Fig 1.
Our XROMM setup for capturing skeletal movements of walking rats.
Rats were trained to walk down a narrow trackway towards a dark hide box placed on the other side of the two C-arm videofluoroscopes.
Fig 2.
The reference frame (zero position) of the left forelimb rig in (A) left lateral and (B) dorsal views. The bones have been made semi-translucent to enhance visualization of the three Joint Coordinate Systems (JCS) that comprised the virtual shoulder, elbow, and radioulnar joints. All angles and translations are recorded in relation to the reference frame. Note that the reference frame is not intended to be a natural orientation: in fact, in this orientation the radius is unnaturally rotated so that it is entirely supinated relative to the ulna, a posture impossible for a rat. However, this reference posture provides a point against which the degree of pronation can be quantified. To account for body movements, the shoulder JCS has the sternal manubrium centered on the caudal humeral head. Each JCS was based on an Euler angle ZYX rotation order that followed the right-hand rule. In this way, movement of the Z-axis also moved the Y- and X-axes as well as the bone model; movement of Y-axis also moved the X-axis and the bone model; and movement of the X-axis only moved the bone model.
Fig 3.
Joint coordinate systems illustrated.
Each joint coordinate system (JCS) of the forelimb as well as the JCS of the skull and sternum utilized in the gold standard accuracy test are isolated and illustrated to show greater detail. Each JCS was based on an Euler angle ZYX rotation order that followed the right-hand rule. For all JCS, the Z-axis is blue, the Y-axis is green, and the X-axis is red. For all forelimb JCS, the Y-axis measures abduction/adduction and the X-axis measures long-axis rotation (LAR). At the shoulder JCS (A) shown in oblique left cranial view, the Z-axis measures protraction/retraction of the humerus relative to the sternum. At the elbow JCS (B) and the radioulnar JCS (C) (both shown in oblique caudodorsal view), the Z-axis measures flexion/extension of the ulna relative to the humerus or of the radius relative to ulna, respectively. To determine the body midline frame of reference, the skull and sternum were linked together as a separate rig (D). A skull-sternum JCS was created for the gold standard to test how accurately manual registration of the skull allowed us to determine the midline of the body using the sternum as a reference. The skull and sternum rig is shown in left lateral view and the bones are semi-translucent to facilitate visualization of the skull-sternum JCS. For the skull-sternum JCS (D), the pitch (Z-axis), yaw (Y-axis), and roll (X-axis) of the sternum was measured relative to the skull.
Fig 4.
Lateral, ventral, and radioulnar joint views of the humerus (sea green), radius (black), and ulna (red) in a typical step cycle in Rattus norvegicus.
Long-axis rotation (LAR) of the radius about the ulna (radius pronation) is shown in cranial view from the perspective of the ulna (the ulna appears to be stationary in the radioulnar joint view relative to the humerus and radius). Note radius (black) LAR relative to the ulna (red). Percentages = portion of the step cycle. Black bar in ventral view = body midline based on sternum.
Fig 5.
Average motion in degrees at the shoulder joint coordinate system (JCS) for a R. norvegicus step cycle.
Above the graph is a representation of the forelimb posture relative to the step cycle. Here, all ten trials from all three rats were binned for every 5% of the step cycle. Blue = Z-axis (protraction/retraction); Green = Y-axis (abduction/adduction); X-axis (long-axis rotation).
Fig 6.
Average motion in degrees at the elbow joint coordinate system (JCS) for a R. norvegicus step cycle.
Above the graph is a representation of the forelimb posture relative to the step cycle. Here, all ten trials from all three rats were binned for every 5% of the step cycle. Given the tiny rotational movements at the Y- and X-axes for the elbow JCS, only the Z-axis rotations are shown. Blue = Z-axis (flexion/extension).
Fig 7.
Average motion in degrees at the radioulnar joint coordinate system (JCS) for a R. norvegicus step cycle.
Above the graph is a representation of the forelimb posture relative to the step cycle. Here, all ten trials from all three rats were binned for every 5% of the step cycle. Radius long axis rotation (LAR, pronation) is shown in cranial view from the perspective of the ulna (the ulna appears to be stationary in these figures compared to the humerus and radius). Note the close synchrony between elbow flexion (Fig 7) and radius LAR. Given the small rotational movements at the Z- and Y-axes for the radioulnar JCS, only the X-axis rotations are shown. Red = X-axis (radius LAR relative to the ulna).
Table 1.
Joint excursions based on joint coordinate systems (JCS) for the shoulder, elbow, and radioulnar joint.