Facts Labrador Retriever, 6YO -Not very likely it is a congenital disorder due to the age, or for that matter is it possible that the injury affects any growth plate because the physis is closed. Rule outs still include trauma, neoplasia, infection, developmental, etc. based on signalment. In terms of neoplasia, large breed signalment suggests osteosarcoma, fibrosarcoma, chondrosarcoma, hemangiosarcoma but certainly other tumors are just as likely. Since this problem seems to involve the cruciate ligament (cranial drawer sign), synovial sarcoma has to be considered. It is a benign or malignant giant cell tumor that arises from the joint capsule, tendon sheaths, and bursae but not directly from synovium. There is a high metastatic rate, complete excision guarded due to 'stump' recurrence. No other joints affected ? therefore not as likely. As you approach the woman to shake her hand and introduce yourself the dog raises its head and wags its tail slowly. It does not get up. -Since it is a friendly dog, you would expect it to greet you as you enter the exam room. Dog wags its tail to let you know that it is still BAR. Possibly painful to get up. With cranial cruciate ligament rupture/tear, behavior is appropriate. Since Wednesday she has not been walking normally and I'm afraid she might be in pain -Not sure when Wednesday is compared to the examination day, but is certainly within the week. Thus, it appears that there is an acute problem, since the dog was behaving normally prior to the problem. I feed Bonnie dry dog food twice a day (at the suggestion of my trainer). It's Adult Maintenance Hills Diet and she gets a total of about 4 cups. Bonnie is quite overweight but she has no other abnormalities. - Average weight should be 55-70 lbs for a female. Dog is eating way too much. Dog is exercising a decent amount, but not enough to burn the excess 3000kcal of energy. *See Learning Issues for calculations*. Dog’s weight can be predisposing it to osteoarthritis. It may also be placing abnormal strenuous forces on the CCL, which is already under constant mechanical stress. She's up to date on her vaccinations and deworming - Clinical signs are not likely to be viral or parasitic in nature with a dog that has been dewormed and previously vaccinated. As far as I know she has never been on any medication other than her heart worm medicine, which I give to her once a month - Clinical signs not attributed to exogenous drugs. No corticosteroids were given that would immunosuppress the dog and make it susceptible to infection, which could lead to infectious arthritis. Bonnie's a very active dog when she can be. We go on walks mornings and evenings, between 30 and 60 minutes each time. A couple of times a week she jogs with me for about 3 miles. On the weekends we walk in the woods with friends whenever we can, sometimes for a couple of hours. But she does chase cats and other dogs when she is allowed to do so. -A daily exercise routine is beneficial for a dog that is obese. However, long exertional jogs may be difficult for an obese dog and may be causing cartilage damage due to abnormal forces and abrasion at the two ends of the joint. It is possible that the dog injured itself while running about the woods chasing after an animal at seeded its joint with a bacterial or fungal infection. I t is not likely that the infection would have resulted from hematogenous spread because only one joint is affected and there are no systemic signs of sepsis (no abnormal signs like fever were noted on the exam). Since no wound was found, it is possible that it was a small puncture wound and was missed by the owner. Clinical signs consistent with septic arthritis include grade III/IV partial weight bearing lameness, the stifle is swollen, painful, and warm. Also, the joint has a reduced range of motion. Bonnie has a partial weight bearing L hind limb lameness. She has difficulty getting up, but can walk quite well once she is up. When she stands still she is barely toe touching on the L hind leg. There is effusion of the L stifle joint with a distention of the joint capsule on either side of the straight patella ligament. There is pain on manipulation of the stifle. - Toe touching lameness indicates that the left rear leg is painful somewhere. The difficulty from getting up can be due to muscle damage, ligament/tendon tear or rupture, and pain from the stress of the whole weight of the dog on that leg. Effusion of the stifle joint with distention of the joint capsule cause from the trauma associated with an inflammatory response. The trauma causes an inflammatory response, leading to the release of cytokines which causes destruction of the proteoglycan and collagen network of articular cartilage. Exposed collagen from the torn ligament also elicits an autoimmune response exacerbating the state of intra-articular inflammation. There is joint effusion in the L stifle joint. A joint tap was performed. While awake, no cranial drawer can be palpated in the stifle joints. While under sedation a 4 - 5 mm cranial drawer can be palpated in the L stifle, with less than 2 mm palpable in the right. The patellae appear correctly positioned and normally mobile. The collateral ligaments are intact. The hip joints do not have any palpable laxity or pain when run through a full range of motion. No other abnormalities could be found. - It can be normal for no cranial drawer to be palpated in the stifle joints while awake. This is due to proliferative response of the fibrous joint capsule. A few millimeters of drawer are enough for a diagnosis, especially if the opposite limb is completely stable. Lateral projection rads are useful in identifying joint effusion causing a cranial displacement of the intrapatellar fat body. This is an indicator in those patients with a partial tear, and maybe normal when patellae appear correctly positioned. Other joints in that leg do not seem to be affected, though more information should be garnered with a full orthopedic exam under anesthesia.