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Stifle (Knee) Problems

Cranial Cruciate Ligament Rupture

The cranial cruciate ligament (CCL) is analogous to the human anterior cruciate ligament (ACL).  Degeneration and rupture of the CCL is one of the most common orthopedic conditions in middle aged to older dogs, especially in medium and large breeds of dogs, such as Labrador Retrievers, Rottweilers, Bernese Mountain Dogs, etc. 

Unlike ACL ruptures in people that are almost always sporting injuries, cranial cruciate ligament ruptures (CCLR) in dogs are almost always due to slow degeneration of the ligament with eventual failure. Both CCL may be affected.

Dogs with CCL disease often have an obvious limp or lameness, and complete rupture of the CCL often results in non weight-bearing lameness. Instability of the joint results in osteoarthritis in just a few weeks. Muscle atrophy, joint swelling (effusion), and decreased stifle joint range of motion occur as a result of the CCL rupture and arthritis.  The abnormal motion in the joint during weight bearing causes excess stress on the meniscal cartilage, especially on the medial (inside) of the knee.  This is sometimes referred to as "torn cartilage" in human athletes.  The longer the unstable joint is present, the greater the chance of a torn meniscus. Owners sometimes hear a snapping or popping sound during weight bearing or manipulation of the joint. 

Your veterinarian will do an examination to determine if the cruciate ligament is damaged.  The cranial drawer test is the traditional method of diagnosing a CCLR.  The cranial tibial thrust test may also be performed.  They may also assess for effusion in the joint and firm swelling on the inside of the stifle.  Flexion and extension may reveal crepitus, which indicates the presence of arthritis, and a meniscal click, indicating a meniscal tear. 

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Radiograph of a dog with a cranial cruciate ligament rupture.  There is severe displacement of the tibia in a forward (cranial) direction. 

Osteoarthritis and a torn meniscus are secondary issues that often compound a torn cranial cruciate ligament.

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Stifle (knee) joint of a dog. The solid black arrow points to the cranial cruciate ligament, the open arrow to the medial meniscus, and the open arrowhead to the caudal cruciate ligament

Surgery is generally recommended to stabilize the stifle joint, unless a medical condition would make general anesthesia too risky, or if there are financial concerns.  Although conservative treatment and physical therapy are often recommended in people with ACL tears, the anatomy and biomechanics are different in the dog stifle, making conservative management less effective.  At a minimum, there will be advanced arthritis in the stifle within 6-12 months.  Also, for best results, a number of medications and treatments are most likely to result in better results.  However, the cost of those treatments over a long time period may result in more expense than surgery.

A number of surgical options are available. The most successful procedures to improve function and reduce the progression of arthritis involve changing the biomechanics of the stifle joint.  Although you should discuss which procedure your veterinarian is most comfortable with and achieves the best results, several studies have suggested that the tibial plateau leveling osteotomy (TPLO) appears to be the best surgery to improve function and reduce arthritis. A similar procedure, the CORA-based leveling osteotomy (CBLO) may give similar results.  Both of these procedures alter the weight-bearing surface of the tibia so that it is more level, resulting in less tendency of the femur to slide down an inclined tibial surface. 

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The Tibial Plateau Leveling Osteotomy (TPLO) is based on altering forces acting on the unstable stifle joint. Because the weight-bearing surface of the tibia is normally sloped, you can think of bowling ball sitting on a sloped surface -- the bowling ball will roll down the slope.  The same thing happens in a dog with a ruptured cranial cruciate ligament -- the femoral condyle (ball) will slide down the sloped tibial plateau. 
The TPLO is performed by making a curved osteotomy of the tibia, then rotating the tibial plateau so that it is level. Now the femoral condyle (ball) part of the joint has no reason to roll because it is on a flat surface.  The muscles around the joint provide additional stability. 

Another surgery that alters stifle biomechanics is the tibial tuberosity advancement (TTA). There are a number of variations and different implants used in this procedure, but the principle is essentially the same, which is to move the tibial tuberosity, which is the insertion of the quadriceps muscle, further forward.  In a normal stifle joint, the quadriceps muscle causes extension of the stifle joint.  If the cruciate ligament is ruptured, the tibial will slide forward as a result of contraction of the quadriceps muscle and weight-bearing on an inclined tibial slope. With the TTA, the pull of the quadriceps muscle causes compression at the joint rather than sliding. 

Other common techniques involve some type of suture restraint to prevent the tibia from sliding, including the Flo technique, lateral suture fabella-tibial suture, modified reticular imbrication technique, tightrope, suture anchors and Swivelock.  All of these techniques are extracapsular techniques, meaning that the repair is outside the joint, but they try to mimic the path of the CCL as closely as possible.

Exercise restriction and physical rehabilitation are necessary to have the best possible result and maximum chance of recovery. 

Patella Luxation

The patella or kneecap may dislocate either medially (to the inside of the stifle) or laterally (to the outside) of the stifle. The main issue is a malalignment of the quadriceps mechanism, the groove that the patella rides in in the femur, and the insertion of the patella ligament on the tibial tubersity. Patella laxation is graded based on the severity of the malalignment, and the ease of patella luxation.

  • Grade 1 - minimal malalignment, the patella can be pushed out of position, but it pops back into place

  • Grade 2 - mild malalignment, the patella may spontaneously luxate, and may stay or out or pop back into place

  • Grade 3 - moderate malalignment, the patella is out of place and can be manually reduced, but wants to pop out of position

  • Grade 4 - severe malalignment, patella is out of place and cannot be reduced. Sometimes called an ectopic patella

Patella luxation is typically found in small breeds of dogs.  The direction of luxation is usually medial. Larger dogs and dogs such as Dachshunds and Bassett hounds may have lateral luxation.  However, medial luxation is still more common than lateral luxation in breeds such as Labrador retrievers. It is common that both patellas luxate.

Owners may notice chronic or intermittent lameness. Sometimes the patella will slip out of place, and the dog will skip or carry the leg for several strides, stretch the leg out behind, and then be normal. There are very few conditions that cause intermittent non weight-bearing lameness for a brief period, and then have a normal gait. Other clinical signs include difficulty or inability to jump onto furniture or go up stairs.

Dogs will try to use their muscles to keep the patella tracking correctly, but if the malalignment is great enough, they will be unable to keep the patella from dislocating.  Therefore, surgery is the only realistic option to maintain the patella in place. Although conservative treatment is an option if the dogs has a serious medical condition that makes anesthesia risky, or if financial concerns preclude surgery, owners should be aware that the degree of patella luxation will likely worsen, cartilage degeneration will continue, and there is a 15-20% chance of also developing a CCLR. 

Surgery aims to correct the malalignment of the quadriceps mechanism and stabilize the patella to prevent re-luxation.  The first decision after entering the joint is to determine if the groove housing the patella is deep enough. If it is not, the groove is deepened usually by a trochlear wedge or block recession trochleoplasty. The next step is to move the tibial tuberosity (insertion of the patella ligament) to realign the quadriceps mechanism, and hold it in place with pins +/- wire. Finally, the loose tissue is tightened or even removed to help keep the patella in place, and the joint capsule is sutured closed.  On occasion, additional procedures may be necessary, especially for grade 4 patella luxation.  Larger dogs, in particular, may benefit from correction of an excessively angled femur (varus deformity). In this case, a wedge of bone may be removed to straighten the femur.  A special bone plate is used to hold the femur in place. 

Exercise restriction and physical rehabilitation are necessary to have the best possible result and maximum chance of recovery. 

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CT of a dog with a medial patella luxation on one side with malaligned tibia and femur, and normal patella on the other side. 

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Preoperative radiograph of a dog with a medial patella luxation.

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Post-operative radiograph of a dog following surgery with the patella now in proper position.  A pin and tension band has been used to secure the tibial tuberosity after transposition. 

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