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Despite clinical and experimental reports of digit tip regrowth, bone regrowth after amputation through terminal phalanges has not been methodically documented. We have examined bone regrowth in mice after amputation through the terminal phalanx to determine how the level of amputation affects the response and whether the response varies between adults and neonates. Digit tips were amputated, and, at selected intervals greater than 5 weeks after amputation, digits were photographed and processed for whole mount staining with alizarin red stain. Amputations within the distal 40% of the terminal phalanx yielded grossly normal digits within 5 weeks and bone regrowth which usually attained or surpassed the original length. Amputations through the proximal 20% of the distal phalanx precluded nail plate regrowth, and bone grew minimally or regressed. Amputation through the intermediate 40% of the distal phalanx produced digit tips in which bone regrowth was correlated with nail regrowth and in which bone regrowth did not reach original levels. The response in adults and neonates was similar. The correlation between nail regrowth and bone regrowth may help to predict phalangeal bone regrowth after amputation in adults and juveniles.

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Recent studies of postamputational repair following digit-tip amputation revealed an unexpected correlation between nail regrowth and bone regrowth in mice. To examine putative effects of nail on bone regrowth, phalangeal tips were amputated such that nail was artificially removed from distal levels or retained following proximal level amputations. In the absence of nail, bone did not regrow at distal levels. Conversely, when nail was surgically retained bone regrew from proximal levels. The nail organ profoundly influences bone regrowth.

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