Cranial cruciate ligament pathology is a leading cause of lameness in dogs.1 Recent advances in diagnostic visualization and surgical treatments have stimulated an increased emphasis on early clinical recognition of cranial cruciate ligament pathology. This article describes characteristics of normal and pathologic cranial cruciate ligaments and details clinical techniques to help you diagnose cranial cruciate ligament pathology earlier.
Four ligaments passively stabilize the canine stifle joint: the cranial cruciate, caudal cruciate, medial collateral, and lateral collateral ligaments. The cranial cruciate ligament originates from the caudomedial aspect of the lateral femoral condyle and courses in a craniomedial direction to insert on the cranial intercondyloid area of the tibia immediately caudal to the intermeniscal ligament (Figure 1).2 The cranial cruciate ligament is functionally composed of a craniomedial band and a caudolateral band.3 While the craniomedial band remains taut throughout a full range of extension and flexion, the caudolateral band becomes lax during flexion. The caudal cruciate ligament arises from the lateral surface of the medial femoral condyle and passes caudodistally to insert on the lateral aspect of the popliteal notch of the tibia (Figure 1). The cranial and caudal cruciate ligaments spiral around one another as they course distally. The orientation of the cranial cruciate ligament prevents cranial tibial translation through a full range of motion, excessive internal rotation during flexion, and stifle hyperextension.
The medial collateral ligament passes distally from the medial femoral epicondyle, sharing a firm attachment to the abaxial margin of the medial meniscus, to insert along a rectangular footprint on the medial aspect of the tibia. Portions of the medial collateral ligament remain taut throughout a full range of extension and flexion. The lateral collateral ligament originates on the lateral femoral epicondyle and passes distally before inserting primarily on the fibular head. The lateral collateral ligament is taut in extension, but its laxity during flexion permits a physiologic internal rotation of the stifle joint. Conversely, during stifle extension, the lateral collateral ligament draws taut and causes external rotation of the tibial plateau with respect to the femur in what is called the screw-home mechanism.4
Figure 1 The ligaments and menisci of the canine stifle joint.
The medial and lateral menisci are semilunar fibrocartilage structures positioned between the articular surfaces of the femoral and tibial condyles (Figure 2). The menisci have several important functions, including energy absorption and stress transfer across the femorotibial joint, joint stabilization, prevention of synovial membrane impingement between the femur and tibia, and joint proprioception.5 The menisci stabilize the joint by functionally deepening the articular surface of the tibial plateau—much like a chock behind a tire. In cross section, the menisci are wedge-shaped, and the peripheral circumference is thick and white while the axial margins are thin and almost translucent. The femoral surface of each meniscus is concave to receive the curved surface of the femoral condyle. The tibial surface is relatively flat. Cranial and caudal tibial ligaments of the medial and lateral menisci anchor each meniscus to the tibial plateau. The cranial meniscal horns are united by the intermeniscal, or transverse, ligament (Figure 2). This ligament is an important landmark because it borders the cranial margin of the tibial insertion of the cranial cruciate ligament.
Figure 2 The medial and lateral menisci; dorsal view. Note the caudal margin of the lateral meniscus is attached to the femur by way of the meniscofemoral ligament.