Simon C. Roe, BVSc, PhD, DACVS
Disease of the cranial cruciate ligament (CCL) is a common cause of hind limb lameness in the dog. The cause is still unknown, is likely multifactorial, and may even be different in different patients. On the "biological" side of the discussion, many joints present with mild or moderate degeneration despite a short history of lameness and a fresh appearance to the ligament damage. It is presumed that infectious or immune factors may initiate this process. Concurrent hip or elbow dysplasia may play a role. On the "mechanical" side of the discussion, it may be that micro-injury to the CCL initiates both an intra-ligamentous degeneration and joint inflammation. Hyperextension is a possible mechanism, given that the craniomedial band is most commonly found damaged in partial tear injuries. The role of tibial slope in this mechanism is still being studied, but excessive slope does limit extension, and likely increases the load on the CCL.
Whatever the initiating process, once injury is present, clinical symptoms are frequently present, and degeneration progresses. Dogs with partial cruciate tear may be more lame than those with complete tear because they often have a more intense inflammatory process within the joint. This may be due to the amount of collagen being released, as cartilage and meniscal injury from instability is not present. Once a complete tear occurs, most dogs develop significant functional drawer, and joint damage, particularly of the medial meniscus begins. While dogs less than 15 kg have been shown to clinically improve with conservative management, this is usually accompanied with significant periarticular fibrosis secondary to joint degeneration. The "clinical" success is most likely because small dogs tolerate stifle arthritis better than larger dogs.
While I have at times tried many techniques for stabilization of the cruciate deficient stifle, I am currently using either a lateral extracapsular suture (LECS) or a tibial wedge ostectomy (TWO). I do not have objective data on which I base my recommendations to clients (and I tell them that), but I do tend to influence them a little when certain factors are present. I am still happy with the outcome of most of my LECS cases. I do feel there are aspects of the surgery that can make it more likely to be successful, and I will outline those below. However, it is obvious that a significant group of dogs have abnormally steep tibial slopes. This limits their stifle extension and, once the CCL is torn, makes it easier for functional drawer to occur. Also, as the slope becomes steeper, the alignment of the LECS relative to the direction of drawer becomes more perpendicular, thus, potentially, reducing its ability to counteract that motion.
My current approach to a case with cruciate disease is to radiograph the tibia to measure the slope of the tibial plateau. The limb is positioned on the table top with the stifle and hock at approximately 90° and the foot raised slightly. The beam is centered on the stifle to ensure a true medio-lateral view, with the femoral condyles superimposed. Based on Dr. Marcellin-Little's evaluation of measurement techniques, we use the joint line rather than the landmarks described by Slocum. This results in a slope that is 5 to 7° greater than would be calculated by the Slocum method. A slope of 23 to 26° is considered normal. If the slope is greater than 30°, then a TWO is suggested. If the slope is greater than 36°, the tibia is considered deformed, and a corrective ostectomy is recommended.
I had worked on a number of projects aimed at improving the performance of the extracapsular suture. For a single strand secured with a knot, clamping the first throw after tensioning, followed by 4 more throws, produced a secure knot. Cyclic loading suggested that the knot tightened under load causing a little elongation, and some loss of the initial tension. When the self-locking knot was described, I found that it was easy to tie while maintaining tension. It could also be secured by a single surgeon. Recently, I compared the crimp systems to the self-locking knot, and found that crimped loops retained more of the initial tension, and maintained that tension better under cyclic loading, when compared to the self-locking knot. I also like the reduced bulk. I now use two lateral fabella-tibial crest sutures, tensioned by hand, and secured with a crimp, as my stabilizing suture.
Another aspect of the extracapsular suture procedure that I have examined is the effect of the location of the origin and insertion points of the suture on its isometry. Using stifles implanted with markers in a grid pattern over the proximocranial tibia, the distance from the fabella center to each marker was measured on radiographs taken with the joint in progressive degrees of flexion. The ideal hole location (the least change in length) was proximal and cranial. The effect of different femoral origins was also examined, as it has been proposed that a suture anchor can be used instead of encircling the fabella. Isometry of the suture is influenced much more by the placement of the femoral attachment than it is by the tibial attachment. The ideal position was directly cranial to the fabella-femoral articulation, staying as caudal on the condyle as possible.
When exploring a stifle, I also feel that the patient is much more comfortable if the patella is not dislocated during the approach. I perform a small medial arthrotomy, excise a portion of the infrapatellar fat pad, and debride the ligament and examine the meniscus through this window. If there is meniscal damage, it is usually possible to remove the damaged portion though this small opening, but occasionally, it is necessary to extend the arthrotomy and laterally dislocate the patella to access the joint completely.
The lateral fabella is exposed by a para-patella incision in the lateral retinaculum that extends into the biceps fascia and tensor fascia, staying cranial to the biceps muscle. The biceps is retracted caudally. The gastrocnemius muscle head is carefully elevated from the proximal aspect of the fabella, immediately adjacent to the femur so that the needle and suture do not entrap that soft tissue. I use a ½ circle cutting Masons uterine needle that will take the nylon leader line needed for the size of the patient. The needle is bent in its caudal third to narrow the diameter and elevate the point above the eye. I like to pass my needle from distal to proximal staying cranial to the bulk of the fabella.
The tibial crest is exposed by elevation of the biceps insertion on to the proximocranial tibial plateau (Tubercle of Gerdy) until the groove of the long digital extensor tendon is exposed. The origin of the cranial tibialis muscle is sharply elevated to expose the proximocranial tibial crest. Two holes are drilled in the tibial crest--the first is eight in, or immediately beneath the Tubercle of Gerdy, and the second is immediately caudal to the point of insertion of the patella tendon to the tibial crest.
The nylon loop is cut after passage around the fabella, leaving two strands. These are both passed through one hole in the crest from lateral to medial, and then back through the other, from medial to lateral. One of the sutures is pulled tight and held while the joint is moved from extension to flexion. If there is more than 2 mm of relative motion between the strands, this suggests that the positioning is not isometric, and a different configuration is tried, or another hole drilled. Once the suture isometry is established, the crimp is placed, the line tensioned, and the crimp squeezed. The lateral retinaculum is closed with a vest-over-pants suture pattern, in order to imbricate the joint laterally.
Leveling the slope of the tibial plateau to eliminate functional drawer can be done in a number of ways. Tibial plateau leveling osteotomy (TPLO) has some advantages but, when the slope is steep, the fragment must be rotated a large amount, and the tibial crest portion protrudes significantly, and is at risk of fracture. I have used a tibial wedge ostectomy (TWO) to level the slope. While the tibia is shortened, the amount is usually small. In planning the size of the wedge, it is important to remember that the functional axis of the tibial will move cranial, reducing the actual amount of correction achieved. This is countered by increasing the size of the ostectomy, and by aligning the cranial cortices rather than the caudal cortices. While I have done some planar wedges, I have mostly used a chevron ostectomy. This is formed using a cutting guide that has a 135 deg angle. The chevron shape of the ostectomy makes it easier to place a lag screw across the ostectomy after initial reduction, and adds a little to the stability of the fragment interaction. After some failures when using a locking TPLO plate for the TWO, I have gone back to the regular clover headed TWO plate.
Post-operatively, I manage the patients similarly. After 2-3 days of bandage support, I have the clients begin ice packing, massage and passive range of motion exercises. Activity is strictly limited for the first 4 weeks. As long as the patient is using the limb at this point, I have them begin to increase the length of the controlled walks. After 2 to 3 weeks, they can do 20 minutes twice a day. Activities to improve range of motion are suggested--walking in shallow water or tall grass, slow stair climbing or low cavalettis. After a physical examination (and a radiographic examination for the TWO's) at 8 weeks, the exercise regimen is increased so that muscle strength and condition returns.