Postural abnormalities to multidirectional stance perturbations in Parkinson's disease

Abstract

Objective: We investigated trunk control, protective arm movements, and electromyographic responses to multidirectional support-surface rotations in patients with Parkinson's disease (PD), aiming to better understand the pathophysiology underlying postural instability in PD, on and off antiparkinson medication. Methods: Ten patients with PD were compared with 11 age matched healthy controls. Seven patients were also tested without (OFF) antiparkinson medication. All subjects received rotational perturbations (7.5 deg amplitude) that were randomly delivered in six different directions. Results: The PD patients had decreased trunk rotation and ankle torque changes, consistent with a stiffening response. Stiffness appeared to be caused by the combined action of three factors: cocontraction that interfered in particular with the normal response asymmetry in trunk muscles; increased response amplitudes in agonist and antagonist muscles at both medium (,80 ms) and balance correcting (,120 ms) response latencies; and increased background activity in lower leg, hip, and trunk muscles. Although the patients had significantly earlier onset of deltoid muscle responses, this gave no functional protection because the arm movements were abnormally directed. Most instability in PD occurred for backward falls, with or without a roll component. Medication provided partial improvement in arm responses and trunk roll instability. Conclusions: Our results confirm previous findings in ankle muscles, and provide new information on balance impairments in hip, trunk, and arm responses in PD.

The influence of artificially increased hip and trunk stiffness on balance control in man

“…The observed changes in trunk movements and resultant instability were greater for the full-corset, compared to the half-corset, particularly in the roll plane, suggesting that flexibility of the entire trunk normally plays a vital role in maintaining balance. The observed reversal of trunk roll motion with the full-corset (but not the half-corset) replicated earlier findings in a total leg proprioceptive loss patient and, to a lesser extent, in healthy elderly subjects and patients with Parkinson's disease (Carpenter et al 2004), thereby suggesting that axial stiffness of the entire trunk and pelvis plays a key role in causing instability in these subjects, and perhaps in those normal subjects that stiffen with a fear of falling. The instability that resulted from wearing the full-corset was associated with reversed and larger arm movements in roll, presumably reflecting compensation.…”

“…This observation has several implications concerning the effect of "tensing up" muscles, be it as the result of a disease state or a fear of falling. The reversal of trunk roll motion during the full-corset condition sheds an interesting new light on our observations of increased background muscle activity both in totally proprioceptive loss patients , those with bilateral vestibular loss (Carpenter et al 2001) and those with Parkinson's disease (Carpenter et al 2004). We wondered whether this excessive background muscle activity caused increased stiffness of the hips and trunk leading to poor trunk control in the roll planes.…”

“…Second, arm movements are obviously linked to those of the trunk, and perhaps initially are always similarly directed as the trunk. Indeed, in all our previous studies, the arms always moved in the same direction as the trunk Carpenter et al 2004). It would be interesting to determine if the coupling between movements of these body segments can be dissociated under different experimental conditions.…”

“…Our second goal was to clarify the pathophysiology of trunk stiffness which we suggested helps cause impaired balance control with ageing and in neurological disorders, including Parkinson's disease and severe proprioceptive loss (Carpenter et al 2004;Allum et al 2002;Bloem et al 2002). In all these groups, changes in trunk roll motion were noted as early as 50 ms after a postural perturbation, suggesting that active stiffening prior to the perturbationrather than inappropriate active postural reactions-was mainly responsible for the loss of trunk flexibility.…”

Balance and Gait Rehabilitation in Patients with Parkinson’s Disease

“…If balance impairment in patients with PD could be related to a global loss in proprioception, then their postural responses would be expected to be attenuated, and potentially delayed if proximal deficits are involved. However, patients with PD have normal timing of postural reactions, and in fact show excessive muscle activity in their automatic balance reactions (Carpenter et al, 2004). Furthermore, unlike kinaesthetic abnormalities, which appear to b e w o r s e n e d b y d o p a m i n e r g i c m e d i c a t i o n (Wright et al, 2007), postural reactions are typically not responsive to dopaminergic medications (Carpenter et al, 2011;Bloem et al, 1996).…”