The calcified cartilage breaks down allowing for vascular invasion and osteoblastic/osteoclastic bone matrix deposition and remodeling. The physis is split into 4 zones: (1) the reserve or resting zone, which is made up of hyaline cartilage (2) the zone of proliferation, which is made up of multiplying chondrocytes that arrange into lacunae (lakes) (3) the zone of hypertrophy, where the chondrocytes stop dividing and start enlarging and (4) the zone of calcification, where minerals are deposited into the lacunae to calcify the cartilage. However, long bones like the phalanges have only one physis. Long bones like the femur have 2 physes separated by a diaphysis, which is the shaft of a long bone. The physis is located towards the end of the long bone, with the epiphysis above it and metaphysis below it. It allows for bone growth from a cartilage base, known as endochondral ossification, which differs from bone growth from mesenchymal tissue, or intramembranous ossification. The physis is the growth plate in long bones including phalanges, fibula, tibia, femur, radius, ulna, and humerus. The majority of differences between adult and pediatric skeletal systems are due to the open physis in the pediatric population, which allows for continued growth prior to skeletal maturation during puberty and adulthood. The makeup, anatomy, and histology of the pediatric skeletal system is not just a smaller version of the adult form rather, it is unique in that it allows for rapid growth and change throughout development from childhood to adulthood. Buckle fractures are incredibly common injuries that present to the emergency department, which are invariably always managed conservatively, and do not routinely require orthopedic input. However, if there is a fracture with a cortical breach, it is termed a greenstick fracture if unicortical, or a complete fracture if bicortical. The appearance on plain X-ray shows the fracture site as two outcroppings of bone, as though the long bone has collapsed or ‘buckled.’ This appearance also resembles the horns of a bull viewed head-on, hence the alternative nomenclature – ‘torus’ fracture. In long bones, injuries without a cortical break either lead to plastic deformation through microfracture or to a ‘kink’ within the long bone, described as a ‘buckle’ or ‘torus’ fracture. Two of the major differences include the presence of the physeal growth plate and a thicker periosteum with the softer underlying bone. With soft, malleable bone, and a thick protective periosteal covering, minor injuries can result in a spectrum of deformities with or without a cortical break. The pediatric skeletal anatomy has unique properties that lead to varied pathology to that of the adult skeleton.
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