Fractures make up about 25% of injuries in children. The patterns and incidence depend on a number of variables including age, sex, climate, time of year, and environmental and cultural differences. Several studies have reported on the incidence of fractures in children (3, 4 and 5). In children from birth to 16 years of age, 42% of boys and 27% of girls suffer a fracture and about 2% of children sustain at least one fracture per year (3). The vast majority of these do not require an inpatient admission (5).

The number of fractures increases with age in boys into their late teen years. Girls have a similar pattern of incidence of fractures when young, but fracture occurrence decreases prior to the teenage years (3, 5). These injury patterns differ from the incidence of other types of childhood injures, such as head and soft-tissue injuries, which peak by age 2 (6). Child abuse as an etiology of fractures is less common as children age but must always be considered when fractures occur in young children, especially prior to walking age.

Fracture incidence varies by location. Upper extremity fractures account for two-thirds of childhood fractures, with the forearm being the most common location. The most commonly fractured bone in children is the radius (4). Physeal fractures make up about 20% of fractures in children (7). Open fractures are uncommon in children, occurring in only 2% of fractures, and multiple fractures occur in 4% of injuries (5).

About 1% of children who use playgrounds sustain injuries, mostly from activities on playground equipment, according to one study. While most injuries are fractures (39%) and soft-tissue injuries, such as contusions and sprains (48%), traumatic brain injuries are not uncommon (8.5%). Most children, however, do not require hospital admission for playground injuries (10). Changing playground surfaces from concrete to more impact-absorbing surfaces, such as bark or sand, can reduce the incidence and severity of head injury and potentially other injuries. Fracture risk, however, may be more related to the height of the fall than to the playground surface (11).

The four sports activities associated with the most injuries to bones and muscles are bicycle riding, basketball, football, and roller sports (12). Over 400,000 injuries occur to children in the United States while bike riding. While most are minor soft-tissue injuries, over one-third are fractures. More significantly, bicycle accidents are the most common causes of serious head injury in children (13). A well-fitting helmet is the best source of protection. Unfortunately not all children use helmets. Recently, however, evidence suggests that the use of helmets is increasing over the last several years (14). Roller sport injuries include those from skateboarding, roller skating, and inline skates. These activities commonly involve fractures, most often to the upper extremity. Skateboarding tends to result in the most severe injuries (15), with a high incidence of fractures. Inline skating also frequently results in musculoskeletal injury. In one report, as many as 60% of inline skaters sustained a traumatic injury, mostly contusions but occasionally fractures (16). Injuries often occur early in the child’s roller sport experience (17). Ice skating has a higher incidence of head injury than roller skating, making use of head protection for these athletes particularly important (18). Appropriate instruction, supervision, and protective equipment, including helmets, wrist guards, and elbow and knee pads, should be mandated (18). Trampoline-related injuries are becoming much more common and, like skateboard injuries, are frequently high-energy injuries. These injuries typically occur in the home setting often under the supervision and with the knowledge of the parents, most of whom know of the potential dangers of trampoline use (21, 22). Jumping with more than one person on the trampoline increases the risk of injury significantly. It is unclear if trampolines at home or on playgrounds can ever be used safely, and some advise that trampolines be used only in supervised training programs (20). Motorized recreational sports, such as motocross and use of all-terrain vehicles, are also associated with serious musculoskeletal injuries when safety guidelines are disregarded. Vehicles that are too heavy or powerful to be handled properly and poor driver judgment are important factors in injury occurrence.

Important anatomical and physiological features distinguish children’s bones from those of adults. Like adult bone, the diaphysis of long bones is comprised of dense cortical bone and the metaphysis is comprised of spongy, cancellous bone. Toward the ends of long bones, however, is where the child’s bone differs from that of an adult. There are four distinct areas that are associated with growth and remodeling processes. These include the epiphysis, physis, metaphysis, and diaphysis. Each area has its own unique structural and biomechanical characteristics.

Fractures to the immature skeleton, like in the adult, are described by location and fracture pattern. Many of these fracture patterns are similar to adult fractures, but others are unique to the growing child. Children’s bone is less mineralized, more porous, and has more vascular channels compared to adults. Because of its lower density, growing bone has a lower modulus of elasticity, diminishing its strength and response to bending forces but allowing it to absorb greater energy before failure. This mechanical property explains the occurrence of some of the fracture types unique to children. While children sustain complete fractures like adults, incomplete fracture types are more common in children compared to adults. As the child matures, fracture patterns sustained more closely resemble those of an adult.

Incomplete fractures include stress fractures and insufficiency fractures in adults. A stress
fracture is an incomplete fracture that is caused by repetitive stress in a person with normal bone quality. Once thought to be uncommon in children, they are becoming more widely recognized, especially in adolescent athletes. Insufficiency fractures are incomplete fractures that occur in weakened bone as a result of minor trauma. In the adult, this is most often seen in the elderly with osteoporotic bone. In children, these fractures are seen in individuals with an underlying bone disorder, such as osteogenesis imperfecta, or in those who have osteoporosis from disuse, such as a nonambulatory child with cerebral palsy. Both stress and insufficiency fractures can progress to complete fractures.

Children can also have unique types of incomplete fractures, including plastic deformation, greenstick fractures, and torus or so-called buckle fractures (Fig. 32-1).

Complete fractures in children may be similar to adult fractures or involve the physis. Diaphyseal fracture patterns are directly related to their mechanisms of injury: torsional forces result in spiral fractures, a perpendicular moment force results in a transverse fracture, and longitudinal compressive forces result in oblique fractures. A combination of compressive and moment forces results in a higher energy “butterfly” fracture pattern. The last two fracture patterns, butterfly and oblique, may be length unstable (Fig. 32-2).

This description of fracture patterns, although basic, can guide treatment. The general principles of fracture reduction in order are: re-creation of the mechanism of injury to displace the interposing soft tissue (usually the infolded periosteum) followed by reversal of the mechanism of injury to realign the fracture, using the intact periosteum hinge to help stabilize the reduction. Spiral fractures, particularly those that are “greenstick” fractures, are reduced by de-rotating the fracture back to the reduced position. These fractures typically have an intact longitudinal band of periosteum that provides enough stability such that cast immobilization is successful in maintaining reduction in most cases (52). Transverse fractures have intact periosteum on the compression side of the fracture, which may interpose into the fracture site and interfere with reduction. These fracture types often can be simply reduced by following the principles of fracture reduction described above. Fracture reduction for transverse fractures is best maintained by three-point molding of the cast
around the fracture site. Butterfly and oblique fractures may be length unstable. Because of this, closed reduction and cast immobilization may not always be adequate. Maintenance of length in a cast is more difficult for these fractures compared to length-stable patterns, such as the transverse fracture. Fixation is sometimes necessary to maintain the length of butterfly and oblique fracture types.

Fracture patterns in children are different when compared to adults because of other anatomical and mechanical differences. Comminuted fractures are less common because pediatric bone more readily dissipates energy before failure and its porosity limits the propagation of fracture lines (30). The smaller diameter of a child’s bone also influences its strength. Because bone resistance to torque is proportional to the fourth power of its radius, even a small increase in cortical diameter with growth results in a large increase in the bone’s ability to resist torsional loading. The epiphysis, which is largely cartilaginous in younger children, transmits the energy of the injury to the metaphysis, explaining the increased frequency of metaphyseal fractures in this age group.

The immature skeleton is defined by an open physis, and the manipulation and preservation of the physis is the most unique, and challenging, feature of children’s fracture care. Fractures that extend through the physis or traverse the physis and its adjoining metaphysis or epiphysis are best described by the Salter-Harris classification (Fig. 32-3). This radiographic classification system is based on the location of the fracture with respect to the physis. It reliably describes physeal fractures and helps to guide treatment, but is less useful for assessing long-term prognosis.

Ham Peterson carefully reviewed physeal fracture classifications and developed a revised classification which may have better prognostic significance (53).

The physis has unique biomechanical properties that are determined by several factors. In studies of the physes of animals, the zone of provisional calcification is the weakest area when subjected to mechanical stress (33, 34). Physeal fractures in these studies occurred predominantly through this zone. Microfractures, however, were identified in other zones of the physis, including the germinal zone. In a study of human cadavers, forces applied across joints resulted in physeal fractures more frequently than ligament disruptions (35). Physeal fractures in children occur mostly through the zone of hypertrophying cells (36).

The biomechanical stability of the physis is not solely determined by the zone of provisional calcification. Physeal resistance to shear forces is improved by both its nonplanar topography and its reinforcing structures. Many physes are not flat but are instead undulating, as best seen in the distal femoral physis.
Smaller projections within the physis also have been identified and are called mamillary processes. Some physes overlap the edges of their adjacent metaphyses with cup-shaped contours called lappet formations, as in the proximal tibia. There are two major microscopic structures unique to the physis. The Perichondrial Groove of Ranvier is composed of both resting and proliferating cells, and the Perichondrial Ring of Lacroix, comprised of cartilage cells contiguous with the metaphyseal periosteum, surround the physes. In addition to contributing to circumferential bone growth, these structures reinforce the physeal periphery. Additionally, some muscular, capsular, and ligamentous attachments span the physis and contribute to its stability. With progression of skeletal maturity, the size of the epiphysis and its ossification increases while the perichondrial ring weakens, making the physis more vulnerable to failure. These changes with age are one of the explanations for the increasing occurrence of physeal fractures with increasing age in children.

Fractures in children heal more rapidly and reliably than in adults. Nonunion is rare, especially after closed fractures. Increased bone vascularity, highly osteogenic periosteum, and limited soft-tissue disruption with most fractures are important factors (29). This improved ability to heal fractures influences fracture management. Cast immobilization is adequate for healing and maintenance of alignment for the vast majority of children’s fractures. Internal fixation, often needed to promote healing of adult fractures, is less frequently indicated for children and is mostly used to maintain adequate alignment for healing, acting as an “internal splint.” When fixation is necessary, less rigid implants that are easily removed and that do not violate growth plates, such as smooth wires and flexible intramedullary nails, are used in children compared to plate-screw constructs and rigid intramedullary devices typically employed for adults.

Children have the capacity to remodel many fractures that heal with residual angulation (Fig. 32-5). Remodeling is a by-product of the growing bone’s increased vascularity, cellular periosteum, and cellular factors.
Remodeling likely occurs by two different mechanisms. Some remodeling is seen at the site of malunion by gradual resorption on the convexity of the deformity and increased deposition on its concavity, a phenomenon known as “bone drift” (37). In a rat model, analysis of callus on the concave and convex sides of remodeling deformities shows important immunohistochemical differences between these areas (38). Most remodeling, however, occurs through changes within the physis that cause asymmetric longitudinal growth and reorientation of the physis (37, 39).

Three important factors affect the capacity of immature bone to remodel: (a) Remodeling capacity is best for fractures close to active growth plates. (b) Remodeling occurs most reliably after fractures that heal with residual angulation in the plane of motion of the nearest joint. (c) Remodeling does not occur to any significant degree in children with <2 years of skeletal growth remaining.

While restoration of anatomic alignment remains an important goal of children’s fracture management, some degree of nonanatomic reduction is acceptable in many types of children’s fractures because of the capacity for remodeling. Exceptions to this include fractures that cross the physis and fractures that extend into the articular surface, both of which require anatomic realignment. Remodeling may continue for 5 to 6 years after fracture healing (39). Severe residual angular deformities and rotational malunions remodel less predictably (37, 40). Because of the limitations of remodeling, the surgeon must be aware of the degree of residual angulation that is “acceptable” when making management decisions. This varies based on the child’s skeletal maturity, the particular bone that is angulated, the location and direction of angulation, and its degree of deformity. Limitations of space do not permit a complete discussion of the accepted limits of remodeling. A good discussion of this topic has been published by Kaye Wilkins (41).

Symmetrical growth stimulation, or overgrowth, is another characteristic of fracture healing that is unique to children. While its etiology is not fully understood, loss of periosteal tension and increased blood flow to the physes of the fractured bone are potential causes. Experimentally, transverse sectioning of the periosteum, especially near a growth plate, reduces the tension within the periosteum and results in limb overgrowth. Incomplete transverse sectioning has been shown to cause asymmetric physeal stimulation, resulting in angular deformity (42). By contrast, longitudinal sectioning of the periosteum does not have the same effect (29, 43). Hyperemia is a plausible explanation based on the observation that limb overgrowth occurs in some childhood conditions associated with inflammation or increased vascularity such as inflammatory arthritides and congenital vascular
malformations (44). Clinically, overgrowth is most common after femoral shaft fractures in children between the ages of 2 and 10 years of age, averaging 0.9 cm with a range of 0.4 to 2.4 cm (45).

Asymmetrical overgrowth is less common than symmetrical overgrowth. The case of the proximal tibia fracture may offer important insights into the etiology of remodeling and asymmetric bone stimulation after fracture. Incomplete fractures of the proximal tibial metaphysis in children sometimes result in an asymmetrical growth stimulation, typically valgus overgrowth of the tibia, within 1 to 2 years after the fracture. This deformity is likely the result of both asymmetrical hyperemia leading to overgrowth at the fracture site and asymmetric periosteal tethering of physeal growth on the contralateral side. Fortunately for most children, remodeling or reversal of the overgrowth occurs spontaneously, obviating the need for guided growth techniques or osteotomies to correct the overgrowth.

The etiology of this phenomenon of asymmetric overgrowth leading to proximal tibia valgus after an incomplete proximal tibia fracture is likely multifactorial and is not, however, completely understood (Fig. 32-6). Various theories have been proposed. Ogden (46) has demonstrated in cadaver studies that the blood flow to the medial side of the proximal tibial metaphysis is significantly greater than on the lateral side. Most of the data supporting the theory that intact periosteum inhibits longitudinal growth comes from animal studies. Early studies show that in chickens (47, 48) circumferential release of the periosteum resulted in overgrowth of the long bone affected. Subsequent studies in rabbits (49, 50) have shown that the release of only one side of the metaphyseal periosteum can produce asymmetrical growth stimulation. In none of the above animal studies were structural changes able to be demonstrated in histological examination of the physes.

Most fractures in children are isolated injuries. Emergency department assessment of the injured child begins with the history. High-energy mechanisms of injury, multiple fractures, or other obvious nonskeletal injuries warrant a complete evaluation from the trauma team. For the isolated injury, the extremity is first inspected for swelling or deformity and the skin for abrasions or lacerations, soft-tissue defects, and exposed bone. The neurovascular status limb is determined by testing motor and

sensory function distal to the fracture site, palpation of distal pulses, and assessment of capillary refill. For grossly displaced or unstable fractures, application of gentle longitudinal traction and gross realignment may be done before further evaluation, especially for the limb with vascular compromise. Splinting of the grossly malaligned limb or unstable fracture immediately after evaluation before taking radiographs may be necessary to enhance the child’s comfort and to prevent further trauma. After obtaining high-quality orthogonal radiographic views of the fracture, including images of the joints proximal and distal to the injury site, preparation is made for fracture reduction.