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Evidence-based physiotherapy and rehabilitation resources
Editorial & review policyHuman Anatomy · Upper limb
Everything above exists to position the hand. Twenty-seven bones, three nerves and more muscles than any comparable region — arranged so that the same structure can hold a hammer and thread a needle. Losing a little of it costs a great deal.
| Joint | Between | Note |
|---|---|---|
| Radiocarpal | Lower end of the radius and the articular disc above; scaphoid, lunate and triquetrum below | A condyloid joint. Note the ulna does not reach the carpus - a disc separates them, which is why the radius takes most of the load. |
| Midcarpal | The proximal row of carpals against the distal row | Contributes a large share of movement, particularly flexion. |
Because two joints share the work, wrist movement is rarely lost completely from a single problem, and range should be compared with the other side rather than against a textbook figure.
| Movement | Muscles | Note |
|---|---|---|
| Flexion | Flexor carpi radialis, flexor carpi ulnaris, palmaris longus when present | Greater range than extension |
| Extension | Extensor carpi radialis longus and brevis, extensor carpi ulnaris | The position of function, and the position grip depends on |
| Radial deviation | Flexor and extensor carpi radialis together | Limited by the radial styloid, so range is small |
| Ulnar deviation | Flexor and extensor carpi ulnaris together | Greater range, because the ulnar styloid is shorter |
Why wrist position decides grip strength
The long finger flexors cross the wrist. Let the wrist flex and they are shortened over both joints at once, so they cannot pull — active insufficiency. Extending the wrist puts them at a good length instead. That is why the wrist extensors fire whenever you grip, and why a patient with wrist extensor weakness complains of a weak hand.
Figure 1 · The carpal tunnel and the tunnels at the wrist
Illustration to be added
Two panels. Panel one: a cross-section through the wrist at the level of the carpus, showing the carpal arch formed by the carpal bones concave forwards, the flexor retinaculum bridging it and attaching to the pisiform and hook of hamate medially and the tubercles of scaphoid and trapezium laterally. Inside the tunnel show the median nerve lying immediately beneath the retinaculum, the four tendons of flexor digitorum superficialis, the four of flexor digitorum profundus, and flexor pollicis longus, in their correct relative positions. Show Guyon's canal separately, superficial to the retinaculum, containing the ulnar nerve and artery. Panel two: the back of the wrist with the extensor retinaculum and its six compartments numbered, naming the tendons in each. Bone warm ivory, nerve gold, tendons pale, retinaculum heavy navy, artery red.
Structures crossing the wrist are held down by fascial bands, which creates confined spaces where things can be compressed.
| Tunnel | Roof | Contents | When it goes wrong |
|---|---|---|---|
| Carpal tunnel | Flexor retinaculum, bridging the carpal arch | Median nerve and the long flexor tendons of the fingers and thumb | Numbness and tingling in the thumb, index, middle and half the ring finger; later, wasting of the thenar eminence. Worse at night. |
| Ulnar tunnel Guyon's canal |
A separate band, superficial to the flexor retinaculum | Ulnar nerve and artery | Numb little finger and weak intrinsic muscles, with sensation on the back of the hand spared. |
| Extensor compartments | Extensor retinaculum, divided into six compartments | The extensor tendons in their synovial sheaths | Irritation of the first compartment - the thumb tendons - is a common and easily tested complaint. |
The detail that distinguishes the two nerve problems
The median nerve gives off a palmar cutaneous branch before it enters the carpal tunnel. That branch supplies the skin over the base of the palm, and it is therefore spared in carpal tunnel syndrome. Numbness over the palm itself suggests the problem is higher up. This is a genuinely useful examination point and a reliable examination question.
The hand is moved by two sets of muscles: long ones in the forearm that reach it by tendon, and small ones lying entirely within the hand.
| Group | Muscles | Does | Nerve |
|---|---|---|---|
| Thenar | Abductor pollicis brevis, flexor pollicis brevis, opponens pollicis | Position and oppose the thumb | Median |
| Hypothenar | Abductor, flexor and opponens digiti minimi | Move the little finger and cup the palm | Ulnar |
| Adductor pollicis | Two heads, deep in the palm | Draws the thumb towards the palm | Ulnar - the exception among thumb muscles |
| Lumbricals | Four small muscles from the flexor digitorum profundus tendons | Flex at the knuckles while extending the finger joints | Lateral two median, medial two ulnar |
| Interossei | Four dorsal, three palmar | Dorsal ABduct, Palmar ADduct - remember DAB and PAD | All ulnar |
Figure 2 · Nerve supply of the hand
If you learn one thing from this chapter, learn this figure. Almost every hand problem you meet can be localised by working out which of the three territories is affected.
Why clawing looks worse in a low ulnar lesion
This catches everyone out. A lesion at the wrist paralyses the intrinsics but leaves flexor digitorum profundus working, so the fingers are pulled into a marked claw. A lesion at the elbow also paralyses part of that long flexor, so the fingers cannot curl as strongly and the claw looks less severe. A worse-looking hand can mean a lower, less serious lesion - the ulnar paradox.
Figure 3 · The arches of the hand
Illustration to be added
A hand shown from the front and in two cross-sections. Mark the proximal transverse arch across the carpus (rigid, maintained by bone shape and the flexor retinaculum), the distal transverse arch across the metacarpal heads (mobile, maintained by the interossei and the thenar and hypothenar muscles), and the longitudinal arch running from wrist to fingertip along each ray. Beside it, a three-frame sequence showing the hand flat, then cupping around a small round object, then around a large one, with the arches deepening. Add a fourth frame showing an intrinsic-minus hand with the arches collapsed and the palm flattened, for comparison. Bone warm ivory, muscle brick, arch lines in gold.
The hand is not flat. It is arched in three directions, and the arches are what let it wrap around objects of different shapes.
| Arch | Runs | Maintained by |
|---|---|---|
| Proximal transverse | Across the carpus | The shape of the carpal bones and the flexor retinaculum. Rigid. |
| Distal transverse | Across the metacarpal heads | The interossei and the thenar and hypothenar muscles. Mobile. |
| Longitudinal | From wrist to fingertips along each ray | The long flexors and the intrinsic muscles |
When the intrinsic muscles are paralysed the mobile arches collapse, and the hand becomes flat. A flat hand cannot grip a round object properly however strong the long flexors are, which is why intrinsic loss is so disabling.
| Grip | What it is | Depends on |
|---|---|---|
| Power grip | The object is held against the palm with all fingers, thumb wrapped round | Long flexors, with the wrist held extended |
| Hook grip | Carrying a bag; the thumb is not involved | Long flexors alone. Survives median nerve loss. |
| Precision grip | Object held between thumb and fingertips | Thumb opposition and the intrinsics. Lost early in median nerve problems. |
| Key or lateral pinch | Object held between thumb and the side of the index finger | Adductor pollicis, which is ulnar. Tested by Froment's sign. |
Figure 4 · The four grips
| Problem | Anatomy behind it | What you see |
|---|---|---|
| Carpal tunnel syndrome | Median nerve compressed under the flexor retinaculum | Night symptoms, thumb to half the ring finger, thenar wasting later, palm sensation spared |
| Ulnar claw hand | Intrinsics paralysed, long flexors unopposed | Ring and little fingers clawed; worse in a low lesion |
| Wrist drop | Radial nerve lesion, usually much higher in the arm | Wrist and fingers cannot be extended; grip is weak because the wrist collapses |
| Trigger finger | A thickened flexor tendon catching at a pulley | The finger locks bent and releases with a snap |
| Mallet finger | The extensor tendon avulsed at the last joint | The fingertip droops and cannot be straightened actively |
| Dupuytren's contracture | The palmar aponeurosis thickens and shortens | A cord in the palm pulling the ring and little fingers into flexion; painless and progressive |
An articular disc separates them, which is why the radius carries most of the load and why its lower end fractures so often.
Grip will be weak in anyone. The long flexors become actively insufficient. Test with the wrist in slight extension.
Adductor pollicis is ulnar. It is the basis of Froment's sign and a standard examination question.
The palmar cutaneous branch leaves before the tunnel and is spared. Numbness over the palm points higher up.
The ulnar paradox: a lesion at the wrist produces a more obvious claw than one at the elbow, because the long flexor still works.
Intrinsic paralysis flattens the hand. Strong long flexors cannot compensate, because the hand can no longer shape itself around an object.
Ten questions on this chapter. Tap one to see the answer and the reasoning.
Answer: (B) An articular disc separates the ulna from the carpus, so the radius carries most of the load transmitted from the hand. This is why the lower end of the radius fractures so often.
Answer: (C) Extension puts the long finger flexors at a good working length. In wrist flexion they are shortened over both joints and become actively insufficient.
Answer: (C) The flexor retinaculum, bridging the carpal arch between the pisiform and hook of hamate medially and the tubercles of scaphoid and trapezium laterally.
Answer: (B) The palmar cutaneous branch arises proximal to the retinaculum and does not pass through the tunnel. Numbness over the palm therefore suggests a lesion higher up.
Answer: (D) Adductor pollicis is the exception among the thumb muscles. Its weakness is the basis of Froment's sign.
Answer: (B) Dorsal AB-duct, palmar AD-duct - DAB and PAD. All the interossei are supplied by the ulnar nerve.
Answer: (B) A low lesion spares flexor digitorum profundus, so the unopposed long flexor pulls the fingers into a marked claw. A higher lesion also weakens that flexor, so the claw is less obvious.
Answer: (C) The radial nerve. It supplies the extensors in the forearm and sensation to part of the back of the hand, but no intrinsic hand muscle.
Answer: (C) The interossei and the thenar and hypothenar muscles maintain the distal transverse and longitudinal arches. Without them the hand flattens and cannot shape itself around an object.
Answer: (B) Adductor pollicis, supplied by the ulnar nerve. When it is weak the patient substitutes flexor pollicis longus and the thumb's terminal joint bends.
Everything on this page, in one screen
| Book | What it adds here |
|---|---|
| B D Human Anatomy, Volume 1: Upper Limb and Thorax Chaurasia |
The detailed regional anatomy of the hand at examination level. |
| Anatomy and Human Movement Palastanga, Field and Soames |
The arches, the grips, and how the hand works as a mechanism. |
| Examination of Peripheral Nerve Injuries: An Anatomical Approach | For the nerve territories and the tests that separate them. |
| Clinical Anatomy by Regions Snell |
The clinical conditions set alongside the anatomy that produces them. |
Reviewed by the Physiotherapist India Team. · Human Anatomy contents