股骨骨折

股骨（大腿骨）的骨折，為犬貓最常見的長骨骨折之一。因股骨承受強大肌肉力量，幾乎所有股骨骨折都需手術內固定。常因車禍或高處墜落引起。

Femoral fractures occur when a single high-energy load — vehicular impact, a fall from height, or a kick — exceeds the bending and torsional tolerance of the femoral diaphysis or its physes. The femur is completely enveloped by the quadriceps, hamstring and adductor muscle masses, and their sustained contraction after failure overrides the fragments, producing the limb shortening, external rotation and crepitus seen on presentation; this same muscular pull is why external coaptation cannot hold a reduction and why almost every femoral fracture requires internal fixation. Disruption of the medullary canal and periosteal vessels bleeds into the thigh compartment, and the resulting haematoma with its inflammatory mediators sensitises local nociceptors, generating pain severe enough to drive tachycardia and anorexia. In immature animals the capital and distal femoral physes are the mechanical weak points, so an equivalent load produces Salter-Harris separation instead of diaphyseal failure, with prognosis governed by the fracture type and remaining growth potential. Healing proceeds through haematoma organisation, soft then hard callus, and remodelling, but only where fragments are held in stable apposition with an intact blood supply: interfragmentary motion, devitalised bone in comminuted patterns, and bacterial contamination in open fractures divert healing toward delayed union, nonunion or osteomyelitis. Prolonged immobilisation of the stifle in a shortened position adds quadriceps contracture and periarticular fibrosis, which limit functional recovery even after the bone has united.