Idiopathic scoliosis and brace treatment: an innovative device to assess corrective pressure.

The biomechanical influence of brace treatment for scoliosis is not understood. This prospective pilot study analyzed reliability of a system based on 100% textile sensors for measurement of pressure exerted by brace on trunk. Evaluation of modifications during changes in the location of the support zones and variations in amplitude of the pressure was observed in four patients, when considering three main daily positions mimicking day and nighttime wear. A calibration step allowed the determination of a conversion law between sensor data and pressure unit using a second order polynomial function with a high r2 of 0.99. This prototype is the first of a new generation. Experimental pressure distribution could be useful for the further brace development.

Delay of intracortical bone remodelling following a stress change: a theoretical and experimental study.

BACKGROUND: A theoretical model and an experimental setup were specifically designed to identify and determine the delay of the cortical bone response (restricted to mineralization and demineralization) to a stress change. METHODS: The in vivo experiment considered two groups of rats: a running group and a control sedentary group. The running group rats were compelled to a running activity for 15 weeks, followed by a sedentary activity for 15 weeks. Bone density was derived from hardness measurements. The parameters of the remodelling theory, including the response delay and the remodelling rates, were determined from these experimental measurements. FINDINGS: Bone density increased significantly during the activity period, and decreased rapidly when rats returned to sedentary state. The identification of the model's parameters produced evolution curves that were within the limits of the standard deviation of the experimental data. The densification rate was lower than the resorption rate, and the densification delay was greater than bone resorption delay. INTERPRETATION: The delays determined with this macroscopic model are related to response delays due to biological internal processes in bone.

Detraining effects on the mechanical properties and morphology of rat tibiae.

To study bone adaptation to detraining in growing rats, nine weeks-old immature female Wistar rats (n=110) were subjected to treadmill running programs (30 or 60 minutes-a-day) for up to 15 weeks, followed by unrestricted cage activities for the subsequent 15 weeks. The results revealed that (1) the cross-sectional area and mechanical properties of the midshaft bone significantly increased in response to running exercise, (2) its structural properties remained unchanged after the cessation of exercise, whereas the material properties returned to control level at a relatively early stage, (3) in the metaphysis, cortical bone area remained unchanged but trabecular bone area decreased in response to running exercise, (4) both areas slightly increased after the cessation of exercise, and (5) the changes in the mechanical properties and morphology of bone depended upon the repetition number and/or the duration of exercise, and were larger with longer duration of exercise.

Can the increase of bone mineral density following bisphosphonates treatments be explained by biomechanical considerations?

OBJECTIVE: We hypothesized that bone mineral density increase following bisphosphonates treatments may be explained by the influence of the drug on the mechanical bone remodeling parameters. BACKGROUND: Patients treated with bisphosphonates continuously increase their bone mineral density. This increase is explained in the first 12-18 months following the treatment by the filling of the transient remodeling deficit. Recently, results of a clinical study of alendronate treatment over 7 years still show a continuous increase of bone mineral density. These results raised several questions regarding our understanding of bisphosphonates mode of action. METHODS: Bone remodeling is influenced by different factors including mechanical forces. In the present study, we propose then to consider the effect of bisphosphonates also under biomechanical considerations. RESULTS: Identification of the model with the clinical data showed that daily treatment of 10 and 20 mg alendronate decreased the bone turnover rate by 2% and 11%, respectively, in comparison with the 5 mg alendronate treatment. Moreover, the alendronate treatments decreases the resorption threshold stimulus by 19% (25%, 28%) for the 5 mg (10 and 20 mg, respectively) compared to placebo. CONCLUSIONS: The increase of bone mineral density following bisphosphonates treatment may then be explained by biomechanical considerations. Based on this description, bisphosphonates treatment may indeed change the susceptibility of bone to its biomechanical environment decreasing the mechanical threshold where bone should undergo resorption.

Effect of micromechanical stimulations on osteoblasts: development of a device simulating the mechanical situation at the bone-implant interface.

Many experimental models have been developed to investigate the effects of mechanical stimulation of cells, but none of the existing devices can simulate micromotions at the cellular-mechanical interface with varying amplitudes and loads. Osteoblasts are sensitive to mechanical stimuli, so to study the bone-implant interface it would be important to quantify their reaction in a situation mimicking the mechanical situation arising at that interface. In this study, we present the development of a new device allowing the application of micromotions and load on cells in vitro. The new device allowed the cells to be stimulated with sinusoidal motions of amplitudes comprised between +/- 5 and +/- 50 microm, frequencies between 0.5 and 2 Hz, and loads between 50 and 1000 Pa. The device, with a total length of 20 cm, was designed to work in an incubator at 37 degrees C and 100% humidity. Expression of various bone important genes was monitored by real-time RT-PCR. Micromotions and load were shown to affect the behavior of osteoblasts by down-regulating the expression of genes necessary for the creation of organic extracellular matrix (collagen type I) as well as for genes involved in the mineralization process (osteocalcin, osteonectin). The developed device could then be used to simulate different mechanical situations at the bone-implant interface.