Surgical Anatomy of the Elbow

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Chapter 2 Surgical Anatomy of the Elbow

Osteoarticular anatomy

The elbow is formed by three bones: the humerus, ulna and radius. These bones articulate in three joints: the radiohumeral, ulnohumeral and proximal radio-ulnar joints.

Humerus

The shaft of the humerus ends distally in both lateral and medial ridges. Thereafter lateral and medial epicondyles are formed (Figs 2.1 and 2.2). They can be inspected and palpated during clinical examination, the medial part being better defined than its lateral counterpart. The flexion crease of the skin on the anterior aspect of the elbow is at the same level as a line joining the two epicondyles, 1 cm proximal to the elbow joint. The presence of an accessory origin of the pronator teres muscle, approximately 5 cm superior to the medial epicondyle on the anterolateral side of the humeral shaft, can be found in 1–3% of individuals. In these cases, the ligament of Struthers attaches to a bony prominence and can sometimes cause compression of the median nerve that travels beneath the ligament along with the brachial artery.

Two indentations on the anterior side of the humerus prevent impingement of the coronoid process and the radial head during flexion: the coronoid fossa is located medial to the smaller radial fossa. The olecranon fossa is located on the posterior side to allow space for the olecranon during extension of the elbow (Fig. 2.2).

It is important to note that the distal humerus is a strong structure, owing to its triangular shape with the articular surfaces as the base, and the lateral and medial columns as the other two limbs of the triangle. The bony surface of this triangle, however, is thin and weak: the coronoid and radial fossae on the anterior side and the olecranon fossa posteriorly. These regions provide minimal support for the distal humerus, as highlighted by the fact that in some individuals there is no bone in the centre of the olecranon fossa but only membranous tissue.

The medial epicondyle forms the trochlea, which articulates with the greater sigmoid notch of the olecranon. This asymmetric hyperbolic spool is covered with cartilage over a 300° arc. It has a more prominent medial lip that also projects more distally than the lateral lip. The trochlear groove is oriented in a helical manner from anterolaterally to posteromedially.

The lateral epicondyle forms the capitellum. This is hemispheric in shape and articulates with the concave head of the radius. It is separated from the trochlea by a groove, which articulates with the rim of the radial head throughout flexion/extension and pronation/supination. The trochlear–capitellar articular axis is oriented approximately 5–7° internally rotated in relation to the humeral epicondyles; in addition, this axis has an approximately 6–8° valgus tilt in relation to the humeral axis.1 The capitellum is oriented anteriorly and cannot therefore be observed when the elbow is visualized posteriorly. When fixing transverse distal humeral fractures it allows the application of a plate more distally on the posterior side of the lateral column. The distal part of the humerus is angulated 30° anteriorly, such that the centres of the two condyles are collinear with the anterior humeral cortex on a lateral radiograph.

Ulna

The olecranon is the subcutaneous portion of the ulna and therefore the most prominent bony surface landmark of the elbow (Figs 2.32.5). It forms the trochlear notch (incisura semilunaris) on its anterior side with the coronoid process, a protuberance that demarcates the articular surface anteriorly. This coronoid process can fracture during dislocation of the elbow. The trochlear notch forms an arc of approximately 190°. While most of this articular surface is covered with cartilage, there is an area in the centre where either the cartilage is thin or absent. This is a normal finding and should not be interpreted as osteochondral damage. It is, however, a safe area through which an olecranon osteotomy can be performed. The shape of this notch is elliptical, with a longitudinal ridge articulating with a deeper portion of the trochlea. This affords bony stability.

image

Figure 2.4 Left ulna, lateral view.

Redrawn with permission of http://www.graysanatomyonline.com, Elsevier Ltd. Chapter II. Osteology. 6a.4 Fig. 212.

The medial and lateral condyles appear collinear with the olecranon when the elbow is in extension and when viewed posteriorly. In flexion, they form a triangle. Intra-articular fractures or dislocations can cause a disruption of the normal anatomical position of these landmarks.

The long axis of the ulna and the humerus determines the overall carrying angle of the elbow. Studies report a valgus angle ranging from 11° to 14° in men and from 13° to 16° in women.2

The lesser sigmoid (semilunar) notch or radial notch is located just distal and radial to the coronoid process. This depression articulates with the side of the radial head. The lateral ulnar collateral ligament inserts onto the tubercle of the supinator crest, from which the supinator muscle also gains origin. The medial aspect of the coronoid process, the sublime tubercle, serves as an insertion site for the medial ulnar collateral ligament.

Radius

The radial head can be palpated 1 cm distal to the lateral epicondyle when rotating the forearm in flexion. The triangle formed by the radial head, the olecranon and lateral epicondyle defines the most accessible portion of the elbow for palpation of joint effusions and performing aspirations or intra-articular injections. This is often referred to as the ‘soft spot’.

The radial head is shaped like a concave disc and is attached to the radial shaft by the radial neck (Figs 2.3 and 2.5). The proximal end articulates with the capitellum and the circumferential surface articulates with the lesser sigmoid notch. Therefore not only is the proximal end covered with articular cartilage but also a 280° arc about the circumference. The 80° arc that remains uncovered can be used to place screws in case of displaced radial head fractures. The angle between radial head and shaft is 13°. The radial head is not a perfect circle and is variably offset from the axis of the neck. This has important implications for reconstruction of the radial head.3,4 On the anteromedial side just distal of the radial neck lies the bicipital (also called radial) tuberosity: a bony tuberance into which is inserted the biceps tendon.5,6

Articulations

The elbow is one of the most congruent joints in the body. As mentioned before, there are three articulations in the elbow: ulnohumeral, radiohumeral (or radiocapitellar) and proximal radio-ulnar joint. The elbow has been called the trochleogingylomoid joint: the ulnohumeral is a hinge (ginglymus) joint that allows flexion and extension and the radiohumeral (or radiocapitellar) and proximal radio-ulnar joint are trochoid joints, allowing axial rotation or pivoting.1 The radial head and the ulna articulate during pronation and supination of the forearm at the proximal radio-ulnar joint.

Clinical Pearl 2.1

Capsuloligamentous anatomy

Medial collateral and the lateral collateral ligament complexes

On the lateral and medial sides of the elbow the capsule thickens to form ligaments: the medial and lateral collateral ligaments.

The medial collateral ligament consists of an anterior and a posterior bundle. In between lies a transverse ligament (Fig. 2.6). The anterior bundle is the primary restraint to valgus stress. It originates on the central two-thirds of the antero-inferior aspect of the medial humeral epicondyle. The anterior bundle inserts at the base of the coronoid on average 18 mm posterior from the tip. The width of its origin averages about 10 mm and involves 67% of the epicondyle In the coronal plane.8,9 Knowledge of the insertion sites is clinically important: for example, when medial epicondylectomy is being performed, only 20% of the epicondyle can be removed without violating the origin of the anterior medial collateral ligament. Also, its deep origin allows elevation of the flexor tendons off the medial epicondyle without detaching the ligament. The posterior location of the insertion site prevents damage to the ligament from fractures of the tip of the coronoid, although it does become detached with fractures at the base of the coronoid. The mean length of the anterior bundle is about 27 mm, with a width of 4–5 mm. Some studies have also shown that the anterior medial collateral ligament can be subdivided into anterior and posterior bands. These bands demonstrate a different tension in various positions of the elbow, due to a ‘cam effect’.10 Finally, some authors claim a third central portion which remains isometric throughout elbow movement. The latter can be used as a guide for ligament reconstruction.11 This deep bundle runs from 5 mm anterior to the distal tip of the medial epicondyle to the most prominent part of the sublime tubercle on the ulna. The posterior bundle of the medial collateral ligament inserts slightly posterior to the anterior medial collateral ligament and fans out along the base of the greater sigmoid notch. It has an average width of 8 mm and a thickness of 4–8 mm. The function of this ligament is to restrain valgus stress, especially during flexion.1,10,12

image

Figure 2.6 Medial collateral ligament.

Reprinted with permission of Lockard L, J Hand Ther.20

The transverse ligament, which originates and inserts on the ulna, covers a depression along the medial ulna below the greater sigmoid notch. It spans the insertion of the anterior and posterior bundles, but appears to have no role in elbow stability.

Microscopic evaluation has revealed distinct collagen bundles within the capsular layers. The anterior bundle has an additional ligament complex superficial to the capsular layer confluent with the flexor muscle mass.13

Four distinct bundles comprise the lateral collateral ligament complex: the lateral ulnar collateral ligament, the radial collateral ligament, the annular ligament and the accessory lateral collateral ligament (Fig. 2.7). It is a key stabilizer for varus stress and posterolateral stability.

image

Figure 2.7 Lateral collateral ligament complex.

Reprinted with permission of Lockard L, J Hand Ther.20

The most important part of the lateral collateral ligament complex is the lateral ulnar collateral ligament, which is responsible for the prevention of posterolateral elbow instability. The origin is situated on the centre of the lateral epicondyle of the humerus, blends with the annular ligament and inserts onto the tubercle of the supinator crest. During surgery to the radial head or surgery for lateral epicondylitis, it is obviously important to leave the lateral ulnar collateral ligament intact, to prevent subsequent instability of the elbow.

The radial collateral ligament, which originates at the centre of the lateral epicondyle, extends to the annular ligament. This ligament provides an additional origin for the supinator muscle. The radial collateral ligament has an average length of 20 mm and a width of 8 mm.

The ulnar insertion of this ligament complex varies, being described as either a broad insertion blending the lateral and annular ligaments, or as being bilobed with more distinct insertions.14

The annular ligament inserts on the anterior and posterior margins of the radial notch and encircles the radial head, binding it to the lesser sigmoid notch of the ulna to prevent inferior or lateral subluxation. The collective function of the annular ligament and the radial collateral ligament is to maintain stability during varus stress and posterolateral directed forces on the elbow. The annular ligament also stabilizes the proximal radio-ulnar joint together with the quadrate ligament.

Additional structures

The quadrate ligament is a thin fibrous covering of the capsule connecting the inferior margin of the annular ligament to the ulna.

The accessory lateral collateral ligament helps to stabilize the annular ligament by connecting its inferior fibres to the supinator crest.

An additional ligament is the oblique cord: a fascial thickening of the deep head of the supinator that runs from the lateral ulnar tubercle to the radius just below the radial tuberosity. It is of limited functional importance.

As with the medial collateral ligament, various components of the lateral collateral ligament play a different role in maintaining stability during varus stress. The anterior and posterior parts of the radial collateral ligament are taut in extension and flexion respectively, while the middle part is taut in mid range. The lateral ulnar collateral ligament is taut in extreme elbow flexion and is tightened further with additional varus stress.

The interosseous membrane between the ulna and the radius prevents divergence of the radius or ulna and regulates the forces acting on these two bones.10 Together with the distal radio-ulnar joint it is a key component in forearm rotation and stability.

Other clinically important structures around the elbow are the subcutaneous bursa over the olecranon and the subtendinous bursa of the triceps brachii muscle. These structures can become inflamed or/and infected, resulting in bursitis. A bicipitoradial or interosseous bursa is located at the insertion of the distal biceps tendon on the radial tuberosity. When this bursa is inflamed or infected it is known as cubital bursitis.

Muscular anatomy

The extensor apparatus contains both the triceps and anconeus muscles. Proximally, the triceps possesses three origins: the lateral, long and medial heads. The three heads meet and end as one tendon distally (Fig. 2.8). The lateral head has three origins, including the humerus between the teres minor insertion and the proximal part of the radial groove, the lateral border of the humerus, and the lateral intermuscular septum. The long head originates from the infraglenoid tuberosity of the scapula. The medial head originates from the posterior humerus distal to the spiral groove. Distally the extensor mechanism of the triceps consists of two components: the principal part and the expansion part. The principal part is the larger tendon, which inserts onto the olecranon. This insertion consists of both tendon and muscle. The expansion inserts onto four different sites: the posterior crest of the ulna medially, the fascia of the extensor carpi ulnaris origin laterally, the antebrachial fascia distally, and the anconeus insertion deeply. The principal part seems to be able to compensate for the expansion part in case of injury. However, the reverse does not appear possible.

image

Figure 2.8 Posterolateral view of the musculus triceps brachii.

Redrawn with permission of http://www.graysanatomyonline.com, Elsevier Ltd. Chapter IV. Myology. 7c Fig. 412.

Madsen et al discovered that the tendon of the triceps consists of two components: a superficial part which originates from the lateral and long head of the triceps, and a deep part which originates from the medial head. Both merge prior to insertion.15 The deep tendon seems to be responsible for most of the strength generated when the arm is extended between maximum flexion and 90°, whereas both generate the maximum amount of force near terminal extension.

The anconeus muscle is a small triangular muscle that arises from the lateral epicondyle of the humerus and inserts onto the lateral side of the olecranon as well as the posterior surface of the proximal ulna (Fig. 2.9). The exact function of the anconeus muscle is still a point of discussion: some believe it functions as an abductor of the ulna in pronation,16 while others claim that it has a joint-stabilizing effect. The anconeus muscle receives its blood supply from the recurrent posterior interosseous artery, the medial collateral artery and the posterior branch of the radial collateral artery. This muscle is often used as a transposition flap to cover defects around the elbow, the size of the defect ranging from 6 to 25.5 cm2.17

The flexor apparatus contains the biceps brachii, the brachialis and the brachioradialis muscles.

The biceps brachii consists of two parts: the short and long heads (Fig. 2.10). The short head originates from the coracoid process and the long head from the superior aspect of the glenoid. Initially both heads were thought to fuse into a single tendon and insert onto the ulnar aspect of the bicipital tuberosity of the radius. However, further recent research indicates that the distal biceps tendon can be divided into an anterior layer (linked to the short head) and a posterior layer (linked to the long head). An important landmark is the bicipital aponeurosis, which arises from the distal short head of the biceps tendon. Some cadaver studies, however, show that the two heads are not always separated at the distal tendon, and that it would be more accurate to describe the biceps as two fully independent muscles and tendons with a variety of connections between the two structures. Finally, the biceps rotates 90° externally from origin to insertion. This rotation is of relevance to the surgeon during the surgical repair of a ruptured biceps tendon.

The brachialis muscle is also divided into two heads: a superficial head and a deep head (Fig. 2.10). The superficial head, which is larger than the deep head, originates from the anterolateral aspect of the middle third of the humerus and the lateral intermuscular septum, distal to the deltoid tuberosity. The superficial head inserts as a circular tendon on the ulnar tuberosity. The deep head originates from the distal third of the anterior aspect of the humerus and the medial intermuscular septum. The deep muscle head ends as a sagittally oriented aponeurosis that inserts on the ulna. This aponeurosis covers the space between the ulnar tuberosity and the coronoid process.

Because of the position of the deep and superficial heads, the assumption is that the deep head provides a greater flexion moment when the elbow is fully extended. Conversely, in flexion, the superficial head provides the greatest moment.

There are also a number of fibres running from the deeper aspect of the deep head to the anterior elbow joint capsule; these prevent capsular impingement during elbow flexion as the brachialis muscle contracts.

The superficial and deep heads are easy to separate proximally from the lateral side. This interval can easily be identified as the radial nerve lies in the apex between the two heads. This is relevant during surgery as via an anterolateral approach heads can be retracted, whereas via a direct anterior approach the superficial head has to be split.

The position of the superficial head makes it suitable for transfer to the radial tuberosity if the biceps cannot be reconstructed after injury. In addition, it can also be used for reconstruction of the medial collateral ligament or annular ligament.

The brachioradialis muscle originates from the proximal part of the lateral supracondylar ridge of the humerus and the adjacent intermuscular septum (Fig. 2.9). Distally, the conversion from muscle to tendon is situated between the proximal and middle thirds of the forearm. The brachioradialis muscle inserts at the base of the first dorsal compartment, beginning 17 mm from the radial styloid tip and extending 15 mm proximally. This compartment is surrounded by bony protuberances from which the fascial septa on the radial aspect of the distal part of the radius arise, resulting in a tunnel-like structure. The whole length of the tendon attaches firmly to the underlying antebrachial fascia, thus limiting possible excursion.

The superficial flexors of the forearm include all those muscles that originate at the medial epicondyle by a common tendon (Fig. 2.11). The pronator teres, flexor carpi radialis, palmaris longus, flexor carpi ulnaris and flexor digitorum superficialis muscles all belong to this group (superficial to deep).

image

Figure 2.11 Flexors of the forearm, superficial muscles.

Redrawn with permission of http://www.graysanatomyonline.com, Elsevier Ltd. Chapter IV. Myology. 7e Fig. 414.

The pronator teres muscle has two attachments around the elbow: the humeral head and the ulnar head. The humeral head is larger and is situated more superficially. It has three origins: the common flexor origin, just proximal to the medial epicondyle, the intermuscular septum and the antebrachial fascia. The ulnar head originates from the medial side of the coronoid process of the ulna. Where the two heads meet, they form a narrow angle, under which the median nerve enters the forearm. This angle also separates the median nerve from the ulnar artery. From this point the muscle runs obliquely across the forearm and the tendon inserts along the lateral surface of the radial shaft.

The flexor carpi radialis muscle also arises from the medial epicondyle. It is situated medially to the pronator teres. It has three origins around the elbow: the common flexor origin, the antebrachial fascia and the adjacent intermuscular septum. Distally it inserts on the palmar surface of the base of the second (sometimes also third) metacarpal. In the lower part of the forearm, the radial artery lies between the distal tendon of the flexor carpi radialis muscle and the brachioradialis tendon.

The palmaris longus originates from the medial epicondyle, medially to the flexor carpi radialis. It also springs from the adjacent intermuscular septa and the deep fascia. This structure has a long tendon, ending in a flat sheet, connecting the muscle with the palm. Distally, the tendon of the palmaris longus attaches to the flexor retinaculum. Here the tendon lies medial to the flexor carpi radialis and superficial to median nerve. The palmaris longus tendon is important in that it can be used as a graft for collateral ligament reconstruction. It is of note, however, that this tendon is absent in approximately 15% of people.18,19

The most medially located muscle of the superficial forearm group is the flexor carpi ulnaris muscle. It has two heads: the humeral and the ulnar. The humeral small head arises from the common tendon. The large ulnar origin is formed from the intermuscular septum (between the flexor carpi ulnaris and flexor digitorum superficialis) and the aponeurosis (the same as the extensor carpi ulnaris and flexor digitorum profundus). The aponeurosis is spread between the medial margin of the olecranon and the posterior border of the ulna. The two heads are connected by a tendinous arch. Both the ulnar nerve and the posterior ulnar recurrent artery pass underneath this arch. The tendon inserts into the pisiform bone in the hand.

The final muscle of the superficial forearm muscles group is the flexor digitorum superficialis (or flexor digitorum sublimis). This muscle is situated deep to the preceding muscles, and is the largest muscle of the group. Its origin is again formed by two heads: the humero-ulnar head and the radial head. The humero-ulnar head arises from the common tendon, the anterior band of the ulnar collateral ligament, the adjacent intermuscular septa and the medial side of the coronoid process (proximal to the origin of the pronator teres). The radial head arises from the anterior radial border, between the radial tuberosity and the insertion of pronator teres (Fig. 2.11).

The superficial extensor group of the forearm contains the following structures: the extensor carpi radialis longus and brevis, the extensor digitorum communis, the extensor digiti minimi and the extensor carpi ulnaris (Fig. 2.9). All these muscles, except the carpi radialis longus, originate from the lateral humeral condyle through a common extensor tendon.

The extensor carpi radialis longus originates from the distal third of the lateral supracondylar humeral ridge and the lateral intermuscular septum. Some fibres also arise from the common extensor tendon. The muscle belly is partially overlapped by the brachioradialis muscle. The tendon then runs under the abductor pollicis longus and extensor pollicis brevis and finally passes under the extensor retinaculum, to insert on the radial side of the dorsal surface of the base of the second metacarpal.

The extensor carpi radialis brevis arises from the lateral epicondyle via the common extensor origin, the radial collateral ligament of the elbow joint, an aponeurosis which covers its surface, and the adjacent intermuscular septa. The carpi radialis brevis, as well as being shorter, lies under the carpi radialis longus. The tendon of the extensor carpi radialis brevis also runs under the abductor pollicis longus and extensor pollicis brevis before finally passing under the extensor retinaculum, to insert on the dorsal surface of the base of the third metacarpal.

The extensor digitorum communis again springs from the common extensor tendon, the adjacent intermuscular septa and the antebrachial fascia. The muscle is divided into four tendons. Along with the tendon of the extensor indices, they run through a separate tunnel under the extensor retinaculum in a common synovial sheath. Eventually each tendon runs to an individual finger.

The extensor digiti minimi originates from adjacent intermuscular septa and through a thin slip via the common extensor tendon. The distal tendon runs through a separate compartment in the extensor retinaculum, and then divides into two before inserting into the little finger together with the tendon of the extensor digitorum.

The last structure belonging to the superficial extensor group is the extensor carpi ulnaris. This extensor muscle arises via the common extensor tendon, the posterior border of the ulna (through an aponeurosis, shared with the flexor carpi ulnaris and flexor digitorum profundus muscles) and overlying fascia (Fig. 2.11).

Summary Box 2.4

The muscles around the elbow can be divided into the extensor apparatus, the flexor apparatus and the extensors/flexors of the wrist. The extensor apparatus contains the triceps and anconeus muscles. Distally the extensor mechanism of the triceps consists of two components: the principal part and the expansion. The insertion onto the olecranon consists of both tendon and muscle. The anconeus muscle is a small triangular muscle that inserts on the lateral side of the olecranon and on the posterior surface of the proximal ulna.

The flexor apparatus contains the biceps brachii and the brachialis. Distally, the biceps brachii inserts onto the ulnar aspect of the bicipital tuberosity of the radius. Some say it would be more accurate to look at the biceps as two fully independent muscles and tendons with a variety of interconnections between the distal muscle heads and tendons. The biceps rotates 90° externally from origin to insertion. The superficial head of the brachialis inserts as a circular tendon on the ulnar tuberosity, whereas the deep muscle ends as a sagittal-oriented aponeurosis that inserts onto the ulna. There are a number of fibres running from the undersurface of the deep head to the anterior elbow joint capsule. These prevent capsular impingement during elbow flexion as the brachialis muscle contracts.

The superficial flexors of the forearm include all those muscles that originate from the medial epicondyle by a common tendon. The pronator teres, flexor carpi radialis, palmaris longus, flexor carpi ulnaris and flexor digitorum superficialis all belong to this group.

The superficial extensor group of the forearm contains the following structures: the extensor carpi radialis longus and brevis, the extensor digitorum communis, the extensor digiti minimi and the extensor carpi ulnaris. All these muscles, except the carpi radialis longus, originate from the lateral humeral condyle through a common extensor tendon.

Neurovascular structures

Neural structures

The most important nerves crossing the elbow are the median, the radial and the ulnar.

The median nerve is derived from the C6–T1 nerve roots, and is formed distal to the axilla. The median nerve runs down parallel and anterior to the medial intermuscular septum, lateral to the brachial artery and medial to the biceps brachii muscle. At the middle of the brachium, the nerve crosses over to run medial to the brachial artery. The nerve and artery then pass under the bicipital aponeurosis on reaching the elbow. At this point both structures lie medial to the biceps brachii tendon and anterior to the brachialis muscle. Thereafter, the nerve passes beneath the humeral head of the pronator teres, between the humero-ulnar and radial portions of the flexor digitorum superficialis and finally under the proximal arch of the flexor digitorum superficialis muscle belly. The arch formed by the ulnar and humeral heads of the pronator teres separates the nerve from the ulnar artery (a branch of the brachial artery).

Further down the forearm, the median nerve runs between the flexor digitorum superficialis and flexor digitorum profundus. The anterior interosseous nerve, which is the last major branch of the median nerve, branches off about 4 cm distally to the elbow.

The radial nerve is derived from the C5–C8 nerve roots. It runs through the triangular space (formed by the teres major, the long head of triceps and the humerus) to the dorsal aspect of the humerus. There it winds around the humerus in the spiral groove, to appear on the lateral aspect of the humerus between the brachioradialis and the brachialis muscles. It is critical therefore during surgery not to place any hardware either directly over the spiral groove or on the lateral aspect of the humerus approximately between one and two times the length of the epicondylar interval measured from the lateral epicondyle in order to avoid compression of the radial nerve.

Further down it is covered by the extensor carpi radialis longus and brevis. At this point the nerve is situated above the elbow joint capsule and the capitellum of the humerus. The space between the joint capsule and the proximal supinator is called the ‘radial tunnel’. The radial nerve ends as the superficial sensory and the posterior interosseous branches. The superficial sensory branch of the radial nerve comes off just before this ‘radial tunnel’, running distally beneath the brachioradialis. The posterior interosseous nerve is located anterior to the radiocapitellar joint capsule.

The place where the radial nerve pierces the lateral muscular septum is called the lower margin of the radial nerve. Here it runs from the lateral to the anterior aspect of the humerus. The lower margin is located at least 60 mm from the lateral epicondyle. This means that there is a safe zone for placing distal locking screws or fixator pins from lateral to medial within 60 mm of the lateral condyle.18

The ulnar nerve is formed by the nerve roots C8–T1. It initially travels down the arm medial to the brachial artery. At the middle of the humerus, it pierces the medial intermuscular septum to enter the posterior aspect of the arm. The nerve then runs between the medial intermuscular septum (anterior to the ulnar nerve) and the medial head of the triceps (posterior), to enter the sulcus of the ulnar nerve, which is situated posterior to the medial epicondyle of the humerus. Before the nerve enters the forearm it runs through the cubital tunnel, between the medial epicondyle and the olecranon (the walls of the tunnel). The cubital tunnel retinaculum or Osborne’s band is the fibrous aponeurosis that links the medial epicondyle and the olecranon to form the roof of the cubital tunnel. This structure also connects the humeral and ulnar heads of the flexor carpi ulnaris muscle. The floor of the cubital tunnel is formed by the elbow joint capsule and the medial collateral ligaments. The cubital tunnel is approximately 2–4 cm in length. As the ulnar nerve passes through this tunnel, it gives branches to the elbow joint. Distal to the cubital tunnel it runs between the humeral and ulnar heads of the flexor carpi ulnaris, innervating both heads. It continues deep to the aponeurosis, which connects the two heads of the flexor carpi ulnaris and runs distally between the flexor carpi ulnaris and the belly of the flexor digitorum profundus. Approximately 5 cm distal to the medial epicondyle, the ulnar nerve supplies a branch to the ulnar portion of the flexor digitorum profundus.

The medial cutaneous nerve of the arm arises from C8, T1. It descends medial to the brachial artery and basilic vein. At about midway along the upper arm, it pierces the deep fascia to supply the medial, distal third of the arm before dividing into posterior and anterior branches. The medial cutaneous nerve supplies the skin over the anterior surface of the upper arm and the anteromedial surface of the forearm.

The lateral cutaneous nerve of the forearm is a continuation of the musculocutaneous nerve. It passes deep to the cephalic vein, between the brachial and biceps muscle, and descends along the radial border of the forearm, medial to the brachioradial muscle. The lateral cutaneous nerve of the forearm supplies the anterolateral surface of the forearm. Damage to this nerve should be avoided, especially during an anterior approach to the elbow, as it can result in continuing pain and paraesthesia.

Vascular structures

Arteries

The vascular supply of the elbow is provided by the brachial artery and its branches, the ulnar and radial arteries. The brachial artery originates from the axillary artery. In the upper arm it runs between the ulnar and median nerves. As the artery approaches the elbow it passes into the triangular intermuscular cubital fossa. The brachialis and supinator muscle form the posterior border of this triangle, whereas the lateral border consists of the biceps tendon and the radial nerve. At this point the median nerve no longer runs medial to the brachial artery, as it is separated by the ulnar head of the pronator teres muscle. The ‘roof’ of the cubital fossa is formed by the bicipital aponeurosis, which separates it from the superficial fascia and median cubital vein. Close to the neck of the radius, the brachial artery is divided into its terminal branches: the ulnar and radial arteries.

Proximally the radial artery is covered anteriorly by the belly of the brachioradialis muscle. At this point the pronator teres lies posteriorly and the flexor carpi radialis medially.

Just distal to the bifurcation of the brachial artery, the radial recurrent artery arises from the radial artery. The recurrent artery runs proximally between the superficial and deep branches of the radial nerve to arrive between the brachioradialis muscle (anterior) and the supinator and brachialis muscles (posterior). Finally, it anastomoses with the radial collateral branch of the profunda brachii.

The ulnar artery runs more posteriorly in the antebrachium in relation to the radial artery. Close to the elbow it is covered by the pronator teres, the flexor carpi radialis, the palmaris longus and the flexor digitorum profundus muscles. The ulnar nerve runs anterior to the flexor digitorum profundus and lateral to the flexor carpi ulnaris.

The common interosseous artery is the only branch that runs laterally from the ulnar artery. It is a short structure that divides into the anterior and posterior interosseous arteries.

The anterior interosseous artery descends on the anterior aspect of the interosseous membrane, whereas the posterior interosseous artery descends on the posterior aspect. The posterior interosseous artery branches and forms the interosseous recurrent artery. This last structure ascends between the olecranon and the lateral epicondyle, deep to the anconeus muscle, to anastomose with the middle collateral branch of the profunda brachii.

The first of two branches medial to the ulnar artery is the anterior ulnar recurrent artery. This artery passes anterior to the medial epicondyle, between the brachialis muscle and the pronator teres muscles, to anastomose with the inferior ulnar collateral artery.

The second branch (which is larger than the first branch) is the posterior ulnar recurrent artery; it lies posterior to the medial epicondyle. It ascends primarily between the flexor digitorum profundus and superficialis, between the heads of the flexor carpi ulnaris (at this point along with the ulnar nerve), finally to anastomose with the ulnar collateral and interosseous recurrent arteries.

Lymphatics

The axillary lymph nodes drain the whole upper limb, directly or through peripheral groups. The lymphatic vessels that drain directly to the axillary lymph nodes drain the elbow. These vessels are responsible for the drainage of all the superficial tissues. Additionally, there are two outlying groups close to the elbow. The supratrochlear nodes are situated above the medial epicondyle, medial to the basilic vein and superficial to the deep fascia. The efferent vessels originating from the supratrochlear nodes run together with the basilic vein to communicate with the deep lymph vessels. Sometimes small isolated nodes occur around the radial artery, ulnar artery or in the cubital fossa.

The deep lymph vessels run alongside the main neurovascular structures to terminate in the lateral axillary nodes. They communicate with the superficial vessels at different levels.

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