Imaging has become an important clinical tool in the evaluation of articular cartilage, both in the clinical and research setting. This article reviews the mechanisms of articular cartilage injury in the lower extremities and their implications. Specific examples of acute and chronic repetitive injuries in the hip, knee, and ankle are used to demonstrate the characteristics of articular cartilage lesions on magnetic resonance imaging and multidetector computed tomographic arthrography. Loss of meniscal function in the knee and femoroacetabular impingement in the hip represent sources of repetitive cartilage injury that predispose the joint to osteoarthritis. Acute cartilage injury is exemplified by osteochondral lesions of the talus, which may result in post-traumatic osteoarthritis. Recognition of early cartilage damage and associated lesions may help determine the proper treatment for the patient to delay or prevent progression to osteoarthritis.