anatomyphysiologyblog - Joints of Pectoral Girdle: Anatomy of Shoulder Joint, Acromioclavicular Joint in addition to Sternoclavicular Joint
Pectoral Girdle
Pectoral Girdle or Shoulder Girdle connects the costless purpose of the upper limb alongside the trunk. It consists of scapula too clavicle on each side. Influenza A virus subtype H5N1 serial of anatomical scheme makes the girdle extremely mobile. The mobility of scapula is essential for costless displace of upper limb. The clavicle acts every bit a strut which holds the scapula laterally allowing the upper limb to swing freely from the side of the trunk.
Pectoral girdle consists of 3 joints: i) Sternoclavicular joint, ii) Acromioclavicular articulation too iii) Glenohumeral joint. The scapula is connected to the clavicle too humerus (bone of the arm) past times acromioclavicular too glenohumeral joints respectively. The upper limb too pectoral girdle are connected to the torso (axial skeleton) solely through the sterno-clavicular joint. Scapula does non brand whatever anatomical articulation alongside axial skeleton rather it is connected to the vertebral column too chest solely past times the muscles. This connecter of scapula alongside the chest is sometimes referred every bit conceptual scapula-thoracic joint or physiological scapula-thoracic joint. Thus the extremely mobile pectoral girdle is supported too stabilized past times the muscles that are attached to the ribs, sternum too vertebrae.
Joints of Pectoral Girdle
Sternoclavicular Joint
Type: Saddle type of synovial joint.
Articulation:
The sternal halt of the clavicle articulates alongside the manubrium sterni too the showtime costal cartilage.
Capsule: This surrounds the articulation too is attached to the margins of the articular surfaces.
Synovial membrane: This lines the within of capsule too extends to the margins of the cartilage roofing the articular surfaces.
Ligaments:
Anterior too Posterior sternoclavicular ligaments reinforce the capsule from the front end too behind.
Interclavicular ligament strengthens the capsule superiorly. It extends from sternal halt of i clavicle to the sternal halt of the other.
Costoclavicular ligament connects the inferior surface of sternal halt of clavicle to the 1st rib too its costal cartilage.
Articular disc: It is a fibrocartilaginous disc which divides the interior of the articulation into 2 compartments. The peripheral margin of the disc is attached to the interior of the capsule. It is besides strongly attached to the superior margin of the articular surface of the clavicle inwards a higher house too to the showtime costal cartilage below.
Movements:
It is really mobile to allow movements of the pectoral girdle too upper limb. The movements that occur inwards SC articulation are: forward too backward movements too elevation too depression. During total elevation of upper limb the clavicle is raised to unopen to a 600 angle.
Muscles producing the movement:
Forward movement: Serratus anterior
Backward movement: trapezius too rhomboids
Elevation: trapezius, sternocleidomastoid, levator scapulae too rhomboids
Depression: pectoralis tyke too subclavius
Nerve supply: The supraclavicular nervus too the nervus to the subclavius muscle.
Blood supply: past times internal thoracic too suprascapular arteries.
Acromioclavicular Joint
Type: Plane synovial joint
Articulation: lateral halt of clavicle articulates alongside the acromion of the scapula.
Capsule: Capsuleis relatively loose too is attached to the margin of the articular surfaces. From the capsule an incomplete wedge shaped fibrocartilaginous disc projects into the articulation cavity from the above.
Ligaments: Superior too inferior acromioclavicular ligaments reinforces the capsule. The integrity of the articulation is maintained past times the extrinsic ligament called coracoclavicular ligament. It consists of a twosome of rigid bands that connect the coracoid procedure of scapula to the clavicle. The coracoclavicular ligament consists of 2 parts: conoid too trapezoid part.
The conoid ligament is cone shaped alongside its apex directed downward too attached to the root of the coracoid procedure too its base of operations to the conoid tubercle on the undersurface of the clavicle. The trapezoid ligament is extends laterally for its attachment from the superior surface of coracoid procedure to the trapezoid draw of piece of job on the inferior surface of the clavicle. The coracoclavicluar ligament is besides responsible for suspending the scapula too costless limb from clavicular strut.
Movement: Influenza A virus subtype H5N1 gliding displace takes house when the scapula rotates or when the clavicle is elevated or depressed. The thoraco-appendicular muscles that attach to too displace the scapula drive the acromion to displace on the clavicle.
Nerve supply: Supraclavicular, lateral perctoral too axillary nerves
Blood Supply: Suprascapular too thoracoacromial arteries
Glenohumeral Joint
Glenohumeral articulation is besides called shoulder joint.
Type: Ball too Socket synovial joint
Articulation: occurs betwixt the large rounded head of the humerus too a shallow glenoid cavity of the scapula. The articular surfaces are lined past times the hyaline cartilage. The shallow glenoid cavity is deepened past times a fibrocartilaginous tissue called glenoid labrum. The cavity receives to a greater extent than than a 3rd of humeral caput which is held inwards seat past times the tonus of the musculotendinous rotator cuff muscles.
Capsule:
The fibrous capsule surrounds the articulation too is relatively sparse too lax allowing the greater gain of movement. Superiorly it is strengthened past times the fibrous slips from the rotator cuff muscles. Inferiorly it is relatively weaker too is mutual site for dislocation of the joint.
Attachment of the capsule:
Medially – it is attached to the margin of the glenoid cavity exterior the labrum. It besides enclosed the source of long caput of biceps brachii.
Laterally – it is attached to anatomical cervix of humerus except at 2 places, a) upper halt of bicipital groove to allow the passage of tendon of long caput of biceps brachii too b) inferomedially, the draw of piece of job of attachment extends downward for nigh 1 cm to the surgical neck.
Synovial Membrane: it lines the within of the capsule too reflects from it onto the glenoid labrum too humerus every bit far every bit the articular margin of the head. It forms a tubular sheath about the long tendon of biceps brachii. It passes through the anterior wall of the capsule to cast the subscapular bursa beneath the subscapularis muscle.
Ligaments:
Glenohumeral ligament
Coracohumeral ligament
Transverse humeral ligament
Coracoacromial ligament (accessory ligament)
Glenoid labrum
Glenohumeral too coracohumeral ligaments are the thickening of articulation capsule that strengthens the anterior too superior aspects of the capsule respectively.
Glenohumeral ligaments are 3 fibrous bands, evident solely on the interior of the articulation capsule. The superior, middle too inferior bands of the glenohumeral ligaments are attached medially to the superomedial margin of glenoid cavity too blends alongside glenoid labrum. Laterally, all 3 bands radiate too are attached to the upper purpose of lesser tubercle, lower purpose of lesser tubercle too lower purpose of anatomical cervix respectively.
The coracohumeral ligament extends from the root of the coracoid procedure to anatomical cervix reverse the greater tubercle of the humerus.
The transverse humeral ligament bridges the gap betwixt the 2 tubercles too strengthens the capsule.
Coracoacromial ligament is an accessory ligament which along alongside the inferior aspects of acromion too coroacoid procedure of scapula forms coracoacromial arch too protects the superior human face of the articulation every bit it prevents the superior displacement of humeral head. Influenza A virus subtype H5N1 subacromial bursa intervenes betwixt the arch inwards a higher house too the tendon of supraspinatus too greater tubercle below.
Glenoid labrum:
It is made upwardly of fibrocatilaginous tissue too helps deepening the glenoid cavity. It is attached to the margin of the glenoid cavity except inwards a higher house from where the long caput of biceps brachii arises.
Movements at shoulder joint:
The shoulder articulation has greater mobility. (Its stability has been compromised at the toll of the mobility every bit compared to hip articulation which has greater stability but has express gain of movements). The liberty of displace is mainly due to the sparse too lax capsule too the large size of humeral caput compared to the receiving socket provided past times the glenoid cavity. The glenohumeral articulation produces movements about 3 axes too permits flexion-extension, adduction-abduction, medial-lateral rotation too circumduction.
Flexion too Extension:
Flexion too extension cause got house correct angle to the airplane of the body of scapula about an axis that passes through the humeral caput too middle of glenoid cavity. Flexion moves the arm forrard too medially too is nigh 900. Extension moves the arm backward too laterally too is nigh 450.
Adduction-abduction:
Abduction too adduction cause got house parallel to the airplane of the body of scapula about an axis which passes through the caput of humerus too is parallel to the glenoid cavity. The abduction carries the arm laterally too adduction medially. During adduction the arm tin can survive swung 450 across the front end of the chest.
Mechanism of Abduction:
Abduction of the arm is accomplished past times displace at shoulder articulation every bit good every bit past times the rotation of scapula at conceptual scapula-thoracic joint. The abduction is initiated for the showtime 150 past times supraspinatus musculus which besides holds the caput of the humerus against the glenoid cavity. The afterward activity so allows deltoid to cause got over too consummate the farther abduction. The limb tin can survive elevated past times 1800 during abduction. Except for the showtime thirty score of abduction which occur due to displace at shoulder articulation only, inwards every 150 elevation, 100 occurs at shoulder articulation too 50 past times rotation of scapula at conceptual scapula-thoracic articulation inwards the ration of 2:1. When the arm is abducted to 900, the farther elevation is prevented every bit the articular surface is exhausted too the greater tubercle impinges on the lateral border of acromion. The farther elevation is so accomplished past times the lateral rotation of humerus past times 1800 which brings the greater tubercle posteriorly thence providing to a greater extent than articular surface to perish along elevation. From 1200-1800, the abduction is accomplished past times the rotating the scapula.
Medial too lateral rotations:
The airplane producing these movements is a vertical axis passing through middle of the humeral caput to the middle of the capitulum. In a semi-flexed elbow, the medial rotation at shoulder articulation carries the manus medially too lateral rotation moves the manus laterally.
Circumduction:
It is a combination of inwards a higher house mentioned movements so that the lower halt of the humerus defines the base of operations of the amount too the humeral caput forms apex of the cone.
Muscles producing the movements at shoulder joint:
Flexion: Anterior fibers of Deltoid, Pectoralis Major too Coracobrachialis (weak flexor)
Extension: Posterior fibers of Deltoid, Latissimus Dorsi too Teres Major
Abduction: Supraspinatus (initial 150) too Deltoid
Adduction: Pectoralis Major, Latissimus Dorsi, Teres Major too Subscapularis
Medial Rotation: Subscapularis, Latissimus dorsi, Teres Major, Pectoralis Major, Anterior Fibers of Deltoid
Lateral Rotation: Infraspinatus, Teres Minor too Posterior Fibers of Deltoid
Factors stabilizing the shoulder joint:
As noted earlier, the shoulder articulation is relatively weaker articulation owing to its sparse too lax articulation capsule, greater mobility too shallow glenoid fossa to have larger caput of the humerus.
Rotator cuff: The tendons of little muscles namely subscapularis, supraspinatus, Infraspinatus too teres tyke on their agency to insertion on humerus flatten too blend alongside each other too alongside the fibrous capsule of shoulder joint. The tone of these muscles back upwardly too strengthen the shoulder articulation from the front, inwards a higher house too from the behind.
Glenoid labrum: this fibrocartilaginous tissue deepens the glenoid cavity.
Glenohumeral too Coracohumeral ligaments back upwardly the articulation from anterior too superior aspects respectively.
The coracoacromial arch prevents the upwards displacement of the joint. Similarly, the tendon of long caput of biceps brachii besides holds the caput of the humerus inwards seat during abduction. Similarly, the downward displacement of humerus during abduction is prevented past times the long caput of triceps brachii.
Blood Supply:
Anterior circumflex humeral artery, branch of 3rd purpose of axillary artery
Posterior circumflex humeral artery, branch of 3rd of axillary artery
Branches of suprascapular artery, branch of thyrocervical torso of subclavian artery or straight from subclavian artery
Nerve Supply:
Axillary nervus too suprascapular nerve
REFERENCES:
Following resources are used piece preparing this post (readers are strongly recommended to become through them for to a greater extent than details):
Gray's Anatomy
K. L. Moore's Clinically Oriented Anatomy
R. Snell's Clinical Anatomy