The cubital fossa is a triangular hollow area that lies in front of the elbow joint (Figure 1). It is bounded:
- superiorly by an imaginary line connecting the medial and lateral epicondyles
- medially by the pronator teres muscle
- laterally by the brachioradialis muscle.
Its floor is formed of the brachialis and supinator muscles overlying the capsule of the elbow joint. The deep fascia of the forearm forms its roof, which is strengthened by fibres of the bicipital aponeurosis. Lying on the roof in the superficial fascia are the anterior branches of the medial and lateral cutaneous nerves of the forearm and the median cubital vein, which joins the cephalic and basilic veins.
The cephalic, basilic and median cubital veins are usually easily seen and palpated in the roof of the fossa, and this is therefore a common site for venepuncture. It is worth noting that variations in venous anatomy at this site are common (Figure 2). The use of the cubital fossa for intravenous fluid therapy is not recommended because movement of the elbow joint disturbs the cannula and irritates the vein wall with the consequence that thrombosis of the vein quickly occurs.
The contents of the fossa from medial to lateral are:
- median nerve
- brachial artery and its terminal branches, the radial and ulnar arteries
- biceps tendon and bicipital aponeurosis (which separates the median cubital vein from the brachial artery)
- radial and posterior interosseous nerves, which are often overlapped by the fibres of brachioradialis.
The brachial artery is palpated here when the arterial pressure is being taken using a sphygmomanometer but, because of the bicipital aponeurosis, the elbow should be fully extended so that the artery is pressed back on to the elbow joint to render palpation a little easier. The brachial artery is in close relation to the median nerve, which lies on its medial side. Awareness of this relationship should minimize the incidence of nerve trauma during arterial puncture for blood sampling or the insertion of arterial catheters for cardiac or other investigations. Rarely, the cubital fossa is used for distal nerve blocks.
The median nerve can be anaesthetized by injecting 5 ml of local anaesthetic solution through a weal raised midway between the outer side of the tendon of biceps and the medial epicondyle. This anaesthetizes the lateral half of the palm and fingers.
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