Cruciate Disease
About the Cranial Cruciate Ligament
The cranial cruciate ligament is a fibrous structure band sitting within the stifle (knee joint). This connects the tibia (shin bone) to the femur (thigh bone) and has a mechanical function.
During the motion (flexion and extension movements), the ligament stabilises the joint avoiding the tibia moving forward with respect to the femur (cranial drawer movement) and limiting movements of rotation and hyperextension.
The loading of the bodyweight on the leg causes a compression of the femur (thigh bone), one of the tops of the tibia (shin bone), which has a slop shape. This compression, in absence of a healthy and strong cranial cruciate ligament, results in rolling between the two bones (pushing forward of the tibia and backward of the femur).
About the Menisci
The two menisci are localised within the stifle joint, in a medial and lateral position. They are two fibro-cartilage discs between the femur (thigh bone) and the tibia (shin bone) with a shock absorber function.
Rupture of the Cranial Cruciate Ligament
In most cases, the failing of the cranial cruciate ligament is secondary to slow degeneration of the ligament. Even though a precise cause is unknown, genetic predisposition, obesity, bone anatomy, hormonal problems, immune-mediated and chronic inflammation are believed to be predisposing factors. A rupture of the cranial cruciate ligament is often detected on both stifles. However, an acute rupture of the cranial cruciate ligament secondary to trauma is also possible.
A cruciate failing leads to joint instability, lameness, pain and sometimes meniscal injuries. Once the cruciate mechanical function is lost, a cranial drawer movement (sliding forward and backward of the two bones) is detected during exercise. The rubbing of the two bones causes pain and makes meniscal injury likely.
Furthermore, the loss of the mechanical function will also lead to the tibia pushing forward when the patient is weight bearing. When describing the mechanics of this movement , we will refer to the tibial plateau as a slope. During the loading of the weight, the femur (thigh bone) compresses on the tibial slope causing a forward pushing of the tibia and backward rolling of the femur (thigh bone).
The joint instability and unusual rolling movements of the two bones will cause osteoarthritis from the early stages.
Normal stifle
Rupture of the cranial cruciate ligament.
(Hill's pet products, 2006)
(Hill's pet products, 2006)
Cranial drawer and Tbial Trust movements
Cruciate Treatment
Medical
Medical treatment (non-surgical) may be recommended when the general anaesthetic is a higher risk, for example with patients affected by other medical conditions, or old inactive patients.
This treatment could be successful for patients weighing less than 15 kg, treated with an anti-inflammatory medication, kept on a strict diet and with controlled exercise.
A successful outcome is enabled through the use of physiotherapy/hydrotherapy but signs of improvement may take up to several months.
Despite the healing process, a lack of joint stability will still lead to the progression of osteoarthritis.
Medical treatment is not recommended for young or active patients regardless of their body weight.
Surgical treatment
Stabilisation of the stifle joint can be obtained using different surgical techniques. The most common ones aim to change the biomechanics of the joint cutting the top of the tibia, which are discussed below. Whereas other techniques rely on synthetic materials to stabilise the joint, for example, Lateral Fabella Suture.
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Tibial Plateau Level Osteotomy (TPLO)
The aim of this surgery is to stabilise the stifle joint by modifying its biomechanics.
A flattening of the tibial plateau is achieved by making a circular incision on the top of the tibia (osteotomy). The top bony fragment is rotated and fixed with plates and screws. The amount of rotation will be measured on good quality radiographic images taken prior to the surgery. We always use a high-quality locking plate system, which reduces postoperative complications.
Once the slope is not present anymore, the knee will no longer need the cranial cruciate ligament to stabilise the leg during weight bearing.
A meniscus inspection is always performed as a routine procedure before performing a bone cut. The meniscus treatment is performed in case of additional injury.
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Closing Wedge Osteotomy (CWO)
The aim and the mechanic of this procedure are exactly the same as the TPLO. The main difference is that a wedge of bone is removed from the tibia to achieve a flat tibial plateau.
This will lead to the shortening of the leg.
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Tibial Tuberosity Advancement (TTA)
The aim of the surgery is to modify the biomechanics of the joint making a vertical straight cut on the top and front of the tibia. The tibial front fragment is pulled forward and secured with a metallic cage, plate, and screws. The goal of the advancement of the tibial crest is to modify the angle between the patellar tendon and tibial plateau (top of the tibia). The stability of the joint is achieved when the tibial plateau has an angle of 90 degrees with the patellar tendon.
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Lateral Fabella Suture
The stifle is initially stabilized with extra-capsular synthetic suture material. The suture is traditionally passed behind the lateral fabella (small bone on the back of the femur) and in a predrilled hole within the top-front of the tibia. The suture is secured with a crimp. This initially stabilises the joint, however, the suture loses strength with time, thus the long–term joint stability will relay on the fibrotic tissue as a body reaction to the suture material.
Video: TPLO, TTA, Lateral Fabella Suture
What are the complications and
why we prefer TPLO
The rate of complications is quite low with all three procedures. The common complications are infection, implant-associated failing, or late meniscal injury.
Infections are most commonly controlled with antibiotics; however, in some cases, the bacteria remains attached to the implant. In this case, a review surgery would be required to remove the plate or the implant, resulting in different infection management for each procedure.
In case of severe infections following a TPLO surgery, the plate would be removed after bone healing and antibiotics would be continued according to lab results. Once the bone is healed and the plate removed, no additional surgeries would be required.
The treatment of severe infection after a Lateral Fabella Suture would be more challenging. In this case, a second surgery would be required to remove the implant; this will result in a stifle joint instability. An antibiotic would be administered according to lab results until the joint is completely healed. Once the joint will be free from infection, a third surgery would be required to stabilise the joint.
Management of severe infections is also challenging in cases of TTA surgeries. Removal of some parts of the implant (screws) could be enough to treat the infection. However, in rare cases, a removal of the cage and screws may be required (Serratore and Bernhard, 2018). The cage removal from the bone is challenging because this involves another bone being cut close to the cage. Once the cage is removed, the patient will have joint instability until the bone is free from infection. A third surgery will be performed to stabilize the joint after bone healing.
According to scientific studies, the rate for a late meniscal injury, around 6 months after surgery, varies in percentage according to the type of surgery performed: 3.6% for TTA, 2.4% for TPLO and 1.9 % for lateral suture. The treatment of a late meniscal tear could be through keyhole surgery (arthroscopy) or a review surgery.
Even though the TPLO is the most complex between the procedures described above, this has a lower complication rate in comparison with the other techniques and it is easier to manage infections if they occur postoperatively.
Osteoarthritis Progression
Joint stability and patients free of lameness is the aim of the surgery. However, whichever type of surgery is performed, a minimal progression of osteoarthritis will always be detected. This is due to a lack of the current surgical techniques in reproducing the same degree of stability that is present in a normal healthy cruciate ligament.
Osteoarthritis will be significantly less in comparison with a joint that is not treated surgically.
References
Hill’s Pet Products (2006). Hill’s Atlas of Veterinary Clinical Anatomy. Topeka, USA: Veterinary Medicine Publishing Company.14