Carlos Salinas de Gortari de héroe a villano, las vitudes

Overview of bone repair

Fracture healing is a special form of wound healing. Therefore, the normal three phases of repair also occur, i.e. inflammation, proliferation and remodelling. The proliferative phase is subdivided into soft and hard callus formation. The soft callus is an equivalent to granulation tissue in soft tissue injuries. Bone is formed in the soft callus by two mechanisms: intramembranous bone formation and endochondral replacement. The former occurs by the rapid proliferation

and differentiation of osteoblast progenitor cells in the periosteum (Kelly et al,

1985). The latter follows as cartilage adjacent to this intramembranous bone undergoes hypertrophy and vascular invasion; bone then replaces the cartilage by endochondral ossification (hard callus). Healing is functionally complete when new bone bridges the fracture site, restoring bone continuity and

mechanical stability (Yang et al, 1996). A definitive transition from a cartilage

model to woven bone is not readily seen in mammalian bone although it does

occur in experimental fractures in rats (1?ahn '

Wolff (1892) is believed to have been the first to report that mechanical forces regulate the structure and function of skeletal tissue. Many orthopaedic scientists have attempted to advance bone formation by intensifying or controlling the mechanical forces at the fracture site. The clinical success of these treatments indicates that cells in the fracture callus can “translate” mechanical forces into biological signals that modify the metabolic activity of cells. Furthermore, these observations imply that mechanical loading is one of

the local regulatory signals guiding gene expression in the callus (Yang et a/y

1996).

Ultrasound effects on bone repair

Dyson and Brookes (1983) showed that it was possible to accelerate the repair of fibula fractures using 1.5 or 3 MHz, pulsed, 0.5 W/cm^ levels of ultrasound. Therapy was carried^or 5 minutes, four times per week, and the most effective

Chapter 2 - Literature Review - Section III - Ultrasound

treatments were found to be those which were carried out during the first two weeks of repair (inflammatory phase). Of the frequencies used, 1.5 MHz was

the most effective. Pilla et al (1990) showed that low intensity ultrasound (1.5 or

3 MHz, pulsed, 30 mW/cm^^®^^^^) could stimulate fracture repair in rabbits to such a degree that maximum strength was gained in the treated limbs by 17

days after injury compared to 28 days in the controls. Tsai at a! (1992a) showed

that low intensities of ultrasound (1.5 MHz, pulsed, 0.5 W/cm^) stimulated fracture healing in a rabbit fibulae model. However, they also showed a deleterious effect when ultrasound was applied at 1.0 W/cm^. The same team also reported high production of PGEg at the best stimulatory ultrasound intensities for bone repair, suggesting that bone healing may be mediated via production of cytokines, although PGEg is usually associated with resorption

(Tsai etal, 1992b).

Wang et al (1994) using a rat femoral fracture model, observed that

ultrasound enhanced the mechanical properties of healing calluses. The stiffness of treated fractures was greater than that of the control fractures, at 0.5 and 1.5 MHz, but the difference was significant only with the 1.5 MHz signal (p<0.02). This report shows accelerated endochondral ossification in the callus after ultrasound exposure, whereas other authors have reported that ultrasound

exposure changes the calcium content of cultured cells (Ryaby et al, 1989).

Either advanced endochondral ossification or increased matrix calcium, conditions that may be closely related, could result in stronger fracture callus.

Yang et al (1996) using 0.5 MHz (50 or 100 mW/cm^ in a rat

femoral fracture model similar to that used by Wang et al (1994), showed that

the average maximum torque and torsional stiffness were greater than in controls, reaching statistical significance at 50 mW/cm^. They could not measure any significant difference in the collagen content measured in the soft callus 7, 14 or 21 days after fracture. However evaluation of gene expression showed a shift in the expression of genes associated with cartilage formation: aggrecan gene expression was significantly higher on day 7 after fracture, and significantly lower on day 21. They suggest that ultrasound stimulation increases the mechanical properties of the healing fracture callus by stimulating

earlier synthesis of extracellular matrix proteins in cartilage, possibly altering chondrocyte maturation and endochondral bone formation.

Heckman et al (1994), investigated the effectiveness of low intensity

ultrasound on the healing of human tibial fractures. The fractures were examined in a prospective, randomised, double-blind evaluation of low intensity ultrasound, applied to a group of 67 closed or grade-1 open fractures of the tibial shaft. The treated group showed a significant decrease in the time to clinical healing (86 +/- 5.8 days) as compared to the control group (114 + /-1 0 .4 days) (p=0 .01) and also a significant decrease in the time to over-all i.e. clinical and radiographic healing (9 6 + M .9 days compared to 154 +/-13.7 days in the control group).

Finally we come to the use of ultrasound applied to bone is in the treatment of mandibular osteoradionecrosis (Harris, 1992). The patients were treated with ultrasound (3 MHz, pulsed 1:4, 1 W/cm^) for 40 sessions of 15 minutes per day. Ten out of 21 (48%) cases showed healing when treated with debridment and ultrasound alone. The remaining 11 cases unhealed after ultrasound therapy received debridment and cover with a local flap, and only one needed mandibular resection and reconstruction. These results are significantly better than the conventional treatment with hyperbaric oxygen therapy and surgery, but needed scientific validation. Marx (1983b) himself concluded that hyperbaric oxygen alone cannot heal ORN wounds, since only 15% responded, and 70% of his patients required major reconstruction. In our department, Telfah (1995) using near infrared spectroscopy has demonstrated that patients with ORN who received ultrasound therapy showed significant improvements of the metabolic activity as measured by increase in their deoxyhaemoglobin concentrations, but the reliability of this work will be discussed later in chapter 11.

Section IV - Hypothesis and Alms

1. Hypothesis

Therapeutic ultrasound can be used in the treatment and prevention of osteoradionecrosis because itslimuUlV^ cell proliferation, cell differentiation, healing, and angiogenesis, therefore reversing the long term effects of radiotherapy.

2. Aims

1. To establish this hypothesis by a series of controlled experiments examining cell, matrix and vascular factors in response to two ultrasound modalities.

2. To evaluate the use of near infrared spectroscopy (NIRS) as a diagnostic tool for measurements of deoxyhaemoglobin concentrations in the mandibles of volunteers and patients treated with radiotherapy, establishing the risks of development of osteoradionecrosis and evaluating the efficacy of therapeutic ultrasound clinically.

Ultrasound - a Pilot Study

1. Introduction

As shown in chapter 2, ultrasound has proved to be therapeutically valuable in many ways, through its thermal and non-thermal effects. Several ultrasound applications using non-thermal effects have been shown in the literature, the majority observed in soft tissue healing.

Using human skin fibroblasts insonated in suspension and subsequently

cultured in vitro, Harvey et al (1975) found an increase of both collagen and

non-collagenous protein (NCP) synthesis, which was intensity dependent.

Fibroblasts exposed to continuous ultrasound (0.5 W/cm^ showed a 20%

increase in collagen secretion which was increased to 30% when the ultrasound was pulsed (0.5 W/cm^ (sapa)j

The use of mouse calvaria has been found to be a successful tool to

study bone formation in vitro (Raisz et al, 1978). A relatively new method for

estimating collagen and non-collagenous (NCP) synthesis has been used in this study. This is a modification of the conventional assay in which ^H-proline- labelled calvaria are exposed to highly purified bacterial collagenase to release labelled collagen (Peterkofsky and Diegelman, 1971). In the modified assay

developed by Meghji et a! (1992a and b), pepsin is used to lyse the calvaria

_________ Chapter 3 - Bone formation induced by therapeutic ultrasound - a pilot study_________

2. Hypothesis and Aims

This work tests the hypothesis that ultrasound promotes healing in osteoradionecrosis and bone fractures by enhancing bone formation through the stimulation of collagen and non-collagenous protein synthesis.

The aims of this chapter are:

1. To identify if ultrasound at 3 MHz, pulsed 1:4 is able to stimulate the production of collagen and non-collagenous proteins in neonatal mice calvaria.

2. Verify if these effects are due to thermal or non-thermal effects, by measuring the heat production caused by different intensities of ultrasound at 3 MHz, pulsed 1:4.