Step 3: Proper Diagnosis
Clinical signs of early (partial) CCLR may include an acute onset of hind limb lameness following activity (can be weight bearing or non-weight bearing) that improves with time and is followed by intermittent stiffness after rising or mild to moderate lameness following heavy activity. As the disease advances and the ligament progressively tears, the lameness may become more consistent. Acute complete tears may initially result in a non-weight bearing lameness on the limb, but as time goes on the dog may intermittently use the limb. Instability in the joint associated with CCLR can also lead to injury of the meniscus. Injury of the meniscus can be extremely painful for pets and may, for a period of time, lead to a non-weight bearing lameness.
There are multiple tests your veterinarian can perform to help diagnose a cranial cruciate ligament tear. One of the first signs present prior to instability may be pain with full extension (hyperextension) of the knee. This pain is likely due to stretching of the intact or strained fibers of the cruciate ligament. Once the ligament tears to a certain degree the tibia can be manually manipulated to show instability in what is called the “cranial drawer test” in which the tibia can be moved forward in relation to the femur. Another sign referred to as tibial thrust, may be elicited as well. With this test, weight bearing is mimicked and the front of the tibia can be noted to be pushing forward in relation to the femur. It is important to keep in mind that many patients with clinical signs of pain and lameness may have a partial tear of the CCL. In these cases, there may not be any obvious instability (cranial drawer or tibial thrust) on the exam, however, the patient has a torn CCL that will likely progress to a complete tear.
Other signs that may be noted on the physical exam include loss of muscle mass (atrophy), detection of effusion (swelling) within the joint, and scar tissue formation around the knee (buttress). This scar tissue is the body’s natural response to try and stabilize an unstable joint. Long-term this scar tissue leads to a decreased range of motion in the knee. Finally, a “clicking” sound may be noted in a small percentage of patients with meniscal tears.
Though the cranial cruciate ligament is not visible on an x-ray, radiographs can help confirm a diagnosis of a CCLR by detecting changes that occur in the joint following a CCL injury. These changes may include effusion (excess fluid in the stifle), arthritis, and forward movement of the tibia relative to the femur. Radiographs can also help rule out other concurrent injuries.