Measurement of Dynamic Scapular Kinematics Using an Acromion Marker Cluster to Minimize Skin Movement Artifact

The goal of this procedure is to obtain non-invasive dynamic measurements of scapular kinematic. This is accomplished by attaching retroreflective markers to the thorax and a marker cluster to the flat portion of the acromion. The second step is to determine the location of scapular anatomical landmarks with respect to the marker cluster using a calibration wand.

Once calibrated, the participant performs arm elevation and lowering movements in relevant planes of motion. The final step is to determine the location of the scapular anatomical landmarks during the dynamic movements based on the known location with respect to the acromion marker cluster. Ultimately, the location of the scapular anatomical landmarks is used to show the orientation of the scapular with respect to the thorax.

This technique can help answer key questions in the fields of biomechanics and rehabilitation, such as what are the movement patterns of the scapula that are associated with solid dysfunction. It also allows the assessment of treatment interventions that are targeted towards the treatment of shoulder dysfunction. To begin, ask the participant to remove their upper body clothing or to wear clothing that does not interfere with the movement of the markers or occlude them from the view of the motion capture system.

Construct an acromium marker cluster or a MC consisting of an L-shaped piece of plastic. Attach three retroflective markers, one on the end of each aspect from one where they meet. Use double-sided adhesive tape to attach the A MC onto the posterior portion of the acromion where it meets the scapular spine.

One aspect of the plate should follow the spine of the scapular pointing medially. The other should point anterior to the scapular plane. Next strap.

A cluster marker set to the participant's upper arm retroreflective markers should then be attached to the following anatomical landmarks, the sternal notch, the xiphoid process, the C seven vertebra, T eight vertebra, sternoclavicular, joint ulnar styloid, and radial styloid. Anatomical landmarks with respect to the A MC need to be calibrated for each participant. To do this, construct a calibration wand consisting of four reflective markers placed into a T formation.

Measure the distance from the tip of the calibration wand to the first wand marker. To take a measurement. Place the tip of the wand on the landmark to be calibrated and to capture three seconds of data with the motion capture system, ensuring that the markers on the wand the A MC and upper arm cluster are all visible to the cameras.

First, locate the acromioclavicular joint by placing a hand on the clavicle and moving laterally until the point where the clavicle reaches the acromion. Place the tip of the wand at the joint between the clavicle and the acromion to measure the acromion angle. Als along the spine of the scapula to the most lateral point.

Place the tip of the wand on the dorsal aspect of the acromion at this point. Next, ALS along the spine of the scapula to the most medial point. To locate the medial spine of the scapula, place the tip of the wand at the point where the spine meets the medial border of the scapula.

To locate the inferior angle of the scapula, palpate inferiorly along the medial border of the scapula and place the tip of the wand on the most cordal point with the participant's elbow bent at 90 degrees and their thumb pointing upwards. Place a hand on the medial side of the elbow to locate the medial epicondyle. Place the tip of the wand on the most cordal point of the medial epicondyle.

In the same position, place a hand on the lateral side of the elbow to locate the lateral epicondyle and place the tip of the wand on the most cordal point. To determine the glenohumeral joint center, ask the participant to perform a circumduction movement with their upper arm. With the elbow fully extended from zero degrees arm elevation to approximately 40 degrees, a participant must perform this movement while aiming to minimize protraction retraction, elevation, or depression of the shoulder complex.

The investigator can provide assistance if necessary. Record this movement for approximately 30 seconds. Once calibrated, begin data collection by asking the participant to perform arm elevations from zero to 120 degrees, and then to lower their arm back down to rest by their side.

Direct the participant to perform this action in the sagittal frontal and scapular plane. The scapular plane is approximately 40 degrees anterior to the frontal plane to calculate scapular kinematic. During the dynamic movement trials, kinematic modeling software is used.

The software contains commands to enable creation of local coordinate systems, the conversion of coordinates from local to global coordinate systems, and the calculation of oiler angle rotations. First, use the coordinates of the markers on the A MC to define an arbitrary local coordinate system. Next, calculate the location of the one tip in the global coordinate system for each scapular anatomical landmark calibration trial.

Determine the location of the one tip with respect to the A MC local coordinate system. Next, determine the location of the medial and lateral epic condyles with respect to the humerus marker cluster. Use the known position of the anatomical landmarks with respect to the A MC to determine the location within the global coordinate system for each time point during the dynamic trial.

Repeat these steps for each anatomical landmark, the medial and lateral epic condyles. Use the upper arm cluster. Next, calculate the glenohumeral joint center using the pivot point of the helico axis between the humerus and scapular.

Next, define a local coordinate system for the thorax, scapula, and humerus by calculating the unit vectors between the relevant markers, following the recommendations of the International Society of Biomechanics for each rigid body segment to determine the orientation of the scapular relative to the thorax for each time point, use the oiler angle decomposition method with a rotation sequence of internal rotation, upper rotation, then posterior tilt. Next, determine the orientation of the humerus with respect to the thorax, using a non cardin rotation sequence of the plane of elevation.Elevation. Then axial rotation.

Perform the data reduction and analysis steps using numerical modeling software such as matlab. Divide the kinematic data into the elevation and lowering phases of humeral movement. Normalize the time for each phase of movement and express the scapular kinematic relative to the humeral elevation angle.

In this example, humeral elevation and lowering with the start and end of each phase is denoted by the green dotted lines. The elevation and lowering phases are determined using the angular velocity of humeral elevation. The uppermost red dash line represents the threshold used to determine the start and end of the elevation phase.

The lowermost red dash line represents a threshold used to determine the start and end of the lowering phase. Green dotted lines represent the points at which the angular velocity exceeded the thresholds. This graph shows scapular upward rotation during arm elevation that has been interpolated with over 101 data points.

To normalize with respect to time. Scapular rotations during sagittal plane arm movement are shown for upward rotation during the elevation and lowering phase, as well as the posterior tilt during the elevation and lowering phase and internal rotation during the elevation and lowering phase. While attempting this procedure, it's really important to remember that careful placement of the markers and palpation of the anatomical landmarks are vital in obtaining valid and reliable results.

It's also important to remember that this technique is only valid up to 120 degrees worth of humeral elevation.