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CHAPTER-3_SKELETAL SYSTEM CHAPTER-3_SKELETAL SYSTEM
Typology: Summaries
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Axial skeleton: skull, spine, ribs, sternum. Appendicular skeleton: upper and lower limbs, shoulder, and pelvic girdles. Function: support, movement, protection, mineral storage (Ca, P), blood formation (marrow).
Compact (cortical) bone: dense outer layer; structural unit = osteon. Cancellous (trabecular) bone: inner spongy network containing marrow. Cells: o Osteoblasts – build bone.
o Osteocytes – maintain bone tissue. o Osteoclasts – resorb bone. Periosteum: membrane covering bone surface; active in growth and repair.
Technical Adequacy When evaluating skeletal radiographs:
1. Correct positioning (e.g., joints open, entire anatomy visualized). 2. Proper exposure — must display cortical outline and trabecular detail. 3. No rotation or motion blur. 4. Compare sides when evaluating suspected pathology.
1. Congenital / Hereditary. 5. Metabolic / Endocrine (often grouped later).
3. Arthritic Disorders Type Description Imaging Features Osteoarthritis (degenerative joint disease) Non-inflammatory wear and tear of articular cartilage. Joint-space narrowing, osteophyte formation, subchondral sclerosis, cysts. Rheumatoid arthritis Autoimmune inflammatory destruction of synovium. Bilateral symmetric joint involvement, soft-tissue swelling, marginal erosions, late deformities (ulnar deviation).
Type Description Imaging Features Ankylosing spondylitis Chronic inflammatory arthritis of spine and SI joints. “Bamboo spine,” SI joint fusion, squaring of vertebral bodies. Gout Uric acid crystal deposition. Joint effusion, punched-out erosions with overhanging edges (“rat bite”).
4. Neoplastic Disorders A. Benign Bone Tumors Tumor Site / Age Radiographic Features Osteochondroma (exostosis) Metaphysis, near knee. Bony outgrowth with cartilage cap, cortex continuous with parent bone. Enchondroma Small bones of hands/feet. Well-circumscribed, radiolucent lesion with calcifications. Giant cell tumor (osteoclastoma) Epiphysis of long bones, young adults. “Soap-bubble” appearance, locally aggressive.
B. Malignant Bone Tumors Tumor Characteristics Imaging Osteosarcoma Most common primary malignant bone tumor in adolescents. Mixed lytic and sclerotic lesion, “sunburst” periosteal reaction, Codman triangle. Ewing sarcoma Malignant tumor of bone marrow in children. “Onion-skin” periosteal reaction, diaphyseal lesion. Chondrosarcoma Malignant cartilage tumor, adults. Calcified cartilage matrix, irregular radiolucent lesion. Metastatic disease Most common skeletal malignancy overall. Lytic (lung, kidney, thyroid) or blastic (prostate, breast) lesions; bone scan highly sensitive.
5. Metabolic / Endocrine Disorders Disorder Description Radiographic Findings Osteoporosis Generalized reduction in bone density. Thin cortices, vertebral compression fractures, decreased trabecular pattern. Osteomalacia / Rickets Defective mineralization (Vit D deficiency). Bowing of long bones, Looser zones (pseudofractures). Paget disease (Osteitis deformans) Disordered bone remodeling; increased bone turnover. Mixed lytic–sclerotic pattern, thickened bone, “cotton-wool skull.” Fig - Osteoporosis Fig – Osteomalacia
