Center of mass trajectories during turning in patients with Parkinson's disease with and without freezing of gait

• Freezers showed a reduced step width compared to non-freezers during turning.
• In turning sections preceding actual freezing episodes, step width decrease even more.
• The COM is deviated less medially and more anteriorly, preceding freezing episodes.
• Freezing-associated COM abnormalities compromise stability and fluent weight shifting.

BackgroundDespite the strong relationship between freezing of gait (FOG) and turning in Parkinson's disease (PD), few studies have addressed specific postural characteristics during turning that might contribute to freezing.MethodsThirty participants with PD (16 freezers, 14 non-freezers) (all tested OFF medication) and 14 healthy controls walked 5 meters and turned 180° in a 3D gait laboratory. COM behavior was analyzed during four turning quadrants of 40° between 10° and 170° pelvic rotation and during 40° before actual FOG episodes. These pre-FOG segments were compared with similar turning sections in turns of freezers without FOG. Outcome parameters were turn time, COM distance, COM velocity, step width and the medial- and anterior COM position.ResultsTurn time was increased in freezers compared to non-freezers (p = .000). No differences were found regarding COM distance and velocity during turning quadrants between groups and between freezers’ pre-FOG segments and similar turning segments without FOG. Medial COM deviation was reduced in PD patients compared to controls (p = .004), but no differences were found between freezers and non-freezers. In turns with freezing, turn time increased (p = .005) and step width decreased (p = .025) pre-FOG. Freezers also showed a less medial (p = .020) and more anterior (p = .016) COM position pre-FOG compared to turning sections without FOG.ConclusionsOur results revealed no subgroup differences in COM behavior during uninterrupted turning. However, we found a reduced medial deviation, a forward COM shift and a decreased step width in freezers just before FOG episodes. These abnormalities may play a causal role, as they could hamper stability and fluent weight shifting necessary for continued stepping during turning.