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.

Morphology of Humeral Head and Glenoid in Normal Shoulder of Indonesian Population

Purpose

Shoulder prostheses designed and used around the world may not fit an Asian shoulder. Normal shoulder morphology in Asian population had been reported, ie, Chinese, Indian, Japanese, and Thai populations, but no data from the Indonesian population. The aim of this study was to evaluate the three-dimensional (3D) morphology of the glenohumeral joint in the normal Indonesian population, identify its normal values, and compare them with those of other populations in the literature.

Patients and Methods

Images for analysis were computed tomography (CT) scans of 85 normal shoulders from 71 patients who had CT scans for another diagnosis. Morphometry of the humeral head and glenoid were measured using 3D reconstruction. Gender differences and correlations between age, height, and glenohumeral morphometry were evaluated. Indonesians' glenohumeral morphometry was compared with those of other populations in the literature.

Results

In the normal Indonesian population, the mean of humeral head inclination (HHI), height (HHH), diameter in sagittal plane (DS), diameter in frontal plane (DF), radius of curvature in sagittal plane (RS), and radius of curvature in frontal plane (RF) were 134.1°, 15.6mm, 39.3mm, 41.3mm, 20.4mm, and 21.4mm, respectively. The glenoid height (GH), upper width (GUW), lower width (GLW), inclination (GI), and version (GV) mean values were 34.2mm, 18.4mm, 24.5mm, 74.0mm, and 12.3mm, respectively. There was a significant difference in HHH, DS, DF, RS, RF, GH, GUW, GLW between males and females. Except for HHI and GI, glenohumeral morphometry was correlated with patient height. Age was not correlated with any glenohumeral morphometry.

Conclusion

In the Indonesian population, males had a larger humeral head and glenoid than females, and the size of the humeral head and glenoid was correlated to body height. Indonesians' humeral head and glenoid sizes were smaller than those of Western populations, but close to those of other Asian populations.