HP Sassoon(1) 206.14 :בכרעה בתריאתא‏ : its [i.e. the animal's] hind legs
See the entire entry for bāṯrāy adj. last

HP Sassoon(1) 206.14 :חוסרנא ויותרנא בכרעה בתריאתא‏ : a deficiency or an excess (in length) in its hind legs
See the entire entry for ḥusrān, ḥusrānā n.m. loss, damage