Fracture Remodeling

Remodeling is the 3rd and final phase in biology of fracture healing, preceded by the inflammatory and reparative phases. This occurs from a combination of appositional bone deposition on the concavity of deformity, resorption on the convexity, and asymmetric physeal growth. Thus, reduction accuracy is somewhat less important than it is in adults (Fig. 675-2). The 3 major factors that have a bearing on the potential for angular correction are skeletal age, distance to the joint, and orientation to the joint axis. The rotational deformity and angular deformity not in the axis of the joint motion are less likely to remodel. The amount of remaining growth provides the basis for remodeling; younger children have greater remodeling potential. Fractures adjacent to a physis undergo the greatest amount of remodeling, provided that the deformity is in the plane of the axis of motion for that joint. The fractures away from the elbow and closer to the knee joint have greater potential to remodel because this physis provides maximal growth to the bone. One can expect remodeling to occur over the next several months following injury throughout skeletal maturity. Skeletal maturity is reached in girls between 13 and 15 yr and in boys between 14 and 16 yr of age.

Figure 675-2 Remodeling in children is often extensive, as in this proximal tibial fracture (A) and as seen 1 yr later (B).

(From Dormans JP: Pediatric orthopedics: introduction to trauma, Philadelphia, 2005, Mosby, p 38.)

Overgrowth

Physeal stimulation from the hyperemia associated with fracture healing causes overgrowth. It is usually prominent in long bones such as the femur. The growth acceleration is usually present for 6 mo to 1 yr following the injury and does not present a continued progressive overgrowth unless complicated by a rare arteriovenous malformation. Femoral fractures in children <10 yr of age often overgrow by 1-3 cm. Bayonet apposition of bone is preferred to compensate for the expected overgrowth. This overgrowth phenomenon will result in equal or near equal limb lengths at the conclusion of fracture remodeling. After 10 yr of age, overgrowth is less of a problem and anatomic alignment is recommended. In physeal injuries, growth stimulation is associated with use of implants or fixation hardware that can cause chronic stimulus for longitudinal growth.

Progressive Deformity

Injuries to the physes can be complicated by progressive deformities with growth. The most common cause is complete or partial closure of the growth plate. As a consequence, angular deformity, shortening, or both, can occur. The partial arrest may be peripheral, central, or combined. The magnitude of deformity depends on the physis involved and the amount of growth remaining. CT and MRI are important for assessing partial arrests and formulating treatment (Fig. 675-3).

Figure 675-3 MRI with gradient echo sequence, illustrating distal femoral physeal bar.

(From Dormans JP: Pediatric orthopedics: introduction to trauma, Philadelphia, 2005, Mosby, p 43.)

Rapid Healing

Children’s fractures heal quickly compared with those of adults. This is due to children’s growth potential and thicker, more active periosteum. As children approach adolescence and maturity, the rate of healing slows and becomes similar to that of an adult.

Plastic Deformation

Plastic deformation is unique to children. It is most commonly seen in the ulna and occasionally the fibula. The fracture results from a force that produces microscopic failure on the tensile side of bone and does not propagate to the concave side (Fig. 675-4). The concave side of bone also shows evidence of microscopic failure in compression. The bone is angulated beyond its elastic limit, but the energy is insufficient to produce a fracture. Thus, no fracture line is visible radiographically (Fig. 675-5). The plastic deformation is permanent, and a bend in the ulna of <20 degrees in a 4 yr old child is expected to correct with growth.

Figure 675-4 Graphic relation of bony deformation (bowing) and force (longitudinal compression) showing that the limit of an elastic response is not a fracture but plastic deformation. If the force continues, a fracture results. A, reversible bowing with stress; B, microfractures occur; C, point of maximal strength; between C and D, bowing fractures; D, linear fracture occurs.

(Modified from Borden S IV: Roentgen recognition of acute plastic bowing of the forearm in children, Am J Roentgenol Radium Ther Nucl Med 125:524–530, 1975; from Slovis TL, editor: Caffey’s pediatric diagnostic imaging, ed 11, vol 2, Philadelphia, 2008, Mosby, p 2777.)

Figure 675-5 Plastic deformation is a microfailure in tension without a visible fracture line.

(Courtesy of Dr. John Flynn, Children’s Hospital, Philadelphia.)

Buckle or Torus Fracture

A compression failure of bone usually occurs at the junction of the metaphysis and diaphysis, especially in the distal radius (Fig. 675-6). This injury is referred to as a torus fracture because of its similarity to the raised band around the base of a classic Greek column. They are inherently stable and heal in 3-4 wk with simple immobilization.

Figure 675-6 Buckle fracture is a partial failure in compression: anteroposterior (A) and lateral (B) radiographs of the distal radius.

(From Dormans JP: Pediatric orthopedics: introduction to trauma, Philadelphia, 2005, Mosby, p 37.)

Greenstick Fracture

These fractures occur when the bone is bent, and there is failure on the tensile (convex) side of the bone. The fracture line does not propagate to the concave side of the bone. The concave side shows evidence of microscopic failure with plastic deformation. It is necessary to break the bone on the concave side because the plastic deformation recoils it back to the deformed position.

Complete Fractures

Fractures that propagate completely through the bone are called complete fractures. These fractures may be classified as spiral, transverse, or oblique, depending on the direction of the fracture lines. A rotational force usually creates the spiral fractures, and reduction is easy due to the presence of an intact periosteal hinge. Oblique fractures are in the diaphysis at 30 degrees to the axis of the bone and are inherently unstable. The transverse fractures occur following a 3-point bending force and are easily reduced by using the intact periosteum from the concave side.

Epiphyseal Fractures

The injuries to the epiphysis involve the growth plate. There is always a potential for deformity to occur, and hence long-term observation is necessary. The distal radial physis is the most commonly injured physis. Salter and Harris (SH) classified epiphyseal injuries into 5 groups (Table 675-1 and Fig. 675-7). This classification helps to predict the outcome of the injury and offers guidelines in formulating treatment. SH type I and II fractures usually can be managed by closed reduction techniques and do not require perfect alignment, because they tend to remodel with growth. SH type II fractures of the distal femoral epiphysis need anatomic reduction. The SH type III and IV epiphyseal fractures involve the articular surface and require anatomic alignment to prevent any step off and realign the growth cells of the physis. SH type V fractures are usually not diagnosed initially. They manifest in the future with growth disturbance. Other injuries to the epiphysis are avulsion injuries of the tibial spine and muscle attachments to the pelvis. Osteochondral fractures are also defined as physeal injuries that do not involve the growth plate.

Table 675-1 SALTER-HARRIS CLASSIFICATION