ACL Injuries in Dogs: Causes, Signs, and Diagnosis
How cruciate ligament injuries happen in dogs, what they look like at home, and how veterinarians pin down the diagnosis.
The short version
- In dogs the ligament is called the cranial cruciate ligament, or CCL.
- Most tears follow gradual degeneration rather than a single accident.
- Over 50% of dogs that rupture one side may rupture the other later.
- Diagnosis usually starts with the cranial drawer and tibial thrust tests.
- Partial and complete tears can look different and are managed differently.
A dog who suddenly holds up a back leg sends most owners straight to the phone. Very often the culprit is the cranial cruciate ligament, the structure people usually call the ACL. It is one of the most common orthopedic injuries veterinarians see, and understanding it helps you make sense of what comes next.
What This Ligament Does
The cranial cruciate ligament, abbreviated CCL, is the veterinary name for what most people know as the ACL. It runs between the femur and the tibia inside the knee joint. Its job is to keep the shin bone from sliding forward and to limit the knee from rotating inward.
When it fails, that control disappears. The bones shift against each other with every step, which is why an affected dog looks so uncomfortable putting weight on the leg.
Why It Tears
Owners often assume a specific accident caused the injury, but in dogs the story is usually longer than that. The ligament tends to weaken over time until an ordinary movement finishes the job. Contributing factors include:
- Gradual degeneration of the ligament itself
- Obesity or carrying extra weight
- Poor overall conditioning
- A sudden twist or awkward landing
- Inherited predisposition in certain dogs
- Weakening that comes with age
- Abnormal leg conformation
What You Might See at Home
Some signs are obvious and some are easy to write off as your dog slowing down. Watch for lameness in a hind leg that appears abruptly or worsens gradually, difficulty getting up, hesitation on stairs or before jumping, and a general drop in how much your dog wants to move.
There are subtler clues too. Many dogs sit with the sore leg stuck out to the side rather than tucked underneath. You may hear clicking or popping from the knee, see swelling around the joint, or notice that the thigh muscle on the affected side has started to shrink from disuse.
How Veterinarians Confirm It
The examination itself does most of the work. Your veterinarian will feel for instability using the cranial drawer test and the tibial thrust test, both of which check whether the tibia moves forward when it should not. A tense or painful dog can make these harder to interpret, which is one reason sedation is sometimes suggested.
Radiographs are commonly taken as well. They do not show the ligament directly, but they reveal swelling inside the joint and any osteoarthritis that has already developed. In more complicated cases, or when another injury is suspected alongside the tear, advanced imaging such as MRI or CT may be used.
Distinguishing a partial tear from a complete one matters. A partially torn ligament may still provide some stability, and the knee can feel different on examination than one where the ligament has given way entirely. That distinction shapes the conversation about treatment.
Why Timing Matters, and What Comes Next
Catching the problem early is worth real effort. An unstable joint keeps grinding, and the longer that continues, the more arthritis and secondary damage tend to accumulate. Dogs also lose muscle quickly on a leg they will not use.
There is one more thing worth knowing. More than half of dogs that rupture the ligament on one side go on to rupture the other side at some point. That is not a certainty, but it is a good reason to stay attentive to the leg that currently looks fine.
Once the diagnosis is made, treatment options usually include surgical stabilization. Tibial plateau leveling osteotomy and extracapsular repair, also called lateral suture, are two of the approaches your veterinarian may discuss. Which one fits your dog depends on details only the person examining your dog can weigh, so bring your questions to them.
This article is general information, not a diagnosis. Every pet is different, and your own veterinarian knows yours. Talk to them about anything here that applies to your animal.
Has your vet mentioned surgery?
Ask them about a referral, or call us and describe what you are seeing. We serve Nassau and Suffolk County, at your veterinarian's practice or at our Lake Grove center.