The knee joint in the dog is composed of three bones: the femur, tibia and patella. There are four ligaments that stabilize the knee (stifle) joint. Two collateral ligaments on either side of the bone and two ligaments that form an “x” on the inside of the knee joint. Theses ligaments that form an “x” are the cranial and caudal cruciate ligaments. They prevent forward and backward movement of the tibia relative to the femur. The cranial cruciate ligament also plays a role in preventing internal rotation of the tibia. The cranial cruciate ligament in dogs is the same as the ACL (anterior cruciate ligament) in people. The menisci are paired thin layers of cartilage located between the surfaces of the knee joint. The menisci help to distribute load on the tibia and help provide stability to the joint.
Torn Cranial Cruciate Ligament (CrCL)
The cause of a torn CrCL can be from multiple factors, including ageing of the dog, obesity, poor physical condition, conformation, trauma, and other factors not clearly yet defined. Complete and partial tears occur. Partial tears frequently develop into full tears. As many as fifty percent of dogs who tear one CrCL may tear the other one.
The diagnosis of a CrCL tear is made by establishing that joint instability exists by performing a cranial drawer test. Forward motion of the tibia relative to the femur (just like a drawer being pulled forward) confirms that the CrCL is either partially or completely torn. While x-rays cannot show that the ligament is damaged they are taken to evaluate the degree of arthritis, confirm swelling within the joint and rule out other disease such as infection, bone tumor or fractures. If the owners wish to pursue the surgical repair of the CrCL, x-rays are necessary. It is not uncommon for the veterinarian who is performing the surgery to require specific views of the knee to measure the tibial slope and plate size thus x-rays from a referring veterinarian may need to be repeated.
Surgical Treatment – TPLO
The TPLO (Tibial Plateau Leveling Osteotomy) has been a very successful surgical option for treating CrCL tears. This procedure does not repair the ligament itself but rather changes the biomechanics of the joint in order to stabilize the knee. Dogs have a steep tibial plateau (usually between 20 and 30 degrees) this makes their knee (stifle) very unstable when they tear their CrCL. The procedure involves performing a curved osteotomy (a cut in the bone) below the joint surface of the tibia. The top of the tibia is then rotated to decrease its slope or flatten the tibial plateau resulting in a dynamic stabilization. A bone plate and screws are placed across the cut bone to secure the top of the tibia in its new position. It takes approximately 8 weeks for the bone to heal; restricted activity is necessary during this period of time. Recheck x-rays are taken 8 weeks post operatively to ensure that the bone has healed and the dog is ready for an increase in activity.
Surgical Treatment – Suture Repair
The Modified DeAngelis and Tightrope are extra-capsular suture stabilization techniques. These procedures involve using strong suture to mimic the CrCL. In general these procedures are reserved for smaller and/or older patients. Failure of the suture is a common problem likely because of the dog’s steep tibial plateau and unstable joint seen with CrCL tears. This procedure requires restricted activity for 6 weeks post operatively.
Post Operative Care
Whether it be a TPLO or extra-capsular repair it is important that care be taken during the six to eight weeks following surgery. Avoiding vigorous activity is very important. Vigorous activity includes: jumping on and off furniture, rough play, chasing balls or squirrels, etc. It has been shown that a rehabilitation program is helpful in maintaining and/or regaining muscle mass. These exercises along with hydrotherapy are also beneficial to the physiological well-being of dogs recovering from surgery. Post-Operative Advice
- Your dog must be on leash at all times when going outside.
- Leash walks should be slow to encourage your dog to use the surgery leg.
- Don’t let your dog jump on and off high couches or beds. Low couches and beds are fine.
- When unattended keep your dog confined to a single room. No running to the door/window.
- Don’t let your dog jump on and off high couches or beds. Low couches and beds are fine. If your dog is used to sleeping with you, you may try putting your mattress on the floor.
- Please put non-slip mats on your floors if they are slippery.
- Please block off all staircases. If your dog needs to walk up or down stairs walk slowly holding their post-operative harness. You can use the harness to support them, but you don’t need to actually lift the dog.
- Help protect the operated leg when your dog is getting in and out of the car. For bigger dogs, using two people is helpful.
- Be prepared to use the e-collar for two weeks.
- Please keep the bandage dry and do not allow your pet to chew the bandage off. The bandage will typically slip down the leg exposing some skin sutures.
- Monitor the leg for redness, swelling, heat, excessive pain or any odor. Do not allow your dog to lick or chew at the incision.
- After the bandage is removed you may ice the leg for 10 minutes once or twice a day. When your dog is lying down, place the ice pack around both sides of the joint. The best time to ice your dog is after your walks. If your dog doesn’t like the icing it is not critical to their recovery.
- Follow all directions for all medications carefully. If your dog vomits, has diarrhea or loss of appetite please call the clinic.
Treatment – Conservative Management
Conservative management is an option though smaller breed dogs have a better chance of success than larger breeds. Conservative management often requires a lifestyle change for the pet. Avoidance of prolonged overly vigorous activity along with joint supplements and additional medications are strategies to help manage CrCL tears conservatively.
Complications Associated with CrCL Tear
As mentioned above the most common complication associated with a torn CrCL is increased discomfort due to progression of arthritis. Another problem can be a torn meniscus. It can be painful when torn and is commonly seen with complete CrCL tears, in particular those with marked instability. In some cases the meniscus that was healthy at the time of surgery can tear at a later date. Other complications related to the surgical repair of the CrCL can include delayed bone healing and infection.
Andrew E. Sams, DVM, MS, Diplomate ACVS
American College of Veterinary Surgeons: www.acvs.org
Paul A. Manley, DVM, MSc, Diplomate ACVS
Slocum B., Slocum T.: Cranial Cruciate Ligament
Synthes Vet: www.tploanswers.com