A, Common fracture pattern in Kienböck disease is so-called anterior pole type, isolating anterior pole of lunate from remaining portion of bone. Distraction of fracture caused by compressive force exerted by capitate diminishes likelihood of fracture healing. This detail usually is invisible on routine radiographs because radial styloid process is superimposed on fracture gap. As dorsal portion of lunate collapses further, anterior pole may be extruded volarly. B, Ratio of height of carpus to length of third metacarpal is reduced in this patient with Kienböck disease. This ratio in normal wrists has been reported to be 0.54 ± 0.03, and significantly reduced ratios indicate overall carpal collapse. (From Armistead RB, Linscheid RL, Dobyns JH, et al: Ulnar lengthening in the treatment of Kienböck’s disease, J Bone Joint Surg 64A:170, 1982. By permission of Mayo Foundation.)