Eleven fractured Sutter metacarpophalangeal prostheses were obtained from the hands of three patients. All of the implants had fractured at the junction of the distal stem and the hinge. After visual examination, the fracture faces were prepared and viewed using a scanning electron microscope. These images indicated that fracture was initiated by abrasion on the dorsal aspect of the distal stem of the prostheses, close to the hinge. Crack propagation was shown to be due to a fatigue process. Once a crack started, its direction of travel could be followed, using topographical features common to engineering fracture analyses. Propagation was from radial to ulnar and from dorsal to palmar.