Anatomy
Thumb side (radial) of nearer row of carpal bones, shape and size of cashew nut. Articulates up (proximally) with radius (lunate is other carpal that articulates with radius), down (distally) with trapezoid and trapezium, in (medially) with capitate and lunate.
Clinical
Commonest carpal bone fracture (60%). Requires prompt treatment. Pain, swelling and tenderness at base of thumb (anatomical snuff-box). As blood supply mostly from below, risk of avascular necrosis of upper fracture segment. Failure to heal (non-union) or deformed healing (mal-union) can lead to osteo-arthritis.
Fractures at all ages. Fall, outstretched hand, weight on palm. Difficult to diagnose. Initial X-ray often unrevealing; repeated after 7-10 days, often shows healing, confirms diagnosis.
Vignette
Anatomical snuff-box; depression at base of thumb, most easily visible between 2 tendons (extensor pollicis brevis, abductor pollicis longus) when give thumbs up sign.
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