Cranial Cruciate Ligament: Injuries and Repair

Anatomy:

The cruciate ligaments are two small ligaments inside of the knee joint. They cross each other (thus the name), and they prevent the tibia (the shin bone) from sliding forwards and backwards relative to the femur (the thigh bone) as well as limit rotation, ensuring that the knee acts like a hinge.  Tearing, or rupture of the cranial (anterior) cruciate ligament, partially or entirely, is very common in dogs. This injury allows the tibia and femur to slip and rotate relative to each other, which stresses the joint capsule, and can lead to a tear in the meniscus, which is the padding between the femur and the tibia.  A torn meniscus will often fold within the joint, and is comparable to a ‘rock in the shoe’.  This is a common reason for a dog to be completely non-weight bearing on the affected limb. The instability from either or both of these tears causes the joint to fill with fluid.  This causes the pain. When the knee joint is unstable long-term, the body will attempt to stabilize the joint by laying down bone around the joint (osteophytes).  This is degenerative joint disease (DJD), also known as arthritis.  Without repair of the ligament, the knee will be a recurring source of pain for the dog, and will go through periods of re-injury over and over, each resulting in more arthritis, decreased range of motion and decreased ability to bear weight.  After one to two years, some patients form enough peri-articular fibrosis to regain partial weight bearing function.

Some dogs rupture their ligament traumatically, but many dogs experience gradual tears over time.  Several breeds including Labrador Retrievers and Staffordshire Terriers are at high risk for chronic tears.  There are studies that are trying to find any possible reasons for this disease that appears to be increasing in prevalence.  Some studies identify a correlation with early spay and neuter programs, but results seem variable amongst breeds and different studies.  Dogs that have gradual tears in one knee, have a much higher risk of tearing the ligament in the opposite knee and on average this occurs within 10 to 24 months.  The top, or plateau, of the tibia, is not parallel to the ground, but has a slope towards the rear.  Steep tibial plateau slopes are correlated with cruciate disease, and are the basis of the TPLO method of repair.

Purpose and Methods of Repair:

The purpose of repair is to stabilize the joint and eliminate the drawer motion, resulting in a stable knee joint that does not cycle through degenerative disease, and thereby help pets to lead active, normal lives after cruciate ligament injury.  The top 3 current methods of repair are Lateral Suture (LS), TPLO, and TTA (chronologically listed).  Both TTA and TPLO are methods of stabilization whereby the bone is cut and plated, while lateral suture is placement of a large, non-absorbable suture outside of the joint.  TPLO cuts and plates the tibia to eliminate significant tibial slope, which limits tibial movement.  TTA cuts the tibia and advances it such that the patellar tendon limits tibial drawer.  Lateral suture prevents tibial movement by use of a suture, often nylon, from the lateral fabella (a small bone behind the femur) to a hole drilled through the tibia.  Several studies have compared various aspects of these methods of repair.  No method has been shown to be superior overall, but did show that any of these methods are most successful in the hands of a veterinarian whom does them on a regular basis.

Here are some interesting facts:  In 2012, Nelson et al demonstrated no difference in ground reaction forces and other indices between lateral suture and TPLO in 38 dogs in the period from 6 months to 12 months post-op.  Au et al, in 2010, found no significant difference in osteoarthritis scores in 65 dogs at 3, 5, or 7 weeks, or 6 or 24 months, post lateral suture or TPLO.  In 2013 Gordon-Evans et al identified a 5 to 11 percent advantage in weight bearing for TPLO vs. LS, and a 93% vs. 75% owner satisfaction score for TPLO vs. LS in 80 dogs.  Cook et al found no significant difference between TPLO and LS based on owner outcome questionnaires.  Molsa et al concluded that a significant number of dogs still experienced chronic pain two and a half years after any type of cruciate surgery with no difference in TPLO vs. LS.  In 2009 Casale et al found a significantly lower number of complications following LS vs. TPLO surgery in 305 dogs.  A 2012 study by Wolf et al, of 458 dogs undergoing 501 TTA’s, highlighted an overall 19% complication rate, with 11% needing a second surgery.  In 2017 Knight et al identified a pivot shift phenomenon (rotation) in TPLO patients that was effectively eliminated by adding a lateral suture to the TPLO.  DeSandre-Robinson et al, in 2017, identified thickening of the patellar tendon in 106 dogs undergoing TPLO or TTA.

I share these numbers not to bore the potential client into submission, but to highlight that if one wanted to sell TPLO’s, one could just share the 93%vs75% study, while someone selling lateral sutures could share one of the other studies. The cost and probability of a second TTA surgery could certainly be persuasive as well.

 

My Opinion:

I have performed countless lateral sutures (thousands) since 1997, and have also had many patients whom have had TPLO and TTA.  These are my thoughts:

  1. The most important decision is choosing to have the knee surgically repaired by a veterinarian whom performs the chosen method of repair often, and in such circumstances, each method (LS, TPLO, TTA) has a high rate of success (>95%).
  2. A tibial slope of greater than 30 degrees is one compelling reason to consider TPLO over other methods. Radiographs of the knee are necessary to evaluate tibial slope.
  3. A patient whom is young, large (>70 lbs) and difficult to keep calm post operatively, may benefit from a TPLO, as the plate is stable a couple weeks before the suture. This may be an advantage in individual cases.
  4. Dogs that are diagnosed and repaired when 50% or more of their ligament is still intact tend to have the absolute best outcomes as pertains to weight bearing, gait normality, and arthritis formation. Therefore, early diagnosis and repair are worthy goals.
  5. Lateral suture has a high rate of success (97%) on dogs ranging from 4 lbs to 155 lbs in my career, and is an excellent option for most pets.
  6. In the next ten years, a cruciate implant will be developed that will be superior to and replace all of these methods.

 

Lateral Suture repair details:

The joint is opened surgically, and examined.  The torn pieces of cruciate ligament are removed.  If the meniscus is torn, the damaged section is removed.  Osteophytes that may cause pain or decrease range of motion on articular surfaces are commonly removed and smoothed.  Polypropylene line, strength and thickness determined by size of patient is placed behind the fabella through the fabellar ligament next to the femur, routed through the joint, placed through a small hole drilled in the tibia, routed under the patellar tendon, (around the circuit a second time in larger dogs) and then tightened to themselves via a Securos tightening and crimping system.  This ‘lateral suture’ takes the place of the cranial (anterior) cruciate ligament.

 

TPLO details:

The joint is opened surgically, and examined.  The torn pieces of cruciate ligament are removed.  If the meniscus is torn, the damaged section is removed.  Osteophytes that may cause pain or decrease range of motion on articular surfaces are commonly removed and smoothed.  The top of the tibia is cut, rotated and plated to a prescribed tibial plateau angle, which thereby eliminates the drawer motion encountered with a torn cranial cruciate.

Expected Results / Risks:

Most dogs will gain complete use of their leg from this surgery, and will experience only mild arthritis in the knee.  Degree of arthritis is related to chronicity of the injury, disposition of the dog, and the success of the recovery period.  Most dogs will experience mild arthritis late in life if the injury is repaired in a timely fashion.  Risks associated with the surgery include infection, implant failure, injury to the contralateral (opposite) knee, and degenerative joint disease.

Recovery:

All methods of repair require a period of 8 to 12 weeks post-operatively where activity is limited but gradually increased over time.  Over use of the leg too soon after surgery can lead to implant failure and need for another surgery.

 

Lateral suture is available at AOSSD or on a travelling basis at veterinary offices in the county.  TPLO is available at AOSSD.