Postoperative Deltoid EMG Activity and Function in Patients After Reverse Total Shoulder Arthroplasty: A Comparison of Standard Implantation Technique and Lateralization
Phase: NA
Conditions: Cuff Tear Arthropathy, Omarthrosis, Rotator Cuff Tear Arthropathy
Sponsor: Vienna Hospital Association

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Postoperative deltoid EMG activity and function in patients 
after Reverse Total Shoulder Arthroplasty: A comparison of 
standard implantation technique and lateralization  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1.) Department of Orthopedics and Trauma Surgery 
Klinik Donaustadt, Vienna 

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TABLE OF CONTENTS 
TABLE OF CONTENTS .................................................................................................................... 2 
STUDY SYNOPSIS .......................................................................................................................... 3 
ABSTRACT .................................................................................................................................... 5 
INTRODUCTION ................................................................................................................................ 5 
MATERIAL AND METHODS .................................................................................................................. 5 
AIM OF THE STUDY ........................................................................................................................... 5 
INTRODUCTION ............................................................................................................................ 6 
MATERIAL AND METHODS ............................................................................................................ 7 
STUDY DESIGN ................................................................................................................................. 7 
AIMS OF THE STUDY .......................................................................................................................... 7 
MAIN HYPOTHESIS ........................................................................................................................... 8 
SECONDARY HYPOTHESES ................................................................................................................... 8 
PATIENTS........................................................................................................................................ 9 
EMG MEASUREMENTS ...................................................................................................................... 9 
SURGICAL TECHNIQUE AND POSTOPERATIVE CARE ..................................................................................... 9 
RADIOLOGICAL MEASUREMENTS ........................................................................................................ 10 
CLINICAL OUTCOME AND ADDITIONAL MEASUREMENTS ............................................................................ 10 
STATISTICS .................................................................................................................................... 11 
PRIVACY ..................................................................................................................................... 15 
TIME SCHEDULE ......................................................................................................................... 15 
RISK BENEFIT RATIO ................................................................................................................... 15 
INSURANCE ................................................................................................................................ 15 
GOOD CLINICAL PRACTICE .......................................................................................................... 16 
REFERENCES ............................................................................................................................... 17 
 

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Study synopsis 
Title: 
Postoperative deltoid EMG activity and function in patients after 
Reverse Total Shoulder Arthroplasty: A comparison of standard 
implantation technique and lateralization 
Background: 
Reverse total shoulder arthroplasty (RTSA) is a well-established 
method to treat patients with irreparable rotator cuff tears and 
glenohumeral osteoarthritis. The biomechanical principle implies a 
medialization and distalization of the center of rotation (COR). 
Deficiencies in internal and external rotation constitute frequently 
encountered functional problems. Some studies showed reduced 
activation of the posterior deltoid in EMG measurements, which may 
explain the inability to compensate these movements. Lateralized 
prosthetic designs demonstrated increased external rotation through 
an alteration of the deltoid’s lever arm.  
Aim of the study: 
The aim of the study is to investigate the impact of lateralization on 
functional outcome and deltoid EMG activity in comparison to a 
standard implantation technique.  
Primary outcome: 
pre- and postoperative maximal voluntary contraction of deltoid 
muscle on EMG 
Secondary outcomes: pre- and postoperative ROM of shoulder joint, pre- and postoperative 
clinical scores (Constant-Murley score, Quick DASH questionnaire, 
pASES and SVV) and pre- and postoperative radiographic humeral 
length, comparison of the two groups in all parameters 
Study design: 
randomized prospective single-center study with 4 follow-up 
investigations within a time interval of two years. 
Subjects: 
A total of approximately 130 subjects, who are scheduled either for 
standard or lateralized RTSA at the Department of Orthopedics and 
Trauma Surgery at Klinik Donaustadt 
Methods: 
The patients will be divided into two groups, standard RTSA and 
lateralized implant via randomization. Preoperative and at 4 follow-up 
controls, surface EMG measurements of the deltoid will be obtained 
and clinical scores (Constant-Murley score and Quick DASH 
questionnaire) will be assessed. As patient related outcome measures, 
pASES-S and SVV will be evaluated. Pre- and postoperative x-rays and 
CT scans for lateralization measurement and routine follow-ups for 
screening of complications will be performed. 
Statistical analysis: 
For group comparisons, categorical variables will be given as frequency 
and percentage, while continuous variables will be given as mean ± 
standard deviation. Primary and secondary outcome parameters will 
be analyzed in both groups prior and after surgery. The Kolmogorov-
Smirnov test will be applied to test for a possible normal distribution 
of the data. Group comparisons will be performed with t-test 
respectively Mann Whitney U-Test depending if normal distribution is 
given or not. Correlations between various parameters (preoperative 

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EMG and postoperative functional outcomes; radiographic humeral 
lengths and EMG respectively functional outcomes) will be 
investigated. IBM SPSS Statistics 25 will be used to perform group 
comparisons and correlations. A p-value ≤0.05 (two-tailed) is 
considered significant and correlation coefficients >.30 respectively 
>.60 are regarded moderate respectively strong. Other standard 
calculations using statistical tests may be added as needed. 
 
 
 
 

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Abstract 
Introduction 
Reverse total shoulder arthroplasty (RTSA) is a well-established method to treat patients with 
irreparable rotator cuff tears and glenohumeral osteoarthritis. The biomechanical principle is 
a medialization and distalization of the center of rotation (COR) to provide a compensatory 
role for the insufficient rotator cuff. Deficiencies in internal and external shoulder rotation 
constitute frequently seen functional problems. Some studies showed reduced activation of 
the posterior deltoid in EMG measurements, which may explain the inability to compensate 
these movements. Lateralized prosthetic designs implants demonstrated increased external 
rotation force through an alteration of the deltoid’s lever arm.  
Material and Methods 
This study will be conducted as a monocentric randomized, prospective trial. Approximately 
130 patients, scheduled for reversed total shoulder arthroplasty (RSA), will be enrolled.  The 
patients will be divided into two groups depending on receiving RSA or a lateralized implant 
via randomization. Preoperatively and at 4 follow-up visits, a surface EMG (sEMG) of the 
deltoid muscle will be conducted and clinical scores (Constant-Murley Score and Quick DASH 
questionnaire) will be assessed. As patient related outcome measures, p-ASES-S and SVV will 
be evaluated. Pre- and postoperative x-rays and CT scans will be conducted for preoperative 
planning and measurement of achieved lateralization. Clinical and radiological complications 
will be routinely documented. Group comparisons and correlations will be performed to 
compare both groups pre- and postoperatively. The study’s duration is scheduled for 2 years. 
Aim of the Study 
The aim of the study is to evaluate a possible difference in function and EMG activity between 
the two patient groups. Especially a different increase in external rotation range of motion 
and strength shall be investigated. Furthermore a possible connection between preoperative 
deltoid muscle activity and postoperative outcome shall be pointed out. Lastly, the impact of 
lateralization on functional outcome, shall be evaluated compared to the standard 
implantation technique. 
 

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Introduction 
Reverse total shoulder arthroplasty (RTSA) is a well-established method to treat patients with 
irreparable rotator cuff tears and glenohumeral osteoarthritis (1). The biomechanical principle 
is a medialization and distalization of the center of rotation (COR) in the glenohumeral joint, 
which induces an elongation of the deltoid muscles’ lever arm and therefore tensioning of the 
muscle (2,3). This in consequence increases deltoid strength, alters its moment arm in order 
to generate more elevation torque, which in turn provides a compensatory role for the 
insufficient rotator cuff (4,5). Although acceptable results could be achieved with the original 
Grammont prosthetic design (6), some serious issues arose with the original conception, such 
as acromial fracture, instability, dislocation and scapular notching (7–9).  Furthermore, 
deficiencies in internal and external arm rotation constitute frequent functional problems (8–
10).  Concomitant altered lever arms of the teres minor and subscapularis muscles seem to 
play a key role in this matter (11). Some studies showed reduced activation of the posterior 
deltoid in EMG measurements, which may explain the inability to compensate these 
movements (5,12,13). To counter these drawbacks, newer, lateralized prosthetic designs have 
been introduced (7). In particular, lateralization restores tension in the remaining rotator cuff 
and improves efficiency of the posterior deltoid muscle (14). Several studies showed an 
improved range of motion for this type of prosthetic design, in particular regarding external 
rotation (15,16). The lateralization can be reached via different means, for example BIO-RSA, 
where a autologous humeral head bone graft is used or artificial glenoid augments, which are 
implanted above the base-plate (17). Evaluation of shoulder muscle condition can be 
performed via use of magnetic resonance imaging (MRI), but no information can be attained 
about dynamic muscle function (18,19). However, especially for the deltoid and adjacent 
upper trapezius muscles, surface EMG assessment is an easily applicable, non-invasive and 
cheap way to assess and objectify muscle function (5,12,13). A clinical improvement of the 
rotatory capability could already be shown for lateralized designs. The deltoid muscle is the 
key to functionality after reversed shoulder arthroplasty and the main muscle to undergo 
compensatory changes (12). The influence of preoperative deltoid activity on postoperative 
functional outcomes, as well as the altered muscle activation of a lateralized implant to a 
standard prosthetic design will be investigated in this study. 

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Material and Methods 
Study design  
The study will be conducted as a randomized, single-center, prospective trial at the Klinikum 
Donaustadt Vienna with a total of 4 (6 weeks, 3 months, 6 months, 1 year) follow-up 
investigations. Primarily, the patients will be asked for participation in the study and full 
written consent for the operation and the trial will be obtained. At the same visit, the 
preoperative surface EMG measurement will be undertaken and the preoperative clinical 
scores as well as patient related outcome measures (PROM) will be assessed. Furthermore an 
MRI scan for evaluation of muscle quality and a CT scan for preoperative implant planning will 
be scheduled. Patients will be randomized via sealed envelope technique. After surgery, all 
patients receive standardized postoperative mobilization treatment starting on the first 
postoperative day. Furthermore, pre- and postoperative x-rays will be obtained for 
measurement of reached lateralization. All patients will be provided with a standardized 
exercise regimen, which they will pursue in an outpatient physiotherapy setting. The patients 
will be examined for possible clinical or radiological complications at our outpatient clinic 6 
weeks, 3 months, 6 months and 12 months postoperatively. During every outpatient follow-
up visit, clinical scores, PROMs and standardized x-rays and a final CT scan will be obtained, 
and the EMG measurements will be undertaken according to protocol.  The duration of the 
study is scheduled for 3 years. 
 
Aims of the Study 
• To evaluate deltoid muscle activity using surface EMG measurements in patients after 
implantation of a lateralized glenoid in comparison to a standard prosthesis (Univers 
Reverse, FA Arthrex). 
• To assess differences in pre- and postoperative EMG activity of the deltoid muscle  
• To evaluate the influence of preoperative EMG muscle activity on postoperative 
functional outcomes, i.e. shoulder range of motion and arm abduction strength 
• To compare the clinical outcomes of lateralized to standard prosthesis 
• To assess possible postoperative differences in EMG activity comparing lateralized and 
standard prostheses 

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• To evaluate the influence of the extent of deltoid lengthening and therefore lever arm 
increase on EMG activity and functional outcome 
 
Main Hypothesis 
• H1: Delta muscle activity in superficial EMG is higher in patients after lateralized 
glenoid than in patients treated with standard RTSA. 
Secondary Hypotheses 
• H2: Delta muscle activity in superficial EMG increases significantly in both groups when 
compared between pre-and postoperatively 
• H3: The postoperative increase in delta muscle activity, especially of the posterior 
parts, measured via superficial EMG is significantly higher in patients treated with 
lateralized glenoid in comparison to patients after standard RTSA. 
• H4: A higher preoperative delta muscle activity results in a higher postoperative 
muscle activity in superficial EMG measurements 
• H5: Range of motion, especially in external rotation is significantly higher in patients 
treated with lateralized glenoid than in patients with standard RTSA. 
• H6: The clinical outcome in objective (Constant score) and subjective (SVV, p-ASES, 
Quick-DASH) outcome scores is significantly higher in patients treated with lateralized 
glenoid in comparison to standard RTSA. 
• H7: The lateralization via glenoid augmentation is achievable and measureable via 
radiological means (X-ray, CT scan) 
• H8: The extent of lateralization correlates with the increase of delta muscle activity in 
superficial EMG measurements 
• H9: The extent of lateralization correlates with the increase in range of motion, 
especially in external rotation 
• H10: The extent of lateralization correlates with the increase in clinical outcome 
measures (Constant score, SVV, p-ASES, Quick-DASH) 
• H11: There is no significant difference in the rate of surgical related complications 
between the two groups 
 

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Patients 
Approximately 130 patients scheduled for Reverse total shoulder arthroplasty after failed 
conservative treatment will be included. Inclusion criteria: diagnosis of Cuff tear arthropathy 
(CTA), irreparable rotator cuff tear or severe osteoarthritis (OA), primary RSA, age 60-85, 
verified rotator cuff tear in preoperative MRI, absence of severe cognitive impairment. 
Exclusion criteria: previous muscle transfer, revision surgery, highly dysplastic glenoid, axillary 
nerve palsy, upper limb radiculopathy, cervical myelopathy, degenerative muscular disease, 
previous proximal humeral fracture, revision arthroplasty, rheumatoid arthritis. 
 
EMG Measurements 
For EMG measurements, a surface EMG set-up (FreeEMG, BTS, Italy) is used. Before 
attachment of the transcutaneous electrodes, the skin is cleansed with an alcoholic 
disinfectant to minimize impedance. The surface EMG electrodes are attached at specific 
muscle areas: the anterior, middle and posterior deltoid muscle according to SENIAM 
recommendations (http://seniam.org/). The measurements are recorded in 3 different 
motions: external/internal rotation, abduction and forward flexion/extension. The ratio 
between peak torque and EMG root mean square is quantified to assess neuromuscular 
efficiency (20).  
Arm strength is evaluated using a spring balance dynamometer.  
 
Surgical technique and postoperative care 
The patients are implanted with the same reversed shoulder prosthesis (Univers Reverse + 
Universal Glenoid, FA Arthrex) according to a standardized protocol following the 
manufacturer’s instructions. Surgery is performed in beach chair position via delto-pectoral 
approach in a cementless technique. Lateralization is reached via metal glenoid augment / 
lateralized glenosphere or a combination of both of at least 4mm, according to the 
manufacturer’s protocol as well, when randomization demands it.  
Standardized postoperative rehabilitation starts on the first postoperative day according to 
protocol. The patients are allowed free ROM in all directions adapted to pain from the early 
beginning of post-operative rehabilitation. All patients receive 3 months of outpatient physical 
therapy at our department of Physical medicine. 
 

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Radiological Measurements 
Radiographs of the operated side are obtained pre- and postoperatively as true antero-
posterior views of the entire humeral bone and glenohumeral joint in neutral rotation. 
According to the protocol by Greiner et al. the change in center of rotation (COR) is measured 
preoperatively from the center of the humeral head, and postoperatively as the distance from 
the center of the baseplate to the outer border of the acromion (21). In every patient the 
critical shoulder angle (CSA) will be measured at the a.p. radiograph (22). Humeral lengthening 
is determined postoperatively on the operated and non-operated side. The distance between 
the midpoint of the epicondylar line and a perpendicular line from the most lateral point of 
the acromion through the shaft axis is measured. The difference is considered humeral 
lengthening 
according 
to 
the 
protocol 
by 
Lädermann 
et 
al. 
(23).  
Preoperatively every patient will have to undergo a shoulder MRI for rotator cuff assessment 
and a CT scan for classification of the glenoidal bone stock and preoperative planning of the 
implant via Virtual Implant Planning (VIP, FA Arthrex) . 
All measurements are performed twice by two experienced orthopedic surgeons. Intra- and 
inter-observer reliability is calculated. 
 
Clinical outcome and additional measurements 
Demographic data (age, sex, dominant side, height, weight, BMI, medication, comorbidities, 
especially osteoporosis) is obtained via the clinical information system. Active range of motion 
(ROM) of both shoulders in all standard directions is measured pre-and postoperatively as well 
as at every follow-up visit using a goniometer. At the same occasions, the absolute and relative 
(age adapted) Constant score, the self-reported QuickDASH, the p-ASES and the SVV will be 
assessed (24–27). 
The Quick DASH (Disability of Arm, Shoulder, Hand) is a validated tool to evaluate upper 
extremity function. It consists of 11 questions, regarding complaints (pain, tingling) as well as 
activities of daily living. 
The Constant score is a well validated tool for shoulder function assessment. It consists of four 
items: evaluation of pain, activities of daily living, range of motion and strength. 
The p-ASES (patient assessment American Shoulder and Elbow Surgeons Score) is a validated 
patient related outcome measure (PROM) tool which consists of 11 questions and can be 
extended with a clinical assessment tool. The patient related part queries the parameters pain, 

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instability and activities of daily living.  Moreover questions regarding pain medication and 
subjective instability are asked. 
The Subjective Shoulder Value (SVV) is a simple, reproducible and validated question for a 
exclusively subjective evaluation of a patient’s shoulder. The patient is asked to assess his/her 
shoulder from 0-100%, when 100% stands for a fully functional, pain free shoulder. 
 
Statistics 
All calculations will be made using SPSS® (Version 25.0, SPSS Inc., Chicago, IL, USA). Descriptive 
statistics, including means and standard deviations respectively frequency and percentage, 
will be performed for both groups and at pre- and postoperative time points. Primary and 
secondary outcome parameters will be analyzed in both groups prior and after surgery. The 
Kolmogorov-Smirnov test will be applied to test for a possible normal distribution of the data. 
In normally distributed values, the t-test will be applied to compare the continuous outcome 
parameters. If the values are not normally distributed, the Mann Whitney U-Test will be 
applied. Correlations between various parameters (preoperative EMG and postoperative 
functional outcomes; radiographic humeral lengths and EMG respectively functional 
outcomes) will be investigated. 
 
A probability value of p ≤0.05 (two-tailed) is considered significant. Correlation coefficients 
>.30 are considered moderate and >.60 strong. Other standard calculations using statistical 
tests may be added as needed. 
Both groups (lateralization vs. standard reverse shoulder prostheses) are independent. The 
primary endpoint is a continuous variable (maximal postoperative voluntary contraction of 
the deltoid muscle in EMG) of the voluntary contraction of the deltoid muscle in EMG in the 
lateralization group. As there is no recent research about the topic of interest, we assume a 
medium effect, based on theoretical considerations as described in the introduction. Further 
information regarding the statistical considerations, including reference values for the 
Constant Score, Quick-DASH, ROM and external rotation can be found in Rienmüller et al (12). 
Reference values for ASES are proposed by Pegreffi et al. (5). Li et al. (13) provides values of 
orientation for the muscle activity measurements. As the main hypothesis is directed, a one-
sided analysis is appropriate (with an alpha error level of 0.025). Standard effect sizes (Cohen’s 
d and r) will be provided to determine the clinical relevance of conducted analysis.  

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Assuming a medium effect with a power of 0.8 and an alpha error level of 0.025 for the main 
hypothesis the a priori calculated sample size results in 128 participants. 
 
 
Statistical Tests planned: 
Note that in case of a significant result of the Kolmogorov-Smirnov test for the respective 
variables the calculations will be done with non-parametric tests. 
 
In general the calculated for each variable as well as the two subgroups of interest 
(lateralization glenoid, RTSA) and the overall sample will be mean, sd, number of participants, 
as well as age. In case of non-normally distrubuted data median and range of the respective 
variables will be provided.  
  
Hypothesis 
Statistical Test 
Variables 
H1 (one-tailed) 
Independent t-test 
Muscle activity after lateralized glenoid vs. 
Muscle activity RTSA 
 
Expectation: Significantly higher means of 
muscle activity in the lateralized glenoid 
group 
 
Multiple comparison correction: Bonferroni 
H2 (one-tailed) 
Dependent t-test 
Muscle activity preoperative vs. Muscle 
activity postoperative for both groups 
(lateralized glenoid and RTSA) 
 
Expectation: Significantly higher means of 
muscle activity in the postoperative group. 
 
Multiple comparison correction: Bonferroni 

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H3 (one-tailed) 
Independent t-test 
Change in muscle activity laterialized 
glenoid vs. Change in muslce activity RTSA 
 
Change in muscle activity = Postoperative 
posterior muscle activity – Preoperative 
muscle activity 
 
Expectation: Significantly higher means of 
muscle activity in the lateralized glenoid 
group. 
 
Multiple comparison: 
Bonferroni 
H4 
Correlation 
Preoperative muscle activity x Postoperative 
muscle activity 
 
Expectation: r>.3 
H5 (one-tailed) 
Independent t-test 
ROM/external rotation laterialzied glenoid 
vs. ROM/external rotation RTSA 
 
Expectation: Significantly higher means in 
the ROM/external rotation in the laterialized 
glenoid group 
 
Multiple comparison correction: Bonferroni 
H6 (one-tailed) 
Independent t-test 
Constant Score laterialized glenoid vs. 
Constant Score RTSA 
 
SVV laterialized glenoid vs. SVV RTSA 
 
p-ASES laterialized glenoid vs. P-ASES RTSA 
 
Quick-DASH laterialized glenoid vs. Quick-
DASH RTSA 
 
Expectation: Significantly higher mean 
scores in the laterialized glenoid group 
 
Multiple Comparison Correction: Bonferroni 
H7 
Qualitative description 
Subjective radiological ratings by experts 
H8 
Correlation 
Lateralization x muscle activity 
 
Expectation: r>.3 
H9 
Correlation 
Lateralization x ROM 
 

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Laterialization x external rotation 
 
Expectation: r>.3 
H10 
Correlation 
Lateralization x Constant Score 
 
Lateralization x SVV 
 
Lateralization x p-ASES 
 
Lateralization x Quick-DASH 
 
Expectation: r>.3 
H11 (two-tailed) 
Chi-Square Test 
Complication rate (dichotomous) 
lateralization glenoid vs. Complication rate 
(dichotomous) RTSA 
 
Expectation: no significant differences in 
complication rates 
 
 
 
 
 

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Privacy 
The original patient data will be accessible for authorized personnel only and will be worked 
on in a pseudonymised form. 
The data is saved on working stations at the Department of Orthopedics and Traumatology in 
the Klinik Donaustadt. It is secured by password and cannot be accessed from anywhere else.  
 
Time schedule 
After positive ethic vote, enrolling the patients will start immediately. Recruiting phase will 
take approximately 2 year. The follow-up will take 1 year for every patient. Therefore a total 
duration of 3 years can be assumed. Finally there should be a phase of 6 months in which the 
paper should be written.  
 
Risk Benefit Ratio 
The included patients will not derive a direct benefit of this study. Hence to the planned 
examinations, there is no additional risks for the included patients, which surpasses the 
anyway existing common risk of surgery. The risk of leakage of patient data, will be minimized 
by pseudonymization of the data. 
Working with patient related data will only be possible at working stations at the Department 
the Department of Orthopedics and Traumatology in the Klinik Donaustadt, password 
secured. Only authorized personnel will have access to original data, which consists of the 
involved authors mentioned above. 
The collected data can be published for research purpose but only after strict anonymization. 
The results of these study will be used to generate further information about the impact of 
lateralization on postoperative function in patients after reversed total shoulder arthroplasty. 
 
Insurance 
According to legal requirements, a no-fault insurance – i.e. damage-based insurance with 
absolute liability will be arranged for every participant, in order to guarantee appropriate 
coverage of potential risks, which can arise while participating in the study. 
The insurance will be made with Zurich Insurance Group.  

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Zurich Insurance Group 
Leopold-Ungar-Platz 2 
1190 Wien 
+431217201673 
 
The maximum payment by the insurer is up to € 500.000 for each insured participant, but is 
limited to € 3.000.000 for all of the insured participants in total. 
 
Period of insurance: 28.07.2023 – 01.09.2026, 0:00; 
Policy Number: 25896093-9 
Good Clinical Practice 
All authors have carefully read and checked this document. They comply with the 
requirements and conditions specified therein and agree to perform the study according to 
the regulations of Good Clinical Practice (GCP). The requirements concerning original data and 
the auditings of the study will be observed. They accept that modifying the study protocol is 
only permitted by amendments, which have to be confirmed by the ethic review board in 
writing. They acknowledge that any infringement of these regulations can lead to termination. 
They agree to above mentioned time schedule.

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