Canine Cranial Cruciate Ligament Rupture
Overview: The cranial cruciate ligament (CrCL) in dogs is similar to the anterior cruciate ligament (ACL) in humans. This cruciate ligament within the knee joint (stifle joint) stabilizes the joint during movement by preventing the tibia from sliding forward relative to the femur. It also prevents hyperextension of the knee and, to a lesser extent, internal rotation of the tibia. Rupture or tearing of the CrCL is a common orthopedic issue in dogs, occurring due to acute trauma or, more frequently, chronic degeneration.
Causes:
Acute Trauma: Sudden injuries from activities like running, jumping, or quick turns can cause an acute rupture. This is the most common cause of ACL injuries in humans. Although this can happen in dogs, the majority of CrCL ruptures in dogs result from an inflammatory or degenerative process in the knee that weakens the ligament over time, leading to eventual rupture.
Chronic Degeneration: This is the primary cause of CrCL rupture in dogs, making it more of a condition than an acute injury. While it may seem like a traumatic event triggered the rupture, in most cases, there was already an ongoing degenerative process in the ligament, making it more prone to rupture during activity. The exact cause of this degeneration is not fully understood, but multiple factors are involved, with genetic predisposition being the most influential. Studies have shown this genetic basis across various breeds. However, due to the prevalence in many breed types, the condition is likely rooted in the genome of domestic dogs rather than only specific breeds. If a dog is genetically predisposed, CrCL rupture is likely to occur eventually.
Symptoms:
Lameness: This can manifest as a sudden onset of severe lameness in the affected leg of a previously unaffected dog or as chronic, non-resolving low-grade lameness, which may temporarily improve but usually returns.
Swelling: Noticeable swelling around the knee joint.
Pain: The dog may show signs of pain, such as reluctance to bear weight on the leg, yelping, changes in behavior, or decreased willingness to be active.
Diagnosis:
A thorough physical and orthopedic examination is the primary tool for diagnosing CrCL rupture in dogs. Key examination findings include:
- Lameness in the affected limb(s)
- Palpable effusion (increased joint fluid)
- Palpable accumulation of peri-articular fibrosis on the inner aspect of the knee (medial buttress)
- Pain on knee extension
- Palpable instability, including cranial drawer instability and cranial tibial thrust instability
In many cases, palpable instability clearly indicates a ruptured CrCL. In cases of partial rupture, the knee may feel stable, but other examination findings are typically present.
Diagnostic imaging is often unnecessary for an accurate diagnosis. However, in partial rupture cases, standard radiographs (X-rays) can be helpful. While cruciate ligaments are not visible on X-rays, the presence of effusion and varying levels of arthritic changes correlate with partial CrCL degeneration and help exclude other conditions contributing to lameness.
Advanced cross-sectional imaging, such as CT and MRI, is generally not needed to diagnose this condition in dogs.
Surgical treatment is the most common recommendation for this condition. Although the cause of the instability is typically different from that in humans, the result is similar: instability, pain, and progressing arthritic and fibrotic changes. The role of any surgery is to resolve the instability in the knee during active weight bearing.
Over the years, many surgical procedures have been developed to address CrCL ruptures in dogs. While some have stood the test of time, others have fallen out of favor due to inconsistent positive outcomes. Among the existing procedures, the Tibial Plateau Leveling Osteotomy (TPLO) has consistently shown the most reliable short- and long-term positive results in dogs.
Surgical Overview
The TPLO procedure stabilizes the knee by changing the biomechanics of the interaction between the femur and tibia during weight-bearing. Rather than repairing or replacing the CrCL, this surgery eliminates the ligament’s role in maintaining stability during weight-bearing.
In dogs, the top of the tibia has an angled surface where the femur rests. The angle is typically between 25 and 32 degrees. With a healthy ligament, this angle poses no issues. However, if the ligament is ruptured, the femur tends to slide backward off this angle, while the tibia is thrust forward during weight-bearing. If the ligament is partially ruptured, it stretches and causes pain while attempting to maintain stability.
During TPLO, an osteotomy (a purposeful cut in the bone) is made in the upper portion of the tibia. This allows the upper portion, which has the angled plateau, to be repositioned. Pre-operative measurements guide the rotation to reduce the plateau angle to around 0-5 degrees. This flatter surface allows the femur and tibia to interact more stably, even without a CrCL. The rotated upper portion of the tibia is then stabilized with a bone plate and screws, allowing it to heal in its new position.
Joint Inspection
During the procedure, the knee joint is inspected, often without needing to visualize the CrCL for diagnosis. The primary reason for inspecting the joint is to evaluate the menisci for concurrent injury. Like humans with an injured ACL, dogs with CrCL rupture are susceptible to meniscal injury due to knee instability. Approximately 35-40% of dogs with CrCL rupture also have a meniscal injury. Damaged portions of the meniscus are removed carefully to preserve as much of the normal meniscus as possible. If no meniscal injury is observed, the meniscal cartilage is likely to remain functional due to the restored knee stability. However, about 6% of dogs may develop a meniscal injury in the future that will require additional surgery.
Post-Surgery Care:
After surgery, patients will need to restrict their activity levels to prevent complications during the healing process. Despite this, frequent controlled walking and physical rehabilitation are important to maintain range of motion, muscular strength, and limb function.
Follow-up visits with the surgeon are essential to assess recovery progress and perform X-rays (approximately eight weeks post-surgery) to evaluate the healing of the osteotomy site. Based on these assessments, recommendations for future activity levels will be provided.
Full recovery time varies between patients, typically taking several months. Most dogs return to near-normal function within 4-6 months. TPLO has a high success rate, with the goal of surgery being to enable the patient to return to their optimal activity level for their stage of life. In the vast majority of cases, this goal is achieved.