CRANIAL CRUCIATE LIGAMENT DISEASE (known in people as ACL tear)
ABOUT THE PROBLEM
Cranial cruciate ligament rupture (tear) (CrCLR) is the most common cause of hind leg lameness in dogs. Because CrCLR always leads to osteoarthritis, it is also the most common cause of arthritis in dogs.
Lameness occurs with cruciate tears for two primary reasons:
1) Mechanical instability of the joint
2) Inflammation (arthritis) of the joint
Despite extensive research for years, the cause of CrCLR remains a chicken-or-the-egg problem for veterinary medicine: did the ligament rupture because it was weakening in a joint that was already arthritic, or did the joint become arthritic only after the ligament ruptured?
CrCLR is inherited in Newfoundlands, with a heritability index of 0.27. It is strongly suspected that Labrador Retrievers, Rottweilers, and Bichon Frises have the same recessive trait.
At the time of diagnosis of CrCLR in one leg, Up to 30% of large breed dogs have also ruptured the ligament in the other leg. (Rupture of the ligament in both legs is less common in small breeds.)
Of the large breed dogs that have ruptured the ligament in one leg and not the other, 50% or more will ultimately rupture the ligament in the other leg. This may happen in weeks, months, or years after the rupture of the first one. The additional weight load on the leg without the rupture is not the primary reason why the second rupture occurs. There are unfortunately no good predictors for rupture of the second cruciate ligament but it is very likely we will eventually have a reliable genetic test. Given the high probability that it will occur, it is wise to use therapies (e.g. anti-inflammatory medications and supplements, weight loss and exercise management) to improve and maintain the dog’s overall orthopedic health status.
CAUSES AND PREDISPOSING FACTORS
In small breed dogs CrCLR is most often associated with sudden trauma or chronic patella luxation (slipping kneecap), with the probable exception of Bichon Frises.
In large breed dogs there are two versions of the problem:
1) A very small number of large breed dogs have no preexisting evidence of CrCLR and tear the ligament suddenly. This usually happens during very energetic activity.
2) The vast majority of large breed dogs have arthritis in their knee at the time of CrCLR. A slow degeneration of the ligament has occurred due to an unknown cause or causes, and the ligament weakens until it ruptures, even with modest or no activity.
Other than genetics, obesity and aging appear to be the most significant risk factors for degeneration and rupture of the CrCL. Other factors include an excessively straight hind leg anatomy and immune-mediated joint disease. Neutering has been suspected but not proven to be a risk factor. Two anatomical problems, excessive patellar ligament - tibial plateau angle and increased tibial plateau angle, have been associated w CrCLR in some studies but not others.
Eighty to 90% of dogs with CrCLR are diagnosed by the presence of a positive cranial drawer sign. Cranial drawer is a manipulation that veterinarians are trained to do; it is a simple procedure to perform, but results can be difficult to interpret. Also, in my experience, many patients with CrCLR are negative for cranial drawer when awake and positive for cranial drawer when under general anesthesia.
A medial buttress is a firm swelling over the inside of the knee. It develops within days to weeks of CrCLR and it remains forever. Because it is present in almost every dog with CrCLR it is particularly useful for raising the level of suspicion high enough that further diagnostics are clearly worthwhile. It is sometimes present when the cranial drawer is negative, indicating a probable partial CrCLR.
In addition to a positive cranial drawer sign and a medial buttress, dogs with CCrLR often have other evidence on physical exam that aids in diagnosis. Lameness varies from completely non-weight-bearing to no lameness at all, and from persistent to intermittent. Some dogs will have a decreased range of motion in their knee. Some, but, interestingly, not all dogs will be painful during non-weight-bearing examination of their knee. Cranial tibial thrust is another exam technique veterinarians are trained to perform; it is somewhat more difficult to do and to interpret, and it is positive in some dogs with CrCLR. Dogs who have lameness for weeks to months usually have detectable muscle atrophy.
At YVC, if we suspect CCrLR on the awake exam we recommend orthopedic evaluation under general anesthesia as the next step. This evaluation includes palpation of all four legs and the spine and x-rays of the rear legs, pelvis and lower spine. General anesthesia is essential for proper positioning for x-rays and complete, accurate palpation results, even with the most laid-back, cooperative patients. This thorough evaluation allows us confirm the diagnosis of CrCLR, and to detect other orthopedic problems that might have led to the ligament rupture or that might complicate the patient’s recovery.
The degree of arthritis is not of value in making treatment decisions, though, because scientific studies have shown there is no correlation between the diagnostically determined degree of arthritis and the degree of lameness and measurements of gait. In other words, some dogs with arthritis that appears mild will not respond well to medical or surgical treatment, and some dogs with arthritis that appears severe will respond very well to treatment.
CrCLR is not a curable problem; this is true for a number of reasons. The two most important are:
1) CrCLR always results in a mechanically unstable knee. Surgery to restore stability can be done, and is usually recommended, but the surgically restored mechanics will never completely duplicate normal mechanics.
2) CrCLR always results in osteoarthritis (OA), and OA is always a progressive and degenerative problem. Using the combination of surgery and medical treatments we can usually manage OA very effectively, but there is no way to stop or reverse it.
Most of our clients want to know if their pet will eventually return to normal activity, including running and other athletic pursuits. The most accurate answer that we can give is that most, but not all, pets eventually return to normal activity with minimal or no signs of lameness.
Put another way:
A prognostic point that we believe is very important for a pet owner to understand is that there is no way to know how every patient will respond to the chosen treatment. The scientific evidence and our clinical impression are that somewhere between 5 and 20% of dogs with CrCLR will not respond as well to treatment with medical therapy and surgery as the other 80 to 95% of patients.
Going a step further, another one of our clinical impressions for which there is scientific evidence is that there is no way to predict which patients will respond less well to treatment: some dogs with very minimal evidence of OA at the time of diagnosis will have prolonged and ultimately unsatisfactory recoveries, and some dogs with severe OA at the time of diagnosis will make rapid and excellent recoveries.
The flip side of this perspective is, in our opinion, the best way to view the prognosis: 80 to 95% of dogs with CrCLR will make good to excellent recoveries when treated with surgery and medical therapy.
AN OVERVIEW OF SURGERY AND MEDICAL THERAPY
Surgery and medical therapy are the two treatment options for dogs with CrCLR. Statistically, 81 to 100% of large breed dogs will remain lame without surgery, and 73 to 90% of small breed dogs (less than 20 lbs) and cats will have their lameness resolve with a combination of exercise restriction, weight loss, and physical therapy.
CrCLR always results in arthritis in affected knees, it always results in a mechanically unstable knee, and it always results in periarticular fibrosis (scar tissue around the knee). The fibrosis will re-stabilize the joint to some degree (often to a large degree and occasionally completely), but it takes months to years for that process to provide significant help and, until it does, the arthritis is probably progressing much more quickly than it would in a stable joint.
Despite extensive research, there is no known medical treatment that will restore a ruptured ligament to good health and no known medical treatment that will re-stabilize the knee. Surgery is currently our only option for stabilizing the knee.
We recommend medical therapy for all patients that are diagnosed with CrCLR.
CrCLR always results in osteoarthritis in the affected knee. Osteoarthritis (OA) is always a progressive, incurable problem, but medical therapy is usually very successful at slowing the progress and minimizing the symptoms.
We recommend starting medical therapy for OA as soon as a diagnosis of CrCLR is suspected. Medical therapy has several different components. Almost all of our CrCLR patients begin with a regimen that includes pain medication, exercise/activity management, weight control, and two supplements (joint protective compounds such as glucosamine/chondroitin and fish oil). Additional options include laser therapy, intra-articular injections (injections into the knee), and stem cell therapy. Therapy is tailored for each individual dog.
SURGERY OR NO SURGERY?
The question that most dog owners have immediately after their pet is diagnosed with CrCLR is whether or not to pursue surgery.
When medical therapy without surgery is used the usual progression of events is usually:
1) A period of 2 to 4 weeks of obvious lameness, followed by
2) 6 to 12 weeks of gradually improving lameness, followed by
3) Significant and gradually increasing life-long lameness due to OA.
Because of the false confidence that the dog is genuinely improving that phase (2) can instill, when an owner would like to try medical therapy before deciding for or against surgery, I recommend making this decision within 2 to 4 weeks after diagnosis. It is still often reasonable to decide for surgery after 4 weeks, but owners should be aware that beginning about 12 weeks after diagnosis surgery becomes significantly less likely to result in significant improvement.
In cases when the dog has apparently torn the cruciate ligament as a purely traumatic event (this is not the most common situation) and had a completely normal knee prior to the tear, then our usual recommendation is to have surgery as soon as possible.
There are several different surgeries that can be used for re-stabilizing the knee with CrCLR. They fall into two categories, extracapsular repair and geometry modifying surgery. With extracapsular repair a suture, usually made of nylon (it looks like ultra-heavy fishing line) is surgically placed in a position outside the joint that allows it to provide stability in the same way the ligament once did.
With geometry modifying surgery, the tibia (the lower bone in the knee) is osteotomized (cut), re-positioned, and held in place with a special bone plate or other metal implant. This type of surgery has the possible (not definitively proven) advantages of correcting angles that were abnormal in the knee and minimizing the mechanical forces that led to the ligament rupture.
At YVC we have many years of experience performing extracapsular repair surgery. We also are familiar with local board-certified orthopedic surgeons that we can refer clients to when they want to pursue geometry modifying surgery.
Despite intense and extensive research it is still not clear whether one type of surgery is better than the other. Our patients have had good, excellent, and less-than-ideal outcomes to both types of surgery. Many veterinarians have the opinion that geometry modifying surgery is preferable for larger, more athletic dogs, but, again, there is not currently definitive evidence that this is true. A few considerations that seem to have been important to our clients when they are making this decision:
- Geometry modifying surgery is three to four times the cost of extracapsular repair surgery.
- Geometry modifying surgery is significantly more extensive and involves significantly larger implants than extracapsular repair surgery.
- If we achieve a less-than-ideal outcome with extracapsular repair surgery, the patient can still have geometry modifying surgery. If geometry modifying surgery does not work well, there is no second surgical option that can be pursued.
ANOTHER SURGICAL CONSIDERATION: ARTHROTOMY
An arthrotomy is a surgical incision into a joint. A knee arthrotomy is needed to inspect the inside of a dog’s knee, and to remove a torn meniscus. (In people this is often done with a tiny incision and an endoscope, but even the largest dog’s knee is small enough that endoscopy is usually not a viable option, and the high cost of endoscopy equipment and difficulty of obtaining adequate training make endoscopy a seldom-used procedure in veterinary medicine. Also, recently a landmark, placebo-controlled human trial demonstrated that arthroscopy of the knee may not provide improved results compared to not invading the joint at all.)
Currently most veterinary surgeons will perform an arthrotomy as a routine part of every knee surgery for CrCLR. But recovery from an arthrotomy is the most difficult part of recovery from knee surgery for a dog. Also, treatment of most meniscal injuries has not been proven to result in better long-term outcomes.
For these reasons we avoid arthrotomy whenever possible. Our approach to knee surgery is to carefully palpate the patient’s knee immediately before and immediately after anesthesia for surgery; if there is evidence of a torn meniscus in addition to the torn cruciate ligament then we will usually do an arthrotomy in addition to restabilizing the joint. If there is no evidence of a meniscal injury then we restabilize the joint without an arthrotomy. Medical therapy for CrCLR is essentially medical therapy for arthritis, with a focus on the hind leg and knee.
Research has greatly enlightened us but has yet to yield substantial improvements in medical therapies for CrCLR. Until it does, surgery will remain a necessary treatment option for most dogs with the problem.
SURGERY AT YVC
The following is an excerpt from the information we provide when a patient is discharged from YVC following knee surgery:
HOSPITALIZATION AND SURGERY Patients are admitted in the morning on the day of surgery. Following their procedure, they remain hospitalized overnight and they are discharged the next day.
POST-SURGICAL CARE - PHYSICAL THERAPY Cruciate surgery patients have a skin incision that is not covered by a bandage or a splint. Most dogs do not lick at their incision, but they may go home with a protective collar that should be used at least whenever the patient is left unobserved. Some swelling, redness and bruising are common. Rarely, a patient will develop severe edema (swelling) from the knee down to the foot within a few days of surgery. This condition is not painful, typically resolves quickly with little or no treatment, and does not affect the ultimate outcome of the procedure.
Dogs usually carry their operated leg for up to two weeks following surgery. From the time they start bearing weight they usually progress to a sound walk and trot in two to three months (A "sound walk and trot" is not necessarily the same thing as "no lameness". Most patients are still lame to some degree at this time. Most patients continue to improve for several months, even a year or more from the time of surgery. It is not possible to predict with certainty if or when lameness will completely resolve.)
Exercise is severely restricted for the first two weeks, and increased just a bit for weeks 2 to 4. This means very short leash walks for the purposes of urinating, defecating and getting a bit of fresh air. Patients that are prone to being very active indoors may need to be confined to a crate or a small area. Most dogs are sure-footed enough on three legs to climb stairs but they should not be allowed to do so unassisted. They must be lifted in and out of the car.
Starting with week five, leash walks of gradually increasing duration are done at least twice and up to four times daily:
Week 5 - 5 minute leash walks
Week 6 - 10 minute leash walks
Week 7 - 15 minute leash walks
Week 8 - 20 minute leash walks
Swims of the same duration are acceptable, but running on the beach is not! Patients must be carefully led on leash into the water.
Gentle massage and gently flexing and extending the operated knee, for 5 to 10 minutes at least once daily during this time is also important.
Beginning with week 9 post-surgery and progressing to week 16, a GRADUAL return to normal duration and intensity of activity is encouraged. A leash must be used if the intensity of the patient's activity cannot be controlled when they are unleashed.
POST-SURGICAL CARE - MEDICAL THERAPY Despite years of extensive study, the causes of cruciate injury remain elusive. Our perspective on this problem focuses on two points:
1. Most dogs do not suffer a cruciate tear simply as a consequence of trauma to the knee; instead, they have multiple underlying conditions that predispose them to cruciate tears.
2. Many, if not the majority of dogs that tear their cruciate ligament in one knee will eventually tear the ligament in the other knee.
Because of this perspective we utilize short-term post-surgical medical therapy and we strongly recommend long-term medical therapy.
SHORT-TERM MEDICAL THERAPY We will use a pain control medication for at least 2 to 4 months after surgery. Sometimes we will use other medications in the short-term, including additional pain medications, tranquilizers, and antibiotics.
LASER THERAPY Application of laser light to body tissues stimulates healing and provides pain relief in a variety of ways. It is non-painful - people receiving laser therapy report that it feels good, and our patients often behave as though it does - and only takes several minutes per treatment.