- April 0201
- Posted By Jesse Davicioni
- 2 Comments
The Basics of Pet Knees
The knee is a fairly complicated joint. It consists of the femur above, the tibia below, the kneecap (patella) in front, and the bean shaped fabellae behind. Flat pieces of cartilage called the medial and lateral menisci fit between the femur and tibia like cushions. An assortment of ligaments holds everything together, allowing the knee to bend the way it should and keep it from bending the way it shouldn’t.
There are two cruciate ligaments that cross inside the knee joint: the anterior (or, more correctly in animals, cranial) cruciate and the posterior (in animals called the caudal) cruciate. The anterior cruciate ligament prevents the tibia from slipping forward out from under the femur.
How Rupture Happens
Several clinical pictures are seen with ruptured cruciate ligaments. One is a young athletic dog playing roughly who takes a bad step and injures the knee. This is usually a sudden lameness in a young large-breed dog.
On the other hand, a middle aged or older large dog, especially if overweight, can have weakened ligaments and slowly stretch or partially tear them. The partial rupture may be detected or the problem may not become apparent until the ligament breaks completely. In this type of patient, stepping down off the bed or a small jump can be all it takes to break the ligament. The lameness may be acute but have features of more chronic joint disease or the lameness may simply be a more gradual/chronic problem.
As often the underlying reason for the tear is a gradual weakening of the cruciate ligaments, the problem often occurs in the other knee joint as well within a few months to a year or two. Owners therefore should be prepared for the possibility of another surgery in this time frame.
Finding the Rupture
The ruptured cruciate ligament is the most common knee injury of dogs; in fact, chances are that any dog with sudden rear leg lameness has a ruptured anterior cruciate ligament rather than something else. The history usually involves a rear leg suddenly so sore that the dog can hardly bear weight on it. If left alone, it will appear to improve over the course of a week or two but the knee will be notably swollen and arthritis will set in quickly. Dogs are often seen by the veterinarian in either the acute stage shortly after the injury or in the chronic stage weeks or months later.
The key to the diagnosis of the ruptured cruciate ligament is the demonstration of an abnormal knee motion called a drawer sign. It is not possible for a normal knee to show this sign.
The Drawer Sign
It is not unusual for animals to be tense or frightened at the vet’s office. Tense muscles can temporarily stabilize the knee, preventing demonstration of the drawer sign during examination. Often sedation is needed to get a good evaluation of the knee. This is especially true with larger dogs. Eliciting a drawer sign can be difficult if the ligament is only partially ruptured.
Since arthritis can set in relatively quickly after a cruciate ligament rupture, radiographs to assess arthritis are helpful. Arthritis present prior to surgery limits the extent of the recovery after surgery though surgery is still needed to slow or even curtail further arthritis development.
What Happens if the Cruciate Rupture is Not Surgically Repaired?
Without an intact cruciate ligament, the knee is unstable. Wear between the bones and meniscal cartilage becomes abnormal and the joint begins to develop degenerative changes. Bone spurs called osteophytes develop resulting in chronic pain and loss of full joint motion. This process can be arrested or slowed by surgery but cannot be reversed.
What Happens in Surgical Repair?
Tibial Tuberosity Advancement (TTA) via the MMP procedure
The TTA represents changing the biomechanics of the knee to create stabilization. The theory behind this procedure is that when the cruciate ligament is torn, the tibial plateau (the top of the tibia) and the patellar ligament should be repositioned at 90 degrees to one another to combat the shear force generated as the dog walks. To make this happen, the tibial tuberosity (front of the tibia where the patellar ligament attaches) is separated and anchored in its new position by a titanium foam wedge, pin and titanium bone staple. The newly developed titanium foam allows and induces bone to grow through it’s micropores, enabling faster healing than previous techniques.
The patient’s activity must be restricted and confinement is a must with gradually increased activity over 2 months. Most dogs can return to normal activity by 2-3 months after surgery.
Tibial Plateau leveling and tibial tuberosity advancement via the TTO procedure:
The TTO also represents changing the biomechanics of the knee to create stabilization. The TTO procedure has been developed as a hybrid of two previously available orthopaedic procedures, the tibial tuberosity advancement (TTA) and the tibial plateau leveling osteotomy (TPLO). The TTA neutralises shear force within the stifle by advancing the tibial tuberosity until the tibial plateau is at right angles to the patellar ligament. The TPLO neutralises shear force by rotating the tibial plateau so that it is approximately horizontal with respect to the long axis of the tibia. The TTO combines both of these procedures and as such less radical changes than either are required.
The knee joint is often required to be opened and inspected. The torn or partly torn cruciate ligament is removed. If the meniscus is torn, the damaged portion is removed. A large, strong suture is passed around the fabella behind the knee and through a hole drilled in the front of the tibia. This tightens the joint to prevent the drawer motion, effectively taking over the job of the cruciate ligament.
- Typically, the dog may carry the leg up for a good 2-4 weeks after surgery but will increase knee use over the next 2 months, eventually returning to normal.
- Typically, the dog will require 8 weeks of exercise restriction after surgery (no running, only outside on a leash, including the backyard).
- The suture placed will break 2 to 12 months after surgery and the dog’s own healed tissue will hold the knee.
With cruciate surgery, there is not one superior technique. As each dog’s conformation is different, it would be incorrect to make a straight comparison of the TTA/TTO/TPLO or extracapsular repair techniques. At Anderson Vets we will advise which technique is most suitable for your pet.
Potential (but rare) Complications
What are the possible complications of these procedures? Any general anaesthetic involves a potential risk but our staff is trained and highly competent. We also have a range of modern monitoring equipment which helps increase the safety of the procedure. All surgical procedures carry risk of potential problems such as infection or complications following implant placement. We have a very low complication rate and if dealt with correctly these problems are resolved swiftly. You will notice your dog’s stifle may look at little different after the operation: there will be a small “bump” below the joint after an MMP surgery, which is the new tibial crest position, although to the untrained eye this is rarely noticeable.