INTRODUCTION

Within the adult population, 67% of individuals will experience shoulder pain at some point throughout their lifetime.1 There are numerous factors related to the etiology of shoulder pain and it has been hypothesized that the presence of scapular dyskinesis (SD) is a contributing factor to shoulder pathology.2,3 Scapular dyskinesis has been defined as alterations in scapular positioning at rest as well as during dynamic movement. Common variations in scapular movement4,5 include increased scapular superior translation along with reduced scapular posterior tilt, upward rotation, and internal rotation.6 Give the theorized relationship between SD and certain shoulder pathologies there have been several methods proposed to evaluate these alterations in scapular positions and movements.

McClure et al.7 developed a commonly used method of identifying SD, the scapular dyskinesis test (SDT), to identify the presence of SD and classify individuals into three levels: normal motion, subtle dyskinesis, and obvious dyskinesis. This is one of several methods commonly used during an evaluation related to shoulder pathology presented in Supplement A Though the SDT has been proven to be a reliable and valid method of identifying SD6,7 not all clinicians are trained to use this tool and current literature describes a wide variation of assessment methodology.6 Along with this lack of homogeneity in assessment of SD, there is a lack of evidence to support the idea that identification and correction of SD may help to prevent or treat shoulder pathology. Even with this lack of evidence, identifying SD is a common screening tool for both symptomatic and asymptomatic individuals. The evaluation is especially common in predicting or preventing injury in overhead athletes, however there is conflicting evidence regarding the link between SD and injury in this population exists.8,9 Clinicians often direct their treatment toward correcting the SD which could be normal movement variability.10,11

Because the identification of SD is a common part of a patient evaluation, it is often used to guide clinical decision making; however, there is considerable debate around linking the presence of SD to certain shoulder pathologies. Some studies have shown no difference in the prevalence of SD between symptomatic and asymptomatic populations.12 This raises the question of utility when screening for SD in patients seeking treatment for shoulder pain as well as for the asymptomatic population.

The purpose of this systematic review of the current literature to investigate the prevalence of SD among both symptomatic and asymptomatic populations. Understanding the relationship between SD and the presence or absence of symptoms may help to direct conversations regarding the clinical utility of SD. The authors hypothesized that SD is a common finding that has been medicalized (clinical findings suggested to require treatment but is ultimately a normal finding).

MATERIALS AND METHODS

Guidelines

This systematic review utilized the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines during the search and reporting phase of the research process. The PRISMA statement includes a 27-item checklist designed to improve reporting of systematic reviews and meta-analyses.13

An online literature search was conducted utilizing PubMed, EMBASE, Cochrane and CINAHL from the dates of their origin until July 2021. The search strategy was created and performed by a biomedical librarian. An example of the search strategy used for the PubMed database is provided (Supplement B) and similar strategies were utilized for the remaining databases. The study was registered using the International Prospective Register of Systematic Reviews (PROSPERO) in May of 2020 with a corresponding reference number: CDR42020187045.

Study selection

All titles were independently appraised by two authors (TB) and (AW) after the initial online literature search for studies to be retained. The abstracts of these titles were read to determine if the studies met the inclusion criteria. Studies with abstracts that met the inclusion criteria were accessed in their full-text format and then read to determine their eligibility for the review. The same two authors performed the study selection process for this review with a third author (PS) available to handle disagreements. The inclusion criteria for studies to be retained in the present review consisted of: (a) individuals being assessed as having SD, including reliability and validity studies (b) subjects aged 18 or older; (c) sport and non-sport participants; (d) no date restriction; I symptomatic, asymptomatic, or both populations; (f) all study designs except case reports. Studies were excluded if: (a) they were not published in the English language; (b) they were a case report design; (c) the presence of SD was part of the studies inclusion criteria; (d) data were not present distinguishing the number of subjects with or without SD; I they did not define participants as having or not having SD.

Data extraction

The data and results from the studies that were retained as part of the review were extracted using a format to identify study type, population, methods for evaluating SD, and the prevalence of SD. Data were extracted, reviewed, and analyzed by the primary author (PS) and verified by a research assistant (ZS). Discrepancies in data collection were resolved through discussion.

Methodological Quality Assessment Tool

The Joanna Briggs Institute (JBI) checklist for prevalence studies was used to evaluate methodological quality within the individual studies.14 There are nine items related to methodological quality included in the checklist which can be answered as yes, no, unclear, or not applicable. Following the scoring of each item, those individuals scoring the study are asked to provide an overall appraisal to include, exclude, or seek further information regarding if the article should be retained. The decision to include or exclude each article is then made by the reviewer(s) based on the completed checklist and consensus. Two authors, (DH) and (AM), performed the methodological quality assessment independently with discrepancies handled by the primary author if necessary. Prior to methodological quality assessment those involved in worked through scoring several unrelated prevalence studies in order to align definitions and interpretations of the various elements present in the JBI tool.

Data Synthesis and Analysis

Data were extracted and pooled to include the incidence of scapular dyskinesis, as defined by the authors, among those individuals that were symptomatic and those that were asymptomatic. The results were reported on percentage of incidence differentiating between classification of individuals with SD and shoulders with SD among each identified population. Data on relevant subcategories were identified and individually accounted for with separate analyses. Data from the identified studies did not allow for a quantitative analysis given the heterogeneity of several variables.

RESULTS

Search Results

The initial search resulted in 11,619 after duplicates were removed. Following title and abstract screening 11,505 were removed. Full text articles were retrieved for the remaining 114 studies of which 77 were removed due to not meeting the inclusion criteria. The remaining 37 studies were retained for quality assessment Figure 1.

Figure 1
Figure 1.PRISMA flow diagram outlining study selection process

Following quality assessment 34 articles were ultimately retained for analysis. Study characteristics for each of the 34 studies consisting that examined 2,365 individuals can be seen in Table 1. Retained studies were categorized into either symptomatic or asymptomatic within either an athletic population or a general orthopedic population.

Table 1.Characteristics for each of the retained studies
Authors Setting Type Population Type Total Population/Shoulders (n/n) With Scapular Dyskinesis (n) Symptomatic (Y or N) Methods
Akodu et al 2018 General population (from Department of Physiotherapy, U of Lagos) 77 undergraduates without history of shoulder or neck pathology 77/77 (reported as individuals with SD) 54 (a 1.5 cm asymmetry between R/L scapulae was considered the threshold for SD) No SICK scapula, Static Measurements 0 to 20 Point Rating Scale
Alves de Oliveira et al 2013 Amateur Athletes 30M amateur athletes (15 with SIS and 15 without); SIS mean age 22; control mean age 20.27 30/30 (dominant shoulders only) SIS (14 (93.3%) present, 1 (6.7%) absent)
Control (6 (40%) present, 9 (60%) absent)		 15 symptomatic
15 asymptomatic		 LSST
Balci et al 2016 Outpatient clinic at a university 53 subjects (40F/13M); diagnosed as unilateral AC (stage II) and SPN for at least 3 months 53/53 (shoulder in pain) 22 Yes LSST
Bullock et al 2021 Wake Forest pitching lab 33 asymptomatic M high school baseball pitchers; mean age 16.3 33/33 15 No McClure method (5 reps, etc.)
Camci et al 2013 General population 64 asymptomatic individuals 64/64 (reported as individuals with SD) 40 yes (24 no) No Yes/no method
Castelein et al 2016 General F population 19F with idiopathic neck pain; mean age 28.3
19F without (serving as control); mean age 29.3		 38/38 (dominant shoulders only) Neck pain group (9 yes, 10 no)
Control group (8 yes, 11 no)		 19 symptomatic
19 asymptomatic		 Yes/no method described by Uhl et al. (visual observation)
Chen et al 2018 General orthopedic with SPN 186 (115F and 71M) individuals with shoulder conditions; mean age 45.74
SIS: 59, partial cuff tear: 6, FS: 23, bicep tendonitis: 15, GH OA: 13, cuff tendonitis: 10, SLAP tear: 10		 186/186 (reported as individual, not shoulder) Yes: 140 (type I, II, III)
No: 46 (type IV)		 Yes (all) Kibler method
Christiansen et al 2017 Rehabilitation units, physical therapy clinics, and hospital setting 40 patients (27M and 13F) with SIS 40/40 (reported as individual with SD) 18 Yes (SIS) McClure method (5 reps, etc.)
Da Silva et al 2008 Elite tennis players and controls (compare SD and subacromial space in tennis players) 73 individuals (53 elite tennis players (31M and 22F) and 20 controls (9M and 11F)); tennis players mean age 14.8; control mean age 14.6 73/73 (reported individuals but then also broke it down into bilateral and dominant %) Tennis:
23/53 had SD (19 bilateral, 3 dominant, and 1 non dominant)
Control:
4/20 had SD (2 dominant and 2 non dominant)		 No Kibler method (static, dynamic and ascending, descending)
Deng et al, 2017 Rehabilitation outpatient departments 102 patients (49M and 53F) with shoulder conditions (SIS: 28, cuff tear: 27, SLAP: 16, OA:15, FS: 8, bicipital tendonitis: 8) 102/102 (reported as individuals with SD) Rest (type I-III): 83
Anterflexion (type I-III): 37
Scaption (type I-III): 39
Abduction (type I-III): 36		 Yes Kibler method
Frizziero et al 2018 Bowed string instrument students at conservatory 32 individuals (27F and 5M) 32/32 (reported as individuals with SD) 15 No Flexion and abduction with 1 or 2 kg weight and videotaped.
Scapular movement was classified as: normal (both
tests were evaluated as normal, or one movement is
evaluated as normal and the other as slightly abnormal); slightly abnormal (both movements are evaluated as slight or uncertain abnormality); abnormal
(one of the two movements is evaluated as severe
abnormality)
Hannah et al 2017 Strength profiles in healthy individuals with and without SD 40 healthy college aged participants (12M and 28F) *initial before age matched brought in to even SD numbers; mean age 22.2 40/40 (individuals with SD) 27 of 40 No Yes/no method
Huang et al 2015 Outpatient clinic at a university hospital 60 patients (4 M and 15F) with unilateral shoulder condition 50/60 for raising phase
41/60 for lower phase
(reported as individuals with SD and agreement levels)		 Raising phase 6 of 50 had SD
Lowering phase 29 of 41 had SD		 Yes Kibler and McClure combined method
Johansson et al 2016 Pain in flatwater kayakers and relationship to ROM and SD 31 kayakers (20M and 11F) (17 with SPN and 14 without SPN); F mean age 16.6; M mean age 18.2 31/31 (reported as individuals with SD) Pain: 15/17 had SD
No Pain: 4/14 had SD
Total: 19/31 had SD		 Yes and No Kibler and Sciasca method
Kawasaki et al 2012 Does SD effect Rugby players during a season 103M rugby players; mean age 24.6 103/103 used for primary analysis Type I: 6
Type II: 4
Type III: 23
Total Yes: 33
Type IV (No): 70		 No Kibler method Type I-IV
Lee et al 2017 Findings in asymptomatic elite volleyball players 26 elite indoor volleyball players 26/26 (dominant asymptomatic shoulders utilized) 7 No Visual examination
Madsen et al 2011 Training and SD in competitive swimmers 78 competitive swimmers (44F and 34M); mean age 17 78/78 (athletes with SD) After first time trial: 29
After half of training session: 53
Last three quarters of the training session: 57
Last quarter of the training session: 64		 No Yes/No system by McClure
Maor et al 2017 SD among competitive swimmers 20 competitive swimmers (6F and 14M); mean age 15.35 20/20 (athletes with SD) Baseline: 6
1 hour of practice: 14
1.5 hours of practice: 17		 No Yes/No system by McClure
Moghadam et al 2018 General orthopedic 100F (47 hypermobile and 53 non-hypermobile) 100/200 Total (shoulders)
Dominant
Flexion: 60
Scaption: 62
Abduction: 61
Nondominant
Flexion: 68
Scaption: 71
Abduction: 65		 No (47 with GHJ generalized joint hypermobility but no symptoms) Visual SD test
Nodehi et al 2020 Acromiohumeral distance and SD comparison 44F (21 with RSP and 23 controls); mean age of control 22.43; mean age of RSP 22.95 44/88 (looked at dominant vs non-dominant) Total (shoulders)
Flexion: 17
Abduction: 29
RSP: (flexion dominant: 4, non-dominant: 5; abduction dominant: 22, non-dominant: 4)
Control: (flexion dominant: 3, non-dominant: 5; abduction dominant: 1, non-dominant: 2)		 No Uhl yes/no method
Park et al, 2013 Athletic population assessment of SD 89 athletes (178 shoulders) (75 baseball players, 7 other overhead sports, 2 golf, and 5 occasional sport)
SLAP: 15, SIS:12, SLAP + SIS: 6, MCL: 22, SLAP + MCL: 2, VEO: 9, cuff tear: 5, glenoid OCD: 4, capitellum OCD: 4, multidirectional instability: 5, posterior labral tear: 5		 89/178 Type I: 73
Type II: 39
Type III: 10
122: Total shoulders with SD out of 178 shoulders		 Yes Type I-IV via visual observation
Park et al, 2014 Athletic population evaluation of SD 165 patients, 127 were baseball
players, 5 were athletes of other over-
head sports, 5 played golf, 2 played table tennis, 1 was a diver,
1 participated in bowling, 1 was an archer, and 26 enjoyed occasional sports activities.
Elbow: MCL tear: 54, VEO: 40, OCD: 3, medial epicondylitis: 2, common flexor muscle strain: 3
Shoulder: SLAP: 49, multidirectional instability: 6, SLAP: 31, Bennett lesion: 3, internal impingement: 8, long head of biceps tendon tendonitis: 20, cuff tear: 3, impingement: 44, functional impingement: 8, sub coracoid impingement: 8, GIRD: 53, subscapularis tear: 1		 165/330 Type I: 130
Type II: 98
Type III: 52
280: Total shoulders with SD out of 330		 Yes Kibler’s 4 type method
Plummer et al 2017 Observational SD 135 individuals (67 with shoulder pain (33 F and 34 M) and 68 healthy controls (41 F and 27 M); pain mean age 32.5; control mean age 27.4 135/135 (individuals with SD) Flexion (87/135)
Symptomatic:45
Asymptomatic:42
Abduction (81/135)
Symptomatic: 45
Asymptomatic:36		 67 symptomatic
68 asymptomatic		 McClure Method
Rabin et al 2018 Shoulder outpatient clinic 74 consecutive patients referred to an outpatient shoulder surgery unit (6F/68M) 74/74 (reported as individual) 33 Yes Visual observation, Kibler method
Sahinoglu et al 2020 Posterior shoulder tightness on SD 121 college aged M (non-overhead athletes); mean age 21 121/242 (dominant and non-dominant shoulder) Total-115
(dominant-56)
(non-dominant-59)		 No McClure yes/no method
Sant et al 2018 SD in asymptomatic water polo players 25M semi-professional water polo players; study group mean age 23.3; control mean age 23.1 25/25 (individuals with SD) 23 No Kibler method Type I-IV
Seitz et al 2015 Overhead athletes, comparing change in scapular kinematics between unweighted & maximal weighted contractions 25 asymptomatic overhead athletes (swimming-5, volleyball-15, water polo-5); SD mean age 20.3; w/o SD mean age 20.5 25/25, dominant shoulder 14 No SD test, visual observation
Shah et al 2016 Musicians (guitar): presence of SD 40 participants
(20 guitar professional guitar players and 20 age matched non guitar players)		 40/40 (dominant shoulders only) Asymmetrical (5 guitar players)
(0 non guitar players)
Dyskinetic
(4 guitar players)
(0 non guitar players)		 No LSST at 0, 45, and 90 with and without weights
Silva et al 2018 Musicians: presence of SD 72 musicians (24M & 48F). Selected 36 symptomatic (cervical, shoulder or upper extremity pain in the last year with constant symptoms lasting more than 1 week) & 36 control; symptomatic mean age 23.28; control mean age 25.03 72/72 Total - 35
(26 from symptomatic group, 9 from control group)		 36 McClure and Tate method (Visually assessed participants by having them do five repetitions of bilateral, active, weighted shoulder flexion in the sagittal plane and bilateral, active, weighted shoulder abduction in the frontal plane)
Struyf et al 2014 Amateur sports, evaluating risk factors for developing SPN 113 recreational overhead athletes (59F & 54M), all aged>18 (tennis: 26, volleyball: 27, baseball: 5, badminton: 35, handball: 10); pain mean age 36.6; pain free mean age 33.2 113/113 62/113 demonstrated SD in dominant shoulder (33 winging & 29 forward tilting) Baseline no pain
25/113 developed pain within 2 years		 Diagnosed by visual observation in 3 positions: static with both arms relaxed (thumbs facing forward), hands placed on ipsilateral hips (thumbs facing backward) and arms in 90° of humeral abduction in the frontal plane (thumbs facing up)
Tsuruike et al 2018 Sport study (collegiate baseball) 30M collegiate baseball players (13 pitchers) 30/30 14 (Mild SD in 7 pitchers + 7 position players) No Kibler method
Welbeck et al 2019 Link between thoracic rotation, SD, and pain among swimmers 34 division I swimmers (13M and 21F); mean age 19.6; 34/34 (as individuals, not shoulders) Total: 15 (6 male and 9 female) No McClure yes/no method
Yesilyaprak et al University research laboratory 148 participants (58F/90M); no sporting activity or work with overhead movements 148/296 87 (reported as individual shoulder: 87/296) No SDT
Yüksel et al 2014 Reliability of SDT & LSST 83 healthy participants (32F & 51M), mean age 21.74, have active full shoulder motion 83/83 SDT detected 44 (53%), LSST detected 30 (36%). Both detected 20 (24%) No SDT & LSST

Abbreviations: AC; acromioclavicular, FS; frozen shoulder, GHJ; glenohumeral joint, GH OA; glenohumeral joint osteoarthritis, GIRD; glenohumeral internal rotation deficit, LSST; lateral scapular slide test, MCL; medial collateral ligament, OCD; osteochondritis dissecans, ROM; range of motion, ROTC; reserve officer training corps, RSP; rounded shoulder posture, SD; scapular dyskinesis, SDT; scapular dyskinesis test, SICK scapula; scapular malposition + inferior medial border prominence + coracoid pain and malposition + dyskinesis of scapular movement, SIS; shoulder impingement syndrome, SLAP; superior labrum anterior to posterior, VEO; valgus extension overload, M; Male, F; female, SPN; shoulder pain.

The general orthopedic population among the retained studies included study participants where the upper extremity was of interest, primarily the shoulder. However, there were a small number of individuals that had neck pain where SD was also evaluated, which is more clearly identified in the results section.

Methodological Quality

Of the 37 articles assessed three15–17 were excluded and 3412,18–50 were included for synthesis (Table 2).

Table 2.Joanna Briggs Institute critical appraisal checklist for studies reporting prevalence data
Authors 1 2 3 4 5 6 7 8 9 Overall
Akodu et al 2018 1 1 1 0 1 0 0 1 0 I
Alibazi et al 2017 1 0 1 0 0 0 0 1 0 E
Alves de Oliveira et al 2013 1 0 1 0 1 0 0 1 0 I
Camci et al 2013 1 0 1 1 1 1 1 1 0 I
Castelein et al 2016 0 1 1 0 1 0 1 0 0 I
Chen et al 2015 0 0 1 0 1 0 0 1 0 E
Chen et al 2018 1 1 1 0 1 0 0 1 1 I
Christiansen et al 2017 1 1 1 0 1 1 1 1 1 I
Balci et al 2016 1 1 1 0 1 0 1 1 0 I
Bullock et al 2021 1 1 1 1 1 1 1 1 1 I
Da Silva et al 2008 1 1 1 1 1 1 1 1 0 I
Deng et al 2017 1 1 1 1 1 0 1 1 0 I
Frizziero et al 2018 1 1 1 0 1 0 0 1 0 I
Hannah et al 2017 1 1 1 1 1 1 1 1 0 I
Huang et al 2015 1 1 1 0 1 0 1 1 0 I
Johansson et al 2016 1 0 1 1 1 0 0 1 0 I
Kawasaki et al 2012 1 0 1 0 1 0 0 1 0 I
Lee et al 2017 1 0 1 0 1 1 0 0 0 I
Madsen et al 2011 1 0 1 1 1 0 0 1 0 I
Maor et al 2017 1 1 1 1 1 1 0 1 1 I
Moghadam et al 2018 1 0 1 0 1 0 0 1 0 I
Murty et al 2015 0 0 1 0 1 0 0 0 0 E
Nodehi Moghadam et al 2019 1 0 1 0 1 0 0 1 0 I
Park et al 2013 1 0 1 0 1 1 0 1 0 I
Park et al 2014 1 0 1 0 1 1 0 1 0 I
Plummer et al 2017 1 1 1 1 1 1 0 1 0 I
Rabin et al 2018 0 1 1 1 1 0 1 1 0 I
Sahinoglu et al 2020 0 1 1 0 1 1 0 1 0 I
Sant et al 2018 1 1 1 0 0 0 0 1 1 I
Seitz et al 2015 1 1 1 0 1 0 1 1 0 I
Shah et al 2016 1 1 1 0 1 0 0 1 1 I
Silva et al 2018 1 1 1 0 1 1 0 1 0 I
Struyf et al 2014 1 1 1 1 1 1 0 1 1 I
Tsuruike et al 2018 1 0 1 0 1 1 0 1 1 I
Welbeck et al 2019 1 0 1 1 1 1 0 1 0 I
Yesilyaprak et al 2016 1 1 1 1 1 0 0 1 0 I
Yüksel et al 2014 1 0 1 0 1 0 0 1 0 I

1=Yes, 0=No, Unclear, or Not Applicable, I=Included, E=Excluded; 1. Was the sample frame appropriate to address the target population?; 2. Were study participants sampled in an appropriate way?; 3. Was the sample size adequate?; 4. Were the study subjects and the setting described in detail?; 5. Was the data analysis conducted with sufficient coverage of the identified sample?; 6. Were valid methods used for the identification of the condition?; 7. Was the condition measured in a standard, reliable way for all participants?; 8. Was there appropriate statistical analysis?; 9. Was the response rate adequate, and if not, was the low response rate managed appropriately?

The excluded articles all had a score ≤ 3 on the JBI tool. The reasoning for exclusion of articles was to remove poor quality studies due to low quality or high risk of bias. Otherwise, there would be little value in scoring quality if high- and low-quality studies are all given the same “voice”. Additionally, the JBI tool is specifically designed to give the raters the choice of including or excluding the scored study based on their interpretation of the scoring. Of the included studies, 1812,21–27,32,37–41,44,45,49,50 addressed the target population appropriately with the sample frame and had adequate sample sizes. However, only 13 studies12,19,23,24,26,28,31,32,41,42,47,49,50 reported both the study subjects and setting in detail. Additionally, 11 studies19,20,22–24,26,27,38,45,47,50 measured the condition in a standard reliable way, 15 studies12,19,22,23,26,30,32,34–36,40–42,48,50 used valid methods to identify the condition, and 8 studies21,22,32,37,39,41,48,50 included information on response rate as most studies were one-time measures. The JBI tool, like other quality and risk of bias assessment tools, does not advocate for a summative score as the constructs being scored are not similar. Therefore, in order to be as transparent as possible, we listed each item in the table along with their score, as well as provided a summary of those studies and which were the most common items not reported as you mention above.

Prevalence Results

The number of studies with available data for the asymptomatic and symptomatic populations and relevant subgroups are reported. Table 3 reflects studies with available subgroup data for asymptomatic and symptomatic populations. Data for asymptomatic individuals are reported in Table 4. Finally, symptomatic athletic population results are reported in Table 5 while the asymptomatic general population results ae reported in Table 6.

Table 3.Studies with available subgroup data for both asymptomatic and symptomatic populations
SYMPTOMATIC - Individuals (counted SD for an individual)
Athletic/Musicians Study Individuals (n) With Scapular Dyskinesis (n) Percentage Without Scapular Dyskinesis (n) Percentage
Alves de Oliveira et al 2013 15 14 93% 1 7%
Johansson et al 2016 17 15 88% 2 12%
Sliva et al 2018 36 26 72% 10 28%
Total 68 55 81% 13 19%
General Orthopedic Population Study Individuals (n) With Scapular Dyskinesis (n) Percentage Without Scapular Dyskinesis (n) Percentage
Balci et al 2016 53 22 42% 31 58%
Castelein et al 2016 19 9 47% 10 53%
Chen et al 2018 186 140 75% 46 25%
Christiansen et al 2017 40 18 45% 22 55%
Deng et al 2017 102 37 36% 65 64%
Huang et al 2015 41 29 71% 12 29%
Plummer et al 2017 67 45 67% 22 33%
Rabin et al 2018 74 33 45% 41 55%
Total 582 333 57% 249 43%
Symptomatic
Total		 Individuals (n) With Scapular Dyskinesis (n) Percentage Without Scapular Dyskinesis (n) Percentage
650 388 60% 262 40%
Table 4.Asymptomatic Individuals (counted SD for an individual)
ASYMPTOMATIC - Individuals (counted SD for an individual)
Athletic / Musicians Study Individuals (n) With Scapular Dyskinesis (n) Percentage Without Scapular Dyskinesis (n) Percentage
Alves de Oliveira et al 2013 15 6 40% 9 60%
Bullock et al 2021 33 15 45% 18 55%
Da Silva et al 2008 53 23 43% 30 57%
Frizziero et al 2018 32 15 47% 17 53%
Johansson et al 2016 14 4 29% 10 71%
Kawasaki et al 2012 103 33 32% 70 68%
Lee et al 2017 26 7 27% 19 73%
Madsen et al 2011 78 29 37% 49 63%
Maor et al 2017 20 6 30% 14 70%
Sant et al 2018 25 23 92% 2 8%
Seitz et al 2015 25 14 56% 11 44%
Shah et al 2016 20 4 20% 16 80%
Silva et al 2018 36 9 25% 27 75%
Struyf et al 2014 113 62 55% 51 45%
Tsuruike et al 2018 30 14 47% 16 53%
Wellbeck et al 2019 34 15 44% 19 56%
Total 657 279 42% 378 58%
General Population Study Individuals (n) With Scapular Dyskinesis (n) Percentage Without Scapular Dyskinesis (n) Percentage
Akodu et al 2018 77 54 70% 23 30%
Camci et al 2013 64 40 63% 24 37%
Castelein et al 2016 19 8 42% 11 58%
Da Silva et al 2008 20 4 20% 16 80%
Hannah et al 2017 40 27 68% 13 32%
Plummer et al 2017 68 42 62% 26 38%
Shah et al 2016 20 0 0% 20 100%
Yüksel et al 2014 83 54 65% 29 35%
Total 391 229 59% 162 41%
Asymptomatic Total Individuals (n) With Scapular Dyskinesis (n) Percentage Without Scapular Dyskinesis (n) Percentage
1048 508 48% 540 52%
Table 5.Athletic Population - Symptomatic
Study Shoulders (n) With Scapular Dyskinesis (n) Percentage Without Scapular Dyskinesis (n) Percentage Shoulders (n)
Park et al 2013 178 122 69% 56 31% 178
Park et al 2014 330 280 85% 50 15% 330
Total 508 402 79% 106 21% 508

*Shoulders (counted SD for each shoulder)

Table 6.General Population – Asymptomatic
Study Shoulders (n) With Scapular Dyskinesis (n) Percentage Without Scapular Dyskinesis (n) Percentage
Moghadam et al 2018 200 128 64% 72 36%
Nodehi et al 2020 88 17 19% 71 81%
Sahinoglu et al 2020 242 115 48% 127 52%
Yesilyaprak et al 296 87 29% 209 71%
Total 826 347 42% 479 58%

*Shoulders (counted SD for each shoulder)

Although the inclusion criteria were intentionally broad in respect to diagnoses for the symptomatic population, all but three studies20,35,40 consisted of individuals with some form of shoulder pain including diagnoses such impingement, instability, rotator cuff tear, labral tear, and upper extremity pain, all of which are listed in Table 1. Two of the three studies35,40 consisted of mixed upper extremity diagnoses but the SD data was not parsed out by diagnosis. The authors were able to examine them based on the inclusion criteria. This was an attempt to be transparent in instances were other diagnosis outside of shoulder conditions may have been considered as we were examining those studies that identify SD but could have been in a population of individuals with cervical or upper extremity conditions. The remaining study20 included individuals with neck pain only with a total number of 19 subjects. Within the studies for the symptomatic athletic and general orthopedic population there were 81% and 57% individuals with SD, respectively, and a total of 60% among both groups. The two studies within symptomatic athletic population that looked at both shoulders individually demonstrated a total of 79% of individuals with SD considering at least one shoulder. Within the studies for the asymptomatic athletic and general population there were 42% and 59% individuals with SD, respectively, and a total of 48% among both. The four studies within asymptomatic general population that looked at both shoulders individually there was a total of 42% of individuals with SD.

DISCUSSION

The purpose of this systematic review was to examine the available literature in order to report the prevalence of SD among both the symptomatic and asymptomatic population. The results of this systematic review indicate that there is an overall presence of SD of 60% among symptomatic individuals. Among the asymptomatic population there is an overall presence of SD of 48% among those studies that identify individuals with SD. The low number of studies that identified individuals with SD per shoulder makes it difficult to determine true differences between those with and without symptoms. Despite the overall prevalence of SD being higher among those with symptoms compared to those without, there is still a considerable number of those that present with SD (nearly half of those studied) that are asymptomatic which questions the relevance of this finding. Furthermore, the total number of symptomatic individuals, 650, within studies investigating SD was just over half the number of those studies investigating SD among asymptomatic individuals, 1,048. This was reported for transparency in how the data were presented.

When considering the population of those with general shoulder pain there were a total of 582 individuals within the studies examined in this review. Among this population there was a higher percentage of individuals with SD (57%) compared to those without (43%). However, whether SD is contributing to the symptoms experienced by this populations remains unclear. If SD is a contributing factor to the symptoms among the general orthopedic population with shoulder pain, then how is the high prevalence (57%) of SD among the general population studied without symptoms explained?

There is considerable discussion in the literature regarding the presence of SD among overhead athletes with or without symptoms, as well as the presence of SD being a potential risk factor for sustaining injury in the future.8,9,31,32,37 The current findings from the current study support the high incidence of SD among athletes with shoulder symptoms. However, it is important to note that only three studies with a total of 68 individuals investigated the presence of SD within the symptomatic athlete population while 16 studies with a total of 657 individuals investigating the presence of SD in the asymptomatic athletic population were included. Given the larger number of asymptomatic athletes who were described as having SD (from 20%-92%) it is clear that a large number of athletes present with SD and have no symptoms. This may indicate that it is a possibility that SD may be a normal adaptation for those participating in overhead sports.

Additionally, the timing of measuring SD is not consistently reported among the studies that contain overhead athletes and may add further evidence that SD is a normal adaptation within this population. Two studies31,32 measured SD of asymptomatic competitive swimmers at various points of an individual training session. Both studies found that as training progressed, the number of individuals presenting with SD increased with a large number of participants presenting with SD at the end of the training session (82%31 and 85%32). At first glance the initial perception may be that these results are suggestive of weakness or some compensatory mechanism that requires attention, however, it is possible that there is a normal adaptation related to the overall shoulder complex that causes this change to occur, particularly since these athletes were all competing at a high level without symptoms. This would not be unlike what is known regarding the increase in external rotation range of motion at the glenohumeral joint within a single game and over the course of the season in a baseball pitcher.51 Within baseball pitchers this adaptation is not only normal, but necessary to perform at a high level.

Limitations

There are several limitations to this systematic review. The first limitation is that only included studies published in the English language were included which may have excluded published studies on this topic. Additionally, a very strict inclusion and exclusion criteria was applied in order to identify those studies that would provide the appropriate data for the purpose of this study. Lastly, there is a lack of consistency among how SD is measured across studies as well as populations, so it was not possible to perform a meta-analysis.

CONCLUSION

Within the symptomatic population, athletes have a higher percentage SD than the general orthopedic population. However, there are a considerable number of individuals with symptoms that do not present with SD. Perhaps more revealing is the number of asymptomatic individuals that present with SD, suggesting that SD may be a relatively normal finding among nearly half of the asymptomatic population studied within the literature. Until longitudinal studies are completed that monitor the predictive value of SD over time amongst asymptomatic populations, the relevance of this finding will remain uncertain.

Acknowledgements

Melinda Johnson, Reference/Academic Support Services Librarian, Nova Southeastern University and Zachary Smith

Conflict of interest declaration

The authors declare no conflict of interest.