Differences in Muscle Activities of the Infraspinatus and Posterior Deltoid during Shoulder External Rotation in Open Kinetic Chain and Closed Kinetic Chain Exercises

Which muscle is the external rotation compensator after superior capsular reconstruction?

Background

Superior capsular reconstruction (SCR) is a surgical option for massive irreparable rotator cuff tears, particularly involving the supraspinatus and infraspinatus. In this procedure, the torn infraspinatus is not repaired or reconstructed. However, an improvement in postoperative external rotation (ER) angle and strength is observed. There is a lack of studies explaining how ER is restored after SCR. The aim of this study is to identify the ER compensator by assessing the muscle volume of the posterior deltoid and teres minor.

Methods

Sixty-eight patients with massive rotator cuff tears underwent SCR during 2016-2021. Of these patients, 28 who met the following inclusion criteria were retrospectively reviewed: (1) massive rotator cuff tears, including the supraspinatus and infraspinatus, (2) severe muscle atrophy and fatty change, (3) intact or reparable subscapularis tendon, and (4) Hamada of grade 3 or lower. Posterior deltoid and teres minor volume were measured using open-source medical image processing software preoperatively and 1-year postoperatively. The percentage of the posterior deltoid and teres minor muscle volume change was compared between patients with 1-year postoperative ER manual muscle testing (MMT) of grade 5 and of grade < 5. The relationship between grade of fatty change, percentage of the muscle volume change, and ER angle and strength were evaluated.

Results

There was a significant increase in the 1-year postoperative teres minor volume compared with the preoperative volume (24.6 ± 10.3 cm³ vs. 20.9 ± 8.3 cm³, P < .000), while the posterior deltoid volume remained unchanged (178.1 ± 48.3 cm³ vs. 178.8 ± 47 cm³). Patients with ER MMT of grade 5 had a greater teres minor volume change compared to those with an ER MMT grade of less than 5 (22.3% vs. 9.4%), although this difference was not significant (P = .074, 95% CI = -1.3 to 27.0). The posterior deltoid volume showed no significant change. The percentage of teres minor volume change had a weak positive correlation with ER strength (r = 0.308, P = .055, 95% CI = -0.02 to 1.0). There was a significant negative correlation between ER strength and the severity of both preoperative and postoperative fatty changes in the teres minor (r = -0.258, P = .065, 95% CI = -1.0 to -0.042 and r = -0.323, P = .028, 95% CI = -1.0 to -0.113, respectively). The pre and postoperative fatty changes in the teres minor were negatively correlated with the percentage of teres minor volume change (r = -0.298, P = .062, 95% CI = -1.0 to 0.031 and r = -0.413, P = .015, 95% CI = -1.0 to -0.1, respectively).

Conclusion

The teres minor may serve as a potential compensator for ER in patients with massive rotator cuff tears following SCR.

The Effects of Body Positions and Abduction Angles on Shoulder Muscle Activity Patterns during External Rotation Exercises

BACKGROUND

Excess and repetitive glenohumeral external rotation (ER) is at a higher risk for shoulder injuries, which occurs frequently in professional sports and specific occupations. Current rehabilitation programs emphasize selective targeting of muscle activity, which can help restore dysfunctional muscle imbalances or prevent injuries. However, the impact of different body postures on GH muscle activity during ER exercises has not been fully understood. Therefore, the purpose of this study was to investigate shoulder EMG activity for different body positions and humeral abduction angles during ER exercises.

METHOD

Twenty-three healthy young men (age: 22.3 ± 2.3, height: 175.75 ± 4.02, mass: 75.37 ± 9.14) participated in this study. Surface Electromyography was recorded from seven shoulder muscles: upper trapezius, lower trapezius, serratus anterior, infraspinatus, and deltoid. Six ER exercises: three postures (sitting, supine lying, and prone lying) and two abduction angles (ABD; 45° and 90°) were tested using an isokinetic dynamometer.

RESULTS

During a sitting position, the lower trapezius/upper trapezius muscle activity ratios were significantly increased for sitting compared to supine lying and prone lying (p < 0.001, p = 0.004). Serratus anterior/upper trapezius co-contraction indices were significantly increased for 90° than 45° ABD (p < 0.001).

CONCLUSION

These findings can provide insight into new training programs aimed at restoring GH muscle imbalances.

A Comparison of Resting Scapular Posture and the Davies Closed Kinetic Chain Upper Extremity Stability Test

BACKGROUND

In orthopaedic practice, it is well established that weak scapular stabilizers and an unstable scapula is related to shoulder dysfunction. Faulty scapular position has been linked to decreased scapular stability and is thought to be a result of weak or unbalanced timing in the recruitment of scapulothoracic dynamic stabilizing muscles. Kibler has described a four-type classification of scapulothoracic dysfunction. Functional performance testing is used to objectively measure activities that simulate various desired activities. The reliability of assessing the four static scapular positions may be important in diagnosing shoulder dysfunction. An understanding of the scapular position and its relationship to functional performance testing is needed.

PURPOSE

The purpose of this study was to determine if a static scapular test, the Kibler scapula classification, in healthy participants affects the ability to perform a closed chain functional test that involves the use of the scapula and the upper extremity, the Davies Closed Kinetic Chain Upper Extremity Stability Test (CKCUEST). A secondary analysis was performed to evaluate the reliability of a student physical therapist and an experienced physical therapist to identify scapular type by observation.

STUDY DESIGN

Multicenter, single session descriptive cohort.

METHODS

Sixty-one healthy participants (33 males, 28 females; mean age 24.19±2.61) completed testing across two locations in one testing session. Blood pressure and heart rate as well as height and weight were measured for each participant. Participants were classified by visual observation of Kibler scapular classification. The average number of CKUEST touches, a normalized score, and a power score were calculated for each participant. Three trials were performed and participants were required to take a 45-second rest break between each CKCUEST trial.

RESULTS

One way analysis of variance (ANOVA) showed statistically significant differences in Type I and Type IV Kibler scapula classification for the CKCUEST power score, however when an ANCOVA controlled for body mass index, there was no statistically significant difference. A strong correlation r=.94 was observed between student and experienced physical therapist in evaluating all four types of Kibler scapular classification.

CONCLUSIONS

Visually observed Kibler scapular position does not affect the ability to perform the Davies CKCUEST in healthy young adults. The ability to identify Kibler scapular position was reliable between student and experienced physical therapists. Additional studies are required to identify the usefulness of the Kibler scapular position classification.

LEVEL OF EVIDENCE

2b: Individual Cohort Study.

REHABILITATION FOLLOWING DISTAL BICEPS REPAIR

BACKGROUND AND PURPOSE

Distal biceps rupture is less common than injury to the proximal biceps; however, injury distally has profound functional implications on activities which rely on power during elbow flexion and forearm supination. The majority of distal biceps ruptures can be treated with surgical repair of the distal biceps utilizing either a single or two-incision technique; both of which achieve comparable improved outcomes and reported minimal pain and disability at two years. Safe and effective rehabilitation following distal biceps repair is accomplished through a phased progression, with avoidance of premature stress to the healing soft tissue repair.The purpose of this clinical commentary is to provide a concise review of distal biceps tendon injury, including relevant anatomy, etiology, diagnosis, and operative intervention as well as post-operative factors influencing the pursuit of a criterion based, progressive rehabilitation program after distal biceps tendon repair. This commentary seeks to provide an update on current treatment strategies used in distal biceps rehabilitation with accompanying scientific rationale.

LEVEL OF EVIDENCE

5.

Rehabilitation Following Sternoclavicular Joint Reconstruction for Persistent Instability

BACKGROUND

Sternoclavicular (SC) joint instability is a rare injury, but one with profound implications given its proximity to vital structures and function as the only true articulation between the upper extremity and axial skeleton. The majority of SC joint instability can be treated non-operatively; however, there is a role for reconstruction in the presence of instability that results in pain and dysfunction that is refractory to conservative management or deformity resulting in functional impairment. Given the lack of inherent osseous stability at the sternoclavicular joint and the role of ligaments as primary stabilizers, surgical intervention with emphasis on ligament reconstruction may be recommended. Safe and effective rehabilitation is conducted through phase progression, with avoidance of premature stress to the healing soft tissue graft. The purpose of this clinical commentary is to provide the senior author's rehabilitation protocol, which utilizes the available scientific literature to inform phase content and progression.

LEVEL OF EVIDENCE

5.

Infraspinatus Isolation During External Rotation Exercise at Varying Degrees of Abduction

CONTEXT

External rotation (ER) strengthening exercises are a common component of shoulder injury prevention and rehabilitation programs. They are primarily intended to target the infraspinatus muscle, based on its role in glenohumeral stabilization and inferior humeral glide. ER also recruits the posterior deltoid, which can be undesirable due to its role in subacromial space narrowing.

OBJECTIVE

To determine the angle of humeral abduction that maximizes the infraspinatus to posterior deltoid activation ratio (INFRA/PD) during ER.

DESIGN

Within-subjects repeated-measures controlled lab trial.

PARTICIPANTS

A total of 10 healthy participants (5 males, 5 females) aged 21 (0.67) years participated in the study.

INTERVENTION

7 consecutive repetitions of ER at 7 different abduction angles ranging from 0° to 90°, with resistance normalized to 3% body mass.

MAIN OUTCOME MEASURES

Surface electromyography was performed on the infraspinatus, middle deltoid, and posterior deltoid. Surface electromyography data were processed to determine absolute muscle activation as well as INFRA/PD at each abduction angle. Group means were compared between abduction angles using 1-way analysis of variance.

RESULTS

Abduction significantly reduced overall infraspinatus activity but increased posterior deltoid activity (P < .01). Average and peak INFRA/PD decreased as the angle of abduction increased (P < .001 and P < .01, respectively).

CONCLUSION

Our findings suggest that ER should be performed in 0° of abduction to maximize infraspinatus isolation. Slight abduction, such as placing a towel under the humerus, as recommended by some clinicians, may improve patient comfort, but did not increase infraspinatus isolation in this study.

Effect of axial shoulder external rotation exercise in side-lying using visual feedback on shoulder external rotators

[Purpose] This study aimed to determine effectiveness of axial side-lying wiper exercise using the visual feedback with a laser pointer on infraspinatus and posterior deltoid muscles. [Subjects and Methods] The subjects were 22 healthy adults (18 males, 4 females) in their 20s who consented to participate in the present study. Surface Electromyography was used to measure the infraspinatus and posterior deltoid muscle activity before and after an intervention. The intervention consisted of performing side-lying wiper exercise with a 1-kg dumbbell and a ruled paper for 30 minutes. [Results] The infraspinatus illustrated significantly increased muscle activity after intervention. The posterior deltoid also showed increased activity after intervention but it was not significant. [Conclusion] Axial side-lying wiper exercise using the visual feedback has the therapeutic effectiveness for the selective infraspinatus muscle strengthening. Therefore it can be useful to provide shoulder movements with stability.

Effects of kinetic chain exercise using EMG-biofeedback on balance and lower extremity muscle activation in stroke patients

[Purpose] The purpose of this study was to examine the effect of kinetic chain exercise using EMG-biofeedback on balance and lower extremity muscle activation. [Subjects and Methods] For this study, 30 stroke patients participated in this study and they were divided into closed kinetic chain exercise using EMG-biofeedback group (CKCE+EB) and open kinetic chain exercise using EMG-biofeedback group (OKCE+EB), each group consisting of 15 patients. The kinetic chain exercise using EMG-biofeedback was performed by the patients for 20 minutes once a day, 5 days a week, for 6 weeks using an Myo-Ex. BioRescue was used to measure balance ability, while surface EMG was used to measure the lower extremity muscle activation. [Results] According to the results of the comparison within the groups, after the intervention, both groups showed significant increases in the balance ability and lower extremity muscle activation. In the comparisons between the groups, after the intervention, balance ability and lower extremity muscle activation were significantly higher in the CKCE+BE than in the OKCE+EB. [Conclusion] This study showed that closed kinetic chain exercise using EMG-biofeedback is effective for improving balance ability and lower extremity muscle activation in stroke patients.

Changes in the electromyographic activities of the infraspinatus and posterior deltoid according to abduction angles of the shoulder joint during shoulder external rotation in closed kinetic chain exercise

[Purpose] This study's purpose was to identify abduction angles of the shoulder joint that can provide effective infraspinatus muscle exercises while minimizing the muscle activity of the posterior deltoid muscle. [Subjects and Methods] The subjects of this study were 15 healthy young students in their 20s. Subjects adopted a standing position and performed shoulder external abduction while pushing their hands against the wall. The current research was undertaken to compare the activity of the infraspinatus muscle and the posterior deltoid muscle at abduction angles of 45, 90 and 135° of the shoulder joint during closed kinetic chain exercises. [Results] A activity of the infraspinatus muscle showed no statistically significant differences. The activities of posterior deltoid muscle were greater at the angle of 45° than at 90 and 135°. [Conclusion] These results indicate that to strengthen the infraspinatus, shoulder external rotation exercises at abduction angles of the shoulder joint greater than 45° are more effective.

The effect of exercise types for rotator cuff repair patients on activities of shoulder muscles and upper limb disability

[Purpose] This study investigated the effect on activities, shoulder muscle fatigue, upper limb disability of two exercise types performed by patients in the post- immobilization period of rotator cuff repair. [Subjects and Methods] The intervention program was performed by 20 patients from 6 weeks after rotator cuff repair. Ten subjects each were randomly allocated to a group performing open kinetic chain exercise and a group preforming closed kinetic chain exercise. Muscle activity and median frequency were measured by using sEMG and the Upper Extremity Function Assessment before and after conducting the intervention and changes in the results were compared. [Results] There was a significant within group increases in the activities of the shoulder muscles, except for the posterior deltoid. The median power frequencies (MFD) of the supraspinatus, infraspinatus and anterior deltoid significantly increased in the open kinetic chain exercise group, but that of the posterior deltoid decreased. There were significant differences in the changes in the upper limb disability scores of the two groups, in the shoulder muscle activities, except for that of the posterior deltoid, in the comparison of the change in the muscle activities of the two groups, and in the MDFs of all shoulder muscles. [Conclusion] The Median power frequencies of all these muscles after closed kinetic chain exercise increased indicating that muscle fatigue decreased. Therefore, research into exercise programs using closed kinetic chain exercises will be needed to establish exercise methods for reducing muscle fatigue.

The influence of various resistance loads on the ratio of activity of the external rotator muscles of the shoulder and the anterior gliding of the humeral head during external rotation exercise

[Purpose] To quantify the ratio of activation of the infraspinatus and posterior deltoid muscles and the anterior gliding motion of the humeral head during external rotation (ER) motions of the shoulder performed in prone position against different external resistance loads. [Subjects] Twenty healthy women between the ages of 20 and 30 years. [Methods] Activity ratio was quantified as the difference in the root mean square of the smoothed electromyography signal (EMG) of the posterior deltoid to the infraspinatus muscle, and anterior gliding pressure of the humeral head using a pressure biofeedback unit (PBU), for three resistance loads: 0, 1 and 2 kg. [Results] There was a significant correlation among all three variables (load, ratio, and pressure). Anterior gliding pressure correlated with the activity ratio, with activity of the posterior deltoid increasing with the magnitude of the resistance load. [Conclusion] There was a positive association between the magnitude of resistance load, activity of the posterior deltoid and anterior gliding pressure of the humeral head. The PBU could be used to facilitate the recruitment of the infraspinatus muscle at higher loads to improve glenohumeral joint stability during ER exercise against higher resistance.

Effect of exercise at light loads with manipulative resistance on infraspinatus, trapezius (upper fiber) and deltoid (middle fiber) muscle activities in shoulder joint elevation

[Purpose] To clarify rotator cuff muscular activity in the raised position of the closed kinetic chain (CKC) exercise. [Subjects] Twenty-nine cases were studied, 19 men and 10 women (average age 21.5 ±4.7 years old, average body weight 60.1 kg ±11.4). [Methods] To determine the effects of the closed kinetic chain exercise on the upper limb, we measured the surface EMG of the infraspinatus muscle, the trapezius (upper fiber) and the deltoid (middle fiber) with the arm elevated. [Results] Our results show that at an elevation angle of 150° in the scapular plane of the upper limb, with 5% body weight load, the EMG activities of the infraspinatus muscle are approximately 30% of maximum voluntary contraction (MVC). [Conclusion] The raised position of the CKC exercise is effective in physical therapy for functional recovery of the infraspinatus muscle.