Greenstick Fractures

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.

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.[1] The physis is the growth plate in long bones including phalanges, fibula, tibia, femur, radius, ulna, and humerus. It allows for bone growth from a cartilage base, known as endochondral ossification, which differs from bone growth from mesenchymal tissue, or intramembranous ossification.[2] The physis is located towards the end of the long bone, with the epiphysis above it and metaphysis below it.[1] Long bones like the femur have 2 physes separated by a diaphysis, which is the shaft of a long bone. However, long bones like the phalanges have only one physis. 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. The calcified cartilage breaks down allowing for vascular invasion and osteoblastic/osteoclastic bone matrix deposition and remodeling. Therefore, prior to ossification, the majority of pediatric bone is just calcified cartilage, which is very compliant when compared to the ossified bones of adults.[1] Due to their increased compliance, pediatric bones tend to have more bowing and bending injuries under stress that would cause a fracture in an adult bone.[1] Furthermore, the pediatric periosteum is more active, thicker and stronger in children, which greatly decreases the chance of open fractures and fracture displacement. These and other qualities of the pediatric periosteum, as well as the increased compliance of the pediatric bone, are responsible for the unique fracture patterns seen in pediatric patients. These fracture patterns include greenstick, torus, and spiral injuries, which are bending injuries rather than full thickness cortical breaks.[1] A greenstick fracture is a partial thickness fracture where only cortex and periosteum are interrupted on one side of the bone, while they remain uninterrupted on the other side.[1]