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

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.

The effect of pathological shoulder rhythm on muscle and joint forces after reverse shoulder arthroplasty, a numerical analysis

BACKGROUND

Compromised abduction ability after reverse shoulder arthroplasty is primarily linked to limited glenohumeral range of motion while scapulothoracic mobility can typically be maintained. Glenohumeral joint forces strongly depend on the resulting scapulohumeral rhythm, however, an association between the acting muscle and joint forces and the subject-specific scapulohumeral rhythm after reverse shoulder arthroplasty has not been established.

METHODS

Eleven reverse shoulder arthroplasty patients were divided into groups of poor and excellent abduction ability. Subject-specific models were developed and scaled for each patient using existing motion capture data in AnyBody™. Shoulder muscle and joint forces were obtained using inverse dynamics calculations during shoulder abduction to 100° in the scapula plane. The scapulohumeral rhythm, the resting abduction angle and internal body forces between the outcome groups were compared using a Mann Whitney U test.

FINDINGS

The mean glenohumeral and scapulothoracic contribution to overall shoulder abduction for the excellent group was on average 9.7% higher and 21.4% lower, respectively, compared to the mean of the poor group. For shoulder abduction angles between 30° and 60°, the excellent group demonstrated on average 25% higher muscle forces in the anterior deltoid which was significantly higher compared to the poor outcome patients. Scapulothoracic muscle activity did not differ significantly between the two functional groups.

INTERPRETATION

Accordingly, rehabilitation strategies focusing on strengthening the anterior part of the deltoid in particular may improve clinical outcomes.

High and low performers in internal rotation after reverse total shoulder arthroplasty: a biplane fluoroscopic study

BACKGROUND

Internal rotation in adduction is often limited after reverse total shoulder arthroplasty (rTSA), but the origins of this functional deficit are unclear. Few studies have directly compared individuals who can and cannot perform internal rotation in adduction. Little data on underlying 3D humerothoracic, scapulothoracic, and glenohumeral joint relationships in these patients are available.

METHODS

Individuals >1-year postoperative to rTSA were imaged with biplane fluoroscopy in resting neutral and internal rotation in adduction poses. Subjects could either perform internal rotation in adduction with their hand at T12 or higher (high, N = 7), or below the hip pocket (low, N = 8). Demographics, the American Shoulder and Elbow Surgeons score, Simple Shoulder Test, and scapular notching grade were recorded. Joint orientation angles were derived from model-based markerless tracking of the scapula and humerus relative to the torso. The 3D implant models were aligned to preoperative computed tomography models to evaluate bone-implant impingement.

RESULTS

The Simple Shoulder Test was highest in the high group (11 ± 1 vs. 9 ± 2, P = .019). Two subjects per group had scapular notching (grades 1 and 2), and 3 high group and 4 low group subjects had impingement below the glenoid. In the neutral pose, the scapula had 7° more upward rotation in the high group (P = .100), and the low group demonstrated 9° more posterior tilt (P = .017) and 14° more glenohumeral elevation (P = .047). In the internal rotation pose, axial rotation was >45° higher in the high group (P ≤ .008) and the low group again had 11° more glenohumeral elevation (P = .058). Large rotational differences within subject groups arose from a combination of differences in the resting neutral and maximum internal rotation in adduction poses, not only the terminal arm position.

CONCLUSIONS

Individuals who were able to perform high internal rotation in adduction after rTSA demonstrated differences in joint orientation and anatomic biases versus patients with low internal rotation. The high rotation group had 7° more resting scapular upward rotation and used a 15°-30° change in scapular tilt to perform internal rotation in adduction versus patients in the low group. The combination of altered resting scapular posture and restricted scapulothoracic range of motion could prohibit glenohumeral rotation required to reach internal rotation in adduction. In addition, inter-patient variation in humeral torsion may contribute substantially to postoperative internal rotation differences. These data point toward modifiable implant design and placement factors, as well as foci for physical therapy to strengthen and mobilize the scapula and glenohumeral joint in response to rTSA surgery.

Optimizing Outcomes After Reverse Total Shoulder Arthroplasty: Rehabilitation, Expected Outcomes, and Maximizing Return to Activities

PURPOSE OF REVIEW

Given the touted clinical and patient-reported outcomes of reverse shoulder arthroplasty (RTSA) in improving pain and restoring function, shoulder surgeons are rapidly expanding the indications and utilization of RTSA. Despite its increasing use, the ideal post-operative management ensuring the best patient outcomes is still debated. This review synthesizes the current literature regarding the impact of post-operative immobilization and rehabilitation on clinical outcomes following RTSA including return to sport.

RECENT FINDINGS

Literature regarding the various facets of post-operative rehabilitation is heterogeneous in both methodology and quality. While most surgeons recommend 4-6 weeks of immobilization post-operatively, two recent prospective studies have shown that early motion following RTSA is both safe and effective with low complication rates and significant improvements in patient-reported outcome scores. Furthermore, no studies currently exist assessing the use of home-based therapy following RTSA. However, there is an ongoing prospective, randomized control trial assessing patient-reported and clinical outcomes which will help shed light on the clinical and economic value of home therapy. Finally, surgeons have varying opinions regarding return to higher level activities following RTSA. Despite no clear consensus, there is growing evidence that elderly patients are able to return to sport (e.g., golf, tennis) safely, though caution must be taken with younger or more high-functioning patients. While post-operative rehabilitation is believed to be essential to maximize outcomes following RTSA, there is a paucity of high-quality evidence that guides current rehabilitation protocols. There is no consensus regarding type of immobilization, timing of rehabilitation, or need for formal therapist-directed rehabilitation versus physician-guided home exercise. Additionally, surgeons have varied opinions regarding return to higher level activities and sports following RTSA. There is burgeoning evidence that elderly patients can return to sport safely, though caution must be taken with younger patients. Further research is needed to clarify the optimal rehabilitation protocols and return to sport guidelines.

Comparison of Clinical Performance of Inlay versus Onlay Humerus Implants in Reverse Total Shoulder Arthroplasty

Background

Reverse total shoulder arthroplasty (RTSA) has become the treatment of choice for the management of massive rotator cuff tears combined with cuff tear arthropathy, and many novel designs have been proposed to overcome the shortcomings of classic RTSA. This study sought to evaluate and compare RTSA outcomes among patients with cuff tear arthropathy treated by a medialized inlay humerus implant with a neck shaft angle of 155° or a lateralized onlay implant with a neck shaft angle of 145°.

Methods

A retrospective review of 32 inlay implants and 32 onlay implants was performed. The active range of motion (ROM), visual analog scale (VAS) for pain, motor power for elevation and external rotation, and functional scores including the American Shoulder and Elbow Surgeons score, Constant score, and Korean Shoulder Scoring system were assessed before surgery, at 3, 6, and 12 months after surgery, and at the last follow-up at least 24 months after surgery. Scapular notching, lateral humeral offset, and deltoid wrapping offset were assessed for radiographic evaluation.

Results

The preoperative demographic data of both groups showed no significant differences (p > 0.05). The mean follow-up period was 24.9 months. Significant improvements in forward flexion, functional scores, and pain VAS score were observed in both groups at the last follow-up. No significant differences in ROM or functional scores were found between two groups at each time point, except that the onlay implant group exhibited a significantly greater range of external rotation at 3 and 12 months after surgery and at the last follow-up. The rate of scapular notching and the final power improvement did not show significant differences between the groups.

Conclusions

Primary RTSA using inlay or onlay humerus implants was associated with recovery from pseudoparalysis and good clinical outcomes. However, RTSA with onlay humerus implantation led to clinically superior results in terms of external rotation.

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.

Can you maintain a competitive golf swing after total shoulder arthroplasty?

PURPOSE

Return to sports after joint arthroplasty is mainly evaluated for lower limbs procedures. When a return to a specific sport is mentioned, no technical approach nor level consideration are specified. We suggested that patients who undergo total shoulder arthroplasty will be able to maintain playing golf at same high level.

METHODS

We performed a retrospective study on active golf players who have undergone shoulder arthroplasty. Inclusion criteria were: (1) over 50 years old (2) handicap < 54 (3) playing golf before the procedure (4) minimum follow-up of 1 year. Patients were divided into two groups: ASA group and RSA Group. A clinical assessment was performed using the following scores: Constant, ASES and QuickDash.

RESULTS

Sixty-one patients were retrospectively included in the cohort. Mean age was 69.1 years old. Mean follow-up was 79 months. Preoperative golf frequency and handicap were similar between the two groups. Surgery resulted in significant pain relief in both groups. No difference was shown between the two groups in clinical assessment. Satisfaction rate was 95%. Return to golf time was done progressively from the twentieth week for putting until the twenty-seventh week for playing on the course. Handicap analysis did not show any difference between the level before surgery and the current level in ASA group (23.7 vs. 22.9,p = 0.33) and RSA group (24.2 vs. 23.3,p = 0.63).

CONCLUSION

Our study suggested that both patients with ASA or RSA can maintain an active lifestyle with moderate to high frequencies of participation after surgery, particularly in golf. Surgeons can reassure their patients about their recovery and show confidence with regard to their ability to return to a similar golf practice also after RSA. Prospective study with larger cohort is required to confirm the results.

LEVEL OF EVIDENCE

Level IV, cases study.

Comparison of Lateralized Versus Medialized Reverse Total Shoulder Arthroplasty: A Systematic Review and Meta-analysis

Background:

Reverse total shoulder arthroplasty (rTSA) is an established procedure for cuff tear arthropathy. More lateralized prostheses have been designed to overcome the reported adverse outcomes of Grammont-style rTSA.

Purpose:

To compare the clinical and radiological outcomes of medialized and lateralized center of rotation (COR) in rTSA.

Study Design:

Systematic review; Level of evidence, 3.

Methods:

This review followed the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Included were studies with a level of evidence ≥3 that compared medialized and lateralized rTSA with a minimum follow-up of 12 months. Functional scores including the American Shoulder and Elbow Surgeons (ASES) score and Constant score (CSS), range of motion at final follow-up, gain of external rotation (ER), visual analog scale (VAS) pain score, scapular notching, and heterotopic ossification (HO) were compared. Data were analyzed using random-effects or fixed-effects models in accordance with heterogeneity.

Results:

Five retrospective cohort studies and 1 randomized controlled study (n = 594 patients) were included. Lateralized rTSA resulted in greater improvement in ER degree (P < .001), a lower VAS pain score (standardized mean difference [SMD], –0.39; P = .002), and a lower rate of scapular notching (risk ratio [RR], 0.40; P < .001) and HO (RR, 0.52; P < .001). Final forward flexion (SMD, –0.14; P = .629) and ER (SMD, 0.21; P = .238) did not differ significantly between the 2 groups. Overall functional scores, including ASES score (SMD, 0.22; P = .310) and CSS (SMD, 0.37; P = .077), also did not differ significantly (SMD, 0.28; P = .062). The overall complication rate did not differ significantly between the 2 groups (RR, 0.71; P = .339).

Conclusion:

Compared with medialized rTSA, lateralized COR rTSA results in greater improvement in ER and the VAS pain score, decreased rates of scapular notching and HO, and no significant changes in functional outcome scores or the complication rate.