Some dogs present with a mild, chronic lameness. These dogs may have no cranial drawer sign, but exhibit discomfort when tested
for drawer or when the stifle is placed in hyperextension. They may have a partial CrCL rupture, with minimal effusion and
no osteoarthritis visible on radiographs.
Less commonly, dogs may present acutely non-ambulatory, or with difficulty rising, or with shifting leg lameness. These dogs
often have bilateral CrCL rupture, but may present with a variety of previous diagnoses, including spinal cord disease and
hip dysplasia. When assisted to walk, they may have a very short-strided gait, mimicking dogs with lower motor neuron dysfunction
due to lumbosacral spinal cord disease. A full neurologic exam, paying close attention to proprioception and spinal reflexes
is needed to rule out neurologic disease. To make things more challenging, these patients sometimes DO have concurrent hip
dysplasia/DJD and lumbosacral disease. Even with concurrent diseases, a good orthopedic exam can evaluate CrCL status with
Most cases of CrCL rupture can be diagnosed by a complete physical exam. After obtaining a thorough history from the client,
observe the dog at a walk and a trot in a straight line. Non-weightbearing lameness is not a challenging observation to make,
but more subtle lameness can become apparent with gait analysis. Dogs with a CrCL injury and a subtle lameness may exhibit
a shortened stride and a somewhat extended stifle. The normal limb will appear to land harder on the ground. Pay attention
to how the dog sits. A dog with a CrCL injury often will not sit with its legs squarely beneath it, due to the stress placed
on the CrCL in this position. Instead, the dog may sit with the leg extended and out to the side. Some clinicians refer to
this as "the positive sit test".
Begin the physical exam with the dog standing and an assistant gently restraining the dog. This allows palpation and comparison
of both hindlimbs, with the dog in a relatively relaxed position. Begin proximally, palpating the thigh muscles to assess
atrophy. Continue distally, sliding the patella and patellar ligament between the thumb and index finger. The medial and lateral
edges of the patellar ligament should palpate sharply. Indistinct margins indicate possible joint effusion distending the
cranial joint capsule. Continue distally, palpating the medial aspect of the stifle for medial buttress, or periarticular
fibrosis, a response to stifle instability. Medial buttress may be felt with or without concurrent cranial drawer.
After palpation, examine the dog in lateral recumbency on an exam table or the floor. Proceed to the good leg first, to allow
the dog to relax and get an idea of what baseline responses are for the individual dog. The limb should be examined from the
toes to the hip. When the stifle is reached, begin by flexing and extending the joint to assess range of motion, crepitus,
or clicking noise. Patients may have diminished range of motion due to fibrosis, pain, or effusion. Crepitus can be consistent
with degenerative joint disease (osteoarthritis). A palpable or audible click may indicate a meniscal tear.
Next, test cranial drawer by placing the thumb and index finger of one hand on the lateral fabella and patella, respectively.
Place the other thumb and index finger on the fibular head and tibial tuberosity. Hold the patella/fabella firmly, while moving
the tibia caudally and cranially. Except for puppies, which may have a small amount of motion, any amount of cranial drawer
motion is abnormal. The cranial drawer test should be done with the leg in flexion and extension, to test both parts of the
CrCL. If no drawer is palpated, but CrCL injury is still suspected, cranial drawer should be re-evaluated under sedation.
Dogs with ACL injury may not exhibit cranial drawer either because they are resisting your palpation with their leg muscles,
they have significant periarticular fibrosis which has stabilized the stifle, or they have a partial tear and the remaining
intact ligament resists gross displacement. Remember that the craniomedial band is under tension both during flexion and extension.
Thus a tear in the caudolateral part may not be appreciated with a drawer test. However, these dogs often are painful when
cranial drawer is attempted, or on hyperextension of the stifle. They may also exhibit stifle effusion and buttress. In cases
of suspected partial tears, an MRI, or arthroscopy/arthrotomy may be needed to confirm diagnosis of CrCL injury.
Even in cases where a clear diagnosis of CrCL rupture can be made in the exam room, radiographic examination of the joint
is indicated. Radiographs are used to rule out concurrent diseases such as neoplasia and OCD. They are used to evaluate the
degree of secondary signs of CrCL rupture, primarily: joint effusion with infrafatellar fat pad displacement, caudal joint
capsule displacement, and degenerative joint disease (DJD) noted on the patella, trochlear ridges, and tibial plateau. The
degree of DJD may be an indicator of prognosis, as dogs with minor degenerative changes probably have a better prognosis for
long-term function than do those with advanced osteoarthritis. In cases without positive cranial drawer, these secondary signs
give support to a diagnosis of CrCL rupture.
While very light dogs (<15lbs) may do well with medical management, heavier dogs have a significantly faster and more complete
return to function with surgery. The goal of surgery is stabilization of the joint and thus minimization of DJD progression,
as well as management of meniscal injury.
A variety of repair methods have been described for treatment of CrCL insufficiency. They can be divided into static repairs,
which attempt to replace the function of the CrCL, and dynamic repairs, which alter joint biomechanics to absolve the need
for a functioning CrCL. Static repairs include intracapsular grafting techniques, extracapsular lateral suture techniques
and fibular head advancement. These techniques stabilize the joint through static neutralization of cranial drawer without
alteration of stifle joint anatomy. Dynamic repairs include tibial plateau leveling osteotomy (TPLO) and tibial tuberosity
advancement (TTA). These techniques provide dynamic stability to the stifle joint by altering tibial plateau angle and the
insertion point of the patellar ligament. Neutralization of cranial tibial thrust by TPLO has been shown to provide stability
to the CrCL deficient stifle by generation of caudal tibial thrust and increased stress on the caudal cruciate ligament during
mid stance phase of the gait. The TTA neutralizes the contribution of the quadriceps muscle to cranial tibial thrust and also
results in generation of caudal tibial thrust at certain points of the stance phase. Good results, often with maintenance
of full range of motion and normal activity levels can be achieved with any of the above techniques. In a study comparing
force plate analysis of dogs undergoing 3 different techniques for stabilization of CrCL deficient stifles, lateral suture
technique and TPLO were found to result in similar clinical results.