimal mobility of the hand).
C Distal radius fractures
Accounting for 20 to 25% of all fractures, the distal (or near the wrist) radius fracture as a result of falling on the hand is the most common fracture in humans. Affected are almost 80% of women over the age of 50 (main cause: postmenopausal osteoporosis). Depending on the position of the carpus relative to the distal radius at the moment of impact, 90% of falls result in extension fractures (Colles’ fracture; see a and b), and 10%, in flexion fractures (see e, from Henne-Bruns D, Dürig M, Kremer B. Chirurgie. 2nd ed. Stuttgart: Thieme; 2003).
In distal radius fractures, one generally differentiates between extra- and intra-artciular fractures, with the extra-articular fractures typically located 3 to 4 cm proximal to the radiocarpal joint. The standard criteria for such a diagnosis are determined by taking conventional X-ray images of the wrists in two planes (see e lateral view). The therapeutic procedure (conservatively using casts or surgically through osetosynthesis) depends on the angle and direction of dislocation (fracture stability), the course of the fracture line (intra-/extra-articular), and the severity of accompanying injuries (e.g., involvement of the ulna, most notably the styloid process). Less complicated (nondislocated, easy-to-reposition) and primarily stable fractures are conservatively treated using “Chinese finger traps” (f) with the help of an image intensifier. Axial alignment, most notably of the original radial length and angle (ulnar and palmar inclination angles, see Ba and Bb), are being restored through vertical extension and joint immobilization with the help of a dorsopalmar splint. With intra-artciular fractures involving large articular fragments, osteosynthetic stabilization is generally recommended.
D Scaphoid fractures
a Scaphoid fracture as seen on X-ray, dorsopalmar view (from Matzen P. Praktische Orthopädie. 3rd ed. Stuttgart: J. A. Barth Verlag Thieme; 2002).
b Frequency and distribution of scaphoid fractures.
Carpal fractures, most notably scaphoid fractures (accounting for two thirds of all cases), are another injury caused by falling on the outstretched hand extended in the dorsal direction. Unlike distal radial fractures (see C), young people are predominantly affected by scaphoid fractures (typical sports injury). During physical examination, the symptoms can be relatively discrete. Usually the symptoms include tenderness on palpation of the area around the anatomic snuff box with simultaneous radial or ulnar abduction and compressive pain around the thumb and index finger. In the case of a suspected scaphoid fracture, conventional radiographs of the wrist in four different planes (so-called scaphoid quartet series) should be taken (see a, white arrow), in order to determine the direction of the fracture gap. If the X-ray image fails to confirm the suspected diagnosis 10 to 14 days after initially stabilizing the fracture, a follow-up X-ray must be taken (if needed using CT scans). At this point, the process of resorption in the fracture hematoma is usually completed so that the fracture gap is wider and thus more clearly visible. Depending on the location, scaphoid fractures are classified into fractures of the proximal third, central third, or distal third (see b). The healing process is especially lengthy in fractures of the proximal third (up to 3 months in an upper arm cast for stabilization with inclusion of the thumb basal joint, see c) because this part of the bone has few blood vessels (the scaphoid receives the majority of its blood supply via distal vessels). The healing process is just as lengthy in slanted or vertical fractures due to the resulting shearing forces pushing in opposite directions (see d).
Note: The scaphoid bone is involved in all movements of the hand, which makes long-term stabilization rather difficult. Thus, pseudo-osteoarthritis is a typical complication of scaphoid fracture (= false joint after failed fracture healing, see 42).
1.11 The Joints of the Shoulder: Overview and Clavicular Joints
A The five joints of the shoulder
Right shoulder, anterior view. A total of five joints contribute to the wide range of arm motions at the shoulder joint. There are three true shoulder joints and two functional articulations:
• True joints:
1. Sternoclavicular joint
2. Acromioclavicular joint
3. Glenohumeral joint
• Functional articulations:
4. Subacromial space: a space lined with bursae (subacromial and subdeltoid bursae) that allows gliding between the acromion and the rotator cuff (= muscular cuff of the glenohumeral joint, consisting of the supraspinatus, infraspinatus, subscapularis, and teres minor muscles, which press the head of the humerus into the glenoid cavity; see p. 305).
5. Scapulothoracic joint: loose connective tissue between the subscapularis and serratus anterior muscles that allows gliding of the scapula on the chest wall.
Besides the true joints and functional articulations, the two ligamentous attachments between the clavicle and first rib (costoclavicular ligament) and between the clavicle and coracoid process (coracoclavicular ligament) contribute to the mobility of the upper limb. All of these structures together comprise a functional unit, and free mobility in all the joints is necessary to achieve a full range of motion. This expansive mobility is gained at the cost of stability, however. Since the shoulder has a loose capsule and weak reinforcing ligaments, it must rely on the stabilizing effect of the rotator cuff tendons. As the upper limb changed in mammalian evolution from an organ of support to one of manipulation, the soft tissues and their pathology assumed increasing importance. As a result, a large percentage of shoulder disorders involve the soft tissues.
B The sternoclavicular joint and its ligaments
Anterior view. The sternoclavicular joint (also called the medial clavicular joint) and the acromioclavicular joint (the lateral clavicular joint, see below) together make up the true joints within the shoulder girdle itself. In the figure, a coronal section has been made through the sternum and adjacent clavicle to demonstrate the inside of the left sternoclavicular joint. A fibrocartilaginous articular disk compensates for the mismatch of surfaces between the two saddle-shaped articular faces of the clavicle and manubrium.
C The acromioclavicular joint and its ligaments
Right shoulder, anterior view. The acromioclavicular joint (the lateral clavicular joint) has the form of a plane joint. Because the articulating surfaces are flat, they must be held in place by strong ligaments (acromioclavicular, coracoacromial, and coracoclavicular ligaments). This greatly limits the mobility of the acromioclavicular joint. In some individuals the acromioclavicular joint has a variably shaped articular disk that gives the joint greater mobility.
1.12 The Joints of the Shoulder: Ligaments of the Clavicular and Scapulothoracic Joints
A Ligaments of the sternoclavicular and acromioclavicular joints
Right side, superior view.
B Injuries to the acromioclavicular ligaments
These injuries often result from falling on a shoulder or an outstretched arm. According to Tossy, they can be classified into three types:
The acromioclavicular and coracoclavicular ligaments are stretched but still intact.
The acromioclavicular ligament is ruptured, with subluxation of the joint.
Ligaments are all disrupted, with complete dislocation of the acromioclavicular joint.
Rockwood added three more types that occur less frequently:
Dislocation of the clavicle shifts dorsally, due to the clavicular part of the deltoid being pulled off the clavicle.
Dislocation of lateral end of the clavicle is increased in the cranial direction, due to the deltoid and trapezius being pulled off the clavicle.
The lateral end of the clavicle underneath the acromion or the coracoid is dislocated (very rare).
Depending on the extent of the injury, the so-called piano-key phenomenon can be triggered through palpation (caution: painful!). The lateral end of the clavicle, which is elevated due to the injury, can be reduced by applying pressure from the cranial direction, but it pops back up when pressure is released. Radiographs in different planes will show widening of the space in the acromioclavicular joint. Comparative-stress radiographs with the patient holding approximately 10-kg weights in each hand will reveal the extent of upward displacement of the lateral end of the clavicle on the affected side (is not performed in cases of visible partial rupture of ligaments in order to avoid further damage).