The effect of vibration training on macro-architecture of bone and blood flow in chronic spinal cord injured individuals

Investigators: Dr Prisca Eser, Prof Mary Galea, A/Prof Shona Bass

Osteoporosis or bone loss, commonly regarded as a disease affecting the elderly, is also a significant clinical concern in people subjected to immobilisation, such as patients with stroke or spinal cord injury (SCI). As a result of bone loss after SCI, fractures of the paralysed extremities are a common complication in these individuals. Fractures often result from minor trauma, such as falls out of the wheelchair, normally require hospitalisation for orthopaedic surgery, and result in a high incidence of complications . It is an important goal to reduce the risk for bone fracture in this population.

The rapid and massive bone loss experienced by SCI individuals has been attributed to disuse. There has been limited investigation into non-pharmacological treatments for disuse osteoporosis. Two studies have shown that muscle exercise by means of electrical stimulation resulted in large (up to 30%) increases in bone mass in SCI individuals. While this has been successful, the program has limited application because it cannot be performed by individuals with lesions of the cauda equina, intact sensation, or restricted range of motion. Vibration intervention may offer an alternative non-invasive, inexpensive and convenient therapy for SCI individuals that may result in clinically important increases in bone mass and structure. Vibration intervention has recently prevented bone loss in subjects completing an 8-week bedrest study, during which the control subjects lost almost 4% bone mass. Despite vibration being recommended as an osteoporosis therapy the underlying mechanisms associated with an osteogenic effect of vibration intervention on bone are not known. One or a combination of the following are thought to be involved: direct mechanical deformation of bone, muscle forces acting on bone, increased blood supply to bone, or direct stimulation of bone fluid flow.

The current study is aimed at testing the efficacy of vibration intervention in increasing bone mass and strength in individuals with chronic SCI. This study population provides the ideal human immobilisation model, which is less influenced by confounding factors than human bed-rest studies.

We propose to conduct a randomised controlled intervention study in 25 subjects with complete, chronic SCI using vibration. The intervention group (n=15) will perform vibration intervention (VI) on a tilting table (Fig. 1) with a vibrating foot plate (Galileo, Novotec, Pforzheim, Germany) and the control group (n=10) will perform passive standing (PS) training for 12 months (3x20 min/week). Both groups will include two subgroups of spastic (lesion level above T12 and muscle tone present) and flaccid (lesion level below L1 and muscle tone absent) subjects in order to isolate the effect and assess the importance of muscle reflex activity on potential vibration effects on bone and blood flow.

Figure 1 : The Galileo tilting bed is mounted on a wooden frame and fitted with an electrical motor that can tilt the bed to any desired angle from horizontal to vertical. The patient's feet are strapped to the vibration plate that oscillates around an axis between the feet at frequencies between 0 and 30 Hz and amplitudes between 2.5 and 5 mm.

To test the effectiveness of vibration intervention on restoring bone mass, bone mass and geometry will be measured in the femur and tibia by peripheral quantitative computed tomography. To investigate the underlying mechanisms of a potential osteogenic effect, we will measure leg muscle activity using EMG and leg blood flow using Doppler ultrasound.

The results of the proposed study will have direct implications in reducing the occurrence of fractures in individuals with SCI. Furthermore, if or when a cure for SCI becomes available, an intervention to restore bone strength in the legs of practically all individuals with chronic SCI will be necessary to support normal ambulation. The results of this study will also be applicable to improvement of bone health in other conditions leading to increased fracture risk, such as stroke, cerebral palsy, and other neurological impairments. Additionally, this study will make an important contribution to the paucity of data currently available on the effects and underlying mechanisms of vibration training in humans.

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