Relation between preoperative electromyographic activity of the deltoid and upper trapezius muscle and clinical results in patients treated with reverse shoulder arthroplasty

Muscle activation patterns during active external rotation after reverse total shoulder arthroplasty: an electrophysiological study of the teres minor and associated musculature

BACKGROUND

Preoperative teres minor insufficiency has been identified as a risk factor for poor restoration of external rotation (ER) after reverse total shoulder arthroplasty (RTSA). However, there has been little investigation regarding muscle activation patterns generating ER. This prospective study sought to determine the timing and activation levels of the shoulder girdle musculature during ER in well-functioning RTSAs with an intact teres minor using a lateralized design.

METHODS

Patients who underwent RTSA ≥1 year previously with functional ER, an American Shoulder and Elbow Surgeons (ASES) score >70, superior rotator cuff deficiency, and an intact teres minor were identified. Electrophysiological and kinematic analyses were performed during ER in the modified neutral position (arm at side with 90° of elbow flexion) and in abduction (AB) (shoulder abducted 90° with 90° of elbow flexion). Dynamometer-recorded torque and position were pattern matched to electromyography during ER. The root-mean-square and integrated electromyography (in microvolts × milliseconds with standard deviation [SD]), as well as median frequency (MF) (in hertz with SD), were calculated to determine muscle recruitment. Pair-wise t test analysis compared muscle activation (P < .05 indicated significance).

RESULTS

After an a priori power analysis, 16 patients were recruited. The average ASES score, visual analog scale pain score, and ASES subscore for ER in AB ("comb hair") were 87.7, 0.5, and 2.75 of 3, respectively. In AB, muscle activation began with the upper trapezius, middle trapezius, and latissimus dorsi, followed by the anterior deltoid activating to neutral. With ER beyond neutral, the teres major (9.6 μV × ms; SD, 9.2 μV × ms) initiated ER, followed by the teres minor (14.1 μV × ms; SD, 18.2 μV × ms) and posterior deltoid (11.1 μV × ms; SD, 9.3 μV × ms). MF analysis indicated equal contributions of the teres major (1.1 Hz; SD, 0.5 Hz), teres minor (1.2 Hz; SD, 0.4 Hz), and posterior deltoid (1.1 Hz; SD, 0.4 Hz) in ER beyond neutral. In the modified neutral position, the upper trapezius and middle trapezius were not recruited to the same level as in AB. For ER beyond neutral, the teres major (9.5 μV × ms [SD, 9 μV × ms]; MF, 1.1 Hz [SD, 0.5 Hz]), teres minor (11.4 μV × ms [SD, 15.1 μV × ms]; MF, 1.1 Hz [SD, 0.5 Hz]), and posterior deltoid (8.5 μV × ms [SD, 8 μV × ms]; MF, 1.2 Hz [SD, 0.3 Hz]) were activated in similar sequence and intensity as AB. No differences in muscle activation duration or intensity were noted among the teres major, teres minor, and posterior deltoid (P > .05).

CONCLUSION

Active ER after RTSA is complex and is not governed by a single muscle-tendon unit. This study establishes a sequence, duration, and intensity of muscle activation for ER in well-functioning RTSAs. In both tested positions, the teres major, teres minor, and posterior deltoid function equally and sequentially to power ER.

Relationship between the preoperative grip strength and postoperative shoulder strength of patients treated via reverse shoulder arthroplasty

BACKGROUND

Systemic disorders including diabetes mellitus, obesity, and depression affect the outcomes of reverse shoulder arthroplasty (RSA). Sarcopenia (a general skeletal muscle disorder) is common in elderly people, but its effect on patients after RSA is not clear. We hypothesized that the preoperative sarcopenia indices of grip strength and general skeletal muscle mass would correlate with the clinical outcomes of RSA.

METHODS

Grip strength and general skeletal muscle mass were measured in patients scheduled (between 2016 and 2021) for primary RSA to treat cuff tear arthropathy, an unrepairable cuff tear, or osteoarthritis with a large cuff tear. Before surgery, grip strength was measured using a hydraulic dynamometer and general skeletal muscle mass was calculated from the appendicular relative skeletal muscle mass index (aRSMI) using dual-energy X-ray absorptiometry. In all, 58 patients were included; the minimal follow-up duration was 12 months. The postoperative clinical results (pain, active range of motion, shoulder strength, and functional scores) were evaluated during scheduled outpatient visits. We calculated correlations between the preoperative sarcopenia indices, and the clinical results at the final follow-up.

RESULTS

The mean preoperative grip strength and aRSMI were 21.6 ± 4.0 kg and 5.98 ± 0.84 kg/m2 in females and 30.6 ± 7.5 kg and 7.21 ± 0.94 kg/m2 in males, respectively; the grip strength and aRSMI were not associated with each other (P = .083). Ten females (25%) and 10 males (56%) met the criteria for sarcopenia. The postoperative abduction shoulder strength and Constant-Murley shoulder score increased significantly with higher preoperative grip strength (R = 0.420 and P = .001; and R = 0.497 and P < .001, respectively) and the American Shoulder and Elbow Surgeons score was related to the preoperative aRSMI (R = 0.320, P = .039).

CONCLUSIONS

The shoulder strength and functional score after RSA correlated positively with the preoperative grip strength. Measuring grip strength before RSA allows the surgeon to predict shoulder strength after RSA.

The influence of preoperative rotator cuff cross-sectional area and strength on postoperative outcomes in reverse shoulder arthroplasty

BACKGROUND

Although preoperative function and range of motion (ROM) are determinants of postoperative outcome following reverse shoulder arthroplasty (RSA), there is limited data on the influence of preoperative rotator cuff status. The purpose of this study was to evaluate the relationship between preoperative rotator cuff physiologic cross-sectional area (PCSA) and strength on postoperative RSA outcome.

METHODS

A retrospective review was conducted on 53 primary RSAs from a multicenter database performed between 2015 and 2019 using a 135° humeral neck-shaft angle. Preoperative magnetic resonance imaging and computed tomographic scans were used to assess the PCSA of the subscapularis, supraspinatus, infraspinatus, and teres minor. American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form (ASES) scores, ROM, and strength were measured preoperatively and at a minimum of 2 years postoperatively. Correlation coefficients were used to determine the relationship between variables.

RESULTS

There were no significant correlations between preoperative PCSA of any rotator cuff muscles and postoperative ASES scores. Preoperative subscapularis PCSA positively correlated with change in belly press (BP) strength following RSA (⍴ = 0.37, P = .006). Preoperative abduction strength was significantly correlated with postoperative abduction strength (⍴ = 0.297, P = .006). Preoperative external rotation (ER) strength was significantly correlated with postoperative ER (⍴ = 0.378, P = .005) and abduction (⍴ = 0.304; P = .032) strength. Preoperative BP strength negatively correlated with postoperative ASES (⍴ = -0.283, P = .042) but positively correlated with postoperative BP (⍴ = 0.411, P = .001) and abduction (⍴ = 0.367, P = .009) strength.

CONCLUSION

With the use of a 135° humeral implant, there is limited correlation between preoperative PCSA and postoperative outcomes 2 years following RSA; the only significant correlation was between preoperative subscapularis PCSA and postoperative BP strength. Preoperative strength is positively correlated with postoperative strength but not ROM or ASES scores.

Effects of neuromuscular electrical muscle stimulation on the deltoid for shoulder function restoration after reverse total shoulder arthroplasty in the early recovery period: a prospective randomized study

INTRODUCTION

Neuromuscular electrical stimulation (NMES) is a treatment modality that has been used to accelerate the rehabilitation of patients with neurological damage. However, it is unclear whether NMES of the deltoid can lead to the early restoration of shoulder function after reverse total shoulder arthroplasty (RSA).

MATERIALS AND METHODS

In this prospective and randomized study, 88 patients who underwent RSA with the same prosthesis design for cuff tear arthropathy or irreparable rotator cuff tear were assessed. The patients were divided into two groups (NMES group and non-NMES group, 44 patients each). For the NMES group, two pads of the NMES device were placed over the middle and posterior deltoid area, and NMES was maintained for 1 month after surgery. Shoulder functional outcomes and deltoid thickness were compared at 3, 6, and 12 months postoperatively. Shoulder functional outcomes were assessed based on the visual analog scale (VAS) for pain, American Shoulder and Elbow Surgeons (ASES), and Constant scores and the range of motion (ROM) and power of the affected shoulder. The thickness of the anterior, middle, and posterior deltoid was measured by ultrasonography.

RESULTS

A total of 76 patients (NMES group, 33 patients; non-NMES group, 43 patients) were enrolled in the final analysis. The preoperative demographics and status of the remaining rotator cuff of both groups were not significantly different. At postoperative 3 months, the ROM and power of external rotation of the NMES group were significantly greater than those of the non-NMES group (ROM, 36° ± 14° vs. 29° ± 12°; P = .003; power, 4.8 kg ± 1.8 kg vs. 3.8 kg ± 1.0 kg; P < .002). The ROM of external rotation of the NMES group at postoperative 6 months was also greater than that of the non-NMES group (41° ± 12° vs. 34° ± 11°; P = .013). However, there was no significant difference in the VAS, ASES, and Constant scores at all follow-up points despite gradual improvements until 1 year postoperatively. Serial measurements of the thickness of the anterior, middle, and posterior deltoid of both groups did not show significant differences.

CONCLUSIONS

Postoperative NMES of the deltoid after RSA contributed to significantly faster ROM restoration and considerable improvement in the power of external rotation. Therefore, NMES following RSA could lead to the early restoration of external rotation and recovery of deltoid function.

Association Between Preoperative Shoulder Strength and Clinical Outcomes After Primary Reverse Total Shoulder Arthroplasty

INTRODUCTION

We aimed to determine whether preoperative shoulder strength predicts postoperative values and improvement in strength, range of motion (ROM), and outcome scores after primary reverse total shoulder arthroplasty (rTSA).

METHODS

We retrospectively reviewed 264 shoulders with a minimum of 2-year follow-up after primary rTSA. Preoperative external rotation (ER) strength, supraspinatus strength, and abduction strength were analyzed to establish their correlation with postoperative values and improvement in strength, ROM, and outcome scores (Constant score, American Shoulder and Elbow Surgeons Shoulder score, Shoulder Pain and Disability Index, Simple Shoulder Test, and the University of California, Los Angeles score). Multiple linear regression models were used to identify the preoperative shoulder strength measures that most affected postoperative outcomes and improvement in outcomes.

RESULTS

Preoperative measures of shoulder strength were positively correlated with all measures of postoperative shoulder strength, active abduction and elevation, and all outcome scores studied. On multivariate analysis, greater preoperative ER, supraspinatus, and abduction strength were significantly associated with greater corresponding postoperative values (P = 0.009, P = 0.041, and P = 0.008, respectively); however, they were also associated with less respective improvement (P < 0.001 for all) because the weakest patients tended to see the largest improvements. Notably, preoperative values of ER and supraspinatus strength exceeding 17.5 and 20.5 lbs were associated with a decline in their respective values postoperatively, but no limit was identified for ROM or outcome score measures. On multivariate analysis, reduced preoperative abduction strength was markedly associated with greater improvement in 3 of 4 ROM measures and 4 of 5 outcome scores.

CONCLUSION

Preoperative shoulder strength, especially abduction strength, predicts superior postoperative outcomes and greater improvement in shoulder strength, ROM, and outcome scores after primary rTSA. However, a minority of patients with well-preserved strength may lose strength after surgery, and patients who are weaker preoperatively tend to see larger improvements in postoperative outcomes.

LEVEL OF EVIDENCE

Ⅳ, prognostic study.

Maximizing Muscle Function in Cuff-Deficient Shoulders: A Rehabilitation Proposal for Reverse Arthroplasty

Purpose

The purpose of this review is to describe the role of altered joint biomechanics in reverse shoulder arthroplasty and to propose a rehabilitation protocol for a cuff-deficient glenohumeral joint based on the current evidence.Methods and Materials: The proposed rehabilitation incorporates the principles of pertinent muscle loading while considering risk factors and surgical complications.

Results

In light of altered function of shoulder muscles in reverse arthroplasty, scapular plane abduction should be more often utilized as it better activates deltoid, teres minor, upper trapezius, and serratus anterior. Given the absence of supraspinatus and infraspinatus and reduction of external rotation moment arm of the deltoid in reverse arthroplasty, significant recovery of external rotation may not occur, although an intact teres minor may assist external rotation in the elevated position.

Conclusion

Improving the efficiency of deltoid function before and after reverse shoulder arthroplasty is a key factor in the rehabilitation of the cuff deficient shoulders. Performing exercises in scapular plane and higher abduction angles activates deltoid and other important muscles more efficiently and optimizes surgical outcomes.

Analysis of the coaptation role of the deltoid in reverse shoulder arthroplasty. A preliminary biomechanical study

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 3D models), first without lateralization and then with simulated lateralization of 6, 9 and 12mm. This static model enables to compute a Coaptation/Elevation Ratio and to measure the Deltoid’s Moment Arm. The inter- and intra-rater agreement of the 3D models was evaluated.

Results

One patient was excluded due to motion during imaging. The inter- and intra-rater agreement was over 0.99. The ratio increased starting at 6 mm of lateralization (p<0.05), compared to the initial position. The moment arm was not affected by lateralization (p<0.05), except in two slices starting at 9 mm (S1 p<0.05 and S2 p<0.05).

Conclusion

Our hypothesis that the Middle Deltoid’s coaptation role would be greater with glenosphere lateralization was confirmed. This trend was not found in the moment arm, which showed little sensitivity to lateralization. The stabilizing effect therefore appears to stem from the coaptation role of the Middle Deltoid.

Electromyographic and kinematic study of reverse total shoulder arthroplasty: an observational prospective cohort study

BACKGROUND

Reverse total shoulder arthroplasty (RTSA) procedures have significantly increased in the last decade as an alternative to the current treatments for cuff-tear arthropathy. Since Grammont's theory in 1987, few data about the in vivo kinetics of the shoulder-girdle musculature in patients with RTSA have been available. The goals of this study are to (1) describe the contribution of principal muscles around the shoulder by electromyography and (2) access the range of motion of 5 movements of patients with RTSA compared with normal shoulders.

METHODS

This is an observational prospective cohort study of 21 patients divided into 11 patients with RTSA and 10 controls. The muscular activity was recorded with bipolar cutaneous electrodes, whereas the range of motion was synchronized and recorded by 8 motion cameras. Five movements (flexion, abduction, neutral external rotation, external rotation in 90° of abduction, and internal rotation in 90° of abduction) were studied.

RESULTS

The upper trapezius is the main activator in all directions with early and constant activity (P < .01). The latissimus dorsi demonstrates increased muscular activity in internal rotation (P < .01) as well as the posterior deltoid in external rotation in the RTSA group compared with control (P < .01).

CONCLUSION

RTSA shoulder muscle activation is significantly different than in normal shoulders. The significant contribution of the trapezius in all directions, latissimus dorsi in internal rotation, and posterior deltoid in external rotation has never been described within the same study until today. New rehabilitation protocols targeting those muscles could demonstrate better and more homogeneous results and increase patient satisfaction.

Reversed shoulder arthroplasty leads to significant histological changes of the deltoid muscle: a prospective intervention trial

INTRODUCTION

Reverse shoulder arthroplasty (RSA) shows promising short- and mid-term results in cuff tear arthropathy. However, functional impairments are described in long-term findings. Micromorphological changes in the periarticular musculature could be in part responsible for this, but have not yet been analysed. Thus, histological changes of the deltoid muscle and their association to the functional outcome were evaluated in this study.

MATERIAL AND METHODS

A total of 15 patients treated with RSA were included in this prospective study. Functional outcome was assessed using the Constant Score (CS) and the DASH (disabilities of the arm, shoulder and hand) Score before RSA and after a mean follow-up of 12 months. Deltoid muscle biopsies were harvested intraoperatively and 12 months postoperatively. Mean deltoid muscle fibre area (MMFA) was calculated histologically after haematoxylin-eosin staining.

RESULTS

Postoperative shoulder function significantly improved within 12 months (CS: Δ 37.4 ± 22.6, p = 0.001; DASH: Δ 27.1 ± 29.1, p = 0.006). The MMFA significantly decreased (p = 0.02), comparing the results from the intraoperative biopsy (MMFA: 8435.8 µm², SD ± 5995.9 µm²) to the 12 months biopsy (MMFA: 5792. µm², SD ± 3223.6 µm²). No correlation could be found between the functional score results and MMFA.

CONCLUSION

Signs of deltoid muscle changes in terms of a reduced MMFA can be detected 1 year after RSA and thus already a long time before long-term functional impairments become apparent. Further studies with larger patient series and longer follow-up periods as well as extended histological assessments and simultaneous radiological examinations are required.

Conversion to reverse shoulder arthroplasty fifty-one years after shoulder arthrodesis: A case report

BACKGROUND

Patients with a shoulder arthrodesis generally experience restriction in range of motion and limitations in activities of daily living. In addition, up to one-third of the patients deals with serious peri scapular pain. The conversion of a shoulder arthrodesis in a reverse shoulder arthroplasty (RSA) has been described as an effective treatment to achieve better function and decreased pain, although literature is sparse. We present the case of a conversion from a painful shoulder arthrodesis to RSA, after a 51 years interval.

CASE SUMMARY

A 71-year-old male presented with severe peri scapular pain and limited function 51 years after shoulder arthrodesis. Preoperative workup showed a normal bone stock of the glenoid and an intact axillary nerve, but atrophic posterior part of the deltoid muscle. The shoulder arthrodesis was successfully converted to RSA. Twelve months postoperative the patient was very satisfied. He has no pain at rest, nor with exercise and experienced definite improvements in activities of daily living, despite his limited range of motion.

CONCLUSION

Conversion from shoulder arthrodesis to a RSA can be performed safely, with a high chance of peri scapular pain relief; even after a longstanding arthrodesis.

Shoulder Muscle Strength and Neuromuscular Activation 2 Years after Reverse Shoulder Prosthesis-An Experimental Case Control Study

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 < 0.05). Antagonist deltoid coactivation was higher on the operated side for external rotation (p < 0.001). Large correlation coefficients were observed between shoulder adductor strength asymmetry and both center-of-rotation medialization (r = −0.73) and humerus lengthening (r = 0.71). Shoulder abduction strength and neuromuscular activation were well preserved 2 years after RSA, while persistent strength and activation deficits were observed for shoulder adduction and internal and external rotation. Additional studies are required to elucidate shoulder neuromuscular activation patterns before and after RSA to support decision making for surgical, implant design, and rehabilitation choices.