Pectoral Girdle Flashcards
What is the scapula?
The scapula is also known as the shoulder blade. It articulates with the humerus at the glenohumeral joint, and with the clavicle at the acromioclavicular joint. In doing so, the scapula connects the upper limb to the trunk.
It is a triangular, flat bone, which serves as a site for attachment for many (17) muscles.
Describe the costal surface of the scapula
The anterior surface of the scapula is termed ‘costal’, this is because it is the side facing the ribcage.
This side of the scapula is relatively unremarkable, with a concave depression over most of its surface, called the subscapular fossa. The subscapularis muscle, one of the rotator cuff muscles, originates from this side.
Originating from the superolateral surface of the costal scapula is the coracoid process. It is a hook-like projection, which lies just underneath the clavicle. The short head of the biceps brachii and the pectoralis minor attach here, while the coracobrachialis muscle originates from this projection.
Describe the lateral surface of the scapula
The lateral surface of the scapula faces the humerus. It is the site of the glenohumeral joint, and of various muscle attachments.
Glenoid fossa – A shallow cavity, which articulates with the humerus to form the glenohumeral joint. The superior part of the lateral border is very important clinically, as it articulates with the humerus to make up the shoulder joint, or glenohumeral joint.
Supraglenoid tubercle – A roughening immediately superior to the glenoid fossa, this is the place of attachment of the long head of the biceps brachii.
Infraglenoid tubercle – A roughening immediately inferior to the glenoid fossa, this is the place of attachment of the long head of the triceps brachii.
Describe the posterior surface of the scapula
Spine – The most prominent feature of the posterior scapula. It runs transversely across the scapula, dividing the surface into two.
Infraspinous fossa – The area below the spine of the scapula, it displays a convex shape. The infraspinatus muscle originates from this area.
Supraspinous fossa – The area above the spine of the scapula, it is much smaller that the infraspinous fossa, and is more convex in shape. The supraspinatus muscle originates from this area.
Acromion – projection of the spine that arches over the glenohumeral joint and articulates with the clavicle.
What are the functions of the clavicle?
- Attaches the upper limb to the trunk.
- Protects the underlying neurovascular structures supplying the upper limb.
- Transmits force from the upper limb to the axial skeleton.
Describe the sternal end of the clavicle
The sternal end contains a large facet – for articulation with the manubrium of the sternum at the sternoclavicular joint.
The inferior surface of the sternal end is marked by a rough oval depression for the costoclavicular ligament (a ligament of the SC joint).
Describe the shaft of the clavicle
The shaft of the clavicle acts a point of origin and attachment for several muscles – deltoid, trapezuis, subclavius, pectoralis major, sternocleidomastoid and sternohyoid
Describe the acromial end of the clavicle
Conoid tubercle – attachment point of the conoid ligament, the medial part of the coracoclavicular ligament.
Trapezoid line – attachment point of the trapezoid ligament, the lateral part of the coracoclavicular ligament.
The coracoclavicular ligament is a very strong structure, effectively suspending the weight of the upper limb from the clavicle.
Can you label the clavicle?
What type of joint is the acromioclavicular joint?
The acromioclavicular joint is a plane type synovial joint. It is located where the lateral end of the clavicle articulates with the acromion of the scapula.
Describe the articulating surfaces of the acromioclavicular joint
The acromioclavicular joint consists of an articulation between the lateral end of the clavicle and the acromion of the scapula. It has two atypical features:
The articular surfaces of the joint are lined with fibrocartilage (as opposed to hyaline cartilage).
The joint cavity is partially divided by an articular disc – a wedge of fibrocartilage suspended from the upper part of the capsule.
Describe the joint capsule of the acromioclavicular joint
The joint capsule consists of a loose fibrous layer which encloses the two articular surfaces. It also gives rise to the articular disc. The posterior aspect of the joint capsule is reinforced by fibres from the trapezius muscle.
As would be expected of a synovial joint, joint capsule is lined internally by a synovial membrane. This secretes synovial fluid into the cavity of the joint.
Describe the ligaments of the acromioclavicular joint
Acromioclavicular – runs horizontally from the acromion to the lateral clavicle. It covers the joint capsule, reinforcing its superior aspect.
Conoid – runs vertically from the coracoid process of the scapula to the conoid tubercle of the clavicle.
Trapezoid – runs from the coracoid process of the scapula to the trapezoid line of the clavicle.
Collectively, the conoid and trapeziod ligaments are known as the coracoclavicular ligament. It is a very strong structure, effectively suspending the weight of the upper limb from the clavicle.
What movements occur at the acromioclavicular joint?
The acromioclavicular joint allows a degree of axial rotation and anteroposterior movement.
As no muscles act directly on the joint, all movement is passive, and is initiated by movement at other joints (such as the scapulothoracic joint).
Describe the neurovascular supply of the acromioclavicular joint?
The arterial supply to the joint is via two vessels:
Suprascapular artery – arises from the subclavian artery at the thyrocervical trunk.
Thoraco-acromial artery – arises from the axillary artery.
The veins of the joint follow the major arteries.
The acromioclavicular joint is innervated by articular branches of the suprascapular and lateral pectoral nerves. They both arise directly from the brachial plexus.
Describe the articulating surfaces of the sternoclavicular joint
The sternoclavicular joint consists of the sternal end of the clavicle, the manubrium of the sternum, and part of the 1st costal cartilage. The articular surfaces are covered with fibrocartilage (as opposed to hyaline cartilage, present in the majority of synovial joints). The joint is separated into two compartments by a fibrocartillaginous articular disc.
What are the ligaments of the sternoclavicular joint?
Sternoclavicular ligaments (anterior and posterior) – these strengthen the joint capsule anteriorly and posteriorly.
Interclavicular ligament – this spans the gap between the sternal ends of each clavicle and reinforces the joint capsule superiorly.
Costoclavicular ligament – the two parts of this ligament (often separated by a bursa) bind at the 1st rib and cartilage inferiorly and to the anterior and posterior borders of the clavicle superiorly. It is a very strong ligament and is the main stabilising force for the joint, resisting elevation of the pectoral girdle.
