Anatomic study and electromyographic analysis of the teres minor muscle

Teres Minor Muscle Atrophy: Anatomy, Patterns, and Clinical Manifestations

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Isolated teres minor atrophy has a reported incidence in the literature of 3% to 6.2%.

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There are 2 distinct muscular bundles of the teres minor that have varying degrees of atrophy. Fatty degeneration of the medial-dorsal component exceeds that of the lateral-ventral component in most cases.

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A healthy and intact teres minor muscle is of functional importance in the setting of a complete infraspinatus tear because it becomes the only external rotator of the shoulder joint.

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Clinical and functional outcomes after rotator cuff repair and reverse shoulder arthroplasty for patients with teres minor atrophy in the setting of a rotator cuff tear are still controversial.

The Use of Scapular Bone Flaps During Head-and-Neck Reconstruction: Functional, Orthopedic, and Quality of Life Analyses of Flap-Harvest-Related Deficits

ABSTRACT

The authors sought correlations between harvesting of the scapular bone tip free flap used for head-and-neck reconstruction and any shoulder function deficit, particularly at the level of the rotator cuff. The flap permits reconstruction of large and diverse regions of the head and neck, but long-term harvest morbidity has not been investigated extensively. The authors analyzed the clinical records of all patients who underwent head-and-neck reconstructions using free scapular tip flaps in our department over the past 5 years. The inclusion criteria were complete clinical and radiological documentation and follow-up for at least 12 months. Two populations, a surgical and control population, were analyzed. All patients in both populations underwent the simple shoulder test, an internationally validated self-administered test that highlights functional shoulder deficits, and 3 additional tests at orthopedic visits: the external rotation test, Patte test, and external rotation lag sign test. A head-and-neck cancer-specific questionnaire (University of Washington Quality of Life, version 4) was completed by the surgical patients. All statistical analyses were performed using Software IBM SPSS Statistics (IBM Corp., Armonk, NY).A total of 19 patients met the inclusion criteria: 11 males (57.8%) and 8 females (42.2%) of mean age 60.9 years (range 23-75 years). In addition, 20 age-and sex-matched volunteers with no history of shoulder pathology were evaluated in terms of shoulder functionality. The average score on the simple shoulder test was 10.55 in the healthy population versus 8.31 in the study population (P < 0.001); in particular, shoulder strength differed between the groups. Similarly, the orthopedic examinations revealed clinically significant differences between the controls and patients on the Patte test and external rotation lag sign test (both P < 0.001), but not the external rotation test (P > 0.001). The mean University of Washington Quality of Life was 73.39; most patients reported good quality of life (52.6%), followed by very good (15.7%).The free scapular bone tip flap is valuable for reconstruction of head-and-neck defects; the long and reliable vascular pedicle allows rapid patient mobilization. Morbidity was confined to small reductions in shoulder strength and external rotation, which do not affect quality of life.

A comparison of teres minor and infraspinatus muscle activation in the prone position

Background

Methods

Results

Conclusion

Revisiting the rotator cuff footprint

Newer studies challenged the traditionally held belief that the supraspinatus inserts on the entire superior facet and the infraspinatus is attached on the entire middle facet of the greater tuberosity. They showed that the infraspinatus tendon is thicker anteriorly and can be differentiated from the posterior part of the supraspinatus. Hence, the newer studies showed that the supraspinatus attached in a much smaller area than previously thought, and infraspinatus occupied the lateral part of the superior facet of the greater tuberosity. This review aimed to present all the older and current knowledge of the rotator cuff insertion and discuss how this knowledge may affect the surgical repair of the rotator cuff tendons. Our review has synthesized and compared the differences and similarities between the older and the newer knowledge about the footprint anatomy of the cuff tendons and the capsule attachment. We have also highlighted how the newer knowledge impacts the way we treat the tears of the rotator cuff tendons.

LEVEL OF EVIDENCE

Review of basic science studies.

Electromyography activity of the teres minor muscle with varying positions of horizontal abduction in the quadruped position

Background

The teres minor (TMi) muscle exposed relatively high activity during the acceleration and deceleration phases of the throwing motion, compared with the infraspinatus muscle. However, few studies have identified TMi muscle activity in intervention exercises. The purpose of this study was to investigate TMi muscle activities in different horizontal adduction positions in the quadruped horizontal abduction exercise. This study hypothesized that TMi muscle activity would differ in response to resistance application across different horizontal adduction positions.

Materials and methods

Nineteen collegiate baseball players volunteered their participation. Raw electromyography activity of the TMi muscle along with 7 different muscles attached to the scapula on the dominant-side were collected, and normalized by each of the corresponding maximum voluntary isometric contractions. All subjects performed manual isometric resistance horizontal abduction exercises at 90° and 135° of abduction with 3 horizontal adduction angles in the quadruped position: 1) coronal, 2) scapular, and 3) sagittal plane. Electromyography data were also collected from rhythmical concentric contraction of horizontal abduction at 90° of abduction in the quadruped position.

Results

TMi muscle activity was significantly greater with the arm positioned in the coronal plane than that of the scapular and sagittal planes (41, 26, and 17% maximum voluntary isometric contraction, respectively) (P < .05).

Conclusion

The present study demonstrated that TMi muscle activity varied depending on horizontal adduction positions.

Compensatory Movement Patterns Are Based on Abnormal Activity of the Biceps Brachii and Posterior Deltoid Muscles in Patients with Symptomatic Rotator Cuff Tears

BACKGROUND

Abnormal movement patterns due to compensatory mechanisms have been reported in patients with rotator cuff tears. The long head of the biceps tendon may especially be overactive and a source of pain and could induce abnormal muscle activation in these patients. It is still unknown why some patients with a rotator cuff tear develop complaints and others do not.

QUESTIONS/PURPOSES

(1) Which shoulder muscles show a different activation pattern on electromyography (EMG) while performing the Functional Impairment Test-Hand and Neck/Shoulder/Arm (FIT-HaNSA) in patients with a symptomatic rotator cuff tear compared with age-matched controls with an intact rotator cuff? (2) Which shoulder muscles are coactivated on EMG while performing the FIT-HaNSA?

METHODS

This comparative study included two groups of people aged 50 years and older: a group of patients with chronic symptomatic rotator cuff tears (confirmed by MRI or ultrasound with the exclusion of Patte stage 3 and massive rotator cuff tears) and a control group of volunteers without shoulder conditions. Starting January 2019, 12 patients with a chronic rotator cuff tear were consecutively recruited at the outpatient orthopaedic clinic. Eleven age-matched controls (randomly recruited by posters in the hospital) were included after assuring the absence of shoulder complaints and an intact rotator cuff on ultrasound imaging. The upper limb was examined using the FIT-HaNSA (score: 0 [worst] to 300 seconds [best]), shoulder-specific instruments, health-related quality of life, and EMG recordings of 10 shoulder girdle muscles while performing a tailored FIT-HaNSA.

RESULTS

EMG (normalized root mean square amplitudes) revealed hyperactivity of the posterior deltoid and biceps brachii muscles during the upward phase in patients with rotator cuff tears compared with controls (posterior deltoid: 111% ± 6% versus 102% ± 10%, mean difference -9 [95% confidence interval -17 to -1]; p = 0.03; biceps brachii: 118% ± 7% versus 111% ± 6%, mean difference -7 [95% CI -13 to 0]; p = 0.04), and there was decreased activity during the downward phase in patients with rotator cuff tears compared with controls (posterior deltoid: 89% ± 6% versus 98% ± 10%, mean difference 9 [95% CI 1 to 17]; p = 0.03; biceps brachii: 82% ± 7% versus 89% ± 6%, mean difference 7 [95% CI 0 to 14]; p = 0.03). The posterior deltoid functioned less in conjunction with the other deltoid muscles, and lower coactivation was seen in the remaining intact rotator cuff muscles in the rotator cuff tear group than in the control group.

CONCLUSION

Patients with a symptomatic rotator cuff tear show compensatory movement patterns based on abnormal activity of the biceps brachii and posterior deltoid muscles when compared with age-matched controls. The posterior deltoid functions less in conjunction with the other deltoid muscles, and lower coactivation was seen in the remaining intact rotator cuff muscles in the rotator cuff tear group than the control group.

CLINICAL RELEVANCE

This study supports the potential benefit of addressing the long head biceps tendon in the treatment of patients with a symptomatic rotator cuff tear. Moreover, clinicians might use these findings for conservative treatment; the posterior deltoid can be specifically trained to help compensate for the deficient rotator cuff.

The Application of Double Elastic Band Exercise in the 90/90 Arm Position for Overhead Athletes

BACKGROUND

Traditional exercises performed with the shoulder in the position of 90° abduction and external rotation with elbow flexion (90/90) while using a single elastic band showed moderate activity of both the lower trapezius (LT) and infraspinatus (IS) muscle. The purpose of this study was to investigate activity of the teres minor (TMi) and the LT muscles during standing external rotation exercise with the shoulder in the 90/90 position with 2 elastic bands in both the frontal and the scapular plane.

HYPOTHESIS

TMi, IS, and LT muscle activities will vary depending on whether the shoulder is positioned in the frontal or scapular plane with the application of 2 elastic bands. Also, the serratus anterior (SA) and teres major (TMa) muscles will produce different muscular activity patterns during exercises performed with 2 elastic bands in the frontal plane compared with the TMi and LT muscles.

STUDY DESIGN

Controlled laboratory study.

LEVEL OF EVIDENCE

Level 4.

METHODS

A total of 21 collegiate baseball players volunteered to participate. The electromyography (EMG) activities of the TMi, IS, LT, SA, TMa, middle deltoid (MD), posterior deltoid, and upper trapezius (UT) muscles were measured with the 90/90 arm position during both isometric and oscillation resistance exercises with 2 elastic bands oriented in the frontal and scapular planes.

RESULTS

A significant difference was observed in EMG activity of both the TMi and the LT muscles between single and double elastic band applications in the frontal plane (P < 0.05). In contrast, EMG activity of the IS, SA, and TMa muscles was significantly increased in the scapular plane compared with the frontal plane (P < 0.05).

CONCLUSION

The standing 90/90 position effectively increased both TMi and LT muscle EMG activity with the double elastic band in the frontal plane while minimizing UT and MD muscle activity. EMG activity of the IS, SA, and TMa muscles increased with exercise in the scapular plane as compared with the frontal plane.

CLINICAL RELEVANCE

Oscillation movement under double elastic band application differentiated external rotator muscle and scapular muscle activities between the frontal and scapular plane during the 90/90 exercise in the frontal plane compared with the scapular plane. Clinicians can utilize each of the scapular and frontal positions based on their desired focus for muscular activation.

Kinematic Differences between Two Types of Forward Elevations of the Shoulder Joint: Flexion and Reaching Elevation

Background:

Extension of the elbow joint is maintained during shoulder flexion. In contrast, the arm starts from the flexed position of the elbow joint and the joint gradually extends during reaching elevation.

Objectives:

This study aimed to compare the kinematic elements and electromyographic (EMG) activities of the rotator cuff muscles between flexion and reaching elevation.

Methods:

The study included 10 healthy young men. (average age, 21.5 ± 3.4 years), and measurements were performed on their dominant arms. A three-dimensional motion analyzer was used to record the following elements during shoulder flexion and reaching elevation: the angles of glenohumeral joint elevation and scapular upward rotation, scapulohumeral rhythm, external rotation of the humerus, and glenohumeral plane shifting from the coronal plane. The EMG activities in the supraspinatus, infraspinatus, subscapularis, and teres minor were recorded simultaneously.

Results:

The plane of reaching elevation was retained at 60° from the coronal plane. The glenohumeral planes (P < 0 .01) and the external rotation angles of the humerus below 90° of elevation (P < 0.05) were significantly different between both the motions. The EMG activities in the supraspinatus (P < .01), infraspinatus (P < 0.05), and teres minor (P < 0.01) were significantly lower while reaching elevation than those during flexion.

Conclusion:

The motion plane at 60° from the coronal plane, movement of the humeral external rotation, and EMG activities of the rotator cuff muscles were different during reaching elevation and shoulder flexion.

The pattern of idiopathic isolated teres minor atrophy with regard to its two-bundle anatomy

OBJECTIVE

We aimed to analyze the pattern of teres minor atrophy with regard to its two-bundle anatomy and to assess its association with clinical factors.

MATERIALS AND METHODS

Shoulder MRIs performed between January and December 2016 were retrospectively reviewed. Images were evaluated for the presence and pattern of isolated teres minor atrophy. Isolated teres minor atrophy was categorized into complete or partial pattern, and partial pattern was further classified according to the portion of the muscle that was predominantly affected. The medical records were reviewed to identify clinical factors associated with teres minor atrophy.

RESULTS

Seventy-eight shoulders out of 1,264 (6.2%) showed isolated teres minor atrophy; complete pattern in 41.0%, and partial pattern in 59.0%. Most cases of partial pattern had predominant involvement of the medial-dorsal component (82.6%). There was no significant association between teres minor atrophy and previous trauma, shoulder instability, osteoarthritis, and previous operation. The history of shoulder instability was more frequently found in patients with isolated teres minor atrophy (6.4%), compared with the control group (2.6%), although the difference was not statistically significant.

CONCLUSION

Isolated teres minor atrophy may be either complete or partial, and the partial pattern may involve either the medial-dorsal or the lateral-ventral component of the muscle. The imaging findings of partial pattern teres minor atrophy indicate that the two muscle components may have separate innervation.

Isolated loss of active external rotation: a distinct entity and results of L'Episcopo tendon transfer

BACKGROUND

The purpose of this study was to characterize a subgroup of cuff-deficient patients with isolated loss of active external rotation (ILER) but preserved active elevation and to evaluate the outcomes of the L'Episcopo procedure to restore horizontal muscle balance.

METHODS

During a 10-year period, 26 patients (14 men, 12 women) were identified with ILER in the setting of massive irreparable posterosuperior cuff tears. A modified L'Episcopo tendon transfer was performed to restore active external rotation and to improve shoulder function. The mean age at surgery was 64.5 years (29-83 years). Patients were evaluated with a mean follow-up of 52 months (range, 24-104 months).

RESULTS

Preoperatively, despite maintained active elevation (average of 161°), ILER patients complained about loss of spatial control of the arm and difficulties with activities of daily living. On computed tomography scan or magnetic resonance imaging, there was severe fatty infiltration of infraspinatus and absent or atrophic teres minor. After L'Episcopo transfer, 84% of patients were satisfied. The gain in active external rotation was +26° in arm at the side and +18.5° in 90° abduction. Adjusted Constant score and Simple Shoulder Value increased from 63.6% to 86.9% and from 36.9% to 70.8%, respectively (P < .001). The ADLER score increased from 10 to 24.5 points (P < .002). Two patients with advanced cuff tear arthropathy (Hamada stage 3 and 4) required conversion to a reverse shoulder arthroplasty (RSA) 7 and 9 years after the index surgery.

CONCLUSIONS

ILER is a distinct entity that is a cause of severe handicap because of loss of spatial control of the upper limb. This symptom is related to absent or atrophied infraspinatus and teres minor. In properly selected cases (Hamada stage 1 or 2), the modified L'Episcopo transfer is effective at restoring anterior-posterior rotator cuff force balance. In more advanced cuff tear arthropathy (Hamada stage ≥3), the tendon transfer should be performed with an RSA because of possible secondary degeneration of the glenohumeral joint.

Piriformis electromyography activity during prone and side-lying hip joint movement

[Purpose] To measure electromyographic activity of the piriformis using fine-wire electrodes during 7 hip movements. [Subjects and Methods] Eleven healthy men, without severe low back pain or lower limb injury, participated in this study. Fine-wire electrodes were inserted into the piriformis and surface electrodes were attached to the muscles in the hip region and the trunk muscles on the dominant arm side. Electromyographic signal amplitude was measured during 7 hip movements: side-lying external rotation in hip neutral position, side-lying abduction in hip neutral position, side-lying abduction in hip external rotation, side-lying abduction in hip internal rotation, prone extension in hip neutral position, prone extension in hip external rotation, and prone extension in hip internal rotation. Repeated-measures one-way analysis of variance was used to examine electromyographic activity in each of the 7 hip movements. [Results] Piriformis electromyographic activity was highest during prone hip extension in external rotation. Both the superior and inferior portions of the gluteus maximus were also highly activated during prone hip extension in external rotation. [Conclusion] Prone hip extension in external rotation induced high electromyographic activity in the piriformis and superior and inferior gluteus maximus muscles.