We believe it's important to share our protocol and what we've learned using this technology in our research, because the participants in these studies are exposed to radiation and therefore, the margin for error is very small. The main advantage of this technique is the accuracy with which the joint motion can be quantified, which allows researchers to pursue questions that otherwise, would not be possible. Before beginning an analysis, position the chair in the biplane imaging volume so that the shoulder to be tested is centered at approximately the point where the biplane x-ray beams intersect.
Ask the participant to be seated in a comfortable, upright posture with arms at their sides. Adjust the preliminary chair position based on the participant's anthropometrics, the motion to be tested, and the bones to be tracked. And secure a lead-lined protective vest across the participant's torso to cover the abdomen and contralateral shoulder and chest.
Turn on the light within the x-ray source of the system and raise the system until the shadow cast onto the image intensifier is at the level of the participant's axilla. Gently move the participant on the chair within the biplane image volume while watching the shadow on the intensifier. Once the participant's position is set for both systems keeping the light source on, ask the participant to perform the motion that will be tested during the procedure.
The participant's shoulder should remain within the radiographic field. To verify the participant's position in the control room set the x-ray control panel to low fluoroscopy mode and the pulse generator to a 0.25-second acquisition. Have an assistant explain the process to the participant including warning the participant about any sounds they might hear during the imaging.
Before starting the imaging, the assistant should put on a lead-lined protective vest and move away from the x-ray sources while maintaining a clear line of sight and communication with the participant. To acquire an image, start the cameras and prime the X-ray control panel. When the system is ready, instruct the assistant to begin acquiring the radiographic images using a handheld remote trigger.
Inspect the images after they have been acquired to determine whether the participant's position was satisfactory for visualizing all of the necessary bones. For static image acquisition set the optimized radio technique on the x-ray control panel as determined from the preliminary imaging and have the assistant ask the participant to sit upright with their arms resting at their sides. After acquiring an image in this position, inspect the image for quality, bone of interest visibility, and technical condition.
When an optimal image has been acquired, save the trial from each camera. For dynamic image acquisition, using the same parameters, but with the pulse generator set to a two-second exposure, have the assistant practice the motion to be performed with a participant, using a verbal cue, paced so that the motion is performed in two seconds. When the participant is ready, start the cameras and prime the control panel as demonstrated and notify the assistant that the system is ready.
Have the assistant ask whether the participant is ready before giving the verbal cue, Ready and go, so that the participant performs the motion as the assistant triggers the x-ray system to acquire a dynamic image. When good quality images for all the motion trials have been acquired, save the trials from each camera. In this representative analysis a 52-year-old asymptomatic female underwent motion testing on her dominant shoulder as demonstrated.
CT scan images of the shoulder joint were also obtained in the coronal, sagittal and transverse planes to include the entire scapula, humorous and ribcage. These radiographic images illustrate the complexity of acquiring biplane radiographs of the shoulder at lower angles of humeral elevation, the lateral acromion and distal clavicle appear overexposed in the green view, but are well visualized in the red view, due to the lower volume of soft tissue within the area. However, as the arm elevates, the bulk of the deltoid becomes projected over the area resulting in a better radiographic exposure.
As observed in this kinematics analysis, the glenohumeral motion consisted of elevation and a slight external rotation and was generally in-plane posterior to the scapula. The scapula thoracic motion consisted of an upward rotation with a posterior tilt and a slight internal-external rotation. During the motion trial, the minimum subacromial distance decreased until approximately 90 degrees humoral thoracic elevation, at which point the distance began to increase.
The average subacromial distance followed a similar trajectory. The minimum subacromial distance followed a complimentary trajectory to the surface area metric, such that the minimum distance tended to be smaller when the surface area was larger. Having the participant practice the motion is critical to ensuring that they understand the procedure and that they can perform the desired motion with the correct pace and timing.
