Fascia over deltoid

The deep fascia over deltoid sends numerous septa between its fasciculi and is continuous with the pectoral fascia in front and the thick and strong infraspinous fascia behind. Above it is attached to the clavicle, acromion and crest of the scapular spine; below it is continuous with the brachial fascia.

Subscapular fascia

The subscapular fascia is a thin aponeurosis attached to the entire circumference of the subscapular fossa; subscapularis itself is partly attached to its deep surface.

Supraspinous fascia

The supraspinous fascia completes the osseofibrous compartment in which supraspinatus is attached. It is thick medially, but thinner laterally under the coraco-acromial ligament. It is attached to the scapula around the boundaries of the attachment of supraspinatus.

Infraspinous fascia

The infraspinous fascia covers infraspinatus and is attached to the margins of the infraspinous fossa. The fascia is continuous with the deltoid fascia along the overlapping posterior border of deltoid.

Pectoral and axillary fascia

The pectoral fascia is a thin lamina which covers pectoralis major and extends between its fasciculi. It is attached medially to the sternum, above to the clavicle and is continuous inferolaterally with the fascia of the shoulder, axilla and thorax. Although thin over pectoralis major, it is thicker between this muscle and latissimus dorsi, and forms the floor of the axilla as the axillary fascia. The latter divides at the lateral margin of latissimus dorsi into two layers, which ensheathe the muscle and are attached behind to the spines of the thoracic vertebrae. As the fascia leaves the lower edge of pectoralis major to cross the axilla, a layer ascends under cover of the muscle and splits to envelop pectoralis minor: it becomes the clavipectoral fascia at the upper edge of pectoralis minor. The hollow of the armpit is produced mainly by the action of this fascia in tethering the skin to the floor of the axilla, and it is sometimes referred to as the suspensory ligament of the axilla. The axillary fascia is pierced by the tail of the breast (Ch. 54).

Clavipectoral fascia

The clavipectoral fascia is a strong fibrous sheet behind the clavicular part of pectoralis major. It fills the gap between pectoralis minor and subclavius, and covers the axillary vessels and nerves. It splits around subclavius and is attached to the clavicle both anterior and posterior to the groove for subclavius. The posterior layer fuses with the deep cervical fascia which connects omohyoid to the clavicle and with the sheath of the axillary vessels. Medially it blends with the fascia over the first two intercostal spaces and is attached to the first rib, medial to subclavius. Laterally, it is thick and dense, and is attached to the coracoid process, blending with the coracoclavicular ligament. Between the first rib and coracoid process the fascia often thickens to form a band, the costocoracoid ligament. Below this the fascia becomes thin, splits around pectoralis minor and descends to blend with the axillary fascia and laterally with the fascia over the short head of biceps. The cephalic vein, thoraco-acromial artery and vein, and lateral pectoral nerve pass through the fascia.

Lateral third

The lateral third of the clavicle is flattened and has a superior and an inferior surface, limited by an anterior and a posterior border. The anterior border is concave, thin and roughened and may be marked by a small deltoid tubercle.

The posterior border, also roughened by muscular attachments, is convex backwards. The superior surface is roughened near its margins but is smooth centrally, where it can be felt through the skin. The inferior surface presents two obvious markings. Close to the posterior border, at the junction of the lateral fourth with the rest of the bone, there is a prominent conoid tubercle which gives attachment to the conoid part of the coracoclavicular ligament. A narrow, roughened strip, the trapezoid line, runs forwards and laterally from the lateral side of this tubercle, almost as far as the acromial end (Fig. 46.1B). The trapezoid part of the coracoclavicular ligament is attached to it. A small oval articular facet, for articulation with the medial aspect of the acromion, faces laterally and slightly downwards at the lateral end of the shaft.

Subclavius lies in a groove on the inferior surface (Fig. 46.1B). The clavipectoral fascia is attached to the edges of the groove; the posterior edge of the groove runs to the conoid tubercle, where fascia and conoid ligament merge. Lateral to the groove there is a laterally inclined nutrient foramen. Deltoid (anterior) and trapezius (posterior) are attached to the lateral third of the shaft: both muscles reach the superior surface. The coracoclavicular ligament, which is attached to the conoid tubercle and trapezoid line (Fig. 46.1B), transmits the weight of the upper limb to the clavicle, counteracted by trapezius which supports its lateral part. From the conoid tubercle this weight is transmitted through the medial two-thirds of the shaft to the axial skeleton.

The clavicle is often fractured, commonly by indirect forces, as a result of a violent impact to the hand or shoulder. The break is usually at the junction of the lateral and intermediate thirds, where the curvature changes, for this is the weakest part of the bone. A fracture medial to the conoid tubercle interrupts weight transmission from the arm to the axial skeleton. The resulting deformity is caused by the weight of the arm, which acts on the lateral fragment through the coracoclavicular ligament and draws it downwards. The medial fragment, as a rule, is a little displaced.

Medial two-thirds

The medial two-thirds of the shaft of the clavicle is cylindrical or prismoid in form and possesses four surfaces, but the inferior surface is often reduced to a mere ridge. The anterior surface is roughened over most of its extent but it is smooth and rounded at its lateral end, where it forms the upper boundary of the infraclavicular fossa. The upper surface is roughened in its medial part and smooth at its lateral end. The posterior surface is smooth and featureless. The inferior surface is marked, near the sternal end, by a roughened oval impression, which is often depressed below the surface. Its margins give attachment to the costoclavicular ligament, which connects the clavicle to the upper surface of the first rib and its cartilage. Rarely, this area is smooth or raised to form an eminence which may articulate with the upper surface of the first rib by means of a synovial joint. There is a groove in the long axis of the bone in the lateral half of the posterior surface.

The medial two-thirds provide attachment, anteriorly, for the clavicular head of pectoralis major: the area is usually clearly indicated on the bone. The clavicular head of sternocleidomastoid is attached to the medial half of the superior surface, but the marking on the bone is not very conspicuous. The smooth, posterior surface is devoid of muscular attachments except at its lower part immediately adjoining the sternal end, where the lateral fibres of sternohyoid are attached. Medially, this surface is related to the lower end of the internal jugular vein (from which it is separated by sternohyoid), the termination of the subclavian vein, and the start of the brachiocephalic vein. More laterally, it arches in front of the trunks of the brachial plexus and the third part of the subclavian artery. The suprascapular vessels are related to the upper part of this surface. The inferior surface gives insertion to subclavius in the subclavian groove: the clavipectoral fascia, which encloses subclavius, is attached to the edges of the groove. The posterior lip of the groove runs into the conoid tubercle and carries the fascia into continuity with the conoid ligament. A nutrient foramen is found in the lateral end of the groove, running in a lateral direction: the nutrient artery is derived from the suprascapular artery. The impression for the costoclavicular ligament is very variable in its character.

Sternal end

The sternal end of the clavicle is directed medially, and a little downwards and forwards, to articulate with the clavicular notch of the manubrium sterni. The sternal surface, usually irregular and pitted, is quadrangular (sometimes triangular). Its uppermost part is slightly roughened for attachment of the interclavicular ligament, sternoclavicular capsule and articular disc. Elsewhere the surface is smooth and articular and it extends onto the inferior surface for a short distance, where it articulates with the first costal cartilage. The sternal end of the clavicle projects upwards beyond the manubrium sterni and can be felt without difficulty and usually seen (a prominent clinical landmark), in the lateral wall of the jugular fossa.

Ossification

The clavicle begins to ossify before any other bone in the body, and is ossified from three centres. The shaft of the bone is ossified in condensed mesenchyme from two primary centres, medial and lateral, which appear between the fifth and sixth weeks of intrauterine life, and fuse about the 45th day. Cartilage then develops at both ends of the clavicle. The medial cartilaginous mass contributes more to growth in length than does the lateral mass: the two centres of ossification meet between the middle and lateral thirds of the clavicle. A secondary centre for the sternal end appears in late teens, or even early twenties, usually 2 years earlier in females (Fig. 46.2). Fusion is probably rapid but reliable data are lacking. An acromial secondary centre sometimes develops at around 18 to 20 years, but this epiphysis is always small and rudimentary and rapidly joins the shaft.

Fig. 46.2 The three constant centres of ossification of the clavicle.

The clavicle does not ossify exclusively by intramembranous ossification. In 14 mm embryos the clavicle is a band of condensed mesenchyme between the acromion and apex of the first rib, which is continuous with the sternal rudiment. Medial and lateral zones of early cartilage transformation (‘precartilage’) occur within this band, and intramembranous centres of ossification appear, and soon fuse, in the mesenchyme between them. Sternal and acromial zones soon become true cartilage into which ossification extends from the shaft. Length increases by interstitial growth of these terminal cartilages; the latter develop zones of hypertrophy, calcification and advancing endochondral ossification like other growth cartilages. Diameter increases by subperichondral deposition in the extremities and subperiosteal deposition in the shaft. Epiphyses are endochondral and probably fuse in the same way as they do in long bones. Defects of ossification in the clavicle and those cranial bones which ossify by intramembranous ossification occasionally coincide, e.g. in cleidocranial dysostosis.

Costal surface

The costal surface, which is directed medially and forwards when the arm is by the side, is slightly hollowed out, especially in its upper part (Fig. 46.3B).

Near the lateral border there is a longitudinal rounded ridge, prominent near the neck, but less so below, which is separated from the lateral border by a narrow grooved area.

Subscapularis arises from nearly the whole of the costal surface, including the grooved area immediately adjoining the lateral border, but excluding the area next to the neck of the bone. Small intramuscular tendons are attached to the roughened ridges which subdivide this surface incompletely into a number of smooth areas. The anterior aspect of the neck is separated from subscapularis by a bursal protrusion of the synovial membrane of the shoulder joint (subscapular ‘bursa’). The lower five or six digitations of serratus anterior are attached to an oval area near the inferior angle. The remainder of the muscle is inserted into a narrow strip along the ventral aspect of the medial border, which is wider above, where it receives the large first digitation. The longitudinal thickening of the bone near the lateral border provides a lever of the necessary strength to withstand the pull of serratus anterior on the inferior angle during lateral scapular rotation, when the glenoid cavity is turned to face more directly upwards as the arm is raised from the side and carried above the head against gravity.

Dorsal surface

The dorsal surface is divided by the shelf-like spine of the scapula into a small upper and a large lower area, which are confluent at the spinoglenoid notch between the lateral border of the spine and the dorsal aspect of the neck (Fig. 46.3A).

Supraspinatus is attached to the medial two-thirds of the supraspinous fossa on the dorsal surface: the fascia which covers the muscle is attached to the margins of the fossa. Teres minor is attached to the upper two-thirds of a flattened strip which adjoins the lateral border. The strip is grooved near its upper end by the circumflex scapular vessels, which pass between teres minor and the bone as they enter the infraspinous fossa. The lower limit of the attachment of teres minor is indicated by an oblique ridge, which runs from the lateral border to the neighbourhood of the inferior angle and cuts off a somewhat oval area where teres major is attached. The dorsal aspect of the inferior angle may give origin to a small slip which joins the deep surface of latissimus dorsi. The infraspinous fossa is hollowed out laterally but is convex medially. Infraspinatus is attached to the infraspinous fossa, with the exception of an area near the neck of the bone. The strong infraspinatus fascia passes onto teres minor and teres major, and sends fascial partitions between them which reach the bone along the ridges which mark the limits of their attachments.

Superior border

The superior border, thin and sharp, is the shortest. At its anterolateral end it is separated from the root of the coracoid process by the suprascapular notch (Fig. 46.3B). Near the suprascapular notch it gives origin to the inferior belly of omohyoid. The notch is bridged by the superior transverse ligament which is attached laterally to the root of the coracoid process and medially to the limit of the notch. The ligament is sometimes ossified. The foramen, thus completed, transmits the suprascapular nerve to the supraspinous fossa, whereas the suprascapular vessels pass backwards above the ligament.

Lateral border

The lateral border of the scapula forms a clearly defined, sharp, roughened ridge, which runs sinuously from the inferior angle to the glenoid cavity. At its upper end it widens into a rough, somewhat triangular area, which is termed the infraglenoid tubercle (Fig. 46.4B). The lateral border separates the attachments of subscapularis and teres minor and major. These muscles project beyond the bone and, with latissimus dorsi, cover it so completely that it cannot be felt through the skin. The long head of triceps is attached to the infraglenoid tubercle.

The grooved part of the costal surface, the narrow flat lateral strip of the dorsal surface and the adjacent thickened ridge (Fig. 46.4B), are often included in the ‘lateral border’ during clinical examination.

Medial border

The medial border of the scapula extends from the inferior to the superior angle. In its lower two-thirds this border can easily be felt through the skin, but its upper third is more deeply placed and cannot be palpated. It is thin and often angled opposite the root of the spine. Levator scapulae is attached to a narrow strip, extending from the superior angle to the root of the spine, and rhomboid minor is attached below this, opposite the root of the spine. Rhomboid major is attached to the remainder of the border.

Scapular angles

The inferior angle overlies the seventh rib or intercostal space. Palpable through the skin and covering muscles, it is also visible as it advances round the thoracic wall when the arm is raised. It is covered on its dorsal aspect by the upper border of latissimus dorsi, a small slip from which is frequently attached to the inferior angle. The superior angle, at the junction of the superior and medial borders, is obscured by the upper part of trapezius. The lateral angle, truncated and broad, bears the glenoid cavity which articulates with the head of the humerus at the glenohumeral joint. It provides a shallow, and limited, socket for the humeral head. Its outline is piriform, narrower above (Fig. 46.4B). The glenohumeral ligaments are attached to its anterior margin. When the arm is by the side, the cavity is directed forwards, laterally and slightly upwards. When the arm is raised above the head it is directed almost straight upwards. Just above it a small rough supraglenoid tubercle encroaches on the root of the coracoid process. The anatomical neck, the constriction adjoining the rim of the glenoid cavity, is most distinct at its inferior and dorsal aspects. Anteriorly and posteriorly it extends between the infraglenoid and supraglenoid tubercles, passing lateral to the root of the coracoid process. The long head of biceps brachii is attached to the supraglenoid tubercle, and the long head of triceps brachii is attached to the infraglenoid tubercle.

Spine of the scapula

The spine of the scapula forms a shelf-like projection on the upper part of the dorsal surface of the bone, and is triangular in shape (Fig. 46.3A). Its lateral border is free, thick and rounded and helps to bound the spinoglenoid notch, which lies between it and the dorsal surface of the neck of the bone. Its anterior border joins the dorsal surface of the scapula along a line which runs laterally and slightly upwards from the junction of the upper and middle thirds of the medial border. The plate-like body of the bone is bent along this line, which accounts for the concavity of the upper part of the costal surface. The dorsal border is the crest of the spine, and is subcutaneous throughout nearly its whole extent. At its medial end the crest expands into a smooth, triangular area. Elsewhere the upper and lower edges and the surface of the crest are roughened for muscular attachments. The upper surface of the spine widens as it is traced laterally, and is slightly hollowed out. Together with the upper area of the dorsal surface of the bone, the upper surface of the spine forms the supraspinous fossa. The lower surface is overhung by the crest at its medial, narrow end, but is gently convex in its wider, lateral portion. Together with the lower area of the dorsal surface of the bone, the lower surface of the spine forms the infraspinous fossa, which communicates with the supraspinous fossa through the spinoglenoid notch.

Supra- and infraspinatus are attached to the upper and lower surfaces of the spine of the scapula, respectively. The flattened triangular area at its root lies opposite the spine of the third thoracic vertebra and is covered by the tendon of trapezius; a bursa intervenes to enable the tendon to play over this part of the bone. The posterior fibres of deltoid are attached to the lower border of the crest. The middle fibres of trapezius are attached to the upper border of the crest, and the lowest fibres of trapezius terminate in a flat triangular tendon which glides over the smooth area at the base of the spine and inserts into a rough prominence, erroneously called the deltoid tubercle, on the dorsal or subcutaneous aspect of the spine near its medial end.

Acromion

The acromion projects forwards, almost at right angles, from the lateral end of the spine, with which it is continuous. The lower border of the crest of the spine becomes continuous with the lateral border of the acromion at the acromial angle, which forms a subcutaneous, bony landmark. The medial border of the acromion is short and is marked anteriorly by a small, oval facet, directed upwards and medially, for articulation with the lateral end of the clavicle. The lateral border, tip and upper surface of the acromion can all be felt through the skin without difficulty. There may be an accessory articular facet on the inferior surface of the acromion.

The acromion is subcutaneous over its dorsal surface, being covered only by the skin and superficial fascia. The lateral border, which is thick and irregular, and the tip of the process, as far round as the clavicular facet, give origin to the middle fibres of deltoid. The medial aspect of the tip gives attachment, below deltoid, to the lateral end of the coraco-acromial ligament. The articular capsule of the acromioclavicular joint is attached around the margins of the clavicular facet. Behind the facet, the medial border of the acromion gives insertion to the horizontal fibres of trapezius. The inferior aspect of the acromion is relatively smooth, and together with the coraco-acromial ligament and the coracoid process forms a protective arch over the shoulder joint. The tendon of supraspinatus passes below the overhanging acromion and is separated from it and from deltoid by the subacromial bursa.

Coracoid process

The coracoid process arises from the upper border of the head of the scapula and is bent sharply so as to project forwards and slightly laterally (Fig. 46.3B, Fig. 46.4A). When the arm is by the side, the coracoid process points almost straight forwards and its slightly enlarged tip can be felt through the skin, although it is covered by the anterior fibres of deltoid. The supraglenoid tubercle marks the root of the coracoid process where it adjoins the upper part of the glenoid cavity. There is another impression on the dorsal aspect of the coracoid process at the point where it changes direction: it gives attachment to the conoid part of the coracoclavicular ligament.

The coracoid process lies about 2.5 cm below the clavicle at the junction of the lateral fourth with the rest of the bone and is connected to its under surface by the coracoclavicular ligament. It is covered by the anterior fibres of deltoid and can be identified only on deep pressure through the lateral border of the infraclavicular fossa. The attachment of the conoid part of the ligament has already been considered: the trapezoid part is attached to the upper aspect of the horizontal part of the process. Pectoralis minor is attached to the superior aspect of the coracoid process. The wider, medial end of the coraco-acromial ligament and, below that, the coracohumeral ligament, are attached to the lateral border. Coracobrachialis is attached to the medial side of the tip of the process, and the short head of biceps is attached to the lateral side of the tip. The inferior aspect of the process is smooth and helps to complete the coraco-acromial arch.

Ligaments

The main scapular ligaments are the coracoacromial and superior transverse scapular; there may also be a weaker, variable inferior transverse scapular (spinoglenoid) ligament (see below Fig. 46.13, see below Fig. 46.14).

Fig. 46.13 Interior of the left shoulder joint: anterolateral aspect.

(From Sobotta 2006.)

Fig. 46.14 A, The anterior aspect of the left shoulder. B, A deeper view of the anterior aspect than in (A), showing the subscapularis bursa.

Ossification

The cartilaginous scapula is ossified from eight or more centres: one in the body, two each in the coracoid process and the acromion, one each in the medial border, inferior angle and lower part of the rim of the glenoid cavity (Fig. 46.5). The centre for the body appears in the eighth intrauterine week. Ossification begins in the middle of the coracoid process in the first year or in a small proportion of individuals before birth and the process joins the rest of the bone about the 15th year. At or soon after puberty centres of ossification occur in the rest of the coracoid process (subcoracoid centre), in the rim of the lower part of the glenoid cavity, frequently at the tip of the coracoid process, in the acromion, in the inferior angle and contiguous part of the medial border and in the medial border. A variable area of the upper part of the glenoid cavity, usually the upper third, is ossified from the subcoracoid centre; it unites with the rest of the bone in the 14th year in the female and the 17th year in the male. A horse-shoe shaped epiphysis appears for the rim of the lower part of the glenoid cavity; thicker at its peripheral than at its central margin, it converts the flat glenoid cavity of the child into the gently concave fossa of the adult. The base of the acromion is formed by an extension from the spine; the rest of the acromion is ossified from two centres which unite and then join the extension from the spine. The various epiphyses of the scapula have all joined the bone by about the 20th year.

Fig. 46.5 Ossification of the scapula. A, Dorsal aspect; B, Lateral aspect.

(Adapted from Drake, Vogl and Mitchell 2005.)

Head

The head of the humerus forms rather less than half a spheroid; in sectional profile it is spheroidal (strictly ovoidal) (Fig. 46.7). Its smooth articular surface is covered with hyaline cartilage, which is thicker centrally. When the arm is at rest by the side, it is directed medially, backwards and upwards to articulate with the glenoid cavity of the scapula. The humeral articular surface is much more extensive than the glenoid cavity, and only a portion of it is in contact with the cavity in any one position of the arm.

Anatomical neck

The anatomical neck of the humerus immediately adjoins the margin of the head and forms a slight constriction, which is least apparent in the neighbourhood of the greater tubercle, and superiorly, and for some distance anteriorly and posteriorly: it indicates the line of capsular attachment of the shoulder joint (Fig. 46.7), other than at the intertubercular sulcus, where the long tendon of biceps emerges. Medially, the capsular attachment diverges from the anatomical neck and descends 1 cm or more onto the shaft.

Lesser tubercle

The lesser tubercle is anterior to and just beyond the anatomical neck. It has a smooth, muscular impression on its upper part palpable through the thickness of deltoid 3 cm below the acromial apex. The bony prominence slips away from the examining finger when the humerus is rotated. The lateral edge of the lesser tubercle is sharp and forms the medial border of the intertubercular sulcus. Subscapularis is attached to the lesser tubercle (Fig. 46.6A), and the transverse ligament of the shoulder joint is attached to the lateral margin.

Greater tubercle

The greater tubercle is the most lateral part of the proximal end of the humerus. It projects beyond the lateral border of the acromion. Its posterosuperior aspect, near the anatomical neck, bears three smooth flattened impressions for the attachment of supraspinatus (uppermost), infraspinatus (middle) and teres minor (lowest and placed on the posterior surface of the tubercle) (Fig. 46.6). The attachments of subscapularis and teres minor are not confined to their respective tubercles, but extend for varying distances on to the adjacent metaphysis. The projecting lateral surface of the tubercle presents numerous vascular foramina and is covered by the thick, fleshy deltoid, which produces the normal rounded contour of the shoulder. A part of the subacromial bursa may cover the upper part of this area and separate it from deltoid.

The intertubercular sulcus (bicipital groove) lies between the tubercles. It contains the long tendon of biceps, its synovial sheath, and an ascending branch from the anterior circumflex humeral artery. The rough lateral lip of the groove is marked by the bilaminar tendon of pectoralis major, its floor by the tendon of latissimus dorsi and its medial lip by the tendon of teres major; the attachment of pectoralis major extends beyond that of teres major, that of latissimus dorsi is least extensive.

Anterior border

The anterior border starts on the front of the greater tubercle and runs downwards almost to the lower end of the bone. Its proximal third forms the lateral lip of the intertuberculous sulcus and is roughened for muscular attachments. The succeeding portion is also roughened and forms the anterior limit of the deltoid tubercle; the lower half of the border is smooth and rounded.

Lateral border

The lateral border is conspicuous at the lower end of the bone, where it is thickened to form the lateral supracondylar ridge and its sharp edge is roughened along its anterior aspect. In its middle and upper thirds the border is barely discernible, but in a well-marked bone it can be traced upwards to the posterior surface of the greater tubercle. A little above its middle it is marked by a V-shaped roughened area, the deltoid tubercle. The limbs of the V are broad: the groove for the radial nerve runs downwards behind the posterior limb and fades away on the lower part of the surface.

Medial border

The medial border, although rounded, can be identified without difficulty in the lower half of the shaft, where it becomes the medial supracondylar ridge. In the proximal third the medial border is indistinct until it reappears as the medial lip of the intertubercular sulcus, where it is again rough and reaches the lesser tubercle. In its middle third, the border is interrupted by a wide, shallow groove, the radial or spiral groove, which crosses the bone obliquely, passing downwards and forwards from its posterior to its anterior surface.

Surfaces

The anterolateral surface is bounded by the anterior and lateral borders and is smooth and featureless in its upper part, which is covered by deltoid. About, or a little above, the middle of this surface, deltoid is inserted into the deltoid tubercle; further distally the surface gives origin to the lateral fibres of brachialis, which extend upwards into the floor of the lower end of the groove for the radial nerve (Fig. 46.6). Brachioradialis is attached to the proximal two-thirds of the roughened anterior aspect of the lateral supracondylar ridge, and extensor carpi radialis longus is attached to its distal third. Behind these muscles, the ridge gives attachment to the lateral intermuscular septum of the arm.

The anteromedial surface is bounded by the anterior and medial borders. Rather less than its upper third forms the rough floor of the intertubercular sulcus; the rest of the surface is smooth. Distal to the intertubercular sulcus a small area of the anteromedial surface is devoid of muscular attachment, but its lower half is occupied by the medial part of brachialis (Fig. 46.6A). Coracobrachialis is attached to a roughened strip on the middle of the medial border. The humeral head of pronator teres is attached to a narrow area close to the lowest part of the medial supracondylar ridge, and the ridge itself gives attachment to the medial intermuscular septum of the arm.

A little below its midpoint, the nutrient foramen, which is directed downwards, opens close to the medial border. A hook-shaped process of bone, the supracondylar process, from 2 to 20 mm in length, occasionally projects from the anteromedial surface of the shaft, approximately 5 cm proximal to the medial epicondyle. It is curved downwards and forwards, and its pointed apex is connected to the medial border, just above the epicondyle, by a fibrous band to which part of pronator teres is attached. The foramen completed by this fibrous band usually transmits the median nerve and brachial artery, but sometimes encloses only the nerve, or the nerve plus the ulnar artery (in cases of high division of the brachial artery). A groove which lodges the artery and nerve usually exists behind the process, and may protect the nerve and artery from compression by muscles.

The posterior surface, between the medial and lateral borders, is the most extensive surface and is occupied mostly by the medial head of triceps. A ridge, sometimes rough, descends obliquely and laterally across its proximal third, and gives attachment to the lateral head of triceps. Above triceps, the axillary nerve and the posterior circumflex humeral vessels wind round this aspect of the bone under cover of deltoid. Below and medial to the attachment of the lateral head of triceps, a shallow groove which contains the radial nerve and the profunda brachii vessels, runs downwards and laterally to gain the anterolateral surface of the shaft. The area for the origin of the fleshy medial head of triceps includes a very large part of the posterior surface of the bone. It covers an elongated triangular area, the apex of which is placed on the medial part of the posterior surface above the level of the lower limit of the insertion of teres major. The area widens below and covers the whole surface almost down to the lower end of the bone.

Fractures of the humeral shaft

Fractures of the humerus are comparatively common and may occur at almost any level. The humerus is fractured by muscular action probably more frequently than any other long bone: usually the shaft is broken below the attachment of deltoid. The radial nerve may be injured in its groove or may very rarely become involved later in the growth of callus. Fractures at the proximal end of the humerus may rarely damage the axillary nerve, and similarly fractures of the medial epicondyle may be complicated by damage to the ulnar nerve. Supracondylar fractures are relatively common in children: the end of the proximal fragment can sometimes injure the brachial artery or median nerve. In adults, non-union is more common in the humerus than in any other long bone, although contemporary management of humeral fractures has rendered non-union rare: the incidence of scaphoid non-union is similar, if not greater.

Trochlea

The trochlea is a pulley-shaped surface that covers the anterior, inferior and posterior surfaces of the condyle of the humerus medially. It articulates with the trochlear notch of the ulna. On its lateral side it is separated from the capitulum by a faint groove; its medial margin projects distally beyond the rest of the bone. When the elbow is extended the inferior and posterior aspects of the trochlea are in contact with the ulna, but, as the joint is flexed, the trochlear notch slides on to the anterior aspect and the posterior aspect is then left uncovered. The downward projection of the medial edge of the trochlea is the principal factor in determining the angulation between the long axis of the humerus and the long axis of the supinated forearm when the elbow is extended.

Medial epicondyle

The medial border of the humerus ends by turning slightly backwards as the medial epicondyle, which forms a conspicuous, blunt projection on the medial side of the condyle. It is subcutaneous and usually visible, especially in passive flexion of the elbow. Its posterior surface is smooth and is crossed by the ulnar nerve, which lies in a shallow sulcus as it enters the forearm. In this situation the nerve can be felt and rolled against the bone, and if it is jarred against the epicondyle, characteristic tingling sensations result. The lower part of the anterior surface of the medial epicondyle is marked by the attachment of the superficial group of forearm flexors. They arise from the epiphysis for the epicondyle, but are entirely extracapsular.

Lateral epicondyle

The lateral border of the humerus terminates at the lateral epicondyle, and its lower portion constitutes the lateral supracondylar ridge. The lateral epicondyle occupies the lateral part of the non-articular portion of the condyle, but does not project beyond the lateral supracondylar ridge. It turns slightly forwards, unlike the medial epicondyle, which turns slightly backwards. Its lateral and anterior surfaces show a well-marked impression for the superficial group of the extensor muscles of the forearm (Fig. 46.6B), which arise from the lateral side of the lower humeral epiphysis, and, like the flexors, are situated outside the articular capsule. The posterior surface, which is very slightly convex, is easily felt in a depression visible behind the extended elbow. A small area on the posterior surface gives origin to anconeus.

Olecranon, coronoid and radial fossae

The olecranon fossa is a deep hollow on the posterior surface of the condyle, immediately above the trochlea, that lodges the tip of the olecranon of the ulna when the elbow is extended. The floor of the fossa is always thin and may be partially deficient. A similar but smaller hollow lies immediately above the trochlea on the anterior surface of the condyle and is termed the coronoid fossa. It accommodates the anterior margin of the coronoid process of the ulna during flexion of the elbow. A very slight depression lies above the capitulum on the lateral side of the coronoid fossa. It is termed the radial fossa, since it is related to the margin of the head of the radius in full flexion of the elbow.