L6 - Cartilage and Bone PDF

General Anatomy on Bone Dr Mya Thein Shin Assistant professor Definition Bone is a living structure composed of highly vascularized & mineralized connective tissue. It is remarkable for its hardness, resilience and regenerative properties. Human body contains 206 bon...

General Anatomy on Bone Dr Mya Thein Shin Assistant professor Definition Bone is a living structure composed of highly vascularized & mineralized connective tissue. It is remarkable for its hardness, resilience and regenerative properties. Human body contains 206 bones. Bone matrix composed of organic materials mainly collagen fibers and inorganic salts rich in calcium and phosphate. Functions 1. Provides a bony framework to give form & support. 2. Provides a lever for movements in locomotion 3. Provides areas for attachment of muscle & ligaments 4. Protection of viscera (e.g. skull, ribs) 5. Production of blood cells by marrow. 6. Storage of calcium & phosphate ions. 7. Transmission of weight & force. Classification of Bones a. According to development i. Membranous bone – skull bones ii. Endochondral bone – limb bones b. According to region i. Axial bone – skull, vertebra, ribs ii. Appendicular bone – bones of limb & girdles c. According to structure i. Spongy bone – ends of long bones & short bones. ii. Compact bone – shaft of long bones  Compact bone Spongy bone d. According to maturation i. Immature bone – foetal bones ii. Mature bone – adult bone e. According to shape – long bone, - short bone, - irregular bone, and - others (sesamoid bone, pneumatic bone, heterotopic bone, accessory bone) Characteristics of bone Long bone Confined to limbs Develop in cartilage with the exception of clavicle. Length is greater than breadth and thickness  It has a tubular shaft which is usually cylindrical & contains a marrow cavity It has 2 ends which is articular & covered with hyaline cartilage; it may be convex or concave and enlarged. Short bone 1. Length, breadth & thickness are approximately equal; 2. Cubical in shape with 6 surfaces -4 are articular and -the other two is free for attachment of ligaments & for the entry of blood vessels. 3. It consists of spongy bone & marrow covered by a thin layer of compact bone. 4. They develop in cartilage. Flat bone - Resemble sandwiches; - consists of 2 layer of compact bone with spongy bone & marrow between them. - Some flat bones are so thin that there is no intervening spongy bone. - Most bones of the skull, sternum, scapula,ribs are examples. Irregular bone 1.They are irregular or mixed shape & do not fit into the above types. 2. They are spongy bones covered by a thin layer of compact bone. 3. All skull bones (except flat bones) are irregular – sphenoid, temporal, maxilla; vertebra & hip bone Others: Sesamoid, accessory, pneumatic, heterotopic bones Sesamoid bone are nodules of bone found embedded in certain tendons at places where they are exposed to severe pressure or friction. Example – patella Patella in tendon Accessory bone Not regularly present. In bones that ossify from many centers, one or more of these centers may fail to fuse with the main mass & thus remain as a separate bone.(wormian bone) Example – supernumerary digits, sutural or wormian bones, Metopic suture in frontal bone → is persistence of a suture between the right & left halves of the frontal bone after 6 years of age. Usually found in primitive races. This suture may be mistaken for fracture Pneumatic bone are skull bones with air cavities Example – ethmoid, maxillary & sphenoid bones Ethmoid bone  Heterotopic bone - are bone pieces found in places other than its normal sites such as scars or calcified tendons. Horse riders often develop heterotopic bones in their thighs (rider's bones), probably because of chronic muscle strain resulting in small hemorrhagic (bloody) areas that undergo calcification and eventual ossification. Applied anatomy 1. Total number of bones in the body → 206 of which 126 are in appendicular skeleton & the rest in axial skeleton. 2. Single bones → 33 ( 26 vertebra, sternum, occipital, sphenoid, frontal, mandible, vomer and hyoid); the rest are paired. 3. Bones of the males are usually larger & heavier than females. 4. Bones are useful for the assessment of sex, age, skeletal maturity, to diagnose nutritional and endocrine disorders. 5. Human bones can be differentiated from animal bones.  PARTS OF A YOUNG LONG BONE Each long bone has a shaft (diaphysis) and two ends (epiphyses). At birth both ends are cartilaginous – cartilaginous epiphyses. The part of the bone between the two ends is the diaphysis. Diaphysis It is a thick walled tube composed of compact bone which surrounds a central marrow cavity containing red or yellow marrow. The diaphysis is compact bone and is covered by periosteum. It is the site of primary ossification.  The region of the diaphysis adjacent to the epiphyseal plate is the metaphysis. The layer of cartilage between the diaphysis & epiphysis is an epiphyseal plate. Metaphysis It is the part of the diaphysis adjacent to the epiphyseal cartilage plate. It is highly vascular and is the area of greatest growth activity in the long bone.  It is the growth zone of the bone and also the weakest point. When growth stops the diaphysis fuses with the epiphysis and the cartilaginous epiphyseal plate becomes bony. Epiphyseal plate Is a plate of hyaline cartilage intervening between the diaphysis & epiphysis. From this plate growth in length of the bone occurs by addition of osseous tissue to related parts of diaphysis & epiphysis. It changes into bone when growth ceases. Epiphysis Epiphysis are usually Epiphyseal wider than the shaft. It is plate the site of secondary ossification. Epiphysis is composed of spongy bone covered by a periosteum thin layer of compact bone. The surface of the endosteum epiphysis which articulate with a neighboring bone is called articular surface and is always covered by hyaline cartilage. Periosteum It is the connective tissue that covers the long bone except at the articular surfaces. It is composed of an outer fibrous layer and an inner cellular layer which is osteogenic. Endosteum is the thin cellular membrane which lines the marrow cavity of compact bone & trabecular spaces of spongy bone.  Blood Supply of a Long Bone A long bone is supplied by the following arteries:- 1. Nutrient artery 2. Branches of periosteal arteries 3. Epiphyseal & metaphyseal arteries epiphyseal and epiphysis -metaphyseal artery metaphysis marrow cavity nutrient artery diaphysis branches of periosteal artery epiphyseal and metaphyseal artery epiphyseal disc hyaline cartilage (growing end) - Responsible for length of bone  Nutrient artery It is the main artery of the shaft. It is a branch of a larger artery which runs adjacent to the bone. - It enters through a nutrient foramen and in the medullary cavity it divides into 2 branches - proximal & distal branches which runs toward the metaphysic of both ends. - It supplies the inner part of the compact bone, the marrow cavity and the metaphyseal region. 2.Periosteal arteries The periosteum has a rich blood supply from which many vessels enter the shaft at numerous points and run in the Harvesion canals. They supply the outer compact bone of the shaft. 3. Epiphyseal & metaphyseal arteries They arise from arteries around the joint. These arteries pierce the capsule and supply the capsule, the epiphysis and the metaphyseal region. All these arteries come into communication at the metaphysic which is an extremely vascular zone and is called “a lake of blood”. Compact bone Spongy Bone (Histology) Applied anatomy 1. Blood borne infection are commonly found at the ends of long bones due to the anastomoses which exist between the nutrient & metaphyseal arteries. 2. In fractures, one or the other branch of the nutrient artery is torn, but the anastomoses of these branches with the articular arteries will maintain the blood flow. 3. Rupture of epiphyseal & metaphyseal arteries will result in interference of growth in length of the long bone as they supply the epiphyseal plates. 4. It is difficult to interrupt the blood supply sufficiently to kill the bone because it has a very extensive supply. For this reason, a metal pin can be inserted into the medullary cavity to repair a fracture without damaging the bone. 5. Avascular necrosis – loss of arterial supply to an epiphysis or other parts of the bone will result in avascular necrosis, resulting in death of the bone Unused bones, such as in a paralyzed limb, atrophy (decrease in size). Bone may be absorbed, which occurs in the mandible when the teeth are extracted. Bones hypertrophy (enlarge) when they support increased weight for a long period. Fracture Trauma to a bone (e.g., during an accident) may break it. During bone healing, the surrounding fibroblasts (connective tissue cells) proliferate and secrete collagen, which forms a collar of callus to hold the bones together. Bone remodeling occurs in the fracture area, and the callus calcifies. Fractures are more common in children than in adults because of the combination of their slender, growing bones and carefree activities. Fortunately, many of these breaks are greenstick fractures (incomplete breaks caused by bending the bones). Fractures in growing bones heal faster than those in adult bones. Osteoporosis During the aging process, the organic and inorganic components of bone both decrease, in osteoporosis, a reduction in the quantity of bone, or atrophy of skeletal tissue. The bones become brittle, lose their elasticity, and fracture easily. Sternal Puncture Examination of bone marrow provides valuable information for evaluating hematological diseases. Sternum (breast bone) is a commonly used site for taking bone marrow. Bone marrow transplantation is sometimes performed in the treatment of leukemia. X’ray of neonate (at birth) car tilage General Features Resilient , semi rigid connective tissue. That forms the part of the skeleton where more flexibility is required. Eg; costal cartilages attach to the sternum. articular surface of the bone capped with cartilage. To provide low friction gliding surface for free movement. Avascular Cells obtain their nutrient by diffusion. Function - supports soft tissue - sliding surface for joint - necessary for growth of long bone Classification - hyaline - fibrocartilage - elastic cartilage growth - interstitial growth - appositional growth applied anatomy - immune to cancer - fairly easy to perform transplant 1. Hyaline cartilage It is bluish white and resilient. It has a glassy, translucent appearance and pearly white in colour. It is covered by perichondrium on its outer surface. Site: It is found in the walls of the respiratory passages, on the ventral ends of ribs, on the articular surfaces of bones and in the epiphyseal plates of growing bones and foetal skeleton.  Examples of Hyaline cartilage Articular surface of the long bone. Epiphyseal plate of long bone. costal cartilage Hyaline cartilage Functions of hyaline cartilage 1. Supports soft tissue 2. Provides a sliding surface for joints and facilitate movements. 3. Necessary for the growth of long bone before and after birth.. 3 Fibro-cartilage Fibrocartilage is a tissue with characteristics intermediate between those of dense connective tissue & hyaline cartilage. It is opaque in appearance. It is tough, strong and resilient. Therefore it has NO perichondrium. Site: It is found in inter-vertebral discs, rims of articular sockets, lining of tendon grooves and in symphysis pubis.  Examples of fibrocartilage pubic symphysis intervertebral disc Fibrocartilage (H&E) 2. Elastic cartilage It is yellowish in colour and more opaque than hyaline cartilage. It occurs in sites where support with elasticity is required. It is covered by perichondrium. Site: It is found in the auricle, external acoustic meatus, auditory tube and epiglottis. Unlike hyaline cartilage, it rarely calcifies with age.  Example of elastic cartilage external acoustic meatus auditory tube auricle, epiglottis Elastic Cartilage