introduction

Dr Hiba Abdulmoneim

Definition

• A is a rigid organ that constitutes part of the vertebrate skeleton • Bone tissue is a hard tissue, a type of dense connective tissue. It has a honeycomb-like matrix internally, which helps to give the bone rigidity. Bone tissue is made up of different types of bone cells • The mineralised matrix of bone tissue has an organic component of mainly called ossein and an inorganic component of bone mineral made up of various salts. Bone tissue is a mineralized tissue of two types, cortical and cancellous bone. Other types of tissue found in include bone marrow, endosteum, periosteum, nerves, blood vessels and . structure functions

• Provide structural support for the body • Provide protection of vital organs • Provide an environment for marrow (where blood cells are produced) • Act as a storage area for minerals (such as calcium)

Synthetic

• Cancellous bones contain bone marrow. Bone marrow produces blood cells in a process called hematopoiesis.Blood cells that are created in bone marrow include red blood cells, platelets and white blood cells Metabolic

• Mineral storage — bones act as reserves of minerals important for the body, most notably calcium and phosphorus. • Growth factor storage — mineralized bone matrix stores important growth factors such as insulin-like growth factors, transforming growth factor, bone morphogenetic proteins and others. • Fat storage — the yellow bone marrow acts as a storage reserve of fatty acids. • Acid-base balance — bone buffers the blood against excessive pH changes by absorbing or releasing alkaline salts.

• Detoxification — bone tissues can also store heavy metals and other foreign elements, removing them from the blood and reducing their effects on other tissues. These can later be gradually released for excretion • Endocrine organ — bone controls phosphate metabolism by releasing fibroblast growth factor – 23 (FGF-23), which acts on kidneys to reduce phosphate reabsorption • Calcium balance—The process of bone resorption by the osteoclasts releases stored calcium into the systemic circulation and is an important process in regulating calcium balance

• The matrix is made up of between 90 and 95% collagen fibers, and the remainder is ground substance . The primary tissue of bone, bone tissue , is relatively hard and lightweight. Its matrix is mostly made up of a composite material incorporating the inorganic mineral calcium phosphate in the chemical arrangement termed calcium hydroxylapatite (this is the bone mineral that gives bones their rigidity) and collagen, an elastic protein which improves fracture resistance. The collagen of bone is known as ossein. Bone is formed by the hardening of this matrix around entrapped cells. When these cells become entrapped from osteoblasts they become osteocytes

Cortical bone

• The hard outer layer of bones is composed of cortical bone also called compact bone. Cortical referring to the outer (cortex) layer. The hard outer layer gives bone its smooth, white, and solid appearance, and accounts for 80% of the total bone mass of an adult human skeleton.Cortical bone consists of multiple microscopic columns, each called an osteon Cancellous bone • Cancellous bone also known as trabecular or spongy bone tissue is the internal tissue of the skeletal bone and is an open cell porous network. Thin formations of osteoblasts covered in endosteum create an irregular network of spaces, known as trabeculae. Within these spaces are bone marrow and hematopoietic stem cells that give rise to platelets, red blood cells and white blood cells Bone is also composed of:

• Bone forming cells (osteoblasts and osteocytes) • Bone resorbing cells (osteoclasts) • Nonmineral matrix of collagen and noncollagenous proteins (osteoid) • Inorganic mineral salts deposited within the matrix

Cells

• Bone is a metabolically active tissue composed of several types of cells. These cells include osteoblasts, which are involved in the creation and mineralization of bone tissue, osteocytes, and osteoclasts, which are involved in the reabsorption of bone tissue • Osteoblasts: These cells are derived from mesenchymal stem cells and are responsible for bone matrix synthesis and its subsequent mineralization They are located on the surface of osteon seams and make a protein mixture known as osteoid, which mineralizes to become bone. In the adult skeleton, the majority of bone surfaces that are not undergoing formation or resorption (i.e. not being remodeled) are lined by bone lining cells. • Osteocytes: are mostly inactive osteoblasts.These cells are osteoblasts that become incorporated within the newly formed osteoid, which eventually becomes calcified bone. Osteocytes situated deep in bone matrix maintain contact with newly incorporated osteocytes in osteoid, and with osteoblasts and bone lining cells on the bone surfaces, through an extensive network of cell processes (canaliculi). They are thought to be ideally situated to respond to changes in physical forces upon bone and to transduce messages to cells on the bone surface, directing them to initiate resorption or formation responses. • Osteoclasts: These cells are large multinucleated cells, like macrophages, derived from the hematopoietic lineage. Osteoclasts function in the resorption of mineralized tissue and are found attached to the bone surface at sites of active bone resorption. Their characteristic feature is a ruffled edge where active resorption takes place with the secretion of bone-resorbing enzymes, which digest bone matrix.

Bone matrix

• Osteoid is comprised of type I collagen (~94%) and noncollagenous proteins. The hardness and rigidity of bone is due to the presence of mineral salt in the osteoid matrix, which is a crystalline complex of calcium and phosphate (hydroxyapatite). Calcified bone contains about 25% organic matrix (2-5% of which are cells), 5% water and 70% inorganic mineral (hydroxyapatite). Bone modelling

• Modeling is when bone resorption and bone formation occur on separate surfaces (i.e. formation and resorption are not coupled). An example of this process is during long bone increases in length and diameter. Bone modeling occurs during birth to adulthood and is responsible for gain in skeletal mass and changes in skeletal form Bone remodelling

• Remodeling is the replacement of old tissue by new bone tissue. This mainly occurs in the adult skeleton to maintain bone mass. This process involves the coupling of bone formation and bone resorption and consists of five phases: • 1. Activation: preosteoclasts are stimulated and differentiate under the influence of cytokines and growth factors into mature active osteoclasts 2. Resorption: osteoclasts digest mineral matrix (old bone) 3. Reversal: end of resorption 4. Formation: osteoblasts synthesize new bone matrix 5. Quiescence: osteoblasts become resting bone lining cells on the newly formed bone surface

NORMAL JOINT ANATOMY AND PHYSIOLOGY Synovial joint:  Consists of two bone ends covered by articular cartilage.

 The roles of articular cartilage include:

1. Enabling frictionless movement of the joint.

2. Distributing the load across the joint (shock absorber), to prevent damage.

3. Promoting stability during use. Cartilage:  Is avascular and aneural.  It is metabolically active and undergoes continual internal remodeling.  It is composed primarily of water but is also made from chondrocytes and .

Chondrocytes  Control the synthesis and degradation of the matrix.  They produce proteoglycans and collagen in the extracellular matrix to maintain the integrity of the matrix in healthy cartilage. Joint capsule:  Fibrous outer layer that encapsulates the joint.  Lined by synovium, a membrane that produces a viscous fluid that lubricates the joint.

 Is composed, in part, of hyaluronic acid.

 Glucosamine is a component of hyaluronic acid.

 The role of hyaluronic acid is to maintain functional and structural characteristics of the extracellular matrix.

Bursae:

 Are small sacs that are lined with synovial membrane and filled with fluid to provide cushioning and lubrication for the movement of the joint. Therapy goals

Relieve pain Maintain or improve joint function Prevent loss of function Maintain or improve quality of life.