Hypothesis one: Degenerative bone disease Musculoskeletal changes due to trauma are characterized by joint pain, tenderness, limitation of movement, crepitus, occasional effusion, and variables degrees of local inflammation, but without systemic effects. Pathologically we see irregular distributed loss of cartilage, sclerosis of subchondral bone, subchondral cysts, osteophytes, increased metaphysal blood flow and synovial inflammation. Cartilage damage results in release of cytokines that induce prostaglandin E and metalloproteinases. Ultimately we see cartilage matrix depletion and initiation of cartilage degradation. These changes are considered inflammatory, although degenerative bone disease is not considered to be an inflammatory disease. In addition, the joint capsule undergoes hypertrophy and hyperplasia in order to compensate and help aid joint stability. This might lead to a decreased range of motion. Muscles may become weak with disuse, and therefore are unable to transmit load across the joint increasing to the problem. Joint dysfunction occurs to loss of lubrication, smooth gliding function, decreased range of motion secondary to a particular change. Nearly all degenerative bone disease is secondary to some type of trauma, including fracture, cranial cruciate ligament rupture, meniscal tears, OCD and patellar luxations although the cause might not be apparent in all cases. For example, if an animal were to fracture a bone during play or due to other physical injury, the homeostasis of the surrounding tissues would be disrupted. If the bone were allowed to heal on its own, it might not heal perfectly straight leading to abnormal stretching of surrounding structures. This would lead to abnormal pressure stress on the joint causing pain and eventually degenerative joint or bone disease. Pain is the predominant sign. Pain occurs due to stimulation of nociceptors in tissues. Stimulation can be mechanical or chemical. Some clinical signs include: Altered gait, joint swelling, fibrosis, effusion, crepitus, friction created by thickened synovium and joint capsule and it moves over cartilage and osteophytes, decreased range of motion due to joint capsule fibrosis or pain associated with motion, muscle atrophy and pain.