Whilst in humans, most repair techniques centre around creating a replacement ligament from your patellar ligament, our dogs are too small to really do this.
Many surgeons do now favour an 'osteotomy' technique but not always.
It is fair to say that many dogs will actually do reasonably well in the long term without surgery, but it may takes months. If 1 human year is equivalent to 7 dog years, then spending 3 and a half years recovering doesn't sound that great to me.
So we look to alter the shape of the bones to remove the force that causes the slide. When a dog is standing on its leg, we want the resulting forces to be perpendicular to the tibial surface - as shown by the pink arrow on the right image.
Therefore, we need to alter the functioning angle of the tibial plateau - the surface of the shin bone.
The cuts in the shin bone alter the slope on the surface of the shin bone to alter the way the joint behaves when the dog i standing on the leg and weight is transferred down through the joint. The idea is to change the direction of the force acting upon the knee and actually remove the need for the ligament.
A variety of these techniques have been developed but the technique that I currently favour for most dogs is a relatively new addition - Tibial Tuberosity Advancement or ‘TTA’, show on the far left.
The other main technique involves a curved cut called TPLO - tibial plateau levelling osteotomy, or a straight cut called a Tibial Wedge Osteotomy, shown on the near left. A recent addition to the repertoire is based on rotating the whole top of the shin bone - CBLO.
Tibial Tuberosity Advancement (TTA)
This technique favoured by myself is one of the most recent additions. It is called Tibial Tuberosity Advancement and involves changing the shape of the shin bone.
The tibial crest, where the patellar ligament attaches, is pushed forwards and held in place by a Titanium plate and a cage. The picture on the right shows a post-operative x-ray.
Initially we remove debris from the joint before making a cut in the shin bone. After surgery, healing of the bone will take 6 weeks on average and we generally check progress of bone healing using an x-ray at this point. Many patients are already up to taking on decent walks by this point but we do take immense care not to allow them to do too much, too soon.
In smaller breeds such as terrier breeds, we can also do this, however I tend to remove a triangle of bone from the shin bone. The red lines on the picture (left) show where cuts are made.
I can then rock the surface forwards and close the gap.
This changes the forces acting upon the knee when it is weight bearing.
This is a Tibial Wedge Osteotomy.
These pictures show a West Highland Terrier's knee before and after surgery. You can see how the surface of the thigh bone is sitting right at the back of the shin bone. After surgery , it takes up a more natural position.
A complication of rupturing the cruciate ligament and the resulting instability in the joint is damage to the meniscus. This crescent shaped piece of cartilage evens out the contours between the thigh bone and the shin bone. Damage to it can be very painful, even just very small areas.
When the unstable thigh bone moves during bending of the knee, the meniscus can be crushed - the area in red on the left..
We see all sorts of patterns of damage. The picture on the right shows two areas where the meniscus has torn along its length - shown by the arrows.
Basically this structure does not heal well so we generally have to remove the meniscus or areas of it when damaged.
Unfortunately some dogs can damage this in the days, weeks, or months after surgery
Unfortunately when we damage a joint , we will ultimately develop arthritis, and so will our pets. Regardless of which technique we may choose, arthritis is ultimately going to affect the joint.
Some studies have shown some techniques superior to others, but there is also a breed and individual variation.
Nevertheless, they can go on to have a very enjoyable and active life, with the occasional anti-inflammatory painkiller to help them. Joint supplements can also be beneficial, but one of my key messages must be that you need to make sure they don’t gain too much weight.
I hope these notes go a little way to explaining the nature of the surgery. It is a major orthopaedic surgery but the immediate recovery is remarkably good, in fact much better than that observed by myself with the previously used techniques and we see these patients getting back to a remarkably active life.
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Helping pet owners learn a little about their pet's problem and how to fix it.