The immediate effect of thumb orthoses on upper extremity's movement: A kinematic analysis of five unique devices.

Background: Thumb orthoses are a standard treatment modality, with substantial evidence to support its usage for multiple conditions affecting the upper extremity. Despite commonly prescribed, little is known about the immediate impact of such devices on the upper extremity, including potential modifications on motor patterns.

Research Question: We aimed to determine the changes in the upper limb kinematics during the usage of thumb orthotics, comparing differences in orthotic design, length, and fabrication materials.

Methods: In this cross-sectional study, subjects performed a standardized reaching task and the placing subtest of the Minnesota Manual Dexterity Test (MMDT) while wearing five unique thumb orthoses. Besides the active range of motion of the shoulder, elbow, wrist and hand joints, movement smoothness (Number of Movement Units-NMU), speed, and motion control strategies were analyzed through eight Qualisys Oqus 300 cameras (Qualisys AB, Göteborg, Sweden).

Findings: Ten non-disabled, university students participated in this study. Despite differences in fabrication materials, all orthotics reduced thumb's abduction (13.3° to 4.3°), and metacarpophalangeal flexion (11.5° to 4.2°). Although orthotics impacted movement smoothness and hand function during its usage, forearm-based devices further increased the NMUs and the time required for the MMDT performance (Control: NMU = 4.8, MMDT = 58.1; Long Orthotics: NMU = 6.6, MMDT = 78.2), while short, flexible orthoses provided thumb stabilization without significant impact on upper extremity movement strategies.

Significance: Although joint stabilization was similar among orthotics fabricated with rigid and flexible materials, the improved hand dexterity observed during the use of flexible devices suggests an advantage of flexible orthotics for enhanced stability and hand function. These results can assist healthcare professionals during the selection and prescription of thumb orthotics, providing information not only on the range of motion but other sensorimotor aspects involved in upper extremity movement patterns that may be affected by orthotics usage.