Cranial cruciate ligament disease (CrCLD) is a leading cause of lameness in the dog. Many surgical treatments have been described that aim to restore stifle joint stability and minimize the progression of subsequent osteoarthritis. Recent advances in diagnostic visualization and surgical treatments have stimulated an increased emphasis upon early clinical recognition of cranial cruciate ligament pathology. Early diagnosis is essential if the benefit of surgical treatment for CrCLD is to be realized. A comprehensive approach to diagnosis that incorporates consideration of signalment, history, gait evaluation, physical examination and radiography is often needed to make the earliest possible diagnosis of CrCLD.

Signalment

Dogs of most any breed, sex or age can develop cranial cruciate ligament disease (CrCLD) or injury. Labrador Retrievers, Chesapeake Bay Retrievers, Rottweilers, Mastiffs, American Staffordshire Terriers, Akitas, Saint Bernards, and Newfoundlands are predisposed. Neutered males and spayed females are at increased risk as are larger breeds and obese dogs.

History

The onset varies from peracute after a traumatic or athletic injury to an insidious onset, slowly progressive lameness typical of CrCLD.

Gait Evaluation

Dogs with even subtle lameness often lean away from the affected limb while standing. Sitting in a normal posture requires maximal stifle and hock flexion that is often uncomfortable in dogs with CrCLD causing them to abduct the limb or shift it cranially. Dogs with bilateral CrCLD often shift their weight to the thoracic limbs while sitting and rising.

Physical Exam

The standing exam is helpful in detecting subtle changes in muscle mass, periarticular fibrosis and joint effusion. Medial buttress, associated with CrCLD chronicity, is palpable as an exaggerated bump extending across the medial aspect of the stifle joint. The normal stifle has a discretely palpable patellar ligament that feels similar to a pencil with small indentations on each side that feel similar to a bruise on an apple. The loss of these normal findings indicates periarticular fibrosis, joint effusion or both. Pain upon forced full extension of the stifle is a simple test that is suggestive of early CrCLD. The cranial drawer test and tibial compression tests are important for assessing palpable instability. Some dogs are more relaxed in the standing position than when restrained in lateral recumbency. For this reason, I prefer to perform a "tibial compression test" for evaluation of cranial tibial thrust instability at the conclusion of my standing examination. In order to perform this test on the left stifle, the examiner's right index finger is placed on the tibial tuberosity and squeezed toward the right thumb that is secured behind the lateral fabella (Figure 1). This maneuver shifts the tibia of the CrCL-deficient stifle caudally into its "neutral" position under the femur. The right hand also holds the stifle in a standing angle (neither fully flexed, nor fully extended) while the examiner's left hand flexes the hock to simulate weight-bearing. This maneuver creates cranial tibial thrust by tensing the gastrocnemius muscle. In the CrCL-deficient stifle this cranially-directed shear force palpably shifts the tibia cranial relative to the femur. With practice, the tibial compression test becomes an extremely reliable method to test for gross stifle instability, especially in larger breed dogs where the cranial drawer test is difficult due to muscular strength or sheer size. The patient is often positioned in lateral recumbency for the remainder of the examination. The cranial drawer test on the left stifle is performed with the examiner placing his right index finger firmly upon the patella and the thumb behind the lateral fabella in order to secure the distal femur (Figure 2). The examiner's left index finger is placed on the tibial crest and the thumb behind the fibular head to secure the proximal tibia. Slowly rolling tissues away from the fibular head with the thumb and a gentle grip will prevent patient discomfort associated with squeezing the peroneal nerve against the fibular head. With the femur held in place with the right hand, the examiner applies a firm cranially directed force to the tibia with the left hand. In the mature dog, the healthy, intact CrCL will not permit cranial tibial translation with the stifle held in extension or in flexion.² In the immature dog, "puppy laxity" may permit a few millimeters of cranial and caudal tibial translation, but the end-points are crisp and distinct. In the dog with complete CrCL rupture there is obvious cranial tibial translation and an indistinct, ill-defined end-point. Next, a firm caudally-directed translational force is applied to the tibia while holding the distal femur stable. Integrity of the CdCL is confirmed by a distinct endpoint to caudal tibial translation. The drawer test is performed with the stifle in extension, flexion and a standing angle. Partial tears of the CrCL often reveal cranial drawer instability only when the stifle is flexed. Such a finding implies tearing primarily in the craniomedial band of the CrCL because the remaining caudolateral band relaxes in flexion and permits drawer movement. It is important to realize that periarticular fibrosis or early stage CrCL pathology may prevent the detection of palpable instability. Thus, the absence of palpable instability does not necessarily preclude the clinical diagnosis CrCL pathology or its surgical treatment.

Finally through the recumbent and standing examinations, the examiner should be sensitive to detecting "clicks" typical of meniscal injury. Gross injury to the medial meniscus is very common in conjunction with CrCL pathology especially in large breed dogs with chronic CrCL pathology and/or gross stifle instability.

Figure 1. Tibial Compression Test for cranial tibial thrust instability.

Figure 2. Cranial Drawer test.

Radiography

Radiographs showing joint effusion, osteophytosis, or cranial tibial displacement lend support for a diagnosis of CrCLD while screening for coincident pathology such as osseous neoplasia or osteochondritis dissecans (Figure 4). Radiographs also offer insight into skeletal conformation that may influence the decision for or against geometry-altering surgical treatments.

Making a Diagnosis

Many dogs with CrCLD do not have palpable stifle instability. In these dogs, a compatible history, signalment, and gait evaluation in conjunction with medial buttress, pain on full stifle extension, and/or radiographic joint effusion support a presumptive diagnosis of CrCLD that may be confirmed upon exploration. In instances where one suspects CrCLD but the combination of findings do not warrant exploratory arthrotomy, one may consider advanced imaging or arthroscopic evaluation versus a more conservative "watchful waiting" approach where the patient is re-evaluated in 4 to 8 weeks or at the first sign of symptomatic progression (whichever is sooner).

Treatment Options

Surgical treatment is advised for most dogs with CrCLD. A wide array of surgical techniques has been described for CrCLD dogs. They can be divided into static-constraint or dynamic-constraint (geometry-altering) methods.

Traditionally, surgical treatments have sought to statically constrain the stifle joint by substituting the CrCL with autologous tissues or synthetic materials placed as an intracapsular or extracapsular stabilization. Extracapsular stabilization is more commonly performed than intracapsular stabilization. Concerns with traditional extracapsular stabilization techniques include lack of isometric suture position, mechanical compliance of the circum-fabellar anchor point and suture/knot failure. A recently developed extracapsular stabilization technique, marketed as the TightRope CCL® technique, utilizes femoral and tibial bone tunnels and toggles to secure the proprietary braided stabilizing suture in a relatively isometric position (Figure 3).

Geometry-altering procedures such as tibial plateau leveling osteotomy (TPLO), tibial tuberosity advancement (TTA), and triple tibial osteotomy (TTO) have been advocated as methods to dynamically constrain the stifle by altering the mechanical forces acting upon it such that the CrCL is rendered unnecessary (Figure 4).

Figure 3. TightRope® CCL technique.

Figure 4. TPLO (left), TTA (center) and TTO (right).

The quest to find evidence to determine "the best" technique for stabilization of the canine CrCL-deficient stifle is likely to go unrealized. The wide variety of patient sizes, conformations, activity levels and performance goals along with varying degrees of stifle instability, osteoarthritis, and meniscal pathology likely dictate that no single technique is best suited to all of our patients.