Low-intensity ultrasound stimulation in distraction osteogenesis in rabbits

Effect of low-intensity pulsed ultrasound on distraction osteogenesis: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Low-intensity pulsed ultrasound (LIPUS) is a common adjunct used to promote bone healing for fresh fractures and non-unions, but its efficacy for bone distraction osteogenesis remains uncertain. This study aims to determine whether LIPUS can effectively and safely reduce the associated treatment time for patients undergoing distraction osteogenesis.

METHODS

MEDLINE, EMBASE, and the Cochrane Library were searched until May 1, 2018, without language restriction. Studies should be randomized controlled trials (RCTs) or quasi-RCTs of LIPUS compared with sham devices or no devices in patients who undergo distraction osteogenesis. The primary outcome was the treatment time. The secondary outcome was the risk of complications. Treatment effects were assessed using mean differences, standardized mean differences, or risk ratios using a random-effects model. The Cochrane risk-of-bias tool was used to assess the risk of bias. The I² statistic was used to assess the heterogeneity. The GRADE system was used to evaluate the evidence quality.

RESULTS

A total of 7 trials with 172 patients were included. The pooled results suggested that during the process of distraction osteogenesis, LIPUS therapy did not show a statistically significant reduction in the treatment time (mean difference, - 8.75 days/cm; 95% CI, - 20.68 to 3.18 days/cm; P = 0.15; I² = 72%) or in the risk of complications (risk ratio, 0.90 in favor of LIPUS; 95% CI, 0.65 to 1.24; I² = 0%). Also, LIPUS therapy did not show a significant effect on the radiological gap fill area (standardized mean difference, 0.48 in favor of control; 95%CI, - 1.49 to 0.52; I² = 0%), the histological gap fill length (standardized mean difference, 0.76 in favor of control; 95%CI, - 1.78 to 0.27; I² = 0%), or the bone density increase (standardized mean difference, 0.43 in favor of LIPUS; 95%CI, - 0.02 to 0.88; I² = 0%).

CONCLUSIONS

Among patients undergoing distraction osteogenesis, neither the treatment time nor the risk of complications could be reduced by LIPUS therapy. The currently available evidence is insufficient to support the routine use of this intervention in clinical practice.

TRIAL REGISTRATION

CRD 42017073596.

Ultrasound as a stimulus for musculoskeletal disorders

Ultrasound is an inaudible form of acoustic sound wave at 20 kHz or above that is widely used in the medical field with applications including medical imaging and therapeutic stimulation. In therapeutic ultrasound, low-intensity pulsed ultrasound (LIPUS) is the most widely used and studied form that generally uses acoustic waves at an intensity of 30 mW/cm², with 200 ms pulses and 1.5 MHz. In orthopaedic applications, it is used as a biophysical stimulus for musculoskeletal tissue repair to enhance tissue regeneration. LIPUS has been shown to enhance fracture healing by shortening the time to heal and reestablishment of mechanical properties through enhancing different phases of the healing process, including the inflammatory phase, callus formation, and callus remodelling phase. Reports from in vitro studies reveal insights in the mechanism through which acoustic stimulations activate cell surface integrins that, in turn, activate various mechanical transduction pathways including FAK (focal adhesion kinase), ERK (extracellular signal-regulated kinase), PI3K, and Akt. It is then followed by the production of cyclooxygenase 2 and prostaglandin E2 to stimulate further downstream angiogenic, osteogenic, and chondrogenic cytokines, explaining the different enhancements observed in animal and clinical studies. Furthermore, LIPUS has also been shown to have remarkable effects on mesenchymal stem cells (MSCs) in musculoskeletal injuries and tissue regeneration. The recruitment of MSCs to injury sites by LIPUS requires the SDF-1 (stromal cell derived factor-1)/CXCR-4 signalling axis. MSCs would then differentiate differently, and this is regulated by the presence of different cytokines, which determines their fates. Other musculoskeletal applications including bone–tendon junction healing, and distraction osteogenesis are also explored, and the results are promising. However, the use of LIPUS is controversial in treating osteoporosis, with negative findings in clinical settings, which may be attributable to the absence of an injury entry point for the acoustic signal to propagate, strong attenuation effect of cortical bone and the insufficient intensity for penetration, whereas in some animal studies it has proven effective.

Effects of ultrasound on estradiol level, bone mineral density, bone biomechanics and matrix metalloproteinase-13 expression in ovariectomized rabbits

The aim of the present study was to observe the effect of ultrasound (US) on estradiol level, bone mineral density (BMD), bone biomechanics and matrix metalloproteinase-13 (MMP-13) expression in ovariectomized (OVX) rabbits. A total of 28 virgin New Zealand white rabbits were randomly assigned into the following groups: Control (control group), ovariectomy (OVX group), ovariectomy with ultrasound therapy (US group) and ovariectomy with estrogen replacement therapy group (ERT group). At 8 weeks after ovariectomy, the US group received ultrasound treatment while the ERT group were orally treated with conjugated estrogens, and the control and OVX groups remained untreated. The estradiol level, BMD and bone biomechanics, cartilage histology and the MMP-13 expression were analyzed after the intervention. The results indicate that the US treatment increased estradiol level, BMD and bone biomechanical function. Furthermore, the US treatment appeared to improve the recovery of cartilage morphology and decreased the expression of MMP-13 in OVX models. Furthermore, the results suggest that 10 days of US therapy was sufficient to prevent the reduction of estradiol, BMD and bone biomechanical function, to protect osteoarthritis cartilage structure, and to reduce MMP-13 transcription and expression in OVX rabbits. Therefore, US treatment may be a potential treatment for postmenopausal osteoarthritis and osteoporosis.

Genes responsive to low-intensity pulsed ultrasound in MC3T3-E1 preosteoblast cells

Although low-intensity pulsed ultrasound (LIPUS) has been shown to enhance bone fracture healing, the underlying mechanism of LIPUS remains to be fully elucidated. Here, to better understand the molecular mechanism underlying cellular responses to LIPUS, we investigated gene expression profiles in mouse MC3T3-E1 preosteoblast cells exposed to LIPUS using high-density oligonucleotide microarrays and computational gene expression analysis tools. Although treatment of the cells with a single 20-min LIPUS (1.5 MHz, 30 mW/cm(2)) did not affect the cell growth or alkaline phosphatase activity, the treatment significantly increased the mRNA level of Bglap. Microarray analysis demonstrated that 38 genes were upregulated and 37 genes were downregulated by 1.5-fold or more in the cells at 24-h post-treatment. Ingenuity pathway analysis demonstrated that the gene network U (up) contained many upregulated genes that were mainly associated with bone morphology in the category of biological functions of skeletal and muscular system development and function. Moreover, the biological function of the gene network D (down), which contained downregulated genes, was associated with gene expression, the cell cycle and connective tissue development and function. These results should help to further clarify the molecular basis of the mechanisms of the LIPUS response in osteoblast cells.

The potential of pulsed low intensity ultrasound to stimulate chondrocytes matrix synthesis in agarose and monolayer cultures

Pulsed low intensity ultrasound (PLIUS) has been used successfully for bone fracture repair and has therefore been suggested for cartilage regeneration. However, previous in vitro studies with chondrocytes show conflicting results as to the effect of PLIUS on the elaboration of extracellular matrix. This study tests the hypothesis that PLIUS, applied for 20 min/day, stimulates the synthesis of sulphated glycosaminoglycan (sGAG) by adult bovine articular chondrocytes cultured in either monolayer or agarose constructs. For both culture models, PLIUS at either 30 or 100 mW/cm(2) intensity had no net effect on the total sGAG content. Although PLIUS at 100 mW/cm(2) did induce a 20% increase in sGAG content at day 2 of culture in agarose, this response was lost by day 5. Intensities of 200 and 300 mW/cm(2) resulted in cell death probably due to heating from the ultrasound transducers. The lack of a sustained up-regulation of sGAG synthesis may reflect the suggestion that PLIUS only induces a stimulatory effect in the presence of a tissue injury response. These results suggest that PLIUS has a limited potential to provide an effective method of stimulating matrix production as part of a tissue engineering strategy for cartilage repair.

Low-intensity pulsed ultrasound increases bone ingrowth into porous hydroxyapatite ceramic

Synthetic porous ceramic made of hydroxyapatite (HA) has been used as a bone graft substitute. In the present study we investigated whether low-intensity pulsed ultrasound (LIPUS) accelerates bone ingrowth into the pores of HA ceramic. Application of LIPUS did not mechanically weaken porous ceramic that was immersed in water in vitro. In vivo experiments using rabbits showed that LIPUS application for 2 weeks significantly increased osteoblast number and bone area in the central part of the porous HA ceramic implanted in the femoral condyle in comparison with similarly implanted HA ceramic that was not exposed to LIPUS. LIPUS application for 3 weeks significantly increased mineralized tissue volume and mineral content in the porous HA ceramic. Wound healing assays revealed increased migration of MC3T3-E1 cells as a result of LIPUS treatment, partly accounting for the increased osteoblast number. Use of porous HA ceramic combined with LIPUS may be a promising treatment for filling large bone defects in a clinical setting.