Different Thumb Positions in the Tetraplegic Hand.

Area of Science:

• Neurology
• Rehabilitation Medicine
• Spinal Cord Injury Research

Background:

• Tetraplegia, resulting from cervical spinal cord injuries, often leads to functional impairments, including thumb malposition.
• Thumb dysfunction significantly impacts hand function and independence in individuals with tetraplegia.
• Understanding the factors contributing to thumb malposition is crucial for developing targeted rehabilitation strategies.

Purpose of the Study:

• To investigate the factors associated with thumb malposition affecting hand function in individuals with tetraplegia.
• To analyze the relationship between lower motor neuron (LMN) integrity, extrinsic thumb muscle strength, and thumb positioning.

Main Methods:

• Retrospective cross-sectional study of 82 individuals with cervical spinal cord injury (C2-C8, AIS A-D).
• Evaluated 159 hands using motor point (MP) mapping and manual muscle testing (MRC) for three extrinsic thumb muscles: flexor pollicis longus (FPL), extensor pollicis longus (EPL), and abductor pollicis longus (APL).
• Classified thumb positions into "key pinch," "slack thumb," and "thumb-in-palm."

Main Results:

• Significant differences (P<.0001) in LMN integrity and muscle strength were observed across the three thumb positions.
• Both MP mapping and MRC values differed significantly (P<.0001) between the "slack thumb" and "key pinch" positions.
• The flexor pollicis longus (FPL) showed significantly greater MRC in the "thumb-in-palm" group compared to the "key pinch" group (P<.0001).

Conclusions:

• Thumb malposition in tetraplegia is associated with the integrity of LMNs and the voluntary muscle activity of extrinsic thumb muscles.
• MP mapping and MRC assessments are valuable tools for identifying individuals at risk of developing thumb malposition.
• These findings can inform the development of interventions to improve thumb function in tetraplegia.