Palmar arch modulation in patients with hemiparesis after a stroke.

Hand shape modulation has traditionally been studied within the framework of reach-to-grasp tasks by examining the control of arm transport, grip aperture scaling, and finger joint excursions. However, global parameters characterizing arm and hand movement can be enhanced by additional knowledge of biomechanical changes in the hand. We previously examined palmar arch modulation during grasping in healthy subjects by identifying thenar and hypothenar displacement. This method was used to characterize hand shape modulation in 10 stroke survivors with mild hand paresis, as assessed by the Chedoke-McMaster clinical scale, during two types of grasps (spherical, cylindrical). Palmar arch modulation was examined during the three phases of prehensile movement: transport shaping (P1), preshaping (P2), and contact shaping (P3). Compared to the control group, the stroke survivors showed significant differences (spherical: F (2,18) = 12.025, P < 0.001; cylindrical: F (2,18) = 9.054, P < 0.001) in palmar arch modulation particularly during P3 wherein fine adjustments are made to the grip in preparation for object manipulation. While control subjects completed most of hand shape modulation early in the task, stroke survivors took longer to complete each phase. Furthermore, stroke survivors started with a flatter hand which required relatively more arch modulation during the latter part of the task, thereby reflecting a temporal and spatial concurrency between the phases. Stroke survivors with well-recovered hand grasping ability tended to incorporate compensations/adaptations in hand posture during specific grasping phases. Palmar arch analysis provides us with a more complete understanding about how hand biomechanics, specifically palmar concavity articulation, is changed post-stroke. This will allow us to better identify the motor compensations used for grasping and to re-focus rehabilitation interventions to reduce compensations and improve functional motor recovery.