Comparison of the morphology of the rotator cuff muscles across age groups

Human lower leg muscles grow asynchronously

Muscle volume must increase substantially during childhood growth to generate the power required to propel the growing body. One unresolved but fundamental question about childhood muscle growth is whether muscles grow at equal rates; that is, if muscles grow in synchrony with each other. In this study, we used magnetic resonance imaging (MRI) and advances in artificial intelligence methods (deep learning) for medical image segmentation to investigate whether human lower leg muscles grow in synchrony. Muscle volumes were measured in 10 lower leg muscles in 208 typically developing children (eight infants aged less than 3 months and 200 children aged 5 to 15 years). We tested the hypothesis that human lower leg muscles grow synchronously by investigating whether the volume of individual lower leg muscles, expressed as a proportion of total lower leg muscle volume, remains constant with age. There were substantial age-related changes in the relative volume of most muscles in both boys and girls (p < 0.001). This was most evident between birth and five years of age but was still evident after five years. The medial gastrocnemius and soleus muscles, the largest muscles in infancy, grew faster than other muscles in the first five years. The findings demonstrate that muscles in the human lower leg grow asynchronously. This finding may assist early detection of atypical growth and allow targeted muscle-specific interventions to improve the quality of life, particularly for children with neuromotor conditions such as cerebral palsy.

Cross-sectional areas of rotator cuff muscles in males without tears on shoulder MRI

OBJECTIVE

To establish reference values of rotator cuff (RC) cross sectional area (CSA) in males.

MATERIALS AND METHODS

We retrospectively analyzed shoulder MRIs from 500 patients aged 13-78 years, grouped as follows (N=100 in each): <20, 20-30, 30-40, 40-50, >50 years. All examinations were reviewed to exclude prior surgery, tears, or significant RC pathology. We segmented a standardized T1 sagittal MR image in each case to obtain CSA of supraspinatus (SUP), infraspinatus/teres minor (INF), and subscapularis (SUB) muscles. Across age groups, we recorded individual and total muscle CSA. We also performed ratios between individual muscle CSA and total CSA to examine total muscle mass contribution over age groups. We tested for differences between age groups controlled for BMI.

RESULTS

CSAs for SUP, INF, SUB, and total RC CSA were lower in subjects >50 years compared to all other groups (P<0.003 for all comparisons), persisting after controlling for BMI (P<0.03). Relative contribution of SUP CSA to total RC CSA was stable across age groups (P>0.32). INF CSA relative to total RC CSA increased with age, whereas SUB decreased (P<0.005). Subjects >50 years showed lower SUP (-15%), INF (-6%), and SUB (-21%) CSA, when compared to mean CSAs of all subjects <50 years. Total RC CSA significantly correlated with age (r=-0.34, P<0.001), persisting after controlling for BMI (r=-0.42, P<0.001).

CONCLUSION

RC muscles in male subjects with no tears on MRI show decreasing CSA with age, independent of BMI.

The subscapularis muscle: A meta-analysis of its variations, prevalence, and anatomy

BACKGROUND

The subscapularis (SSC) is the largest rotator cuff muscle and is involved in the medial rotation, abduction, adduction, and anterior stabilization of the shoulder. It is anatomically variable, as is the morphology and prevalence of the accessory SSC (aSSC), a rare muscle slip attached to the SSC. There is no current review investigating the prevalence and morphometrics of the SSC and aSSC.

PURPOSE

To investigate the prevalence of the morphological variants of the SSC and aSSC via meta-analysis and review the relevant literature involving cadaveric, magnetic resonance imaging, and ultrasonographic studies.

STUDY DESIGN

Meta-analysis.

MATERIALS AND METHODS

Literature data reporting the prevalence rates and morphometrics of the SSC and aSSC and their variants were pooled. Literature searches and data analyses were performed in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses and Anatomical Quality Assurance guidelines.

RESULTS

Forty-six studies, totaling 2166 shoulders, were assessed. The SSC showed an overall length, thickness, cross-sectional area, and volume of 152.2 mm (95% confidence interval, CI, 103.8-200.5 mm), 5.6 mm (95% CI, 4.6-6.6 mm), 18.1 cm² (95% CI, 14.2-22.0 cm² ), and 126.9 cm³ (95% CI, 87.2-166.5 cm³ ), respectively. The SSC displayed substantial variations in its origin and insertion points and in the composition of its tendon. The aSSC had an overall pooled prevalence of 24.6% (95% CI, 0.0%-76.9%).

CONCLUSIONS

The SSC and aSSC have been implicated in multiple shoulder pathologies, including muscle and tendon ruptures and neurovascular compromise. A better understanding of SSC and aSSC variants when diagnosing and treating their related pathologies will reduce patient morbidity and improve treatment regimens.

The internal structure of the infraspinatus muscle: a magnetic resonance study

Purpose

This study aimed to describe the internal structure of the infraspinatus muscle. A secondary aim was to explore differences in internal structure between genders, sides, and correlations to demographic data.

Methods

In total, 106 shoulder MRI examinations of patients between 18 and 30 years of age seeking care in 2012–2020 at The Sahlgrenska University Hospital in Gothenburg, Sweden were re-reviewed.

Results

The number of intramuscular tendons centrally in the infraspinatus muscle varied between 3 and 8 (median = 5). Laterally, the number of intramuscular tendons varied between 1 and 5 (median = 2). There was no difference in the median between the genders or sides. No correlations between the number of intramuscular tendons and demographic data were found. The muscle volume varied between 63 and 249 ml with a median of 188 ml for males and 122 ml for females. There was no significant difference in volume between the sides. The muscle volume correlated with body weight (Pearson’s correlation coefficient, r = 0.72, p < 0.001) and height (r = 0.61, p < 0.001).

Conclusion

The anatomical variations of the infraspinatus muscle are widespread. In the medial part of the muscle belly, the number of intramuscular tendons varied between 3 and 8, while the number of intramuscular tendons laterally varied between 1 and 5. Results of our study may help to understand the internal structure of the infraspinatus muscle and its function in shoulder stabilization.

Agreement in rotator cuff muscles measurement between ultrasonography and magnetic resonance imaging

Background/objective

It is important to assess the atrophy of the rotator cuff to better understand shoulder function and pain. Previously, magnetic resonance imaging has been used for the evaluation of atrophy of rotator cuff muscles, which is time consuming. Therefore, a measurement tool requiring little time and easy accessibility is clinically desirable to be used frequently in rehabilitation. Recently, rotator cuff muscles have been evaluated using ultrasonography. However, little is known about the agreement of evaluation in rotator cuff muscles between magnetic resonance imaging and ultrasonography. The purpose of this study was to demonstrate the agreement between the muscle thickness measurements of supraspinatus, infraspinatus, and teres minor muscles by ultrasonography and the cross-sectional area measured by magnetic resonance imaging in the patient with rotator cuff tears.

Methods

A total of 47 patients with rotator cuff tears were enrolled. There were the 37 small tears, four medium tears, and six large tears, and the involved rotator cuff muscles were the supraspinatus in 37 shoulders, and the supraspinatus and infraspinatus in 10 shoulders. The measuring variables were muscle thickness and cross-sectional area of supraspinatus, infraspinatus, and teres minor muscles by using magnetic resonance imaging. Further, the muscle thickness of the rotator cuff were assessed using ultrasonography. A single regression model was used for demonstrating the agreement between the cross-sectional area measurement by magnetic resonance imaging and the muscle thickness measured using ultrasonography and magnetic resonance imaging of rotator cuff muscles. Additionally, the Bland-Altman plots between magnetic resonance imaging and ultrasonography was analyzed.

Results

The cross-sectional area were correlated with the muscle thickness measurement of rotator cuff muscles by magnetic resonance imaging, significantly (supraspinatus: r = 0.84, infraspinatus: ρ = 0.63, teres minor: ρ = 0.61, all p < 0.001). There were significant agreements between the cross-sectional area measured by magnetic resonance imaging and muscle thickness measured by ultrasonography (supraspinatus: r = 0.80, infraspinatus: ρ = 0.78, teres minor: ρ = 0.74, all p < 0.001). Bland-Altman plots revealed significant correlations between the average and the difference of the two measurements in supraspinatus (r = 0.36, p = 0.012), infraspinatus (r = 0.38, p < 0.001), and teres minor (r = 0.42, p < 0.001). These results clarified the proportional bias between MRI and US.

Conclusion

This study showed that, similar to magnetic resonance imaging, ultrasonography is a useful tool for assessing muscle atrophy of supraspinatus, infraspinatus, and teres minor muscles.

Infraspinatus and deltoid length and patient height: implications for lateralization and distalization in reverse total shoulder arthroplasty

BACKGROUND

Restoration of muscular strength is predicated on restoration of muscle length. The purpose of this study was to describe infraspinatus and deltoid length preoperative to reverse total shoulder arthroplasty (RTSA) to guide distalization and lateralization to restore preoperative muscle length.

METHODS

This was a retrospective radiographic study. We measured the infraspinatus length on preoperative computed tomographic images and the deltoid length on preoperative radiographs. For all measurements, reliability was first established by comparing measurements between 2 observers, and intraclass correlation coefficients (ICCs) were calculated. We then calculated descriptive statistics for these muscle lengths and developed a formula to predict these muscle lengths from patient demographics.

RESULTS

We measured infraspinatus length in 97 patients and deltoid length in 108 patients. Inter-rater reliability was excellent, with all ICCs >0.886. The mean infraspinatus length was 15.5 cm (standard deviation 1.3) and ranged from 12.6-18.9 cm, whereas the deltoid length was 16.2±1.7 cm and ranged from 12.5-20.2 cm. Both infraspinatus (r = 0.775, P < .001) and deltoid length (r = 0.717, P < .001) were highly correlated with patient height but did not differ between diagnoses. Formulae developed through linear regression allowed prediction of muscle length to within 1 cm in 78% and within 2 cm in 100% for the infraspinatus and 60% and 88% for the deltoid.

CONCLUSION

Deltoid and infraspinatus length are variable but highly correlated with patient height. To maintain tension, 2 mm of lateralization and distalization should be added for every 6 inches (∼15 cm) of height above average for a Grammont-style RTSA.

Defining massive rotator cuff tears: a Delphi consensus study

BACKGROUND

A standard definition for massive rotator cuff tears (MRCTs) has not been identified. The purpose of this study is to use the modified Delphi technique to determine a practical, consensus definition for MRCTs.

METHODS

This study is based on responses from 20 experts who participated in 4 rounds of surveys to determine a consensus definition for MRCT. Consensus was achieved when at least 70% of survey responders rated an item at least a 4 on a 5-point scale. A set of core characteristics was drafted based on literature review and then refined to achieve a consensus MRCT definition.

RESULTS

The following core characteristics reached consensus in the first round: tear size, number of tendons torn, and degree of medial retraction. Magnetic resonance imaging (MRI) and intraoperative findings reached consensus as the modalities of diagnosis. The second round determined that tear size should be measured as a relative value. An initial definition for MRCT was proposed in the third round: retraction of tendon(s) to the glenoid rim and/or a tear with ≥67% greater tuberosity exposure (65% approval). A modified definition was proposed that specified that degree of retraction should be measured in the coronal or axial plane and that the amount of greater tuberosity exposure should be measured in the sagittal plane (90% approval).

CONCLUSIONS

This study determined with 90% agreement that MRCT should be defined as retraction of tendon(s) to the glenoid rim in either the coronal or axial plane and/or a tear with ≥67% of the greater tuberosity exposed measured in the sagittal plane. The measurement can be performed either with MRI or intraoperatively.

Reliability of Ultrasound Measurement of Muscle Thickness in Patients with Supraspinatus Tendon Pathology

Objectives of the study were to observe supraspinatus muscle thickness in patients with supraspinatus tendon pathology using ultrasound (US) and examining inter- and intra-rater reliability, and to compare muscle thickness with cross-sectional area (CSA) and occupation ratio measured by both US and magnetic resonance imaging (MRI). The investigation was designed as a prospective cohort study. Two groups of patients were included in the study: 43 patients with tendon rupture and 44 patients without tendon rupture as a control group. A written consent was obtained from all patients. In both groups, muscle thickness, CSA and occupation ratio were measured with US, and CSA and occupation ratio with MRI. Study results showed statistically significant between-group differences. The mean supraspinatus muscle thickness measured by US was 14.01 mm and 19.83 mm in patients with and without tendon rupture, respectively. CSA and occupation ratio measured by US and MRI also showed statistically significant between-group differences. Pearson correlation coefficient between supraspinatus thickness and occupation ratio and CSA measured by US and MRI showed strong to moderate correlation. US measurements showed moderate to strong intra- and inter-rater reliability. In conclusion, supraspinatus muscle thickness measurement by US is a reliable method for muscle atrophy evaluation and strongly correlates with other acknowledged methods.

An age- and gender-related three-dimensional analysis of rotator cuff transverse force couple volume ratio in 304 shoulders

PURPOSE

The rotator cuff transverse force couple (RCTFC) is fundamental in the shoulder biomechanics, as the balance of its muscle components (the subscapularis relative to the infraspinatus and teres minor) provides stability to the joint. The chronic progression of rotator cuff tears usually present alterations in muscle volume, along with atrophy and compensatory hypertrophy, which can be determined using imaging techniques. The aim of this study was to quantify RCTFC muscle volume in a large sample taking into account the age and gender of the participants involved.

METHODS

An observational, retrospective, cross-sectional, descriptive and comparative study was conducted, evaluating thoracic computed tomography scans from 152 patients (304 shoulders) of indistinct gender, with ages ranging between 18 and 85 years. The RCTFC muscle volume was quantified with an oblique/multiplanar segmentation technique. Measuring time was also documented.

RESULTS

We observed that muscle volume decreases among the different age (p < 0.04) and gender (p < 0.001) groups. However, the RCTFC volume ratio remained constant at 1.02 ± 0.18 without significant differences throughout all age and gender groups evaluated (p > 0.298).

CONCLUSION

The decrease in the RCTFC muscle volume is proportional during the different stages of life, maintaining a constant ratio between its components (physiological RCTFC muscle atrophy). The time-saving segmentation method and volume ratio formula proposed in this study contribute to the management and understanding of rotator cuff tear/pathology.

Reliability and Limits of Agreement of the Supraspinatus Muscle Anatomical Cross-Sectional Area Assessment by Ultrasonography

The purpose of this study was to evaluate the reliability and limits of agreement for assessment of the anatomical cross-sectional area (ACSA) of the supraspinatus muscle using B-mode ultrasonography. Sixteen participants were examined with two different protocols, on two different days. There were no statistically significant differences (p > 0.05) in ACSA values between days 1 and 2 or between protocols 1 and 2; the average intra-class correlation coefficient ranged from 0.93 to 0.96. The limits of agreement for supraspinatus ACSA were, in both protocols, about ± 1 cm(2). Our findings revealed that both protocols had high reliability in distinguishing differences of about 1 cm(2) between groups or after interventions and that ultrasonography can be used for experimental designs in which the expected changes in ACSA would be higher than 14%.