Causes & Symptoms
Stability of the stifle (knee) is provided by several different structures:
- Cruciate ligaments
- Cranial cruciate ligament (CrCL)
- Caudal cruciate ligament (CdCL)
- Medial and lateral collateral ligaments
- Joint capsule
- Peri-articular muscles
Instability can cause pain, lameness, and osteoarthritis. The number one reason for lameness in the knee is a ruptured CrCL.
The origin of the CrCL is the medial aspect of the lateral condyle, and it inserts on the cranial aspect of the tibial plateau. It prevents cranial translation of the tibia (“drawer motion”), excessive internal rotation and hyperextension of this joint. There are 2 parts of the CrCL which makes it complex: “craniomedial band” (taught flexion and extension) and “caudolateral band” (lax in flexion).
CrCL rupture is the most common reason for rear limb lameness in the dog. It is more common in large and giant breed dogs but is also commonly recognized in smaller breeds of dogs and cats. The three most common implemented causes for rupture of the CrCL include:
Supra-physiologic loads (athletic dogs in which hyperextension or severe internal rotation occurs)
Ligament degeneration (occurs in older dogs and sedentary life style)
Other causes (conformational abnormalities, joint inflammation, primary degenerative changes, and immune mediated causes).
Clinical signs can be very subtle from barely lame (common with partial tear or hyperextension) to non-weight bearing lameness (full tear with meniscal tear). Most patients with CrCL rupture present to your regular veterinarian for acute non-weight bearing lameness that may improve initially, then worsen again. Some ruptures may go unnoticed or undetected and can present as a chronic, insidious, or intermittent lameness. However, commonly with a CrCL rupture there is stifle (knee) pain and joint effusion palpated on orthopedic exam.
An orthopedic examination is needed to find or confirm the CrCL rupture. Joint effusion (swollen joint) and medial buttress (fibrous tissue on the inner aspect of the stifle) are almost always present on orthopedic exam when a CrCL rupture is present. Most dogs have cranial drawer (see video below), but with chronic ruptures and severe ruptures, the stifle may already be sitting in the cranial drawer position, therefore, this orthopedic exam finding may be absent.