Thursday, February 2, 2017

Objective measurement of shoulder motion

Digital data acquisition of shoulder range of motion and arm motion smoothness using Kinect v2

These authors evaluated the accuracy of Kinect v2  as a digital tool for measuring shoulder ROM objectively and proposed a concept of motion smoothness reflecting the quality of arm motion.

In 10 male participants they measured the arm position in flexion, abduction, external rotation, and internal rotation) in three ways: (1)  Kinect v2, (2) a 3-dimensional (3D) motion analysis system, and (3) goniometry. Participants then performed a point-to point arm motion as naturally as possible. Kinematic data were collected with Kinect v2 and the 3D motion analysis system and then postprocessed to acquire parameters related to motion smoothness, including peak to mean velocity ratio, acceleration to movement time ratio, and number of peaks.

They found that Kinect v2 resulted in very good agreement of ROM measurement (r > 0.9) with the 3D motion analysis (95% limits of agreement < ±8°) compared with goniometry (95% limits of agreement <±10°). The Kinect v2 also showed a good correlation and agreement of measurement of motion quality parameters compared with the 3D motion analysis (peak to mean velocity ratio, acceleration to movement time ratio, and number of peaks.

The figures below show a comparison of a normal shoulder's motion with that of a patient with a cuff tear.

 What was particularly telling is the comparison of the precise measurements of motion by the Kinect in comparison to the highly variable measurements made with a goniometer.

Comment: This work builds on that previously presented:

Measurement of active shoulder motion using the Kinect, a commercially available infrared position detection system

These authors demonstrated the practicality of using an inexpensive, validated, commercially available infrared position sensor, the Kinect, for the observer-independent recording of the active ranges of motion of patients' shoulders. This device - familiar to computer gamers - does not require the application of sensors or markers to the patient and functions well in the clothed subject.

When mounted to a wheeled frame along with a laptop computer, the Kinect can be easily moved from one examination room to another. 

The Kinect outputs numerical data that can also be represented as a stick figure. The device measures the angles between the arm (A) and the trunk (T), automatically correcting for the patient leaning to one side or the other.

In 10 control subjects, they compared Kinect motion measurements to measurements made on standardized anteroposterior and lateral photographs taken concurrently. The Kinect measurements strongly agreed with photographic measurements. 

In 51 patients, they correlated active motion with the ability to perform the functions of the Simple Shoulder Test (SST). The total SST score was strongly correlated with the range of active abduction. The ability to perform each of the individual SST functions was strongly correlated with active motion. 

The active motion in well-functioning patient shoulders averaged 155° ± 22° abduction, 159° ± 14° flexion, 76° ± 18° external rotation in abduction, −59° ± 25° internal rotation in abduction, and −3.3 ± 3.7 inches of cross-body adduction, values similar to the control shoulders. 

Use of the Kinect system was practical in clinical examination rooms, requiring <5 minutes to document the 5 motions in both shoulders.

Comment: The shoulder's ability to participate in sports and activities of daily living depends on its active range of motion. Because of inter-observer variability, range of motion measurements with a goniometer are of limited utility in rigorously assessing limitation of motion and the effectiveness of treatment. The use of an objective system for the observer-independent measurement of active shoulder motion - such as the Kinect - holds promise for clarifying the indications for and the results of therapeutic interventions designed to improve shoulder function and for the comparison of results among surgeon-scientists.