MSK 🇺🇸

• Greenstick fracture is an incomplete fracture extending partway through the width of the bone following bending stress, where the bone is bent like a green twig and the bone fails on the tension side while the compression side remains intact
• Torus (buckle) fracture is caused by an axial force applied to an immature bone, where the cortex buckles on the compression (concave) side and fractures while the tension (convex) side remains solid (intact)

  
• Achondroplasia


  Failure of longitudinal bone growth (endochondral ossification) leading to short limbs, while membranous ossification is not affected leading to a large head relative to the limbs. Mental function, life span and fertility are normal. Caused by constitutive activation of fibroblast growth factor receptor (FGFR3) which inhibits chondrocyte proliferation. Over 85% of mutations occur sporadically and it is autosomal dominant with full penetrance (homozygosity is lethal). Associated with increased paternal age. Most common cause of short-limbed dwarfism.
• Osteoporosis


  Trabecular (spongy) and cortical bone lose mass despite normal bone mineralization and lab values (serum Ca2+ and PO4-3). Most commonly due to increased bone resorption related to decreased estrogen levels and old age. Can also be secondary to drugs, hyperparathyroidism, hyperthyroidism, multiple myeloma, malabsorption syndromes, anorexia. Diagnosed by bone mineral density measurement by DEXA with a T-score of ≤ -2.5 or by a fragility fracture. Prophylaxis includes weight-bearing exercise and adequate Ca2+ and vitamin D intake. Treatment includes bisphosphonates, teriparatide, SERMs, denosumab.
• Glucocorticoids cause osteoporosis by increasing osteoclastic activity/differentiation, decreasing osteoblastic activity and decreasing vitamin D-mediated intestinal absorption of Ca. The risk of glucocorticoid induced osteoporosis increases with systemic therapy for >6 months or extremely long term inhaled cortisone treatment.
• Thiazide diuretics are recommended in the treatment of hypertension with osteoporosis because they increase calcium level in the blood.
• Teriparatide or Forito


  An impurity of the parathyroid hormone, used in construction processes within the body such as bone building and treating some types of bones.
• Osteopetrosis is a failure of normal bone resorption due to defective osteoclasts, leading to thickened, dense bones that are prone to fracture. It can result in cranial nerve impingement and palsies due to narrowed foramina.
• Osteomalacia is a defective mineralization of osteoid, and rickets is a defective mineralization of cartilaginous growth plates, most commonly due to vitamin D deficiency. This leads to osteopenia, "Looser zones" (pseudo fractures) in osteomalacia, and epiphyseal widening and metaphyseal cupping/fraying in rickets.
• Osteitis deformans (Paget's disease of bone) is a common, localized disorder of bone remodeling caused by increased osteoclastic activity followed by increased osteoblastic activity that forms poor-quality bone. It can lead to increased blood flow and high-output heart failure, and increased risk of osteosarcoma.
• Avascular necrosis of bone is an infarction of bone and marrow, usually very painful, most commonly occurring in the femoral head. Causes include corticosteroids, alcoholism, sickle cell disease, trauma, SLE, "the Bends", Legg-Calvé Perthes disease, and Gaucher disease.
• Rickets and vitamin D deficiency occur in children due to lack of sun exposure, dark skin, and exclusive breastfeeding (breast milk is deficient in vitamin D).
• Avascular necrosis of bone microscopically shows empty bony lacunae and fat necrosis.
• In Paget's disease of bone, the lytic stage occurs due to overactive RANK/OPG receptor leading to hyperactive osteoclasts, which destroy bone and release cytokines activating osteoblasts, leading to the sclerotic phase.
• Lab values in bone disorders

  • Osteoporosis: Decreased Ca2+, PO4-3, ALP, PTH

  Osteopetrosis: Decreased Ca2+, PO4-3, ALP, PTH

  Paget's disease of bone: Normal Ca2+, Increased PO4-3, ALP

  Primary hyperparathyroidism: Increased Ca2+, Decreased PO4-3, Increased ALP, Increased PTH

  Secondary hyperparathyroidism: Decreased Ca2+, Increased PO4-3, Increased ALP, Increased PTH

  Osteomalacia/rickets: Decreased Ca2+, Decreased PO4-3, Increased ALP, Increased PTH

  Hypervitaminosis D: Increased Ca2+, Increased PO4-3, Decreased PTH
• Metastatic disease is more common than primary bone tumors.
• Osteochondroma


  • Most common benign bone tumor, usually solitary but can be multiple in hereditary hyperostosis, consisting of a lateral bony projection of the growth plate covered by a cartilaginous cap.
• Osteoma


  • Benign tumor of the surface of facial bones, associated with Gardner syndrome.
• Osteoid osteoma


  • Benign tumor of the cortex of long bones, presenting as bone pain (worse at night) relieved by NSAIDs, with a radiolucent osteoid core.
• Osteoblastoma


  • Similar histology to osteoid osteoma but larger size (>2 cm) and pain unresponsive to NSAIDs, often occurring in the vertebrae.
• Chondroma


  • Benign tumor of cartilage, occurring in the medulla of small bones of the hand and feet.
• Giant cell tumor


  • Locally aggressive benign tumor formed of neoplastic mononuclear cells that express RANKL and reactive multinucleated giant (osteoclast-like) cells, occurring in the epiphysis of long bones (often in the knee region) with a "soap bubble" appearance on x-ray.