Rupture of the CrCL is one of the most common reasons for hind limb lameness and osteoarthritis formation in dogs.
The cranial cruciate ligament (CrCL), also known as the anterior cruciate ligament (ACL) in people, is one of the most important stabilizers of the canine knee (stifle) joint. This ligament has several functions, including prevention of the thigh (femur) bone sliding down the back of the shin (tibia) bone and the shin bone moving forward against the thigh bone. This happens because the plateau of the shin bone where it inserts is flat in people but has a slope in dogs.
The meniscus, is the cushion pad of the stifle. There are 2 menisci per knee (one medial or inside, and one lateral or outside). They are located in between the thigh and shin bones. They are responsible for shock absorption, position-sensing, and load-bearing. They can become damaged when the CrCL is ruptured, especially so the medial meniscus, that is much more frequently affected due to variance in the attachment to the surrounding structures.
Contrary to people, in dogs cranial cruciate ligament rupture more often is a result of degeneration rather than the result of a sudden trauma to an otherwise healthy ligament. Partial tearing of the CrCL is common in dogs and almost always progresses to a full tear over time.
Cruciate disease is multifactorial. Factors that influence degeneration of the ligament include activity level, obesity, poor physical condition, genetics, conformation (skeletal shape, configuration, and additional issues with for example the knee cap – patellar luxation), and breed.
Cranial cruciate ligament disease can affect dogs of all sizes, breeds, and ages. However, it is less commonly seen in sighthound breeds as well as cats. In those patients it is more likely to be trauma related. A genetic mode of inheritance has been shown for Newfoundlands and Labrador Retrievers but it is suspected to be present in most dog breeds.
Both, overweight and high activity levels are the more common additional risk factors for the development of CrCL disease. Consistent lower impact physical activity to strengthen muscles and keeping dogs at a lean body condition is recommended. While it is helpful to maintain a well muscled dog at a good weight, it will not necessarily prevent CrCL disease as we are currently unable to treat the degenerative forces inside the joint as well as the genetic component.
Clinical signs can vary as dogs try to prevent us from noticing that there is an issue. Dogs also don’t tend to cry or vocalize and signs are often much more settle.
Signs can include but are not limited to difficulty standing up from a sit and/or laying down, extending the leg when sitting (“positive sit test”), difficulty or unwillingness to jump, decreased activity level, lameness – this is sometimes only noted after long periods of rest and gets better as the day goes on; muscle atrophy (decreased muscle mass in the affected leg), and decreased range of motion of the knee joint. Sometimes a popping or clicking noise can be heard (this could indicate a meniscal tear), as well as stiffness.
As already mentioned, pain and discomfort are expressed differently in people compared to dogs. While dogs may not whine/cry out, or hold up their affected limb constantly, the persistence of their lameness is a sign of pain.
Cruciate tears can often be diagnosed from an orthopedic hands-on exam alone. Diagnosis is made upon eliciting forward motion of the shin bone against the thigh bone, which is called the cranial drawer sign or, a little different but a similar concept, the tibial thrust test. This is easy in acute, complete ruptures, but may be more subtle in chronic or partial tears. Sedation to allow muscle relaxation and radiographs to demonstrate arthritic changes and effusion (more fluid in the joint) along with thickening of the joint capsule (scar tissue formation) may be necessary to obtain a diagnosis. Generally, radiographs are only required if surgery is performed to allow for surgical planning. However, radiographs may help support the exam findings in difficult cases and also help exclude other issues that we may not be able to identify as easily with an orthopedic exam alone.
Because CrCL tears are one of the most common orthopedic injuries we see in dogs, many treatment options are available for cruciate injury. The first major decision is between surgical treatment and non-surgical/conservative treatment.
Surgical treatment is typically the best treatment for cruciate injury for most otherwise healthy patients as it is the only way to permanently control the instability present in the knee joint and the pain it causes as a consequence of the loss of normal CrCL structural support.
In humans, the cruciate ligament is often replaced with a graft. This has not been very successful in dogs so far. However, there are several other treatment options.
Osteotomy-based techniques require a bone cut (osteotomy), which changes the forces on the knee joint and prevents instability when walking. One of these procedures (the TPLO procedure) is currently considered the gold standard because of their consistent outcomes in most patients and reduction in the rate of arthritis formation:
Tibial Plateau Leveling Osteotomy (TPLO) This is a procedure where a semicircular blade is used to make a cut through the upper shin bone in order to rotate the plateau of the shin bone to a flat plateau, like people have. With this procedure the biomechanics are changed so the dog doesn’t need the CrCL anymore. Unlike people, they cannot tear the same side again.
The cut in the bone is then stabilized with a plate and screws. Once the bone has healed, the plate and screws are no longer needed, but they are rarely removed unless there is an issue noted such as irritation or infection. This procedure has consistent outcomes, and the majority of dogs can go back to an active lifestyle after they have healed. While it sounds invasive, dogs recover quite well from this procedure with weight bearing shortly after surgery (24-48 hours for most dogs). Healing typically takes about 8 weeks.
- Tibial Tuberosity Advancement (TTA) requires a linear cut along the front of the shin bone. This piece is then advanced forward to neutralize forces around the knee. The cut in the bone is then again stabilized by a plate and screws. Similar to the TPLO, this procedure requires several weeks of confinement while the bone heals.
- CORA-Based Leveling Osteotomy (CBLO) is similar to the TPLO, but changes where the cut is placed on the shin bone. This procedure can be useful in young animals with open growth plates or sometimes in dogs with excessive plateau angles.
Suture-based techniques involve placing suture to mimic what the intact cruciate ligament does in the dog. However, they are located on the outside of the joint since we have not been successful with suture implants inside the joint. This leads over time to stretching out or even breaking of the suture. Therefore, the goal for these procedures is to have the body lay down scar tissue on the outside of the joint before the suture breaks or stretches too much and stabilize it that way.
- Extra-capsular suture stabilization (also called “lateral suture stabilization,” or “fishing line technique”). In this procedure, heavy suture is placed outside of the joint that runs in the same direction as the cranial cruciate ligament. The most common complications after this procedure involve failure of the suture and development of arthritis. While this technique is often less costly, it may not be the best choice for lots of patients due to the complications.
- The Tightrope® utilizes a specifically developed suture and toggle implants that are placed in holes drilled through the thigh and shin bones. This allows more accurate placement of the implant and better “suture” strength compared to the extra-capsular suture. However, stretching out, or breaking of the suture can still happen. Sometimes, this procedure is necessary to add on to a TPLO if there is residual instability after appropriate flattening of the plateau angle.
Non-surgical treatment usually involves a combination of pain medications, exercise modification, joint supplements, physical rehabilitation, and possibly braces/orthotics.
- Activity restriction and anti-inflammatories – While administration of pain medications in dogs with cruciate disease may improve their comfort, knee pain persists because of continued knee instability. For this reason, activity restrictions and modification (e.g., low impact leash-based activities) are typically most effective. Over time, the body may stabilize the knee joint with scar tissue, but the knee is predisposed to reinjury when the patient is active in the future. Osteoarthritis also progresses during this time.
- Rehabilitation therapy – Rehabilitation may help strengthen the muscles around the knee joint and can help dogs cope with partial cruciate tears for a while.
- Custom knee bracing/orthotics – Custom knee bracing is relatively new to canine orthopedics and there is little information on outcomes. Braces can be pricey and have potential complications such as sores, continued pain, and patient intolerance.
- Intra-articular injections – There are various options available for injectable therapies that can be used to attempt to address cruciate ligament injury. Platelet-rich plasma (PRP) or autologous conditioned plasma (ACP) is a specialized blood product made by concentrating a patient’s own platelets. The concentrated platelets can be used to supplement the patient’s own growth factors to improve the recruitment of cells to an injury site. Joint injections do not replace surgery in most cases but are rather supplemental. PRP is currently under investigation to be given into the joint alongside the TPLO with promising outcomes.
Aftercare and Outcome
Appropriate postoperative care at home is critical to a good outcome.
Activity must be restricted for about 8 weeks after surgery to ensure that there are no complications with the implants or healing after surgery. This is done with a mix of calming medications and confinement, such as a crate, pen, or small room without furniture. Surgical complications can include but are not limited to infection, dehiscence of the suture (breaking of the suture), implant breakage (breaking of the plates or screws, stretching of sutures), fractures of the shin bone, meniscal tears, continued lameness, arthritis progression, and muscle loss.
The long-term prognosis for animals undergoing a TPLO is quite good, with reports of significant improvement in 85-90% of the cases. While arthritis can progress over the years regardless of treatment type, it’s expected to be at a slower rate when a TPLO surgery is performed compared to medical management.
Since this is a degenerative process with a genetic component in most dogs, it’s important to note that up to 50-60% of patients will develop the same condition in the other knee within 12 months of diagnosis regardless of the treatment chosen.
Veterinary Orthopedic Specialist as United Vision Pet Partners
If your pet is limping or painful on a limb, then please schedule a consult at UVPP by calling (610) 983-8381. Dr. Michaela Gruenheid is a board-certified surgeon who performs comprehensive orthopedic examinations along with diagnostics such as radiographs or CT scans, when necessary. Dr. Gruenheid will provide you with a personalized assessment along with recommendations and surgery, if indicated.