Thoracic Skeleton PDF

THORACIC SKELETON, CLASSIFICATION OF JOINTS Sophio Kakabadze, MD  Thoracic cage The bony framework of the chest (thorax), called the thoracic cage, is roughly barrel-shaped and includes the thoracic vertebrae posteriorly, the ribs laterally, and the sternum and cos...

THORACIC SKELETON, CLASSIFICATION OF JOINTS Sophio Kakabadze, MD  Thoracic cage The bony framework of the chest (thorax), called the thoracic cage, is roughly barrel-shaped and includes the thoracic vertebrae posteriorly, the ribs laterally, and the sternum and costal cartilages anteriorly It is formed by the 12 thoracic vertebrae, 12 pairs of ribs and associated costal cartilages and the sternum.  Thoracic cage support thorax and protect its vital structures (e.g., heart, lungs, aorta, etc). attachment point for many muscles facilitates breathing  Sternum Composed of 3 flat bones Manubrium: cartilages of 1st ribs articulate here Sternal body: cartilages of 3rd–7th ribs attach here Xiphoid process  Sternum manubrium is the superiormost part of the sternum. thicker and wider than other parts of the sternum. forms articulations with the clavicle (sternoclavicular joint), body of the sternum (manubriosternal joint), first rib and superior half of the second rib (sternocostal joints).  Sternum manubrium The superior aspect of the manubrium- jugular notch – this is visible underneath the skin. Either side of the jugular notch, there is a large fossa lined with cartilage. These fossae articulate with the medial ends of the clavicles, forming the sternoclavicular joints.  sternoclavicular joint formed by an articulation between three structures: Sternal end of the clavicle Manubrium of the sternum First costal cartilage (cartilage associated with the first rib)  sternoclavicular joint Ligaments The ligaments of the sternoclavicular joint provide much of its stability. There are four main ligaments: Sternoclavicular ligaments (anterior and posterior) – reinforces the joint capsule anteriorly and posteriorly. Interclavicular ligament – attaches to the sternal end of both clavicles and reinforces the joint capsule superiorly. Costoclavicular ligament – attaches the first rib and costal cartilage to the inferior surface of the clavicle. It is the main stabilising force for the joint, resisting elevation of the pectoral girdle.  sternoclavicular joint Movements The sternoclavicular joint has a large degree of mobility, with several movements possible: Elevation of the shoulders – shrugging the shoulders or abducting the arm over 90º Depression of the shoulders – drooping shoulders or extending the arm at the shoulder behind the body Protraction of the shoulders – moving the shoulder girdle anteriorly Retraction of the shoulders – moving the shoulder girdle posteriorly Rotation – when the arm is raised over the head, the clavicle rotates passively as the scapula rotates.  Sternum manubrium sternocostal joints lateral edges - facet (cartilage lined depression in the bone), for articulation with the costal cartilage of the 1st rib, and a demifacet (half- facet) for articulation with part of the costal cartilage of the 2nd rib.  Sternum manubrium Inferiorly, the manubrium articulates with the body of the sternum, forming the sternal angle. This can be felt as a transverse ridge of bone on the anterior aspect of the sternum. The sternal angle is commonly used as an aid to count ribs, as it marks the level of the 2nd costal cartilage.  Sternum Body The body is flat and elongated – the largest part of the sternum. It articulates with the manubrium superiorly (manubriosternal joint) and the xiphoid process inferiorly (xiphisternal joint). The lateral edge - articular facets articulate with the costal cartilages of ribs 3-6. There are smaller facets for articulation with parts of the second and seventh ribs – known as demifacets.  Sternum Xiphoid Process The xiphoid process is the most inferior and smallest part of the sternum Tip is located at the level of the T10 vertebrae. The xiphoid process is part of the inferior margin of the thoracic cavity and marks the infrasternal angle (subcostal angle) of the inferior thoracic aperture.  Ribs There are 12 pairs of ribs separated by intercostal spaces (ICSs) atypical and typical. The typical ribs have a generalised structure, while the atypical ribs have variations on this structure.  Ribs Typical Ribs The typical rib consists of a head, neck and body: The head has two articular facets separated by a wedge of bone. One facet articulates with the numerically corresponding vertebra and the other articulates with the vertebra above. The neck - connects the head with the body. Where the neck meets the body there is a roughed tubercle, with a facet for articulation with the transverse process of the corresponding vertebra. The body, or shaft of the rib is flat and curved. The internal surface of the shaft has a groove for the neurovascular supply of the thorax, protecting the vessels and nerves from damage. Atypical Ribs Ribs 1, 2, 10 11 and 12 can be described as ‘atypical’ – they have features that are not common to all the ribs. Rib 1 is shorter and wider than the other ribs. It only has one facet on its head for articulation with its corresponding vertebra (there isn’t a thoracic vertebra above it). The superior surface is marked by two grooves, which make way for the subclavian vessels. Rib 2 is thinner and longer than rib 1, and has two articular facets on the head as normal. It has a roughened area on its upper surface, from which the serratus anterior muscle originates. Atypical Ribs Rib 10 only has one facet – for articulation with its numerically corresponding vertebra. Ribs 11 and 12 have no neck and only contain one facet, which is for articulation with their corresponding vertebra.  Ribs Articulations Anteriorly Costochondral joints: Connect the ribs to their costal cartilages. Chondrosternal joints: Connect the costal cartilage of the true ribs with the sternum. Costochondral joints  Ribs Types: True ribs (ribs 1–7): Connect directly to the sternum via costal cartilage. False ribs (ribs 8–10): Connect indirectly to the sternum via the costal arch. Floating ribs (ribs 11–12): Do not connect to the sternum. Accessory ribs: Anatomical variant in up to 0.5% of the population that usually arises from the seventh cervical vertebra (cervical rib).  Ribs Articulations Posteriorly Costovertebral joints: Connect the rib heads to the vertebral bodies. Costotransverse joints: Connect the rib tubercle to the transverse processes of the vertebral bodies. Thoracic vertebrae Demifacets on the vertebral bodies and transverse costal facets on the transverse processes articulate with the ribs  Costovertebral joints The superior demifacet articulates with the head of the rib corresponding to the vertebral level. The inferior demifacet articulates with the head of the rib inferior to the vertebral level.  Costotransverse joints: synovial joints between the transverse costal facets on the transverse processes of T1 to T9/T10 and the rib tubercle of the rib inferior to the vertebral level Ligaments Present Throughout Vertebral Column Anterior and posterior longitudinal ligaments: Long ligaments that run the length of the vertebral column, covering the vertebral bodies and intervertebral discs. Ligamentum flavum: Connects the laminae of adjacent vertebrae. Interspinous ligament: Connects the spinous processes of adjacent vertebrae. Supraspinous ligament: Connects the tips of adjacent spinous processes.  Ligaments Unique to Thoracic Spine Radiate ligament of head of rib – Fans outwards from the head of the rib to the bodies of the two vertebrae and intervertebral disc. Costotransverse ligament – Connects the neck of the rib and the transverse process. Lateral costotransverse ligament – Extends from the transverse process to the tubercle of the rib. Superior costotransverse ligament – Passes from the upper border of the neck of the rib to the transverse process of the vertebra superior to it. CLASSIFICATION OF JOINTS  Joint Video - Types of joints A joint is defined as a connection between two bones in the skeletal system. Classification by type of tissue: Fibrous – bones connected by fibrous tissue. Cartilaginous – bones connected by cartilage. Synovial – articulating surfaces enclosed within fluid-filled joint capsule.  Joint Classification by degree of movement: Synarthrosis – immovable. Amphiarthrosis – slightly moveable. Diarthrosis – freely moveable.  Fibrous Joints A fibrous joint is where the bones are bound by tough, fibrous tissue. These are typically joints that require strength and stability over a range of movements. Fibrous joints can be further sub-classified into sutures, gomphoses, and syndesmoses.  Fibrous Joints Sutures Sutures are immovable joints (synarthrosis), and are only found between the flat, plate-like bones of the skull. Sutures not only knit the bones together but also allow growth so that the skull can expand with the brain during childhood. During middle age, the fibrous tissue ossifies, and the skull bones fuse together. At this stage, the closed sutures are called synostoses, literally, “bony junctions.”  Fibrous Joints Syndesmoses Syndesmoses are slightly movable joints (amphiarthroses). They are comprised of bones held together by an interosseous membrane. The middle radioulnar joint and middle tibiofibular joint  Fibrous Joints Gomphoses Gomphoses are also immovable joints. They are found where the teeth articulate with their sockets in the maxilla (upper teeth) or the mandible (lower teeth). The tooth is bound into its socket by the strong periodontal ligament.  Cartilaginous joint In a cartilaginous joint, the bones are united by fibrocartilage or hyaline cartilage. There are two main types: synchondroses (primary cartilaginous) and symphyses (secondary cartilaginous).  Cartilaginous joint Synchondroses In synchondrosis, the bones are connected by hyaline cartilage. These joints are immovable (synarthrosis). An example of synchondrosis is the joint between the diaphysis and epiphysis of a growing long bone.  Cartilaginous joint Symphyses Symphysial joints are where the bones are united by a layer of fibrocartilage. They are slightly movable (amphiarthrosis). Examples include the pubic symphysis, and the joints between vertebral bodies.  Synovial Joint A synovial joint is defined by the presence of a fluid-filled joint cavity contained within a fibrous capsule. They are freely movable (diarthrosis) and are the most common type of joint found in the body. Synovial joints can be sub-classified into several different types, depending on the shape of their articular surfaces and the movements permitted  Synovial Joint Hinge – permits movement in one plane – usually flexion and extension. E.g. elbow joint, ankle joint, knee joint.  Synovial Joint Saddle – named due to its resemblance to a saddle on a horse’s back. It is characterised by opposing articular surfaces with a reciprocal concave-convex shape. E.g. carpometacarpal joints.  Synovial Joint Plane – the articular surfaces are relatively flat, allowing the bones to glide over one another. E.g. acromioclavicular joint, subtalar joint.  Synovial Joint Pivot – allows for rotation only. It is formed by a central bony pivot, which is surrounded by a bony-ligamentous ring E.g. proximal and distal radioulnar joints, atlantoaxial joint.  Synovial Joint Condyloid – contains a convex surface which articulates with a concave elliptical cavity. They are also known as ellipsoid joints. E.g. wrist joint, metacarpophalangeal joint, metatarsophalangeal joint.  Synovial Joint Ball and Socket – where the ball-shaped surface of one rounded bone fits into the cup-like depression of another bone. It permits free movement in numerous axes. E.g. hip joint, shoulder joint.