William Fullington
Coordinated Motion of the Thumb and Index Finger Due to the Passive Movement of the Wrist

SchoolPadua Franciscan High School


MentorVernon Lin, MD, PhD

DepartmentPhysical Medicine and Rehabilitation

Coordinated Motion of the Thumb and Index Finger Due to the Passive Movement of the Wrist
There is a linear correlation between the coordinated movement of the thumb and index finger as the wrist is passively moved into flexion and extension.
The tenodesis effect is defined as “the passive finger flexion as a result of wrist extension,” which is controlled by the flexion and extension of the wrist. As the wrist extends, this triggers the natural mechanism, with the flexion of the fingers and the opposition of the thumb. Patients who suffer from spinal cord injuries use the tenodesis mechanism in order to correctly position their fingers and thumb. These patients have difficulty maintaining a functional hand posture necessary to grasp an object. Five trials were run on three normal subjects, cycling between flexion and extension of the wrist. A mechanical apparatus was developed for this study which allowed for full flexion and extension. Reflective markers were placed on the joints of the thumb, index finger and wrist in order to be detected by the motion analysis system. Markers were placed on the nail, metacarpophalangeal (MCP), interphalangeal (IP), and trapeziometacarpal (TMC) joints of the thumb as well as on the nail, MCP, proximal and distal interphalangeal (PIP, DIP) joints of the index finger. Joint angles were calculated from the 3D coordinates of the markers.
The thumb and index finger are always closest at full extension and furthest apart at full flexion. The index finger MCP joint had a greater range of motion than the thumb MCP joint. The thumb IP joint had the greatest range of motion when compared to the index PIP and DIP joints.