P. 591

A. Pozzi1
1Clinic for Small Animal Surgery, Department of Small Animals, Vetsuisse-Faculty, University of Zurich
Cranial cruciate ligament (CrCL) rupture is one of the most common causes of hind lameness in dogs. The CrCL maintains stability of the sti e joint, thus injury to the CrCL will result in joint instability and predispose the joint to degenerative changes. In dogs, the majority of CrCL ruptures occur under normal activity, likely
due to structural deterioration of the ligament and not because of a traumatic injury. Rupture of the CrCL due
to degeneration can present acutely even in young dogs and eventually becomes bilateral. Osteoarthritis, meniscal injury, and persistent lameness commonly occur with CrCL rupture. Therefore, the pathological condition related to CrCL rupture is often referred to as “cruciate disease”. Cranial cruciate ligament rupture is particularly common in large and giant breed dogs; however, any breed, size, or age of dog may be affected. Although clinical features and treatment options have been
well discussed in the veterinary literature, the disease mechanisms for CrCL rupture are poorly understood.
The sti e is a complex, diarthrodial, synovial joint that allows motion in three planes. Sti e motion occurs through a combination of rolling and gliding of the femur on the tibia. Rollback is asymmetric: femorotibial contact translates more caudally on the lateral than on the medial plateau, resulting in internal tibial rotation during sti e  exion. Due to the tibial translation coupled with  exion and extension, it is clear that the sti e does not function as a pure hinge joint. Although the rotational motion about the medial-lateral axis far exceeds the motion about the other two axes, approximately 20° of varus- valgus and internal-external rotation occurs over an entire walking-gait cycle in normal dogs. Re-establishing this complex motion should be the goal of CrCL reconstruction techniques. However, normal kinematics is dif cult to achieve. Both lack of neutralization (e.g tibial osteotomies), or absolute constraint (e.g. extracapsular stabilization) of internal-external rotation may lead to abnormal mechanical stresses on the articular surfaces and progression of osteoarthritis.
Traditional surgical techniques attempt to impart stability by utilizing an autogenous, allogenic, or synthetic structure placed within or about the sti e that mimics the function of the normal CrCL. Extra-articular stabilization techniques are predicated on transiently restraining abnormal sti e motion until suf cient joint adaptation
occurs to provide functional stability and improved
limb function. A recent development in extra-articular prosthetic stabilization techniques was the use of suture anchors. Suture anchors are used to provide secure, precise  xation of the prosthesis’ origin, insertion, or both. A recent development of suture anchors is the knotless design that allows to secure the suture with an interference screw. The absence of a knot increase the stiffness of the  xation and decrease the creep, typically caused by the knot. Different anchor sizes are available, allowing to select the anchor base don size of the dog (or cat). Another extra-articular stabilization technique was developed by Cook, termed the TightRope CCL®. The technique utilizes bone tunnels drilled in the femur and tibia to place a braided polyester coated polyethylene suture on the lateral aspect of the sti e. The suture is passed through the tunnels and anchored to the medial aspect of the femur and tibia where the bone tunnels emerge using toggle buttons.
Another approach to sti e stabilization uses the concept of creating dynamic stability in the CrCL-de cient
sti e by altering bone geometry. Among several tibial osteotomies, the tibial plateau leveling osteotomy (TPLO) attempts to provide stability by decreasing the tibial plateau angle, while the tibial tuberosity advancement (TTA) procedure attempts to dynamically neutralize cranio-caudal instability by altering the relative alignment of the patellar tendon to the tibial plateau.
The clinical results of both TPLO and TTA are favorable, although complications such late meniscal injury suggest that instability may persist in some cases. The meniscus acts as a secondary stabilizer in the stable sti e, while become a primary stabilizer in the CrCL-de cient sti e. Thus, a meniscal injury occuring after an extra-articular technique, TPLO or TTA suggest that these techniques do not fully re-establish normal joint stability. The concern about persistent instability after TPLO and TTA has
been raised in two studies evaluating joint stability with weight-bearing radiographs. Based on these studies (n=15 TPLO; n=30 TTA) a group of dogs (30% TPLO and 70% TTA) may have a degree of tibial subluxation postoperatively, despite having a good clinical outcome. Postoperative instability after TPLO and TTA has been con rmed in in vivo studies using  uoroscopy to perform 3-dimensional kinematics.
The cause of postoperative instability after TPLO or TTA is unclear. Possible causes include 1) lack of secondary stabilization provided by the meniscus (meniscectomy); 2) rotational instability due to acute CrCL ruptures
(no periarticular  brosis) or mild joint malalignment;
3) failure of the dynamic stabilization mechanism
due to other causes. Ideally, these cases at risk of persistent postoperative instability should be recognized
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