To test for cranial tibial translation, perform the cranial drawer test (Figure 6). In a mature dog, a healthy, intact cranial cruciate ligament will not permit cranial tibial translation with the stifle
held in extension or in flexion.3 In an immature dog, puppy laxity may permit a few millimeters of cranial and caudal tibial translation, but the endpoints
are crisp and distinct (similar to reaching the end of a taut rope). In a dog with complete cranial cruciate ligament rupture,
cranial tibial translation is obvious and an indistinct, ill-defined endpoint exists.
Figure 6 To perform the cranial drawer test on the left stifle of a patient in right lateral recumbency, place your right
index finger firmly on the patella and right thumb behind the lateral fabella to secure the distal femur. Place your left
index finger on the tibial crest and left thumb behind the fibular head to secure the proximal tibia. Slowly rolling tissues
away from the fibular head with your thumb and using a gentle grip will prevent patient discomfort associated with squeezing
the peroneal nerve against the fibular head (a painful response from the patient is most often associated with the examiner's
grip on the limb and does not indicate cranial cruciate ligament pathology). While holding the femur in place with your right
hand, apply a firm cranially directed force to the tibia with your left hand.
Next, apply a firm caudally directed translational force to the tibia while holding the distal femur stable. Caudal cruciate
ligament integrity is confirmed by a distinct endpoint to caudal tibial translation. Perform the drawer test with the stifle
in extension, flexion, and a standing angle. Partial tears of the cranial cruciate ligament often produce cranial drawer instability
only when the stifle is flexed. Such a finding implies tearing primarily in the craniomedial band of the cranial cruciate
ligament because the remaining caudolateral band relaxes in flexion and permits drawer movement.
It is important to realize that periarticular fibrosis or early-stage cranial cruciate ligament pathology may prevent the
detection of palpable instability. Thus, the absence of palpable instability does not necessarily preclude the clinical diagnosis
of cranial cruciate ligament pathology or its surgical treatment.
During the recumbent and standing examinations, remain alert for the clicks typical of meniscal injury. Gross injury to the
medial meniscus is common in conjunction with cranial cruciate ligament pathology, especially in large-breed dogs with chronic
cranial cruciate ligament pathology or gross stifle instability.5,16
Caudocranial and mediolateral radiographs are used to stage any associated osteoarthritis, lend support to a cranial cruciate
ligament pathology diagnosis, and screen for complicating or coincident pathology, such as osteochondrosis or neoplasia. The
cranial cruciate ligament cannot be visualized radiographically—a fact worth pointing out when discussing radiographic findings
with pet owners. With many dogs, sedation is required for high-quality radiographs. Joint effusion, osteophytosis, or cranial
tibial displacement lends support to a diagnosis of cranial cruciate ligament rupture. The findings vary depending on the
chronicity of the disease.
On the mediolateral view, joint effusion is seen as a gray halo surrounding the distal femur that compresses a radiolucent
infrapatellar fat pad within the cranial joint space and distends the caudal joint capsule to varying degrees (Figure 7). Osteophytes along the margins of the medial and lateral femoral trochlear ridges and the distal pole of the patella are
seen with chronic disease. Cranial tibial displacement can be seen in selected instances of acute, complete cranial cruciate
ligament rupture and is more commonly noted in small-breed dogs.
Figure 7 A mediolateral radiograph of the stifle of a dog with cranial cruciate ligament pathology. Joint effusion is the
gray halo surrounding the distal femur that compresses the infrapatellar fat pad (white arrows) within the cranial joint space
and distends the caudal joint capsule (black arrows). An osteophyte is present on the distal pole of the patella (single gray
arrow). In more chronic cases, osteophytes may be seen along the margins of the medial and lateral femoral trochlear ridges.
SYNOVIAL FLUID ANALYSIS
Synovial fluid analysis can be helpful in assessing the more subtle presentations of lameness. Synovial fluid analysis helps
distinguish acute from chronic cranial cruciate ligament pathology and detect septic or immune-mediated joint disease. Diagnosing
septic or immune-mediated joint disease greatly affects the treatment and possibly the prognosis.