Abstract
Dear Dr Curran,
Upon reading the above named article by Darter and Wilken 1 we note the very important issue of energy consumption in transtibial amputees. The study aims at investigating the effect of a microprocessor-controlled ankle with adaptive ankle motion on metabolic energy expenditure during slope walking in persons with a transtibial amputation.
We recognize that research within the field of prosthetics faces challenges inherent to the studied topics and reflected in lack of randomized controlled trials, low numbers of included subjects, difficulties in blinding subjects, variability in subject populations, threats to internal and external validity, and a host of other challenges. 2
The main outcome measures of the Darter and Wilken’s study are energy expenditure and energy cost measurements. In a 2008 publication, Brehm et al. 3 proposed a tool for planning a clinically applicable protocol for use in energy expenditure studies. Among the issues addressed are the selection of the study group, selection of protocol, and the importance of defining a clinically relevant change. Comparative clinical intervention studies should either include a defined control group receiving no treatment (or the standard of care) or the subjects should be randomized for different treatment options. Furthermore, it is important that the subjects included in a clinical study fit the medical indication/criteria described for the treatment under study. In a fitness study, the effect of any intervention will be highly influenced by the baseline fitness levels.4,5 Treatment indicated for individuals with a low fitness level may not have a large effect in a group of individuals with higher fitness levels. Furthermore, subjects’ resting energy cost can significantly influence the study results and rather than only considering gross energy cost of physical activity, the net energy cost (gross energy cost − resting energy cost) should be considered, as it probably has a greater clinical meaning.
A small number of subjects will further reduce the likelihood of statistical differences between groups. Even though descriptive observational data from small samples can be valuable, interpretation of data from studies is further hampered without a prior definition of a clinically meaningful difference.
Based on the above, readers may find that some additional information would have been useful to the Darter and Wilken publication, such as at what stage of rehabilitation the subjects were when entering the study, subjects’ functional/fitness levels at baseline, the subject treatment assignment protocol, and whether or not the subjects were receiving clinical rehabilitation simultaneously to participating in the study.
We would like to point out that even though the authors state that “no formal device-specific gait training was provided,” this would not be true for a clinical situation where users would be trained in using a new device in order to be able to fully gain from the additional features. And finally, the authors frequently relate their results to a previous publication of a biomechanical analysis of ramp ambulation of transtibial amputees with an adaptive ankle foot system. 5 The publication by Fradet et al. 6 is based on a different protocol, including older subjects and longer time since amputation. The slope angles in the Fradet et al.’s study are also greater than in the Darter and Wilken’s study. It would have been helpful if Darter and Wilken had discussed how the different sample and greater angles may affect gait biomechanics and metabolic energy expenditure differently.