Bone Morphology and Fracture Healing

Bone Morphology and Fracture Healing free pdf ebook was written by Heather on January 09, 2007 consist of 12 page(s). The pdf file is provided by meds.queensu.ca and available on pdfpedia since May 06, 2011.

3. identify the function of different types of bone cells. 4. describe fracture healing as a sequence of stages. 5.…...

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Bone Morphology and Fracture Healing pdf




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Bone Morphology and Fracture Healing - page 1
Bone Morphology and Fracture Healing Objectives Upon completion of this module, the student will be able to: 1. 2. 3. 4. 5. Describe the primary functions of bone Describe the structure of bone at the macroscopic and microscopic level Identify the function of different types of bone cells Describe fracture healing as a sequence of stages Predict anomalies in fracture healing based on information about the patient, the fracture and other clinical modifiers Reference SEER online module (review of bone morphology, formation and skeletal structure) - individual webpages from this site will be referenced in the module. Related websites and image collections University of Ottawa Histology website American Society for Bone and Mineral Research - Bone Curriculum School of Anatomy and Human Biology - The University of Western Australia - Blue Histology webpage Start by reviewing the following two webpages: 1) Functions of the Skeletal System and 2) Structure of Bone Tissue. Based on your understanding of this material, summarize the key functions of the skeletal system: (Answer A1 on answer sheet) Describe a pathological situation where one of the mechanical functions of the skeleton is disturbed. What long term deficit may result? (Answer A2 on answer sheet)
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Bone Morphology and Fracture Healing - page 2
At the macroscopic level, bone is organized into cortical and cancellous bone. The metaphyseal and epiphyseal regions consist of cancellous bone. In these areas, bony trabeculae are arranged for maximum strength and have capacity to realign in the direction of an applied stress. This is an illustration of Wolff's law: "bone is deposited and resorbed in accordance with the stresses placed upon it". The diaphyseal areas of the long, tubular bones (femur, tibia, humerus, etc.) are made of cortical bone. These have a thin endosteal membrane lining the inner surfaces. All bones (with the exception of those portions that are intra-articular) are covered with periosteum on their outer surface. Periosteum (image Copyright Lutz Slomianka 1998-2004) is thickest in young children and may provide a degree of stabilization in certain pediatric fractures. Biochemically, the skeleton contains 65% inorganic elements (minerals) and 35% organic bone matrix. Three types of bone cells, osteoblasts, osteocytes and osteoclasts, function together to regulate mineral homeostasis in response to endocrinological and mechanical signals. Review histologic specimens of the two types of bone tissue found in the skeleton by clicking on the links provided: cortical (a.k.a. compact - image Copyright Lutz Slomianka 1998-2004) and cancellous (a.k.a. spongy or trabecular) bone. Bone healing is influenced by the potential and activity of the cells that line the surface of the bone (osteoblasts and osteoclasts). Based on this fact alone, the greater the surface are of bone involved in the healing process, the more rapid the healing is likely to be. Which type of bone tissue will heal the fastest? (Answer A3 on answer sheet) a) b) Cortical bone Cancellous bone Bone Cells There are three types of cell in bone. Their functions are outlined below: Osteoblasts Osteoblasts line the inner (endosteal) and outer (periosteal) surfaces of the bone. Osteoblasts synthesize organic bone matrix (osteoid) and collagen. Osteoblasts also synthesize the enzyme alkaline phosphatase and initiate the process of mineralization. Osteoblasts represent the final stage of differentaition of pluripotential stem cell in the bone marrow. They typically live about three months before flattening to become metabolically inactive bone lining cells. About 10-15% of osteoblasts become osteocytes. Osteocytes The most abundant cell in bone is the osteocyte. The cells known as osteocytes are formed from metabolically inactive osteoblasts which have become entombed in a newly formed bone matrix during active bone formation. Osteocytes no longer secrete osteoid; however they do maintain their sensitivity to PTH and vitamin D and participate in calcium regulation. Osteocytes are interconnected by tiny channels called canaliculi.
Bone Morphology and Fracture Healing - page 3
Osteoclasts Osteoclasts are multi-nucleated giant cells that resorb bone by enzymatic degradation. These cells are characterized by a ruffled border and lie in bone resorption pits called Howship's lacunae. Osteoclasts are related to hematopoietic cell lines (monocytes, macrophages). Osteoclasts are seen in increased numbers in diseases with increased bone turnover. How many types of bone cells can you identify in this histological slide? What biological process does it illustrate? from the PEIR pathology library © Copyright UAB and the UAB Research Foundation, 1999- 2000. All rights reserved.
Bone Morphology and Fracture Healing - page 4
This is a high magnification view of bone remodeling during fracture healing; osteoclasts, osteocytes and osteoblasts are shown. adapted from from the PEIR pathology library © Copyright UAB and the UAB Research Foundation, 1999-2000. All rights reserved. Bone is a composite material, consisting of inorganic and organic components as well as the cellular elements discussed previously. Inorganic matrix The inorganic matrix of bone consists of a calcium hydroxyapatite, which is in a crystalline structure. This serves to: 1. Mineralize the osteoid produced by osteoblasts, 2. Provide strength and hardness to the bone, 3. House the body's mineral reserves, including: o 99% of the body's calcium, o 85% of its phosphorous, o 65% of its sodium and magnesium Organic matrix Thirty-five percent (35%) of bone is organic. The organic matrix is composed of the bone cells that you have just learned about, and of protein. Ninety percent (90%) of bone protein is Type I collagen which has a triple helical structure, and ten percent (10%) consists of noncollagenous
Bone Morphology and Fracture Healing - page 5
proteins. Abnormalities of collagen formation may occur and lead to bone fragility. Watch a flash movie depicting the normal sequence of collagen synthesis on the American Society for Bone and Mineral Research Bone Curriculum webpage. This newborn male is observed to have shortened, excessively bowed limbs. He cries with even gentle manipulation of his arms and legs. Xrays reveal multiple fractures in various stages of healing. What abnormality of bone could result in this clinical picture? (Answer A4) Complete this gap-fill exercise to test your knowledge about bone cells. This type of bone is found in abundance in the metaphyseal regions of long bones, contains irregularly arranged trabeculae and has an ability to remodel secondary to mechanical stresses. Choose the correct answer: (Answer A5) a) b) Cancellous bone Cortical bone
Bone Morphology and Fracture Healing - page 6
Which of the following statements about bone matrix is CORRECT? (Answer A6) a) b) c) d) e) Most of the collagen found in bone is Type II collagen Calcium carbonate crystals act to mineralize osteid The inorganic matrix of bone houses the body's mineral reserves Osteoid is produced by osteocytes The organic bone matrix is arranged in a crystalline structure Before we discuss fracture healing, it is important to understand some basic principles about bone growth. Review this related webpage from the Association for Bone and Mineral Research, with a particular focus upon the growth of long bones, flat bones and bone remodeling. Make sure that you watch the movies that outline these three important processes. Which of the following statements best describes the growth of long bones? (Answer A7) FIbroblasts transform into osteoblasts and create woven bone which is subsequently reorganized into lamellar bone Microscopic cracks are created by activity. These stimulate first bone resorption and subsequently bone formation. Cartilage is transformed as the chondrocytes hypertrophy and eventually die; there is vascular ingrowth and mineralization resulting in bone formation. a) b) c) Which type of bone growth is similar to fracture healing? If you are not sure of the answer, review the reference cited above. (Answer A8) *Bone is a unique tissue as it is able to reform itself and does not heal with scar as other tissues do. Stages of fracture healing A fracture occurs when the continuity of a bone is broken and local blood supply is interrupted. If the overlying soft tissues are also injured, fracture healing may be delayed or disrupted, particularly in anatomic regions with decreased vascular networks such as the tibial diaphysis. Bone is unique in its ability to regenerate itself. Healing occurs via reactivation of embryologic processes resulting in the formation of bone not scar. Fracture healing can be described in three conceptual stages. An understanding of the timing and mechanisms associated with each stage is important in planning fracture treatment. The stages are:
Bone Morphology and Fracture Healing - page 7
Inflammation This begins immediately after bone injury with the formation of a local hematoma or fibrin clot. There is local cell death where vessel disruption has resulted in ischemia - usually at the very ends of the fractured bone. Over the course of the next few days, this area becomes infiltrated by inflammatory cells and is characterized by local swelling and warmth. The inflammatory cells release lysosomal enzymes and other mediators that attract pluripotent cells to the area; they also act to remove necrotic tissue. Fibroblasts, mesenchymal cells and osteoprogenitor cells appear and may transform nearby tissues. The fracture is tender and may be grossly mobile to physical examination at this stage. Inflammation is at its peak 48 hours after a fracture. Repair The reparative phase begins a few days after the injury with the arrival of mesenchymal cells able to differentiate into fibroblasts, chondroblasts and osteoblasts. The repair phase persists for several months; it can be divided into two distinct phases: soft and hard callus formation. 1. "Soft callus" formation lasts for approximately six weeks from the time of injury. During this preliminary stage of repair, pain and swelling subside and bony fragments become united by fibrous and cartilagenous tissue. Woven bone is formed. While this creates some stability, the fracture may still angulate at this stage if not held with stable external support, such as a cast or external fixator, or internal support provided by plates, screws or intramedullary devices. 2. "Hard callus" formation - During this second stage of repair, woven bone is transformed into lamellar bone. This takes approximately three months. Remodeling Remodeling is the process by which bone is removed in tiny increments and then replaced by new bone. After a fracture, remodeling may continue for months or even years. The adult human skeleton continuously replaces itself at rate of 10-18% per year. The rate of remodeling is accelerated in children and during fracture repair. In addition to being an essential part of fracture healing, remodeling plays an important role in calcium homeostasis. During the remodeling phase the woven bone is converted to lamellar bone and the medullary canal is reconstituted. During this phase, bone responds to loading characteristics according to Wolff's law. Some angular deformity may correct during this stage in children with sufficient growth remaining (up to 5o per year of growth remaining).
Bone Morphology and Fracture Healing - page 8
Factors affecting bone healing Various local and systemic factors affect the duration and effectiveness of the healing process. Abnormalities in any of these areas may lead to abnormally slow healing (delayed union) or failure to heal (non union). These include: Systemic factors 1. Age: Children heal more quickly than adults; healing potential is decreased with advancing age 2. Nutrition: Poor nutrition and/or vitamin deficiency adversely affects healing 3. General health: Chronic illness depresses healing response (diabetes, anemia, systemic infection) 4. Generalized atherosclerosis: Decreases healing 5. Hormonal factors: Growth hormone enhances healing; corticosteroids depress healing 6. Drugs: Non steroidal anti-inflammatory drugs (e.g. ibuprofen) depress healing 7. Smoking: Decreases healing Local factors 1. Degree of local trauma/bone loss: A comminuted fracture with more soft tissue injury is slower to heal 2. Area of bone affected: Metaphyseal fractures heal faster than diaphyseal 3. Abnormal bone (infection, tumour, irradiated): Slower to heal 4. Degree of immobilization of fracture: Motion at site delays healing Disruption of vascular supply: Delays healing Abnormal Healing in Bone Although, in most cases, fracture healing proceeds uneventfully, there are certain situations when the outcome is not normal. Several patterns of abnormal healing are described in this section. Fracture non-union Healing is described as 'delayed' if union is not seen within the expected time after initial treatment. At the six month mark, an unhealed fracture is termed a "non- union". There are two types of non-union: atrophic, where little callus has formed and hypertrophic, where there is obvious callus but continued instability. Atrophic non-unions respond to bone grafting. This involves transplantation of the patient's own healthy bone, often from the iliac crest, to the non- union site. An alternative is the implantation of donor bone or an artificial bone substitute. Hypertrophic non-unions often result from increased motion at the fractures site. These improve with by surgical stabilization of the non-union. If a non-union persists and remains mobile, the fibrous tissue at the fracture site may undergo transformation into synovial cells forming a "false joint" or pseudarthrosis.
Bone Morphology and Fracture Healing - page 9
Stress fractures Stress fractures are the result of an imbalance of bone formation and bone healing, usually in young healthy individuals involved in repetitive physical activity. Common sites include the tibia, metatarsal and femoral neck. The diagnosis is often challenging as plain radiographs may be negative or may reveal calcification only in the late stages of healing. Bone scans and/or Magnetic Resonance Imaging scans are frequently diagnostic. Treatment with immobilization is usually successful. The red arrow points to a stress fracture in this patient's calcaneus Reactive bone formation Reactive bone formation isn't true "healing" but instead a response of the bone to an underlying abnormality. Review this link from the University of Washington School of Medicine to learn more about the different patterns of reactive bone formation. "Sunburst" or "onion skin" patterns are growing rapidly and so are classified as "aggressive", while more solid patterns of periosteal reaction (such as are seen in children's fractures) indicate slower growths that are likely benign.
Bone Morphology and Fracture Healing - page 10
Benign periosteal reaction after fracture This is an example of benign periosteal reaction seen as a normal part of fracture healing in a child four weeks after a supracondylar humeral fracture
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