RUPTURED ANTERIOR CRUCIATE LIGAMENT (RACL)

FIRST, THE BASICS

The knee is a fairly complicated joint. It consists of the femur above, the tibia below, the kneecap (or “patella”) in front, and the bean-like fabellae behind. Chunks of cartilage called the medial and lateral menisci fit between the femur and tibia like cushions and there are an assortment of ligaments holding everything together allowing the knee to bend the way it should and keep it from bending the way it shouldn’t.

Forward View of the Canine Knee Joint
(Photocredit: Public Domain Graphic via Wikimedia Commons)

There are two cruciate ligaments which cross inside the knee joint: the anterior (or, more correctly in animals, “cranial”) cruciate and the posterior (or, more correctly in animals, the “caudal”) cruciate. They connect from one side of the femur on top to the opposite side of the tibia on the bottom, the two ligaments forming an "X" (hence the name "cruciate") inside the knee joint.  They are named for their attachment site on the tibia (the cranial cruciate attaches to the front of the tibia and the caudal cruciate attaches to the back of the tibia).  This may be hard to visualize based on the description but the illustration above shows the orientation of the two crossing ligaments effectively. The anterior/cranial cruciate ligament prevents the tibia from slipping forward out from under the femur.

HOW RUPTURE HAPPENS

There are several clinical pictures seen with ruptured cruciate ligaments. One is a young athletic dog playing roughly who takes a bad step and injures the knee while playing. This is usually a very sudden lameness in a young large breed dog.

A recent study identified the following breeds as being particularly at risk for this phenomenon: Neapolitan mastiff, Newfoundland, Akita, St. Bernard, Rottweiler, Labrador retriever, Golden retriever, and Pit Bull terrier.

On the other hand, an older large dog, especially if overweight, can have weakened ligaments and slowly stretch or partially tear them. The partial rupture may be detected or the problem may not become apparent until the ligament breaks completely. In this type of patient, stepping down off the bed or a small jump can be all it takes to break the ligament. The lameness may be acute but have features of more chronic joint disease or the lameness may simply be a more gradual/chronic problem.

Larger overweight dogs that rupture one cruciate ligament frequently rupture the other one within a year’s time.

An owner should be prepared for another surgery in this time frame.

(Photocredit: Morguefile.com)

The cranial cruciate rupture is not limited to large breed dogs. Small dogs can certainly rupture their ligaments as well and, while arthritis is slower to set in when the patient is not as heavy, there is an association with cruciate rupture and medial luxating patella that is very common in small breed dogs. With the patellar luxation, the kneecap flips in and out of the patellar groove. If the condition is relatively mild, it may not require surgical correction but it does stress the cranial cruciate ligament and can predispose to rupture and need to correct both conditions surgically.

WHAT HAPPENS IF THE CRUCIATE RUPTURE IS NOT SURGICALLY REPAIRED

Without an intact cruciate ligament, the knee is unstable. Wear between the bones and meniscal cartilage becomes abnormal and the joint begins to develop degenerative changes. Bone spurs called “osteophytes” develop and chronic pain and loss of joint motion result. This process can be arrested or slowed by surgery but cannot be reversed.

• Osteophytes are evident as soon as 1-3 weeks after the rupture in some patients.

This kind of joint disease is substantially more difficult for a large breed dog to bear though all dogs will ultimately show degenerative changes. Typically, after several weeks from the time of the acute injury, the dog may appear to get better but is not likely to become permanently normal.

• In one study a group of dogs was studied for 6 months after cruciate rupture. At the end of 6 months, 85% of dogs under 30 lbs of body weight had regained near normal or improved function while only 19% of dogs over 30lbs had regained near normal function. Both groups of dogs required at least 4 months to show maximum improvement.

WHAT HAPPENS IN SURGICAL REPAIR?

There are 3 different surgical repair techniques commonly used today. Every surgeon will have their own preference for which technique is best for a given patient's situation.

TIBIAL PLATEAU LEVELING OSTEOTOMY (TPLO)

This procedure uses a fresh approach to the biomechanics of the knee joint and was developed with larger breed dogs in mind. The idea is to change the angle at which the femur bears weight on the flat "plateau" of the tibia. The tibia is cut and rotated in such a way that the natural weight-bearing of the dog actually stabilizes the knee joint. As before the knee joint still must be opened and damaged meniscus removed. The cruciate ligament remnants may or may not be removed depending on the degree of damage.

TIBIAL TUBEROSITY ADVANCEMENT (TTA)

WHICH PROCEDURE IS BETTER?

The TTA and TPLO are much more invasive, much more expensive, and require special equipment and specially trained personnel. They have greater potential for complication. Are they worth it? For dogs under 45 lbs, it generally accepted that there is no clear advantage of the newer procedures over extra capsular repair. For larger dogs, there is great controversy. For all the theory behind TPLO and TTA, results one year post-operative seem to be the same regardless of which of the three procedures the dog had performed. There is some evidence that recovery to normal function may be faster with the newer procedures. Controversy continues and there are very strong opinions favoring each of the three procedures. We recommend discussing options with your veterinarian in order to decide.

WHAT IF THE RUPTURE ISN’T DISCOVERED FOR YEARS AND JOINT DISEASE IS ALREADY ADVANCED?

A dog with arthritis pain from an old cruciate rupture may still benefit from a TPLO surgery and possibly from the TTA. It may be worth having a surgery specialist take a look at the knee. Most cases must make do with medical management. Visit our section on arthritis treatment.

MENISCAL INJURY

Pets with meniscal damage may have an audible clicking sound when they walk or when the knee is examined, but for a definitive diagnosis the menisci must actually be inspected during surgery. It is difficult to access the menisci and thus repairing a tear in the meniscus is problematic; furthermore, poor blood supply to the menisci also makes good healing less likely. For these reasons, removal of the damaged portion of the meniscus is the most common surgical choice. This leaves some meniscus behind to distribute the compression load on the knee but removes the painful, ineffective portion.

Areas of current research include techniques to improve blood supply to the healing meniscus so that repair can be more feasible. If meniscal damage has occurred in a cruciate rupture, arthritis is inevitable and surgery should be considered a palliative procedure.

ENHANCING RECOVERY AFTER SURGERY

Confinement

Enhancing recovery post-operatively is largely about strict confinement early. This cannot be over-emphasized. Be prepared to crate your dog our employ a pen such as a child's playpen depending on the dog's size. A corral of sorts can be constructed with boxes and a baby gate.  Be sure you understand the instructions with regard to gradual return to exercise over several months.

Adequan^® Injections

A series of adequan injections can help with joint inflammation as well as lubrication. Typically injections are given twice a week for a total of eight injections. For more information on this medication, click here.

Glucosamine

Oral joint supplements such as glucosamine contain cartilage building blocks to help the body repair cartilage damage. This is an excellent time to begin supplementation and there are numerous brands. For more details, click here.

Weight Management

Overweight dogs have an increased risk for arthritis and for cruciate rupture. A weight management program can reduce the potential for arthritis and can reduce the risk of rupture of the opposite cruciate ligament. If your dog is overweight, ask your vet about a weight management plan that might be started during the recovery period.

Professional Rehab/Physical Therapy

Nothing compares to professional rehab for return to function. If you are lucky enough to have such a facility in your area, consider utilizing their services. A list of home exercises may be obtained and/or the dog can visit weekly or a few times weekly for exercise and treatment. Some facilities allow the dog to board and have daily treatment. Ask your vet about this option.

Page last updated: 10/13/2018
Page last reviewed: 1/27/2021