Comparison of Glenohumeral Rotations Between Scaption and Forward Flexion in Healthy Subjects Using Biplane
Fluoroscopy
+1Giphart, J E; 1Horn, N; 1Shelburne, K B; Anstett, T; 1Horne, A; 1Pault, J D; 1Brunkhorst, J P; 1,2Millett, P J; 1Torry, M R
+1Steadman-Hawkins Research Foundation, Vail, CO; 2Steadman-Hawkins Clinic, Vail, CO
Senior author: erik.giphart@shsmf.org
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 cm, 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. Each elevation was performed smoothly in 2
seconds at an even pace with the help of a metronome. The biplane
fluoroscopy system consisted of two BV Pulsera c-arms (Philips
Medical Systems, Best, the Netherlands) which were operated in pulsed
fluoroscopy mode at 30 fr/s. A high-resolution 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.
The three-dimensional geometries of the scapula and humerus
were extracted from the CT data (Mimics, Materialise, Ann Harbor, MI).
For each frame, the 3D bone poses were estimated using a contour
matching algorithm (Model-Based RSA, Medis Specials BV, Leiden, the
Netherlands). Coordinate systems and 3D glenohumeral rotations were
determined according to the ISB standard3
For each subject and each motion a linear regression was
performed to determine the relation between glenohumeral elevation
angle and arm elevation angle. Both the intercept and slope values we
statistically tested using a t-test. For comparison of the plane of
elevation and the humeral rotation, the average values were calculated
over three ranges: < 60; 60-120,>120 degrees of elevation. A 2-way
ANOVA with independent factors of motion and range was performed.
RESULTS:
Table 1 shows the means and standard deviations of the regression
results of the elevation angle, as well as the plane of elevation and
humeral rotation angles across the ranges. The regressions were found
to be highly linear (lowest R2 = 0.96) and the slope of the elevation
angle regression was found to be significantly lower for forward flexion
compared to scaption (p = 0.003), while the intercept was significantly
highter (p <0.001; Figure 1). For the plane of elevation angle there was a
significant main effect of motion (p < 0.001) as well as a significant
interaction effect (p = 0.011; no significant post-hoc results were found).
The plane of elevation for forward flexion was found to be 29.39 deg
anterior to the scapular plane while the scaption was performed at 3.62
deg. For the humeral rotation angle there was only a significant main
effect of motion (p = 0.002) showing there was significantly more
external humeral rotation during forward flexion compared to scaption.
DISCUSSION:
The findings of this study do not support the hypothesis that
glenohumeral rhythm is the same during forward flexion and scaption.
The slope of the regression was found to be lower for forward flexion
meaning that per arm elevation angle traveled there was less
glenohumeral elevation. This is likely due to the fact that the humerus
starts more elevated as evidenced by the 15 deg higher intercept of the
regression, thus, reducing the need for glenohumeral elevation as the
arm is elevating. The regression slopes in this study can be transformed
into the Inman ratio and are 1.52 : 1 for scaption and 1.06 : 1 for forward
flexion, respectively. The information in this study is a valuable baseline
for future comparisons with pathological groups.
REFERENCES:
1. Inman et al., (1944) JBJS Am, 26:1-30.; 2. Bey et al., (2006) J
Biomech Eng, 128:4:604-609.; 3. Wu et al., (2005) J Biomech,
38:5:981-992.; 4. Pronk et al., (1993) Proc Inst Mech Eng {H}, 207:219229.; 5. Karduna et al., (2001) J Biomech Eng, 123:2:184-190.; 7.
Ludwig and Cook (2002) J Orthop Sport Phys Ther, 32:6:248-259.; 8.
McClure et al., (2001) J Elbow Shoulder Surg, 10:3:269-298.; 9.
McQuade and Smidt (1998) J Orthop Sports Phys Ther, 27:2:125-33.
Table 1. Mean and standard deviations of the variables measured during
scaption and forward flexion (* indicates statistical significance).
Scaption
GH Elevation Slope *
GH Elevation Intercept *
GH Plane of Elevation (Low)
GH Plane of Elevation (Med)
GH Plane of Elevation (High)
GH Plane of Elevation (all) *
Humeral Rotation (Low)
Humeral Rotation (Med)
Humeral Rotation (High)
Humeral Rotation (all) *
Forward
Flexion
0.51 ± 0.11
18.9 ± 13.0
31.9 ± 29.6
38.8 ± 13.4
18.0 ± 5.9
29.4 ± 21.1
21.0 ± 21.9
29.2 ± 17.6
26.7 ± 7.5
26.0 ± 16.0
0.60 ± 0.06
3.9 ± 7.5
0.1 ± 11.9
-10.7 ± 6.3
0.1 ± 6.7
3.6 ± 9.8
8.5 ± 10.3
17.1 ± 11.8
15.5 ± 9.4
13.6 ± 10.8
110
Glenohumeral Elevation Angle (deg)
INTRODUCTION:
The shoulder is a very complex joint. Effective shoulder function
is a complicated balance between stabilizing mechanisms which include
the geometry of the articular joint, the labral-capsular-ligamentous
structures, intra-articular pressures and the individual muscle forces.
Essential to understanding how these factors interact to stabilize the
glenohumeral joint is the precise measurement of the glenohumeral joint
kinematics during activities of daily living (ADL). In this regard, ranges
of motion needed to perform scaption (abduction in the scapular plane)
and forward flexion are important, because these are common motions
for ADL, they represent common motions assessed clinically for
shoulder pathology; and, they are often used as the benchmark motions
for the design of new surgical techniques and implants that must be
reached to restore normal function. Inman et al.1 were the first to
quantify that during abduction there is a linear relationship between
glenohumeral and scapulothoracic elevation with a ratio of 2 : 1. Other
researchers have measured this ratio and have found similar but slightly
lower values. However, glenohumeral rhythm has not been reported yet
for forward flexion. Moreover, several investigators have used a skinbased marker approach that involves digitizing discrete bony landmarks
that are palpable through the skin or by capturing 3D scapular
orientation with a magnetic device attached directly to the acromion4-9.
While these methods initially appeared satisfactory, their reliability and
accuracy have been recently questioned9. Most recently, biplane
fluoroscopy has emerged as a new and highly accurate way to measure
3D kinematics of bones inside the body. Accuracies of better than 1mm
and 1 deg have been shown to be possible using this technique at high
frame rates2.
The purpose of this study was to accurately measure the threedimensional glenohumeral rotations during scaption and forward flexion
in healthy subjects. It was hypothesized that there is no difference in
glenohumeral rhythm between scaption and forward flexion and that
only the plane of elevation would be more anterior for forward flexion.
100
Scaption
Fwd Flexion
90
80
70
60
50
40
30
20
10
20
40
60
80
100
120
140
160
180
Elevation Angle (deg)
Figure 1. Glenohumeral elevation for scaption and forward flexion.
ACKNOWLEDGMENTS:
This work was funded in part by the Stavros Niarchos Foundation and
the Steadman Hawkins Research Foundation.
Poster No. 1915 • 55th Annual Meeting of the Orthopaedic Research Society