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.
MRIT(Modified Retinacular Imbrication Technique) or Lateral Suture
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.