The present invention provides a method for creating a computer model of a patient specific joint for treatment planning. The method includes identifying a ligament of a joint of a patient under a load at a predefined position of the joint. The method further includes constructing, with the use of a computer, a computer model of the joint of the patient having: a first bone model, a second bone model, and a ligament model connecting the first and second bone models corresponding to the identified ligament, wherein the ligament model is constructed as at least one fiber based on a predefined slack length.