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Background: This study evaluates the pectoralis major (PM) tendon humeral insertion, using imaging and histologic assessment in cadaveric specimens. Current descriptions of the pectoralis major tendon depict a bilaminar enthesis, and clarification of the anatomy is important for diagnostic and surgical considerations., Materials and Methods: Fourteen fresh-frozen whole upper extremity specimens were used in this study. Magnetic resonance (MRI) and ultrasonographic (US) imaging of the PM muscles, tendons, and entheses were performed, followed by anatomic dissection and inspection. Morphology of the lateral tendon and entheses were evaluated, focused on the presence of layers. In 11 specimens, the lateral 3 cm of the PM tendon was carefully dissected from the footprint, whereas in 3 specimens, the tendon and humeral insertion were preserved and removed en bloc. Histology was performed in axial slabs along the medial-lateral length of the tendon and also evaluated for the presence of layers., Results: The superior-inferior and medial-lateral lengths of the PM footprint were 75 ± 9 mm and 7 ± 1 mm respectively. In all specimens, the clavicular and sternal head muscles and tendons were identified, with the clavicular head tendon generally being shorter. The medial-lateral length of the clavicular head tendon measured 19 ± 8 mm superiorly and 9 ± 3 mm inferiorly. The medial-lateral length of the sternal head tendon measured 38 ± 8 superiorly and 41 ± 18 mm inferiorly. All specimens demonstrated a unilaminar, not bilaminar, enthesis with abundant fibrocartilage on histology. Three specimens demonstrated interspersed entheseal fat and loose connective tissue at the enthesis on MRI and histology., Conclusion: The PM tendon humeral insertion consists of a unilaminar fibrocartilaginous enthesis. US, MRI, and histology failed to identify true tendon layers at the enthesis. Delaminating injuries reported in the literature may originate from a location other than the enthesis., (Copyright © 2020 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved.)

Background: Anterosuperior labrum variations have been generally described as innocent anatomical variations without clinical significance. This study was intended to determine their prevalence and reveal their possible relationship with type II SLAP lesions., Materials and Methods: A total of 713 consecutive shoulder arthroscopies were evaluated retrospectively for anterosuperior labrum variations and co-existing labral pathologies. Twenty two of these were excluded from the study due to the interobserver variability in the categorization process. The relationship of both these anatomic variants and shoulders with a normal appearing anterosuperior labrum to intra-articular pathology was analyzed statistically and compared with each other., Results: Found in 98 patients (14.18%), the anatomic variations in the anterosuperior labrum were classified into 3 groups as the sublabral recess (2.46%), the sublabral foramen (7.67%), and absent anterosuperior labrum with a cord-like middle glenohumeral ligament (4.05%). The latter 2 of these groups displayed a statistically significant relationship with type II SLAP lesions (21 of 53 and 23 of 28 patients; P = .0028 and P < .0001, respectively)., Discussion: Although mostly considered as simple morphological variations, the anatomic variants of the anterosuperior labrum may predispose the shoulder to labrum pathologies by altering the intra-articular biomechanics., Conclusion: As previously suggested in the literature, certain anatomic variants of the anterosuperior labrum are associated with the development of SLAP lesions., (Copyright © 2010 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Mosby, Inc. All rights reserved.)