Turning problems and freezing of gait in Parkinson's disease: a systematic review and meta-analysis.

Objective: To understand the differences of step and turn parameters between freezers and non-freezers during turning and determine the influence of turn angle and turn characteristics on freezing of gait.Data sources: PubMed and Web of Science were searched from the earliest data available to August 2017.Study selection: Case-control studies that examined the differences in turning while walking between freezers and non-freezers were included. Two reviewers selected studies independently.Data extraction: Methodological quality was evaluated by two independent reviewers using the STROBE checklist for case-control studies. Mean differences and 95% confidence intervals were calculated from pooled data for turn duration, peak turn velocity, number of steps and cadence. Center of mass deviation, segmental rotation, phase coordination and freezing of gait frequency were also extracted. When possible, different turning angles or spatial confounds were compared.Data synthesis: Sixteen studies met the inclusion criteria. Freezing of gait occurred in 38.2% of the freezers. Freezing appeared most frequently at the end of a turn and at the inner leg of the turn cycle. The meta-analysis revealed that turning in freezers was characterized by an increased turn duration, cadence and number of steps and a decreased peak turn velocity. Qualitative analysis showed that results concerning step width, step length and step time variability were inconsistent. Turning was characterized by an increased head-pelvis coupling and worse coordination in freezers compared to non-freezers. A decreased medial deviation of the center of mass was present prior to a freezing episode.Conclusions: Both step and rotational parameters differed in freezers compared to non-freezers while turning. These differences increased with increasing task complexity (i.e., larger turning angle or spatial confounds during turning). The results suggest that improving axial rotation could be a valuable rehabilitation target to ameliorate freezing.Implications for rehabilitationPatients with freezing of gait turn with a larger arc and a smaller angle compared to non-freezing patientsFreezing-related turning deficits have both spatiotemporal and rotational motor control componentsImproving axial rotation could be a novel rehabilitation target to ameliorate freezing.