Comparison of 6 DOF Glenohumeral Kinematics During Abduction, Scaption and Forward Flexion in Healthy
Subjects Using Biplane Fluoroscopy
+1Giphart, J E; 1,2Millett, P J; 1Horn, N; 1Anstett, T; 1Brunkhorst, J P; 1Peterson, D S; 1Krong, J; 1Shelburne, K B; 1Torry, M R
+1Steadman-Hawkins Research Foundation, Vail, CO; 2Steadman-Hawkins Clinic, Vail, CO
erik.giphart@shsmf.org
RESULTS:
Figure 1 shows the GH elevation, SI and AP position curves as a
function of arm elevation angle found in this study. A significant main
Table 1. Mean ± std of GH elevation regression, GH plane of elevation
and humeral rotation angle with stat results (p<0.05; *: ANOVA; ∇: one
motion different from other two, ^: motions different from each other).
Abduction
Scaption
Forward Flex
GH Elev Slope *
0.66 ± 0.05
0.60 ± 0.06
0.51 ± 0.11∇
GH Elev Int *
4.1 ± 6.9^
3.9 ± 7.5
18.9 ± 13.0^
GH Plane (Low)
-3.5 ± 22.7
0.1 ± 11.9
31.9 ± 29.6
GH Plane (Mid)
-11.2 ± 3.3
-10.7 ± 6.3
38.8 ± 13.4
GH Plane (High)
1.7 ± 5.6
0.1 ± 6.7
18.0 ± 5.9
GH Plane (all) *
-3.7 ± 10.4
-3.6 ± 9.8
29.4 ± 21.1 ∇
Hum Rot (Low)
16.5 ± 4.5
8.5 ± 10.3
21.0 ± 21.9
Hum Rot (Mid)
18.9 ± 17.6
17.1 ± 11.8
29.2 ± 17.6
Hum Rot (High)
22.2 ± 4.4
15.5 ± 9.4
26.7 ± 7.5
Hum Rot (all) *
19.3 ± 6.2
13.6 ± 10.8^
26.0 ± 16.0^
DISCUSSION:
Our results indicate that flexion in general is different from abduction
and scaption in regards to glenohumeral rotations, while abduction and
scaption are very similar. The GH elevation slope decreased the more
anterior the arm was elevated. The regression slopes in this study can be
transformed into the Inman ratio and are 1.9:1 for abduction, 1.52 : 1 for
scaption and 1.06 : 1 for forward flexion, respectively.
During scaption the humeral head was found to be on average 0.6mm
lower compared to abduction and flexion. Position standard deviations
as well as the differences between the motions were smallest in the mid
range of elevation, supporting the cavity compression mechanism.
The differences between abduction, scaption and forward flexion are
subtle and are expected to have little clinical significance. However,
when detailed kinematics need to be considered it is important to take
into account and control the plane of elevation.
Abduction
Scaption
Forw. Flexion
GH Elevation (deg)
120
100
80
60
40
20
20
6
SI Position (mm)
METHODS:
A biplane fluoroscopy system was used to measure the 3D pose of
the scapula and humerus of 10 healthy male subjects (age: 29.7±6.6 yrs,
height: 183.6±4.6 m, weight: 89.8±8.9 kg) as they performed scaption
and forward flexion over their full ROM with their thumbs pointing up
and in the plane of motion. In addition, 5 subjects (3M, 2F; age: 41±14
yrs; height: 1.77±0.09m; weight: 87±23kg) performed abduction in a
similar fashion. The custom biplane fluoroscopy system consisted of two
modified BV Pulsera c-arms (Philips Medical Systems, Best, the
Netherlands). Data were collected at 30fr/s and 100fr/s, but analyzed at
10fr/s and 12.5fr/s respectively, because the motions were sufficiently
slow. A CT scan of each subject’s shoulder was also obtained. This
protocol was approved by the governing IRB and informed consent was
obtained prior to participation.
First the 3D geometries of the scapula and humerus were extracted
from the CT data (Mimics, Materialise, Ann Harbor, MI). Coordinate
systems and 3D glenohumeral rotations were determined according to
the ISB standard. For each frame, the 3D bone poses were estimated
using a contour matching algorithm (Model-Based RSA, Medis Specials
BV, Leiden, the Netherlands). A glenoid coordinate system (CS) was
created based on the most superior, inferior and anterior points on the
glenoid rim (glenoid center: midway between the superior and inferior
glenoid rim points). The humeral head center was determined by fitting
a sphere to the humeral head. To quantify position, the 3D position of
the humeral head center was determined relative to the glenoid CS.
For each subject the GH elevation, superior-inferior (SI), and
anterior-posterior (AP) position curves were resampled in 10 deg
increments from 30 through 160 degrees of arm elevation. A 2-way
ANOVA was performed with independend factors of motion and arm
elevation angle. In addition, a linear regression was performed to
determine the relation between GH elevation angle and arm elevation
angle. Both the intercept and slope values we statistically tested using a
one-way ANOVA. For comparison of the plane of elevation and the
humeral rotation, the average values were calculated over three ranges: <
60 (Low); 60-120 (Mid), >120 (High) degrees of elevation. A 2-way
ANOVA with independent factors of motion and range was performed.
effect of motion was found for SI GH position (p = 0.028) indicating
that during scaption the humeral head was positioned lower compared to
abduction (p=0.043) and flexion (p =0.025). Table 1 shows the results
for the GH elevation regression, plane of elevation and humeral
rotations, and the significant motion effects on these variables.
40
60
80
100
120
140
160
60
80
100
120
140
160
120
140
160
Superior
4
2
0
-2
20
0
AP Position (mm)
INTRODUCTION:
Effective shoulder function is a complicated balance between
multiple stabilizing mechanisms. Essential to understanding how these
mechanisms interact to stabilize the glenohumeral (GH) joint is the
precise measurement of the GH joint kinematics during activities of
daily living (ADL). In this regard, measurement of the range of motion
(ROM) of arm elevation is important, because it is a common motion for
ADL, it represents a motion assessed clinically for shoulder pathology;
and, it is used as a benchmark motion for the design of new surgical
techniques and implants that must be reached to restore normal function.
Traditional methods of determining in vivo shoulder kinematics
include palpation and attaching markers or sensors to the skin. The fact
that the bones move significantly relative to skin makes the accuracy of
these measurements insufficient for sub-millimeter measurement of GH
joint translation. In recent years, fluoroscopy has emerged as a highly
accurate way to measure three-dimensional (3D) kinematics of bones.
It is not common in kinematic studies to measure shoulder kinematics
during arm elevation in all three standard planes: abduction, scaption
(abduction in the scapular plane) and forward flexion. However, it is
unknown what exactly changes in the shoulder kinematics between these
motions. Therefore, the purpose of this study was to accurately measure
the 3D glenohumeral motions during abduction, scaption and forward
flexion in healthy subjects. It was hypothesized that all motions would
be similar in GH positions and that only the GH plane of elevation and
humeral rotation would be different.
40
Anterior
-2
-4
-6
-8
20
40
60
80
100
Arm elevation (mm)
Figure 1. GH elevation, SI and AP positions as a function of arm
elevation angle.
Poster No. 1810 • 56th Annual Meeting of the Orthopaedic Research Society