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February 1953


Author Affiliations

From the Shriners' Hospital for Crippled Children.

AMA Am J Dis Child. 1953;85(2):141-145. doi:10.1001/archpedi.1953.02050070150002

A TRIGGER mechanism is one in which motion is carried to a certain point, at which a resistance is met, but further motion carries it beyond the resistance with a snapping sensation or a definite "give." In the trigger thumb the motion from flexion to extension is most frequently blocked at about 150 degrees, and then further pressure overcomes the resistance and full extension is obtained. This works in a similar way with motion from full extension to flexion, meeting the same resistance. When the child is seen by the physician, the thumb is frequently locked with the distal phalanx in flexion. However, the history given by the parents shows that the typical trigger mechanism was present at the onset, but gradually the resistance increased until the phalanx locked in flexion. In our series of cases seven of the nine trigger thumbs were in the persistent locked state when the

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