Human Anatomy
Forearm and Hand
Forearm and hand anatomy for MBBS: forearm muscles, median, ulnar and radial nerves, carpal tunnel and palmar arches, mapped to NMC codes AN12.1 to AN12.15.
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Forearm and Hand
Forearm and hand anatomy for MBBS: forearm muscles, median, ulnar and radial nerves, carpal tunnel and palmar arches, mapped to NMC codes AN12.1 to AN12.15.
This chapter covers the muscles, nerves and vessels of the forearm and hand, a region rich in clinical correlations. It details the median, ulnar and radial nerve territories, the carpal tunnel, the palmar arches, and the classic deformities that follow nerve injury.
High-yield: Forearm and Hand
- The flexor muscles of the forearm are supplied by the median nerve, except flexor carpi ulnaris and the medial half of flexor digitorum profundus, supplied by the ulnar nerve.
- The extensor muscles of the forearm are all supplied by the radial nerve or its posterior interosseous branch.
- The median nerve passes deep to the flexor retinaculum through the carpal tunnel with the long flexor tendons.
- Carpal tunnel syndrome compresses the median nerve, causing tingling in the thumb, index, middle and half the ring finger, and thenar wasting.
- The ulnar nerve enters the hand superficial to the flexor retinaculum through Guyon's canal.
- The ulnar nerve supplies all the intrinsic hand muscles except the thenar muscles and the two lateral lumbricals.
- A high ulnar nerve lesion gives a less marked claw than a low lesion, the ulnar paradox, because profundus to the ring and little fingers is also paralysed.
- The recurrent branch of the median nerve supplies the thenar muscles and is superficial and easily cut.
- The radial artery lies lateral in the forearm and is palpated at the wrist for the pulse.
- The superficial palmar arch is mainly formed by the ulnar artery and the deep palmar arch mainly by the radial artery.
- The palmar aponeurosis is a triangular thickening of deep fascia continuous with the palmaris longus tendon.
- Dupuytren's contracture is a thickening of the palmar aponeurosis that flexes the ring and little fingers.
- The dorsal digital expansion of each finger receives the tendons of the lumbricals and interossei.
- The anatomical snuffbox transmits the radial artery, and the scaphoid lies in its floor.
Nerve supply of the hand
- **Median nerve:** Thenar muscles and lateral two lumbricals; sensation to lateral three and a half digits on the palm.
- **Ulnar nerve:** All intrinsic muscles except thenar and lateral two lumbricals; sensation to medial one and a half digits.
- **Radial nerve:** No intrinsic muscles; sensation to the dorsum of the lateral three and a half digits over the proximal parts.
- **Carpal tunnel:** Median nerve and long flexor tendons pass here; compression causes carpal tunnel syndrome.
NMC competencies in this chapter
- **AN12.1:** Flexor compartment muscles of the forearm
- **AN12.2:** Extensor compartment muscles of the forearm
- **AN12.3:** Course and relations of the radial and ulnar arteries
- **AN12.4:** Median nerve in the forearm and hand
- **AN12.5:** Ulnar nerve in the forearm and hand
- **AN12.6:** Radial nerve and posterior interosseous nerve
- **AN12.7:** Flexor and extensor retinacula
- **AN12.8:** Palmar aponeurosis and fascial spaces of the hand
- **AN12.9:** Small muscles of the hand
- **AN12.10:** Superficial and deep palmar arterial arches
- **AN12.11:** Dorsal digital expansion
- **AN12.12:** Synovial sheaths of the hand
- **AN12.13:** Movements of the thumb and fingers
- **AN12.14:** Cutaneous innervation of the hand
- **AN12.15:** Applied anatomy of the forearm and hand
Frequently Asked Questions
What happens in carpal tunnel syndrome?
The median nerve is compressed as it passes under the flexor retinaculum. This causes tingling and numbness in the thumb, index, middle and lateral half of the ring finger and, if prolonged, wasting of the thenar muscles.
Which muscles does the ulnar nerve supply in the hand?
The ulnar nerve supplies all the intrinsic hand muscles except the thenar muscles and the two lateral lumbricals, which are supplied by the median nerve.
What is the ulnar paradox?
A low ulnar nerve lesion at the wrist produces a more obvious claw hand than a high lesion at the elbow, because in the high lesion the profundus to the ring and little fingers is also paralysed, reducing the clawing.
How are the palmar arches formed?
The superficial palmar arch is completed mainly by the ulnar artery, and the deep palmar arch is completed mainly by the radial artery. Together they supply the hand and digits.
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