Rotational Instability of the Knee

Abstract

It is with great honor we present this symposium on rotational instability of the knee. As the Guest Editors, we are proud to have recruited a large group of authors who are international experts and leaders in this field. Over the last 30 years, tremendous efforts have been made to improve treatment of patients with knee disorders. Minimally invasive arthroscopic techniques, sophisticated surgical implant options, advanced rehabilitation protocols, and an improved understanding of the biology, biomechanics, and kinematics of the knee have contributed to improved outcomes. However, as we learn more about the complex anatomy, biomechanics and kinematics of the knee, it is evident there remains room for continued improvement in knee surgery. A detailed understanding of the three-dimensional kinematics of the knee is crucial for orthopaedic surgeons who treat patients with knee disorders. Subtle changes in knee kinematics can have detrimental effects on the function of the knee. Considerable opinion and evidence suggests abnormal knee kinematics contribute to the development of osteoarthritis. Recent studies indicate rotational stability plays an important role in restoring normal function of the knee in patients undergoing anterior cruciate ligament (ACL) reconstruction. Some evidence suggests anatomic ACL reconstruction techniques that restore both the anteromedial and the posterolateral bundle of the ACL provide improved rotational stability which may translate to improved clinical outcomes. Moreover, abnormal kinematics of the knee after total knee arthroplasty may increase production of wear debris and contribute to cyclic fatigue. Therefore, the restoration of normal knee kinematics, including rotational movements, remains a major goal in the treatment of patients with knee disorders, and the accurate assessment of three-dimensional knee kinematics is an important outcome of knee surgery. However, accurate in vivo measurement of pathologic knee instability remains challenging. In particular, measurement of knee instability in all six degrees of freedom remains the subject of ongoing research. Cadaveric studies have provided important information on the biomechanics of the knee and robotic testing machines can accurately measure knee instability in six degrees of freedom. However, biomechanical studies in cadavers have limited clinical utility because of the inability to accurately reproduce muscle forces, normal gait and weight bearing conditions and the inability to consider tissue healing and remodeling that occurs over time. Clinically, tests such as the KT-1000 and Lachman test have been widely used to measure knee instability in vivo, but they only measure anteroposterior instability of the knee and provide no information on rotational instability of the knee. Moreover, these clinical tests cannot provide information on the more important knee kinematics during dynamic activities, such as walking, running, or jumping. Although accurate in vivo measurement of the three-dimensional kinematics and rotational instability of the knee is crucial for assessing the structure and function of the knee, standard techniques that can be applied in the clinical setting are not well established. Current investigations to measure rational instability and three-dimensional kinematics of the knee in vivo employ the use of clinical tests such as the pivot shift test and more sophisticated quantitative techniques such as dynamic radiostereometry, magnetic resonance imaging, use of electromagnetic or reflective skin markers, and computer navigation. These approaches, however, remain under investigation. The ultimate goal of these investigations will be to establish reliable, valid, practical and noninvasive methods to assess three-dimensional in vivo kinematics and the rotational instability of the knee in the clinical setting. Establishing techniques to measure the three-dimensional knee kinematics and rotational instability in research a