Bones of the Upper Limb PDF

The bones of the upper limb The Scapula 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...

The bones of the upper limb The Scapula 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. 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 fields in PA chest radiographs unless the shoulders are rotated forwards. In AP views, it is not usually possible to rotate the scapulae off the lung fields. Similarly, in PA views of the scapula the beam is centered over the head of the humerus 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. Isotope bone scan. The inferior angle of the scapula overlying the seventh rib may appear as a ‘hot spot’. Ossification The scapula ossifies in the eighth week of fetal life. An ossification center appears in the middle of the coracoid process in the first year of life and fuses at 15 years of age. Secondary centers 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. Radiology pearl The glenoid is oblique from posterior to anterior, lateral to medial in orientation. This is an anatomic evolutionary feature that prevents posterior dislocation following fall on an outstretched hand. The same feature leads to the tendency to dislocate anteriorly following a direct fall on the shoulder. The clavicle 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 Radiology pearl The rhomboid fossa is seen in 0.6% of normal chest X-rays and 33% are bilateral. Ossification The clavicle begins to ossify before any other bone in the body It ossifies in membrane from two centers that appear at the fifth and sixth fetal weeks, and fuses in the seventh week. A secondary center appears at the sternal end at 15 years in females and 17 years in males, and fuses at 25 years of age Radiology pearl Being membranous rather than arising from a chondral frame (endochondral), cartilage tumors of the clavicle are extremely uncommon. Multislice CT with reformatted images allows excellent tomographic assessment of the long axis of the clavicle. The articulation with the sternum is best visualized using MRI with a surface coil placed over the anterior chest wall The humerus 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. 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 mid shaft 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 AP view of the humerus is part of the humerus series and is usually taken in a standing position. However, it can also be obtained in a supine position. The projection demonstrates the humerus in its natural anatomical position allowing for adequate radiographic examination of the entire humerus and its respective articulations. 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. These fuse at 17–18 years of age. The radius and ulna 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. 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. 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° with the long axis of the radius (In a lateral radiograph, the articulating surface of the distal radius is angled 10° to a line through the shaft of the radius. Recognition of these normal angles is important in reduction of fractures of the wrist. 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 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.