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Fracture Healing: Four overlapping phases of bone repair: the inflammatory phase; the early callus phase; the mature callus phase; and the remodeling phase.
Inflammatory Phase
- characterized by an inflammatory and marrow response
- immediately following fracture to 3 to 4 days postfracture.
- release of proinflammatory mediators: interleukin 1 (IL-1), IL-6, tumor necrosis factor alpha (TNF-α): peak expression 24 hours after injury with decline to baseline levels by 72 hours post-fracture.
Early Callus Phase
- predominated by mesenchymal and vascular infiltration and chondrogenesis
- From few days to several weeks post-fracture
Mature Callus Phase,
- marked by endochondral ossification and primary bone (also called immature or woven bone) formation.
- cartilaginous matrix is mineralized and primary bone is formed
- fractures are typically considered healed during the late mature callus phase / early remodeling phase.
Remodeling Phase
- secondary bone (also called mature or lamellar bone) formation.
- fractures are typically considered healed during the late mature callus phase / early remodeling phase.
- late remodeling can continue beyond 1 year
Chondrogenesis: divided into six phases: MSC proliferation, MSC condensation, chondrocyte formation, chondrocyte maturation, hypertrophic differentiation, and apoptosis.
Parathyroid hormone (PTH)
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increases the calcium by indirectly stimulating bone resorption, increasing renal reabsorption of calcium, and increasing intestinal calcium absorption
FDA approved for treatment of osteoporosis in postmenopausal women
- high-dose recombinant PTH (40 μg) has demonstrated accelerated cortical bridging in distal radius fractures (Aspenberg P, J Bone Miner Res 2010;25(2):404)
Vitamin D (800 IU) and calcium (1 g) has demonstrated increased callus formation in non-op proximal humerus fracture (Doetsch AM, Calcif Tissue Int 2004;75(3):183-188)
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