What is TPLO Surgery?



Dog’s Anatomy

The knee joint in the dog is called the stifle. The stifle is composed of three bones: the thigh bone (femur), shin bone (tibia) and the kneecap (patella). The knee joint is supported by four main ligaments: two on either side, and two that cross within the joint. The two ligaments inside the joint are the cranial cruciate ligament (CrCL) and caudal cruciate ligament (CdCL). The cranial cruciate ligament is equivalent to the human anterior cruciate ligament (ACL).

X-ray of a dog's cranial cruciate ligament







All About the Cranial Cruciate Ligament

Importance of the cranial cruciate ligament

The anatomy is very similar to the human knee; however, the forces applied to the joint during walking are very different. The top of the dog’s tibia (tibial plateau) is sloped downward, so there is a tendency for the femur to slide down this slope. The force is called “tibial thrust” and it is prevented by the cranial cruciate ligament. If something happens to this ligament, the femur will slide back, and the tibia will slide forward, causing discomfort for your pet.


    What Happens with Cranial Cruciate Ligament Tears?

    When the cranial cruciate ligament tears, the dog usually is not able to bear full w eight on the leg, and may carry the leg. The tibia (shin bone) will move forward in relationship to the femur (thigh bone) while walking. During examination of the joint, this looseness is referred to by your doctor as the “cranial drawer sign.”

    Other Signs

    • Subtle lameness to complete non-weight-bearing lameness
    • Can be acute or chronic
    • Sitting with hind legs out to the side
    • Clicking or popping of the knee


    Orthopaedic examination to check for discomfort and instability on stifle manipulation

    • Cranial drawer test
    • Cranial tibial thrust tests
    • Radiographs (x-rays) of the knee
    • Range of motion?