The expected sample size was 66 preterm infants, 22 for each group; however, due to sepsis affecting the hospital's NICU, the unit was forced to close. No more patients were admitted and ongoing studies had to be postponed. This situation led us to reach the scheduled closing date, so the study had to end. Therefore, the total sample size was 69.69% of the total sample size (46 newborns distributed in three study groups), showing a significant difference in relation to the intervention studied.
The main objective of this research is to verify the effect of RLT, understood as active-resisted mobilizations, on bone mineralization and growth in preterm infants and to compare its effect against other passive Physiotherapy modalities.
In this term, the outcome of this study indicates that RLT has a positive effect on the bone mineralization measured with QUS; consisting on a reduction of the drop in bone mineralization characteristic of preterm infants that can lead to osteopenia.
When comparing the three treatments performed, the modality with RLT has shown better results in the Tibial-SOS values with respect to the group treated with PMC and to the massage group (control) showing a small effect size; however, no significant differences were found between the group treated with PMC and the control group, contrasting with the results obtained by other authors, which highlight the positive effect of PMC compared to control groups where placebo was not applied26,36,37, although in one of them, the times and frequency of PMC treatment were greater37. In our study, in line with other authors22–25, the results show that massage has no impact on bone mineralization.
Despite the energy expenditure that RLT treatment could entail for the baby, considering that it performs active-resisted work, there has been no negative effect in relation to measures of weight, height and head circumference, since as the data showed, all groups evolved equally in terms of anthropometric variables. Anthropometric measurements have also not been diminished in children in the EGpmc and CG groups, same as other studies carried out with low birth weight babies treated with PMC compared with control without treatment or placebo with caresses23,25,26,36, in which, as in our study, no significant differences were found among the study groups in weight, height, and head circumference. These results are supported by those obtained by the Z scores, which show no differences among the groups.
In the present study, the EGrlt group started from a point of significant disadvantage regarding weight, height and head circumference compared to the EGpmc (Table 2). Although infants treated with RLT showed a lower weight than the group treated with PMC, the EGrlt significantly increased their weight in each measure, showing a similar gain to the rest of the groups, since no differences were observed in terms of interaction (Figure 3). An explanatory hypothesis of this result may be due to the consideration of RLT as an active exercise, taking into account the results of different meta-analyzes that relate active physical exercise and weight control, which although are carried out in pediatric population, could be extrapolated to the neonatal population38,39.
The weight gain in the CG of our study is in line with other authors findings, who show weight gain in preterm infants who receive massage40–43, and in contrast to Eliakim, et al. 200222 that found weight improvements in favor of PMC compared to caresses and tactile stimulation.
Some limitations of our trial should be noted. Heterogeneity of the preterm infants risk factors could influence the results obtained. Another limitation is the lack of long-term follow-up to determine the effect of the interventions on the Tibial-SOS.
It would be advisable to carry out multicenter clinical trials with a large sample of preterm infants that guarantees observation of the intervention effect at different gestational ages. It would also be convenient to carry out studies with long-term follow-ups, where the evolution of these children in early childhood and adolescence could be observed.
We can conclude that RLT has been effective in the improvement of Tibial-SOS values, which may have a positive effect in the prevention of osteopenia in preterm infants; furthermore, RLT has proved to be more effective than other physical therapy modalities such as PMC and massage in improving Tibial-SOS.
Due to the characteristics of the sample on which the intervention has been carried out, the results indicate that treatment with RLT is effective in improving bone mineralization in healthy preterm infants; and it could be considered as one of the best treatments to prevent osteopenia in this population.