Musculoskeletal System Notes

Musculoskeletal System Cartilage: Structure, Development & Metabolism Structure Water Cells - Chrondrocytes Matrix - Collagen & Proteoglycans Cartilage collagens ~70% of cartilage dry weight Fibre forming proteins which interact with other matrix molecules Triple helix of 3 amino acid chains, secreted from cell with non-helical terminal regions Proteoglycans Glycosaminoglycans (GAG) - a protein core Proteoglycan aggregate with hyaluronic acid PG & PG aggregates attract water strongly Collagen fibres act as a net, holding PGs together Fibrocartilage High collagen content Slightly compressible, very tough Example: menisci of the knee Elastic cartilage Contains elastic fibres Rigid but elastic Example: external ear Hyaline cartilage Strong but flexible Cover synovial joint surfaces Development & Metabolism Cartilage Metabolism Articular cartilage A type of hyaline cartilage found on articular surfaces of bones No perichondrium It is smooth to reduce friction It is deformable and elastic, distributing load evenly, | surface area ? | force Adaptive remodelling Anabolic and catabolic processes adjusted to adapt matrix to mechanical demand Injury & repair Lack capillaries within cartilage and so nutrients are from diffusion Page 1 Chondrocytes do not divide but still secrete matrix. Tears never fully heal GROWTH PLATE Ageing Decreased PG & collagen turnover Water lost on compression leading to tissue damage Impaired joint lubrication leads to friction and heat, osteoarthritis Musculoskeletal Diseases Types: Soft tissue: tennis elbow, mechanical back pain, repetitive strain Degenerative: osteoarthritis, cervical spondylosis Inflammatory: rheumatoid arthritis, seronegative SpA, crystal arthritis, connective tissue disease Other: fibromyalgia, normality, metabolic disease Causes of arthritis Cartilage death - osteoarthritis Synovial inflammation and overgrowth - rheumatoid arthritis Inflammation and new bone formation at entheses - ankylosing spondylitis Crystals in synovial fluid - gout Cartilage death In OA, the cartilage dies in patches, which results in the bones sitting more closely together and eventually rubbing against each other The joint space is narrower The bone just under the cartilage surface becomes thick and sclerotic (deep yellow colour) The bone at the edges grows out as if to support the failing joint and these are called osteophytes The capsule becomes thickened and fibrotic and the synovium may develop small areas of inflammation Occurs more in women than men and is more common in the elderly Synovial inflammation and overgrowth In RH, the synovium becomes inflamed with a mixture of acute and chronic changes leading to stiffness, pain and destruction Persistent inflammation causes generalised cartilage loss (narrowing the joint space) and thinning (osteoporosis) of the bone close to the joint (juxtaarticular osteoporosis) Synovial cells become overgrown and invasive, eating into the corners of the bones forming erosions More frequent in women than men and commonly starts in the 30-50 year range Inflammation and new bone formation at entheses The main site of this pathology is in the spine, where enthuses abound. However, the pathology can occur at many other sites, including important entheses that are not close to joints, such as where the plantar fascia of the foot joins to the anterior margin of the calcaneus. Ankylosing = sticking together Spondylitis = inflamed spine New bone forms little spurs called syndesmophytes in the spine, which grow into the area of the ligaments Page 2 

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