The cranial cruciate ligament (CCL) is the main stabilizing ligament of the canine knee joint. Specifically, it prevents forward movement of the tibia whenever the dog applies force across the joint when weight bearing, walking, or running. This tendency for forward thrusting of the tibia is a natural process due to the distribution of muscle tendon forces exerting force over the area. Rupture of this ligament leads to acute, severe instability of the dog 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 dog CCL injury are:
1.) High performance dogs, such as agility and field trial competitors.
3.) Sedentary lifestyle with only occasional periods of play.
4.) Genetically inherited steep tibial plateau angles sometimes present in large breed dogs.
Specifically, the affected dog presents at first with toe-touching to non-weight bearing lameness. There is sometimes a significantly thickened appearance 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 ligaments 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 on physical examination. This should not occur in a normal, uninjured dog 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. The doctors of Grant Animal Clinic are trained to recognize, diagnose, and surgically repair injuries and malformations of the canine knee through clinical history, orthopedic examination, and digital x-rays. Dog knee surgery is a special interest of Grant Animal Clinic general partner and Attending Veterinarian, Dr. Roger Welton. Prior to veterinary school graduation, Dr. Welton completed two orthopedic surgery rotations at the prestigious Animal Medical Center in New York City (in addition to his required orthopedic surgery clinical rotation at University of Illinois). In addition to performing dog knee surgery since he graduated in veterinary school in 2002, Dr. Welton has also since earned two post doctoral certifications in reconstructive surgery of the canine knee. He has since trained all of the Grant Animal Clinic doctors in the most cutting edge dog knee surgery techniques, using the most state of the art surgical equipment and hardware.
There are several different surgical procedures utilized for cranial cruciate ligament rupture in veterinary surgery. In the past, the generally accepted notion was that bone cutting (aka, osteotomy) techniques, such as tibial plateau leveling osteotomy (TPLO) or tibial tuberosity advancement (TTA), edged out other surgical techniques where stabilization is provided outside the joint capsule with a suture placed outside the knee joint capsule (aka., extracapsular suture), in terms of overall effectiveness. It was generally accepted that the difference in effectiveness of TPLO, TTA, or MMP 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 subjected to extensive study, we now know that this particular extracapsular suture technique can stack up well with the osteotomy techniques under the correct circumstances.
The main difference in effectiveness of the osteotomy 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 fair 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. TTA, and MMP stabilize the knee by either physically or functionally reducing excessively steep tibial plateau angles, in effect, changing the physics of the knee such that the joint no longer relies on the CCL ligament for stbiliation. 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 still run the risk of gradually stretching over time. These points will also become more clear once each procedure is described below.
Many dogs that present with torn CCL also have a concurrent tear of the medial meniscus, the medial (toward the inside of the joint) cartilaginous padding structure that lies on the articulating surface of the joint. Traditionally, during a CCL surgery, a torn meniscus was also concurrently addressed surgically.
From a physiological perspective, however, this really did not seem to make much sense since cartilage has no nerve 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 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. Addressing the meniscus or not largely remains the discretion of the individual veterinary surgeon. The veterinary surgeons of Grant Animal Clinic do not tamper with the meniscus and have enjoyed better outcomes as a result.
In the tightrope procedure, the knee is stabilized with a soft but very strong (250 pounds of tensile strength) suture called fiber tape that runs along the lateral side of the knee joint. This procedure is best illustrated in the picture below:
The fixation points that anchor the suture make this procedure unique among other suture techniques in that they utilize the hard outer cortex of the long bones as fixation points. This creates a very effective manner in which to anchor the suture, and does so in a way that maximizes stabilization of the joint while maximizing comfort and range of motion.
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, unlike TPLO. the angle of the tibial plateau is not directly reduced but instead is functionally reduced in a somewhat different manner. Instead of cutting and rotating the entire tibial head, a smaller portion of the 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. The TTA also creates tension on the large and strong patellar tendon that runs over the patella and inserts the quadriceps muscle group into the proximal tibia. The subsequent tension removes forward instability caused by the ruptured CCL providing stabilization on two fronts.
Modified Maquet Procedure (MMP)
The MMP is really little more than a modification of the TTA in that it has the same net effect as the TTA, only rather than using a cage and spacer to extend the tibia, a titanium wedge called Orthofoam is used. 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): With a lesser burden of hardware implanted in comparison to TTA, there is less tendency for complication and/or reaction to the hardware The titanium material used is also less reactive to biological systems and is more resistant to bacterial growth and subsequent infection than other metal implantation materials.
Our preference for repair of the CCL at Grant Animal Clinic is the MMP with occasional consideration for tightrope depending on the individual age, size of the patient, lifestyle, and unique anatomic characteristics of each individual patient.
Post-Operative Rehabilitation & Care
Following surgery, the goal is to have the patient using the limb as quickly as possible. As such, we do not generally 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 1-5 days before they are willing to drop the toe down.
Our 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 on three legs, the more likely he may be to drop the limb down. With less stoic (or perhaps 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. For these cases, we have techniques and exercises we can recommend to overcome this obstacle.