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

Summary

This report presents details of how to adopt the acromion marker cluster method of obtaining scapular kinematics when using a passive marker motion capture device. As has been described in the literature, this method provides a robust, non-invasive, three-dimensional, dynamic and valid measurement of scapular kinematics, minimizing skin movement artifact.

Abstract

The measurement of dynamic scapular kinematics is complex due to the sliding nature of the scapula beneath the skin surface. The aim of the study was to clearly describe the acromion marker cluster (AMC) method of determining scapular kinematics when using a passive marker motion capture system, with consideration for the sources of error which could affect the validity and reliability of measurements. The AMC method involves placing a cluster of markers over the posterior acromion, and through calibration of anatomical landmarks with respect to the marker cluster it is possible to obtain valid measurements of scapular kinematics. The reliability of the method was examined between two days in a group of 15 healthy individuals (aged 19-38 years, eight males) as they performed arm elevation, to 120°, and lowering in the frontal, scapular and sagittal planes. Results showed that between-day reliability was good for upward scapular rotation (Coefficient of Multiple Correlation; CMC = 0.92) and posterior tilt (CMC = 0.70) but fair for internal rotation (CMC = 0.53) during the arm elevation phase. The waveform error was lower for upward rotation (2.7° to 4.4°) and posterior tilt (1.3° to 2.8°), compared to internal rotation (5.4° to 7.3°). The reliability during the lowering phase was comparable to results observed during the elevation phase. If the protocol outlined in this study is adhered to, the AMC provides a reliable measurement of upward rotation and posterior tilt during the elevation and lowering phases of arm movement.

Introduction

Objective, quantitative measurement of scapular kinematics can provide an assessment of abnormal movement patterns associated with shoulder dysfunction¹, such as reduced upward rotation and posterior tilt during arm elevation observed in shoulder impingement^2-8. Measurement of scapular kinematics, however, is difficult due to the bone’s deep position and gliding nature beneath the skin surface¹. Typical kinematic measurement techniques of attaching reflective markers over anatomical landmarks do not adequately track the scapula as it glides beneath the skin surface⁹. Various methods have been adopted throughout the lit....

Protocol

NOTE: The use of human participants was approved by the Faculty of Health Sciences Ethics Committee at the University of Southampton. All participants signed consent forms before data collection commenced. For the data presented in this study kinematics were recorded using a passive marker motion capture system consisting of 12 cameras; six 4-megapixel cameras and six 16-megapixel cameras operating at sampling frequency of 120 Hz.

1. Participant Preparation

1. Ask subjects to remove their upper body clothing or to wear a sports bra, vest, or strapless top. It is important that clothing does not interfere with the movement of the ma....

Results

Fifteen participants who had no known history of shoulder, neck or arm injuries were recruited onto the study (Table 2). To assess intra-rater (between-day) reliability, participants attended two data collection sessions separated by at least 24 hours and a maximum of 7 days. During each data collection session, the same investigator performed the protocol for attaching reflective markers, the acromion marker cluster and anatomical landmark calibrations, as detailed above. The reliability of the kinemati.......

Discussion

The choice of methodology for determining scapular kinematics is crucial, and consideration of the validity, reliability and its appropriateness for the research study should be given. Various methods have been adopted throughout the literature but each method has its limitations. The acromion marker cluster overcomes a number of these limitations, such as projection errors from 2D imaging or requiring repeated interpretation of the location of the scapula by providing non-invasive dynamic kinematic measurement of the sc.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Passive marker capture system	Vicon Motion Systems	N/A
Nexus	Vicon Motion Systems	N/A	Data capture software
Bodybuilder	Vicon Motion Systems	N/A	Modeling software
14 mm retro reflective markers	Vicon Motion Systems	VACC-V162B
6.5 mm retro reflective markers	Vicon Motion Systems	VACC-V166
Calibration wand	Vicon Motion Systems	N/A
Plastic base	N/A	N/A	Constructed 'in-house'
Matlab	Mathworks	N/A	Numerical modelling software