There are few commonly used clinical techniques to quantify the rotational stability and joint contact kinematics in knees in vivo. A magnetic-resonance-imaging-compatible device capable of applying axial and torsional loads to the foot was developed and used to measure in vivo knee kinematics in 14 healthy volunteers. The device was used to apply an internal torque and an axial compressive load at the foot, with the thigh held in place. Sagittal scans were made of the knee with and without an applied internal torque, and three-dimensional geometric representations of the knee joint were constructed from the images. Repeat scans of four volunteers were performed to assess precision, and phantom scans were performed to assess accuracy. Rotational measurements had a root mean square error of 0.1 deg, and precision errors for repeat measurements were 1.6 deg for internal tibial rotation, 0.3–1.1 mm for contact centroid translations, and for a contact area. Results indicated that the device induced significant internal tibial rotation with respect to the femur and significant translation of the medial and lateral contact centroids. A preliminary study on five anterior cruciate ligament (ACL)-deficient patients did not detect any rotational difference between ACL-deficient and contralateral knees under an isolated internal torque. This method is able to calculate rotations and centroid translations out of the scan plane and has potential applications in investigating the effects of knee injury and recovery of function.