Plan of Action:
We would like to repeat the orthopedic exam checking the cranial drawer sign in extended and flexed positions. We would also like to do lateral and cranio-caudal radiographs of the stifle joint to check for osteosarcoma lesions and an avulsion fragment of bone in the stifle joint . We also would like left lateral, right lateral and a ventro-dorsal radiograph of the thorax to check for tumor metastasis. We would also like bloodwork done with an added T4 to check for abnormalities.  
If there is a rupture of the cranial cruciate ligament it is important to know whether it is a partial or complete tear. A partial rupture will have minimal movements in the extended position with increased cranial drawer in the flexed position. If the tibia moves one millimeter then the cranial cruciate ligament is only partially torn, of it is displaced more than one millimeter then the CCL is ruptured.  In light of the fact that we already have a 4-5mm positive cranial drawer sign it is not necessary to perform a tibial compression test, which would also have been beneficial in the diagnosis of cranial cruciate rupture.  In repeating the orthopedic exam we will also listen for an audible click which is indicative of a tear or detachment of the medial meniscus.
Rarely, an avulsed fragment of bone is seen lateral to the lateral condyle of the femur on a craniocaudal view of the stifle joint when a cranial cruciate tear is present. A lateral view may show a lucent defect in the lateral condyle, and the fragment may be seen overlying the joint. We might also see intra-articular soft tissue swelling and intracapsular swelling displacing adjacent fascial planes with a cranial cruciate ligament tear. However, the absence of evidence of displacement on radiographs should not be relied on to exclude a diagnosis of a ruptured cranial cruciate ligament. If there is osteosarcoma in the proximal tibia then lateral left hind limb radiographs will give us a diagnosis. Osteosarcomas appear on radiographs as an aggressive bone tumor with focal soft tissue swelling. The metaphysis is the most common location for this neoplasm, but it can be located in other parts of the bone. There would be evidence of cortical and medullary bone lysis and disorganized new bone formation that invades the surrounding tissues. In 50% of the cases a sunburst appearance occurs as periosteal new bone radiates out from the tumor. A pathologic fracture could be visible. It is also possible that joint involvement would be seen. If radiographic evidence points to osteosarcoma, further investigation of he disease can be accomplished through a bone biopsy.  When suspecting osteosarcoma, it is important to also radiograph the lungs to check for metastasis. The tumor foci would appear as rounded discrete opacities in the lungs.
To diagnose OCD, radiographs are necessary.  One looks for an irregular subchondral bone density, surrounded by a zone of increased bone density, increased joint fluid, and possibly the presence of a cartilaginous flap (if it is ossified).