The Role of Motor Zones of Partial Preservation in Conversion from Initially Complete to Motor Incomplete Spinal Cord Injury.

Abstract

Objective: To determine 1) the frequency of persons with spinal cord injury (SCI) presenting with a neurological complete injury (ASIA Impairment Scale [AIS] A) who would be classified as AIS C or D if sensory sacral sparing were present, and 2) if this status is associated with an increase in conversion to motor incomplete status on follow-up (6-24 months post-injury).

Design: Retrospective analysis of longitudinal data.

Interventions: Not applicable.

Setting: National SCI Model Systems data from 2011-2023.

Participants: Persons with AIS A, initial International Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI) examination within 30 days of injury, motor level C1-L2, and aged ≥16 years at time of injury (N=2,018).

Main outcome measures: Motor levels of injury and the motor zones of partial preservation (ZPPs) were determined from the first post-injury examination. Motor levels were defined using both the ISNCSCI definition and an alternate definition (not deferring to sensory level when proximal myotomes [e.g., C5] are intact). Individuals with a motor ZPP >3 levels below the motor level on either side were classified as 'motor incomplete-like'. To evaluate conversion, AIS grades were determined from the follow-up examination (N=500).

Analysis: Frequencies and proportions of persons with a 'motor incomplete-like' status were evaluated to determine whether this classification was associated with conversion to a motor incomplete injury at follow-up.

Results: Of the total sample (N=2,018), using the ISNCSCI definition of motor levels, 12.7% (N=256) presented as 'motor incomplete-like', with the majority 'AIS C-like' (75.4%; N=193). 'Motor incomplete-like' status was more common in those with tetraplegia than paraplegia (18.2% vs. 9.6%). Of the sample, 24.8% (N=500) had a follow-up exam. Those initially with a 'motor incomplete-like' injury had a greater likelihood of conversion to motor incomplete status (AIS C or D) at follow-up compared to those without this designation (42.9% vs. 13.1%). Using the 'alternate motor level' definition, 9.6% (N=194) of individuals presented as 'motor incomplete-like', and the likelihood of conversion to motor incomplete status further increased (53.5% vs. 13.3%).

Conclusion: These findings highlight the importance of the initial motor ZPP in predicting AIS conversion following acute traumatic SCI. This can help identify patients with complete injuries who are more likely to undergo AIS conversion, particularly to motor incomplete status.