Article

Effect of Plane of Arm Elevation on Glenohumeral Kinematics A Normative Biplane Fluoroscopy Study

Department of BioMedical Engineering, Steadman Philippon Research Institute, 181 West Meadow Drive, Suite 1000, Vail, CO 81657.
The Journal of Bone and Joint Surgery (Impact Factor: 5.28). 02/2013; 95(3):238-45. DOI: 10.2106/JBJS.J.01875
Source: PubMed

ABSTRACT

Background:
Understanding glenohumeral motion in normal and pathologic states requires the precise measurement of shoulder kinematics. The effect of the plane of arm elevation on glenohumeral translations and rotations remains largely unknown. The purpose of this study was to measure the three-dimensional glenohumeral translations and rotations during arm elevation in healthy subjects.

Methods:
Eight male subjects performed scaption and forward flexion, and five subjects (three men and two women) performed abduction, inside a dynamic biplane fluoroscopy system. Bone geometries were extracted from computed tomography images and used to determine the three-dimensional position and orientation of the humerus and scapula in individual frames. Descriptive statistics were determined for glenohumeral joint rotations and translations, and linear regressions were performed to calculate the scapulohumeral rhythm ratio.

Results:
The scapulohumeral rhythm ratio was 2.0 ± 0.4:1 for abduction, 1.6 ± 0.5:1 for scaption, and 1.1 ± 0.3:1 for forward flexion, with the ratio for forward flexion being significantly lower than that for abduction (p = 0.002). Humeral head excursion was largest in abduction (5.1 ± 1.1 mm) and smallest in scaption (2.4 ± 0.6 mm) (p < 0.001). The direction of translation, as determined by the linear regression slope, was more inferior during abduction (-2.1 ± 1.8 mm/90°) compared with forward flexion (0.1 ± 10.9 mm/90°) (p = 0.024).

Conclusions:
Scapulohumeral rhythm significantly decreased as the plane of arm elevation moved in an anterior arc from abduction to forward flexion. The amount of physiologic glenohumeral excursion varied significantly with the plane of elevation, was smallest for scaption, and showed inconsistent patterns across subjects with the exception of consistent inferior translation during abduction.

Full-text

Available from: Michael Torry, Dec 11, 2015
Effect of Plane of Arm Elevation on
Glenohumeral Kinematics
A Normative Biplane Fluoroscopy Study
J. Erik Giphart, PhD, John P. Brunkhorst, BA, Nils H. Horn, MD, Kevin B. Shelburne, PhD,
Michael R. Torr y, PhD, and Peter J. Millett, MD, MSc
Investigation performed at the Department of BioMedical Engineering, Steadman Philippon Research Institute, Vail, Colorado
Background: Understanding glenohumeral motion in normal and pathologic states requires the precise measurement of
shoulder kinematics. The effect of the plane of arm elevation on glenohumeral translations and rotations remains largely
unknown. The purpose of this study was to measure the three-dimensional glenohumeral translations and rotations during
arm elevation in healthy subjects.
Methods: Eight male subjects performed scaption and forward flexion, and five subjects (three men and two women)
performed abduction, inside a dynamic biplane fluoroscopy system. Bone geometries were extracted from computed
tomography images and used to determine the three-dimensional position and orientation of the humerus and scapula in
individual frames. Descriptive statistics were determined for glenohumeral joint rotations and translations, and linear
regressions were performed to calculate the scapulohumeral rhythm ratio.
Results: The scapulohumeral rhythm ratio was 2.0 ± 0.4:1 for abduction, 1.6 ± 0.5:1 for scaption, and 1.1 ± 0.3:1 for
forward flexion, with the ratio for forward flexion being significantly lower than that for abduction (p = 0.002). Humeral head
excursion was largest in abduction (5.1 ± 1.1 mm) and smallest in scaption (2.4 ± 0.6 mm) (p < 0.001). The direction of
translation, as determined by the linear regression slope, was more inferior during abduction (22.1 ± 1.8 mm/90)
compared with forward flexion (0.1 ± 10.9 mm/90)(p= 0.024).
Conclusions: Scapulohumeral rhythm significantly decreased as the plane of arm elevation moved in an anterior arc from
abduction to forward flexion. The amount of physiologic glenohumeral excursion varied significantly with the plane of
elevation, was smallest for scaption, and showed inconsistent patterns across subjects with the exception of consistent
inferior translation during abduction.
Clinical Relevance: When ev aluating scapulohumeral kinematics during clinical assessment or for reha bilitation
protocols, it is im po rtant to take into account and control the plane of arm elevation. Abn ormalities in scapular motion
may be be tter evaluated during forward flexion of the arm because gre ater scapular motion is required for this arm
motion.
U
nderstanding glenohumeral motion in normal and
pathologic states requires the precise measurement of
shoulder joint kinematics. Multiple studies have linked
abnormal shoulder joint kinematics with various shoulder dis-
orders including secondary impingement
1-4
, rotator cuff tears
5,6
,
glenohumeral osteoarthritis
7,8
, labral injury, and glenohumeral
instability
9,10
.
Although shoulder pathology is associated with abnormal
kinematics, there is little detailed information about baseline
values that can provide reference points for the restoration of
normal shoulder kinematics. The most commonly studied pa-
rameter for glenohumeral rotation is scapulohumeral rhythm,
defined as the ratio between glenohumeral elevation and upward
scapulothoracic rotation, which was first reported to be 2:1 by
Disclosure: On e or more of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in
support of an aspect of this work. In addition, one or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six m onths
prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written
in this work. Also, one or more of the authors has had another relationship, or has engaged in another activity, that could be perceived to influence or have
the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always
provided with the online version of the article.
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Inman et al.
11
. Two types of abnormalities in scapulohumeral
rhythm have been recognized in shoulders with pathologic
conditions: (1) increased rhythm exacerbating the likelihood of
secondary impingement by biomechanically decreasing the
volume of the subacromial space
1,3,12-14
, and (2) decreased rhythm
serving as a compensatory method that potentially avoids im-
pingement symptoms and improves rotator cuff function
4,6-9,15-17
.
There is considerable variation in the magnitude of ph ysi-
ologic glenohumeral translations reported in the literature. Nor -
mal in vivo glenohumeral translations ranging from 0.3 to 2.6 mm
in the superior -inferior direction have been demonstrated by
means of dynamic measurements involving fluoroscopy
18,19
and
static measurements involving radiography
6,20-23
.Normalinvitro
superior shoulder translations of 2.0 to 5.7 mm hav e been re-
ported
24,25
. Increased mean in vivo glenohumeral translations of
appro ximately 1.5 mm in patients with symptomatic rotator cuff
tears
6
, impingement syndrome
21
, and biceps tenodesis
23
have been
reported, with individual increases of up to 6 to 8.9 mm
6,23
.
In recent years, biplane fluoroscopy has emerged as a highly
accurate and precise method to measure in vivo three-dimensional
kinematics; this method allo ws measur ement of glenohumeral
jointmotiontowithinfractionsofamillimeter
26,27
. Clinically,
measurement of the full range of arm elevation is important be-
cause arm elevation is a common motion during activities of daily
living and athletic activities. It is uncommon for shoulder kine-
matics in fluor osc opic studies to be reported in all three of the
standard planes of arm elevat ion: abduction (coronal plane ele-
vation), scaption (scapular plane elevation), and forward flexion
(sagittal plane elevation). As a result, the relative effect of the plane
of elevation on glenohumeral translation and scapulohumeral
rhythm remains unknown. Our purpose was to measure three-
dimensional glenohumeral translations and rotations during ab-
duction, s caption, and forward fl exion in healthy subjects. Our
hypothesis was that glenohumeral translations and scapulohu-
meral rhythm would change with the plane of elevation.
Materials and Methods
Subjects
A
ll participants provided written consent and the study was approved by the
institutional review board of the Vail Valley Medical Center. Eight male
subjects (Group 1) without a shoulder abnormality performed scaption and
forward flexion. These subjects had a mean age (and standard deviation) of 29 ± 6
years, height of 1.84 ± 0.05 m, weight of 87.4 ± 7.8 kg, and body mass index of
25.7 ± 2.2 kg/m
2
. In addition, three male and two female subjects (Group 2)
performed abduction. These subjects had a mean age of 41 ± 14 years, height of
1.77 ± 0.09 m, weight of 86.5 ± 22.9 kg, and body mass index of 27.2 ± 5.0 kg/m
2
.
The subjects in Group 2 had undergone an isolated biceps tenodesis procedure on
their contralateral shoulder. Data for Group 2 were originally collected for a
previous study comparing glenohumeral translations between the healthy and
tenodesed shoulders of these subjects
28
. Only the healthy shoulder was analyzed
in the present study. Thus, a total of eight right shoulders (all dominant) and five
left shoulders (all nondominant) were analyzed in the present study. All subjects
underwent a detailed shoulder examination by a shoulder specialist to exclude any
pathologic condition in the shoulder of interest.
Instrumentation
A custom biplane fluoroscopy system was constructed from two synchronized and
modified BV Pulsera C-arms (Philips Medical Systems, Best, The Netherlands)
with 30-cm image intensifiers and was used to measure the three-dimensional
position and orientation of the humerus and the scapula. The C-arms were
modified under appropriate Food and Drug Administration guidelines and Col-
orado radiation safety regulations. Motions of the shoulder were performed at a
distance of approxim ately 25 cm from the image intensifiers. For Group 1, data
were collected at 30 Hz with the x-ray generators in a pulsed fluoroscopy mode
(8 milliseconds, 60 mA, approximately 60 kV) and were subsequently analyzed at
10 Hz (i.e., every third frame). For Group 2, following a system upgrade, data were
collected at 100 Hz with the x-ray generator s operating in a continuous fluoros-
copy mode (12 mA, approximately 60 kV) and were then analyzed at 12.5 Hz (i.e.,
every eighth frame) because the movements were sufficiently slow and the analysis
was labor-i ntensive. Image distortion was corrected by imaging a square grid and
then a calibration cube to determine the x-ray focus positions and the relativ e
positioning and orientation of the two fluoroscopes
29
.
The biplane fluoroscopy system was validated with use of standard vali-
dation techniques
26,30,31
. Kinematic data for four cadaveric shoulders with the soft
tissues intact were collected during scaption to simulate the in vivo measure-
ments. These specimens were placed inside the biplane fluoroscopy system in a
comparable position and orientation and were elevated from neutral to maxi-
mum elevation over a two-second period with use of a pulley system. The data
were analyzed in the same manner as described below for the in vivo study. In
addition, five tantalum beads (1.6 mm) were inserted into each scapula and each
humerus to provide reference measurements. Bias and precision were calculated,
in thirty frames
32
for each specimen, as the mean and standard deviation of the
difference in the measured scapular and humeral positions and rotations relative
to the positions and rotations determined by tracking of the beads. The mean
biases and precisions were 0.2 ± 0.5 mm, 0.3 ± 0.3 mm, and 0.3 ± 0.4 mm
for measurements of anterior-posterior, superior-inferior, and distraction-
compression translations, respectively. The mean biases and precisions were
0.1 ± 0.8,0.2 ± 0.2, and 1.7 ± 1.2 for measurements of the glenohumeral
plane of elevation, elevation angle, and internal-external rotation, respectively. As
we had expected because of the increased amount of soft tissue, these values were
generally slightly higher than those reported in a previous study of the knee using
our system (0.2 ± 0.3 mm, 20.1 ± 0.1 mm, and 20.05 ± 0.1 mm for the three
translations and 0.1 ± 0.1,0.3 ± 0.2,0.1 ± 0.3 for the three rotations)
33
, with
the exception of glenohumeral internal-external rotation, which was more difficult
to measure in the shoulder because of the cylindrical geometry of the humerus.
The values were consistent with similar studies using biplane fluoroscopy
26,27,34,35
.
During the in vivo activities, the motion of the subject’s arm and torso
was recorded at 120 Hz with use of an optical motion analysis system (Motion
Analysis, Santa Rosa, California) to track how the exercises were being per-
formed at a global level; this provided a reference for the local biplane fluo-
roscopy data. Thirteen retroreflective markers were placed on the subject’s
trunk, arm, and forearm. However, only the four markers on the left and the
right acromion and on the medial and the lateral epicondyle (elbow joint
center) were used to calculate the plane of arm elevation relative to the trunk for
the frame in which the arm was elevated to 90. Data collection by the motion
analysis system was synchronized with that of the biplane fluoroscopy system.
Procedures
A high-resolution computed tomography (CT) scan of the subject’s shoulder
was obtained (Aquilion 64, Toshiba America Medical Systems, Tustin, Cal-
ifornia). The CT scan was used for reconstruction of the three-dimensional
geometry of the scapula and the upper one-third of the humerus. The sequence
of axial images from the scan (approximate voxel size, 0.5 · 0.7 · 0.7 mm) was
obtained at 120 kVp and 200 mA with shar p-bone CT reconstruction.
The subjects in Group 1 performed two standard range-of-motion
exercises over their full range of motion: (1) scaption (motion in the scapular
plane, 30 to 40 anterior relative to the coronal plane), and (2) forward flexion
(motion in the sagittal plane). The subjects were seated with their back straight
and their arm hanging by their side. They then elevated their arm over their
head as far as possible at an even pace over the course of two seconds, aided by
a metronome, while keeping their elbow fully extended with the thumb pointed
upwards. The subjects in Group 2 performed abduction (motion in the coronal
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plane) in a similar fashion. All subjects performed practice runs to become
acquainted with the motions. To minimize radiation exposure to the subjects, a
single trial was recorded for each motion.
Data Reduction
Data processing consisted of four steps as described previously
28,36
: recon-
struction of the three-dimensional bone geometry of the humerus and scapula
from the CT data, coordinate system assignment and geometric transforma-
tion, determination of bone positions and orientations in the biplane fluo-
roscopy data, and postprocessing to extract the shoulder kinematics.
The three-dimensional geometries of the scapula and the humerus were
extracted from the CT data (Mimics, Materialise, Plymouth, Michigan). Coor-
dinate systems and three-dimensional glenohumeral rotations were determined
by a method that followed the International Society of Biomechanics standard
37
as closely as possible. In summary, the lateral axis of the scapula was directed from
the trigonum spinae scapulae to the angulus acromialis (Fig. 1), and the anterior
axis was perpendicular to the plane of the scapula. The lateral axis of the humerus
was directed parallel to a line connecting the medial and lateral epicondyles,
which was estimated on the basis of the bicipital groove
38
. The superior axis of
the humerus was taken as the center line through the canal of the shaft. In
addition, a more clinically relevant coordinate system was created to quantify
glenohumeral translations. The humeral head center was determined by fitting a
sphere to the articular surface of the humeral head (Fig. 2). A glenoid coordinate
system was created on the basis of the most superior, inferior, and anterior points
on the glenoid rim (Fig. 2). The glenoid center was assumed to lie midway
between the most superior and inferior points on the glenoid rim.
Determination of bone position and orientation from the biplane fluo-
roscopy data was performed for each analyzed frame with use of Model-Based
RSA software (Medis Specials, Leiden, The Netherlands)
31,39
. Contours were
automatically extracted from the biplane fluoroscopy images and were man-
ually assigned to the humerus and the scapula. Subsequently, a fully automatic,
six-degree-of-freedom contour matching optimization algorithm determined
the three-dimensional bone position and orientation. This algorithm optimally
matched the detected contours with the projected contours from the imported
bone geometries (Fig. 3).
The glenohumeral r otations and translations during the motions were
calculated from the optimized bone positions and orientations. Three-dimensional
glenohumeral joint rotations were described (using YXY Euler angles
37
)as(1)the
Fig. 1 Fig. 2
Fig. 1 Scapular coordinate system and glenohumeral plane of elevation represented in a superior view, with arrows depicting the direction of the anterior and
posterior planes. The neutral glenohumeral plane of elevation is determined by the lateral scapular axis (Z), defined as a line running through the angulus
acromialis (junction of the posterior and lateral borders of the acromion) and the trigonum spinae scapulae (root of the spine of the scapula). Fig. 2
The humeral head center (left) is determined by fitting a sphere to the articular surface of the humeral head. The glenoid coordinate system (right) is based on
the most superior, inferior, and anterior points on the computed tomography reconstruction.
Fig. 3
Matching of bone geometries for an abduction
frame. The algorithm matches the detected bone
contours (yellow) with the projected bone contours
(black).
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instantaneous plane of elevation (in front of or behind the scapular plane) about
the superior axis of the scapula, (2) the humeral elevation about the anteriorly
directed axis of the humerus, and (3) the internal-external axial rotation about
the super ior axi s of t he humeru s (Fig . 4). Glenohumeral translation was
defined as the superior-inferior and anterior-posterior motion of the hu-
meral head center relative to the g lenoid coordinate syst em. Lastly, the arm
elevation angle was defined as the angle between the humeral shaft axis and
ver t ic a l.
For each motion performed by the subject, the time series of the gleno-
humeral rotations and translations was filtered at 2 Hz. The glenohumeral ro-
tation and translation curves for each motion were analyzed from 20 to 150 of
arm elevation. A linear regression analysis was performed to determine the slope
(change in glenohumeral elevation/change in arm elevation) and the intercept for
the relationship between glenohumeral elevation and arm elevation angle. The
slope quantifies how much glenohumeral elevation occurs per degree of arm
elevation. Given that arm elevation equals the sum of glenohumeral elevation and
upward scapulothoracic rotation (Fig. 4), upward scapulothoracic rotation was
then calculated by subtracting the glenohumeral elevation from the arm elevation.
Subsequently, scapulohumeral rhythm was determined by calculating the ratio of
glenohumeral elevation to upward scapulothoracic rotation
11
.Themean,stan-
dard deviation, maximum, minimum, and total excursion (maximum minus
minimum) were calculated for each motion for each translation direction. In
addition, linear regression quantified the slope and intercept of the glenohumeral
translations as a function of arm elevation. The slope was expressed as the amount
of translation per 90 of arm elevation. Lastly, the rotation and translation data
as a function of arm elevation were resampled in 10 intervals from 20 to 150 of
arm elevation.
Statistical Methods
A one-way analysis of variance (ANOVA) with the arm plane of elevation
(abduction, scaption, or forward flexion) as the independent variable was
performed to analyze the linear regression results, scapulohumeral rhythm,
glenohumeral plane of elevation and rotation, arm plane of elevation, an d
mean, maximum, minimum, and excursion of the anterior-posterior and
superior-inferior glenohumeral positions. A p value of 0.05 was considered
significant. When significant ANOVA results were found, Bonferroni-corrected
post hoc comparisons were performed to analyze the specific differences be-
tween the elevation planes. A two-way ANOVA with the elevation plane (ab-
duction, scaption, forward flexion) and arm elevation angle (20 to 150 in 10
increments) as the independent variables was performed to statistically analyze the
glenohumeral elevation angle as well as anterior-posterior and superior-inferior
glenohumeral translations. A one-sample t test was used to determine whether
regression slope values were significantly different from zero (at the p < 0.05 level).
Source of Funding
This work was supported by the Steadman Philippon Research Institute and the
Gumbo Foundation. In addition, the Minnesota Medical Foundation supported
the Summer Research Internship position of one of the authors. Neither the
Gumbo Foundation nor any other corporate sponsorship to our institution
played a role in the investigation.
Results
T
he means for the three glenohumeral rotations as a func-
tion of arm e levation angle are shown in Figure 5 . T he
images of the forward flexion trial of one subject were under-
exposed and the trial had to be excluded from the results.
The mean slopes of the g lenohumeral elevation regression
for the abduction, scaption, and forward flexion curves were
0.66 ± 0.05, 0.60 ± 0.06, and 0.52 ± 0.07, respectively, with the
slope for coronal plane abduction being significantly greater
than that for forward flexion (p = 0.001) (see Appendix).
The corresponding scapulohumeral rhythm ratios were 2.0 ±
0.4:1 for abduction, 1.6 ± 0.5:1 for scaption, and 1.1 ± 0.3:1
for forward flexion, with the rhythm for abduction being sig-
nificantly greater than that for forward flexion (p = 0.002).
Overall, the g lenohumeral contribution to arm elevation de-
creased as the plane of arm elevation moved anteriorly from the
coronal plane (abduc tion) toward the sagittal plane (forward
flexion).
The data demonstrated that the glenohumeral plane of
elevation for abduction at 90 of arm elevation, 211.8 ± 4.7,
was similar to that for scaption, 211.6 ± 4.9, with both planes
lying slightly posterior to the plane of the scapula (see Appen-
dix). These motions were also similar globally, with abduction
performed at an arm elevation plane of 16.8 ± 7.9 and scaption
at 30.1 ± 8.2. Forward flexion was significantly anterior
compared with the o ther two motions, w ith a gl enohumeral
elevation plane of 42.4 ± 12.2 and an arm elevation plane
of 81.2 ± 14.7 (p < 0.001). The results for glenohumeral
internal rotation mirrored those for the plane of elevation, with
forward flexion demonstrating significantly more internal ro-
tation (37.2 ± 15.0) compared w ith scaption (19.0 ± 11.9)
and abduction (19.5 ± 9.1)(p= 0.032) (see Appendix).
The group mean and standard deviation of the descriptive
statistics for anterior-posterior glenohumeral translation for all
three motions are presented in the Appendix and depicted as a
Fig. 4
The scapular and humeral coordinate systems as well as glenohumeral
elevation, glenohumeral internal-external rotation, and upward scapular
rotation are indicated in a posterior view of a right shoulder. The origin of the
humeral coordinate system is located in the center of the humeral head
(dotted circle), and the long axis (Y) is determined by calculating the center
line of the proximal aspect of the shaft (dotted line).
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function of the arm elevation angle in Figure 6. On average, the
humeral head was positioned 4 to 5 mm posterior to the midline
of the glenoid for all motions. The glenohumeral excursions
(total amount of translation) for abduction, scaption, and for-
ward flexion for the group were 1.4 mm, 0.7 mm, and 2.4 mm,
respectively, and the between-subject variabilities (i.e., standard
deviation averaged across all arm elevation angles) were 2.1 mm,
1.0 mm, and 1.9 mm. When the parameters extracted from the
individual curves were analyzed, the minimum (most posterior)
position was significantly more posterior for abduction (27.7 ±
1.2) than for scaption (25.6 ± 1.0 mm) (p = 0.025). In addition,
the excursions for all three motions were significantly different
from each other (p < 0.001), with excursion occurring during
abduction (5.1 ± 1.1 mm) being larger than that during flexion
(3.6 ± 1.1 mm), which in turn was larger than that during scaption
(2.4 ± 0.6 mm). N o other significant differenc es were found.
The group mean and standard deviation of each descrip-
tive statistic for superior-inferior position for each motion are
presented in the Appendix, and values are depicted as a function
of arm elevation angle in Figure 6. To demonstrate the between-
subject variability, the descriptive statistics for the individual
subjects and the group mean and standard dev iation for the
superior-inferior g lenoh umeral position for scaption are also
presented in the Appendix. On average, the humeral head was
positioned 1 to 2 mm superior to the midline of the glenoid for all
motions. The glenohumeral excursions for the group for abduc-
tion, scaption, and forward flexion were 3.7 mm, 0.9 mm, and
1.3 mm, respectiv ely, and the between-subject variabilities were
2.3 mm, 1.7 mm, and 1.4 mm. The slope of the linear regression
curve indicated that translation was significantly more inferiorly
directed for abduction (22.1 ± 1.8 mm/90)comparedwith
forward flexion (0.1 ± 0.9 mm/90)(p= 0.024) and approached
being different from zero (p = 0.057). In addition, the two-way
ANOVA showed a significant difference between abduction and
scaption (p = 0.017), with the glenohumeral position during ab-
duction being significantly mor e superior compar ed with scap-
tion. No other significa nt differenc es were found.
Discussion
T
his study indicated that changes in the plane of arm ele-
vation affected glenohumeral kinematics in multiple ways,
including in glenohu meral translations, glenohumeral eleva-
tion, and scapulohumeral rhythm, which confirmed our hy-
pothesis. The scapulohumeral rhythm ratio was significantly
smaller for for ward flexion than for abduction. Therefore,
forward flexion was associated with a greater scapular contri-
bution via upward rotation and relatively less glenohumeral
elevation compared with abduction. This difference in scapu-
lohumeral rhythm suggests that scapular motion abnormalities
may be better examined in forward flexion because any ab-
normalities may be more apparent. This finding supports a
similar recommendation in a recent clinical study
40
.
The glenohumeral translations indicated that, on aver-
age, the humeral head was positioned posteriorly and superi-
orly on the glenoid. Dur ing shoulder motion, the total humeral
Fig. 5
Mean glenohumeral plane of elevation, elevation angle, and internal ro-
tation as a function of arm elevation angle in the three planes of motion
(forward flexion, scaption, and abduction).
Fig. 6
Mean anterior-posterior and mean superior-inferior position of the humeral
head relative to the glenoid as a function of arm elevation angle in the three
planes of motion.
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head excursion was greatest in abduction and smallest in
scaption. Group mean excursion was always less than the
between-subject variability, with the exception of superior-
inferior excursion during abduction (3.7 mm compared with
2.3 mm). The individual excursions, and especially that for
scaption, were relatively small compared with the mean male
glenoid size of 27.4 · 37.5 mm
34
. The excursions equaled
18.6%, 8.8%, and 13.1% of the glenoid size for abduction,
scaption, and for ward flexion, respectively, in the anteri or-
posterior direction and 11.2%, 6.7%, 8.0% in the superior-inferior
direction. The directions of the translations, as determined by
the linear regression slope, were inconsistent among subjec ts
and were not in a specific direction, with the exception of
inferior translation dur ing abduction. The data clearly showed
that the plane of arm elevation needs to be controlled in research
and clinical settings to accurately assess and clinically follow
scapulohumeral rhythm and glenohumeral translations in pa-
tients with shoulder disorders.
U nderstanding normal scapulohumeral rh ythm is key to
identifying and treat ing clinical shoulder disor ders because ab-
normal shoulder kinematics are routinely measured during clinical
examinations and in biomechanical studies inv olving subacromial
impingement, rotator cuff tears, adhesive capsulitis, glenohumeral
osteoarthritis, and glenohumeral instability
1-10,13,14,23,41-44
. In 1944,
Inmanetal.
11
first assigned a value to scapulohumeral rhythm,
reporting that scapulohumeral rh ythm in healthy subjects per-
forming abduction occurred in a 2:1 ratio. However, ratios ranging
from 1.25:1 to 5.3:1 have been subsequently reported with
the advent of newer and more accurate measurement tech-
niques
4,5,12,42,45-52
. Despite these findings, Inmans ratio of 2:1 is
still commonly used in educational and clinical settings and
was further supported by the present study (which found a
ratio of 2.0 ± 0.4:1 for abduction).
Clinically, these results provide valuable baseline data on
both mean translation amplitude and between-subject variability
for future stu dies investigating glenoh umeral translations in
other patient populations such as those with various forms of
impingement, r ot ator cuff disease, instability, and arthritis. In-
deed, one of the theories regarding glenohumeral arthritis is that
theetiologyinvolvesanincreaseinshearforcethatcannotbe
tolerated by the articular cartilage
53
. The results of the pr esent
study demonstrated that, in a healthy glenohumeral joint, only
small excursions of 2.5 mm occur in both principal dir ections
during scaption over the full range of shoulder motion. There-
fore, it is unlikely that shoulder translations in healthy shoulders
are measureable with use of palpation or skin-based measure-
ment methods. Moreover, th e standard deviations for gleno-
humeral position were greater than the measured excursion
amplitudes, indicating that the motion-relate d translations were
smaller than the variations among subjects and can therefore only
be measur ed with advanced imaging techniques. Future studies
of patient populations diagnosed with instability and suspected
of having increased glenohumeral translations will place the
magnitud e of clinically relevant translations in perspective.
Theseresultsalsoprovidevaluablebaselinedataforcom-
puter simulations and i n vitro experimentation. In computer
modeling, the glenohumeral joint is commonly modeled as a
ball and socket joint
54-56
. We found that this approximation was
accurate to within 2.5 mm for scaption and 5.1 mm for ab-
duction, or within 9% and 19% of the mean glenoid dim en-
sion, respectively. Therefore, the ball and socket assumption
may be reasonable (with an error of <10%) for the shoulders of
healthy subjects during scaption, but it may not be acceptable
for other motions or for pathologic conditions. It is unclear
what effect this may have on muscular lines of action and
moment arms, and developers of computer models need to be
mindful when making the assumption of a ball and socket joint
for arbitrary motions. The results of the present study also
indicated that glenohumeral translations previously reported
for some in vitro studies (e.g., 5.7 mm superior translation
25
)
may be excessive and should be treated with caution, as the ir
magnitude is suggestive of loading that is improper for simu-
lating in vivo motion. Therefore, the data from the present
study provide a baseline value to be met by in vitro studies that
are aimed at replicating physiologic loading of the joint.
The present study has several limitations. Firs t, the scapu-
lohumeral rhythm results were derived solely fr om the glenohu-
meral component during arm elevation. Scapulothoracic rotation
was not measured directly but was assumed to equal the difference
between total arm elevation and glenohumeral elevation. Although
this is a simplification, we believe the result to r epresent a valid
estimate for compa ring the different motions. Similar methods
relying on these relationships have been used in previous stud-
ies
45,46,49,51,52
. Second, abduction did not occur in a purely coronal
plane. Even though clinicians confirmed visually during data col-
lection that subjects appeared to be performing the abduction
movement appropriately, kinematic results indicated the arm
motion to be 17 anterior to the coronal plane. The fact that
abduction actually occurred halfwa y between the scapular plane
and the true coronal plane could potentially explain the similarities
between our abduction and scaption rotation results. However,
significant differences between these motions were still found for
the glenohumeral translations. We suggest that future studies use a
guidetoensurethatmotionsareperformedintheproperplanes.
Third, the biplane fluor oscopy methodology used in the
study results in radiation exposure. However, fluoroscopy is the
most accurate measurement technique to date, and it allows
the greatest freedom of movement and the highest frame rates of
an y technique. Care was taken to keep the amount of radiation as
low as possible. This was the reason that only one trial was ob-
tained for each motion. In addition, the lowest technique factors
that still allowed sufficient image quality for motion tracking were
used. Unfortunately, this resulted in the ex clusion of the forward
flexion trial of one subject because of underexposure. Lastly, our
subject population consisted of two distinct groups, which was
not ideal. The data represented the combination of two originally
distinct studies into one. The data could have been improved by
having an entirely new group of subjects perform all three of the
motions. However, this would have exposed additional subjects to
radiation. Therefore, existing data were used to estimate the mean
values for normal, healthy shoulders, and we believe that both of
the included groups accurately represented this population.
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In conclusion, this study helped to characterize the dy-
namic relationship between glenohumeral rotation and trans-
lation in healthy individuals during motion in three arm
elevation planes. There were significant differences in scapu-
lohumeral rhythm between abduction and forward flexion.
Therefore, when evaluating detailed scapulohumeral rhythm
kinematics during clinical assessment of shoulder disorders, it
is important to take into account and control the plane of arm
elevation. The data suggest that evaluation of forward flexion
may represent a better method for assessing scapular abnor-
malities than scaption or coronal plane abduction.
Appendix
Tables showing the descriptive statistics for glenohumeral
rotation, anter ior-posterior and superior-inferior gleno-
humeral position, and between-subject variability in superior-
inferior position during scaption are available with the online
version of this article as a data supplement at jbjs.org. n
NOTE: The authors thank Medis Specials for providing the Model-Based RSA analysis software and
Dr. Robert F. LaPrade for his invaluable input on the manuscript. The authors also acknowledge
Christopher Dewing, Florian Elser, Jacob Krong, Dan Peterson, Tyler Anstett, and J.D. Pault for their
contributions to this investigation.
J. Erik Giphart, PhD
John P. Brunkhorst, BA
Nils H. Horn, MD
Department of BioMedical Engineering,
Steadman Philippon Research Institute,
181 West Meadow Drive,
Suite 1000, Vail, CO 81657.
Kevin B. Shelburne, PhD
Department of Mechanical and Materials Engineering,
the University of Denver, 2390 South York Street,
Denver, CO 80208
Michael R. Tor ry, PhD
College of Applied Science and Technology,
School of Kinesiology and Recreation,
Campus Box 5120, Illinois State University,
Normal, IL 61790
Peter J. Millett, MD, MSc
The Steadman Clinic, 181 West Meadow Drive,
Suite 400, Vail, CO 81657
E-mail address: drmillett@thesteadmanclinic.com
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  • Source
    • "In particular, Inman et al. (1944) measured scapular upward rotation with arm elevation using the goniometric method, and observed that SHR consistently has a 2:1 ratio. Electromagnetic tracking devices and fluoroscopy have also been used for three-dimensional scapular motion analysis (Fayad et al. 2006; Giphart et al. 2013; Kon et al. 2008; Ludewig et al. 2009; McClure et al. 2001), and variations in the ratio according to the arm elevation angle have been reported (0.6–5.9:1 in Braman et al. 2009; 1.3–2.4:1 in Dayanidhi et al. 2005; 2.0–7.8:1 in Forte et al. 2009; 1.2–2.7:1 in Habechian et al. 2014; and 1.9–7.9:1 in McQuade et al. 1998). The changes in the scapular upward rotation according to the arm elevation angle suggest the presence of a kinesiological change point or " knot " during this movement. "
    [Show abstract] [Hide abstract] ABSTRACT: Failure of the scapulohumeral rhythm (SHR) is observed in patients with shoulder joint dysfunction. The SHR reportedly has a 2:1 ratio during scapular upward rotation with arm elevation. However, three-dimensional scapular motion analysis has indicated variations in this ratio according to the arm elevation angle. We observed 2 distinct patterns: the scapular upward rotation decreased after knot formation (type I) or increased after knot formation (type II) during arm elevation. In the present study, we aimed to identify the knot and investigate the influence of varying external loads on this kinesiological change point. We evaluated 35 healthy adult men (35 dominant-side shoulders) with a mean age of 20 ± 1.7 years (mean height: 172 ± 6.4 cm, mean weight: 65.7 ± 5.8 kg). Participants performed scapular plane elevation with no load or with an external load (1–5 kg) while sitting on a chair. The measured scapular upward rotation values were interpolated using the spline function and fitted to line graphs, and the change in these values was compared for various loads. The estimated knot angles (standard error) in the no load condition, and with external loads of 1, 2, 3, 4, and 5 kg were 83.5 (2.9°), 81.2 (2.9°), 81.0 (2.9°), 76.1 (2.9°), 73.4 (3.1°), and 75.8 (3.1°), respectively. No significant difference was noted in the knot position at 1–2 kg (vs. unloaded), although the knot was significantly lower at 3–5 kg (3 kg: p = 0.01, 4 kg: p = 0.001, and 5 kg: p = 0.02). Moreover, we observed that participants either exhibited increased or decreased upward rotational momentum after knot formation. Our results confirm that the kinesiological change point (the knot) during scapular upward rotation occurred at lower angles in cases of increasing external loads.
    Full-text · Article · Dec 2016
  • Source
    • "These exercises, by decreasing the ratio of deltoid to rotator cuff activation, could minimize upward translation (Blasier et al., 1997). Investigations that actually measured glenohumeral translations have shown that upward translation was smaller during scaption than during abduction when the arm is externally rotated (Giphart et al., 2013). However, to the best of our knowledge, no study assessed elevations with other axial rotations of the arm. "
    Dataset: Begon2015
    Full-text · Dataset · Jul 2015
  • Source
    • "hinge, parallel mechanism, ball and socket as well as the segment length become another source of error (Duprey et al., 2010), which could lead to an increased joint kinematics error (Andersen et al., 2010). Double calibrations are efficient for quasi-planar movements in both lower (Stagni et al., 2009) and upper limb (Giphart et al., 2013), but has never been tested on daily living and sports activities. The latter are three-dimensional and may require multiple calibrations and a more complex correction model. "
    [Show abstract] [Hide abstract] ABSTRACT: Local and global optimization algorithms have been developed to estimate joint kinematics to reducing soft movement artifact (STA). Such algorithms can include weightings to account for different STA occur at each marker. The objective was to quantify the benefit of optimal weighting and determine if optimal marker weightings can improve humerus kinematics accuracy. A pin with five reflective markers was inserted into the humerus of four subjects. Seven markers were put on the skin of the arm. Subjects performed 38 different tasks including arm elevation, rotation, daily-living tasks, and sport activities. In each movement, mean and peak errors in skin- vs. pins-orientation were reported. Then, optimal marker weightings were found to best match skin- and pin-based orientation. Without weighting, the error of the arm orientation ranged from 1.9° to 17.9°. With weighting, 100% of the trials were improved and the average error was halved. The mid-arm markers weights were close to 0 for three subjects. Weights of a subject applied to the others for a given movement, and weights of a movement applied to others for a given subject did not systematically increased accuracy of arm orientation. Without weighting, a redundant set of marker and least square algorithm improved accuracy to estimate arm orientation compared to data of the literature using electromagnetic sensor. Weightings were subject- and movement-specific, which reinforces that STA are subject- and movement-specific. However, markers on the deltoid insertion and on lateral and medial epicondyles may be preferred if a limited number of markers is used. Copyright © 2015 Elsevier Ltd. All rights reserved.
    Full-text · Article · Apr 2015 · Journal of Biomechanics
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