What is it?
The cruciate ligaments are a pair of structures in the stifle (like our knee) joint of the dog. These (especially the cranial cruciate ligament or CCL) may rupture or break, causing severe lameness and instability in the joint.
What causes it?
In the majority of cases, the rupture is due to degeneration of the ligament that occurs over some weeks or months before they fail completely. However, an otherwise healthy ligament can rupture if overloaded (typically if the dog slips when running and changing direction fast). The exact cause of the degeneration isn't clear, but is probably due to very mild overloading over months or years, and to some extent to the dog's genetics.
What dogs are at risk?
The biggest risk factor is obesity - a heavier dog means more load on the ligament and more risk that it will start to degenerate. In addition, certain breeds (such as Labradors) are reported to be at higher risk, and there is a (very slight) increase in risk in neutered dogs compared to entire ones.
What are the symptoms?
Cruciate ligament injuries almost always present with moderate to severe lameness. This may appear suddenly ("acute lameness") or more gradually ("chronic lameness"), depending on the exact type of damage. In addition, you may notice a swelling on the inside of the leg, over the joint (this is sometimes called a "medial buttress").
How is it diagnosed?
If the ligament has ruptured, it is possible to move the tibia (shinbone) forward relative to the femur (thigh bone) - this is called cranial draw. When we examine your dog, we may find this sign, but more often we will book your dog in for X-rays; when they're sedated for the X-ray, this cranial draw is much more obvious and will confirm the diagnosis.
How can it be treated or managed?
In dogs under 8kg, the ligament my heal on its own, given strict rest and a very gradual reintroduction to exercise, possibly involving hydrotherapy. However, in heavier and larger dogs, this is very unlikely, and surgery is usually required. There are several different surgical procedures available, and which we'll use depends on the dog in question and the configuration of their stifle joint. The most common surgical procedures are ligament replacement (like a fabellar suture, where an artificial fibre is used to replace the damaged ligament); tibial tuberosity advancement (TTA and MMP operations, where the front of the tibia is cut and moved, so the cruciate ligament isn't needed any more); and tibial plateau levelling osteotomy (TPLO, where the bone is cut and rotated to stabilise the joint without needing a cruciate ligament). The great advantage of bone surgeries (TTA/MMP and TPLO) are that the dog will be up and able to walk within 24 hours, whereas the ligament replacement surgeries require longer. In all cases, however, the dog will need a very gradual return to exercise, and often physiotherapy or hydrotherapy. Too early return to exercise will result in the repair breaking down, and may result in breaking of the affected leg.
Can it be prevented?
To some extent yes - don't let your dog get overweight or obese! That's the best way to minimise the risk - dogs of a healthy weight are at significantly lower risk.