EMG and Delta Function in Standard RTSA vs Lateralization (EMGRTSA)

Postoperative Deltoid EMG Activity and Function in Patients After Reverse Total Shoulder Arthroplasty: A Comparison of Standard Implantation Technique and Lateralization

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.

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.

Study Overview

• Status: Not yet recruiting
• Conditions: Rotator Cuff Tear Arthropathy; Cuff Tear Arthropathy; Omarthrosis
• Intervention / Treatment: Device: Standard implantation technique; Device: Lateralization of glenoid component

Detailed Description

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.

• Study Type: Interventional
• Enrollment (Estimated): 130
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Robert Breuer, MD; Phone Number: 743429 00430128802; Email: robert.breuer@meduniwien.ac.at
• Study Contact Backup: Name: Valentin Pichler, MD; Phone Number: 743400 00430128802; Email: valentin.pichler@gesundheitsverbund.at

Study Locations

• Austria
  • Austria
    • Vienna, Austria, Austria, 1220
      • Klinik Donaustadt

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• male/female, 60-85y
• diagnosis of Cuff tear arthropathy (CTA)
• irreparable rotator cuff tear
• severe osteoarthritis (OA)
• primary RSA
• 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

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Diagnostic
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Single

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Active Comparator: Standard Implantation Group; Subjects treated with a standard glenoid component of the used reverse total shoulder prosthesis	Device: Standard implantation technique; Implantation of a standard glenoid component without any lateralization via metal back on the glenoid site
Active Comparator: Lateralized Implantation Group; Subjects treated with a lateralized glenoid component of the used reverse total shoulder prosthesis	Device: Lateralization of glenoid component; Lateralization of glenoid component in reverse total shoulder arthroplasty via metal augment on the glenoid side with a thickness of at least 4mm

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Delta Muscle activity (especially posterior Delta part)	The ratio between peak torque and EMG root mean square is measured	preoperative
Delta Muscle activity (especially posterior Delta part)	The ratio between peak torque and EMG root mean square is measured	6 weeks postoperative
Delta Muscle activity (especially posterior Delta part)	The ratio between peak torque and EMG root mean square is measured	3 months postoperative
Delta Muscle activity (especially posterior Delta part)	The ratio between peak torque and EMG root mean square is measured	6 months postoperative
Delta Muscle activity (especially posterior Delta part)	The ratio between peak torque and EMG root mean square is measured	1 year postoperative

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Range of movement (forward flexion, abduction, external rotation, extension)	ROM (range of movement) measured with a goniometer according to neutral zero method	preoperative
Range of movement (forward flexion, abduction, external rotation, extension)	ROM (range of movement) measured with a goniometer according to neutral zero method	6 weeks postoperative
Range of movement (forward flexion, abduction, external rotation, extension)	ROM (range of movement) measured with a goniometer according to neutral zero method	3 months postoperative
Range of movement (forward flexion, abduction, external rotation, extension)	ROM (range of movement) measured with a goniometer according to neutral zero method	6 months postoperative
Range of movement (forward flexion, abduction, external rotation, extension)	ROM (range of movement) measured with a goniometer according to neutral zero method	1 year postoperative
Objective and subjective outcome scores / Quality of life scores	Constant score (0-100) (higher = better)	preoperative, 6 weeks postoperative, 3 months postoperative, 6 months postoperative, 12 months postoperative
Objective and subjective outcome scores / Quality of life scores	SVV (subjective shoulder value) (0-100%) (higher = better)	preoperative, 6 weeks postoperative, 3 months postoperative, 6 months postoperative, 12 months postoperative
Objective and subjective outcome scores / Quality of life scores	p-ASES (patient-reported American Shoulder and Elbow Surgeons Score) (0-100) (higher = better)	preoperative, 6 weeks postoperative, 3 months postoperative, 6 months postoperative, 12 months postoperative
Objective and subjective outcome scores / Quality of life scores	Quick-DASH (Quick-Disability of Arm, Shoulder and Hand) (0-100) (higher = better)	preoperative, 6 weeks postoperative, 3 months postoperative, 6 months postoperative, 12 months postoperative
Difference in lateralization between preoperative 3D CT-based planning and postoperative CT-based implant position	Lateralization will be quantitatively assessed by comparing preoperative and postoperative computed tomography (CT) scans. The preoperative CT scan will be used for 3D planning and virtual implantation. The postoperative CT scan will be used to determine the actually achieved implant position. The original preoperative joint line will serve as the reference value. Medialization or lateralization will be measured as the linear distance (in millimeters) between the preoperative joint line and the postoperative implant position. The achieved lateralization will be calculated based on this difference. Additionally, the planned lateralization from the preoperative 3D virtual implantation will be compared with the actually achieved lateralization measured on the postoperative CT scan. The primary metric will be the absolute and mean deviation (in millimeters) between planned and achieved lateralization, allowing assessment of the accuracy of the preoperative 3D planning.	Preoperative and 1 year postoperative
Humeral Length (Millimeters) Measured on Standardized Radiographs	Humeral length will be measured in millimeters on standardized anteroposterior radiographs of the entire humerus obtained according to the Lädermann protocol. Measurements will be performed by comparing preoperative and postoperative radiographs. The primary metric will be the absolute difference in humeral length between preoperative and postoperative images. Measurements will be performed using calibrated digital imaging software by blinded reviewers.	preoperative, 6 weeks postoperative, 3 months postoperative, 6 months postoperative, 12 months postoperative

Collaborators and Investigators

• Sponsor: Vienna Hospital Association
• Investigators: Principal Investigator: Robert Breuer, MD, Vienna HA

Study record dates

Study Major Dates

• Study Start (Estimated): June 1, 2026
• Primary Completion (Estimated): August 1, 2027
• Study Completion (Estimated): December 1, 2027

Study Registration Dates

• First Submitted: August 10, 2024
• First Submitted That Met QC Criteria: March 8, 2026
• First Posted (Actual): March 11, 2026

Study Record Updates

• Last Update Posted (Actual): May 7, 2026
• Last Update Submitted That Met QC Criteria: May 2, 2026
• Last Verified: May 1, 2026

More Information

Terms related to this study

• Keywords: EMG; reverse total shoulder arthroplasty; lateralization; cuff tear arthropathy; deltoid function
• Additional Relevant MeSH Terms: Crystal Arthropathies; Musculoskeletal Diseases; Arthritis; Joint Diseases; Chondrocalcinosis; Rotator Cuff Tear Arthropathy
• Other Study ID Numbers: Protocol EMG RTSA 4.0

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No