Trunk sway measurements during stance and gait tasks in Parkinson's disease.

To achieve a unified assessment of postural instability in Parkinson's disease (PD) over a range of clinical stance and gait tasks, which may provide an insight into a tendency to fall, we measured trunk sway in the anterior-posterior and medial-lateral directions in freely moving PD patients and age-matched controls. We also measured task duration as time to complete the task or time to loss of balance. Patients had larger amplitudes of trunk sway velocities for stance tasks (e.g. mean pitch velocity when standing on two-legs eyes closed equalled 19.1 +/- 6.4 for PD patients on medication versus 4.8 +/- 0.3 degrees/s for controls, p = 0.0003) and for an expected (following prior warning) retropulsion test (mean roll angle equalled 4.3 +/- 0.5 degrees for PD patients versus 2.2 +/- 0.6 degrees for controls, p = 0.0003) than controls. Patients were more likely to fall earlier for stance tasks, and took longer to complete gait tasks (e.g. walking 3 m eyes closed, mean time 6.8 +/- 0.6 sees versus 4.9 +/- 0.1 sees, p = 0.0001). These differences between patients and controls were, in most cases, independent of medication. Based on these results we defined a simple test battery of stance and gait tasks that could discriminate between PD patients who had recent falls and controls. These results indicate that trunk sway measures recorded during stance and gait tasks provide useful information on balance deficits leading to falls in PD patients.