A spontaneous ankle deformity in an inbred strain of mouse.

A spontaneous subluxation and subsequent dislocation of the bones of the ankle has been described in the males of an inbred strain of mouse (STR/ORT). It consisted of a gradual elevation of the calcaneum which eventually came to lie along the distal end of the tibia after 6--8 mth. The astragalus rotated forward. Articulations with the navicular and tarsal bones were severely disrupted with the accompanying development of peri-articular calcifications and ossifications. With one exception the arthropathy only occurred in male mice. Of the male members of the colony over the age of 3 mth, 26.7 per cent. had at least one ankle affected. Possible aetiological factors are discussed.