Cranial Cruciate Ligament Rupture
Cranial cruciate ligament rupture is one of the most common orthopedic injuries in the dog. The primary cause of rupture is degeneration of the ligament and rarely just trauma. Many dogs that tear one cruciate ligament will tear the other within 1 to 2 years of the first injury.
The cranial cruciate ligament is the primary stabilizer of the knee. Once it ruptures the dog will become acutely lame due to severe inflammation that occurs within the joint. This will generally improve within the first few days if the dog is placed on anti-inflammatory medications. We believe the chronic lameness is associated with the instability within the stifle joint. This chronic lameness is caused by the tibial plateau angle. In the dog the tibial plateau slopes caudally. When the dog bears weight the femur hits the top of the tibia and slips backward down the tibial plateau. When this occurs chronically, the immobile medial meniscus can be crushed and torn.
Cranial cruciate ligament injury leads to a cascade of events including progressive osteoarthritis and medial meniscal tears. The instability results in synovitis (inflammation of the joint capsule), articular cartilage degeneration, periarticular osteophyte formation and capsular fibrosis (arthritis). Progressive osteoarthritis continues even after stabilization of the knee regardless of the procedure used for stabilization. There are no studies supporting one method over another with respect to the progression of arthritis.
Many believe there are reasons to choose the tibial plateau leveling osteotomy over the traditional extra-capsular repair utilizing nylon. This procedure is primarily chosen for large breed dogs weighing 70 pounds or more. It is increasingly becoming the procedure of choice for animals of any size for many surgeons. I believe that extra-capsular repair can be very effective in dogs especially utilizing the TightRope implant. There may be a gray area in dogs with very steep tibial plateau and dogs with bilateral disease than cannot walk. Unfortunately many cannot choose the TPLO or TTA for reasons of expense. Now with the development of the TightRope Implant many owners have a choice and can feel good about choosing this over an osteotomy procedure.
The MRIT or Lateral suture is an extracapsular repair (it takes place outside of the joint capsule). The hallmark of this procedure is the elimination of abnormal motion called drawer. The surgery has historically utilized monofilament nylon as the implant. The implant is placed from the lateral fabella to a point in the tibia. It is then tightened and knotted or crimped in a position that is tight enough to eliminate abnormal motion.
This procedure requires the formation of a fibrous tissue bridge across the joint capsule that will maintain stability of the joint over the life of the dog. The healing process takes about 8 weeks. This time is meant to allow the formation, contraction and maturation of a fibrous tissue bridge.
The short comings of the procedure are in large dogs whose weight is such that they elongate the nylon or break the nylon during the healing process. The premature breakage of the nylon to early in the healing process can lead to failure and return of drawer. Elongation of the nylon can lead to return of some degree of abnormal motion or drawer which may or may not be tolerated in a large breed dog. Should either breakage or elongation of the implant occur it is possible to replace the implant without much difficulty and still have a positive outcome.
This is a more economical and less invasive procedure which is appropriate for many dogs. It does not matter how you get to a positive outcome just that you do achieve a stable and comfortable knee for your pet. A dog with Cushing’s Disease or hyperadrenocortisim would be a concern due to the overproduction of endogenous steroids which can inhibit the formation of fibrous tissue.
The TightRope is a vast improvement in the implant utilized in the MRIT or Lateral Suture procedure. The TightRope implant was developed 2 years ago by Arthrex. The procedure does not require an osteotomy(cutting the bone) as do the TPLO or TTA procedure. This implant only requires small bone tunnels in both the distal femur and proximal tibia. The implant is placed in the best isometric position through the tunnels and secured by placing buttons against the bone, knotting one side of the implant. Your goal is to achieve a joint without drawer or instability.
The implant is a FiberTape or Kevlar like material which is much stronger than monofilament nylon. This type of implant has been utilized in human sugery for quite some time. This is a great new option for large breed dogs. The strength of the implant means they are unlikely to stretch or break the nylon. It allows owners to choose a less invasive and more economical procedure for their dog.
The tibial plateau leveling osteotomy is chosen by most surgeons for large breed active dogs. This choice is made over concerns for larger heavier dogs damaging an extra- capsular repair resulting in chronic lameness. Many also believe that dogs receiving a TPLO return to function sooner. Another reason to choose this procedure is for dogs with bilateral disease to get them walking as soon as possible. There is no evidence that choosing a TPLO over another procedure will result in less osteoarthritis.
The tibial plateau leveling osteotomy changes the biomechanics to the canine stifle (knee). Normally the knee is stabilized both passively (cruciate ligament, menisci, joint capsule) and actively (muscles & tendons). The cranial cruciate is a passive constraint to cranial tibial translation as well as internal rotation. The cranial tibial translation is tested by cranial tibial thrust test. The severity of cranial tibial thrust is related to the slope of the tibia. The premise of the TPLO is that if you reduce cranial tibial thrust to neutral the pain associated with cranial tibial translation will resolve.
The tibial plateau leveling osteotomy requires special radiographs that allow the surgeon to measure the slope of the medial plateau. The slope angle is then converted to millimeters depending on the size of the osteotomy. The procedure incorporates the release of meniscus and debridement of remaining cruciate ligament. Once this is completed a jig is placed on the medial aspect of the tibia. A curved saw blade is utilized to make the osteotomy. The osteotomy is then rotated a specified number of millimeters. The osteotomy is then stabilized by a bone plate. Once this is completed cranial tibial thrust should be eliminated.
The tibial plateau leveling osteotomy takes approximately 8 weeks to heal. The osteotomy must go through the process of bone healing just like a fracture. During the healing period your dog should have only controlled exercise. This procedure requires radiographs at the 8 week after surgery to determine if healing is sufficient to allow release back to normal activity.
Tibial Tuberosity Advancement
This is the newest stabilization procedure in veterinary medicine. As with the TPLO the TTA is chosen for larger breed, very active dogs. Early results are very positive. These patients are returning to function more quickly than the extra-capsular repair patients. A surgeon would choose this procedure for the same reasons as the TPLO.
The hallmark of this procedure is to eliminate cranial tibial translation by placing the patellar tendon perpendicular to the shear forces in the knee. This is accomplished by performing an osteotomy of the tibial tuberosity. Once this is completed the tuberosity is advanced or moved forward to place the tendon perpendicular to the tibial plateau. The advancement is maintained by an implant called a cage and the osteotomy is stabilized by a plate.
The tibial tuberosity advancement requires approximately 8 weeks for healing. Ideally radiographs should be performed at 8 weeks to assess healing. During the healing process controlled exercise is the only allowed activity. Once healed your pet may be released to normal activity.
There is no evidence to suggest that this procedure will result in any less osteoarthritis than the TPLO or extra-capsular repair.
In conclusion there are 4 primary procedures available to stabilize the canine stifle. Small breed to medium size dogs are more suited to extra-capsular repair. The TTA, TPLO and Tightrope can be chosen for medium to large breed active dogs. It is important to discuss the options with your board certified veterinary surgeon to make the best choice possible. It does not matter how you get to a stable joint just that we achieve that result. In many cases the TPLO or TTA are better in the short term.