Anatomical and histological observations of fore- and hind limb toes in adult mice after amputations performed at the age of two weeks.

Amputation of fore- and hind limb toes in order to numerically identify mice, although an effective and conditionally accepted method, is an ethical issue because of the pain involved and because of the detrimental long term side effects that may be encountered. In transgenic mice sacrificed between the ages of 1 and 1-1/2 y, and in which toe amputations were performed at the age of 2 wk, we observed anatomical (n = 60) and histological (n = 10) changes in bones and soft tissues. In stumps, meduallary cavities of sectioned phalanges became sealed and, therefore, some regrowth must have occurred distal to the amputation plane. However, an important increase in width is seen in the diaphysis of transected bones (P < 0.001) when compared to normal phalanges. Normal epidermis-dermis reorganisation occurred in the stumps. Therefore, when considering solely detrimental long-term side effects related to bone growth and tissue reorganization, toe amputations to numerically identify mice seems an acceptable procedure.