Orthopaedic implant

Cassey’s case study

Cassey is an 8-year-old cross breed dog who is in the very lucky position of owning a human who is a Student Veterinary Nurse at YourVets! She developed a lameness of her left back leg and was diagnosed with a ruptured cruciate ligament. This is one of the most common orthopaedic injuries that occurs in dogs.

Cassey the dog

The cruciate ligaments are paired ligaments in the stifle (knee) joint of dogs. They cross diagonally between the thigh and shine bone, and act to stabilise the stifle against twisting, and movement of the separate bones toward the head or tail. Together with the collateral ligaments, which stop the thigh and shin bones moving apart from each other to either side, they are all that stabilises the knee.

Diagram of the canine stifle joint

Diagram of the canine stifle joint, highlighting the position of cruciate ligaments (orange), collateral ligaments (yellow) and meniscal cartilage (green)

Cruciate ligament rupture occurs sometimes in humans, particularly athletes, where a traumatic event causes twisting or over-extension of the knee joint, which makes the ligament break. Traumatic rupture is very unusual in dogs, however, and usually the cause of the ligament breaking is a degenerative disease process in the joint. We don’t know exactly why this occurs in dogs, but risk factors include genetics, conformation, and being overweight. However, this is a very important factor when planning treatment for dogs with cruciate ligament rupture, because around two-thirds of dogs who have ruptured one cruciate ligament are likely to rupture the other within two years, so it is important to rapidly stabilise the injured joint as otherwise the poor patient will end up with two bad legs!

Every time a dog puts weight through a stifle joint where the cruciate ligament is ruptured, the thigh bone is displaced behind the shin bone and tends to slip off the back edge. This causes pain with every step, and can damage the C-shaped discs of shock absorbing cartilage, called menisci, on the top of the shin bone, which causes further pain. Treatment is therefore aimed at stabilising the joint so weight transfer from the thigh bone to the shin bone can resume as normal.

Diagrams showing the normal weight bearing position of the stifle and the displacement of the femur

Diagrams showing:  a. the normal weight-bearing position of the stifle b. displacement of the femur (thigh bone) during weight-bearing in a dog with cruciate ligament instability.

There are several options to treat cruciate injury in dogs, and Cassey had a consultation with Kathryn, the surgeon, to examine her and discuss her lifestyle to choose the option that suited her best. Because Cassey enjoys her walks, she was recommended to have a surgery to change the way the mechanics of the knee joint work by cutting the shin bone and fixing it into a different position. This type of surgery is the most likely of the available treatment options to achieve a return to pre-injury levels of exercise and comfort in dogs. The particular surgery Cassey was recommended to have is called a TTA, which stands for tibial tuberosity advancement.

When a TTA is performed, the surgeon first performs a surgical exploration of the stifle joint itself to check for damage to the joint surfaces, and in particular the menisci. In Cassey’s case, a meniscal tear was identified and was treated within the same surgery. Then, a cut was made down the front of the shin bone to separate off a triangle of bone called the tibial tuberosity, which is where the patella tendon (the thick tendon on the front of the knee that contains the kneecap) attaches. The tibial tuberosity is then levered forwards until the patella tendon is at 90 degrees to the top of the shin bone, and a titanium spacer cage is secured behind it to hold it in its new position. The exact amount that the tibial tuberosity needs to be advanced by is calculated before surgery using x-rays.

Creating a 90 degree angle between the patella tendon and the top of the shin bone means that when weight is placed through the knee joint, the patella tendon pulls the thigh bone forward and prevents it sliding off the back of the shin.

Planning TTA surgery

Planning TTA surgery

Once the advancement has been performed, the tibial tuberosity’s new position is reinforced using a titanium plate. Titanium is a very strong metal and inert, which means a very thin and light plate can be used that will not interfere with normal bone healing. The cage and plate are screwed onto the bone to hold them in position. A bone graft is placed into the gap left behind the tibial tuberosity to try and accelerate growth of new bone into the space.

After surgery, Cassey was able to start walking on her operated leg the very same day as she had surgery! She wasn’t allowed to climb any stairs, get on or off the furniture, chase a ball, play with boisterous dogs, or walk off the lead until the gap in the bone had filled in. Instead, she had an appointment with Hollee, the specialist veterinary physiotherapist at YourVets Smethwick, who performed some treatments to help Cassey to feel more comfortable, and gave her owner some exercises for Cassey to follow at home to help to safely build her activity levels up. Physiotherapy treatment is included in all YourVets orthopaedic packages, and following a physiotherapy program dramatically reduces rehabilitation times and improves outcomes for our patients.

Cassey was seen again 8 weeks after surgery for repeat x-rays of her operated leg. They showed that bone was growing into the defect at a normal rate, and she was finally allowed to walk in the park off the lead and play with her friends again!

However, as you can see, the bone is not fully healed at 8 weeks. Cassey won’t be allowed to return to any exercise that involves jumping until 4 months after surgery, and full recovery can take up to a year.

Cassey's x-ray after initial surgery and 8 weeks later

Images show: a. Cassey’s leg after surgery. b. Cassey’s leg 8 weeks after surgery, showing new bone growth into the defect