Pediatric Orthopaedic Surgery: General Principles

OVERVIEW

The development and growth of the skeletal system from gestation to skeletal maturity create interrelated fibrous, tendinous, cartilaginous, and osseous changes resulting in patterns of susceptibility and reparative response that distinguish the pediatric patient from the adult.
As a rule, the younger the patient, the greater the remodeling potential; thus, absolute anatomic reduction in a child is less important than in a comparable injury in an adult.

EPIDEMIOLOGY

The incidence of pediatric fractures is increasing.
- The increasing fracture incidence in children has been mainly attributed to increased sports participation.
- Approximately 50% of all children will fracture at least one bone during childhood.
The overall mortality rate of children has fallen from 1 in 250 per year in 1900 to 1 in 4,000 per year in 1986; this has been attributed to improved public education, preventive devices, and medical care.
The leading cause of death in children ages 1 to 14 years is accidental trauma.
Skeletal trauma accounts for 10% to 15% of all childhood injuries, with approximately 15% to 30% of these representing physeal injuries (phalanx fractures are the most common physeal injury).
From the ages of 0 to 16 years, 42% of boys will sustain at least one fracture compared with 27% of girls.
The overall ratio of boys to girls who sustain a single, isolated fracture is 2.7:1. The peak incidence of fractures in boys occurs at age 16 years, with an incidence of 450 per 10,000 per year; the peak incidence in girls occurs at age 12 years, with an incidence of 250 per 10,000 per year.
Open fractures in this population are rare (<5%).

ANATOMY

Pediatric bone has a higher water content and lower mineral content per unit volume than adult bone. Therefore, pediatric bone has a lower modulus of elasticity (less brittle) and a higher ultimate strain-to-failure than adult bone. It is relatively stronger in tension than compression, as compared to adult bone.
The physis (growth plate) is a unique cartilaginous structure that varies in thickness depending on age and location. It is frequently weaker than bone in torsion, shear, and bending, predisposing the child to injury through this delicate area.
The physis is traditionally divided into four zones: reserve (resting/germinal), proliferative, hypertrophic, and provisional calcification (or enchondral ossification) (Fig. 42.1).
The periosteum in a child is a thick fibrous structure (up to several millimeters) that encompasses the entire bone except the articular ends. The periosteum thickens and is continuous with the physis at the perichondral ring (ring of LaCroix), offering additional resistance to shear force.
As a general rule, ligaments in children are functionally stronger than the physis. Therefore, a higher proportion of injuries that produce sprains in adults result in physeal fractures in children.
The blood supply to the growing bone includes a rich metaphyseal circulation with fine capillary loops ending at the physis (in the neonate, small vessels may traverse the physis, ending in the epiphysis).

FIGURE 42.1 The process of endochondral ossification within the physis. Although not as organized, endochondral ossification follows a similar pattern during fracture repair. (From Bucholz RW, Heckman JD, Court-Brown C, et al., eds. Rockwood and Green’s Fractures in Adults. 6th ed. Philadelphia: Lippincott Williams & Wilkins; 2006.)

MECHANISM OF INJURY

Because of structural differences, pediatric fractures tend to occur at lower energy than adult fractures. Most are a result of compression, torsion, or bending moments.
Compression fractures are found most commonly at the metaphyseal diaphyseal junction and are referred to as “buckle fractures” or “torus fractures.” Torus fractures rarely cause physeal injury, but they may result in acute angular deformity. Because torus fractures are impacted, they are stable and rarely require manipulative reduction.
Torsional injuries result in two distinct patterns of fracture, depending on the maturity of the physis.
- In the very young child with a thick periosteum, the diaphyseal bone fails before the physis, resulting in a long spiral fracture.
- In the older child, similar torsional injury results in a physeal fracture.
Bending moments in the young child cause “greenstick fractures” in which the bone is incompletely fractured, resulting in a plastic deformity on the concave side of the fracture. The fracture may need to be completed to obtain an adequate reduction.
Bending moments can also result in microscopic fractures that create plastic deformation of the bone with no visible fracture lines on plain radiographs; permanent deformity can result.
In the older child, bending moments result in transverse or short oblique fractures. Occasionally, a small butterfly fragment may be seen; however, because pediatric bone fails more easily in compression, there may only be a buckle of the cortex.