What do you do if your dog yelps in pain and suddenly starts holding up one of his or her back legs? Chances are, your dog has injured a cranial cruciate ligament (CCL or ACL) in the knee, the most common cause of hind limb lameness in dogs… and a common injury in human football players too! The Meowing Vet explains the signs to look for, what risk factors dog owners should be aware of, how to diagnose cranial cruciate ligament ruptures, and what the treatment options for CCL injury are.
Keep reading to learn more…
Anatomy of the Knee
Your dog’s knee (or stifle joint) has two ligaments that crisscross each other behind the kneecap (or patella). (FYI: You and your cat also have these same knee structures.) These band-shaped ligaments, known as the cruciate ligaments, are each comprised of a bundle of multiple fibers. The ligaments form an X-shape in the knee and function to connect the femur (thighbone) with the tibia (main leg bone, or shin). This connection allows for uniform motion between the two bones whenever your dog takes a step and also stabilizes these bones in perfect anatomical alignment to prevent their ends from rubbing against one another or from splaying too far away from each another.
As stated, there are two cruciate ligaments: both a cranial and caudal ligament. The cranial cruciate ligament (CCL) is positioned nearer the front of the knee, just behind the kneecap, and is more prone to injury; in human medicine, it is referred as the anterior cruciate ligament (or ACL). The caudal cruciate ligament lies behind the cranial ligament towards the back of the knee. The caudal ligament can also become damaged, though this is less likely because it is thicker than the cranial ligament and under less forces.
The cruciate ligaments reside in close proximity to menisci (plural for meniscus); the menisci act as shock absorbers to offset blunt force from the surrounding soft tissues and bones when your dog takes a step and moves the knee. Because the cruciate ligaments and menisci lie so close together, a tear to a meniscus may often occur along with a cruciate injury (in up to 66% of cases). Meniscal tears are very painful and may be more difficult to treat, typically requiring a meniscectomy (or surgical removal of the damaged meniscus). Furthermore, injuries to the collateral ligaments of the knee (the thick bands felt on each side of the back of the knee) can also occur along with CCL injury.
About Cranial Cruciate Ligament Injury
Though cranial cruciate injury can also occur in cats, it is the most common cause of hind limb (i.e. back leg) lameness in dogs. Such injuries include complete tear of the middle portion of the ligament (often requiring surgical repair), partial tear of some of the ligament’s fibers (which may heal without surgical intervention), or full avulsion of the CCL (meaning its attachment to the femur or tibia is completely torn off, also requiring surgery). If your dog ruptures a CCL in one knee, he or she has a roughly 95% chance of injuring the opposite knee’s CCL with a 50% likelihood of that second rupture occurring within a year of the first injury. The increased likelihood of a bilateral injury occurs because dogs will shift their weight off their bad knee onto their “good” knee, adding increased stress which primes the other knee to injury in time.
What causes CCL injury?
ACL injuries in humans are often associated with acute trauma to the knee joint, as typically experienced by athletes such as football players. However, only a small percentage of cases of CCL injury in dogs happens as a direct result from acute trauma alone (such as getting a back foot caught in a hole or fence). Instead, most dogs with CCL injuries appear to have chronic degenerative changes in the cellular composition of the ligament’s fiberous composition, resulting in poorer and poorer ligament strength as your dog ages. These changes tend to occur in both knees. Repetitive jumping or other activity by a dog with ligament degeneration can suddenly result in a torn CCL. Furthermore, degenerative joint disease (DJD), or osteoarthritis (OA), caused by a variety of factors can also place additional stress on the cranial cruciate ligament, resulting in worsening deterioration and eventual rupture.
Obesity puts your pet at risk of injury to the cranial cruciate ligament.
Risk Factors of CCL Injury
Though any dog (male or female) may experience a cranial cruciate injury, spayed female dogs tend to have a higher incidence of reported issues. Any age of dog may also be affected, yet most tend to be young to middle-aged dogs since this age range tends to be the most active. Young puppies may also experience CCL injuries, which typically result in complete avulsion (often involving the tibia attachment).
Large dogs more commonly sustain CCL rupture. However, Yorkies are a small dog breed at increased risk of CCL injury.
Large breed dogs are more commonly affected by CCL injuries in relation to small breed dogs. However, some small dogs can also develop injuries to the cranial cruciate ligament, especially Yorkshire terriers, which may be born with abnormal contouring of the tibia (i.e. an abnormality of the tibial plateau angle, or TPA). Dogs born with other abnormalities of the tibia or abnormalities of the femur may also be at risk of CCL injuries. Of large breeds, mastiffs, chows, Akitas, Labrador retrievers, rottweilers, Saint Bernards, and Newfoundlands seem to be over-represented breeds for CCL injury.
Moreover, dogs that have very straight hind limbs (without a normal slight “bend” to the knee) may place excessive strain on the stifle (knee) joint and thereby on the CCL. Such dogs are usually also predisposed to patellar luxation (a.k.a. luxating patellas, which occur when the kneecap pops too easily out of place). Patellar luxation in turn increases the risk of CCL rupture. Additionally, obesity puts both dogs and cats at risk of sustaining cranial cruciate ligament ruptures by placing excessive stress on the ligament and contributing to chronic deterioration.
Worried that your pet’s obesity puts him at risk of developing cranial cruciate ligament injury and other health issues? Find out how you can promote weight loss in your dog or cat by clicking here.
Learn more about osteoarthritis and how omega-3 fatty acid supplements, such as fish oil, or glucosamine may help your pet’s joints!
Check back later for a future article on luxating patellas.
Diagnosis of Cranial Cruciate Ligament Injury
Along with the history you provide to your veterinarian (including reports of a sudden non-weight-bearing injury to your dog’s back leg indicating an acute CCL rupture, or a long bout of lameness due to a chronic injury), your vet will perform a physical and orthopedic examination to diagnose a CCL injury. Your vet may notice your dog shifting his or her weight off the affected limb while standing or sitting with the sore leg out to the side.
Due to your dog’s knee pain and because your dog is likely holding his or her knee with great tension in order to protect it from moving and inducing further pain, your vet may suggest sedating or anesthetizing your dog in order to perform a full orthopedic exam. This will make your dog comfortable during the exam while allowing your vet to gather as much information as possible about the status of your dog’s knee. Typical findings include stifle joint swelling (or effusion), decreased thigh muscle mass (or thigh muscle atrophy caused by chronic decreased use of the injured leg), a crunchy sound or feel upon moving the knee (known as crepitus, as caused by improper friction between injured cartilage and bone). If your dog has a chronic CCL injury, your vet may also detect a firm enlargement on the inside of the stifle joint (termed medial buttress); this occurs when the body attempts to stabilize the injured knee joint by forming new bone growth on the inner aspect of the knee. All these findings point to an issue with the knee joint.
To really narrow down the injury to pinpoint damage to the cranial cruciate ligament, your vet will perform several manipulations to assess function of the CCL, including cranial drawer motion, cranial tibial thrust, and the tibial compression test. These tests help your vet distinguish a complete rupture from a partial tear. Furthermore, if your dog has a concurrent meniscal injury, your vet may also hear a clicking sound when your dog walks or moves the stifle.
To further inspect your dog’s injury, your vet may recommend performing x-rays (radiographs) of the affected limb, ultrasound of the knee, or an MRI. Occasionally, a minimally invasive scoping of the knee (known as arthroscopy, in which a small probe with a camera is placed inside the stifle joint) may yield more concrete results before a definitive diagnosis can be made and a treatment option recommended.
Treatment of CCL Injuries
Sometimes, conservative therapy may be recommended over surgery for some CCL injuries. Conservative management includes cage rest to allow the knee to heal, physical therapy, and the use of anti-inflammatory pain medications (such as NSAIDs and omega-3 fatty acid supplements such as fish oil). In addition to fish oil supplements, your vet may recommend additional nutritional management such as a prescription veterinary diet optimized for joint care, such as Hill’s j/d or Purina JM. Because obesity predisposes an animal to CCL injury, a weight loss plan is also a very important part of conservative treatment if your pet is overweight.
Conservative therapy may help in cases of partial CCL tears in which the torn ligament fibers may have a chance to reattach themselves with proper rest (this will not work with a full rupture). Conservative management may also work well with cats with CCL injury as well as for small dogs under 33 pounds (or 15 kilograms). Keep in mind that improvement may take as long as 6-8 weeks.
However, surgery is advised for large dogs with CCL injuries as lameness in large breed dogs often worsens despite conservative therapy due to the development of osteoarthritis. Surgical intervention for small dogs that do not improve after 1-2 weeks of conservative therapy is also advised. Due to a pet’s advanced age, presence of concurrent health problems, worries over post-operative care, or due to financial constraints, some owners with dogs with full CCL ruptures may still opt for conservative treatment rather than surgery (though this is not ideal). In these cases, the MuttKnee Brace may provide some anatomical support and comfort to your dog. Based in the U.S., the MuttKnee Brace company ships internationally. Check out their website to discuss with your vet the possibility of ordering a brace for your dog today! View their informational video below.
For the treatment of cranial cruciate ligament avulsions as well as for most cases of CCL rupture, surgery is advised. The advantages of surgery over conservative management are that in surgery, damaged ligament and meniscal tissue are removed, thereby decreasing pain and slowing the development and severity of osteoarthritis (though some arthritis will likely occur regardless). Additionally, surgery re-stabilizes the stifle joint by either implanting an artificial ligament-like insert or by re-aligning the relationship of the femur to the tibia via cutting and repositioning bone with the use of metal plates.
Several surgical methods for CCL rupture exist, including intracapsular (meaning inside the knee joint capsule), extracapsular (outside the joint capsule), and osteotomy (which involve cutting and repositioning bone) methods. The most common options are lateral fabellar-tibial suture (an extracapsular technique) as well as TPLO and TTA (both being osteotomy methods). The lateral fabellar-tibial suture method (also referred to as the lateral suture method) is commonly performed at a general practitioner’s office. TPLO and TTA procedures are more commonly done at a referral practice (such as a veterinary teaching hospital or a private specialty practice) to be performed by a veterinary surgery specialist or a veterinarian with advanced surgical training. The overall surgery success rate is roughly 90% (meaning about 90% of patients undergoing surgery improve post-op, able to use the injured leg again without pain). Should it occur, surgical failure is most commonly caused by implant complications, progressive osteoarthritis, or overlooked and therefore unrepaired meniscal injuries.
[Other less commonly performed techniques include intracapsular methods of using biological tissue or prosthetic grafts to try to reform a CCL-like tissue, the extracapsular tight-rope technique, TWO (or tibial wedge osteotomy, also called the cranial closing wedge osteotomy or CCWO), and CBLO (or CORA based leveling osteotomy, CBLO, which acts as a combination surgery of the TPLO and TTA methods).]
The lateral suture technique is an extracapsular surgical method that uses a synthetic line of suture material or wire to crisscross between the femur and tibia to mimic the natural action of the cranial cruciate ligament. This procedure is usually more financially feasible than other surgeries, yet it will nearly always end up breaking in time, requiring a subsequent surgical repair in the future. It tends to have a better success rate in smaller dogs, so larger dogs should ideally undergo one of the other surgical methods discussed. Furthermore, infection can occur with the lateral suture method with draining tracts forming due to the use of certain suture materials. Other complications include damage to the peroneal nerve in the leg during surgery. Additionally, the majority of dogs undergoing surgery tend to have more post-operative pain following this option due to more soft tissue trauma in comparison to the other surgery techniques.
As discussed, both the TPLO (tibial plateau leveling osteotomy) and TTA (tibial tuberosity advancement) techniques are osteotomy methods that involve cutting an area of the top (or proximal portion) of the tibia (shin bone) near where it meets the femur (thighbone) in the knee joint. A bone plate with screws or pins will reattach the cut bone in a new position to realign the tibia in relation to the femur for stabilization in order to reduce inappropriate movement of these bones and to reduce excessive forces on the stifle joint. If your dog has or is predisposed to luxating patellas, the TTA option is most recommended. When done correctly, the TPLO or TTA are better surgeries than the lateral suture method, allowing your dog to more quickly return to full function. However, because these surgeries involve cutting the bone, they are more invasive and require longer healing time and post-op management. Since they are more complicated techniques, they are also more expensive than the lateral suture option. Possible adverse complications include bone infection, implant (i.e. bone plate) loosening or breakage, or bone fracture.
Post-Operative Care
For any of the described surgery methods, keeping the incision site clean, dry, and healthy is a necessity post-op. If the wound becomes infected, it can progress to bone infection, which is a catastrophe. Your dog will not be able to be bathed until the sutures or staples at the surgical site are removed, around 2 weeks after your dog’s surgery. Furthermore, your dog absolutely cannot lick the incision site, as this will delay wound healing and may cause infections to develop. Thus, it is imperative your dog wear an Elizabethan collar (or E-collar, a.k.a. “the cone of shame”) until the sutures/staples are removed by your vet. Your vet will also likely prescribe a variety of medications for your dog, such as antibiotics as well as pain medications (such as a non-steroidal anti-inflammatory drug/NSAID and tramadol).
Your dog MUST wear its E-collar after surgery!
For the lateral suture repair, your dog must wear a thick limb bandage (known as a modified Robert-Jones bandage) typically for 48 hours post-op. Once the bandage is off, your vet may advise you to use warm or cold compresses on your dog’s knee to minimize inflammation and discomfort (ask your vet for advice). For TPLO and TTA surgeries, your pet must have strict exercise restriction for 8-12 weeks afterwards. This means strict cage rest to allow the osteotomy site time to heal. If you allow your pet to run around too soon after surgery, this can cause bone fractures to occur as well as dislodging of the bony implant – an absolute disaster! Therefore, keeping your dog quiet and calm after surgery is vital to his or her well-being. Follow-up care also typically includes post-op x-rays around 8 weeks after surgery to ensure that your dog’s knee is healing adequately.
Physical therapy under the discretion of a vet or a CCRT (certified canine rehabilitation therapist) is an important post-op requirement for all surgery options. Physical therapy may involve PT appointments with a specialist, use of an underwater treadmill or swimming (once the initial surgical wound has healed), and at-home light exercises and limb stretches taught to you by your physical therapist.
The Meowing Vet hopes you now fully understand the ins and outs of cranial cruciate ligament (CCL) injury so that you know whether or not your dog is at risk, can recognize signs of injury, and know what to expect if your dog sustains a “football” injury.
– Maranda Elswick, DVM
STAY IN THE LOOP OF OUR DAILY ANIMAL VIDEOS AND SHARED NEWS ARTICLES BY FOLLOWING THE MEOWING VET ON FACEBOOK AND INSTAGRAM (@THEMEOWINGVET). AND SIGN UP FOR OUR BLOG MAILING LIST IN THE RIGHT-HAND SIDEBAR OF YOUR DESKTOP BROWSER SO YOU NEVER MISS OUT ON OUR WEEKLY INFORMATIVE ARTICLES. YOU CAN HELP US (AND ANIMALS) IMMENSELY BY SHARING OUR SITE’S ARTICLES WITH YOUR PET-LOVING FRIENDS AND INVITING THEM TO LIKE OUR FACEBOOK PAGE! BEFORE YOU GO, WE WANT TO SEE YOUR BEST PET PHOTOS TO FEATURE ON OUR WEBSITE; CLICK HERE FOR SUBMISSION GUIDELINES!
Special thanks Otto I. Lanz, DVM, Diplomate ACVS; Robert S. Gilley, DVM, PhD, Diplomate ACVS; and Marian E. Benitez, DVM, MS, Diplomate ACVS-SA of the Virginia-Maryland College of Veterinary Medicine Small Animal Surgery Service for information and training.
