Anterior Cruciate Ligament (ACL) Rupture and Repair

(also called the “Cranial” Cruciate Ligament)

Description:  The anterior cruciate ligament (ACL) is the primary ligament that stabilizes the stifle (knee). ACL disease is usually a slow and ongoing process in which the ACL weakens and causes pain, instability, and osteoarthritis. Eventually the ligament ruptures, further increasing instability and pain in the joint. Usually, clinical signs of lameness are not easily identified until the ligament ruptures.

ACL disease most commonly affects middle-aged, large- and giant-breed dogs, but it occurs somewhat frequently in smaller dogs and occasionally in cats. The disease usually occurs in one leg, but rupture of the ACL in the other leg is common within 6-12 months following the first ligament tear.

Sometimes instability of the stifle results in injury to the medial meniscus. The menisci are two C-shaped cartilages in the knee. The medial meniscus (on the inside of the knee) is torn in about 50% of these cases.

Causes:  The cause of ACL is greatly debated. The shape of the tibial plateau (the top of the tibia, that is the large bone just below the knee), combined with various other factors, has been implicated.

Clinical Signs: Although ACL disease is a chronic, progressive condition, in many cases sudden onset of lameness occurs in association with activity. If not immediately treated, the lameness often improves to some degree but does not completely resolve. Signs typical of arthritis (lameness that is worse with rest and improves with mild exercise, stiffness, and muscle wasting) are usually present and worsen with time.

Diagnostic Tests: Orthopedic examination reveals  varying degrees of stiffness, fluid, pain, and crepitus (crunching sound) in the stifle. The inside edge of the stifle is often thickened as well. Thorough examination of the stifle with the animal under sedation often reveals excessive instability, particularly excessive movement of the tibia with respect to the femur (large thigh bone).

X-rays may reveal signs of osteoarthritis (degenerative arthritis) and misalignment of the tibia with the stifle, but they cannot show a ruptured ligament or torn meniscal cartilage. Sometimes the diagnosis is confirmed only at the time of surgery or with arthroscopy (passage of a fiberoptic viewing scope into the stifle).

Treatment Options: The best treatment for ACL disease typically involves surgical stabilization.

Numerous techniques are available for stabilizing the stifle. Keep in mind that the phrase “cruciate repair” is inaccurate, because in ACL disease the ligament is always beyond repair. Surgery is actually designed to improve stability of the joint. Available surgical techniques can be divided into three different types:

• Intra-articular techniques that create a new ligament and involve opening the joint, such as patellar tendon or biceps fascia grafting

• Extracapsular techniques that stabilize the stifle via surgery outside the joint, such as fibular head transposition and lateral suture placement

• Biomechanical techniques that change the angles and  forces within the stifle, such as tibial plateau–leveling osteotomy (TPLO) and tibial tuberosity advancement (TTA).

Currently, the TPLO is considered the better surgery with quicker ‘return to function’ time frames and less arthritis in the future. Biomechanical techniques are often favored for large and giant breeds, whereas extracapsular techniques are often used for smaller dogs and cats (and in some situations for larger dogs). Many of the described techniques can have good results in the hands of a capable veterinary surgeon. If the medial meniscus is damaged, it is removed.

Follow-up Care: Regardless of which technique is chosen, strict restriction of activity for at least 4-10 weeks after surgery is critical for ultimate success. The incision is observed daily for excessive redness, swelling, pain, or discharge. Physical rehabilitation and/or exercises at home also greatly improve the outcome of surgery.

Prognosis: Most dogs return to normal or near-normal function following surgery, appropriate activity restriction, and rehabilitation. Dogs with a torn meniscus have a slightly worse prognosis, but generally the out- come is still good. Dogs with osteoarthritis may require continued medical therapy if the signs do not completely resolve with surgery.

The Story of Wally P.

Wally is a 7 Year old Black Lab that suddenly ruptured his right ACL ligament. He was unwilling to bear any weight on that right rear leg, unless he was on good footing such as carpet or grass. We often see this in dogs who have ruptured their knee ligament. They can use the leg at times, but usually are ‘toe-touching’ and will pull the leg up on slick footing. Our sense is that they lose confidence that the leg can successfully carry any weight on tile, hardwood or linoleum floors.

X-rays revealed an effusion in the right knee (the increased gray cloudiness that the arrow is pointing at in this picture.)

When compared to the Left Knee, we can definitely see the difference!

When sedated, we were also able to palpate ‘instability’ in the knee. When the top of the tibia can be pushed forward relative to the knee joint, this is the classic finding of a ruptured ACL. In other words, of the ACL ligament is working and intact, the tibia cannot be pushed forward . . . we call this forward sliding of the tibia “Drawer Sign” and it is considered to be the diagnostic test that proves when a dog has a ruptured ACL.

Given Wally’s size and energy level (He’s a VERY happy and energetic dog, we decided that the TPLO surgery was the best choice for him. This surgery yields fantastic results in large breed dogs with a faster return to function and less future arthritis than many other techniques.

The surgery works by rotating the top of the Tibia (what is called the Tibial Plateau) so that it is Level and the femur above cannot slide backward anymore. Very precise measurements are taken (down to fractions of a millimeter) in order to rotate the Tibial Plateau just the right amount!

In this image, you can see the arc of the cut line in the bone (cutting the bone is called an ‘Osteotomy’) and the rotation that was achieved to Level the Tibial Plateau.

This surgery was performed on November 28, 2023. Wally has had a nice recovery and is doing well. For this first month, he is not allowed to do any running or jumping and we discourage a lot of stair climbing. He is allowed to go for walks and he does not have to be kept confined in a crate the whole time!

Luxating (Dislocating) Patella (Kneecap)

Note from Dr. K: I don't know why someone decided to call a Dislocating Kneecap a “Luxating Patella.” But they did and that is the name we have for this problem. I have edited and modified a very nice article by Mark C. Rochat, DVM, MS, DACVS to provide the explanation below:

The patella is the kneecap. Patella luxation is dislocation of the patella from the patellar groove at the bottom of the femur. The Patella is essentially a ‘train on the tracks’ and when it luxates, that train jumps off of the tracks.

The outer aspects of the knee joint is stabilized by two ligaments and one tendon. Visualize a tricycle— the tendon is the front wheel and the two ligaments are the back wheels. When the patella dislocates, it has the same effect as when you abruptly turn the front wheel of a tricycle sideways— that trike isn’t going anywhere until that front wheel straightens back up!

Causes
Patellar luxation is usually a bone abnormality that is ‘built in’ to many small breed dogs such as Chihuahuas and Pomeranians. A luxating patella may also occur as a result of trauma.

Clinical Signs

The most commonly reported sign is a variable degree of intermittent lameness on a rear leg. Classically, the dog suddenly stops, may cry out, picks up the leg for several steps, stretches the leg out behind it, and then resumes normal activity. This sequence of signs occurs because the patella dislocates and then returns to its normal position when the leg is stretched backward. With time, the stifle develops arthritis from abnormal movement of the patella.

Diagnostic Tests

The luxation can usually be detected during a physical examination, and other anatomic abnormalities may also be detected. The extent of the luxation is often graded on a scale of 1 to 4, as follows:

• Grade 1 is the mildest form. In these cases, the patella can be manually luxated during the examination, but then it returns to a normal position. Dogs with grade 1 luxations may have no clinical signs.

• With grade 2 cases, the patella spontaneously luxates and returns to its normal position. A “skipping” gait or lameness is common.

• With grade 3 cases, the patella is dislocated constantly but can be manually returned to a normal position momentarily. Lameness is commonly present but varies in severity.

• Grade 4 is the most severe form. In these cases, the patella is dislocated continuously and cannot be manually replaced, and lameness is significant.

  X-rays may reveal the luxation, show other anatomic abnormali- ties in the leg, and help decide what specific measures should be taken to correct the condition.

  TREATMENT AND FOLLOW-UP

• Treatment Options

  Dogs with patellar luxations that have no clinical (outward) signs (an uncommon event) generally do not benefit from surgery. Young dogs and dogs with patellar luxation and lameness should have the luxation corrected. A number of techniques are commonly used to achieve proper alignment of the patella. Which specific procedure is chosen depends to some degree on the x-ray findings and the results of the initial orthopedic examination. Your dog may be referred to a veterinary orthopedic surgeon for evaluation prior to surgery.

  Techniques that may be considered include the following:

  • If the patellar groove is too shallow, it can be deepened by a couple of different surgical techniques.

  • In some situations, the attachment of the patellar tendon to the tibia (shin bone) is cut & moved laterally (toward the outside of the stifle), and secured to the tibia with a single, small, stainless steel pin.

  • Dogs that have grade 4 luxations often require additional procedures to cut and straighten the femur (thigh bone) and tibia, thereby straightening the leg and resolving the luxation.

    Follow-up Care

    After surgery, activity is limited to short leash walks. Other activities such as running, jumping, stair climbing, and playing are prohibited. Physical rehabilitation therapy can greatly improve the recovery of stifle function. X-rays of the stifle are taken every 4-6 weeks until the osteotomy in the tibia is healed. The pin may be left in place indefinitely. Normal exercise and full activity are allowed after all tissues, including the bone, have healed.Prognosis

    Prognosis is favorable for most dogs. After surgery, about 75% of the dogs becoming normal with 25% of the dogs have an improvement in their luxation by 1-2 grades. Dogs with grade 4 luxations often have a more challenging prognosis but can still improve substantially with proper treatment.