Second Stage Carpal Bones PDF

The carpal bones 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. Toge...

The carpal bones 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. Radiological features of the carpal bones Radiography These are radiographed in the anteroposterior, lateral and oblique positions. Carpal tunnel views are obtained by extending the wrist and taking an inferosuperior view that is centered over the anterior part of the wrist Supernumerary bones These may be found in the wrist and include the oscentrale 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 osradiale 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°. It is reduced to an average 108° 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 inter-phalangeal 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 muscles of the upper limb Modalities such as CT and especially MRI have made imaging of the muscles of the limbs possible. A knowledge of the origin, course and insertion of these muscles is less important in radiology than an understanding of their positions relative to one another in cross-section. In the upper arm the deltoid muscle covers the upper lateral aspect of the humerus. The flexors of the shoulder – the coracobrachialis and biceps muscles – lie anterior to the humerus in its upper third, and the flexors of the elbow – brachialis and biceps muscles – lie anterior to the lower part of the humerus. Extensors of the elbow joint – the triceps muscle with its long, lateral and medial heads – lie posterior to the humerus. The neurovascular bundle of brachial artery, basilic vein and median nerve lies superficially, medial to the humerus. The radial nerve and profunda brachii artery lie deeply close to the humerus, at first medially then passing posteriorly close to the lateral side. In the forearm the interosseous membrane unites the radius and ulna and separates anterior and posterior compartments. Anteriorly lie the flexors of the wrist and fingers, flexor digitorum superficialis and profundus Posteriorly are the extensors of the wrist and fingers and the abductor of the thumb – extensor carpi ulnaris, digitorum and pollicis longus, and abductor pollicis longus The muscles abducting the wrist – flexor carpi radialis and extensor carpi radialis longus and brevis – lie superficially on the radial side and those that adduct the wrist – flexor carpi ulnaris and extensor carpi ulnaris – lie on the ulnar side. The interosseous nerves and arteries lie close to the interosseous membrane. The radial nerve and vessels and the ulnar nerve and vessels lie anteriorly on each side, and the median nerve lies in the midline between the superficial and deep flexor muscles. The individual muscles may be difficult to distinguish on axial CT because of the lack of fat in the forearm. MRI is the superior method in this respect and has the added advantage of allowing direct imaging in many planes. The arterial supply of the upper limb The upper limb receives its supply from the subclavian artery. This has four branches, namely: • the vertebral artery; • the thyrocervical trunk, which supplies the inferior thyroid, suprascapular and transverse cervical arteries; • the internal thoracic artery; and • the costocervical trunk, which divides into the superior intercostal and the deep cervical arteries The subclavian artery becomes the axillary artery at the outer border of the first rib. The axillary artery lies with the brachial plexus and the axillary vein. It supplies six arteries to the chest wall and the shoulder (SALSA): • the superior thoracic artery; • the acromiothoracic trunk; • the lateral thoracic artery; • the subscapular artery; and • the anterior and posterior circumflex humeral arteries The brachial artery begins at the lower border of teres major Its branches are: • the profunda brachii artery (which arises medially); • the nutrient artery to the humerus; • the muscular branches; and • the branches to the elbow joint At the level of the radial head (but sometimes much more proximally) the brachial artery divides into the radial and ulnar arteries. The radial artery passes on the lateral side of the forearm to the wrist, where it gives a branch to the superficial palmar arch and then passes via the floor of the anatomical snuffbox to the dorsum of the hand. It passes between the first and second metacarpals to form the deep palmar arch. The ulnar artery is larger and deeper than the radial artery. It gives rise to the common interosseous artery, which in turn divides into the anterior and posterior interosseous arteries, the latter passing over the top of the interosseous membrane to supply the muscles of the dorsum of the forearm. Close to the wrist the ulnar artery becomes superficial and, having crossed the wrist, becomes the superficial palmar arch and sends a branch to the deep palmar arch. The veins of the upper limb Superficial and deep veins drain blood from the upper limb. The superficial veins commence in the hand, where smaller veins unite to form three veins – the cephalic and basilic veins from the dorsum and the median vein from the palm. The cephalic vein ascends from the radial side of the dorsum of the hand and winds around the forearm towards the elbow. Here it gives the median cubital vein to join the basilic vein and it then continues on the lateral side of the biceps muscle. At the shoulder it passes medially, pierces the clavipectoral fascia to become deep and joins the axillary vein. The basilic vein has a similar course on the medial side of the forearm and elbow. At midhumeral level it passes deeply and joins the brachial vein to become the axillary vein. The median vein of the forearm passes from the palm along the volar aspect of the forearm to join either the basilic or the cephalic veins at the elbow. The deep veins of the upper limb are usually paired venae comitantes, which accompany the arteries. The axillary veins are usually double, whereas the subclavian vein is usually single.