CRANIAL CRUCIATE LIGAMENT DISEASE

Cranial cruciate ligament (CrCL) disease is the most common cause of hindlimb lameness in dogs.  The cranial cruciate ligament in dogs is the same as the anterior cruciate ligament (ACL) in people.  In people, most ACL injuries are traumatic.  However in dogs, the vast majority of CrCL injuries are due to slow and subtle degeneration of the ligament and repeated low-level injury.  Tears can be complete or partial.  CrCL injury is most common in medium to large breed dogs, but smaller breeds can also be affected.

The CrCL runs between the femur (thigh bone) and tibia (shin bone).  It functions to stabilise the knee joint by preventing forward movement and internal rotation of the tibia.  Dogs have a natural backwards slope between the femur and tibia that puts constant stress on the CrCL.  It is important to note that roughly 50% of animals with CrCL injury will injure the ligament in their other hindlimb in 1-2 years.

There are two cartilage pads in the knee joint called the menisci (singular: meniscus), which act as shock absorbers.  Dogs with CrCL injury are prone to damaging their medial meniscus (30-70% of cases).  A torn meniscus is very painful and can contribute to inflammation inside the knee – because meniscal tears occur so commonly with CrCL injury, we always examine the menisci in patients having surgery for CrCL rupture either by arthroscopy (key-hole surgery) or arthrotomy (surgical opening of the joint).  If torn, the damaged portion of meniscus is removed (partial meniscectomy). 

In most cases, damage to the CrCL results in intermittent hindlimb lameness that worsens with activity and improves with rest and pain relief. You may notice that your dog no longer sits square-on to avoid full flexing the knee joint.  In more chronic cases you may also notice reduced muscling to the affected leg.

Diagnosis: 
Most of the time, a strong suspicion of CrCL injury can be made on physical exam.  Your vet will assess for pain in your dog’s knee and apply tests to see if instability is present.  In some patients, sedation may be required.  Radiographs of the affected knee reveals increased joint fluid (effusion) due to the ongoing inflammation.  The ligament itself is not visible on radiographs.  These radiographs also help to plan the surgery. 

Definitive diagnosis of CrCL disease is via direct visualisation of the ligament - performed by arthroscopy or arthrotomy during surgical treatment. 

Treatment Options: 
Many different treatment options have been described for CrCL injury. These are broadly broken down into 3 groups.

1.  Conservative treatment

  • This involves pain relief, activity restriction, weight management and cartilage health promoters (Zydax or Cartrophen injections). 

  • The success rate is <40% in large dogs and <85% in small dogs (<15kg) but on average requires 12 weeks of restriction and invariably leads to progressive arthritis in the knee joint. 

  • Many studies have shown inferior outcomes compared to surgery.

  • Conservative management is rarely recommended for management of CrCL injury.

 

2.  Extracapsular repair 

  • This involves placement of a prosthetic ligament made of nylon or braided polyester that is placed on the outside of the joint mimicking the natural CrCL.

  • The advantages of this procedure include ease of application, lack of need for specialised equipment and relative cost.

  • Disadvantages include the increased risk of arthritis and inferior outcomes compared with osteotomy procedures.

 

3.  Osteotomy procedures (TPLO)

  • Many osteotomy procedures have been described but the preferred surgery is the tibial plateau levelling osteotomy (TPLO).

  • The TPLO involves changing the anatomy of the knee joint by cutting and rotating the tibia – this stabilizes the knee joint despite the lack of CrCL.

  • Several studies have shown superior outcome of TPLO compared to extracapsular techniques as well as other osteotomy procedures.

  • A good to excellent outcome is expected in 95% of cases.