Cruciate Ligament Injury

The aim here is to give:

• An introduction to cruciate ligament injury and terminology associated with the condition.
• How we identify cruciate ligament rupture.
• When to consider a conservative or surgical approach.
• What surgical options are available.

The cranial and caudal cruciate ligaments are located within the stifle (knee) joint. They are arranged in a cross formation, hence the name “cruciate” ligament. The function of these ligaments is to help to control the movement of the femur (thigh bone) with respect to the tibia (shin bone). When either of the cruciate ligaments are completely ruptured, the stifle becomes unstable as the femur moves with respect to the tibia. The surface of the tibia (tibial plateau) is at an angle such that it creates a “downhill slope” for the femur to move on as an animal weight bears.
When the cranial cruciate ligament is intact, the femur does not slide down this slope. When the cranial cruciate ligament is ruptured, it does which creates a mechanical lameness (as the animal is no longer able to weight bear properly) but it also causes pain due to the movement and associated inflammation. Longer term, this leads to degenerative joint changes associated with arthritis.

Instability when the cruciate ligament is ruptured may be identified as:
1) cranial drawer – when the femur can be moved with respect to the tibia when feeling the stifle when holding the bottom of the femur and top of the tibia.
2) tibial thrust – when the tibia thrusts forwards when holding the stifle (knee) static and flexing the hock (ankle).

The cruciate ligament can be thought of as a rope like structure, with the multiple fibrils making up the ligament similar to multiple fibres or threads coming together to form a rope. Ligaments can completely rupture due to a single traumatic incident e.g. where a stifle hyper-extends, or they can undergo injury due to a degeneration and rupture of some (but not all) of these fibrils over time, causing what is known as a partial rupture.

A combination of these can also occur where there is degeneration and therefore rupture of fibres but there is not a complete tear, followed by an acute traumatic injury which causes an already weakened ligament to go from a partial rupture to a full rupture.

Cruciate ligament cases can therefore present as:
1) Acute non weight bearing lameness associated with a trauma, where pain localises to the stifle and instability is present. Here the cruciate ligament is completely ruptured with obvious stifle instability.
2) Intermittent lameness where pain localises to the stifle but instability is not obvious. The lameness responds to rest and anti-inflammatories. As exercise is re-introduced, the lameness returns and owners often report that stiffness on rising has started to emerge after rest. Here the ligament is partially ruptured. Pain is due to injury of the ligament, inflammation associated with this will allow for the progression of degenerative joint changes, and is the cause of the signs associated with arthritis.
3) Intermittent lameness followed by an acute deterioration where a dog becomes non weight-bearing. Pain localises to the stifle and instability is present. This is due to an acute full rupture following degeneration and partial rupture of the cruciate. The time between a partial and full rupture can vary from days to months.

When does a cruciate surgery need to be performed?

A common question we get asked is when should surgery be undertaken for dogs with cruciate ligament injury?

Conservative management (crate restriction for 4-6 weeks) can be attempted for cases that fit into the following criteria:
1) instability is minimal
2) the tibial plateau angle is not steep (less than 26 degrees)
3) the patient is <10kg
4) the patient is <8 years old.

Surgical stabilisation is recommended for cases with the following criteria:
1) the stifle is unstable (pronounced cranial drawer, tibial thrust, internal rotation)
2) dogs with steep tibial plateau angles (greater than 26 degrees)
3) any dog over 10kg
4) the patient is >8 years old

Which surgery?

The type of surgery that you dog is offered will depend on a number of factors and the surgeon performing the surgery itself. Factors that are taken into consideration are:
1) Weight of the patient
2) Age of the patient
3) Other underlying medical factors
4) Tibial plateau angle
5) Conformation of the proximal tibia and size of tibial crest
6) Nature of the patient

What surgeries are offered?
1) Lateral Fabella suture. The aim of this technique is to anchor the stifle so that there is minimal front to back movement, as well as minimising internal rotation of cruciate deficient stifle. The idea is that it allows for the body to lay down fibrotic tissue which will then go on to perform this stabilising function within 4-6 weeks of placement.
2) Tibial Plateau Levelling Osteotomy (TPLO) by way of a Cranial Closing Wedge Osteotomy (CCWO). The aim of this surgery is to reduce the tibial plateau angle to approximately 6 degrees, effectively flattening the weight bearing surface of the tibia preventing the tibia from moving forwards when the dog bears weight.
3) Tibial Tuberosity Advancement (TTA). The aim of this surgery is to make the patella tendon at right angles to the tibial plateau which means that the pull of the quadriceps muscle helps to stabilise the stifle.

The CCWO and TTA are dynamic stabilisation techniques that do not eliminate cranial drawer (instability will still be palpable), the aim is for them to create dynamic stability during weight bearing, eliminating tibial thrust (forward movement of the tibia as the dog weight bears).