Gait patterns comparison of children with Duchenne muscular dystrophy to those of control subjects considering the effect of gait velocity
Introduction
Locomotor system impairments such as progressive muscle weakness, muscle fatigue and the development of joint contractures alter the gait abilities of children with Duchenne muscular dystrophy (DMD) [1], [2] (for review, see Gaudreault et al. [3]). Natural gait velocity is reduced in these children due to decreased step length [4], [5]. As regards kinematics and kinetics, children with DMD modify their trunk and lower limb position so that the flexor muscles sustain the effort rather than the extensors during the stance phase [5], [6]. Patte et al. [5] and Khodadadeh et al. [7] observed that during the initial part of the stance phase, children with DMD straightened their knee in order to rely on an internal knee flexion moment for stability. Conversely, Boccardi et al. [4] observed a knee flexion position and an extension moment as seen in healthy children. These authors concluded that children with DMD can effectively use their quadriceps to sustain an external flexion moment. At the ankle, an ankle plantarflexion position for children with DMD upon foot strike and during the stance phase has been observed [8]. This foot or forefoot contact is associated with an internal plantar flexion moment observed for the entire duration of the stance phase. Again, Boccardi et al. [4] do not entirely support the above description. These investigators observed a dorsiflexion position of the supporting foot upon initial contact and during the stance phase. In their opinion, this position facilitates the forward progression of the pelvis over the supporting foot, thus compensating for hip extensor weakness.
Although more is known about the gait of children with DMD, there is still no consensus on the interpretation of the kinetics and kinematics at the ankle and knee joints. Possible reasons for this disagreement might either be related to variability in the children strength profiles or to the effect of gait velocity. None of the previous studies has considered this factor. The effect of a lower gait velocity on the magnitude of the peak knee flexion angle and peak extension moment during the stance phase is documented in other patient populations [9]. Moreover, Diop et al. [10] and Stansfield et al. [11] report that gait velocity modifies pediatric gait kinematics and kinetics. Therefore, consideration should be given to this confounding variable to determine the pure effect of the disease on gait characteristics of children with DMD. The objective of this study is to compare the gait patterns of children with DMD to those of control children while considering the effect of gait velocity. We hypothesize that consideration for gait velocity attenuates the difference between normal and DMD gait patterns observed at natural velocity, thus revealing the true difference between both groups.
Section snippets
Participants
The study involved 11 children between 7 and 15 years of age who had a confirmed diagnosis of DMD by genetic testing and/or muscle biopsy (9.1 years (2.5); 30.2 kg (8.1); 1.27 m (0.06)). All children were on corticosteroid medication. They were able to walk independently, without braces. Based on the Vignos scale [12], the functional status of the children ranged from grade 2 to grade 5 (Table 1). At grade 2, the child can walk unassisted and climb stairs using a railing; whereas at grade 5, the
Clinical characteristics and time distance variables
Table 1 shows the clinical characteristics of the DMD children whereas Table 2 presents the peak values (mean ± SD) of the gait variables. At natural gait velocity, the children with DMD had a slower gait velocity and a shorter step length than the control children. However, cadence was similar in both groups. By contrast, when the control children walked slower, their mean velocity was similar to that of the DMD children, yet their cadence was lower.
Kinematics and kinetics, sagittal plane
The angular displacements, moments and power
Discussion
In this study, the gait parameters of children with DMD were compared to those of control children with consideration for the effect of velocity. This approach was substantiated by the fact that the natural gait velocity of children with DMD in our sample was effectively reduced in comparison with that of the control children. A decrease in gait velocity in children with DMD is a consistent finding reported by other authors [4], [5]. In this study, since cadence was not different between the
Study limitations
The small number of subjects and the variability in the clinical profiles of the children with DMD represents the main limitation in this study. However, the alterations described in the mean curve profiles are very similar among children with DMD of our sample. Also, data related to the pelvic and trunk segments would have helped in interpreting some findings and should be included in future studies.
Conclusion
For the first time, children with DMD gait characteristics were described relative to healthy children while considering the effect of gait velocity. Low magnitude of the hip extension moment and energy generation during the stance phase as well as the lack of involvement of the knee extensor muscles are not an effect of a lower gait velocity observed in children with DMD. These factors reflect the influence of muscle weakness on the gait of these children. The results of this study highlight
Conflict of interest statement
I confirm that no commercial relationships which may lead to conflict of interest were associated with this work.
Acknowledgements
The project was supported by the Canadian Institutes of Health Research (CIHR) in partnership with Muscular Dystrophy Canada. N. Gaudreault holds a scholarship from the CIHR and S. Nadeau has a junior II scientist salary from Fonds de la Recherche en Santé du Québec.
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