Ligament Surgery

Cruciate ligament ruptures are a very common problem. Here we go through a corrective procedure.

Tibial Plateau Leveling Osteotomy (TPLO)

Procedure of Barclay Slocum DVM., Eugene, Oregon, U.S.A.

One of the most common causes of hind leg lameness in dogs is rupture of the anterior cruciate ligament. Unlike other species the dog can rupture this structure during everyday activities. Other species require some sort of trauma such as being hit by a car or getting their leg hung up.

The reason that dogs produce this injury without trauma is due to the unique anatomy of their knee joint and particularly the slope of the tibia plateau. (fig 1.1 & 1.2).

Fig 1.1	The Normal Knee A: Femur B: Meniscus C: Tibia D: Tarsus E: Achilles Tendon F: Tibial Plateau
Fig 1.2	Lateral view of the stifle with the lateral condyle removed showing cranial cruciate ligament (A) and posterior cruciate ligament (B))

Fig 1.1 & 1.2: The Structure of the Canine Knee

In 1978 Dr Barclay Slocum, an American veterinary surgeon, took a new look at the mechanics of the dog knee. His investigations showed that when the hind limb is used because the Achilles tendon is of a fixed length all forces of the foot are transmitted through the tibia. Because in this species the tibial plateau is sloped, part of this force will be transmitted in a forward (anterior) direction. This force he called 'Cranial Tibial Thrust'. The only passive restraint to this force is the anterior cruciate ligament and it is this force that causes the rupture. (fig 2) 

Once rupture has occurred the tibia can move forward on the femur causing crushing of the medial meniscus (cartilage). This causes the pain and the inevitable arthritic changes. (fig 3)

Fig.3: The cranial cruciate ligament is ruptured (A) and the caudal horn of the medial meniscus (B) is impinged on when the cranial tibial thrust (C) is not neutralised by the pull of the hamstrings and biceps femoris muscles (D).

Since 1958 two methods of surgery have been 'in vogue'; these are ligament substitution (a replacement ligament) or surgery to the lateral aspect of the joint to prevent the tibia moving forward on the femur. These procedures have not been very successful because they have not addressed the cause of the rupture which is cranial tibial thrust.

All authorities agree that whatever traditional surgical method (and the many modifications) is chosen the joint will continue to deteriorate over time. For the large dog this can be a disaster and frequently this situation is reached within a few months. See X-ray below.

Having discovered the reason for the rupture (cranial tibial thrust) Dr Slocum then invented surgery to eliminate or severely reduce this force. The result is TIBIAL PLATEAU LEVELING OSTEOTOMY a surgical procedure that he released to others in 1995.

Tibial Plateau Leveling Osteotomy (TPLO) surgery consists of cutting out the tibial plateau with a special saw blade and rotating it to reduce the slope. The two parts are held together during the healing period with a specially designed bone plate and screws. This surgery eliminates the need for a cruciate ligament as the patient can now hold the knee stable in motion by the action of the hamstring muscles.

Fig 4.1	Tibial Plateau Leveling Osteotomy A: Tibial Axis B: TPLO Plate C: Tibial Plateau Axis (Arrow indicates direction of proximal tibial rotation)
Fig 4.2	The cranial tibial thrust (A) is reduced by the tibial plateau leveling osteotomy until until it is in balance with the pull of the hamstrings and biceps femoris muscles (B). The tibia is functionally stabilised by the caudal pull (B) that is passively opposed by the caudal cruciate ligament. The tibial plateau leveling osteotomy plate (C) maintains bone relationship during the healing process.

CITIVET introduced this technique to the U.K. in 1995 and the results of this surgery have been excellent. The arthritic changes cease to progress, joint swelling and pain quickly subside . It is noticeable that following this operation patients are comfortable with the work and one major problem has been owners have allowed too much activity before bone healing has occurred. Once bone healing has taken place at about eight weeks a rehabilitation program is started. Patients return to light work at 2 - 3 months, light training at 3 -4 months and full training at 6 months.

For us to has been a joy to be able to tell owners that we will be able to return their dog to its pre rupture performance. Dogs that have had previous failed surgery are all improved and if there is not too much damage to the joint these will also return to their pre rupture athletic ability.

Thirty percent of dogs that rupture one cruciate ligament will rupture the one in the other knee. We have noticed that with traditional surgery they are not often presented when this happens. An explanation as to why this should happen may be that the operated knee now being arthritic and with some pain results in reduced activity so when the second ligament ruptures the owner does not notice much change in the walking and running. However following TPLO owners quickly notice the problem in the second leg.

It should be noted that some dogs have a twisted or bent leg or both and in some cases to get the best results with TPLO it is necessary to correct these problems at the same surgery.

Fig 5 An analogy is helpful to understand the process of tibial plateau leveling osteotomy. Consider a wagon parked on a hill. A. The weight of the wagon (C, axial compression), pulls downward because of gravity and creates a force (D) because oft eh slope. If a rope (F, cranial cruciate ligament), is tied from the wagon to a fire hydrant and a chock (E, meniscus), is placed behind the tyre (condyle), then the wagon is prevented from rolling down hill (cranial tibial translation). If the rope breaks, the wagon rolls down hill and crushes the chock B. Force (D) can be eliminated by parking the wagon on a level surface and the rope (F) and chock (E) and not needed. The joint compression force is reduced to the weight of the wagon (C). Although the weight of the wagon (C) is not eliminated, it's destructive effects are overcome.

All the above illustrations are copyright Barclay Slocum and are used with permission.

The following pictures and X-rays were supplied by T. G. Yarrow B.V.Sc., M.R.C.V.S.

13 months post op.

4 years post op.

 

The two X-rays above are of the same Rottweiler and show a lack of degenerative changes at 13 months and four years after surgery.

Fig 9

This radiograph 8 months post surgery (Partial rupture) demonstrates lack of degenerative change. (Bullmastiff)

Fig 7

This dog was purchased as an adult. The owner states that since the right leg had TPLO his performance is much improved. The conclusion therefore would be that he had partial rupture at purchase. He can now jump onto the lorry bed with ease. Prior to surgery he was unable or unwilling to do this.

Fig 8

Notice how the dog sits straight. Dogs with ACL rupture and after traditional repair sit with the injured abducted.

This article kindly written by TG. Yarrow B.V.Sc., M.R.C.V.S.