The Regenerate Bone

and Mark T. Dahl²

(1)

Department of Orthopedic Surgery, University of California – Irvine, Orange, CA, USA

(2)

Limb Length and Deformity Correction Clinics, Gillette Children’s Specialty Healthcare and University of Minnesota, St. Paul / Minneapolis, MN, USA

Keywords

RegenerateRegenerate boneDistraction osteogenesisFibrous interzoneIlizarov’s methodCircular external fixationTensioned wire external fixationRing fixatorCorticotomyOsteotomy

Histologic Features of the Regenerate

Histology, Early Phases

Under the microscope , the tissue that forms in the widening distraction gap under the influence of steady distraction has some interesting features. In the early phases of distraction osteogenesis , the widening gap contains poorly differentiated connective tissue. This substance slowly organizes into small cones of newly forming bone attached to the fragment ends, separated by a fibrocartilaginous layer. With additional time, distraction, and stability, the entire zone fills with osseous tissue, often with a band of cartilaginous tissue zigzagging across the middle (Fig. 2.1).

Fig. 2.1

Formation of the bone in a widening distraction zone . (a) Initially the zone is filled with connective tissue (CT). (b) Next, new osseous tissue (NB) forms at the fragment ends, while fibrocartilage (FC) forms in the middle region. (c) Eventually, the bone, oriented longitudinally, consolidates the distraction zone. Reprinted from Transosseous Osteosynthesis, “The Tension-Stress Effect on the Genesis and Growth of Tissues,” 1992, pp. 137–255, G. A. Ilizarov, Copyright Springer-Verlag Berlin Heidelberg. With permission of Springer

Histology, Vascularization

In the early phases of distraction osteogenesis , parallel longitudinal columns of fibrous tissue form . When cut in cross section and viewed under a microscope, these columns have the appearance of honeycombs, whereas when cut longitudinally, they resemble the striations in a stalk of celery [1, 2] (Fig. 2.2).

Fig. 2.2

Longitudinal (left) and transverse (right) section of newly formed regenerate bone with India ink stain. Blood vessels show as black. Note the vertical striations in the longitudinal section and the honeycomb appearance of the transverse section. Reprinted from Transosseous Osteosynthesis, “The Tension-Stress Effect on the Genesis and Growth of Tissues,” 1992, pp. 137–255, G. A. Ilizarov, Copyright Springer-Verlag Berlin Heidelberg. With permission of Springer

This new tissue is highly vascularized , with newly formed blood vessels occupying the spaces between the longitudinal fibers.

At the electron microscopic level, the newly forming fibrous tissue, subjected to continuous traction by the elongating mechanism, contains stretched out mitochondria and elongated endoplasmic reticulum (Fig. 2.3).

Fig. 2.3

Electron micrograph of a fibrocyte in the distraction zone. Notice the elongated mitochondria (lower arrow) and the stretched-out endoplasmic reticulum. 22,000×. Reprinted from Transosseous Osteosynthesis, “The Tension-Stress Effect on the Genesis and Growth of Tissues,” 1992, pp. 137–255, G. A. Ilizarov, Copyright Springer-Verlag Berlin Heidelberg. With permission of Springer

The Fibrous Interzone

When external fixation is used to create the distraction regenerate, a dark zigzag line often appears traversing the center of the distraction gap [3, 4]. This region is called “the interzone.” It is perceived as a kind of growth plate of the distraction regenerate. The interzone would naturally be hard to see when an intramedullary device occupies the middle of the bone (Fig. 2.4).

Fig. 2.4

India ink preparation showing the fibrous interzone (white arrows) zigzagging across the middle of the regenerate region. Reprinted from Transosseous Osteosynthesis, “The Tension-Stress Effect on the Genesis and Growth of Tissues,” 1992, pp. 137–255, G. A. Ilizarov, Copyright Springer-Verlag Berlin Heidelberg. With permission of Springer

As the white lines get denser and thicker, they eventually cross the interzone, indicating that ossification has proceeded along the entire regenerate. This usually does not occur until the distraction phase of the process has been completed .

Maturation Phases

The fibrous tissue in the elongating distraction zone consists primarily of collagen. Gradually, tiny calcium hydroxyapatite crystals are deposited within the collagen fibers, stiffening them. Such collagen fibers with embedded calcium hydroxyapatite crystals are the basic ingredients of bone. The calcium hydroxyapatite crystals, because of their density, absorb x-ray beams. These absorbed beams never darken an x-ray film, so they appear white when the film is viewed on a translucent view box.

Only gold members can continue reading. Log In or Register to continue