Systems, apparatus, and method of monitoring a position of a joint. An inertial monitoring unit (48A) is configured to be coupled to a portion of a patient, such as a thigh (26). Another inertial monitoring unit (48B) is configured to be attached to another portion of the patient, such as a shank (24), that is connected to the other portion by a joint, such as a joint (28). The inertial monitoring units (48A, 48B) detect motion of their respective portions of the patient and transmit data indicative of this motion. These transmissions may be received by a computer (54) and used to determine an orientation of the joint (28). The inertial monitoring units (48A, 48B) may also be coupled to vibration detection modules (50) and/or ultrasound modules (52) that provide additional data regarding a condition of the joint (28).
