NAVLE（北美执业兽医考题）Day 653

Q1:A 5-year old male castrated Mastiff presents for left pelvic limb lameness. The medial aspects of both stifles are thickened. Manipulation of the left stifle reveals cranial motion of the tibia relative to the femur and a clicking sound from the joint on flexion and extension. What is the most likely diagnosis?一只5岁已绝育雄性獒犬由于左后肢跛行前来就诊。其双侧膝关节内侧明显增厚。控制左侧膝关节运动时出现胫骨相对于股骨的前方移动，并且在关节屈曲和伸展时都会出现咔咔声。最可能的诊断是什么？