Collateral Ligaments of the Canine Stifle Joint: Anatomic and Functional Analysis

The anatomic features and functions of the collateral ligaments of the canine stifle joint were investigated, using cadaver specimens. The structure of the collateral ligaments was examined by dissection, with attention given to the spatial relationships existing between the collateral ligaments and their neighboring structures, such as the menisci and joint capsule. The relative tension of the ligaments was determined by identifying the points of attachment with lead markers and taking a series of radiographs of the joint throughout its range of motion. The distance between the points was measured, and the change in length was determined as a function of joint position. Measurements of internal and external rotation, varus angulation, and valgus angulation were made before and after severance of one or both ligaments. The medial collateral ligament was taut in extension, with only the caudal portion of the ligament becoming lax in flexion. The lateral collateral ligament was also taut in extension; however, its entire bulk because lax as the joint was flexed. In extension, the ligaments were primary restraints preventing varus and valgus angulation, and they functioned to limit internal and external rotation of the tibia. In flexion, the cranial portion of the medial collateral ligament remained taut and prevented external rotation of the tibia, whereas the relaxation of the lateral collateral ligament allowed the tibia to rotate internally, with further rotation limited by the cruciate ligaments.U