{"title":"Cross-sectional and biomechanical investigation of concurrent infraspinatus and teres minor muscle variations: A case report","authors":"Ethan L. Snow , Keland Potthoff , Lina Adwer","doi":"10.1016/j.tria.2023.100278","DOIUrl":null,"url":null,"abstract":"<div><h3>Introduction</h3><p>The infraspinatus and teres minor are scapulohumeral muscles that laterally rotate the arm. Multiple variations in these muscles have been reported; however, the impact of concurrent accessory infraspinatus (a-I) and teres minor (a-TM) muscles has yet to be described. The present study aims to employ gross cross-sectional and biomechanical analyses to investigate a case of coexistent a-I and a-TM muscles for structural effects, functional impacts, and clinical implications.</p></div><div><h3>Methods</h3><p>Bilateral a-I muscles and a left a-TM muscle were discovered during routine dissection of a human cadaver. The aberrations were carefully cleaned of extraneous tissue and photographed. The left glenohumeral joint was sectioned sagittally and photographed to confirm the relation of a-I and a-TM to contiguous structures. The infraspinatus, a-I, teres minor, and a-TM muscles were examined for gross and microscopic structural features that were used to calculate maximal isometric force (<em>F</em><sub><em>max</em></sub>) and bilateral comparability (<em>δ</em>).</p></div><div><h3>Results</h3><p>The 8.66 g (bilateral mean) a-I and 13.42 g (left) a-TM inserted on the greater tubercle just distal to their namesake muscle. At the left glenohumeral joint, a-I remained distinct from infraspinatus while a-TM and teres minor exhibited connected bellies. Bilateral a-I and teres minor muscles were structurally similar (<em>δ</em> < 0.30), while left and right infraspinatus muscles approached non-similarity (<em>δ</em> = 0.69). <em>F</em><sub><em>max</em></sub> of the left infraspinatus, a-I, teres minor, and a-TM were 117.12 N, 26.45 N, 59.93 N, and 29.88 N, respectively.</p></div><div><h3>Conclusions</h3><p>Coexistent a-I and a-TM muscles can increase the rotator cuff's lateral rotation force by 31.82%, but they may imbalance glenohumeral joint stability, complicate injury and surgical repairs to the region, and increase risk of quadrangular space syndrome. This study provides gross and functional analyses of concurrent a-I and a-TM muscles that may help guide diagnosis, treatment, research, and education for related cases.</p></div>","PeriodicalId":37913,"journal":{"name":"Translational Research in Anatomy","volume":"34 ","pages":"Article 100278"},"PeriodicalIF":0.0000,"publicationDate":"2023-12-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S2214854X2300047X/pdfft?md5=53482de0ab8cb22184f163aa867265f3&pid=1-s2.0-S2214854X2300047X-main.pdf","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Translational Research in Anatomy","FirstCategoryId":"1085","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S2214854X2300047X","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"Medicine","Score":null,"Total":0}
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Abstract
Introduction
The infraspinatus and teres minor are scapulohumeral muscles that laterally rotate the arm. Multiple variations in these muscles have been reported; however, the impact of concurrent accessory infraspinatus (a-I) and teres minor (a-TM) muscles has yet to be described. The present study aims to employ gross cross-sectional and biomechanical analyses to investigate a case of coexistent a-I and a-TM muscles for structural effects, functional impacts, and clinical implications.
Methods
Bilateral a-I muscles and a left a-TM muscle were discovered during routine dissection of a human cadaver. The aberrations were carefully cleaned of extraneous tissue and photographed. The left glenohumeral joint was sectioned sagittally and photographed to confirm the relation of a-I and a-TM to contiguous structures. The infraspinatus, a-I, teres minor, and a-TM muscles were examined for gross and microscopic structural features that were used to calculate maximal isometric force (Fmax) and bilateral comparability (δ).
Results
The 8.66 g (bilateral mean) a-I and 13.42 g (left) a-TM inserted on the greater tubercle just distal to their namesake muscle. At the left glenohumeral joint, a-I remained distinct from infraspinatus while a-TM and teres minor exhibited connected bellies. Bilateral a-I and teres minor muscles were structurally similar (δ < 0.30), while left and right infraspinatus muscles approached non-similarity (δ = 0.69). Fmax of the left infraspinatus, a-I, teres minor, and a-TM were 117.12 N, 26.45 N, 59.93 N, and 29.88 N, respectively.
Conclusions
Coexistent a-I and a-TM muscles can increase the rotator cuff's lateral rotation force by 31.82%, but they may imbalance glenohumeral joint stability, complicate injury and surgical repairs to the region, and increase risk of quadrangular space syndrome. This study provides gross and functional analyses of concurrent a-I and a-TM muscles that may help guide diagnosis, treatment, research, and education for related cases.
期刊介绍：
Translational Research in Anatomy is an international peer-reviewed and open access journal that publishes high-quality original papers. Focusing on translational research, the journal aims to disseminate the knowledge that is gained in the basic science of anatomy and to apply it to the diagnosis and treatment of human pathology in order to improve individual patient well-being. Topics published in Translational Research in Anatomy include anatomy in all of its aspects, especially those that have application to other scientific disciplines including the health sciences: • gross anatomy • neuroanatomy • histology • immunohistochemistry • comparative anatomy • embryology • molecular biology • microscopic anatomy • forensics • imaging/radiology • medical education Priority will be given to studies that clearly articulate their relevance to the broader aspects of anatomy and how they can impact patient care.Strengthening the ties between morphological research and medicine will foster collaboration between anatomists and physicians. Therefore, Translational Research in Anatomy will serve as a platform for communication and understanding between the disciplines of anatomy and medicine and will aid in the dissemination of anatomical research. The journal accepts the following article types: 1. Review articles 2. Original research papers 3. New state-of-the-art methods of research in the field of anatomy including imaging, dissection methods, medical devices and quantitation 4. Education papers (teaching technologies/methods in medical education in anatomy) 5. Commentaries 6. Letters to the Editor 7. Selected conference papers 8. Case Reports
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