Disorders of Muscles and Bones: Arthritis, Osteoporosis
Muscles and bones work together for movement, so disorders in either affect daily life. Common problems include arthritis of joints, osteoporosis of bone, muscular dystrophy, myasthenia gravis, tetany and strains.
These disorders matter because they cause pain, weakness, fractures and disability, especially in older adults. Early diagnosis, exercise, nutrition and fall prevention can reduce their impact greatly.
Key Concepts
- Osteoarthritis: Degeneration of articular cartilage causing pain, stiffness and reduced joint movement, common in knee and hip.
- Rheumatoid arthritis: Autoimmune inflammation of synovial joints causing swelling, pain and deformity.
- Gout: Joint inflammation from uric acid crystal deposition, often in the big toe.
- Osteoporosis: Loss of bone mass and strength, increasing fracture risk, common after menopause and in ageing.
- Muscular dystrophy: Genetic disorders causing progressive muscle wasting and weakness.
- Myasthenia gravis: Autoimmune attack on acetylcholine receptors at neuromuscular junctions, causing fatigable weakness.
- Tetany: Muscle spasms due to low blood calcium affecting nerve and muscle excitability.
How It Works
- In osteoarthritis, cartilage wears and bone ends rub, forming spurs and pain that worsens with load.
- In rheumatoid arthritis, the immune system inflames synovium, damaging cartilage and bone in a symmetrical pattern, often in small hand joints.
- Osteoporosis develops when bone resorption by osteoclasts exceeds formation by osteoblasts over years, thinning trabecular and cortical bone.
- Muscle disorders act differently: dystrophy damages fibres internally, myasthenia blocks signal transmission, and low calcium makes nerves hyperexcitable causing tetany.
Worked Example
Bone mineral density is reported as a T-score. A T-score of -1 to -2.5 indicates low bone mass (osteopenia), and -2.5 or below indicates osteoporosis. If a patients score falls from -1.8 to -2.7 over testing, the change crosses the -2.5 threshold, meaning diagnosis changes to osteoporosis and fracture-prevention treatment and fall-risk measures become urgent, even if pain is absent.
Common Misconceptions
- Arthritis is only an old-age wearing problem: Wrong. Rheumatoid arthritis and gout are inflammatory/metabolic and can start earlier.
- Osteoporosis causes pain as its first sign: Often wrong. It is silent until a fracture occurs.
- Muscle weakness is always due to muscle disease: Wrong. Nerve, junction, thyroid and electrolyte problems can also cause weakness.
Real-World Applications
DEXA scans measure bone density. Calcium, vitamin D, weight-bearing exercise and anti-resorptive medicines treat osteoporosis. Physiotherapy, joint protection and disease-modifying drugs are used in arthritis. Genetic counselling helps families with muscular dystrophy.
Overall, muscle and bone disorders arise from wear, autoimmunity, metabolism or genes. Protecting joints, maintaining bone density and seeking early care preserve independence.