Greenstick Fractures

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Introduction

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]

Etiology

Greenstick fractures occur most commonly after a fall on an outstretched arm (FOOSH); however, they can also occur due to other types of trauma including motor vehicle collisions, sports injuries, or non-accidental trauma where the child is hit with an object. Malnutrition, specifically vitamin-D deficiency increases the risk of greenstick fractures of the long bones after a trauma.

Epidemiology

Approximately 12% of all pediatric emergency department visits in the United States are due to musculoskeletal injuries. Fractures make up a large percentage of musculoskeletal injuries resulting in significant morbidity and complications. Greenstick fractures are most likely to be found in the pediatric population under 10 years of age but can occur in any age group, including adults.[3] There is equal incidence rate in female and male patients, however, male patients are more likely to sustain fractures

Pathophysiology

A greenstick fracture is a partial thickness fracture where only cortex and periosteum are interrupted on one side of the bone but remain uninterrupted on the other.[1] They occur most often in long bones, including the fibula, tibia, ulna, radius, humerus, and clavicle. Most commonly, they occur in the forearm and arm involving either the ulna, radius or humerus.[1][3] This is because people brace falls with an outstretched arm, resulting in fractures to the upper extremities.

Greenstick fractures can also occur in the face, chest, scapula and virtually every bone in the body, but with much less frequency than long bones.[3] For example, greenstick fractures can occur in the jaw and nose.[7] Condylar fractures are the most common pediatric mandibular fractures, accounting for up to 55% of all mandibular fractures.[8] There are 3 types of condylar fractures. Low subcondylar fractures are the most common and are incomplete greenstick fractures the majority of the time.[8] Nasal trauma most commonly leads to greenstick fractures in the pediatric population due to an unfused midline suture and majority cartilage make up of the nasal bones.[9]