78 Chapter 5 A disadvantage of increased trunk movements during walking is the inevitable rise in mechanical energy costs related to larger CoM excursions, which most likely results in greater metabolic costs as well. A commonly used method to assess the metabolic costs of walking is indirect calorimetry. 27 Regrettably, indirect calorimetry is not part of our routine clinical gait analysis and could therefore not be included in the current analyses. In line with our clinical observations, our results indicate that markedly increased trunk movements during gait were predominantly present in relatively young people with HSP. It may be that younger people with HSP are able to walk with markedly increased trunk movements, although energy demanding, whereas this is often too demanding for older people with HSP, who therefore opt for the use of walking aids. Alternatively, we found that the group of toe walkers was on average younger than those without toe walking. It might be that people with an earlier disease onset progressed further (resulting in more severe spasticity and development of contractures resulting in pes equinus), compared to ambulatory older people with HSP. Both suggestions require further investigation. This study has several limitations that should be taken into account. First, an objective assessment of trunk movements during gait was lacking, as 3D gait analyses were performed using the lower body marker model. A second limitation is the lack of other clinical participant characteristics, such as disease duration, degree of spasticity and muscle weakness of the lower extremities, presence of sensory impairments, or an indicator of disease severity (e.g., the Spastic Paraplegia Rating Scale). 28 Hence, we could not test whether disease progression itself was associated with increased trunk movements. In addition, it was not possible to extract item subscores off e.g., the BBS from the medical files to investigate the notion that increased truncal movements while walking – although unlikely – might be associated with truncal instability or ataxia while sitting. Thirdly, we could not make use of the same balance score for all participants. This was due to the fact that this retrospective study spanned an extended period of time, in which we initially used the BBS in clinical practice, and later switched to the Mini-BESTest, as this test shows less ceiling effects. 29 Nevertheless, we believe that the current findings may help clinicians and therapists to better relate individual movement patterns to balance and gait capacities and, thus, to select an optimal treatment approach for individual patients with HSP, including ankle-foot surgery (in case of structural ankle-foot deformities) and balance-assistive devices, to reduce the dependence on hip strategies. 4, 15
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