Hand

An easy way to remember the bones of the hand is the following mnemonic (starting radially):

Some Lovers Try Positions That They Can’t Handle

(Scaphoid, Lunate, Triquetrum, Pisiform, Trapezium, Trapezoid, Capitate, Hamate)

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Figure 1. Bones of wrist & hand

Muscles of flexion, extension, adduction & abduction

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Table 1. Muscles affecting the wrist joint

Palmar aponeurosis

  • Thick central layer of deep fascia, which attaches to flexor retinaculum distally
  • Triangle-shaped from palmar longus tendon downwards, distally splitting into 4 parts at the bones of the fingers
  • Protects underlying soft tissues and long flexor tendons

Flexor retinaculum

  • From scaphoid & trapezium laterally to pisiform & hook of hamate medially
  • Important to note that ulnar artery & nerve pass outside it and therefore out of carpal tunnel
  • Thenar & hypothenar muscles arise from it

Carpal tunnel

  • Contains 9 tendons, surrounded by synovial sheaths and the median nerve
  • Palmar cutaneous branch of the median nerve comes off before carpal tunnel and travels outside the flexor retinaculum
  • The flexor digitorum muscles all share a sheath but the flexor pollicis longus has its own sheath
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Figure 2. Transverse view of the carpal tunnel

Thenar eminence

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Figure 3. Muscles of thenar eminence
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Table 2. Muscles of thenar eminence

Hypothenar eminence

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Figure 4. Muscles of the hypothenar eminence
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Table 3. Muscles of the hypothenar eminence

Palmar arches

  • Deep – mainly radial with some contribution from ulnar; 3 palmar metacarpal arteries (middle, ring & little), princeps pollicis (thumb) and radialis indicis (index)
  • Superficial – mainly ulnar, with contribution from radial; 3 common palmar digital arteries (middle, ring & little), thenar muscles

Digital nerves

  • Median nerve – 1 & 2 lumbricals, skin of thumb, middle and 1st half of ring finger, thenar muscles
  • Ulnar nerve – cutaneous supply to medial 1.5 fingers, 3 & 4 lumbricals, all dorsal interossei, adductor pollicis and hypothenar muscles

Lumbricals

  • 4 muscles in the hand
  • Origin – tendons of flexor digitorum profundus
  • Insertion – pass dorsally & laterally around each finger & insert in extensor hood
  • Innervation – index & middle median nerve, ring & little ulnar nerve
  • Action – flex the MCP joints & extend at IP joints
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Figure 5. Lumbrical muscles

Interossei

  • Located between metacarpals
  • Dorsal
    • Origin – lateral & medial surface of metacarpals
    • Insertion – extensor hood and proximal phalanx of each finger
    • Innervation – ulnar nerve
    • Action – ABDuct fingers at MCP
  • Palmar
    • Origin – medial or lateral surface of metacarpals
    • Insertion – extensor hood and proximal phalanx of same finger
    • Innervation – ulnar nerve
    • Action – ADDucts fingers at MCP
  • A good way to remember actions of interossei is PAD & DAB (palmar ADDuct, dorsal ABDuct)
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Figure 6. Interossei

Flexor sheaths

  • Digital flexor tendons are mostly covered by synovial sheaths – they enable tendons to slide freely over each other during movement

References

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