Original contributionSkeletal effects of low-intensity pulsed ultrasound on the ovariectomized rodent
Introduction
Osteoporosis, the preeminent clinical problem resulting from low bone mass and increased bone fragility, represents a major public health concern, causing increased morbidity and mortality in individuals who are often otherwise healthy. The mainstay of osteoporosis management is pharmacological intervention. However, as systemic treatments, these do not specifically target osteoporotic sites prone to fracture. In addition, they can result in a range of undesireable side-effects, limiting their application in various subgroups within the community. Due to the increasing global problem of osteoporosis associated with the aging of the population, there is a need to develop new interventions for this disease. The use of nonpharmacological therapies, either in isolation or in combination with pharmacological intervention, warrants evaluation.
Ultrasound (US) represents a potential nonpharmacological intervention for osteoporosis. Ultrasound refers to high-frequency nonaudible acoustic energy which travels in the form of a mechanical wave (Chivers 1991). A mechanical wave is one in which energy is transmitted by the movement of particles within the medium through which the wave is travelling (ter Haar 1987). As these mechanical waves travel as a relatively focussed beam (typical effective radiating area = 5 cm2), US can be directed onto specific regions to exert a local mechanical stimulus.
There is good biologic rationale to justify the application of US-produced mechanical stimuli to bone for the treatment of osteoporosis. Bone is a dynamic tissue which remodels in response to applied mechanical stimuli. This response has been thoroughly documented both in vitro and in vivo (Duncan and Turner 1995). As a form of mechanical stimulation, US may produce a similar remodeling response. This theory is supported by accumulating evidence demonstrating an osteogenic effect of pulsed-wave US at low (<100 mW/cm2) spatial-averaged temporal-averaged intensities Warden et al 2000a, Warden et al 2000c.
Currently, the most frequent application of low-intensity pulsed US to bone is during fracture repair. In animal fracture models, such US has been shown to facilitate the rate of endochondral bone formation Duarte 1983, Ito et al 1998, Wang et al 1994, increasing the return of bone mineral density (BMD) at the fracture site (Ito et al. 1998). This resulted in the facilitation of mechanical strength return by a factor of 1.4 to 1.6 (Pilla et al. 1990). In humans, low-intensity pulsed US has been shown to facilitate the return of bone mineral content (BMC) during limb lengthening procedures (Sato et al. 1999) and to accelerate fresh fracture repair by 38% Heckman et al 1994, Kristiansen et al 1997. When applied clinically to nonunited fractures, the same US has been shown to stimulate union in over 85% of cases Frankel 1998, Mayr et al 2000.
Additional evidence for an osteogenic effect of low-intensity pulsed US is provided by a growing number of in vitro investigations. These suggest a direct cellular basis for US effects on bone with osteoblastic changes including the transient expression of the immediate-early response genes c-fos (Naruse et al. 2000) and COX-2 (Kokubu et al. 1999), and elevated mRNA levels for insulin-like growth factor-I, osteocalcin and bone sialoprotein (Naruse et al. 2000). Other in vitro findings include an increase in osteoblastic proliferation Doan et al 1999, Reher et al 1998, collagen and noncollagenous protein synthesis Doan et al 1999, Reher et al 1997, calcium uptake (Ryaby et al. 1989) and prostaglandin E2 production (Kokubu et al. 1999). Further, low-intensity pulsed US has been shown to stimulate in vitro endochondral ossification in isolated bone rudiments, resulting in a threefold increase in the length of the calcified diaphysis (Nolte et al. 1999).
Despite this indirect evidence suggesting that low-intensity pulsed US may stimulate osteogenesis in intact bone, there is conflicting research investigating this potential application. In growing rodents, low-intensity pulsed US applied for 4 weeks had no effect on hindlimb BMD (Spadaro and Albanese 1998). Similarly, it had no effect on bone mineral loss associated with wing bandaging in pigeons (Wimsatt et al. 2000). Conversely, in five osteoporotic bedridden patients, daily low-intensity pulsed US applied for 4 weeks to the neck of femur resulted in an 8.9% average increase in BMD compared with baseline (Arai et al. 1993). Bone mineral density on the contralateral nontreated side decreased by 4.0% within the same period. This latter finding suggests an anabolic effect of low-intensity pulsed US on intact bone. It is apparent that further research is necessary to evaluate whether low-intensity pulsed US should be pursued as a possible clinical modality for osteoporosis. The aim of this investigation was to examine the effect of low-intensity pulsed US on hindlimb (distal femoral and proximal tibial) bone loss following OVX in rodents. A second aim was to investigate the effect of the same US on normal rodent bone in animals following sham-OVX.
Section snippets
Animals
Following ethical approval (Pharmacology and Physiology Animal Experimentation and Ethics Sub-Committee, The University of Melbourne, Parkville, VIC, Australia), 70 virgin female Sprague-Dawley rats were obtained at birth from the Biologic Research Facility at the University of Melbourne (Parkville, VIC, Australia). Animals were matured for a period of 26 weeks. Throughout maturation and the duration of the experiment, the housing room was maintained at 20°C with a 12 h light/12 h dark light
Animal weights
There were no significant differences in weight between the groups at baseline (p > .05). Surgery had a significant effect on weight gain, with OVX-C increasing their weight by 28.6% (97.0 ± 26.2 g) over the intervention period compared to a 15.7% (51.8 ± 18.8 g) increase in sham-OVX-C (p < 0.001; OVX-C vs. sham-OVX-C). Weight gain in restrained animals was significantly lower than in cage control animals following both OVX (p = .002; OVX-B vs. OVX-C) and sham-OVX (p = .001; sham-OVX-B vs.
Discussion and summary
To our knowledge, this is the first controlled study investigating the potential of low-intensity pulsed US as a treatment for osteoporosis. Using the OVX rodent as a model of osteoporosis, low-intensity pulsed US at the dose introduced had no effect on bone loss within the distal femur or proximal tibia. Similarly, it had no effect on normal rodent bone following sham-OVX. This nonsignificant finding supports that of Spadaro and Albanese (1998). Using the same dosage, low-intensity pulsed US
Acknowledgements
This work was funded by the Rebecca L. Cooper Medical Research Foundation. The authors gratefully acknowledge the expertise of Dr. A. Richards and Mr. A. Stirling (Ultrasound Standards, National Measurement Laboratory, Division of Telecommunications and Industrial Physics, CSIRO) in providing assistance with ultrasound design and testing, and experimental methodology; Dr K. Lay (Rowville Veterinary Clinic) in performing animal surgery; Ms. E. Wilson in assisting with US interventions; Ms. B.
References (43)
- et al.
Comparative morphometric changes in rat cortical bone following ovariectomy and/or immobilization
Bone
(1993) - et al.
In vitro effects of therapeutic ultrasound on cell proliferation, protein synthesis, and cytokine production by human fibroblasts, osteoblasts, and monocytes
J Oral Maxillofac Surg
(1999) - et al.
Precise accurate mineral measurements of excised sheep bones using X-ray densitometry
Bone Miner
(1994) - et al.
Low intensity pulsed ultrasound exposure increases prostaglandin E2 production via the induction of cyclooxygenase-2 mRNA in mouse osteoblasts
Biochem Biophys Res Commun
(1999) - et al.
Static vs dynamic loads as an influence on bone remodelling
J Biomech
(1984) - et al.
Anabolic response of mouse bone-marrow-derived stromal cell clonal ST2 cells to low-intensity pulsed ultrasound
Biochem Biophys Res Commun
(2000) - et al.
Effects of ultrasound on the pH profiles in the unstirred layers near planar bilayer lipid membranes measured by microelectrodes
Biochim Biophys Acta
(1993) - et al.
Effects of ultrasound on the steady-state transmembrane pH gradient and the permeability of acetic acid through bilayer lipid membranes
Biochim Biophys Acta
(1993) - et al.
Therapeutic ultrasound for osteoradionecrosisAn in vitro comparison between 1 MHz and 45 kHz machines
Eur J Cancer
(1998) - et al.
The stimulation of bone formation in vitro by therapeutic ultrasound
Ultrasound Med Biol
(1997)
Application of low-intensity ultrasound to growing bone in rats
Ultrasound Med Biol
Three rules for bone adaptation to mechanical stimuli
Bone
The effect of ultrasound stimulation on disuse osteoporosis
Trans Bioelectr Repair Growth Soc
Fundamentals of ultrasonic propagation
The stimulation of bone growth by ultrasound
Arch Orthop Trauma Surg
Mechanotransduction and the functional response of bone to mechanical strain
Calcif Tissue Int
WEAC procedures for laboratory testing of ultrasonic therapy devices
Results of prescription use of pulse ultrasound therapy in fracture management
Acceleration of tibial fracture-healing by non-invasive, low-intensity pulsed ultrasound
J Bone Joint Surg
Low intensity pulsed ultrasound accelerates fracture healing in a rat femoral fracture model
Trans Orthop Res Soc
Accelerated healing of distal radius fractures with the use of specific, low-intensity ultrasound
J Bone Joint Surg
Cited by (36)
Therapeutic Effects of Low-Intensity Pulsed Ultrasound on Osteoporosis in Ovariectomized Rats: Intensity-Dependent Study
2020, Ultrasound in Medicine and BiologyCitation Excerpt :Research on LIPUS treatment of osteoporosis, however, is still at an early stage, with only a few reported positive effects on osteoporotic animals (Carvalho and Cliquet Junior 2004; Wu et al. 2009; Ferreri et al. 2011; Lim et al. 2011; Uddin and Qin 2015) and even some conflicting results (Warden et al. 2001a, 2001b; Leung et al. 2004). For example, using LIPUS with almost the same parameters—frequency 1.5 or 1.0 MHz, duty cycle 20%, pulse repetition frequency (PRF) 1.0 kHz, intensity 30 mW/cm2 (spatial average temporal average intensity, ISATA), daily exposure 20 min—Wu et al. (2009), Carvalho and Cliquet Junior (2004) and Lim et al. (2011) found that LIPUS prevented bone loss in ovariectomized (OVX) rats, whereas Warden et al. (2001a) found no stimulatory effects of LIPUS in a similar model, Unfortunately, positive effects on animal models have not translated into similar benefits in human bones (Warden et al. 2001b; Leung et al. 2004; Zhang et al. 2017), In a clinical trial, patients with calcaneal osteoporosis caused by spinal cord injury received LIPUS treatment (frequency 1.0 MHz, duty cycle 3.3%, PRF 3.3 kHz, ISATA 30 mW/cm2, daily exposure 20 min) over 6 wk, but obtained no positive effects (Warden et al. 2001b). Reasons for the controversy revolve around many aspects, such as different skeletal sites, baseline bone mass, pathogenic factors of osteoporosis and, especially, the LIPUS parameters (e.g., center frequency, duty cycle, intensity and PRF), suggesting the necessity for optimization of the treatment regimen.
Ultrasound as a stimulus for musculoskeletal disorders
2017, Journal of Orthopaedic TranslationMuscle-bone interactions: From experimental models to the clinic? A critical update
2016, Molecular and Cellular EndocrinologyCitation Excerpt :Studies in sheep, turkeys and humans further suggest that bone responses may be frequency-dependent, possibly related to lower resonance frequencies in larger species (Christiansen and Silva, 2006; Rubin et al., 2001). Although low-intensity pulsed ultrasound (LIPUS) has been extensively studied in relation to fracture healing (Griffin et al., 2014), studies in osteoporosis models have been disappointing (Warden et al., 2001a, b; Yang et al., 2005). However, other recent pulsed focused ultrasound regimens did prevent bone loss in animal models (Ferreri et al., 2011; Poliachik et al., 2014; Uddin and Qin, 2015).
Effects of low-intensity pulsed ultrasound on healing of mandibular bone defects: An experimental study in rabbits
2015, International Journal of Oral and Maxillofacial Surgery