Different Thumb Positions in the Tetraplegic Hand.

OBJECTIVE

To analyze factors associated with malposition that affects function of the thumb in individuals with tetraplegia.

DESIGN

Retrospective cross-sectional study.

SETTING

Rehabilitation Center for Spinal Cord Injury.

PARTICIPANTS

Anonymized data from 82 individuals (68 men), mean age 52.9±20.2 (SD) with acute/subacute cervical spinal cord injury C2-C8 AIS A-D recorded during 2018-2020.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Motor point (MP) mapping and manual muscle test (MRC) of 3 extrinsic thumb muscles (flexor pollicis longus (FPL), extensor pollicis longus (EPL), and abductor pollicis longus (APL)).

RESULTS

159 hands in 82 patients with tetraplegia C2-C8 AIS A-D were analyzed and assigned to "key pinch" (40.3%), "slack thumb" (26.4%), and "thumb-in-palm" (7.5%) positions. There was a significant (P<.0001) difference between the 3 thumb positions depicted in lower motor neuron (LMN) integrity tested by MP mapping and muscle strength of the 3 muscles examined. All studied muscles showed a significantly different expression of MP and the MRC values (P<.0001) between the "slack thumb" and "key pinch" position. MRC of FPL was significantly greater in the group "thumb-in-palm" compared with "key pinch" position (P<.0001).

CONCLUSIONS

Malposition of the thumb due to tetraplegia seems to be related to the integrity of LMN and voluntary muscle activity of the extrinsic thumb muscles. Assessments such as MP mapping and MRC of the 3 thumb muscles enable the identification of potential risk factors for the development of thumb malposition in individuals with tetraplegia.