Date of Award


Document Type


Degree Name

Master of Science (MS)


Biomedical Engineering

First Advisor

Niccolo Fiorentino

Second Advisor

Matthew Failla


Osteoarthritis (OA) is the leading cause of mobility-related disability. Post-traumatic osteoarthritis (PTOA) is a form of OA that occurs after an acute injury to the affected joint. In the case of the knee, rupture of the anterior cruciate ligament (ACL) is the most common acute injury. ACL injury occurs in sports that involve cutting and pivoting motions, such as soccer, football, and skiing. Many patients opt to undergo ACL reconstructive surgery (ACLR) so that they may return to their sport with restored knee stability and function. Unfortunately, ACLR does not completely restore the knee to its original state, resulting in altered joint mechanics and abnormal loading on the articular cartilage of the tibia and femur. As a result, the majority of patients develop radiographic signs of PTOA within 10 years of their original injury. An important risk factor for knee PTOA is increased joint laxity, or how much the joint moves given an applied force or torque. While standardized devices exist that measure anterior-posterior (i.e., forward-back) laxity in the knee, no such standardized device exists to measure internal-external rotational laxity in the knee. The purpose of this project was to develop a new, portable, user-friendly device to accurately and reliably measure rotational laxity in the knee. We developed a device that measures rotation of the knee joint in response to an applied torque along the axis of the tibia. Measurements from inertial measurement units (IMUs) and a torque sensor were combined to quantify rotational laxity of the knee joint, which were defined based on analysis of the resulting torque-rotation curve. Two Arduino IMU sensors were placed on the anterior tibia and lateral femoral epicondyle along the axes of the tibia and femur, respectively, to measure the internal-external rotation of the knee. A custom Python script found the sensor-to-sensor relative orientation, from which internal-external rotation of the joint was calculated. To verify the accuracy of the joint angle measurement, a custom test jig was built with known angle measurements marked on a rotating flange. After verifying the validity of the rotational measurement, the device was tested on a healthy individual with no history of knee joint injury. Multiple tests were performed to measure test-retest reliability. Determining the accuracy and reliably of the internal-external rotational laxity device presented in this thesis is a critical step prior to employing in population-based studies. Future studies will compare side-to-side variability of laxity measurements in healthy individuals, followed by a study comparing laxity measurements in ACLR patients’ injured knee to their contralateral one. This device will allow researchers and physicians to better understand altered joint mechanics after ACL injury and/or reconstruction, resulting in a better understanding of mechanisms that lead to knee PTOA and ultimately reducing its incidence.



Number of Pages

52 p.