DU Spring 2017

Anterior Cruciate Ligament Repairs

by John Maniatty V.M.D.

There are several types of anterior cruciate ligament repairs, and more are coming out every few years. For the sake of this article, we will cover the three main repair techniques: Lateral imbrication, tibial plateau leveling osteotomy (TPLO), and tibial tuberosity advancement (TTA). They each can be effective, and there are positive and negatives associated with each.

All three techniques start the same by going into the stifle joint to remove the remnants of the broken anterior cruciate ligament, any bony fragments, smooth out roughened areas, and if the meniscus is damaged remove the damaged portion. Then close the joint capsule. From here the three techniques vary.

Lateral imbrication is the oldest of the three techniques and is being tweaked 'till this day. It replaces the anterior cruciate ligament with a monofilament nylon suture. This is accomplished by passing the nylon suture behind the lateral fabella, a small bone on the back of the stifle joint at the level of the distal femur. The nylon suture is passed just below the patella tendon and brought back through a hole that is drilled in the tibial tuberosity. The stifle is then placed in normal position for standing, and we secure the nylon suture by either tying a knot or using a crimp clamp. By doing this, we prevent internal rotation and also keep the tibia from being able to slide forward. This gives the stifle increased joint stability.

The positives of this technique are the lack of need for specialized equipment which keeps the price down; the patient can return to full function in 6 -12 months and minimal bone manipulation means less chance for fractures. The negatives can be a failure in the nylon suture, rupture of the fabella ligament, which decompensates the whole repair, and infection. Which is not great for very large dogs, and studies have shown greater osteoarthritis later in life compared to TPLO/TTA.

TPLO is the next oldest of the techniques and has been around for about 24 years (1.) This technique is based on the fact that the tibial plateau has a natural slope and when the ACL is ruptured forces push the tibia forward, and the femur slides down the slope caudally. The meniscus along with some other tendons and ligaments help prevent it from totally sliding off. The TPLO surgery makes an arc cut in the tibia rotates it to level the tibial plateau and places a specialized plate to hold it in place. By doing this forces are now directed up and down and not cranially or caudally. Before doing the surgery, radiographs are required to calculate the proper rotation needed and size of the curved cutting blade. The positive of this technique, according to some studies, is a faster return to function over lateral imbrication. Others say they are equal (2,3), and better for larger dogs, however, this technique can be performed on almost any size dog. The negatives here include the need for more specialized equipment needed, (higher price) bone cancer associated with the hardware used (i.e. plates and screws), infection and fracture of the bone.

TTA is the newest of the three techniques having come out in the 2000’s and is still being modified. This is why you may see TTA and TTA2 referred to in literature. The principle of the TTA/TTA2 is to alter the angle of the patella tendon that then stabilizes the joint and removes tibial thrust, even in the absence of an ACL. The patella tendon is repositioned by making a cut in the front of the tibia over the tibial crest downward. Then inserting a premeasured box that holds the bone fragment in place, away from the body of the tibia. In the original TTA, it was cut away, and a metal plate was used to reconnect it to the tibia. In the TTA2, it is never fully cut, so the distal end is still connected. By doing either of these techniques the patella tendon is placed at 90 degrees to the slope of the tibia and the tibia is no longer pulled forward by the patella tendon when contracted, and thrust is removed. The positives of this technique offer a faster return to function over lateral imbrication and possibly equal to TPLO. This is a simpler procedure than TPLO and can be done on most size dogs. The negatives include a need for specialized equipment, greater expense than lateral imbrication, plate failure, bone cancer secondary to the plate, infection due to implant, fracture of the bone, and miss calculation, so the patella is not in proper alignment.

Each of these procedures can be successful when chosen correctly. Judgment needs to be based on patient size, activity level, and comfort of the technique by the surgeon. Complications can occur with any surgery and postoperative rehabilitation and follow-up visits to monitor progress help in the overall outcome.