crutiateinjuries

CRANIAL CRUCIATE LIGAMENT

Cranial cruciate ligament (CCL) rupture is one of the most common injuries to the stifle of dogs and is the leading cause of degenerative joint disease in that joint. The annual economic impact of medical and surgical management of CCL insufficiency has becently been estimated to about 1 billion dollars in the United States alone (Wilke et al. 2005). Whereas traumatic rupture of CCL predominates in humans, CCL deficiency in dogs is typically associated with a chronic history of progressive lameness consistent with a degenerative process.
Misalignment of the joint surfaces is a well-recognized cause of arthrosis and gait abnormalities. Techniques altering overall limb, and specific joint alignment have recently gained popularity to prevent or correct surgical diseases of the joints, including CCL disease.

Rupture of the CCL has been associated with degenerative changes, auto-immune diseases, hormones (sex predisposition), collagenase activity and antibodies against type-I and -II collagen in synovial fluid (Comeford 2003, Moore KW, Read RA 1996). However, weakening secondary to repetitive microtrauma is currently believed to cause the majority of CCL instabilities diagnosed in dogs, especially in large breeds such as Rottweilers. A great deal of interest has recently focused on the importance of the "cranial tibial thrust" as an underlying cause for repetitive microtrauma to the CCL. This force generated by compression between the tibia and femur during the stance (weight-bearing) phase, is partly oriented in a cranial direction, leading to cranial translation of the tibia. In a stable knee, this force is actively opposed by the pull of the sifle flexor muscles.

The magnitude of this force generated by contraction of the gastrocnemius depends on the amplitude of the compressive force (70% of the body weight at trot) but also on the slope of the tibial plateau with respect to the axis joining the centers of motion of the stifle and hock. This theory provides a basis for the Tibial Plateau Leveling Osteotomy (TPLO), a procedure that is not aimed at restoring the anatomical stability of the CCL deficient stifle. Instead, it modifies the joint geometry to neutralize cranial tibial thrust during weight bearing. Although this procedure has gained tremendous popularity for treatment of CCL deficiency in large breed dogs, several studies have failed to show a correlation between the steepness of the tibial plateau and the develpment of CCL insufficiency.

This reflects the fact that these stress injuries most likely result from a combination of, rather than from a single factor. Indeed, the biomechanical environment leading to CCL instability can be described as an imbalance between factors contributing to the CTT and its active restraints, eventually leading to fatigue failure of the passive restraints (CCL and medial meniscus). This would explain the association between obesity and CCL deficiency. This could also explain the mechanism of action of conformation abnormalities previously believed to lead to CCL defieciency, such as genu varum, increase in stifle angle, tarsal hyperextension, deformation of the proximal tibia or stenosis of the intercondylar notch. Genu varum consists of a varus deformation of the femur, resulting in a "bow-legged" stance. This conformation has been associated with medial patellar luxation (MPL). MPL tends to cause an internal rotation, whhich is prevented in part by by the CCL. Misalignment of the patellar tendon affects the direction of forces generated by the quadricepts and destabilizes the anterior compartment of the knee.

The impact of the thigh muscles on the magnitude of the CCT remains poorly defined. Yet, an imbalance between flexor and extensor muscles of the thigh would contribute to CCL overuse. This imbalance could result from a difference in muscle distribution that could potentially be corrected via physical therapy. Another potential cause of imbalance between muscle groups could result from a cranio-caudal misalignment of the quadriceps, affecting the direction and moment of forces generated during weight bearing. This theory would support the mechanism of action of tibial buberosity advancement (TTA) as a recently proposed treatment for CCL deficiency. This procedure maintains the angle between the patellar tendon and the tibial plateau to a maximum of 90 degrees in full extension, thereby loading the caudal cruciate ligament throughout the entire range of motion of the knee. TTA involves a pre-determined open wedge osteotomy of the tibial tuberosity that is fixed with a tension band plate and grafted.

Proximal tibial shaft deformity was recently described in 9% of dogs with CCL and steep tibial plateau slope. The deformity consisted of a caudal tipping of the proximal tibia in relationship with its long axis, thereby identifying a distinct subpopulation of dogs with CCL disease. Although these findings warrant further investigation, they may eventually affect our therapeutic recommendations. Indeed, a cranial tibial wedge would re-align the entire proximal tibia, and may therefore be a better option than TPLO in these dogs.

The multifactorial origin of CCL deficiency secondary to repetitive microtrauma most likely involves the tibial plateau slope along with other morphometric parameters, whose relative contributions have yet to be defined. Variations between breeds, difficulties identifying "normal" versus "predisposed" dogs, invasiveness and cost of procedures hinder our ability to design meaninful studies and improve our understanding of pathogenesis of CCL disease.

Cranial Crutiate Ligament (CrCL) injuries are consisting of partial tears and of complete rupture. Partial tears are associated to short term and self limiting acute lameness, evolving in chronic grade 1 lameness, usually underestimated and leading to complete rupture after a variable time. The cranial tibial thrust associated to the tibial slope and the weigh bearing forces has been demonstrated to be responsible of the continuous stress on the damaged ligament leading to its complete rupture.

CrCL complete rupture is clinically associated to acute grade 3 lameness and can be a consequence of a chronic tear or it can be associated to a recent acute trauma, usually consisting of stifle hyperextension and internal rotation, the same condition leading to traumatic partial tears when of less amount.

When CrCL complete rupture is a evolution of partial tears the radiographic findings at time of diagnosis are consisting of chronic signs including ostophytes on the femoral trochlear ridges, on the distal poles of patella and on the tibial plateau, periarticular soft tissue swelling and infrapatellar increased density. When complete rupture is a consequence of acture trauma and immediate radiographic examination of the affected knee shous only periarticular soft tissue swelling and increased density of the infrapatellar triangle without any osteophyte. Clinical observation that several dogs have CrCL partial tears in both knees at the same time, even if with different degrees of severity, and that several dogs presented for acute CrCL complete rupture have partial tears in the opposite knee indicates that CrCL injuries are not always associated to a trauma and that in predisposed dogs they can be a consequence of a biomechanical imbalance of the forces acting on the knee joint causing a continuous stress on the CrCL. Traumatic and non-traumaticl CrCL injuries can be differentiated by investigating the opposite knee too with physical and radiographic examination every time a diagnosis of CrCL lesion is performed. Traumatic injuries should show the opposite knee as normal, while the non-traumatic ones should show signs of chronic inflammation and degenerative joint signs.

Clinical Study
A prospective study of 251 consecutive dogs treated for CrCL failure was performed. Data collection included all relevant findings regarding patient signalment, history, radiographic aspects of both knee joint at the time of diagnosis and the surgical findings. Radiographic data included a thorough evaluation of the knee joint for acute and chronic inflammation signs, using low dose exposure to visualize periarticular soft tissues too, and a stressed position to evidence and measure the tibial compression test. The tibial slope was measured according to the indications described by Slocum. Pictures of dogs in standing position were taken, with adhesive marks on trochanter, lateral femoral condyle and lateral tibial malleolus to calculate the knee angle at rest in standing position. Dogs with both knee joints simultaneously affected, even with different degrees of severity, were listed as affected by non-traumatic CrCL injuries. Dogs with the opposite knee joint normal at the time of diagnosis were listed as affected by traumatic CrCL injuries. A correlation was studied between traumatic and non-traumatic CrCL injuries according to breed, sex, age, weight, tibial slope and knee angle. According to the surgical findings and to the amount of tibial compression test the partial tears or complete rupture were recorded.

This clinical study showed the evidence that in many dogs of several breeds CrCL injuries have a non-traumatic cause, being developed slowly and simultaneously in both knees, even with different degrees of severity. The median age of non-traumatic CrCL injuries is lower than in the traumatic group, indicating a breed and individual predisposition to early CrCL injury. Several breeds, like Boxer, English Bulldog, Dogue De Bordeaux, Newfoundland, Great Dane, Doberman, Corso and Rottweiler show a higher incidence of non-traumatic CrCL injuries compared to other breeds; in these most affected breeds the tibial slope is not indicating an anatomical predisposition as their values are in the average of the dogs most affected by traumatic CrCL injuries and not be non-traumatic CrCL injuries. What appears to be a predisposing factor in the breeds with higher incidence of non-traumatic CrCL injuries is the angle of the knee joint in standing position, being wider than in the other breeds, leading to a more straight rear leg. The open angle of the knee enhances the inclined palnde effect of the tibial slope and diminishes the opposing pull strength on the tibia by the hamstring muscles, leading to a continuous cranial tibial thrust and stress on the CrCL. The consequence of a wider knee angle with a more straight leg is therefore a biomechanical imbalance that could lead to a spontaneous CrCL injuries, particularly when associated to high physical activity or to high body weight. In contrary, in breeds without a significant incidence of non-traumatic CrCL injuries, the knee angle is closer, with a more angled rear leg, diminishing the effect of the inclined tibial plane which is almost parallel to the ground and enhancing the pull effect of the hamstring muscles, with a perfectly balance biomechanics.

Moreover, the incidence of non-traumatic CrCL injuries in breeds that usually have a normal knee angle, like German Shepherds and Laradors, was associated to increased age and body weight of the affected dogs at the time of diagnosis; due to the increased weight of these dogs showed a wider knee angle and more straight leg compared to the average knee angle of the breed, possible because keeping a closer knee angle with an increased body weight would cause an excessive muscular tiring. Keeping the knee in a more straight position releives the muscular effort and the dog is more comfortable, loading his body weight through a bone to bone more vertical contact, but doing so the cranial tibial thrust is enhanced, favoured by the increased body weight too. Their rear legs assume the position of human legs in standing, walking and running, with a vertical loading through bones, but in man the tibial slope, which is about 5 to 7 degrees, has no significant cranial tibial thrust, differently to the forces created by the inclined plane of the canine tibial slope. Increased body weight, particularly without a good muscular strength and exercise, is therefore a predisposing factor for non-traumatic CrCL injuries in dogs of all breeds. Other factors could play a role predisposing to CrCL injuries in some breeds. like the bowlegged conformation which causes stress on the CrCL; nevertheless this conformation does not appear to be determinant for non-traumatic CrCL injuries as it is observed in Rottweilers and Labradors both with traumatic and non-traumatic CrCL injuries. In these breeds, as in other large breeds, the occurrence of traumatic CrCL injuries is associated to very active dog with good muscular mass, enhanced by their overweight and inactive dogs with poor muscular mass; this indicates that the muscular tone and strength are essential to balance the high forces acting in their knee, particularly when their conformation leads to straight rear legs.

More extensive studies should be conducted to investigate the biomechanics alterations in the knee joint due to the different morphology in canine breeds and a thorough morphological analysis in breeds predisposed to high incidence of non-traumatic CrCL injuries should be performed to evaluate the opportunity to influence the breed standards favouring a more physilogical angulation of the rear legs in these breeds. Also to encourage breedings according to the Standard/and not to breed to non-traumatic CrCL injured dogs. According to Riser's studies, any breed selection going away from the ancestral dog is causing orthopaedic problems, because the anatomy of the dog can not match to the so wider variation we see in canine breeds without resulting in biomechanical and physiological imbalance.

Because CrCL injuries of non-traumatic origin have their ethiology in biomechanical imbalance of the knee joint with enhancement of the cranial tibial thrust, and because the predisposing biomechanical alterations can not be modified, the best treatment in the affected dogs is the alteration of the knee biomechanics by neutralizing the cranial tibial thrust with the tibial plateau leveling ostiotomy (TPLO) as proposed by Slocum. In traumatic CrCL injuries, traditional techniques of ligament reconstruction, extra or intra-capsular, can be successful providing the tibial slope is within a normal range.

In this study the evidence that several dogs exhibit CrCL injuries without a traumatic cause was demonstrated, locating predisposing factors in the wider knee angle and straight rear leg conformation of several breeds. Also when CrCL complete rupture is a evolution of partial tears the radiographic findings at the time of diagnosis are consisting of chronic signs including osteophytes on the femoral trochlear ridges, on the distal poles of patella and on the tibial plateau, and infrapatellar increased density.

Cranial Crutiate Ligament Insufficiency