Hand and Wrist Anatomy
Overview
The hand demands precise integration of intrinsic and extrinsic muscles, three major peripheral nerves, and eight carpal bones in two rows. Its anatomy is high-yield for clinical assessment and MSK radiology.
The Carpal Bones
Arranged in two rows (mnemonic: 'Some Lovers Try Positions That They Cannot Handle'):
- Proximal Row (lateral to medial): Scaphoid, Lunate, Triquetrum, Pisiform.
- Distal Row (lateral to medial): Trapezium, Trapezoid, Capitate, Hamate.
Nerve Territories of the Hand
- Median Nerve (LOAF muscles): Lateral two Lumbricals, Opponens Pollicis, Abductor Pollicis Brevis, Flexor Pollicis Brevis (superficial head).
- Ulnar Nerve (all other intrinsics): All 4 dorsal interossei, all 3 palmar interossei, medial 2 lumbricals, hypothenar muscles, Adductor Pollicis, and deep head of FPB.
- Radial Nerve: NO intrinsic motor supply to the hand. Purely sensory over the dorsal lateral hand.
WarningScaphoid Fracture: AVN Risk
The scaphoid receives its blood supply from distal to proximal via dorsal carpal branches. A waist fracture disrupts supply to the proximal pole, which has no independent blood supply and faces a high risk of avascular necrosis (AVN). X-ray may be normal in acute fractures — MRI is the investigation of choice if clinical suspicion is high.
High Yield Facts
LightbulbFRCR / MD Prep Pearl
DAB PAD: Dorsal interossei ABduct the fingers; Palmar interossei ADduct the fingers. The adductor pollicis is innervated by the DEEP ULNAR nerve. Froment's sign tests adductor pollicis: the patient compensates for its loss by flexing the thumb IP joint using FPL (median nerve) when gripping a piece of paper.