1st Joint ESMAC-GCMAS Meeting - Análise de Marcha

O-26
CLINICALLY SIGNIFICANT SHOULDER JOINT KINEMATICS DESCRIPTION
Morrow, Duane A, MS, Lin, Hui-Ting, MS, Kaufman, Kenton R, PhD, An, Kai-Nan, PhD
Department of Orthopedic Research, Mayo Clinic, Rochester, MN, USA
Summary/conclusions
While there are numerous methods available for the calculation of shoulder joint kinematics,
the ability to present these in clinically significant terms has remained a challenge. Through
realignment of coordinate axes on the humerus, shoulder kinematics can be calculated in terms
that are familiar in clinical settings.
Introduction
The ability to describe calculated shoulder joint kinematics in clinically relevant terms has, to
date, been difficult. This difficulty has likely been compounded by the plethora of methods
used to decompose the rotation of the shoulder joint. Rotations captured using motion analysis
techniques are analysed most widely using either Euler angle or screw axis decomposition.
While those who use Euler angles in their analyses may choose to follow the rotation sequence
initially proposed by An [1] and recommended by the ISB [2], This method, however, offers
shoulder motion results in terms of the angle and amount of humeral elevation in lieu of
outright measures of flexion/extension or ab/adduction. Additionally, in the clinical setting,
neural, muscular, or skeletal disorders may cause individuals to take up postures and
compensations that may make recommended coordinate assignments or decompositions
provide unwanted results. Our laboratory has previously advocated the use of screw-axes for
the analysis of shoulder motion to avoid some of the pitfalls of gimbal lock that may be
associated with Euler angle decomposition [3]. However, the problem still remains that
shoulder flexion/extension and ab/adduction are measures of the humerus about axes of the
trunk. Internal/external rotation of the humerus can change the alignment of the humeral
sagittal and coronal axes, confounding the ability to examine the motion of the humerus with
respect to the trunk (or scapula, for glenohumeral motion). The current study outlines a method
for presenting shoulder kinematics in terms of clinical rotations.
Statement of clinical significance
A simple correction algorithm may be applied to
the decomposition of shoulder joint kinematics
to allow for clinically meaningful interpretation
of shoulder joint motions.
Methods
This study was conducted as part of a larger
study for the creation of a database of normal
kinematics during a set of motions used in
clinical upper extremity assessments of the
neck, scapulothoracic, glenohumeral, elbow,
and wrist joints, as well as the thoracohumeral
pseudo-joint. Subjects were asked to perform
select motions (full shoulder flexion, abduction,
touching their head, touching their opposite
shoulder, etc.) in a comfortable motion. For the purposes of this discussion, only motion of the
humerus with respect to the thorax during shoulder flexion will be considered, due to space
constraints. The motion of retro-reflective markers was tracked at 60 Hz using a 10-camera
Motion Analysis EVa RealTime system (Motion Analysis Corp., Santa Clara, CA, USA).
Three markers, on the xiphoid process, sternal notch, and C7, were used to define the trunk
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Figure 1. Schematic showing marker
locations and coordinate axes for
humerus and trunk coordinates
systems. Not shown is the C7 marker.