Developmental Dysplasia of the Hip Quiz

Bone Remodeling Units

• Bone remodeling units (BMUs) are bone precursor cells that differentiate into osteoblasts and osteoclasts.
• BMUs repair microscopic injuries and maintain bone integrity.

Bone-Remodeling Phases

• Phase 1 (activation): A stimulus (hormone, drug, vitamin, physical stressor, injury) activates precursor cells to form osteoclasts, which leads to bone reabsorption. Apoptotic osteocytes guide osteoclast activity, signaling where to resorb damaged bone.
• Phase 2 (resorption): Osteoclasts, large multinucleated cells, gradually absorb bone, creating a "cutting cone" resorption cavity. Lysosomal enzymes digest bone, and osteoclasts release degraded bone products into the vascular system.
• Phase 3 (formation): Osteoblasts, small cells, lay down new secondary bone within the resorption cavity. Osteoblasts lining the cavity secrete osteoid, fostering calcium and phosphorus deposition. Subsequent layers generate a haversian canal around a blood vessel. The old haversian systems are eventually replaced by new ones. This phase takes 4-6 months in humans.

Bone-Remodelling Units (BMU)

• BMUs are composed of precursor cells that differentiate into osteoblasts and osteoclasts.
• BMUs repair micrsocopic injuries and maintain bone integrity.

Fracture Types/Descriptions

• Fracture: a break in the continuity of a bone
• Complete vs Incomplete fractures: Complete fractures go completely through the bone while incomplete fractures do not
• Closed vs Open fractures: Closed (simple) fractures don't pierce the skin; open (compound) fractures do
• Other types include: Comminuted (3+ fragments), Linear (parallel to bone axis), Oblique (slanted across bone), Spiral (twisting of bone ends), Transverse (perpendicular to bone axis), Greenstick (bending fracture that only occurs on one side; usually in children), Torus (buckling of bone), and Bowing (bending)

Typical Complete Fractures

• Closed: Skin over the bone is intact.
• Open: Skin opening exists between bone and the skin
• Comminuted: Multiple bone fragments are present
• Linear: Fracture line is parallel to the bone's axis.

Typical Incomplete Fractures

• Greenstick: Fracture on one side only (common in children)
• Torus: Buckling of the bone cortex
• Bowing: Bending of the bone

Fracture Healing Stages

• Hematoma formation: Formation of blood clot within the injured area
• Procallus formation: Formation of fibrovascular tissue and collagen fibers from fibroblasts and osteoblasts
• Callus formation: Woven bone forms between the broken ends
• Callus replacement: Existing callus is replaced with lamellar bone.
• Remodeling: Bone remodeling occurs to shape and form the bone similar to its original structure.

Osteoarthritis (OA)

• OA is a noninflammatory joint disease.
• Characterized by local areas of damage and loss of articular cartilage, sclerosis of bone beneath the cartilage, osteophyte formation, and variable degrees of mild synovitis and joint capsule thickening.

Rheumatoid Arthritis (RA)

• RA is a systemic inflammatory autoimmune disease primarily affecting the joints.
• Characterized by inflammation in the synovial membrane of the joint, leading to cartilage and bone destruction.
• Systemic signs of inflammation are often present (e.g., fever, leukocytosis, malaise, anorexia, and hyperfibrinogenemia).
• Pathogenesis involves T cell activation, cytokine release, inflammatory cell recruitment, and damage to cartilage and bone.

Gout

• Gout is a metabolic disorder characterized by elevated serum uric acid levels.
• The increased uric acid levels lead to the formation of monosodium urate crystals, which deposit in joints and other tissues, causing inflammation and pain.

Legg-Calve-Perthes Disease (LCP)

• LCP is a self-limited disease of the hip, usually affecting children between the ages of 3 and 10 years.
• Primarily characterized by avascular necrosis (death of bone tissue due to inadequate blood supply) of the femoral head.

Ankylosing Spondylitis (AS)

• AS is a chronic inflammatory disease that primarily affects the spine and sacroiliac joints.
• Causes stiffening and/or fusion of the spine.
• Often associated with HLA-B27.
• Early symptoms include low back pain and stiffness, typically worse after rest.