Page 339 - Canine Lameness

19.2 ­ormal Anatomy 311

The joint capsule volume is large, extending proximally under the quadriceps femoris by approx-
imately one patella’s length, laterally and medially to the margin of the femoral epicondyles, cau-
dally to the femoral articulation of the fabellae, and distally following the course of the long digital
extensor (LDE) tendon. There is a small joint sub-pouch extending around the tibial condyle and
fibular head, as well as the axial surface of the origin of the popliteus. The infrapatellar fat pad is
located just caudal to the patellar ligament but is extracapsular (i.e. located extra-articular). This
becomes important when evaluating lateral view radiographs of the stifle joint to diagnose effusion
of the joint. Understanding the location and volume of the stifle joint space also allows multiple
entry points for therapeutic joint injections and arthrocentesis and also prevents accidental injec-
tions into the infrapatellar fat pad.
The cruciate ligaments of the stifle joint are located intracapsular but are covered by a thin syno-
vial layer. The cranial cruciate ligament originates from the caudomedial aspect of the lateral femo-
ral condyle (i.e. intra-articularly from the caudal aspect of the lateral femoral condyle) and courses
diagonally, cranially, and medially to insert around the cranial intercondyloid area of the tibial
plateau. The CCL serves to limit craniocaudal translation, hyperextension, as well as excessive
internal rotation. The canine stifle joint is highly dependent on the CCL for stability during stand-
ing as well as the stance phase of weight-bearing; loss of this ligament causes profound instability
of the stifle joint (Korvick et al. 1994). The CCL has two functional bands: the craniomedial band
and the caudolateral band (named based on their tibial attachment sites). The craniomedial band
is taut in extension and flexion, and the caudolateral band is taut in extension, but loose in flexion.
This is important to keep in mind when palpating for pathology that exclusively affects the cranio- STIFLE REGION
medial band, as it may be difficult to detect instability unless the stifle is placed in flexion.
The caudal cruciate ligament (CaCL) originates from the craniolateral aspect of the medial femo-
ral condyle (i.e. intra-articular from the cranial aspect of the medial femoral condyle), courses
caudodistally, and inserts on the caudal tibia (lateral edge of the popliteal notch). Its principle
function is to prevent caudal displacement of the tibia relative to the femur. It is larger than the
CCL and, as the name implies, crosses the CCL.
There are two intra-articular tendons in the stifle joint. The tendon of the long digital extensor
muscle originates in the extensor fossa of the femur and courses through the muscular groove of
the tibial plateau located just cranial to the lateral tibial condyle. Its origin on the proximal femoral
condyle can be confused for a stifle OCD lesion (Figure 19.2); this can be distinguished by the
proximal location away from the joint surface, as well as by the small semilunar shape of the exten-
sor fossa. The popliteal tendon is located in the caudal aspect of the joint, runs caudolaterally and
serves to limit external rotation of the stifle in flexion, and has a small attachment to the fibula
(Griffith et al. 2007).
The collateral ligaments serve to prevent varus/valgus joint instability, in addition to limiting
rotational instability. They are principally taut and especially important to joint stability when the
stifle is in extension. With increasing flexion of the stifle, the collateral ligaments, especially the
lateral collateral ligament (LCL), become more lax, and the CCL and CaCL take on additional
varus/valgus stabilization role (Vasseur and Arnoczky 1981).
The menisci (lateral and medial meniscus of the stifle joint) are concave, are semilunar-shaped
fibrocartilages, are wedge-shaped in cross section, and have a thin synovial intimal covering. These
meniscal fibrocartilages provide the majority of the weight-bearing surface of the stifle joint
between the incongruent, unstable, convex surface of the femoral and tibial condyles, making
them a crucial component of stifle joint stability. In the body of the meniscus, collagen bundles are
arranged in a circumferential orientation and bound by perpendicularly oriented radial fibers, an
arrangement that allows to mitigate compressive weight-bearing forces (Fithian et al. 1990). The