The cranial cruciate ligament (CCL) is an important stabilizing ligament of the knee joint. Specifically, it prevents forward thrusting of the tibia whenever the animal steps. This tendency for forward thrusting of the tibia is a natural process due to the distribution of tendon forces exerting tension in the area. Rupture of this ligament leads to acute, severe instability of the knee joint. This injury occurs most commonly in medium to large breed dogs, but is seen occasionally in small dogs and cats. Predisposing factors that may lead to this injury are:
1.) High performance dogs, such as agility competitors.
3.) Sedentary lifestyle with only occasional periods of play.
4.) Genetically inherited steep tibial plateau angles sometimes seen in large breed dogs.
Specifically, the affected dog presents at first with toe-touching to non-weight bearing lameness. There is often significant swelling of the affected knee joint, with moderate to severe pain when the joint is manipulated. On physical examination, dogs and that have ruptured their cranial cruciate ligament have what is called a cranial drawer sign. This is when the femur (thigh bone) is held stationary, and the veterinarian can pull the tibia (chin bone) forward. This should not occur in a normal knee joint.
Left untreated, the instability of the knee causes chronic pain, arthritis, and imminent degenerative joint disease. Treatment is surgical stabilization of the knee joint.
There are many different surgical procedures utilized for cranial cruciate ligament rupture. In the past generally accepted notion was that bone cutting techniques, such as tibial plateau leveling osteotomy (TPLO) or tibial tuberosity advancement (TTA), edged out other popular surgical techniques where stabilization is provided outside the joint capsule with a suture placed outside the knee joint capsule (aka., extracapsular), in terms of overall effectiveness. It was generally accepted that the difference in effectiveness of TPLO or TTA over extracapsular suture was most evident with larger breed dogs 40 pounds or greater. However, the combination of the advent of an extracapsular suture technique that is superior to all past suture techniques for repair of CCL tears in dogs called the tightrope; and with subsequent surgical comparisons having been subject to extensive study, we now know that this particular extracapsular suture technique stacks up quite well with the bone cutting techniques.
There is a recent variation of the TTA called the Modified Maquet Procedure (MMP) that is quickly gaining favor since it is requires less hardware than traditional TTA (see more on this in the detailed procedure explanations below).
The main difference in effectiveness of the bone cutting techniques versus extracapsular suture in certain patients generally has to do with the patient’s size and with the angle of the tibial plateau (the angle of the top of the shin bone that articulates with the femur). Larger dogs with excessively steep tibial plateau angles of greater than 30 degrees tend to do better with bone cutting techniques. The reasons for this are the following:
1.) Steep tibial plateau angles predispose to CCL rupture in the first place due to the resultant pull the steep angles place on the CCL ligament. TPLO or TTA stabilize the knee by reducing excessively steep tibial plateau angles, changing the physics of the knee such that the joint no longer relies on the CCL ligament. This will be further clarified below as each procedure is described in detail.
2.) If a CCL rupture in a knee with excessive tibial plateau angle is repaired with an extracapsular suture, with the steepness of the tibial plateau always having the tendency pull on the suture, over time, this could cause the suture to stretch and lose some stabilization over time. Even in cases where there is not an established excessively steep tibial plateau in large to giant breed dogs, a suture repair technique could run the risk of gradually stretching over time. These points will also become more clear once each procedure is described below.
While tightrope is commonly performed in patients over 40 pounds even with tibial plateau angles greater than 30 degrees with reasonably high rates of success, for dogs with CCL tears that are under 40 pounds and have tibial angles of less than 30 degrees, extracapsular tightrope becomes an even increasingly viable and acceptable option. However, I may still favor the bone cutting MMP procedure depending on the patient’s age, lifestyle, and other conformational/anatomical considerations. For particularly active, stout, and/or muscular, middle aged to younger dogs that fall in this category, I may still steer the client toward selecting the MMP due for the subsequent lack of reliance on a suture for the same considerations I steer large and giant breed dogs toward bone cutting CCL repair procedures: concern for gradual stretching of the suture.
In the past, regardless of the procedure chosen, one aspect of CCL repair in dogs was to open the joint to address concurrent tears of the medial meniscus that that commonly occur in cases of CCL tear. The medial meniscus is the cartilage on the inside edge of the knee that cushions the articulating surfaces of the bone bones that form the joint. It was once universally believed that no matter how stable we make a joint with suture or surgical flattening of the tibial head, a meniscus must be addressed and repaired as well since it is a significant contributing factor to lameness in 80% of dogs with CCL tears that experience concurrent medial meniscal tears.
From a physiological perspective, this really did not make much sense since cartilage padding that has no never endings or blood supply and as such should not realistically cause pain if injured. As such, this point has been challenged for years and many studies have been published to try to prove or disprove the clinical benefit of opening the knee joint to repair the meniscus and not one single study has proven proves that repairing a torn meniscus leads to a better long term clinical benefit in cases where the canine knee is surgically stabilized following a CCL tear. According to renowned British veterinary surgical specialist, Dr. Malcom Ness most veterinary surgeons in Europe have abandoned addressing the meniscus, focusing only on stabilization of the knee joint, refraining from opening the joint at all, and subsequently observing much quicker time to weight bearing as a result for the past 20 years.
Interestingly, the human literature seems to suggest the same concept in the case of meniscal tears in people. According to a July 2014 abstract in the The World Orthopedic Journal, many studies have failed to achieve consensus on whether or not there is clinical benefit to surgical repair of the meniscus in people.
Still, while a number of veterinary surgeons in the US still insist on inspecting the meniscus and repairing it if injured concurrently with a torn CCL, many are increasingly following the European model of leaving the inside structures of the joint alone and focusing repair efforts on stabilization of the knee.
In the tightrope procedure, the knee is stabilized with a soft but very strong (250 pounds of tensile strength) suture called fiber tape. This procedure is best illustrated in the picture below:
Tibal Plateau Leveling Osteotomy (TPLO)
In TPLO, The philosophy behind the surgery is to change the angle of the Tibial Plateau, which is the area where the Femur and the Tibia interact and communicate. By doing so, this eliminates the need for the CCL ligament entirely and returns stability to the joint itself by flattening the head of the tibia and eliminating shear forces across the plateau (the main function of the CCL ligament is to counter shear forces that inevitably pull the tibia forward when walking and running. In order to accomplish this, a portion of the head of the tibia is cut, rotated, and plated in place. The diagram below shows how this works:
Tibial Tuberosity Advancement (TTA)
In TTA, like TPLO, the angle of the tibial plateau is also flattened, but in a somewhat different manner. Instead of cutting and rotating the entire tibial head, a smaller portion of front part of the bone called the tibial tuberosity is cut and extended forward. A relevant analogy as to how this works would be to consider a steep ramp. By extending the length of the ramp, one can effectively decrease the steepness of the angle of the ramp. In the same manner, the TTA, decreases the angle of the tibial plateau:
Modified Maquet Procedure (MMP)
The MMP is really little more than a modification of the TTA in that it has a net effect of flattening the head of the tibial with the insertion of a titanium wedge called Orthofoam. The main difference between traditional TTA and the MMP is that the MMP does not require any screws to keep it in place. The titanium Orthofoam wedge that is placed consists of a very strong but semi-porous matrix that grips the surrounding bone and facilitates bone formation around and within its structure. The gripping effect enables only the placement of a small pin and staple to keep it in place, significantly reducing surgical time and invasiveness; leading to quicker weight bearing and healing (4-6 weeks versus 8-12 weeks with other procedures):
My preference as I have already stated is MMP with occasional consideration for tightrope depending on the individual age, lifestyle, and unique anatomic characteristics of each individual patient. I opt not to explore the joint and leave the meniscus alone. In the end, however, all of these procedures are well accepted means to repair CCL injuries in dogs and cats, regardless of size and physical characteristics. A wise surgical mentor of mine once said, “When it comes down to it, the best CCL repair procedure to choose for any given case is the procedure the individual surgeon is most comfortable with.” These guidelines are presented to you here in this article to offer you a guide to choosing the procedure you are most comfortable with and to be able to ask your veterinary surgeon the right questions.
Post-Operative Rehabilitation & Care
Following surgery, the goal is to have the patient using the limb as quickly as possible. As such, I do not recommend any kind of bandaging or splinting of the operated limb. Some more stoic varieties of dogs will drop the toe down and gingerly weight bear within a few hours of surgery. For others, it may take 1-3 days before they are willing to drop the toe down.
My general recommendation following CCL surgical repair is to leash walk the patient very slowly 4-5 times daily. The slower the patient walks, the more challenging it is to walk to three legs, the more likely he may be to drop the limb down. With less stoics (and stubborn) varieties of dogs such as certain toy or small breeds, it can be particularly challenging to coerce them to use the limb. This is problematic because it significantly slows the healing process, contributes to continued muscle atrophy, and can begin to lead to contraction of the hamstring muscles as they are held in constant flexion.
Just as in orthopedic surgery with people, post-operative rehabilitation is recommended. Below are known effective postoperative CCL rehabilitation techniques for dogs that can dramatically increase healing rates and reduce the potential for post-operative complications.
Class IV Therapy Laser
Classic IV therapy laser gently infuses low level photons of energy into cells and tissues. The resulting physiological effect at the cellular and tissue level is called photobiomodulation. This process dilates arteries and arterioles to bring oxygen and nutrient rich blood to areas. Arterial blood also brings healing cells to help clean up and remodel damaged cells and tissues.
Photobiomodulation also dilates veins and venules, as well as lymphatic vessels. By stimulating venous circulation, this helps to stimulate the removal of inflammatory debris and stagnant blood in a compromised areas. By dilating lymphatic vessels, we potentially stimulate the drainage and replenishment of interstitial fluid, the liquid medium cells and tissues of the body are housed within.
Therapy laser also stimulates the production of adenosine triphosphate (ATP) within cells. ATP is the powerhouse of the cell by from which it derives energy to perform its physiological functions. By increasing ATP within cells, therapy laser serves to provide cells a jolt of energy in the form of increased ATP to enhance cellular repair and the rebuilding of tissues. Protocols vary, but I generally recommend 6 treatments directly over the incision over a course of 3 weeks.
Water treadmill is a device where a treadmill is housed within a tank that is filled with warmed water. As the tank is partially filled up to about the level of the dog’s chest, the resulting buoyancy lightens the dog’s weight bearing, making them more accepting of consistent use of the limb. The warmed water has a hydrotherapy effect that enhances wound healing via increase of blood circulation, while also providing resistance in multiple planes of motion to rebuild muscle and strengthen muscular, tendonous, and ligamentous stabilizers.
A hyperbaric chamber creates a pure oxygen environment. It has notable efficacy in the management of burns, contaminated wounds, surgical incisions, and many other clinical applications where high levels of oxygen are beneficial in restoring cellular and tissue integrity following trauma or conditions that lead to cellular and tissue damage. In the case of orthopedic surgery, hyperbaric chamber therapy reduces the incidence of post-operative infection while hastening incision healing and minimizing scar formation.
Polysulfated Glycosaminoglycan Injections
These injections reduce cartilage degradation, block inflammatory mediators within joints that cause inflammation and pain, and contribute to the building and restoring of cartilage. Courses of injections will vary, but I generally recommend 6 injections over the course of 3 weeks.
Roger L. Welton, DVM
Founder and Chief Editor, Web-DVM.net
President, Maybeck Animal Hospital
Article updated 10/23/2018