Image
Image

Introduction

The anatomy and biomechanics of pediatric bone differ from that of adult bone, leading to unique pediatric fracture patterns, healing mechanisms, and management. In comparison to adult bone, pediatric bone is significantly less dense, more porous and penetrated throughout by capillary channels. Pediatric bone has a lower modulus of elasticity, lower bending strength, and lower mineral content. The low bending strength induces more strain in pediatric bone than for the same stress on adult bone and the low modulus of elasticity allows for greater energy absorption before failure. The increased porosity of pediatric bone prevents propagation of fractures, thereby decreasing the incidence of comminuted fractures. The pediatric periosteum is extremely strong and thick, functioning in reduction and maintenance of fracture alignment and healing.

Anatomy of pediatric bone

Pediatric long bones have three main regions: epiphysis, physis and metaphysis.

Epiphysis: each end of a long bone with associated joint cartilage.

Physis (growth plate): cartilage cells that create solid bone with growth.

Metaphysis: wide area below the physis, closest to the diaphysis/shaft.

Another key component of bone is the periosteum, which is a thick, nutrient layer that wraps circumferentially around bones. It serves a major role in healing the outer layer of bone.

Pediatric fracture patterns

The mechanisms of fracture change as children age. Younger children are more likely to sustain a fracture while playing and falling on an outstretched arm. Older children tend to injure themselves while playing sports, riding bicycles, and in motor vehicle accidents. Also, because a child’s ligaments are stronger than those of an adult, forces which would tend to cause a sprain in an older individual will be transmitted to the bone and cause a fracture in a child. Caution should therefore be exercised when assessing a young child diagnosed with a sprain.

Plastic Deformation

  • A force produces microscopic failure on the tensile/convex side of bone which does not propagate to the concave side. The bone is angulated beyond its elastic limit, but the energy is insufficient to produce a fracture.
  • No fracture line is visible radiographically.
  • Unique to children
  • Most commonly seen in the ulna, occasionally in the fibula.
  • Bend in the ulna of < 20° in a 4 year old child should correct with growth.

Buckle fracture

  • Compression failure of bone that usually occurs at the junction of the metaphysis and the diaphysis
  • Commonly seen in distal radius.
  • Inherently stable
  • Heal in 3-4 weeks with simple immobilization.

Greenstick fracture

  • Bone is bent and the tensile/convex side of the bone fails.
  • Fracture line does not propagate to the concave side of the bone, therefore showing evidence of plastic deformation.
  • If the bone undergoes plastic deformation, it is necessary to break the bone on the concave side to restore normal alignment, as the plastic deformation recoils the bone back to the deformed position.

Complete fracture

  • Fracture completely propagates through the bone.
  • Classified as spiral, transverse, or oblique, depending on the direction of the fracture line.
    • Spiral fractures:
      • Fracture completely propagates through the bone.
      • Created by a rotational force.
      • Fracture completely propagates through the bone.
      • Low-velocity injuries
      • Fracture completely propagates through the bone.
      • An intact periosteal hinge enables the orthopedic surgeon to reduce the fracture by reversing the rotational injury.
    • Oblique fractures:
      • Occur diagonally across the diaphyseal bone at 30° to the axis of the bone.
      • Unstable, therefore alignment is necessary.
      • Fracture reduction is attempted by immobilizing the extremity while applying traction.
    • Transverse fractures:
      • Created by a 3-point bending force.
      • Easily reduced by using the intact periosteum from the concave side of the fracture force.

Physeal fractures

  • Fractures to the growth plate can be caused by i) crushing, ii) vascular compromise of the physis or iii) bone growth bridging from the metaphysis to the bony portion of the epiphysis.
  • Damage to growth plate may result in progressive angular deformity, limb-length discrepancy or joint incongruity.
  • The distal radial physis is the most frequently injured physis.
  • Most physeal injuries heal within 3 weeks. This rapid healing provides a limited window for reduction of deformity.
  • Physeal injuries are classified by the Salter-Harris (SH) classification system, based on the radiographic appearance of the fracture.

Differences between pediatric and adult fracture healing

Fracture Remodeling

  • Process that occurs over time as a child’s bone reshapes itself to an anatomic position.
  • The amount of remaining bone growth provides the basis for remodeling. Thus, the younger the child, the greater remodeling potential, and the less important reduction accuracy is.
  • Occurs over several months following injury.
  • Factors affecting amount of remodeling:
    • Age:- younger children have greater remodeling potential.
    • Location:- fractures adjacent to a physis undergo greatest amount of remodeling.
    • Degree of deformity
    • Plane of deformity with respect to adjacent joint:- remodeling occurs more readily in the plane of a joint than with deformity not in the plane of the joint.

Overgrowth

  • Caused by physeal stimulation from the hyperemia associated with fracture healing.
  • Prominent in long bones (ex. femur).
  • Growth acceleration is usually present for 6 months to 1 year following injury.
  • Does not present a continued progressive overgrowth unless complicated by a rare arteriovenous malformation.
  • > 10 years of age, overgrowth is less of a problem and anatomic alignment is recommended.

Progressive Deformity

  • Injuries to the physis can be complicated by progressive deformities with growth.
  • The most common cause is complete or partial closure of growth plates.
  • Deformities can include angular deformity, shortening of bone, or both.
  • The magnitude of deformity depends on the physis involved and the amount of growth remaining.

Rapid Healing

  • Pediatric fractures heal more quickly than adult fractures due to children’s growth potential and a thicker, more active periosteum (the periosteum contributes the largest part of new bone formation around a fracture)
  • As children reach their growth potential, in adolescence and early adulthood, the rate of healing slows to that of an adult.
  • There is one downside to rapid healing, however; refractures.