We read with great interest the systematic review by Mehrholz et al. We consider it as a comprehensive and innovative systematic review and meta-analysis, but we have a question about the data processing. By checking the data between the systematic review and included original studies, we found Mehrholz et al.  analyzed post-treatment outcomes rather than the difference between pre-treatment and post-treatment, which is at risk of generating an unreliable result. Not only when between-studies baselines are similar, but also when between-groups baselines are not significantly different, we can directly analyze post-treatment outcomes, and generate a stable result.
Considering the included studies’ district, enrollment criteria, and so on, we observed huge heterogeneity of baseline among partial studies. For instance, in Kapadia , subjects were of American Spinal Cord Injury Association Impairment Scale (AIS) C or D grade, while subjects in Sadeghi  were of AIS B and C grade.
Futhermore, we found a huge diversity of baseline between the intervention and control groups in Kapadia  and Sadeghi . In Kapadia , in the 6-min walk test, subjects achieved 187.9 ± 123.4 m in the BWSTT plus FES group, while they achieved 79.4 ± 83.9 m in the group performing resistance and aerobic training. Meanwhile, in Sadeghi , the capacity of 6MWT is 340.00 ± 89.70 m in the BWSTT group, but 685.71 ± 176.51 m in the traditional therapy group. The tremendous diversity at baseline is non-negligible for directly analyzing post-treatment outcomes, because the posttest 6MWT value of the BWSTT group, 640.00 ± 97.99 m, is even lower than the pretest value of the control group, 685.71 ± 176.51 m. Calculating the difference between pretest and posttest, the efficacy of BWSTT is 300 m on average, which is higher than that of the control group (reaching ~130 m on average). Actually, a contrast result was generated by extracting posttest outcomes only (640.00 ± 97.99 versus 814.29 ± 180.51).
In addition, based on our experience and another systematic review published in Spinal Cord , the posttest outcome should be replaced by difference between pretest baselines and posttest outcomes when performing meta-analysis to compare the efficacy of merging physiotherapy interventions.
Mehrholz J, Harvey LA, Thomas S. Is body-weight-supported treadmill training or robotic-assisted gait training superior to overground gait training and other forms of physiotherapy in people with spinal cord injury? A systematic review. Spinal Cord. 2017;55:722–9.
Kapadia N, Masani K, Craven BC, Giangregorio LM, Hitzig SL, Richards K, et al. A randomized trial of functional electrical stimulation for walking in incomplete spinal cord injury: effects on walking competency. J Spinal Cord Med. 2014;37:511–24.
Sadeghi H, Banitalebi E, Dehkordi M. The effect of body-weight-supported training exercises on functional ambulation profile in patients with paraplegic spinal cord injury. Phys Treat. 2015;4:205–12.
Harvey LA, Glinsky JV, Bowden JL. The effectiveness of 22 commonly administered physiotherapy interventions for people with spinal cord injury: a systematic review. Spinal Cord. 2016;54:914–23.
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Cao, G. Letter to the Editor: “Is body-weight-supported treadmill training or robotic-assisted gait training superior to overground gait training and other forms of physiotherapy in people with spinal cord injury? A systematic review”. Spinal Cord 57, 434 (2019). https://doi.org/10.1038/s41393-019-0270-8