BIO CT201 Module 5 - Bones and Joints PDF

BIU CT201 Module 5 – An Introduction to Bone and Joints  Bones and Joints: Structure, Function, Growth, and Clinical Relevance Understanding the framework of life, from growth and remodelling to clinical care. ...

BIU CT201 Module 5 – An Introduction to Bone and Joints  Bones and Joints: Structure, Function, Growth, and Clinical Relevance Understanding the framework of life, from growth and remodelling to clinical care.  Learning Objectives 1 2 3 4 5 1. Describe the functions of 2. Explain the processes of 3. Identify the structural and 4. Analyse the clinical 5. Evaluate the causes, the skeletal system and ossification, bone growth, functional classifications of significance of fractures, effects, and management of classify bones based on their and remodelling, and relate joints, including their including their healing osteoporosis, arthritis, and shapes. these to clinical conditions. anatomy and physiological process and contributing joint injuries. roles. factors.  The skeletal system performs six key functions: Support: Provides the framework for the body, giving it shape and Functions of structure. the Skeletal Protection: Shields vital organs, e.g., the skull protects the brain, and the ribs guard the heart and lungs. System Movement: Acts as a system of levers; muscles pull on bones to create motion. Mineral Storage: Serves as a reservoir for calcium and phosphorus, essential for various physiological processes. Blood Cell Production: Haematopoiesis occurs in the red bone marrow, producing red and white blood cells. Energy Storage: Yellow bone marrow stores lipids as a source of energy. Bones are classified based on their shape, reflecting their function: Long Bones: Cylindrical, longer than wide; act as levers for movement. Examples: Femur, humerus. Short Bones: Cube-shaped, provide stability and limited motion. Examples: Carpals, tarsals. Flat Bones: Thin, often curved; protect organs and provide surfaces for muscle attachment. Examples: Skull bones, sternum. Irregular Bones: Complex shapes; serve various specialised functions. Examples: Vertebrae, pelvic bones. Sesamoid Bones: Small, round, embedded in tendons; reduce friction and improve mechanical efficiency. Example: Patella. Clinical Connection: Long bones are vulnerable to fractures due to their role in weight-bearing and movement. Flat bones like the skull protect critical organs but are prone to impact injuries. Intramembranous Ossification Intramembranous ossification follows four steps. a) Mesenchymal cells group into clusters, and ossification centers form. (b) Secreted osteoid traps osteoblasts, which then become osteocytes. (c) Trabecular matrix and periosteum form. d) Compact bone develops superficial to the trabecular bone, and crowded blood vessels condense into red marrow. Endochondral Ossification Endochondral ossification follows five steps. (a) Mesenchymal cells differentiate into chondrocytes. (b) The cartilage model of the future bony skeleton and the perichondrium form. (c) Capillaries penetrate cartilage. Perichondrium transforms into periosteum. Periosteal collar develops. Primary ossification center develops. (d) Cartilage and chondrocytes continue to grow at ends of the bone. (e) Secondary ossification centers develop. (f) Cartilage remains at epiphyseal (growth) plate and at joint surface as articular cartilage. Ossification: There are two pathways of bone formation: How Bones 1. Intramembranous Ossification: Are Made Bones develop directly from mesenchymal tissue. Occurs in flat bones (e.g., skull, clavicles). Process: Mesenchymal cells → Osteoblasts → Bone matrix formation → Compact bone development. 2. Endochondral Ossification: Bones form by replacing a cartilage template. Occurs in most bones, including long bones (e.g., femur, humerus). Process: Hyaline cartilage → Cartilage calcification → Vascular invasion → Bone matrix formation. How We Grow Progression from Epiphyseal Plate to Epiphyseal Line As a bone matures, the epiphyseal plate progresses to an epiphyseal line. (a) Epiphyseal plates are visible in a growing bone. (b) Epiphyseal lines are the remnants of epiphyseal plates in a mature bone. How We Grow Bone Growth at the Epiphyseal Plate: Zones of Growth Resting zone: Inactive cartilage. Proliferation zone: Chondrocytes divide and push older cells away. Hypertrophic zone: Older chondrocytes enlarge. Calcification zone: Matrix calcifies, and chondrocytes die. Ossification zone: Osteoblasts replace calcified cartilage with bone.  Bone Remodelling: A continuous process replacing old bone with new. Key Players: Osteoclasts: Break down old bone (resorption). Bone Osteoblasts: Build new bone (formation). Remodelling: Osteocytes: Embedded cells that coordinate remodelling in response to mechanical stress. Lifelong Purpose: Adaptation Adapt to mechanical load (e.g., weight-bearing exercises strengthen bones). Repair microdamage to prevent fractures. Maintain mineral homeostasis (calcium and phosphorus). Bone Repair Fracture Repair Stages: 1. Haematoma Formation: Blood clot stabilises the fracture. 2. Soft Callus Formation: Fibrocartilage bridge forms. 3. Hard Callus Formation: Osteoblasts create woven bone. 4. Remodelling: Woven bone replaced with mature lamellar bone. Clinical Connection: Conditions like osteoporosis disrupt the Fractures heal slower in older adults or those remodelling balance, favouring resorption over with poor nutrition. formation. Osteoporosis: Causes and Pathophysiology A systemic skeletal disorder characterised by reduced bone density and Definition: microarchitectural deterioration, increasing fracture risk. Key Pathophysiology: Bone Remodelling Imbalance: Osteoclast activity outpaces osteoblast activity, leading to net bone loss. Oestrogen normally inhibits osteoclast activity. Post-Menopausal Oestrogen Loss: Post-menopause, decreased oestrogen accelerates bone resorption. Ageing: Reduced osteoblast efficiency and calcium absorption compound bone loss. Trabecular Bone Vulnerability: Thin, porous structure makes it more prone to fractures. Osteoporosis Risk Factors Non-Modifiable: Age, gender (women > men), family history, ethnicity (Caucasian, Asian). Modifiable: Poor nutrition (low calcium/vitamin D), sedentary lifestyle, smoking, alcohol use. Clinical Connection: Common fracture Vertebral compression sites: fractures can cause kyphosis, chronic pain, Vertebrae, hip, wrist. and height loss. Diagnosing and Managing Osteoporosis Diagnosis: DEXA Scan: Measures bone mineral density (BMD). T-Scores: Normal: > -1. Osteopenia: -1 to -2.5. Osteoporosis: < -2.5. FRAX Tool: Estimates 10-year fracture risk based on BMD and clinical risk factors. Vertebral imaging: Detects silent fractures in at-risk patients. Treatment: Medications: Bisphosphonates: Inhibit bone resorption (e.g., alendronate, risedronate). Denosumab: Monoclonal antibody reducing osteoclast activity. Agents: Promote bone formation (e.g., teriparatide, romosozumab). Selective Oestrogen Receptor Modulators (SERMs): Mimic oestrogen in bone (e.g., raloxifene). HRT: Hormone replacement therapy (limited use due to risks). Lifestyle Changes: Weight-bearing exercise, smoking cessation, alcohol reduction. Adequate calcium (1,000–1,200 mg/day) and vitamin D (600–800 IU/day). Prevention Strategies: Early screening in at-risk populations. Fall prevention strategies: Home modifications, balance training. Think about this… How would you balance the benefits and risks of bisphosphonates versus anabolic agents in a 70-year-old patient with a history of fractures? Fractures: When Bones Break What Is a Fracture? A structural break in bone due to trauma, stress, or pathological weakness. Common Types of Fractures: 1. Simple (Closed): Bone breaks but doesn’t pierce the skin. 2. Compound (Open): Bone pierces the skin, increasing infection risk. 3. Greenstick: Partial break, common in children due to softer bones. 4. Comminuted: Bone shatters into multiple pieces, often requiring surgery. 5. Spiral: Caused by a twisting force, seen in sports injuries. 6. Compression: Bone is crushed, typical in vertebrae of osteoporotic patients. Types of Fractures Compare healthy bone with different types of fractures: (a) closed fracture, (b) open fracture, (c) transverse fracture, (d) spiral fracture, (e) comminuted fracture, (f) impacted fracture, (g) greenstick fracture, and (h) oblique fracture. Stages of Fracture Healing: 1. Haematoma Formation: The healing of a bone fracture follows a series of progressive steps: Blood clot forms, stabilising the break. 2. Soft Callus Formation: Fibrocartilage bridges the gap. 3. Hard Callus Formation: Woven bone replaces the soft callus. 4. Remodelling: Woven bone matures into lamellar bone, restoring strength. Clinical Considerations: Delayed healing in conditions like osteoporosis, diabetes, or poor nutrition. Infection risk in open fractures. Think about this… Why might a vertebral compression fracture in an osteoporotic patient lead to more severe complications compared to a simple long bone fracture? Joints: Structural and Functional Classifications Functional Classification: Based on range of movement: 1. Synarthroses: Immovable joints. Example: Skull sutures. 2. Amphiarthroses: Slightly movable joints. Example: Pubic symphysis. 3. Diarthroses: Freely movable joints. Example: Synovial joints (hinge, ball-and-socket). Suture Joints of Skull The suture joints of the skull are an example of a synarthrosis, an immobile or essentially immobile joint. Intervertebral Disc An intervertebral disc unites the bodies of adjacent vertebrae within the vertebral column. Each disc allows for limited movement between the vertebrae and thus functionally forms an amphiarthrosis type of joint. Intervertebral discs are made of fibrocartilage and thereby structurally form a symphysis type of cartilaginous joint. An example of a diarthrosis: A multiaxial joint, such as the hip joint, allows for three types of movement: anterior- posterior, medial-lateral, and rotational. The elbow on the other hand is a diarthrosis that is uniaxial – moving like a hinge Structural Classification: Based on how bones are connected 1. Fibrous Joints: Bones are joined by dense connective tissue; no cavity. Example: Skull sutures (immovable). 2. Cartilaginous Joints: Bones are connected by cartilage; no cavity. Example: Intervertebral discs (slightly movable). 3. Synovial Joints: Bones are separated by a fluid-filled cavity; highly movable. Example: Knee, shoulder. Fibrous joints form strong connections between bones. (a) Sutures join most bones of the skull. (b) An interosseous membrane forms a syndesmosis between the radius and ulna bones of the forearm. (c) A gomphosis is a specialized fibrous joint that anchors a tooth to its socket in the jaw. Cartilaginous Joints At cartilaginous joints, bones are united by hyaline cartilage to form a synchondrosis or by fibrocartilage to form a symphysis. (a) The hyaline cartilage of the epiphyseal plate (growth plate) forms a synchondrosis that unites the shaft (diaphysis) and end (epiphysis) of a long bone and allows the bone to grow in length. (b) The pubic portions of the right and left hip bones of the pelvis are joined together by fibrocartilage, forming the pubic symphysis. Synovial Joints Synovial joints allow for smooth movements between the adjacent bones. The joint is surrounded by an articular capsule that defines a joint cavity filled with synovial fluid. The articulating surfaces of the bones are covered by a thin layer of articular cartilage. Ligaments support the joint by holding the bones together and resisting excess or abnormal joint motions. Clinical Connection: Synovial joints are versatile but prone to injury due to their mobility. Conditions like osteoarthritis often affect these highly active joints. Think about this… Why are synovial joints more susceptible to injuries and degenerative diseases than fibrous or cartilaginous joints? Synovial Joints: Engineering for Movement 1. Articular Cartilage: Covers bone ends; smooth surface reduces friction and absorbs shock. 2. Synovial Cavity: Fluid-filled space between bones allowing free movement. 3. Synovial Fluid: Produced by the synovial membrane; lubricates and nourishes cartilage. 4. Joint Capsule: Tough outer layer stabilising the joint, with an inner synovial membrane. 5. Ligaments: Connect bone to bone, reinforcing the joint. 6. Bursae: Fluid-filled sacs reducing friction between bones, tendons, and muscles. Types of Synovial Joints: Ball-and-Socket Hinge Joints (e.g., Joints (e.g., shoulder, knee, elbow): hip): Multidirectional Movement in one movement and plane. rotation. Clinical Connection: Synovial joints, due to their mobility, are prone to injuries (e.g., ligament tears) and degenerative conditions (e.g., osteoarthritis). Think about this… Why is the knee joint particularly susceptible to ligament injuries compared to other synovial joints, like the shoulder or hip Arthritis: Osteoarthritis (OA): Pathophysiology: Degeneration of articular cartilage → bone-on-bone contact → inflammation and osteophyte formation. Symptoms: Pain, stiffness, reduced range of motion. Risk Factors: Age, obesity, joint overuse, previous injuries. Rheumatoid Arthritis (RA): Pathophysiology: Autoimmune attack on the synovial membrane → inflammation → pannus formation → cartilage and bone destruction. Symptoms: Symmetrical joint pain, swelling, deformities. Systemic Effects: Fatigue, anaemia, cardiovascular risk. Summing up Arthritis OA is the most common degenerative joint disease, affecting millions (To be Continued in globally. RA requires systemic treatment due Case Study) to its autoimmune nature. Injuries like ACL tears or dislocations often require surgical repair and extensive rehabilitation. Joint Injuries: Ligament Tears (e.g., Meniscus Tears: Dislocations: Bones ACL): High-stress Cartilage damage in the forced out of alignment, movements or trauma, knee from twisting common in the requiring surgery in motions. shoulder. severe cases.  Key Takeaways 1. Functions of the Skeletal 2. Bone Growth and 3. Clinical Focus on Bones: System: Remodelling: Osteoporosis: Causes, diagnosis, and Support, protection, movement, Ossification processes management strategies. mineral storage, blood cell (intramembranous and Fractures: Types, healing stages, and production, and energy storage. endochondral). factors affecting recovery. Lifelong remodelling maintains bone health and repairs fractures. 4. Joint Classifications and 5. Clinical Focus on Joints: 6. Integration in Clinical Anatomy: Arthritis (OA and RA): Practice: Structural and functional Pathophysiology, symptoms, and Applying anatomical knowledge to classifications. treatment differences. prevent, diagnose, and manage Synovial joints: Anatomy, types, and Joint injuries: ACL tears, meniscus conditions clinical vulnerabilities. injuries, and dislocations.