Anatomical and molecular analyses of the deltoid muscle in chimpanzees (Pan troglodytes) and modern humans (Homo sapiens): Similarities and differences due to the uses of the upper extremity.

In the deltoid muscles of Pan troglodytes and Homo sapiens, we have analyzed the muscle architecture and the expression of the myosin heavy chain (MHC) isoforms. Our aim was to identify differences between the two species that could be related to their different uses of the upper limb. The deltoid muscle of six adult Pan troglodytes and six adult Homo sapiens were dissected. The muscle fascicle length (MFL) and the physiological cross-sectional area (PCSA) of each muscle were calculated in absolute and normalized values. The expression pattern of the MHC-I, MHC-IIa and MHC-IIx isoforms was analyzed in the same muscles by real-time polymerase chain reaction. Only the acromial deltoid (AD) presented significant architectural differences between the two species, with higher MFL values in humans and higher PCSA values in chimpanzees. No significant differences in the expression pattern of the MHC isoforms were identified. The higher PCSA values in the AD of Pan troglodytes indicate a greater capacity of force generation in chimpanzees than in humans, which may be related to a greater use of the upper limb in locomotion, specifically in arboreal locomotion like vertical climbing. The functional differences between chimpanzees and humans in the deltoid muscle are more related to muscle architecture than to a differential expression of MHC isoforms.

Quantitative shape analysis of the deltoid tuberosity of modern humans (Homo sapiens) and common chimpanzees (Pan troglodytes).

PURPOSE: To identify anatomical differences in the deltoid tuberosity of Homo sapiens and Pan troglodytes, potentially relating to the different uses of the forelimb in these two phylogenetically related species. BASIC PROCEDURES: We have used three-dimensional geometric morphometrics (3D GM) to analyze the deltoid tuberosity of scanned humeri from 30 H. sapiens and 27 P. troglodytes. We also used the 3D scans of the humeri to calculate the surface area of the deltoid tuberosity. Finally, we dissected the deltoid muscles of three H. sapiens and three P. troglodytes to determine the relative mass and the physiological cross-sectional area (PCSA) of each part of the muscle. MAIN FINDINGS: The 3D GM analysis of the deltoid tuberosity identified an anteroposterior enlargement of the P. troglodytes tuberosity, with a lateral displacement of the middle segment, whereas in H. sapiens, there was a distal displacement of the middle segment. Muscle architecture analysis indicated higher normalized values ​​of the PCSA of the clavicular and acromial deltoid in P. troglodytes. PRINCIPAL CONCLUSIONS: The anatomical features observed in our P. troglodytes specimens serve to strengthen the three parts of the deltoid muscle. This fact can be related to the use of the forelimb in locomotion, both arboreal and knuckle-walking, in this species. Humans use the forelimb mainly in manipulative tasks, so they do not develop - as do chimpanzees - the anatomical features that increase the deltoid force. Our findings have shown that the different uses of the forelimb in modern humans and common chimpanzees can affect both muscle architecture and bone morphology, either jointly or separately.

Nameless in anatomy, but famous among surgeons: The so called "deltotrapezoid fascia".

Acute dislocation of the acromioclavicular joint (AC-joint) often leads to disruption of the "deltotrapezoid fascia", a common aponeurosis of the deltoid and the trapezoid muscles. Various studies demonstrated that its reconstruction is crucial for functional recovery. Textbooks of anatomy, however, fail to mention this prominent structure that is also not listed in the Terminologia Anatomica provided by the Federative Committee on Anatomical Terminology (FCAT). Here, we demonstrate that the delta-trapezoid fascia is hardly visible in formalin-fixed, but prominent in fresh specimen. We provide an extensive anatomical description based on 11 specimens derived from eight body donators and show, as a major finding that different fixations massively impact on the structural integrity of the DTF. We hypothesize that modern (minimal-invasive) surgical strategies unraveled many structures of fundamental function that are not known by anatomists and therefore not covered by anatomical education.

Validation of the inter-individual variability of the lateral offset of the acromion.

INTRODUCTION: Anatomical variations of the lateral offset of the acromion (LOA) are supposed to be a factor favoring of the development of rotator cuff tears. The primary objective of this study is to quantify the inter-individual variations of the lateral offset of the acromion. METHODS: The morphology of 103 dried scapula was studied. Scapula with an os-acromiale, fractures and osteoarthritic changes of the glenoid cavity were excluded. We measured the distance between the medial edge of the spine and the supra-glenoidal tubercle of the glenoid fossa (L0), as well as the distance between this medial point and the most lateral point of the acromion (Lmax). Then, the acromial offset = (Lmax - L0), in absolute value (mm) and in relative value (% of Lmax) were calculated. RESULTS: The absolute average offset is 3.2 cm (SD = 0.4040 cm), the relative average offset is 23.07% (SD = 2.195%). We observed a non-Gaussian distribution of the LOA, with two peaks of distribution of which average and the median offset measurements are situated between these two distributions. CONCLUSION: This study shows that there are two different morphologies for the scapula, characterized by the lateral offset of their acromion: small or large lateral offset. Clinical implications in shoulder pathology seem important because the resultant of the constraints applied by the deltoid to the joint would favor either rotator cuff tears, or scapulohumeral arthrosis.

Options of bipolar muscle transfers to restore deltoid function: an anatomical study.

PURPOSE: To outline the technical details and determine the ranges of two pedicled functioning flaps that are the upper pectoralis major (UPM) and latissimus dorsi (LD) to elucidate their respective indications with regards to deltoid impairment. METHODS: The UPM and LD bipolar transfers were performed in 14 paired cadaveric shoulders, one on each side. The UPM was flipped 180° laterally over its pedicle to be placed onto the anterior deltoid. The LD flap was elevated on its pedicle to be rotated and positioned onto the deltoid mid-axis. Their respective spans were defined according to the deltoid muscle origin and insertion. RESULTS: The UPM outreached the lateral edge of the anterior deltoid origin with a mean distance of 7.3 cm (range 4-9.1 cm) off the lateral edge of the clavicle. Distally, the flap consistently overcame the proximal end of the deltoid tuberosity for a mean distance of 2.1 cm (range 0.9-3.2 cm). The LD flap mdi-axis could be consistently placed onto the deltoid mid-axis; spans of the anterior and posterior borders of the LD flap averaged 1 cm (range - 1 to 2.3 cm) and 0.2 cm (range -1.8 to 1.9 cm), respectively. CONCLUSIONS: The UPM flap optimal indications would be cases with deltoid defects limited to its anterior portion, whereas the LD bipolar transfer could be used in more extensive lesions. Additionally, the distal span of both transfers appears to allow their use in the setting of a reverse shoulder arthroplasty with subsequent humeral lengthening. LEVEL OF EVIDENCE: Non-applicable-basic science study, cadaver dissection.

Rotator cuff muscles fatty infiltration increases with age: retrospective review of 210 patients with intact cuff on computed tomography arthrography.

HYPOTHESIS: We aimed to demonstrate that rotator cuff fatty infiltration (FI) increases physiologically with age and that a FI degree of 2 might be encountered in patients with an intact cuff. METHODS: We retrospectively evaluated the FI of 210 patients (classified in 7 age groups: <20, 20-30, 30-40, 40-50, 50-60, 60-70, and >70 years) who had an intact cuff on computed tomography (CT) arthrography. The Goutallier grading system was used to assess FI of rotator cuff muscles and of the deltoid muscle. FI was then compared between groups for each muscle, and determinants (age, sex, and body mass index) of FI were assessed. RESULTS: FI of all evaluated muscles progressively increased with age, but a statistically significant increase between 2 consecutive age groups was observed for all muscles only after age 40 years. For each group, intermuscle comparison showed that the FI distribution was not significantly different between each rotator cuff muscle at any age. Age was a determinant for FI for all muscles, but sex and body mass index also influenced deltoid FI. A median FI value of 2 was found in the "over 70 group" for the supraspinatus, but in the 60 to 70 group for infraspinatus and subscapularis and in the 50 to 60 group for the deltoid. CONCLUSION: FI of rotator cuff muscles increased with age, with a significant acceleration after 40 years. Moreover, a FI graded 2, a common threshold for management decision, was commonly found in those aging patients with intact cuff on CT arthrography.

Clinical Anatomy for the Innervated Pattern and Boundary of the Subdeltoid Bursa.

The aim of this study was to accurately identify the distribution of sensory nerve branches running to bursa with mesoscopic dissection and boundaries following the injection of gelatin into the bursa. Eighteen shoulders of 11 Korean soft cadavers (average age, 65 years; age range, 43 - 88 years) were dissected. The most prominent point of greater tubercle of the humerus (GT) was used as a reference point. The horizontal line passing through GT was used as the x-axis while the vertical line passing through the GT was used as the y-axis. Average distances of the anterior, posterior, superior, and inferior from the GT were 1.9±0.6, 2.4±1.3, 2.1±0.7, and 3.2±1.5 cm, respectively. In 15 cases of 18 shoulders, the anterior branch of the axillary nerve was distributed to the subdeltoid bursa that was running posteriorly. The muscular branch of the anterior and middle parts of the deltoid was distributed to the branch of nerve that was running into the subdeltoid bursa. A branch of the posterior cord of brachial plexus was distributed to the subdeltoid bursa that was running anteriorly in three cases. Most of the branches of the axillary nerve were distributed into the posterolateral area. The branches of the posterior cord of brachial plexus were distributed in the anterolateral area. These results might be useful for preventing residual pain on the anterior shoulder region following an injection for the relief of shoulder pain.

Quantitative assessment of the growth dynamics of the teres major in human fetuses.

PURPOSE: The main objective of the study was to examine the use of teres major (TM) as a flap in the pediatric surgeries from an anatomical perspective by: (1) revealing the growth dynamics of the developing TM; (2) assessing the possible interconnecting structures between TM and latissimus dorsi (LD); (3) exposing the innervation patterns of TM in human fetuses. METHODS: Study was conducted on 50 fetuses (26 females and 24 males), on a mean gestational age of 22.86 ± 3.21 (range 18-30) weeks. All the measurements were collected with a digital caliper and a digital image analysis software. Additionally, structural relations between TM and LD were examined in detail and further classified. RESULTS: No significant difference of side and sex was detected on TM measurements (p > 0.05). Linear functions for the surface area, width, length of the superior and inferior margins of TM were detected as follows: y = - 257.142 + 18.334 × age (weeks), y = - 5.497 + 0.545 × age (weeks), y = - 1.621 + 1.068 × age (weeks), and y = - 2.147 + 1.284 × age (weeks), respectively. As classified in five types, a number of 33 muscular or tendinous connections between TM and LD were detected. Musculo-tendinous slips from TM to triceps brachii (TB) were evident in four sides. Innervation of TM was observed to be providing by the lower subscapular nerve in all the cases. CONCLUSION: First, linear functions, representing the developing fetal morphometry obtained by our study can be adapted for estimating the morphometric of this muscle in early childhood. Besides, acknowledging the diverse appointments of TM with the surrounding muscles such as LD and TB may facilitate the prevention of neurovascular structures and the application of surgical procedures during tendon transfers. In brief, our findings are highly potent to bring the attention of pediatric surgeons.

Descriptive characteristics of the area of origin of the deltoid muscle on the human clavicle. Is it necessary to include new terms in the Terminologia Anatomica?

The clavicular portion of the deltoid muscle (CPDM) in the human clavicle does not have a nomenclature in the Terminologia Anatomica (TA). This area is relevant in anatomy since the muscle participates in motions of glenohumeral articulation. The aim of this study was to describe the origin of the CPDM and to propose a name for the structure. Dry clavicles of 176 adults were studied, without distinction by sex. An osteometric board was used to measure the maximum length of the clavicles and a digital caliper to measure length of the CPDM's origin, distance from the origin to the sternal end, distance from the origin to the acromial end, distance of the lateral third and middle vertical diameter. The mean of maximum of the distances and CPDM's origin of left/right clavicle do not present significant differences. The CPDM s origin showed a high prevalence of structures as groove and roughened area (over 96% of cases). In conclusion, our definition of the CPDM shows the importance of clearly describing the observed groove and roughened area. Due to the high prevalence of the structures, the authors suggest that the terms "sulcus musculi deltoidei" and "tuberositas musculi deltoidei" be included in the TA to denominate the CPDM's origin on the human clavicle.

Shoulder muscle volume and fat content in healthy adult volunteers: quantification with DIXON MRI to determine the influence of demographics and handedness.

OBJECTIVE: We aimed to provide mean values for fat-fraction and volume for full-length bilateral rotator cuff and deltoid muscles in asymptomatic adults selected on the basis of their good musculoskeletal and systemic health, and to understand the influence of gender, age, and arm dominance. MATERIALS AND METHODS: Seventy-six volunteers aged 20 to 60 years who were screened for normal BMI and high general health were included in the study. MRI was performed at 3 Tesla using three-point DIXON sequences. Volume and fat-signal fraction of the rotator cuff muscles and the deltoid muscle were determined with semi-automated segmentation of entire muscle lengths. Differences according to age, gender, and handedness per muscle were evaluated. RESULTS: Fat-signal fractions were comparable between genders (mean ± 2 SD, 95% CI, women 7.0 ± 3.0; 6.8-7.2%, men 6.8 ± 2.7; 6.7-7.0%) but did not show convincing changes with age. Higher shoulder muscle volume and lower fat-signal fraction in the dominant arm were shown for teres minor and deltoid (p < 0.01) with similar trends shown for the other rotator cuff muscles. CONCLUSIONS: Bilateral fat-signal fractions and volumes based on entire length shoulder muscles in asymptomatic 20-60 year old adults may provide reference for clinicians. Differences shown according to arm dominance should be considered and may rationalize the need for bilateral imaging in determining appropriate management.

Anatomic feature of deltoid ligament attachment in posteromedial osteochondral lesion of talar dome.

BACKGROUND: Osteochondral lesions of the talus (OLT) are recognized as being commonly associated with trauma. However, the etiology of OLT remains unclear. In the case of a posteromedial lesion of OLT (medial OLT), the deep layer of the deltoid ligament is located close to the medial OLT, and this relationship between a medial lesion and deltoid ligament could be a risk factor for medial OLT. The purpose of this study is to investigate the unique anatomic feature of the deep deltoid attachment to the talus in patients with medial OLT compared with patients with non-medial OLT. METHODS: Forty ankles with medial OLT and 40 ankles without medial OLT were retrospectively reviewed in this study. On the coronal images of MRI, the attachment of deltoid ligament was measured. The continuity of the osteochondral fragment and its bed was evaluated on MRI and arthroscopic findings. RESULTS: Coronal MRI images showed that the attachment of the deep deltoid ligament to the medial OLT was broader and located more proximally than in non-medial OLT. The continuity of fibers from the insertion site of deltoid ligament to the talus to the osteochondral fragment was observed (76.7%). In the arthroscopic findings, the osteochondral fragment was obviously connected to the talus at the medial site in 85.2% of feet. CONCLUSIONS: The location of the deep deltoid ligament attachment to the medial OLT was more proximal and there was the possibility of these anatomic feature might contribute to the pathogenesis of medial OLT.

Qualitative and Quantitative Anatomy of the Proximal Humerus Muscle Attachments and the Axillary Nerve: A Cadaveric Study.

PURPOSE: To provide a quantitative and qualitative anatomic analysis of the pectoralis major, teres major, and latissimus dorsi on the humerus, as well as the deltoid tendinous attachments on the proximal humerus and acromion, and to quantitatively characterize the humeral course of the axillary nerve. METHODS: Ten nonpaired, fresh-frozen human cadaveric shoulders were analyzed. A portable coordinate-measuring device quantified the location of bony landmarks and tendon attachment areas. The tendon footprints were recorded by tracing their outlines and center points. The footprint areas of the tendons, the distances between the footprint areas and pertinent osseous and soft-tissue landmarks, and the distance between where the axillary nerve courses across the humerus relative to the acromion and greater tuberosity were measured. RESULTS: Of the 10 specimens, 9 (90%) had 5 distinct tendinous bands attaching the deltoid to the acromion; 1 specimen had 4 bands. The distances between the center of the deltoid footprint on the humerus and the centers of the pectoralis major, latissimus dorsi, and teres major tendon footprints on the humerus were 43.5 mm, 58.5 mm, and 49.4 mm, respectively. The shortest distances from the perimeter of the pectoralis major to the latissimus dorsi and teres major tendon footprints were 3.9 mm and 9.5 mm, respectively. The distance from the superior aspect of the greater tuberosity to the axillary nerve on the humeral shaft was 50.3 mm (95% confidence interval, 47.0-53.5 mm). The distance from the lateral acromion to the axillary nerve was 69.3 mm (95% confidence interval, 64.1-74.5 mm). CONCLUSIONS: The deltoid muscle had 4 to 5 tendinous insertions on the acromion, and the axillary nerve was 50.3 mm from the tip of the greater tuberosity. The distance between the lower border of the pectoralis major and the axillary nerve was 9.4 mm. CLINICAL RELEVANCE: Knowledge of the quantitative anatomy of the tendons of the proximal humerus and axillary nerve can aid in identifying structures of interest during open shoulder surgery and in avoiding iatrogenic axillary nerve injury. Furthermore, this study provides direction to avoid injury to the deltoid tendons during open surgery.

Quantification of the deltoid muscle height in the region of the coraco-acromial ligament - An ultraso-nographical study

Although the triangular deltoid muscle has three distinct portions originating from the scapula and acromion, the underlying coraco-acromial ligament presents as the stabilizing factor for the anterior deltoid, thus bridging the interval within the coraco-acromial arch. As the deltoid muscle integrity is vulnerable during the resection of the coraco-acromial ligament from the acromion, the purpose of this study was to quantify the height of the deltoid muscle over the region of the coraco-acromial ligament. The superior shoulder region in seventeen nor-mal female individuals (n = 34) were bilaterally examined through an ultrasonographic system (Medelec Synergy: Acertys T2 EDX, 2012). In addition to the length of the coraco-acromial ligament, the height of the deltoid muscle was measured at three selected areas between the posterior aspect of the coracoid process and the anterior acromial tip, just superior to the coraco-acromial ligament. The mean coraco-acromial length was found to be 24.8±7.6mm. The mean deltoid height at regions 1, 2 and 3 were 8.4 ± 2.7 mm, 9.1 ± 2.1 mm and 8.4 ± 3.0 mm, respectively. The height of the deltoid muscle was recorded to be constant across all three regions related to the coraco-acromial ligament. Moreover, the specific height of the deltoid muscle in the region of the coraco-acromial ligament was not reported in the literature reviewed. In addition, this study was done to complement the introduction of the delto-fulcral triangle model by Naidoo et al. (2017). The provision of data regarding the specific deltoid height may assist to preserve the deltoid muscle and the accompanying coraco-acromial ligament during operative procedures

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Establishing a new appropriate intramuscular injection site in the deltoid muscle.

It is becoming increasingly important for clinicians to identify a safer intramuscular (IM) injection site in the deltoid muscle because of possible complications following the vaccine administration of IM injections. We herein examined 4 original IM sites located on the perpendicular line through the mid-acromion to establish a safer IM injection site. Thirty healthy volunteers participated in this study and the distances from our 4 IM sites to some anatomical landmarks on their left arms were measured. Ultrasonography (US) was also performed to measure the thickness of the deltoid muscle and identify the posterior circumflex humeral artery (PCHA) along the course of the axillary nerve. Subcutaneous thickness was measured using 2 methods: measuring the skin thickness with caliper after pinching the skin, and with US. The results obtained revealed that the intersection between the anteroposterior axillary line (the line between the upper end of the anterior axillary line and the upper end of the posterior axillary line) and the perpendicular line from the mid-acromion was the most appropriate site for IM injections because it was distant from the axillary nerve, PCHA, and subdeltoid/subacromial brusa. At this site, depth of needle insertions was 5 mm greater than the subcutaneous thickness at a 90° angle, which was sufficient to penetrate subcutaneous tissue in both sexes. Subcutaneous thickness can be assessed with almost the same accuracy by US or measuring with calipers after pinching the skin. The results of the present study support the improved vaccine practice for safer IM injections.

Anatomical Relationship of the Axillary Nerve to the Pectoralis Major Tendon Insertion.

Axillary nerve injury is a risk of the deltopectoral approach to the proximal humerus. The anterior motor branch is potentially vulnerable during subdeltoid dissection. Insertion of the pectoralis major tendon is an easily identifiable landmark on the humerus. This anatomical study explored whether the superior aspect of the pectoralis major tendon is a useful landmark for localizing the anterior motor branch of the axillary nerve as it travels under the lateral and anterior deltoid muscle. A total of 30 fresh-frozen human bilateral cadaveric upper extremities were examined. A deltopectoral approach was used to expose the pectoralis major tendon insertion and the anterior motor branch of the nerve under the deltoid muscle. The distance between the nerve as it crossed the posterolateral humerus and superior border of the pectoralis major tendon was measured. The axillary nerve was a mean 3.2 mm (range, 0-8 mm) distal to the superior border of the pectoralis major tendon insertion. No significant differences were observed in this anatomical relationship with the shoulder in abduction or external rotation. The nerve was not proximal to the superior border of the pectoralis major tendon in any specimen. The superior border of the pectoralis major tendon insertion represents a reliable landmark for the anterior motor branch of the axillary nerve as it travels under the deltoid muscle. The nerve is located at the level of the proximal centimeter of the pectoralis major tendon. Appreciation of this relationship may decrease risk of injury to the nerve when using a deltopectoral approach. [Orthopedics. 2017; 40(3):e460-e464.].

Ultrasound Dimensions of the Rotator Cuff and Other Associated Structures in Korean Healthy Adults.

In evaluating patients complaining of shoulder pain, ultrasonography is an emerging imaging tool due to convenience, low cost, high sensitivity and specificity. However, normative values of ultrasound dimensions of the shoulder to be compared with pathologic findings in Korean adults are not provided yet. We evaluated the ultrasound dimensions of the rotator cuff, long head of biceps tendon, deltoid muscle and acromioclavicular joint in Korean healthy adults. Shoulder ultrasonography was performed on 200 shoulders from 100 healthy adults. The dimensions of the thickness of rotator cuff (supraspinatus, infraspinatus, subscapularis tendon), deltoid muscle, long head of biceps tendon, subacromial subdeltoid bursa, and acromioclavicular joint interval were measured in a standardized manner. Differences in measurements among sex, age, and dominant arms were compared. The thickness of rotator cuff tendons (supraspinatus, infraspinatus, subscapularis) and deltoid muscle were significantly different between men and women. The thickness of subacromial subdeltoid bursa was significantly different between men and women for non-dominant side. In rotator cuff tendon measurements, the differences between dominant and non-dominant shoulders were not significant, which means the asymptomatic contralateral shoulder can be used to estimate the normal reference values. When stratified by age divided by 10 years, the measurements of supraspinatus, subscapularis and deltoid thickness showed tendency of increase with the age. The acromioclavicular joint interval, on the other hand, revealed decreasing tendency. This report suggests normative values of ultrasound dimensions of healthy Korean population with varying age, and can be useful as reference values in evaluating shoulder pathology, especially in rotator cuff tendon pathology.

The effect of glenosphere diameter and eccentricity on deltoid power in reverse shoulder arthroplasty.

AIMS: The eccentric glenosphere was principally introduced into reverse shoulder arthroplasty to reduce the incidence of scapular notching. There is only limited information about the influence of its design on deltoid power and joint reaction forces. The aim of our study was to investigate how the diameter and eccentricity of the glenosphere affect the biomechanics of the deltoid and the resultant joint reaction forces. METHODS: Different sizes of glenosphere and eccentricity were serially tested in ten cadaveric shoulders using a custom shoulder movement simulator. RESULTS: Increasing the diameter of the glenosphere alone did not alter the deltoid moment arm. However, using an eccentric glenosphere increased the moment arm of the deltoid, lowered the joint reaction force and required less deltoid force to generate movement. CONCLUSION: Eccentricity is an independent variable which increases deltoid efficiency and lowers joint reaction forces in a reverse shoulder arthroplasty. Cite this article: Bone Joint J 2016;98-B:218-23.

Age-related structural changes in upper extremity muscle tissue in a nonhuman primate model.

BACKGROUND: Longitudinal studies of upper extremity aging in humans include logistical concerns that animal models can overcome. The vervet is a promising species with which to study aging-related processes. However, age-related changes in upper extremity muscle structure have not been quantified in this species. This study measured age-related changes to muscle structure, examined relationships between muscle structure and measures of physical performance, and evaluated the presence of rotator cuff tears. METHODS: Muscle structure (volume, optimal fiber length, and physiologic cross-sectional area (PCSA)) of 10 upper extremity muscles was quantified from the right upper limb of 5 middle-aged and 6 older adult female vervets. RESULTS: Total measured PCSA was smaller (P = .001) in the older adult vervets than in the middle-aged vervets. Muscle volume reduction predominate the age-related reductions in PCSA. Total measured PCSA was not correlated to any measures of physical performance. No rotator cuff tears were observed. Supraspinatus volume was relatively larger and deltoid volume relatively smaller in the vervet compared with a human. CONCLUSIONS: The vervet is an appropriate translational model for age-related upper extremity muscle volume loss. Functional measures were not correlated to PCSA, suggesting the vervets may have enough strength for normal function despite loss of muscle tissue. Reduced relative demand on the supraspinatus may be responsible for the lack of naturally occurring rotator cuff tears.

Rare accessory slip of the deltoid muscle conjoined with teres minor

Routine dissection of a 69-year-old American Caucasian female revealed a unique accessory slip of the deltoid muscle which was conjoined with the proximal portion of teres minor. The variant muscle bundle was united with the distal portion of the deltoid, but deviated superomedially and fused with the origin of teres minor. This discovery possesses clinical relevance with respect to surgical repair of shoulder pathology or trauma. Shoulder injuries and their respective repairs are very common. Therefore, consideration of this variant is necessary for the correct diagnosis and treatment of massive trauma or other shoulder pathology that is refractory to standard treatments

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Coaptation/elevation role of the middle deltoid muscle fibers: a static biomechanical pilot study using shoulder MRI.

PURPOSE: It is generally recognized that the middle deltoid muscle fibers (MDMF) have an elevating effect on the humeral head at small abduction angles. These forces are normally counterbalanced by the coaptation effect of the rotator cuff (RC) muscles to maintain shoulder stability. With RC tears, this balance may be jeopardized leading to shoulder dysfunction. Conversely, not all patients with RC tears develop shoulder dysfunction. The purpose of this study was to investigate the coaptation/elevation forces (CEF) ratio of the MDMF in RC tears subjects and in volunteers, using magnetic resonance imaging (MRI). METHODS: Magnetic resonance imaging images in 10 subjects with RC tears and in five volunteers were used to build a three-dimensional model of the shoulder. The CEF ratio of the MDMF was estimated by representing the glenohumeral joint as a pulley. RESULTS: The CEF ratio increased from the posterior to the anterior fibers of the MDMF.The median and interquartile range (IQR) of the CEF ratios of the posterior-third, middle-third, anterior-third and anterior-surface segments of the deltoid were: 0.16 (IQR = 0.23), 0.61 (IQR = 0.4), 1.42 (IQR = 0.41), 1.94 (IQR = 0.56) in subjects, and 0.06 (IQR = 0.24), 0.45 (IQR = 0.28), 1.32 (IQR = 1.01), 1.49 (IQR = 0.39) in volunteers. In the subjects, the CEF ratio of the anterior-surface segment was greater than all other segments (P ≤ 0.03). CONCLUSIONS: The CEF ratio of the MDMF increased from its posterior segment to its anterior segment, indicating a greater stabilizing effect of the anterior segment both in RC tears subjects and in volunteers. Strengthening of the anterior fibers of the MDMF could potentially improve shoulder function in subjects with RC tears.