Why did my dog’s ACL Tear?

In dogs, the tearing of the cranial cruciate ligament or CrCL ligament is by far the most common cause of knee pain. In people, this ligament is referred to as the anterior cruciate ligament (ACL). We’ll be referring to it as ACL here, as it’s easier for people to understand.
The top of a normal dog’s tibia (shin bone) tends to slope backwards at a very steep angle in the knee joint - much steeper than it does in humans. This creates a large force pushing the femur (thigh bone) backwards at all times. The ACL ligament is suppose to hold these bones together and prevent abnormal movement in the joint. However, there is only so much stress the ligament can take before it breaks.
In most dogs, there is no obvious trauma that causes the ACL to tear. They can be happily running in the yard, and then they are suddenly holding up one of their back legs. In reality, the ligament was slowly breaking down for months to get to that point. It was genetically predetermined to happen, and there is nothing you could have done to prevent this eventuality. Larger breeds are predisposed, but it can happen in small dogs too. We usually see this injury happen when dogs are 1-3 years old, but it can happen in elderly pets also.

What is the TPLO?

TPLO stands for Tibial Plateau Leveling Osteotomy. The surgeon makes a planned, curved cut just below the joint surface, on the shin bone. They then rotate the top of the cut bone so that the top surface of the shin bone is almost flat within the knee joint. This takes away the force causing the thigh bone to slip backwards and cause pain. In this procedure, we are not directly replacing the ligament, just changing the slope of the tibia, thus causing the ligament to be no longer be needed.
This surgery has the best long-term outcome of all the ACL surgeries devised. The only other surgery that we would consider equivalent is called the CBLO, and the technique and principle behind that is very similar to the TPLO. We usually recommend the CBLO in dogs that are still growing, or dogs with deformed knees. The other popular ACL procedures, such as the TTA and lateral suture, don’t give quite the same long-term results.

How is a torn ACL diagnosed?

1) Physical Exam: This is the most useful part of diagnosis. Your veterinarian will do a series of tests in the exam room that are very helpful in making a diagnosis. For pets that are hyper, tense, or not very friendly, we may need to give a sedative first to do the tests properly. These test involve putting the knee through a range of motion, and feeling the stability of the knee when certain forces are applied.

2) Radiographs (x-rays)
Even though the ACL ligament doesn’t directly show up on x-rays, veterinarians will still recommend taking x-rays of your limping pet for a few good reasons:
1. Sometimes there are other reasons for limping besides, or in addition to, a torn ACL. Think: bad arthritis, knee cap problems, hip problems, or broken bones.
2. There are common changes that happen to the knee after the ACL tears, and if we see these on x-ray, it further confirms our suspicions. Below, we elaborate on this further.
3. X-rays are needed to measure parts of the tibia, necessary for surgical planning later.

Pre-op x-ray, Lateral View
Pre-Op x-ray Cranial-Caudal View

To the right, we’ve zoomed in on the images above to show you more detail on x-ray changes commonly seen with ACL injury.
1. The nearest image shows a red line and a blue line. The red line is how far out the joint is swollen on this dog. The blue line is where it should normally be.
2. The far image shows a front to back view of the knee. Notice the red arrow, pointing at the joint space on the inner knee. There should be a larger space between the femur and tibia there, and the lack of space means that the medial meniscus is out of place - a common occurrence with an ACL tear.

TPLO Joint Swelling Lateral.jpg
AP close up.jpg

The Surgical Procedure

Based on the size of your pet and the slope of the top of the tibia, the Veterinarian will make calculations as to what size saw blade to use, where to make the cut, how much to rotate the bone fragment, and what size plate and screws to use.
Proper x-rays are very important in the planning. Therefore, even if x-rays have already been taken elsewhere, we re-take x-rays the day of the procedure while your pet is under sedation. These x-rays are not charged for, they just are for our surgeons’ benefit.

TPLO Lateral Preop Planning.jpg

Hardware Used
We use KYON brand surgical implants. These have many benefits over other plate designs, including:
1. Strong, titanium alloy construction which is also very bio-compatible.
2. Locking Screws: The screws lock into the plate and make the entire implant much stronger. This decreases the risk - compared with other plates - that the screws or plate will bend or break.
3. Point Contact Design: The plate is designed to sit 1 mm off the surface of the bone to minimize damage to the bone’s blood supply. This speeds up healing and decreases the risk of infection.
4. Pre-Contoured Design: The plates are pre-shaped to the natural contour of the tibia so that they do not need to be contoured by the surgeon during the procedure. This speeds up the surgery time, which decreases infection risk.

Post-Op X-rays

Once the surgery is completed, we take post-operative x-rays to make sure that everything went according to plan.
The surgeon will ask the following:
1. Is the slope of the tibia acceptable now? A 5 degree slope is ideal, but anything less than 14 degrees will give us good results.
2. Is the bone cut in the ideal place?
3. Are the bone plate and screws appropriate in size for the patient?
4. Are all the screws in the ideal position?
There are many more things that we look at, but these are the obvious questions for the surgeon.

TPLO PostOp AP.jpg

Post-Surgical Instructions and Aftercare

Every clinic has a different protocol, and there is a lot of flexibility here. We’ve listed below just a general outline of what our hospital recommends:

  • Pick-up from surgery is the same day, during the 90 minutes before we close.

  • Items you go home with that day: 1) an e-collar for your pet to wear for 2 weeks, 2) antibiotics and multiple pain medicines, 3) a packet of detailed post-operative instructions (what is the tplo?, acl injuries in dogs, activity restrictions, aftercare instructions, at-home physical therapy, long-term supplement options, common complications, frequently asked questions)

  • We usually place a bandage and splint that we’d like to remove after 3-5 days. Our technicians can help you with this, and there is no charge for this visit.

  • We usually place skin stitches that we’d like to remove in 14 days. Our technicians can help you with this and there is no charge for this visit.

  • We like to see your pet back after 30 days and 60 days. During these visits, we will assess the leg and we will likely also recommend x-rays to confirm proper bone healing.

Long-Term Outcomes

There is a 95% chance that you’ll be happy with your pet’s long-term healing after the surgery.
Surgery success depends on a few factors:
1. How long has the leg been injured? The longer the injury, the worse the long-term outcome. Arthritis sets in quickly after a torn ACL and meniscus and cartilage damage can occur that we can’t reverse. This can cause pain that we can’t fix surgically.
2. Older animals and overweight animals heal slower and have more complications.
3. Pets that are hyper or hard to confine heal slower and have more complications. These usually are related to delayed healing but can also include stitches that need to be replaced or even surgical infections that need to be treated.

About 40% of pets with a torn ACL eventually develop the same problem on the other leg.

How Warm Springs Pet Hospital Can Help

For about 95% of our TPLO clients, we are not their established regular veterinarian. Rather, we are a second or third opinion and clients reach out to us to perform their pets’ knee surgery - as our costs may be more reasonable - and then they return to their regular veterinarian for future routine care. We are understanding of this and can email our surgical notes to your regular veterinarian for their records and follow-up. We do have very friendly and capable veterinarians on staff for everyday issues, but we may be too far away for some of our long-distance clients.

Our fee for performing a TPLO is $3,500. This is the total cost. It includes all x-rays, IV catheter, blood work, the completed surgery, antibiotics and pain medicines, splint and e-collar. What is not included are the 30 day and 60 day follow-up visit fees - as some clients opt to visit their closer, regular veterinarian.

TPLOs at our office are performed by Dr. Mark Doty or Dr. Cynthia Tao. Both have received advanced training on this procedure and both doctors perform this surgery every week.