Applied Surgical Anatomy of the Elbow

Applied Surgical Anatomy

Overview

 

The elbow is the hinge (ginglymus) joint between the lower end of the humerus and the upper end of the radius and ulna. It communicates with the superior radioulnar joint.

The lower end of the humerus articulates in two areas:

1. The lateral capitulum articulates with the radial head. Its shape is reminiscent of a hemisphere.

2. The medial trochlea articulates with the ulna. Its shape resembles a spool of thread. It extends further distally than the capitulum, resulting in a configuration that gives a tilt to the lower end of the humerus and produces the “carrying angle” of the joint. The trochlea is grooved; the groove’s boundaries are marked medially by a prominent, sharp ridge and laterally by a lower, more blunted ridge.

The two articulations are separated by a ridge of bone.

The elbow is supported by strong medial and lateral collateral ligaments. The anterior and posterior ligaments are mainly thickened sections in the capsule, which is exactly what would be expected from a hinge joint. The shape of the bones that comprise the elbow joint and the presence of the strong collateral ligaments make it difficult to explore the joint completely without extensive dissection. Medial and lateral approaches to the joint provide limited access unless they are extended. Complete exposure is obtained most easily through a posterior approach. Four groups of muscles cross the elbow joint:

1. Anteriorly, the flexors of the elbow, which are supplied by the musculocutaneous nerve.

2. Posteriorly, the extensor of the elbow, which is supplied by the radial nerve.

3. Medially, the flexor-pronator group of muscles (the flexors of the wrist and fingers, and the pronators of the forearm), which are supplied by the median and ulnar nerves. They arise from the medial epicondyle of the humerus.

4. Laterally, the extensors of the wrist and fingers, and the supinators of the forearm, which are supplied by the radial and posterior interosseous nerves. They arise from the lateral epicondyle of the humerus.

Between each pair of muscle groups is an intermuscular plane; two are internervous planes and can be explored. A third internervous plane lies

within the lateral group. The internervous planes are as follows:

1. Between the anterior and lateral muscle groups, which are supplied by the musculocutaneous and radial nerves, respectively. The anterolateral approach uses the interval between the brachialis and brachioradialis muscles (see Fig. 3-25).

2. Between the anterior and medial muscle groups, which are supplied by the musculocutaneous and median nerves, respectively. The medial approach uses the interval between the brachialis and pronator teres muscles (see Figs. 3-13 and 3-33).

3. Between two members of the lateral group: The anconeus muscle (which is supplied by the radial nerve) and the extensor carpi ulnaris muscle (which is supplied by the posterior interosseous nerve, a major branch of the radial nerve; see Fig. 3-40). The posterolateral approach to the radial head uses this plane.

The intermuscular plane between the lateral and posterior groups of muscles is not an internervous plane, because both groups are supplied by the radial nerve. The plane is useful, though, because the radial nerve gives off its branches well proximal to the elbow. This pseudointernervous plane, which is used in the lateral approach, falls in the interval between the brachioradialis and triceps muscles (see Fig. 2-31A).

The medial and lateral groups of muscles converge in the forearm, forming a triangular fossa known as the cubital fossa, which is bordered by the pronator teres medially and the brachioradialis laterally. The superior border of the triangle consists of an imaginary line joining the medial and lateral epicondyle of the humerus.

 

Neurovascular Structures

Nerves

The median nerve crosses the front of the joint on its medial side and is covered by the bicipital aponeurosis (lacertus fibrosus) in the cubital fossa. It disappears between the two heads of the pronator teres muscle as it leaves the fossa and runs down the forearm, adhering to the deep surface of the flexor digitorum superficialis muscle (see Fig. 4-12).

The radial nerve crosses the front of the elbow joint in the interval between the brachialis and brachioradialis muscles. It divides in the cubital fossa at the radiohumeral joint line into the posterior interosseous nerve (which enters the substance of the supinator muscle) and the superficial

radial nerve (which descends the lateral side of the forearm under cover of the brachioradialis muscle; see Fig. 3-28).

The ulnar nerve crosses the joint in the groove on the back of the medial epicondyle, where it is easy to palpate. The nerve enters the anterior compartment of the forearm by passing between the two heads of the flexor carpi ulnaris muscle, which it supplies and where it may be entrapped. It then runs down the forearm on the anterior surface of the flexor digitorum profundus (see Figs. 3-49). In the proximal third of the forearm, it supplies the ring and little fingers.

Vessels

The brachial artery enters the cubital fossa, running on the lateral side of the median nerve and lying on the brachialis muscle. The median nerve passes under the bicipital aponeurosis, which separates it from the median basilic vein, a frequent site of venous puncture (see Fig. 3-31). In the days when bleeding was a recognized form of treatment and venesection was done with lancets rather than with needles, this site was a frequent one used by barber surgeons. The reason this site was preferred is because the bicipital aponeurosis protects the vital structures of the artery and nerve, which provided these early practitioners with a margin of safety, because their patients often moved on insertion of the lancet. Halfway down the cubital fossa, the artery divides into two terminal branches: The radial and ulnar arteries. Similar to the median nerve, the artery may be damaged in supracondylar fractures of the humerus (see Fig. 3-35).

The radial artery passes medial to the biceps tendon before turning anteriorly, lying on the supinator muscle and the insertion of the pronator teres muscle. In the upper forearm, it lies under the brachioradialis muscle (see Fig. 4-11).

The ulnar artery usually disappears from the cubital fossa by passing deep to the deep head of the pronator teres, the muscle that separates it from the median nerve (see Fig. 4-13).

 

Applied Surgical Anatomy of the Medial Approaches

 

Five flexor muscles of the forearm fan out from the common flexor origin on the medial epicondyle of the humerus:

1. The pronator teres (humeral head)

2. The flexor carpi radialis

3. The flexor digitorum superficialis (humeral head)

    

    

   Figure 3-44 Medial view of the elbow. Note the sensory nerves and veins on the medial side of the elbow joint.

    

4. The palmaris longus

5. The flexor carpi ulnaris (humeral head) (Fig. 3-45)

The first four muscles are supplied by the median nerve; the flexor carpi ulnaris is supplied by the ulnar nerve. The pronator teres, the most proximal muscle, forms the medial border of the cubital fossa.

All five muscles are retracted distally after osteotomy of the medial epicondyle. They can be retracted only a short distance because the median nerve, passing through the pronator teres muscle, “anchors” the group and prevents distal retraction (Figs. 3-44 to 3-48).

 

Applied Surgical Anatomy of the Anterolateral Approach to the Elbow

 

Two groups of muscles arise from the lateral epicondyle and the supracondylar ridge of the humerus (see Applied Surgical Anatomy of the Posterior Approach to the Radius in Chapter 4):

 

 

Figure 3-45 The five muscles of the forearm have a common flexor origin on the medial epicondyle. All five are supplied by the median nerve. The ulnar nerve passes between the two heads of the flexor carpi ulnaris. The median nerve runs beneath the bicipital aponeurosis.

 

 

 

Figure 3-46 The flexor-pronator group has been resected, revealing the course of the ulnar nerve as it runs around the medial epicondyle, passing distally before entering the plane between the flexor carpi ulnaris and the flexor digitorum profundus.

 

 

Figure 3-47 The flexor muscles have been resected further. The medial epicondyle has been subjected to osteotomy. Distally, the ulnar nerve crosses the forearm between the flexor carpi ulnaris and the profundus. The median nerve enters the forearm between the two heads of the pronator teres, lying on the tendon of the brachialis.

 

 

 

Figure 3-48 The joint capsule has been opened. The brachialis is elevated from the capsule.

 

1. The mobile wad of muscles, consisting of the brachioradialis, the extensor carpi radialis longus, and the extensor carpi radialis brevis

2. Four muscles arising from the common extensor origin: The extensor

digitorum communis, the extensor digiti minimi, the extensor carpi ulnaris, and the anconeus

The anconeus is purely a muscle of the elbow; Its function is unclear. Its more distal fibers run almost vertically and act as a weak extensor of the elbow, whereas its proximal fibers are almost horizontal and abduct and rotate the ulna. This unlikely movement occurs to a slight degree at the elbow. Electromyographic studies suggest that the muscle is most active during extension,19,20 but it probably functions more as a stabilizer while other muscles act on the elbow as prime movers, functioning in much the same way as does the rotator cuff in the shoulder.21

Its major surgical importance lies in the fact that it forms one boundary of the internervous plane that is used in the posterolateral approach to the radial head.

 

Applied Surgical Anatomy of the Anterior Approach to the Cubital Fossa

 

Two flexors, the brachialis and biceps brachii muscles, cross the anterior aspect of the elbow joint. Both are supplied by the musculocutaneous nerve, which runs between the biceps and the brachialis in the upper arm. In front of the elbow, they diverge; the biceps runs laterally to the bicipital tuberosity of the radius, and the brachialis runs medially to the coronoid process of the ulna.

In front of the elbow, the biceps brachii develops a flat tendon, which also overlies the brachialis. The tendon rotates so that its anterior surface faces laterally as it passes between the two bones of the forearm before inserting into the back of the radius at the bicipital tuberosity. A bursa separates the tendon from the anterior part of the tuberosity.

As the biceps tendon crosses the front of the elbow, it gives off fibrous tissue from its medial side. This bicipital aponeurosis, or lacertus fibrosus, sweeps across the forearm by way of the deep fascia to insert into the subcutaneous border of the upper end of the ulna.

The bicipital aponeurosis forms part of the roof of the cubital fossa. It separates superficial nerves and vessels from deep ones. Lying superficial are the median cephalic vein, the median basilic vein, and the medial cutaneous nerve of the forearm. Lying deep are the median nerve and the brachial artery.

The relationship of the median nerve, brachial artery, and brachial vein can be remembered easily through the mnemonic “VAN” (vein, artery, nerve), which labels the structures from the lateral to the medial aspect.

They all pass medial to the biceps tendon under the lacertus fibrosus (see Fig. 3-36).

 

Applied Surgical Anatomy of the Posterior Approaches to the Elbow

 

See Figures 3-49 to 3-52.

 

 

 

Figure 3-49 Superficial view of the posterior aspect of the elbow. The triangular aponeurosis of the triceps runs down to its triangular insertion into the ulna. The ulnar nerve lies in its groove on the posterior aspect of the elbow. The posterior antebrachial cutaneous nerve crosses the intermuscular septum on the posterior aspect of the elbow. Anconeus. Origin. Lateral epicondyle of humerus and posterior joint capsule of elbow. Insertion. Lateral side of olecranon and posterior surface of ulna. Action. Extensor of elbow. Nerve supply. Radial nerve.

 

 

Figure 3-50 The distal part of the triceps, the origins of the flexors and flexor carpi ulnaris, and the extensor tendons have been resected. The ulnar nerve enters the plane between the two heads of the flexor carpi ulnaris. On the radial side, the radial nerve lies anterior to the intermuscular septum, between the brachioradialis and brachialis muscles.

 

 

 

Figure 3-51 The insertion of the anconeus, the origin of the extensor carpi ulnaris, and the common extensor origin are revealed. The radial nerve divides into its

main continuation, the posterior interosseous nerve, as it enters the supinator muscle through the arcade of Frohse. The superficial branch (sensory branch) of the radial nerve enters the undersurface of the brachioradialis. The ulnar nerve gives off its branches to the flexor carpi ulnaris immediately after it passes around the groove between the olecranon and the medial epicondyle.

 

 

 

Figure 3-52 The supinator muscle has been resected, revealing the distal course of the posterior interosseous nerve through its distal portion. The annular portion of the radiohumeral ligament is defined clearly.