Elbow joint - part II

PART I

Blood and nerve supply

The arterial blood supply to the joint is derived from an extensive anastomosis around the elbow involving the brachial artery and its terminal branches. Descending from above are the superior and inferior ulnar collateral branches of the brachial artery, and the radial and middle collateral branches of the profunda brachii artery. These vessels anastomose on the surface of the joint capsule with one another, and with the anterior and posterior recurrent branches of the ulnar artery, the radial recurrent branch of the radial artery and the interosseus recurrent branch of the common interosseus artery.

Venous drainage, by vessels accompanying the above arteries, is into the radial, ulnar and brachial veins. Lymphatic drainage of the elbow joint is predominantly to the deep cubital nodes at the bifurcation of the brachial artery, the efferents of which pass to the lateral group of nodes in the axilla. Some of the lymphatics from the joint may pass to small nodules situated along the interosseus, ulnar, radial or brachial arteries and thence to the lateral axillary group.

The nerve supply to the joint is by twigs derived anteriorly from the musculocutaneous, median and radial nerves, and posteriorly from the ulnar nerve and radial nerve by its branch to anconeus. The root value of these nerves is C5, 6, 7 and 8.

Palpation

Palpation of the joint line anteriorly is not possible because of the muscles crossing the joint and its deepness within the cubital fossa. Nevertheless, it can be approximated by drawing a line joining the points 1cm below the lateral epicondyle and 2cm below the medial epicondyle. Posteriorly the gap between the head of the radius and the capitulum can be palpated in the large dimple present at the back of the extended elbow.

Relations

Posteriorly the olecranon is subcutaneous and can be readily palpated. Either side of the olecranon the medial and lateral epicondyles form easily recognizable bony land marks. Anteriorly lies brachialis forming the majority of the floor of the cubital fossa, a hollow in front of the elbow through which pass many of the vessels and nerves entering or leaving the forearm.

The cubital fossa is a triangular space bounded above by an imaginary line between the medial and lateral epicondyles, and at the sides by the converging medial borders of brachioradialis laterally and pronator teres medially(a). The floor of this region is formed mainly by brachialis with supinator inferolaterally(a). It is roofed over by the deep fascia of the forearm, reinforced medially by the bicipital aponeurosis passing from the tendon of biceps downwards and medially to the deep fascia of the forearm(b). The deep fascia separates the superficial veins and nerves from the deeper more important structures(b).

This region is of considerable importance because the large superficial veins are frequently used for venepuncture, while the deeper brachial artery is used for determining blood pressure. The main superficial veins are the cephalic laterally, the basilica medially and the median cubital passing obliquely upwards and medially between them(b). It is not unusual for the median cubital vein to lie towards the lateral side of the fossa, or to be joined by the median vein of the forearm. Occasionally, the median cubital vein is absent and the median vein of the forearm divides into lateral and medial branches to join with the cephalic and basilic veins respectively. Lateral to the cephalic vein runs the lateral cutaneous nerve of the forearm, the terminal branch of the musculocutaneous nerve. Crossing the median cubital vein and running with the basilica vein and its tributaries are branches of the medial cutaneous nerve of the forearm(b).

Lying within the cubital fossa deep to the deep fascia are several structures passing into the forearm. The most medial of these is the median nerve as it passes downwards through the fossa to emerge between the two heads of pronator teres and thus enter the forearm(a). While in the fossa it gives off a branch to pronator teres, and the anterior interosseus branch as it passes through pronator teres. Lateral to the median nerve is the brachial artery, which bifurcates into the ulnar and radial arteries at the neck of the radius in the lower part of the fossa(a). The ulnar artery passes inferomedially deep to pronator teres, giving off recurrent branches to the elbow joint and the common interosseus artery. The radial artery passes inferolaterally on the tendon of biceps brachii deep to brachioradialis, giving off its recurrent branch to the elbow joint. Running through the central region of the fossa, lateral to both the brachial artery and the median nerve is the tendon of biceps brachii towards its insertion on the radial tuberosity(a). As it passes through the fossa the tendon twists on itself so that its anterior surface faces laterally. The most lateral structure passing through the fossa is the radial nerve. In the upper part of the fossa it lies submerged between brachialis and brachioradialis supplying both muscles, and then divides into its terminal branches, the superficial radial and posterior interosseous(deep radial) nerves. The superficial branch continues downwards into the forearm under cover of brachioradialis. The posterior interosseus nerve passes backwards around the lateral side of the radius to enter the forearm between the two heads of supinator.

The ulnar nerve, passing behind the medial epicondyle of the humerus on the intermediate part of the ulnar collateral ligament, lies posteromedial to the elbow joint. It therefore does not pass through the cubital fossa.

Stability

Stability of the elbow joint is by virtue of the shape of the articular surfaces of the trochlea and capitulum of the humerus, and the trochlear notch of the ulna and head of the radius. Without strong collateral ligaments and the muscular cuff of triceps, biceps, brachialis, brachioradialis, and the common tendons of the superficial flexors and extensors arising from the medial and lateral epicondyles of the humerus, the elbow joint cannot be considered as an inherently stable joint. The bony surfaces are in closest contact when the forearm is flexed to 90° in a position of mid pronation – supination. This, therefore, is the position naturally assumed when fine manipulation of the hand and fingers is required, as for example when writing.

In spite of ligaments and muscles crossing the joint, dislocations of the elbow can and do occur. In the child, because the head of the radius is small relative to the annular ligament, it is commonly dislocated by traction forces applied to the forearm and hand. In older people, a fall on the hand with the forearm extended may tear the annular ligament with a consequent anterior displacement of the head of the radius(a). The head of the radius may also be dislocated by extreme pronation, by tearing the annular ligament. In either case it can be palpated in the cubital fossa.

The majority of elbow dislocations involve a backward movement of the ulna, through the relatively weak posterior capsule, and is often associated with a fracture of the coronoid process(b). Both radius and ulna may be displaced together due to their connections at the superior radioulnar joint. This backward at the superior radioulnar joint. This backward displacement can lead to pressure on the brachial artery which may go into spasm and reduce and blood supply to the forearm and hand. Pressure on the brachial artery can also arise in supracondylar fractures as the lower fragment moves forwards. Either of these events can also lead to injury of the median nerve with a consequent loss of pronation and reduced use of the hand. Both dislocations and supracondylar fractures result in considerable swelling in the region of the elbow. The alignment of the epicondyles of the humerus and the olecranon can be used to determine the nature of the trauma in an individual with a swollen elbow. The alignment remains unchanged in supracondylar fractures(c), while in dislocations it is changed(d). When an apparently dislocated joint cannot be reduced, fracture of the olecranon must be considered, particularly if the joint is extremely unstable.

A forceful abduction applied to the forearm may be sufficient to rupture that ulnar collateral ligament, or more commonly result in avulsion of the medial epicondyle. The ulnar nerve is especially liable to damage at the time of the injury. If the fracture does not unite or the ligament heal, the forearm tends to become more and more abducted with a consequent stretching of the ulnar nerve, leading to sensory disturbances and muscle weakness or paralysis.