Bone popping in the knee can be either physiological or pathological.
Physiological bone rattling usually manifests as a popping joint with no symptoms such as pain or impaired movement in the patient.
Pathological bone rattling generally manifests as persistent, recurrent bone rattling with pain and impaired movement, and may be caused by intra-articular pathology such as meniscal tears, or extra-articular pathology such as changes in the position of the biceps femoris tendon.