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Anatomic shoulder parameters and their
relationship to the presence of degenerative
rotator cuff tears and glenohumeral
osteoarthritis: a systematic review
and meta-analysis
Musa B. Zaid, MD*, Nathan M. Young, PhD, Valentina Pedoia, PhD,
Brian T. Feeley, MD, C. Benjamin Ma, MD, Drew A. Lansdown, MD
Department of Orthopaedic Surgery, University of California, San Francisco, San Francisco, CA, USA
Background: Scapular anatomy, as measured by the acromial index (AI), critical shoulder angle (CSA),
lateral acromial angle (LAA), and glenoid inclination (GI), has emerged as a possible contributor to the
development of degenerative shoulder conditions such as rotator cuff tears and glenohumeral osteoar-
thritis. The purpose of this study was to investigate the published literature on influences of scapular
morphology on the development of degenerative shoulder conditions.
Methods: A systematic review of the Embase and PubMed databases was performed to identify pub-
lished studies on the potential influence of scapular bony morphology on the development of degener-
ative rotator cuff tears and glenohumeral osteoarthritis. The studies were reviewed by 2 authors. The
findings were summarized for various anatomic parameters. A meta-analysis was completed for param-
eters reported in more than 5 related publications.
Results: A total of 660 unique titles and 55 potentially relevant abstracts were reviewed with 30 pub-
lished articles identified for inclusion. The AI, CSA, LAA, and GI were the most commonly reported
bony measurements. Increased CSA and AI correlated with rotator cuff tears, whereas lower
CSA appeared to be related to the presence of glenohumeral osteoarthritis. Decreased LAA correlated
with degenerative rotator cuff tears. Five articles reported on the GI with mixed results on shoulder pa-
thology.
Discussion: Degenerative rotator cuff tears appear to be significantly associated with the AI, CSA, and
LAA. There does not appear to be a significant relationship between the included shoulder parameters
and the development of osteoarthritis.
Level of evidence: Level IV; Systematic Review
Ó2019 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved.
Keywords: Critical shoulder angle; acromial index; glenoid inclination; acromial center-edge angle;
scapular morphology; shoulder shape; scapular shape; anatomic shoulder parameters
*Reprint requests: Musa B. Zaid, MD, Department of Orthopaedic
Surgery, University of California, San Francisco, 500 Parnasssus Ave, MU-
320 W, San Francisco, CA 94143, USA.
E-mail address: Musa.Zaid@ucsf.edu (M.B. Zaid).
J Shoulder Elbow Surg (2019) 28, 2457–2466
www.elsevier.com/locate/ymse
1058-2746/$ - see front matter Ó2019 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved.
https://doi.org/10.1016/j.jse.2019.05.008
Shoulder pain is a common complaint prompting evalu-
ation by orthopedic surgeons and primary care physicians,
with an annual estimated incidence of 14.7 per 1000 patients
in primary care and a lifetime prevalence of up to
70%.
23,26,52
With an aging population, degenerative shoulder
conditions such as rotator cuff tears and glenohumeral oste-
oarthritis are accounting for a majority of these complaints
and are the source of significant pain and disability.
Numerous studies have demonstrated the prevalence of ro-
tator cuff tears to be as high as 22% to 23%,
29,47
whereas the
prevalence of glenohumeral osteoarthritis has been estimated
to be as high as 26%.
48
As patients desire to remain active as
they age, we are beginning to see an increase in the utilization
of surgical resources for rotator cuff repair and shoulder
arthroplasty.
14,17
The development of degenerative shoulder conditions
such as rotator cuff tears and glenohumeral osteoarthritis is
likely multifactorial in nature, with contributors such as age,
sex, genetics, and trauma, although recent attention has been
directed to scapular morphology as a risk factor for the
development of these degenerative conditions.
37,40,53
The
relationship between scapular shape and the development of
rotator cuff tears was first described by Neer
33
in 1972 with
his observation of varying acromial morphology leading to
direct compression on the rotator cuff and resulting pathol-
ogy and has since been explored by numerous other authors
as well.
35
More recently, the critical shoulder angle (CSA),
acromial index (AI), lateral acromial angle (LAA), and gle-
noid inclination (GI) (Fig. 1), as well as myriad other scapular
measurements, have been introduced as potential radio-
graphic measurements that can distinguish which patients are
at risk of the development of rotator cuff tears or gleno-
humeral osteoarthritis.
The primary purpose of this study was to investigate the
influence of scapular morphology on the presence of
degenerative rotator cuff tears and glenohumeral osteoar-
thritis, as well as to identify the supporting literature for
these conclusions. A systematic review of the literature was
performed to summarize the currently available evidence
on this topic, and a meta-analysis was performed to
determine the influence of scapular morphologic parame-
ters on the presence of rotator cuff tears and glenohumeral
osteoarthritis.
Methods
Search strategy and inclusion terms
A systematic review of the literature was performed following the
standardized PRISMA (Preferred Reporting Items for Systematic
Reviews and Meta-analyses) protocol.
42
Prior to initiation of data
abstraction, this review was registered with PROSPERO (Inter-
national Prospective Register of Systematic Reviews). The search
criteria and objectives of the review were defined before a search
of the literature was conducted. Per the protocol, a search of the
English-language literature using PubMed and Embase was con-
ducted for all studies published prior to November 1, 2018. The
search terms used included the following: (rotator cuff tear and
acromial index) or (rotator cuff and critical shoulder angle) or
(rotator cuff and anatomic parameters) or (rotator cuff and scap-
ular shape) or (rotator cuff and scapular morphology) or (rotator
cuff and glenoid inclination) or (rotator cuff and predisposition) or
(arthritis and acromial index) or (arthritis and critical shoulder
angle) or (arthritis and anatomic parameters) or (arthritis and
scapular shape) or (arthritis and scapular morphology) or (gleno-
humeral arthritis and predisposition) or (glenohumeral arthritis
and predisposed).
All titles were reviewed independently by 2 reviewers
(D.A.L. and M.B.Z.) to determine the appropriateness for in-
clusion. All identified abstracts were then reviewed by both re-
viewers. The complete article from any abstract was
subsequently reviewed by 1 reviewer with data verification
performed by a second reviewer. Studies were included if they
included radiographic measurements of bony morphology at the
shoulder in patients with either symptomatic rotator cuff tears or
symptomatic osteoarthritis. Studies were excluded if they re-
ported on only biomechanical data, computer modeling, or
cadaveric findings.
Methodologic study assessment was performed using the Na-
tional Institutes of Health Quality Assessment Tool for Cross-
Sectional Studies. Each reviewer performed the study quality
assessment and recorded his responses (Supplementary Table S1).
Any discrepancies were reviewed by the 2 authors until a
consensus was reached.
Data extraction
Data extraction was performed with items of interest identified a
priori, including sample size of the study, demographic informa-
tion of each cohort, radiographic measurements, and disease
prevalence. The means and standard deviations of the included
anatomic parameters were recorded for analysis.
Meta-analysis
Anatomic parameters reported in more than 5 independent studies
were pooled in a meta-analysis using RStudio software (RStudio,
Boston, MA, USA). As all anatomic parameters were reported as
continuous measures, the pooled effects were presented as mean
differences with confidence intervals (CIs) with an inverse-
variance weighted method. Study heterogeneity was determined
by calculating the I
2
value; a random-effects model was used as
there was significant heterogeneity (I
2
>75%) among all studies.
Results
A search of the literature as outlined earlier resulted in
a total of 427 titles from MEDLINE and 404 from Embase.
A total of 660 unique titles were identified between the
2 searches. Fifty-five unique abstracts were identified
for further review based on the title alone. A total of
30 unique articles were included in the final anal-
ysis
2-5,8-10,12,13,15,16,19-21,24,27,30-32,38,39,41,43-46,49-51
(Fig. 2).
2458 M.B. Zaid et al.
All articles were published after 2004. One study was
longitudinal in nature,
12
with the remainder being cross-
sectional.
Of the studies, 19 examined the
CSA,
2,4,5,9,10,11,13,16,19,21,27,30-32,38,39,44,46,51
8 measured the
AI,
2,3,20,21,24,31,38,45
5 measured the LAA,
2,3,21,32,45
5
examined the GI,
4,5,8,11,16
2 measured the acromial
slope,
2,3
1 measured the acromial center-edge angle
(ACEA),
45
1 measured the acromial coverage index,
49
1
measured the greater tuberosity angle (GTA),
15
1 measured
the coracoid cavity ratio,
41
and 1 measured the coracoid
inclination.
49
All 30 studies included in this review
included a rotator cuff tear group, whereas 10 of these
studies included a glenohumeral osteoarthritis group as
well.
4,5,9,10,16,21,27,30,44,46
For the assessment of scapular parameters, 18 studies
used radiographs alone,
2,3,9,10,11,13,15,19-21,24,27,30-32,38,41,44
5
used plain radiographs and computed tomography (CT)
scans,
4,5,8,16,45
1 used magnetic resonance imaging and CT
scans,
11
and 1 used CT scans alone.
39
Critical shoulder angle
The CSA was significantly elevated in patients with isolated
rotator cuff tears compared with healthy controls in
numerous studies (Table I).
10,11,13,16,19,31,32,39,51
This
finding was consistent across multiple studies. When data
were pooled in a meta-analysis, the mean difference in the
CSA between patients with rotator cuff tears and control
patients was 1(95% CI, 0.59-1.44;P<.05; I
2
¼91%)
(Fig. 3).
In the only longitudinal study identified, Chalmers
et al
11
evaluated the CSA and its effect on the rotator
cuff over time. Although they found that patients with
rotator cuff tears had a significantly elevated CSA at the
time of enrollment (34vs. 32,P¼.003), the CSA did
not correlate with baseline tear size nor was the CSA
different in patients in whom tear enlargement occurred
over time.
One study examined how the CSA differed in patients
with full-thickness vs. partial-thickness tears and found that
the CSA was elevated in both groups compared with
healthy controls (41.01and 38.83vs. 37.28;P<.001
and P¼.02, respectively).
38
In addition, patients with
degenerative rotator cuff tears were found to have an
elevated CSA compared with those with traumatic rotator
cuff tears in 1 study (36.8vs. 35.3,P¼.007).
2
The CSA
appeared to be significantly elevated in patients with iso-
lated degenerative rotator cuff tears compared with those
with isolated glenohumeral osteoarthritis, with the mean
Figure 1 Radiographic measurements of selected anatomic shoulder parameters: critical shoulder angle (CSA) (A), glenoid inclination
(GI) (bangle method of Maurer et al
28
)(B), acromial index (AI) (GA, glenooid-acromial distance; GH, glenoid-humeral distance) (C), and
lateral acromial angle (LAA) (D).
Shoulder anatomy and degenerative conditions 2459
CSA ranging from 34to 34.5in patients with degenera-
tive cuff tears compared with 27.2to 28in patients with
glenohumeral osteoarthritis (P<.001 in all studies).
4,5,10
When comparing patients with cuff tear arthropathy with
those with isolated rotator cuff tears and those with isolated
glenohumeral osteoarthritis, 1 study found that the CSA
was significantly elevated in patients with isolated rotator
cuff tears compared with those with cuff tear arthropathy
(36.3vs. 35.2,P¼.006).
21
In addition, the CSA appeared
to be significantly elevated in patients with cuff tear
arthropathy compared with those with isolated gleno-
humeral osteoarthritis (35-35.2vs. 27.3-30,P<.001
for both studies).
27,38
A lower CSA appeared to be related to the presence
of isolated glenohumeral osteoarthritis. Although
numerous studies concluded this,
9,10,21,27,30,46
multivariate
analysis completed in 1 of the included studies did not
find any significant relationship between the CSA and the
presence of glenohumeral osteoarthritis.
44
When data
were pooled in a meta-analysis, the mean difference in
the CSA in patients with glenohumeral osteoarthritis was
1.42(95% CI, –2.50to –0.35;P<.01; I
2
¼94%)
less than that in controls (Fig. 4). One study did not find
a significant relationship between the CSA and the
presence of rotator cuff tears; however, the authors did
conclude that a lower CSA is associated with
glenohumeral osteoarthritis (rotator cuff tear group: 33.9
vs. 33.6,P¼.063; glenohumeral osteoarthritis group:
31.1vs. 33.2; odds ratio, 2.25; P¼.002).
9
Acromial index
Eight studies reported on the relationship between the AI
and rotator cuff tears,
2,3,20,21,24,32,38,45
and 1 of these 8
studies examined the relationship between the AI and the
presence of glenohumeral osteoarthritis.
21
The AI was
consistently significantly elevated in patients with rotator
cuff tears compared with healthy controls in all but 1 of the
included studies (Table II).
3,20,24,32,45
In the 1 study that did
not find a significant difference between groups, patients
with full-thickness rotator cuff tears were compared with a
composite group of patients with partial or no tears.
20
One study examined the AI in patients with full-thick-
ness tears vs. those with only partial-thickness tears, as well
as a control group.
38
The authors did not find a significant
difference in the AI between patients with full- and partial-
thickness tears; however, the AI in these 2 groups was
significantly elevated compared with the control group
(0.76 for full thickness, 0.74 for partial thickness, and 0.70
for healthy control; P¼.006 between full-thickness group
and no-tear group). In addition, the AI was noted to be
significantly elevated in patients with degenerative rotator
Figure 2 Flowchart of study design and included studies.
2460 M.B. Zaid et al.
cuff tears compared with those with traumatic rotator cuff
tears (0.77 vs. 0.73, P¼.0239).
2
When data were pooled in a meta-analysis, the mean
difference in the AI for patients with rotator cuff tears
compared with healthy controls was 0.75 (95% CI, 0.23-
1.27; P<.01; I
2
¼88%) (Fig. 5). One study examined the
relationship between the AI and rotator cuff tears, as well
as glenohumeral osteoarthritis, and found that the AI was
significantly elevated in patients with rotator cuff tears
compared with those with isolated glenohumeral osteoar-
thritis (0.74 vs. 0.63, P<.001).
21
Lateral acromial angle
A total of 5 studies examined how the LAA correlates with
the presence of rotator cuff tears, and 1 of these studies
examined how the LAA related to the presence of gleno-
humeral osteoarthritis. The LAA was consistently lower in
patients with rotator cuff tears compared with healthy
controls in all included studies (Table III).
3,32,45
One study found that the LAA was significantly lower in
patients with degenerative rotator cuff tears compared with
those with traumatic rotator cuff tears.
2
In addition, the LAA
appeared to be significantly lower in patients with isolated
rotator cuff tears compared with patients with glenohumeral
osteoarthritis (76.7vs. 89.5,P<.001), as well as patients
with cuff tear arthropathy (76.6vs. 82,P<.001).
21
Glenoid inclination
Five studies reported on the GI with varying results
regarding its relationship with rotator cuff tears. Different
methods to measure the GI were used by the various
authors.
Two studies concluded that the GI was significantly
lower in patients with rotator cuff tears compared with
patients with isolated glenohumeral osteoarthritis when
measured on plain radiographs using the bangle method of
Maurer et al
28
(78.7vs. 81.5,P¼.008),
4
as well as when
measured on CT scans (78.8vs. 82.0,P¼.008).
5
Simi-
larly, when examining patients with unilateral degenerative
rotator cuff tears, one study found that the GI was signifi-
cantly lower in the shoulder with the cuff tear than in the
healthy contralateral shoulder using methods previously
described by Hughes et al
22
to measure the GI (90.7vs.
92.3,P¼.04).
8
Two studies primarily used CT scans to measure the GI
and reported opposite results to those in the aforementioned
studies. Chalmers et al
11
measured the superior GI on
coronal CT scans that had been corrected such that the
glenoid was placed in the scapular plane. Using this
method, they found that patients with rotator cuff tears had
a significantly increased superior GI compared with control
patients (11vs. 9,P<.001). Daggett et al
16
measured the
GI on anteroposterior radiographs using the method of
Maurer et al
28
in which the bangle was subtracted from
90, as well as on coronal CT scans corrected to be in the
scapular plane. When measured on CT scans, the GI was
significantly elevated in the rotator cuff tear group
Table I Critical shoulder angle in rotator cuff tear patients
vs. control population
Critical shoulder angle,
mean (SD),
Pvalue
Rotator
cuff tear
Control
Blonna et al
10
(2016) 40 (3.5) 34 (3) <.001*
Chalmers et al
12
(2017) 34 (4) 32 (4) .013*
Cherchi et al
13
(2016) 36.4 (4.4) 33.3 (3.8) .02*
Daggett et al
16
(2015) 37.9 (3) 27.2 (3.4) <.001*
Gomide et al
19
(2017) 39.75 (3.37) 33.59 (5.35) <.007*
Moor et al
31
(2014) 37.8 (3.8) 31.9 (3.8) <.0001*
Moor et al
32
(2014) 38 (3.2) 33 (3.4) <.001*
Peltz et al
39
(2015) 36.9 (5) 34.5 (4.7) .03*
Watanabe et al
51
(2018)
34.4 (3.4) 32.1 (3.1) <.001*
SD, standard deviation.
*
Statistically significant (P<.05).
Table II Acromial index in rotator cuff tear patients vs.
control population
Acromial index, mean (SD) Pvalue
Rotator
cuff tear
Control
Balke et al
3
(2013) 0.75 (0.1) 0.67 (0.1) <.001*
Hamid et al
20
(2012) 0.692 (NR) 0.691 (NR) .92
Kum et al
24
(2017) 0.68 (NR) 0.63 (NR) <.001*
Moor et al
32
(2014) 0.75 (0.06) 0.66 (0.06) <.001*
Singleton et al
45
(2017)
0.755 (0.005) 0.69 (0.003) <.001*
SD, standard deviation; NR, not reported.
*
Statistically significant (P<.05).
Table III Lateral acromial angle in rotator cuff tear patients
vs. control population
Lateral acromial angle, mean
(SD),
Pvalue
Rotator
cuff tear
Control
Balke et al
3
(2013) 77 (6) 84 (6) <.001*
Moor et al
32
(2014) 80 (6.3) 86 (7.7) <.001*
Singleton et al
45
(2017)
76.48 (0.37) 79.71 (0.27) <.001*
SD, standard deviation.
*
Statistically significant (P<.05).
Shoulder anatomy and degenerative conditions 2461
compared with controls (13.6vs. 4.7,P<.001); however,
when measured on plain radiographs, the GI showed no
significant difference in patients with rotator cuff tears
compared with patients without rotator cuff tears (13.6vs.
7.6,P¼not significant).
16
Acromial slope
Two studies examined how the acromial slope relates to the
presence of rotator cuff tears, with different conclusions.
One study found no difference in acromial slope in patients
with rotator cuff tears compared with healthy controls (25
vs. 25,P¼.7),
3
whereas the other study found that the
acromial slope was significantly elevated in patients with
degenerative rotator cuff tears compared with those with
traumatic rotator cuff tears (21.2vs. 19.1,P¼.026).
2
No
study examined how acromial slope related to gleno-
humeral osteoarthritis.
Acromial center-edge angle
One study measured the ACEA and how it relates to the
presence of rotator cuff tears. Singleton et al
45
found that
the ACEA was significantly higher in patients with rotator
cuff tears than in controls (23.89vs. 16.66,P<.001).
Acromial coverage index
One study measured the acromial coverage index and its
relationship to rotator cuff tears. Torrens et al
50
found
that the acromial coverage index was significantly higher
in patients with surgically treated rotator cuff tears than
in healthy controls (0.687 vs. 0.591, P<.001). In addi-
tion, no significant difference was found between patients
with rotator cuff tears treated surgically and those with
tears were managed conservatively (0.687 vs. 0.725, P¼
.219).
Figure 4 Forest plot of studies examining how the critical shoulder angle relates to the presence of symptomatic glenohumeral osteo-
arthritis. The mean difference in the critical shoulder angle in patients with glenohumeral osteoarthritis was –1.42(95% confidence in-
terval [CI], –2.50to –0.35;P<.01; I
2
¼94%) compared with controls. Std, standardized; SD, standard deviation; IV, inverse variance.
Figure 3 Forest plot of studies examining how the critical shoulder angle relates to the presence of symptomatic rotator cuff tears. The
mean difference in the critical shoulder angle in patients with rotator cuff tears compared with controls was 1.01(95% confidence interval
[CI], 0.59-1.44;P<.05; I
2
¼91%). Std, standardized; SD, standard deviation; IV, inverse variance.
2462 M.B. Zaid et al.
Greater tuberosity angle
One study measured the GTA and its effect on rotator cuff
tears and found that the GTA was significantly elevated in
patients with rotator cuff tears compared with healthy
controls (72.5vs. 65.2,P<.001); in addition, a GTA of
more than 70resulted in 93-fold higher odds of detecting a
rotator cuff tear (P<.001).
15
Coracoid cavity ratio
One study measured the coracoid cavity ratio and its impact
on the presence of rotator cuff tears and concluded that
patients with an isolated supraspinatus tendon tear had a
significantly elevated coracoid cavity ratio compared with
healthy controls (65 vs. 43, P¼.0002).
41
Coracoid inclination
One study measured the coracoid inclination from CT scans
by measuring the angle between the coracoid and glenoid
surface (A1), the angle between the coracoid tip and gle-
noid surface (A2), and the angle created by the coracoid
body and coracoid tip (A3).
49
The authors found that all
angles (A1, A2, and A3) were significantly lower in the
rotator cuff tear group compared with the control group
(A1, 49.7vs. 56.1[P¼.011]; A2, 76.45vs. 93.6[P<
.001]; and A3, 132.33vs. 144.34[P<.001]).
Discussion
Scapular morphology as well as how it relates to the
development of degenerative rotator cuff tears and gleno-
humeral osteoarthritis continues to be an area of interest in
modern orthopedics as physicians hope to identify risk
factors for these common degenerative conditions.
Although numerous quantifiable anatomic parameters to
characterize scapular morphology have been identified in
the literature, the AI, CSA, GI, and LAA were the most
commonly examined in the studies in our review.
Overall, the AI, CSA, and LAA are reliably associated
with the presence of degenerative disorders of the shoul-
der. The results of the meta-analysis on the CSA demon-
strate that an increased CSA compared with controls is
associated with the development of degenerative rotator
cuff tears whereas a lower CSA compared with controls is
associated with the presence of glenohumeral osteoar-
thritis. Furthermore, the meta-analysis showed that an
increased AI is associated with degenerative rotator cuff
tears. The majority of studies found that an elevated AI,
usually greater than 0.74, was associated with the pres-
ence of degenerative rotator cuff tears. A conclusion on
how the AI relates to glenohumeral osteoarthritis is
difficult to make as only 1 study looked at this and did not
have a healthy control population; rather, the arthritis
group was compared with a rotator cuff tear group.
21
Similarly to the AI, the CSA was almost consistently
found to be elevated in patients with degenerative rotator
cuff tears compared with healthy controls, and it was
decreased in patients with glenohumeral osteoarthritis in
numerous studies, as well as in our meta-analysis. Because
of the large variation in the measured values of the CSA
between articles (range of 33.9-37.9for patients with
rotator cuff tears and 27.2-37.3for patients without ro-
tator cuff tears), it is difficult to assume an abnormal cutoff
value.
8,21,27,44,46
In addition to the AI and CSA, the LAA
consistently related to the presence of degenerative rotator
cuff tears. A lower LAA was universally associated with
the presence of degenerative rotator cuff tears in the
studies included in this review, usually with a value of less
than 80correlating with cuff tears. As only a single study
looked at how the LAA relates to glenohumeral osteoar-
thritis, it is difficult to assume a conclusion on this
relationship.
The pathomechanics of how scapular morphology re-
lates to the development of degenerative shoulder condi-
tions remains an area of controversy. Whereas numerous
authors have hypothesized that impingement of the rotator
Figure 5 Forest plot of studies examining how the acromial index relates to the presence of symptomatic rotator cuff tears. The mean
difference in the acromial index for patients with rotator cuff tears was 0.75 (95% confidence interval [CI], 0.23-1.27; P<.01; I
2
¼88%)
compared with healthy controls. Std, standardized; SD, standard deviation; IV, inverse variance.
Shoulder anatomy and degenerative conditions 2463
cuff by the underside of the acromion can lead to the
development of rotator cuff tears,
6,7,10,18,34
others have
argued that changes in acromial morphology may occur as
a result of rotator cuff tears.
1,25
For example, Li
et al
25
theorized that rotator cuff degeneration leads to an
imbalance in forces around the shoulder, ultimately
resulting in anterior-superior instability followed by the
formation of bone spurs along the coracoacromial arch with
a resultant deformity in the acromion. Nonetheless, there is
convincing evidence
36
to suggest that increased lateral
extension of the acromion may relate to the development of
rotator cuff tears. Nyffeler et al
36
have hypothesized
that with increasing lateral extension of the acromion,
the deltoid is able to exert a larger force vector on the
glenohumeral joint, leading to increased joint contraction
and subacromial impingement, which in turn may lead
to degenerative rotator cuff tears. This increase in the
lateral extension of the acromion would manifest as an
increased CSA and AI and a decrease in the LAA; these are
the changes that were consistently associated with the
presence of degenerative rotator cuff tears in the published
literature.
Integrating the data from these studies into clinical
practice may allow for the identification of patients at risk
of having degenerative rotator cuff tears and possibly gle-
nohumeral osteoarthritis. As these changes in scapular
morphology are intrinsic in nature, they cannot be changed
without surgical intervention, which is unlikely to be per-
formed. In addition, clinicians should have a higher index
of suspicion for a degenerative rotator cuff injury in pa-
tients with these alterations in scapular shape who may
present with shoulder pain.
Although there was significant consistency in the
aforementioned parameters, there were some studies that
did not come to similar conclusions. The most variable
findings involved the GI: 2 studies concluded that a more
superior GI related to rotator cuff tears,
11,16
whereas 3
concluded the opposite.
4,5,8
These discordant results may
be attributed to a difference in methods used to measure the
GI, as well as the fact that some authors measured this
parameter on plain radiographs whereas others used CT
scans. This point may serve to highlight the importance of
radiographic and measurement techniques in determining
these anatomic parameters. Furthermore, differences in
patient populations between studies may contribute to this
discordance. As with the GI, all of the aforementioned
parameters are subject to variability based on measurement
techniques and the quality of the imaging used for the
measurements. Numerous studies have demonstrated that
these quantitative measures are highly dependent on the
rotation of the image used.
11,12,20
Although some of the
studies included in this review used CT scans, which are
not dependent on patient rotation, the majority used plain
radiographs.
This study comes with strengths and limitations. It
is one of the first of its kind to review the currently
available literature on how anatomic shoulder pa-
rameters affect the development of degenerative ro-
tator cuff tears and glenohumeral osteoarthritis. As it
is a systematic review, it is dependent on the quality
of the studies included. The majority of studies
included in this analysis were retrospective in nature
but did have sufficient sample sizes and control
groups. Although numerous parameters were measured
in the literature, the AI, CSA, and LAA were the
most highly represented. In addition, although some
studies completed a multivariate analysis to control
for confounding factors, this analysis was not
completed in all of the included sources, possibly
introducing some error.
Conclusion
The presence of degenerative rotator cuff tears ap-
pears to be associated with an increased AI and CSA
and a decreased LAA. In addition, a lower CSA ap-
pears to be associated with the presence of gleno-
humeral osteoarthritis. It must be highlighted that
these quantifiable anatomic parameters are highly
dependent on the technique used to obtain the radio-
graphs. Although a few studies used cross-sectional
imaging such as CT scans and magnetic resonance
imaging to more accurately quantify these parameters,
future studies should continue to use these methods to
perhaps look for associations between anatomic
shoulder parameters and the presence of glenohumeral
osteoarthritis.
Disclaimer
Brian T. Feeley reports that he has received grants from
the National Institutes of Health and serves as a journal
editor for the Journal of Shoulder and Elbow Surgery
and CRMSM for work related to the subject of this
article.
C. Benjamin Ma reports that he has received grants
from Zimmer Biomet during the conduct of the study;
grants from Anika, Samumed, and Zimmer; personal
fees from ConMed Linvatec, Medacta, SLACK, and
Stryker; and grants and personal fees from Histogenics
for work related to the subject of this article.
Drew A. Lansdown reports that he has received
grants from Arthrex and Smith & Nephew for work
related to the subject of this article.
The other authors, their immediate families, and any
research foundations with which they are affiliated have
not received any financial payments or other benefits
from any commercial entity related to the subject of this
article.
2464 M.B. Zaid et al.
Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.jse.2019.05.008.
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