Knowledge of diarthrodial joint mechanics and specific function of the ligaments are needed in order to understand injury mechanisms, improve surgical procedures and design better post-surgical rehabilitation protocols. To facilitate these needs, a robotic/universal force-moment sensor (UFS) testing system was developed to measure joint kinematics in multiple degree-of-freedom and the in situ forces in the ligaments. When operated in the position control mode, the testing system applies a known load to the intact joint while the motion and force data are recorded. After transection of a ligament, the recorded motion for the intact joint is repeated and new force and moment data is recorded by the UFS. Since the robot reproduces the identical initial position as well as path of joint motion before and after a ligament is transected, the in situ force in the ligament is the difference between the two sets of force and moment data. In force control mode, a known force is applied to the intact knee while the kinematics are recorded. After ligament transection, the same force is applied while the changes in kinematics are again recorded. Testing in this mode is similar to a clinical examination that diagnoses ligament injury. To date, this testing system has been used for experimental studies that examine the anterior cruciate ligament & posterior cruciate ligament of the knee and ligaments of the shoulder. A three-dimensional finite element model has also been constructed based on CT/MRI scans of a knee specimen and validated using data obtained with the testing system. Once in vivo kinematics (such as during gait analysis or throwing activities) are available, the robotic/UFS testing system can be programmed to reproduce these joint kinematics on young human cadaveric specimens in order to generate a database for in situ forces in the ligaments, or Ligament replacement grafts. With appropriate computational models, the stresses and strains in these tissues in vivo can also be determined. Potential applications of this combined approach include pre-operative surgical planning, improvement of surgical procedures as well as development of appropriate post-operative rehabilitation protocols.