The Bones of the Upper Limb
THE SCAPULA ( Figs. 7.1, 7.2 )
This flat triangular bone has three processes:
- ■
The glenoid process, which is separated from the remainder by the neck of the scapula. The glenoid cavity forms part of the shoulder joint.
- ■
The spine, which arises from the posterior surface of the scapula and separates the supraspinous and infraspinous fossae. The spine extends laterally over the shoulder joint as the acromion (see Fig. 7.2 ).
- ■
The coracoid process, which projects anteriorly from the upper border of the neck of the scapula.
- 1.
Medullary cavity of humeral shaft
- 2.
Cortex
- 3.
Head of humerus
- 4.
Lesser tuberosity
- 5.
Tip of the acromion process
- 6.
Lateral end of the clavicle
- 7.
Acromioclavicular joint
- 8.
Clavicle
- 9.
Glenoid fossa of the scapula
- 10.
Coracoid process of the scapula
- 11.
Acromion process of the scapula
RADIOLOGICAL FEATURES OF THE SCAPULA
Plain Radiographs
The inferior angle of the scapula lies over the seventh rib or interspace – this is a useful guideline in identifying ribs or thoracic vertebral levels.
The scapula lies over the ribs and obscures some of the lung on a posteroanterior (PA) chest radiograph (taken through the subject’s back with their chest next to the plate), unless the shoulders are rotated forwards. In anteroposterior (AP) views it is not usually possible to rotate the scapulae off the lungs. In AP views of the scapula, the beam is centred over the head of the humerus in order to project the thoracic cage away from the scapula.
In lateral chest radiographs, the lateral border of the scapula may be confused with an oblique fissure. The inferior angle of the scapula may be slightly bulbous and simulate a mass on this view.
In an isotope bone scan, injected radioactive technetium is taken up by metabolically active bone and emits a signal detectable by a Gamma camera. This is usually done to detect areas of abnormally active bone (‘hot spots’), such as in arthritis where there is inflammation or in bony metastases. The inferior angle of the scapula overlying the seventh rib may appear as a ‘hot spot’ as the isotope signal from both structures is additive.
Ossification
The scapula ossifies in the eighth week of fetal life. An ossification centre appears in the middle of the coracoid process in the first year of life and fuses at 15 years of age. Secondary centres appear in the root of the coracoid process, the medial border and the inferior angle of the scapula between 14 and 20 years, and fuse between 22 and 25 years of age.
The glenoid is oblique from posterior to anterior, lateral to medial in orientation. This is an anatomic evolutionary feature that prevents posterior dislocation following a fall on an outstretched hand. The same feature leads to the tendency to dislocate anteriorly following a direct fall on the shoulder.
THE CLAVICLE ( Fig. 7.3 ; see also Fig. 7.2 )
The clavicle lies almost horizontally between the sternoclavicular and the acromioclavicular joints. It is also attached to the first costal cartilage by the costoclavicular ligament, which arises from the rhomboid fossa on its inferomedial surface. It is connected to the coracoid process by the coracoclavicular ligament at the conoid tubercle and the trapezoid line on its inferolateral surface. The subclavian vessels and the trunks of the brachial plexus pass behind its medial third.
RADIOLOGICAL FEATURES OF THE CLAVICLE
Chest Radiograph
The clavicle overlies the apices of the lungs in chest radiographs. Apical or lordotic views are used to project the clavicles above the lungs to evaluate this area further. In portable AP chest radiography, if the patient is inclined backwards from a true vertical position the horizontal beam projects the clavicles above the lungs.
On a chest radiograph, the distance between the medial end of the clavicle and the spine of the vertebrae is equal on both sides unless the patient is rotated.
The rhomboid fossa of the clavicle is a concave impression of the inferior surface of the sternal (medial) end of the clavicle. It is a normal anatomical variant that can be seen on 1% of normal chest X-rays. It is more often unilateral than bilateral.
Ossification
The clavicle begins to ossify before any other bone in the body. It ossifies in membrane from two centres that appear at the fifth and sixth fetal weeks, and fuses in the seventh week. A secondary centre appears at the sternal end at 15 years in females and 17 years in males, and fuses at 25 years of age.
Being membranous rather than arising from a chondral frame (endochondral) means that cartilage tumours of the clavicle are extremely uncommon.
Multislice computed tomography (CT) with reformatted images allows excellent tomographic assessment of the long axis of the clavicle. The articulation with the sternum is best visualized using magnetic resonance imaging (MRI) with a surface coil placed over the anterior chest wall. The width of the acromioclavicular joint can also be measured using high-resolution ultrasound.
THE HUMERUS ( Figs. 7.4, 7.5 ; see also Fig. 7.2 )
The hemispherical head of the humerus is separated from the greater and lesser tubercles by the anatomical neck. Between the tubercles is the bicipital groove for the long head of the biceps. The shaft just below the tubercles is narrow and is called the surgical neck of the humerus.
- 1.
Shaft of the humerus
- 2.
Olecranon fossa
- 3.
Medial epicondyle
- 4.
Lateral epicondyle
- 5.
Olecranon process
- 6.
Capitulum
- 7.
Trochlea
- 8.
Head of radius
- 9.
Neck of radius
- 10.
Coronoid process of the ulna
- 11.
Radial tuberosity
- 12.
Shaft of radius
- 13.
Shaft of ulna
The shaft is marked by a spiral groove where the radial nerve and the profunda vessels run. The deltoid tuberosity on the lateral aspect of the midshaft is the site of insertion of the deltoid muscle.
The lower end of the humerus is expanded and has medial and lateral epicondyles. The articular surface for the elbow joint has a capitellum for articulation with the radial head and a trochlea for the olecranon fossa of the ulna. Above the trochlea are fossae, the coronoid anteriorly and the deeper olecranon fossa posteriorly.
RADIOLOGICAL FEATURES OF THE HUMERUS
Plain Radiographs
The lower epiphysis of the humerus lies at a 25-degree angle to the shaft so that a vertical line down the front of the shaft on a lateral radiograph – the anterior humeral line – bisects the capitellum.
An olecranon foramen may replace the olecranon fossa.
A hook-shaped projection of bone – termed the supracondylar process – occasionally occurs about 5 cm above the medial epicondyle. It varies in length between 2 and 20 mm and may be continuous with a fibrous band (ligament of Struthers). When present, the ligament is attached above the epicondyle to form a foramen that transmits the median nerve and the brachial artery.
Avulsion of the Medial Epicondyle
The flexor muscles of the forearm arise from the medial epicondyle of the humerus. Repeated contractions or a single violent contraction of these muscles in a child can result in avulsion of the apophysis (a secondary ossification centre occurring outside a joint) of the medial epicondyle.
Ossification
The primary centre for the humerus appears at the eighth week of fetal life. Secondary centres appear in the head of the humerus at 1 year, the greater tuberosity at 3 years, and the lesser tuberosity at 5 years of age. These fuse with one another at 6 years and with the shaft at 20 years of age. Secondary centres appear in the Capitellum at 1 year, the Radial head at 5 years, the Internal epicondyle at 5 years, Trochlea at 10 years, Olecranon at 10 years and External epicondyle at 10 years (CRITOE). These fuse at 17–18 years of age.
THE RADIUS AND ULNA ( Figs. 7.6, 7.7 ; see also Fig. 7.5 )
The radius has a cylindrical head that is separated from the radial tubercle and the remainder of the shaft by the neck. Its lower end is expanded and its most distal part is the radial styloid. The radius is connected by the interosseous membrane to the ulna.
- 1.
Distal radius
- 2.
Styloid process of the radius
- 3.
Distal ulna
- 4.
Styloid process of the ulna
- 5.
Distal radioulnar joint
- 6.
Radiocarpal joint
- 7.
Scaphoid
- 8.
Lunate
- 9.
Triquetral
- 10.
Pisiform
- 11.
Hamate
- 12.
Hook of hamate
- 13.
Capitate
- 14.
Trapezoid
- 15.
Trapezium
- 16.
First metacarpophalangeal joint
- 17.
Base of fourth metacarpal
- 18.
Shaft of fourth metacarpal
- 19.
Head of fourth metacarpal
- 20.
Fourth metacarpophalangeal joint
- 21.
Shaft of the proximal phalanx, ring finger
- 22.
Proximal interphalangeal joint, little finger
- 23.
Middle phalanx, middle finger
- 24.
Distal interphalangeal joint, index finger
- 25.
Distal phalanx, thumb
- 26.
Sesamoid bone
- 27.
Soft tissues overlying the distal phalanx of the middle finger
The upper part of the ulna – the olecranon – is hook-shaped, with the concavity of the hook – the trochlear fossa – anteriorly. A fossa found laterally at the base of the olecranon is for articulation with the radial head. The shaft of the ulna is narrow. The styloid process at the distal end is narrower and more proximal than that of the radius.
RADIOLOGICAL FEATURES OF THE RADIUS AND ULNA
Plain Radiographs
The head of the radius has a single cortical line on its upper surface and is perpendicular to the neck in the normal radiograph (see Fig. 7.5 ). Angulation of the head or a double cortical line are signs of fracture of the radial head.
The triceps muscle is inserted into the tip of the olecranon. Fracture of the olecranon is therefore associated with proximal displacement by the action of this muscle.
The ulnar styloid is proximal to the radial styloid, with a line joining them on an AP radiograph lying at an angle of 110 degrees with the long axis of the radius (see Fig. 7.7 ). In a lateral radiograph, the articulating surface of the distal radius is angled 10 degrees to a line through the shaft of the radius. Recognition of these normal angles is important in reduction of fractures of the wrist.
Failure to restore volar angulation of the distal radius following a fracture of the distal radius often results in loss of grip strength due to impaired flexor function.
The pronator quadratus is a square, flat muscle that arises on the distal ulna and passes to the distal radius. A thin fat pad overlying this muscle is visible as a linear lucency on a lateral radiograph of the wrist. Thickening of the muscle, such as by haematoma in a fracture of the underlying bone, can be detected on a radiograph by bowing of the pronator quadratus fat pad.
Ossification of the Radius
The primary ossification centre of the radius appears in the eighth week of fetal life. Secondary centres appear distally in the first year and proximally at 5 years of age. These fuse at 20 years and 17 years, respectively.
Ossification of the Ulna
The shaft of the ulna ossifies in the eighth week of fetal life. Secondary centres appear in the distal ulna at 5 years and in the olecranon at 10 years of age. These fuse at 20 and 17 years, respectively.
THE CARPAL BONES ( Fig. 7.8 ; see also Fig. 7.7 )
The carpal bones are arranged in two rows of four each. In the proximal row, from lateral to medial, are the scaphoid, lunate and triquetral bones, with the pisiform on the anterior surface of the triquetral. The trapezium, trapezoid, capitate and hamate make up the distal row.
Together the carpal bones form an arch, with its concavity situated anteriorly. The flexor retinaculum is attached laterally to the scaphoid and the ridge of the trapezium, and medially to the pisiform and the hook of the hamate. It converts the arch of bones into a tunnel, the carpal tunnel, which conveys the superficial and deep flexor tendons of the fingers and the thumb (except flexor carpi ulnaris and palmaris longus tendons) and the median nerve. The extensor retinaculum on the dorsum of the wrist attaches to the pisiform and triquetrum medially and the radius laterally. Six separate synovial sheaths run beneath it ( Fig. 7.9 ).
RADIOLOGICAL FEATURES OF THE CARPAL BONES
Radiography
These are radiographed in the anteroposterior, lateral and oblique positions (see Fig. 7.7 ). Carpal tunnel views are obtained by extending the wrist and taking an inferosuperior view that is centred over the anterior part of the wrist.
Supernumerary Bones
These may be found in the wrist and include the os centrale found between the scaphoid, trapezoid and capitate, which may represent the tubercle of the scaphoid that has not fused with its upper pole, and the os radiale externum, which is found on the lateral side of the scaphoid distal to the radial styloid.
Nutrient Arteries of the Scaphoid
In 13% of subjects these enter the scaphoid exclusively in its distal half. If such a bone fractures across its midportion, the blood supply to the proximal portion is cut off and ischaemic necrosis is inevitable. This occurs in 50% of patients with displaced scaphoid fractures.
Ossification of the Carpal Bones
These ossify from a single centre each. The capitate ossifies first and the pisiform last, but the order and timing of the ossification of the other bones is variable. Excluding the pisiform, they ossify in a clockwise direction from capitate to trapezoid as follows: the capitate at 4 months; the hamate at 4 months; the triquetral at 3 years; the lunate bone at 5 years; and the scaphoid, trapezium and trapezoid at 6 years. The pisiform ossifies at 11 years of age.
THE METACARPALS AND PHALANGES
The five metacarpals are numbered from the lateral to the medial side. Each has a base proximally that articulates with that of the other metacarpals, except in the case of the first metacarpal, which is as a result more mobile and less likely to fracture. The third metacarpal has a styloid process extending from its base on the dorsal aspect. Each metacarpal has a rounded head distally, which articulates with the proximal phalanx.
The phalanges are 14 in number, three for each finger and two for the thumb. Like the metacarpals, each has a head, a shaft and a base. The distal part of the distal phalanx is expanded as the tuft of the distal phalanx.
RADIOLOGICAL FEATURES OF THE METACARPALS AND PHALANGES
Bone Age
A radiograph of the left hand is used in the determination of bone age. Standards of age determined by epiphyseal appearance and fusion have been compiled for the left hand and wrist by Greulich and Pyle, and by Tanner and Whitehouse (TW2 method).
The Metacarpal Sign
A line tangential to the heads of the fourth and fifth metacarpals does not cross the head of the third metacarpal in 90% of normal hands – this is called the metacarpal sign. This line does, however, cross the third metacarpal head in gonadal dysgenesis.
The Carpal Angle
This is formed by lines tangential to the proximal ends of the scaphoid and lunate bones. In normal hands the average angle is 138 degrees. It is reduced to an average 108 degrees in gonadal dysgenesis.
The Metacarpal Index
This is calculated by measuring the lengths of the second, third, fourth and fifth metacarpals and dividing by their breadths taken at their exact midpoint. The sum of these divided by four is the metacarpal index, which has a normal range of 5.4–7.9. An index greater than 8.4 suggests the diagnosis of arachnodactyly.
Sesamoid Bones
Two sesamoid bones are found related to the anterior surface of the metacarpophalangeal joint of the thumb in the normal radiograph. A single sesamoid bone in relation to this joint in the little finger is seen in 83% of radiographs, and at the interphalangeal joint of the thumb in 73%. These are occasionally found at other metacarpal and distal interphalangeal joints. The incidence of sesamoid bones is increased in acromegaly.
Ossification of the Metacarpals and Phalanges
These ossify between the ninth and twelfth fetal weeks. Secondary ossification centres appear in the distal end of the metacarpals of the fingers at 2 years and fuse at 20 years of age. Secondary centres for the thumb metacarpal and for the phalanges are at their proximal end and appear between 2 and 3 years, and fuse between 18 and 20 years of age.
The Joints of the Upper Limb
THE STERNOCLAVICULAR JOINT
Type
The sternoclavicular joint is a synovial joint divided into two parts by an articular disc.
Articular Surfaces
These are the sternal end of the clavicle, the clavicular notch of the manubrium and the upper surface of the first costal cartilage.
Ligaments
These are the anterior and posterior sternoclavicular ligaments, the costoclavicular ligament and the interclavicular ligament.
THE ACROMIOCLAVICULAR JOINT
Type
The acromioclavicular joint is a synovial joint.
Articular Surfaces
These are the outer end of the clavicle and the acromion. In health the undersurface of the acromion will align with the undersurface of the clavicle.
Ligaments
These are as follows:
- ■
Acromioclavicular ligament, which is a thickening of the fibrous capsule superiorly.
- ■
Coracoclavicular ligament, which has conoid and trapezoid parts.
THE SHOULDER (GLENOHUMERAL) JOINT ( Figs. 7.11–7.15 )
Type
The glenohumeral joint is a ball-and-socket synovial joint.
- 1.
Acromion process
- 2.
Infraspinatus muscle
- 3.
Deltoid muscle
- 4.
Teres minor muscle
- 5.
Quadrilateral space (containing the circumflex humeral nerve and vessels)
- 6.
Triceps muscle (lateral head)
- 7.
Triceps muscle (long head)
- 8.
Supraspinatus muscle and tendon
- 9.
Superior labrum (and long head of the biceps muscle anchor)
- 10.
Suprascapular notch (containing the suprascapular nerve artery and vein)
- 11.
Biceps tendon
- 12.
Coracoid process
- 13.
Lesser tuberosity of the humeral head
- 14.
Subscapularis muscle and tendon
- 1.
Acromioclavicular joint
- 2.
Deltoid muscle, lateral belly
- 3.
Supraspinatus tendon insertion
- 4.
Clavicle
- 5.
Acromion process
- 6.
Deltoid muscle, anterior belly
- 7.
Scapula
- 8.
Coracoid process
- 9.
Subscapularis muscle and tendon
- 10.
Anterior glenoid labrum
- 11.
Hyaline articular cartilage
- 12.
Infraspinatus muscle
- 13.
Long head of biceps tendon and sheath
- 14.
Transverse humeral ligament
- 15.
Middle glenohumeral ligament
- 16.
Posterior glenohumeral joint capsule
- 17.
Teres minor muscle
- 18.
Coracobrachialis
- 1.
Clavicle
- 2.
Supraspinatus muscle belly
- 3.
Coracoid process
- 4.
Glenoid
- 5.
Subscapularis
- 6.
Acromion
- 7.
Infraspinatus muscle belly
- 8.
Teres minor muscle belly
- 9.
Deltoid muscle
- 1.
Thickened middle glenohumeral ligament
- 2.
Absent anterior glenoid labrum
- 1.
Superior
- 2.
Middle glenohumeral ligaments
- 3.
Inferior glenohumeral ligaments
- 4.
Supraspinatus tendon
- 5.
Biceps tendon
Articular Surfaces
These are as follows:
- ■
Head of the humerus.
- ■
The glenoid cavity of the scapula, which is made deeper by a fibrocartilaginous ring – the labrum glenoidale.
The articular surface of the humeral head is four times the area of the glenoid cavity.
Capsule
This is attached to the epiphyseal line of the glenoid and humerus, except inferiorly where it extends downwards on the medial aspect of the neck of the humerus as the axillary pouch.
Synovium
In addition to lining the capsule of the joint, the synovium extends along the tendon of the long head of the biceps and beneath the tendon of subscapularis muscle as the subscapular bursa. The long head of the biceps is therefore extrasynovial but intracapsular attaching to the supraglenoid tubercle.
Ligaments
These are as follows:
- ■
Three glenohumeral ligaments: anterior thickenings of the capsule passing from the upper part of the glenoid to the lesser tuberosity and the inferior part of the head of the humerus. These are weak ligaments and not supported by overlying muscles, unlike the posterior capsule which is reinforced by the infraspinatus muscle.
- ■
The coracohumeral ligament.
- ■
The transverse humeral ligament between the greater and the lesser tuberosities of the humerus which maintains the long head of the biceps tendon within the bicipital groove.
Stability
In addition to ligaments, the stability of the shoulder joint depends upon the surrounding muscles. These are:
- ■
The short muscles known as the rotator cuff muscles (i.e. subscapularis, infraspinatus and teres minor muscles).
- ■
The longer muscles, including the long head of the biceps, pectoralis major, latissimus dorsi, teres major and deltoid muscles.
The inferior part of the joint is least well protected by either ligaments or muscles.
RADIOLOGICAL FEATURES OF THE SHOULDER JOINT
Plain Radiographs
The supraspinatus muscle passes on the superior aspect of the shoulder joint to the greater tuberosity of the humerus. Calcification occurs in this muscle owing to degenerative change and may be visible on radiographs.
The supraspinatus muscle is separated from the acromion by the subacromial–subdeltoid bursa, the largest bursa in the body. This bursa does not communicate with the shoulder joint unless the supraspinatus is ruptured by trauma or degeneration. This communication is then visible on arthrography. MRI can also be used to detect this rupture.
The capsule of the shoulder joint is lax and relatively unprotected by ligaments or muscles inferiorly. This is the site of accumulation of fluid in effusion or haematoma of the joint.
Arthrography With or Without CT
In the shoulder joint, arthrography is achieved by injection of contrast into the joint below and lateral to the coracoid process. It shows the features of the joint as outlined above. In particular, the axillary pouch can be seen inferior to the humeral head on external rotation of the arm, and the subscapular (subcoracoid) bursa can be seen on internal rotation of the arm. The subacromial (subdeltoid) bursa is not filled unless the supraspinatus tendon is completely ruptured.
The tendon of the long head of the biceps is seen as a filling defect within the joint and its synovial sheath is opacified outside the joint along the bicipital groove of the humerus.
Subacromial Bursography
Contrast injection to the subacromial bursa with either ultrasound or fluoroscopic guidance is often followed by therapeutic injection of steroid and bupivacaine (Marcaine). Subacromial bursitis or inflammation of the bursa is most frequently secondary to impingement ( Fig. 7.10A and B ).
