Deltoid muscle activity in patients with reverse shoulder prosthesis at 2-year follow-up

Journal of Shoulder and Elbow Surgery, 2013

Background: Frequently, patients who are candidates for reverse shoulder arthroplasty have had prior surgery that may compromise the anterior deltoid muscle. There have been conflicting reports on the necessity of the anterior deltoid thus it is unclear whether a dysfunctional anterior deltoid muscle is a contraindication to reverse shoulder arthroplasty. The purpose of this study was to determine the 3-dimensional (3D) moment arms for all 6 deltoid segments, and determine the biomechanical significance of the anterior deltoid before and after reverse shoulder arthroplasty. Methods: Eight cadaveric shoulders were evaluated with a 6-axis force/torque sensor to assess the direction of rotation and 3D moment arms for all 6 segments of the deltoid both before and after placement of a reverse shoulder prosthesis. The 2 segments of anterior deltoid were unloaded sequentially to determine their functional role. Results: The 3D moment arms of the deltoid were significantly altered by placement of the reverse shoulder prosthesis. The anterior and middle deltoid abduction moment arms significantly increased after placement of the reverse prosthesis (P < .05). Furthermore, the loss of the anterior deltoid resulted in a significant decrease in both abduction and flexion moments (P < .05). Conclusion: The anterior deltoid is important biomechanically for balanced function after a reverse total shoulder arthroplasty. Losing 1 segment of the anterior deltoid may still allow abduction; however, losing both segments of the anterior deltoid may disrupt balanced abduction. Surgeons should be cautious about performing reverse shoulder arthroplasty in patients who do not have a functioning anterior deltoid muscle.

2021

Background: Reverse total shoulder arthroplasty (RSA) increases deltoid muscle fiber recruitment and tension to compensate for deficient rotator cuff activity; however, it is unclear whether the anterior or middle deltoid becomes dominant and how the muscle activation profile changes postoperatively. Using minimally invasive electromyography, this study evaluated the activity of the deltoid and surrounding muscles during shoulder motion to assess muscle activation changes post-RSA. Methods: In this observational study, we assessed change in preoperative to postoperative shoulder muscle activation in 10 patients over 6 months. Muscle activation was measured using 8 surface electrodes. Activation of the anterior, middle and posterior deltoid and surrounding muscles were recorded during shoulder abduction, flexion, external and internal rotation were quantified. One-way analysis of variance was used to identify significant differences in activation and time or speed. Least significant ...

Journal of Clinical Medicine

Although reverse shoulder arthroplasty (RSA) has shown successful postoperative outcomes, little is known about compensatory activation patterns of remaining shoulder muscles following RSA. The purpose of this experimental case control series was to investigate shoulder muscle strength and neuromuscular activation of deltoid and teres minor muscles 2 years after RSA. Humerus lengthening, center-of-rotation medialization, maximal voluntary strength, and electromyographic (EMG) activity were compared between the operated and the non-operated side of 13 patients (mean age: 73 years). Shoulder muscle strength was significantly lower on the operated side for external rotation (−54%), internal rotation (−20%), and adduction (−13%). Agonist deltoid EMG activity was lower on the operated side for shoulder flexion, extension, and internal and external rotation (p &lt; 0.05). Antagonist deltoid coactivation was higher on the operated side for external rotation (p &lt; 0.001). Large correlatio...

PLOS ONE, 2021

Background Lateralization of the glenoid implant improves functional outcomes in Reverse Shoulder Arthroplasty. Lateralization does not appear to impact the Deltoid’s Moment Arm. Therefore, the stabilizing effect described in the literature would not be the result of an increase this moment arm. A static biomechanical model, derived from Magnetic Resonance Imaging, can be used to assess the coaptation effect of the Middle Deltoid. The objective of this study was to analyze the impact of increasing amounts of glenoid lateralization on the moment arm but also on its coaptation effect. Methods Eight patients (72.6 ± 6.5 years) operated for Reverse Shoulder Arthroplasty were included in the study. Three-dimensional models of each shoulder were created based on imaging taken at 6 months postoperative. A least square sphere representing the prosthetic implant was added to each 3D models. A static biomechanical model was then applied to different planar portions of the Middle Deltoid (from...

Journal of shoulder and elbow surgery / American Shoulder and Elbow Surgeons ... [et al.]

Results of the reverse shoulder prosthesis on pain are generally satisfying; however, active range of motion (ROM) is often not optimal, especially after revision. A kinematic and clinical analysis of the reverse prosthesis was performed to provide more precise information on its glenohumeral motion pattern. We hypothesized that the difference in the primary and revision cases is due to differences in the motion in the glenohumeral joint. The motion pattern of 31 patients with a reverse prosthesis (35 shoulders, 19 primary and 16 revisions) was measured during 3 active ROM tasks-forward flexion, abduction, and axial rotation. Average age was 71 ± 8 years (range, 58-85 years). Average follow-up was 23 ± 14 months (range, 4-63 months). Kinematic measurements were performed with a 3-dimensional electromagnetic tracking device. Clinical evaluation was performed by obtaining Constant score, Disabilities of Arm, Shoulder and Hand (DASH) score, and the Simple Shoulder Test (SST). Acromial-...

International journal of shoulder surgery

Optimizing deltoid tension is important to achieve maximal function after reverse total shoulder arthroplasty (RTSA), but the effects of baseplate and glenosphere positions on deltoid tension have not been quantified. To quantify deltoid elongation and elongation to failure under physiologic loads with three baseplate-glenosphere configurations with increasing inferior offset. Cadaver biomechanical study. Twenty-four cadaver shoulders were divided into three groups. The starting point for baseplate insertion in Group 1 was the center of the glenoid, with glenospheres placed in minimal inferior offset (0.5 mm). Groups 2 and 3 baseplates were placed 2 mm inferior to the center point and glenospheres in minimal (2.5 mm) offset (Group 2) or maximal (4.5 mm) offset (Group 3). Tensile testing was done to quantify deltoid elongation and evaluate failure. A one-way analysis of variance was performed to detect statistically significant differences among treatment groups. A post-hoc Neuman-Ke...

The indications for reverse shoulder arthroplasty (RSA) continue to be expanded. Associated impairment of the deltoid muscle has been considered a contraindication to its use, as function of the RSA depends on the deltoid and impairment of the deltoid may increase the risk of dislocation. The aim of this retrospective study was to determine the functional outcome and risk of dislocation following the use of an RSA in patients with impaired deltoid function. Between 1999 and 2010, 49 patients (49 shoulders) with impairment of the deltoid underwent RSA and were reviewed at a mean of 38 months (12 to 142) post-operatively. There were nine post-operative complications (18%), including two dislocations. The mean forward elevation improved from 50° (SD 38; 0° to 150°) pre-operatively to 121° (SD 40; 0° to 170°) at final follow-up (p < 0.001). The mean Constant score improved from 24 (SD 12; 2 to 51) to 58 (SD 17; 16 to 83) (p < 0.001). The mean Single Assessment Numeric Evaluation score was 71 (SD 17; 10 to 95) and the rate of patient satisfaction was 98% (48 of 49) at final follow-up. These results suggest that pre-operative deltoid impairment, in certain circumstances, is not an absolute contraindication to RSA. This form of treatment can yield reliable improvement in function without excessive risk of post-operative dislocation. Cite this article: Bone Joint J 2013;95-B:1106-13.

Journal of Orthopaedics, 2020

Introduction: Patients undergoing a Reverse Total Shoulder Arthroplasty (RTSA) often have functional limitations that affect the range of motion of the shoulder. These limitations are not mechanical in nature, but instead linked to a reduced ability to generate muscle force. The specific aims of this study was to offer a comparison between the muscle activity generated by a post-operative RTSA shoulder in a patient to that of their contralateral shoulder during a series of functional activities. Material & methods: A convenience sample of 10 subjects between the ages of 50-75 years of age were recruited. EMG and kinematic data were concomitantly collected while subjects completed tasks that included common activities of daily living. Results: The main findings of this study were that all sub regions of the deltoid functioned as abductors, versus the native shoulder where the middle deltoid primarily works in abduction. For the scapular elevation activity there was a significant difference in flexion between the surgical and contralateral shoulder (p < .001), with the surgical shoulder having nearly 30°less range of motion. Conclusion: Anticipating limitations in functional outcomes and range of motion for patients after RTSA may inform patient decision-making and improve clinical evaluations. The finding of increased mid deltoid function during lifting activity has implications for rehabilitation and encouraging protocols that strengthen the deltoid in concentric motions. Additionally, the decreased scapular elevation found in this study may guide rehabilitation focusing on regaining range of motion post-operatively.

Clinical orthopaedics and related research, 2015

Reverse total shoulder arthroplasty (RTSA) is widely used; however, the effects of RTSA geometric parameters on joint and muscle loading, which strongly influence implant survivorship and long-term function, are not well understood. By investigating these parameters, it should be possible to objectively optimize RTSA design and implantation technique. The purposes of this study were to evaluate the effect of RTSA implant design parameters on (1) the deltoid muscle forces required to produce abduction, and (2) the magnitude of joint load and (3) the loading angle throughout this motion. We also sought to determine how these parameters interacted. Seven cadaveric shoulders were tested using a muscle load-driven in vitro simulator to achieve repeatable motions. The effects of three implant parameters-humeral lateralization (0, 5, 10 mm), polyethylene thickness (3, 6, 9 mm), and glenosphere lateralization (0, 5, 10 mm)-were assessed for the three outcomes: deltoid muscle force required ...

Official Publication of the National Center for Trauma Research, 2018

Abstract The shoulder is considered to be an important flexible and movable part in the human body. However, it is a wobble joint as its range of motion (ROM) is high. This unstable status increases the rate of joint injury. The processes leading to shoulder joint dysfunction are arthritis, hemiarthroplasty failure, and pseudoparalysis; in turn, one of the main factors contributing to these problems is rotator cuff tear (RCT). Reverse shoulder arthroplasty (RSA)may be a proper treatment for shoulder dysfunction and pain. This treatment elevates shoulder movement and has been augmented by recent advances in the development of the reverse shoulder prosthesis (RSP) design. This current review highlights the recent developments, revisions, and complications. A review of the published literature has been done to determine the overall rates of problems, complications, reoperations, and revisions after RSA. Furthermore, this review discusses the problems concerning RSP, shoulder joint replacement, and improvement in shoulder joint movement after arthroplasty.