The cubital fossa is the triangular intermuscu- lar depression at the front of the elbow [Fig. 7.3].
The base of the fossa is an imaginary line drawn between the two epicondyles of the humerus. The medial border is the pronator teres muscle. The lateral border is the brachioradialis muscle, up to a point where it overlaps the pronator teres. The floor is formed by the brachialis and supinator.
The median nerve, brachial artery, and tendon of the biceps enter the fossa and are important contents. In the cubital fossa, the brachial artery divides into the radial and ulnar arteries. The radial Fig. 7.7 Diagram showing the brachial artery and the anastomo- sis around the elbow joint.
Brachial artery Profunda brachii artery
Superior ulnar collateral artery
Inferior ulnar collateral artery
Radial collateral branch of profunda artery and radial recurrent artery
Radial artery Ulnar artery Ulnar recurrent arteries Interosseous recurrent artery Posterior interosseous artery Anterior interosseous artery
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Posterior compartment
DISSECTION 7.2 Back of the arm Objectives
I. To study the muscles of the back of the arm. II. To
identify and trace the profunda brachii artery, and the radial nerve and its branches. III. To follow the ulnar nerve to the back of the medial epicondyle.
Instructions
1. Remove the deep fascia from the back of the arm to expose the triceps muscle which fills the posterior compartment.
2. Superiorly, separate the medially placed long head of the triceps, which arises from the infraglenoid tub - ercle of the scapula [see Fig. 4.6], from the lateral head, which has a linear origin from the posterior surface of the humerus between the insertions of the teres minor and the deltoid [see Fig. 6.1].
3. Find the radial nerve in the axilla, posterior to the axillary artery. Trace the nerve as far as the triceps, and separate the parts of the triceps by passing a blunt seeker along the nerve in that muscle. Divide and reflect the parts of the lateral head of the triceps
where it covers the radial nerve to expose the radial nerve and the profunda brachii artery in the groove on the back of the humerus. The medial head of the triceps takes origin from the humerus, inferior to the groove [Fig. 7.5].
4. Follow the branches of the radial nerve, and check its continuity with the part of the radial nerve already seen between the brachialis and the brachioradialis.
Follow this part of the nerve distally. Check its branch- es to the brachioradialis, extensor carpi radialis longus, and brachialis. Identify its division into superficial and deep branches at the level of the elbow joint [Fig. 7.3].
5. Follow the ulnar nerve into the posterior compart- ment of the arm with the superior ulnar collateral ar- tery and the branch of the radial nerve to the medial head of the triceps. Trace the ulnar nerve to the back of the medial epicondyle.
6. Remove the connective tissue from the posterior surface of the medial intermuscular septum, and find the posterior branch of the inferior ulnar collateral artery [Figs. 7.5, 7.6].
Fig. 7.8 Muscles of the arm. (A) Anterior view. (B) Posterior view.
Copyright achernishev/Shutterstock. Copyright Fesus Robert/Shutterstock.
Biceps brachii
(A)
Biceps brachii
Triceps brachii
(B)
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The arm
At the lower end of the arm, the nerve pierces the lateral intermuscular septum and descends in the anterior compartment between the brachialis (medially) and the brachioradialis and the extensor carpi radialis longus (laterally). It divides into super- ficial and deep branches. The superficial branch is a sensory nerve to the back of the fingers and hand [see Fig. 5.8]. The deep branch supplies the muscles of the back of the forearm and the joints at the wrist. The radial nerve is sensory to the elbow joint, principally through its branches to the anco- neus and the medial head of the triceps, and to the superior and inferior radio-ulnar joints.
See Clinical Applications 7.1 and 7.2 which demon strate the practical implications of the ana- tomy explored in this chapter.
triceps and then passes into the arm, posterior to the brachial artery. Almost immediately, it gives off the posterior cutaneous nerve of the arm and a branch to the medial head of the triceps (which accompanies the ulnar nerve in the poster- ior compartment). It then passes inferolaterally into the groove for the radial nerve on the posteri- or surface of the humerus [see Fig. 5.1B], and winds around this surface of the humerus with the pro- funda brachii artery. In the groove, the nerve gives off branches to the lateral head of the triceps and a long slender branch which descends through the medial head of the triceps of the anconeus muscle [Fig. 7.5]. Two cutaneous branches—the lower lat- eral of the arm and the posterior of the forearm—
are also given off here.
CLINICAL APPLICATION 7.1 Fracture of the shaft of the humerus Mid-shaft fractures of the humerus are common and
may damage the radial nerve, as it traverses the groove on the back of the humerus. A knowledge of the mus- cular and sensory branches given off by the radial nerve, along with the point of origin of these branches, will help you predict what lesions arise from such a fracture.
Study question 1: name the muscles denervated by such an injury. (Answer: triceps, lateral head; anconeus; brachio- radialis; extensor carpi radialis longus and brevis. The me- dial and long heads are supplied before the nerve enters the groove.) Extensor muscles of the forearm and wrist are also paralysed. You will learn about these in Chapter 8.
Study question 2: name the movements likely to be lost or weakened because of this injury. (Answer: loss of
extension of the wrist, hand, and fingers; weakness of su- pination.)
Study question 3: what sensory nerves will be affected?
(Answer: lower lateral cutaneous nerve of the arm, pos- terior cutaneous nerve of the forearm, superficial branch of the radial nerve.)
Study question 4: what sensory loss will result from this nerve injury? (Answer: loss of sensation over the lateral part of the lower arm, the posterior forearm, the lateral part of the dorsum of the hand, and the dorsal aspect of the lateral three and a half digits, excluding their nail beds.)
Study question 5: name the artery which could be damaged in a fracture of the mid shaft of the humerus.
(Answer: profunda brachii artery.)
CLINICAL APPLICATION 7.2 Measurement of blood pressure Blood pressure is the force exerted by circulating blood
upon the walls of blood vessels. It is one of the vital signs of physical well-being. It is measured using a sphyg- momanometer, an inflatable rubber cuff connected to a manometer. The cuff is tied around the arm, and the pressure in the cuff inflated till the blood flow through the brachial artery is cut off. The cuff is then deflated slowly, allowing blood flow to resume. A stethoscope placed over the brachial artery at the cubital fossa moni- tors the start of blood flow in the artery. When the pres- sure exerted by the cuff is above the systolic pressure, no
sounds are audible, as there is no blood flow. As the cuff pressure falls below the systolic, the sound of spurts of blood flowing past the cuff is heard. When the cuff pres- sure falls below the diastolic, the blood flow through the brachial artery becomes streamlined (not turbulent any more), and no sound is audible through the stethoscope.
The physician measuring the blood pressure makes a note of two pressure readings: (1) when the blood flow first becomes audible with a drop in cuff pressure; and (2) when the blood flow is no longer audible. These two readings give the patient’s systolic and diastolic pressures.