Anterior cruciate ligament (ACL) reconstructive surgery is one of the most common types of orthopedic surgery in humans, with an estimated 1.5 million corrective surgeries being performed over the past several decades (1). Tears to the ACL can occur due to variety of mechanisms including age, gender, and hormonal influences, as well as different biomechanical stressors on the knee joint and local soft tissue structures (2). Domestic pets also suffer from cruciate ligament tears and share many of the same underlying causes and predisposing factors. Due to the mechanics of the canine knee, referred to as the stifle, surgical planning and technique needs to be approached based on size, age, and concurrent local orthopedic problems. One such surgical approach, known as the CORA-based levelling osteotomy (CBLO), allows our four-legged friends to return to function and improve their quality-of-life post-cruciate ligament rupture.
The canine stifle joint is a complex structure integrating several orthopedic and soft tissue structures working in unison to support the region in all stages of rest and motion 3. The stifle joint consists of the femur located proximally, or near the body, and tibia (shinbone) and fibula distally, or away from the body. Connecting the femur to the tibia is the patella, or kneecap, along with the patellar tendon proximally and ligament distally. The joint itself is protected by a fibrous structure known as the capsule, which houses the internal structures of the joint and joint fluid, which aids in lubricating the joint surface for easier motion. On the top surface of the tibia is an area known as the tibial plateau. On this surface rests the right and left menisci, which are cartilaginous structures aiding in shock absorption of the stifle. Preventing excessive joint motion is controlled by four primary ligaments in the stifle: the medial and lateral collateral ligaments, and the cranial and caudal cruciate ligaments. Originating at the rear end, also called caudal surface, of the femur and ending on the front facing, or cranial, region of the tibia are the cranial and caudal cruciate ligaments, called so due to their “X” shape. The function of the cranial cruciate ligament is to prevent stifle hyperextension, excessive internal rotation, cranial drawer (excessive forward and backward motion), and cranial tibial thrust (dynamic motion of the stifle joint when walking).
As previously stated, CCL rupture is a complicate process involving several factors including from mechanical degradation, abnormal hind limb biomechanics, hormonal influences, reproductive status, vascular insufficiencies, and potentially autoimmune interactions (3,4). Dogs over 15 kg, most often large breeds including Rottweilers, Labrador Retrievers, Newfoundlands, and others are most often affected (5). Chronic changes to the ligament involve invasion of inflammatory cells, metaplasia of normal ligament tissue, and loss of collagen (4), which may result in decay of the tissue. The blood supply feeding the cruciate ligaments originates closer to the boney attachments and is limited towards the center, which is also the most common region for tearing (6,7). Sex hormones and reproductive status have been shown to play a role in laxity in the canine CCL. Dogs that have been spayed or neutered were more likely to have a ruptured ligament and other chronic orthopedic diseases 8. Additionally, the hormone relaxin, typically involved in the female reproductive tract, and its corresponding receptors have been in weakened and torn CCLs in the dog (9,10), and may be predisposing the ligament to excess laxity and rupture. Separating the CCL from the rest of the inner joint capsule is the epiligament. When the epiligament becomes compromised, the cruciate ligament becomes exposed, recognized as a foreign material, and is attacked by the immune system (12). Direct trauma to the stifle can result in a CCL rupture, although most cases have one or more of the previously mentioned underlying causes.
The primary goal of surgery is to reduce cranial tibial thrust, which is achieved by increasing the joint angle of the stifle or externally supporting the stifle joint 3,10. Several types of surgeries are used to correct a ruptured cruciate ligament, one such procedure is known as a CORA-based levelling osteotomy (CBLO). CORA, short for center of rotational angle, “is the intersection of the mid-diaphyseal line and the line starting from the middle of the joint and perpendicular to the abnormal” joint angle 13. The surgery involves a dome-shaped cut into the bone, known as an osteotomy, using a unique bone saw. The cut bone tissue is then rotated until the joint angle is increased to around 9 – 12 degrees, which reduces cranial tibial thrust by increasing the tibial plateau angle. The osteotomy site is secured with plates and screws to stabilize the region until the cut bone heals over the next several weeks to months (13). Complications are possible with any surgery, and may include infection (incisional or implant), implant failure and migration, patellar ligament thickening and inflammation (desmitis), and meniscal tears (13). Overall, the surgery has a very good prognosis for return to function in the pet and owner satisfaction with healing progression (13).
Canine cruciate ligament rupture is a complex disease with multiple predisposing factors. Due to these potential causes, the cost of treatment for pets is over $1 billion 14. The canine stifle is a complex structure balancing the dynamics of several bones and soft tissue working together when the dog leg is in motion. While the underlying causes may be difficult to avoid completely, surgical correction of the ruptured ligaments can significantly improve the quality of life and return to function of the dog. While future diseases such as osteoarthritis cannot be avoided with cruciate disease, the overall prognosis with surgery is excellent.
Works Cited:
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5. Vasseur, P. B., Pool, R. R., Arnockzky, S. P., & Lau, R. E. (1985, September 1). Correlative biomechanical and histologic study of the cranial cruciate ligament in dogs. Europe PMC. https://europepmc.org/article/med/3901837
6. Spinella, G., Arcamone, G., & Valentini, S. (2021, September 6). Cranial cruciate ligament rupture in dogs: Review on Biomechanics, ETIOPATHOGENETIC factors and rehabilitation. MDPI. https://www.mdpi.com/2306-7381/8/9/186
7. Kuroki, K., Williams, N., Ikeda, H., Bozynski, C. C., Leary, E., & Cook, J. L. (2019, February 1). Histologic assessment of ligament vascularity and synovitis in dogs with cranial cruciate ligament disease. AVMA. https://avmajournals.avma.org/view/journals/ajvr/80/2/ajvr.80.2.152.xml
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9. Restucci, B., Sgadari, M., Fatone, G., Valle, G. D., Aragosa, F., Caterino, C., Ferrara, G., & Niebauer, G. W. (2022, March 23). Immunoexpression of relaxin and its receptors in stifle joints of dogs with cranial cruciate ligament disease. MDPI. https://www.mdpi.com/2076-2615/12/7/819
10. Berger, G. K., Rockov, Z. A., Byrne, C., Trentacosta, N. E., & Stone, M. A. (2023, June 10). The role of relaxin in anterior cruciate ligament injuries: A systematic review - european journal of orthopaedic surgery & traumatology. SpringerLink. https://link.springer.com/article/10.1007/s00590-023-03618-7
11. Barrett, J. G., Hao, Z., Graf, B. K., Kaplan, L. D., Heiner, J. P., & Muir, P. (2005, December 1). Inflammatory changes in ruptured canine cranial and human anterior cruciate ligaments. AVMA. https://avmajournals.avma.org/view/journals/ajvr/66/12/ajvr.2005.66.2073.xml
12. Bonasia, D. E., Dettoni, F., Femino, J., & Phisitkul, P. (2010, January). Figure 4. the center of rotation of Angulation (CORA) is the... ResearchGate. https://www.researchgate.net/figure/The-center-of-rotation-of-angulation-CORA-is-the-intersection-of-the-mid-diaphyseal_fig4_47661873
13. Kishi, E. N., & Hulse, D. (2016, May). Owner evaluation of a Cora-based leveling osteotomy for treatment of cranial cruciate ligament injury in dogs. Veterinary surgery : VS. https://pubmed.ncbi.nlm.nih.gov/27041682/
14. Wilke, V. L., Robinson, D. A., Evans, R. B., Rothschild, M. F., & Conzemius, M. G. (2005, November 15). Estimate of the annual economic impact of treatment of cranial cruciate ligament injury in dogs in the United States. AVMA. https://avmajournals.avma.org/view/journals/javma/227/10/javma.2005.227.1604.xml
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