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Essay: Exploring the Anatomy of the Shoulder and its Role in Flexibility and Stability.

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atomy I – Back, Thoracic and Abdominal Walls, Upper Limb

Title: The Shoulder: A perfect compromise between flexibility and stability. Discuss with reference to the normal anatomy of the shoulder and at least one shoulder abnormality of your choice.

Name: Polly Lyons

Student ID: 16397276

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Introduction

The shoulder is a perfect compromise between flexibility and stability. The shoulder is an enarthrodial joint. It is essential that the shoulder joint maintains a sufficient amount of stability while simultaneously sustaining mobility to avoid injury and to make the best use of its function and performance. It is quite clear that the shoulder is undoubtedly one of the most intricate joints in the body with the most extensive range of motion. This is evident as it has ten different type of articulations in comparison to that of the hip joints which contain only eight. The shoulder is fundamentally the area where the upper limb connects to the trunk. Every shoulder joint is comprised of the clavicle and scapula, ultimately forming the pectoral girdle and the proximal end of the humerus. The joints that the shoulder consists of are the sternoclavicular joint, the acromioclavicular joint and the glenohumeral joint. These joints and bones are in turn supported by the extensive musculature that surrounds it. It is the superficial muscles such as the trapezius and deltoid muscles that join the scapula and clavicle to the arm and also to the trunk. As well as these major superficial muscles there are also many deep intrinsic muscles that work in harmony with each other in the shoulder that we will also discuss in detail. (Drake et al., n.d.)

The Joints That Make Up The Shoulder

The sternoclavicular joint, the acromioclavicular joint and the glenohumeral joints together are the joints that the shoulder comprises of.

The complex design of glenohumeral joint and the concurrent movement of all the features of the shoulder girdle plays a significant role in the mobility and flexibility. Taking into consideration the flexibility of the joint, its stability arises from the active control of the muscles which leaves a slight role for the glenohumeral capsule, labrum and ligaments in sustaining stability. (FC, 2018) The glenohumeral joint is fundamentally the synovial ball and socket joint or enarthrodial joint which involves the glenoid cavity of the scapula and the globular head of the humerus. This multiaxial joint allows the shoulder to have broad range of motions. The stability of the joint is in turn supplied by muscles such as the long head of the biceps brachii, related bony processes, rotator cuff muscles and finally extrascapular ligaments The rotator cuff muscles ensure the head of the humerus remains in the glenoid cavity without adjusting the flexibility of the ball and socket joint. Flexion, extension, abduction, adduction, medial rotation, lateral rotation and circumduction are the extensive amount of movements available at this specific joint. A true example of flexibility in the shoulder. (Drake et al., n.d.) Encasing the features of the joint is the fibrous joint capsule. The lax nature of the joint capsule allows for a greater range of motion and flexibility. The synovial membrane lies directly underneath the joint capsule. Its function is to generate synovial fluid, decreasing friction and maintaining flexibility in the joint. To alleviate friction and promote flexibility to an even greater extent numerous synovial bursae (synovial fluid filled sac) are present, cushioning between tendons. The subtendinous bursa and subacromial are two of great importance. In the middle of the subscapularis muscle and the fibrous membrane is where the subtendinous bursa of the subscapularis is situated. Ligaments of the shoulder joint are crucial in maintaining stability in the joint. The ligament that develops to form superior, middle and inferior ligaments is the glenohumeral ligament. The glenoid fossa and the humerus are joined together by these particular ligaments which in turn forms the joint capsule. The anterior aspect of the joint is stabilised by the glenohumeral ligaments and they prevent it from dislocation of the joint anteriorly also. Superiorly to the glenohumeral ligament lies the coracohumeral ligament. The coracohumeral ligament adheres to the greater tubercle of the humerus to coracoid processes’ base, in doing so it reinforces the superior component of the joint capsule. (Jones, O., 2018) The transverse humeral ligament ensures that the tendon of the long head of the biceps brachii is retained in the intertubercular sulcus. The remaining ligaments are the coracoclavicular ligament and the coracoacromial ligament which also provide stability in the glenohumeral joint. the anterior and posterior circumflex humeral and suprascapular arteries that are the principal blood supply to the joint. (Drake et al., n.d.)

(Jones, O., 2018)

A synovial joint called the sternoclavicular joint exists in the middle of the clavicle and the manubrium of the sternum. The sternoclavicular joint is a joint of exceptional interest as it holds a great deal of strength and stability while simultaneously acting almost as if it were a ball and socket joint as it allows for a relative amount of motion. It connects the axial skeleton and upper limb. Its mobility arises from the fact it is a saddle joint which allows it to move on two axes; the anteroposterior and vertical planes. It is the posterior and anterior sternoclavicular ligaments, the interclavicular ligaments and the costoclavicular ligaments that support this joint. (Drake et al., n.d.) Its blood supply is from the internal thoracic artery and the suprascapular artery. It is the medial supraclavicular nerve (C3 and C4) and the nerve to subclavius (C5 and C6) that act as the nervous supply to the joint. Motility is a prominent feature of this joint. Its movements include; elevation, depression, protraction, retraction and rotation. Stability arises from the steady joint capsule and the strong, supporting ligaments. (Jones, O., 2018)

The acromioclavicular joint is one of the smaller synovial joints in the shoulder, situated at the point where the lateral end of the clavicle articulates with the acromion of the scapula. Fibrocartilage covers the articular surfaces. Strength and stability in this joint arises from the three main ligaments; acromioclavicular ligament which lies horizontally from the acromion as far as the clavicle, the conoid ligament which lies vertically from the coracoid process of the scapula to the conoid tubercle, and finally the trapezoid ligament which. Is situated from the trapezoid line of the clavicle to the coracoid process. Together the conoid ligament and the trapezoid ligament create the coracoclavicular ligament. The suprascapular and thoraco-acromial artery are the arterial supply to the joint. The joints nervous innervation is the suprascapular and lateral pectoral nerves. The acromioclavicular joint doesn’t allow for a great deal of motility or movement but allows some degree of axial rotation and anteroposterior movement. (Jones, O., 2018)

The Bones That Make Up The Shoulder

As previously stated, the shoulder is comprised of the clavicle, scapula and the proximal humerus.

The clavicle also known as the collarbone connects the trunk and the upper limb, spanning from the manubrium of the sternum to the acromion of the scapula. The clavicle is a bone that is entirely palpable and in thinner specimens can be seen under the skin. It carries out various functions in the human body, for example it shelters the neurovasculature that lies beneath it, this same neurovasculature directly supplies the upper limb. The clavicle also functions in the conduction of force to the axial skeleton that comes from the upper limb, a perfect example of how the shoulder joint displays stability. (Jones, O., 2018) There is a gentle s shaped curvature to the clavicle. Facing forward, the concave part is lateral making the convex part medial. An evident tuberosity can clearly be seen on the inferior lateral third of the clavicle. This tuberosity is the conoid tubercle, which serves as a point of attachment for the coracoclavicular ligament. At the acromial (lateral) end of the clavicle there is a small-scale facet used for articulation with an analogous facet of the scapula, on the medial surface of the acromion at the acromioclavicular joint. (Drake et al., n.d.) This facet also acts as a point of adherence for two ligaments called the conoid ligament which is the medial part of the coracoclavicular ligament and the trapezoid ligament which is the lateral part of the coracoclavicular ligament. (Jones, O., 2018) In contrast to the small facet on the acromial end of the clavicle, the sternal (medial) end possesses a larger, more prominent facet for articulation. This facet articulates with the manubrium of the sternum at the sternoclavicular joint and to a lower degree with the first costal cartilage. (Drake et al., n.d.) The deltoid, trapezius, subclavius, pectoralis major, sternocleidomastoid and sternohyoid are all muscles that either arise from or adhere to the shaft of the clavicle. These muscles surrounding the clavicle stabilise the clavicle itself and also allow a small amount of movement and flexibility. (Jones, O., 2018) It is these muscles that cause the outside of the clavicle to become more rough and coarse. The inferior surface is more coarse than the superior surface of the clavicle. (Drake et al., n.d.)

The scapula, or commonly known as the shoulder blade is a big, flat triangular shaped bone. As I have previously stated, it articulates with the clavicle at the acromioclavicular joint but also with the glenohumeral joint at the humerus. These articulations allow the scapula to join both the upper limb and the trunk, creating stability. (Jones, O., 2018) The scapula is composed of the lateral, superior and inferior angles, the superior, lateral and medial boarders and the acromion, spine and the coracoid processes. On the superior side of the lateral angle of the scapula lies a shallow glenoid cavity. This glenoid cavity is what articulates alongside the humerus’ head forming the glenohumeral joint. Directly inferior to the glenoid fossa lies the infraglenoid tubercle, which is a roughening that takes the shape of a triangle. The long head of the triceps brachii adheres itself to the infraglenoid tubercle. A more obscure supraglenoid tubercle lies superior to the glenoid fossa and it is the biceps brachii that adheres itself here. (Drake et al., n.d.) A vast amount of rotator cuff muscles adhere to the posterior surface of the scapula, which faces outwards, allowing the shoulder flexibility if required. The posterior surface holds one of the more distinct features of the scapula known as the spine. The spine stretches transversely across the length of the scapula, which splits the scapula into two subdivisions. Underneath the spine of the scapula lies the convexly shaped infraspinous fossa, the place of origin of the infraspinatus muscle. Superior to the spine is a smaller convexly shaped supraspinous fossa, the place of origin of the supraspinatus muscle. There is a visible anterolateral protrusion known as the acromion on the spine. The acromion curves over the glenohumeral joint and articulates at the acromioclavicular joint at the clavicle. The anterior surface known as the costal surface, which faces towards the ribcage. The subscapular fossa is a large impression in the costal surface. The muscle that originates in the subscapular fossa is the subscapularis. Another process called the coracoid process begins from the superolateral surface of the costal scapula. It is a beak shaped protrusion that can be found directly underneath the clavicle. A muscle known as the pectoralis minor adheres here. Other muscles called the coracobrachialis and biceps brachii (short head) begin at this protrusion. (Jones, O., 2018) Directly medial to the coracoid process lies a small evident notch, known as the suprascapular notch. Quite a copious amount of the scapula’s features can be palpated such as the coracoid processes tip, the inferior angle and the majority of the inferior angle and the medial boarder. (Drake et al., n.d.)

The humerus spans from the shoulder to the elbow, and is a long bone. When we are discussing the humerus in terms of the shoulder joint we are focusing on the proximal end of the bone. The head of the bone, the anatomical neck, the surgical neck the greater and lesser tubercles, intertubercular sulcus and the superior half of the humerus is what the proximal end of the humerus is constructed of. (Drake et al., n.d.) The shallow glenoid fossa of the scapula receives the head of the humerus this articulation forms the glenohumeral joint. This particular articulation allowing a huge range of movement, flexibility and stability. The large globular head of the humerus faces medially and it is the anatomical neck of the humerus that divides it from the lesser and greater tubercles. (Jones, O., 2018) Rotator cuff muscles of the glenohumeral joints site of attachment is on the lesser and greater tubercles, which are promontory features of the humerus. The greater tubercle is situated laterally on the proximal end of the humerus. Three considerably big facets lie on the superior and posterior face of the greater tubercle, these facets supply a place for muscles to adhere to. The supraspinatus attaches to the superior facet, the infraspinatus attaches to the middle facet and the teres minor attaches to the inferior facet on the greater tubercle. On the anterior side of the proximal end of the humerus you will find the lesser tubercle. The lesser tubercle is identifiable due to its large smooth depression used for the attachment of the subscapularis muscle. In-between the greater and lesser tubercle lies the intertubercle sulcus in which the tendon of the long head of the biceps brachii runs through. (Drake et al., n.d.) The lips of the intertubercle sulcus run along the outer margins of the sulcus, it is here muscles such as the pectoralis major, teres major and latissimus dorsi attach themselves. The lateral surface of the humerus houses a structure known as the deltoid tuberosity which is v shaped. The deltoid tuberosity of course is the site of insertion of the deltoid muscle. These muscles work in stabilising or flexing the shoulder when needed. Running distally to the tubercles on to the shaft of the humerus is the surgical neck of the humerus in which the axillary nerve and the humeral vessels rest against. The anatomical neck is situated posterior to the head. (Jones, O., 2018)

Image: Skeleton of the Proximal Upper Limb, An Anterior View.

Copyright @ 2009 Walters Kluwer Health | Lippincott Williams & Wilkins

(Web.duke.edu, 2018)

Muscles That Make Up The Shoulder

1. Table of Extrinsic Muscles of the Shoulder  

Muscle Origin Insertion Innervation Function

Trapezius Originates from the nuchal ligament and spinous processes CVII to TXII and its associated supraspinous ligaments. Inserts itself at the superior boarder of the crest on the scapula’s spine. Also inserts at the acromion, posterior edge of the clavicles lateral third. It innervations include the accessory nerve (XI) and also the sensory rami of C3 and C4. Its role is to elevate and rotate the scapula. It rotates the scapula during abduction of the humerus. The scapula is retracted by the middle fibres and depressed by the lower fibres.  

Latissimus dorsi Begins at T6-T12 of the spinous processes. Iliac crest, thoracolumbar fascia and the inferior three ribs are also places or origin. Floor of intertubercular groove of the humerus is the place of insertion.

Thoracodorsal nerve. Its function is to extend, adduct and rotate the upper limb medially.

Levator scapulae Originates from the transverse processes of the CI and the CII vertebrae. It also arises from the posterior tubercles of the transverse processes of CIII and CIV vertebrae. Posterior surface of medial boarder of scapula from superior angle to root of the spine of the scapula. Branches of the dorsal scapular nerve (C5) and branches of the anterior rami of C3 and C4 spinal nerves. Elevation of the scapula.

Rhomboid minor Stems from the lower part of the ligamentum nuchae and the spinous processes CVII and TI. Inserts itself on the posterior surface of the medial boarder of the scapula. Another area of insertion is at the start of the scapula’s spine. Dorsal scapular nerve. (C4, C5) Functions in elevating and retracting the scapula.

Rhomboid major Origin is the spinous processes of the vertebrae TII- TV. It also originates at the supraspinous ligaments. Inserts itself on the posterior surface of the medial boarder of the scapula. Another area of insertion is at the start of the scapula’s spine all the way to the spines inferior angle. Dorsal scapular nerve. (C4, C5) Functions in elevating and retracting the scapula.

(Drake et al., n.d.)

2. Table of Intrinsic Muscles of the Shoulder

Muscle Origin Insertion Innervation Function

Deltoid It originates at the inferior boarder of the crest of the scapula’s spine. Also stems from the lateral boarder of the acromion and the anterior margin of the clavicles lateral third. Deltoid tuberosity of the humerus. Axillary nerve. (C5, C6) Plays a vital role in the abduction of the arm beyond the initial 15 degrees. Flexion of the arm is helped by the clavicular fibres. Its posterior fibres help in the arms extension.

Teres major It arises from an oval shaped area on the inferior angle of the scapula’s posterior surface. It inserts itself on the medial lip of the intertubercular sulcus. It is innervated by the inferior subscapular nerve. (C5, C6, C7) It functions in the rotation of the arm medially. It also extends the arm.

Supraspinatus Origin is the medial area of the supraspinous fossa and the deep fascia that lays over the muscle. Inserts itself on the greater tubercles superior facet. Innervated by the suprascapular nerve. (C5, C6) It functions as a rotator cuff muscle. It also begins the first 15 degrees of abduction of the arm.

Infraspinatus Its origin is the medial area of the infraspinatus fossa and the deep fascia that lays over the muscle. It inserts itself on the greater tubercle’s middle facet. Innervated by the suprascapular nerve. (C5, C6) It functions as a rotator cuff muscle and is involved in lateral rotation of the arm.

Subscapularis Its origin is at the subscapular fossa. Attaches to the humerus’ lesser tubercle. Innervated by the subscapular nerves. Functions in the medial rotation of the arm.

Teres minor Arises from the superior two thirds of an area of bone on the posterior surface of the scapula. This area of bone sits adjacent to the lateral edge of the scapula. Inserts itself into the greater tubercles’ inferior facet. Innervated by the axillary nerve. (C5, C6) Functions in extending the forearm at the site of the elbow joint. It also helps in extension and adduction of the arm.

(Drake et al., n.d.)

Shoulder Abnormality

1. Dislocation of the glenohumeral joint

The glenohumeral or shoulder joint is the most crucial site for mobility in the shoulder. So it is clear that dislocation of the glenohumeral joint hinders the amount of mobility and flexibility of the shoulder. Dislocations of the glenohumeral joint can be defined in as to where the humeral head is situated relative to the glenoid fossa. The most common form of dislocation of the shoulder is an anterior dislocation which occurs almost 95 percent of the time opposed to posterior and inferior dislocations. Superior dislocation is one that almost never occurs due to avoidance by the coraco-acromial arch. (Jones, O., 2018)

Typically the leading cause of anterior dislocation is extreme extension and lateral rotation of the humerus. This occurs when the head of the humerus is pushed anteriorly and inferiorly into the joint capsule at its most feeble point. The rupturing of the joint capsule causes a higher risk for dislocations, Hill-Sachs lesions and Bankart lesions further on in life. There is a risk of paralysing the deltoid muscle after dislocation of the shoulder due to the fact that the axillary nerve runs extremely close to the head of the humerus. Damage to the axillary nerve also results in inability to feel any sensation around the regimental badge area. (Jones, O., 2018)

(Kerkar, 2018)

2. Frozen shoulder syndrome or adhesive capsulitis

Frozen shoulder or adhesive capsulitis the is a condition that usually is associated with restriction of mobility and a substantial amount of pain, typically over time the shoulder is difficult to move. This syndrome is capable of being treated and the person effected should feel loss of pain and gain the majority of movement back in most cases, but it may not be re-established in everyone. Studies show that there is lack of proof for capsular adhesions which suggests that the name ‘adhesive capsulitis’ is essentially incorrect and should be abandoned. (Lewis, 2015)

As frozen shoulder sets in the capsule of the shoulder begins to stiffen and will feel tight. The capsule itself thickens, scars, shrinks and begins to inflame. (William C. Shiel Jr., 2018) Bands of tissue begin to form they are known as adhesions and are quite thick. Another feature of frozen shoulder is that in many cases there is a considerable amount of synovial fluid missing. Frozen shoulder sets in in three different phases known as; freezing, frozen and thawing. The initial phase is freezing. This stage includes loss of movement and can last approximately 6 weeks – 9 months. In the frozen phase loss of motion is still evident but pain can disappear. Finally thawing occurs when the range of motion available begins to improve. The thawing stage can last up to two years. The cause of frozen shoulder remains uncertain but factors such as diabetes and other diseases such as Parkinson’s disease are influential factors in obtaining frozen shoulder. Frozen shoulder syndrome ultimately impedes the stability and flexibility of the shoulder. (Orthoinfo.aaos.org, 2018)

(Orthoinfo.aaos.org, 2018)

References

1. Drake, R., Vogl, W., Mitchell, A. and Gray, H. (n.d.). Gray's Anatomy for students..

2. Jones, O. (2018). TeachMeAnatomy.com

3. Web.duke.edu. (2018). Duke Anatomy – Lab 10 Prelab: Shoulder, Axilla, & Arm. [online]

4. FC, V. (2018). Shoulder function: the perfect compromise between mobility and stability. – PubMed – NCBI. [online] Ncbi.nlm.nih.gov.

5. Lewis, J. (2015). Frozen shoulder contracture syndrome – Aetiology, diagnosis and management. Manual Therapy, 20(1), pp.2-9.

6. Orthoinfo.aaos.org. (2018). Frozen Shoulder – Adhesive Capsulitis – OrthoInfo –

AAOS. [online]

7. Kerkar, P. (2018). Shoulder Joint Dislocation: Causes, Types, Complications. [online]

8. William C. Shiel Jr., F. (2018). Frozen Shoulder Treatment, Diagnosis & Causes. [online]

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