Does thermoplastics' thickness influence joint stabilization and movement coordination? An inferential study of wrist orthoses

Background: Given the existence of multiple low-temperature thermoplastics, clinicians fabricating can readily modify an orthoses' thickness, weight and flexibility, among other properties. However, there is limited evidence on the impact of such different materials on upper extremities' biomechanics.

Objective: Our study aimed to investigate differences in joint stabilization and movement coordination provided by upper extremity orthotics fabricated with low-temperature thermoplastics of different thicknesses.

Study design: Inferential, cross-sectional study.

Method: We conducted a kinematic analysis of a standardized task through a three-dimensional motion capture system. Ten participants (5 female) performed the same task under three circumstances: 1) wearing a volar wrist immobilization orthosis, made with a 3.2-mm thick low-temperature thermoplastic; 2) using the same orthotic fabricated with a 1.6-mm thick material; and (3) without orthoses. We divided the standardized task into five logical phases for data analysis, obtaining the active range of motion of the shoulder, elbow, forearm, and wrist joints as the primary outcome. Secondary outcomes included movement smoothness and coordination, measured by the number of motor units, time, and distance travelled by the upper extremity.

Results: Despite changes in thermoplastic thickness, both orthotics significantly restricted the wrist motion during task performance (F(2,16) = 14.32, P < .01, and η2p = 0.797), with no difference between the 2 devices and no significant changes to proximal joints' active range of motion. Although orthoses use increased the time required for task performance (F(2,16) = 23.05, P < .01, and η2p = 0.742), no significant differences in movement smoothness or coordination were noted.

Conclusion: Our results indicate that wrist orthoses fabricated with a 1.6-mm thick low-temperature thermoplastic can provide joint stabilization similar to a device made from a 3.2-mm thickness material, suggesting thinner thermoplastics' efficacy to stabilize joints in the absence of contractures or preexisting chronic conditions.