The cranial cruciate ligament (CrCL) counteracts cranial tibial translation, excessive internal rotation, and hyperextension of the stifle joint. In the CrCL-deficient stifle, alteration of joint biomechanics negatively impacts surrounding structures such as the menisci and cartilage, and likely cause accelerated progression of osteoarthritis. In order to suppress rapid progression of stifle osteoarthritis, normal loading and contact biomechanics of the stifle must be restored. Multiple surgical treatments exist, all of which attempt to eliminate cranial translation and hyperextension, as well as restore normal range of internal rotation 2 . Extracapsular stabilization (ES) is a suture technique that has been used to correct stifle instability since the 1960s. It involves the use of synthetic materials to stabilize the stifle through femoral and tibial fixation points such that sufficient periarticular fibrosis can be produced for long- term stability and function. Once fibrous connective tissue has formed, the suture material is no longer needed as a single form of stability 2 . For ES, femoral and tibial fixation points should be placed in anatomic locations that are as isometric as possible; i.e. should remain the same distance apart throughout range of motion-- too lax and cranial tibial translation prevails, too taught and range of motion will be restricted or the suture may rupture. In theory, the use of isometric points will allow for greater stifle stability for a longer duration, until sufficient connective tissue has formed 2 . To date, the recommended femoral fixation point is located at the caudal border of the lateral condyle adjacent to the level of the fabella’s distal pole. It is also acceptable to circumscribe the lateral fabella as an anchor point. The recommended tibial fixation point is located at the bony protuberance 2mm caudal to the sulcus of the long digital extensor tendon, as proximal as possible while avoiding the joint. Care should also be taken surrounding the long digital extensor tendon while creating this bone tunnel 2 . Once the bone tunnel has been created, pass the suture lateral-medial through the bone tunnel, then back lateral under the patellar ligament or through a second bone tunnel depending on which technique you use. With the other side of the suture, circumscribe the lateral fabella, ending with both strands on the lateral aspect of the stifle. Pass both strands of suture through a crimp clamp (primary crimp clamp) in the center. Place a secondary crimp clamp on each strand of suture and crimp both. Apply the tensioning device to the construct on the inside of the secondary crimp clamps. Tension the construct to eliminate thrust and drawer, and upon achieving adequate tension crimp the primary crimp clamp. The secondary crimp clamps may now be removed as their sole purpose was to tension the construct. The completed procedure can be seen below 2 . Two other stifle stabilization techniques herein discussed are osteotomy techniques, which rely on a tibial osteotomy to alter biomechanics of the stifle joint. By producing a 90 degree angle between the attachment of the quadriceps and the tibial plateau, the need for a CrCL to constrain tibial thrust is essentially eliminated. These osteotomy techniques focus on adjusting the biomechanics to produce a stabile stifle joint without a CrCL. The Tibial Tuberosity Advancement (TTA) procedure advances the tibial tuberosity to create the 90 degree angle, while the Tibial Plateau Leveling Osteotomy (TPLO) rotates the contact surface of the tibial plateau. The two procedures differ, as the TTA alters the location of quadriceps insertion relative to the tibial plateau, while the TPLO alters the tibial plateau relative to hock 2 . The TTA procedure advances the tibial tuberosity through a linear cut along the cranial portion of the tibial tuberosity. This cut portion is advanced forward until the quadriceps insertion is oriented 90 degrees to the tibial plateau. Specially designed implants are used to maintain the new position of the tibial tuberosity. These implants include a cage that is the width of the amount of advancement required to achieve the 90 degree angle, and a plate to act as a tension band to hold the construct in place 2 . Cranial Cruciate Ligament Rupture Article by Olivia Doane, BS Biomedical & Mechanical Engineering. Edited by Steven M. Fox, MS, DVM, MBA, PhD CONTINUED ON NEXT PAGE Messenger | November 2015 25 Securos Surgical Insight