Defining age-related differences in outcome after traumatic spinal cord injury: analysis of a combined, multicenter dataset.
BACKGROUND CONTEXT: The existing evidence suggests that, although older spinal cord injury (SCI) patients experience a similar degree of neurologic recovery to younger patients, older patients experience diminished functional outcomes at follow-up. However, all studies have assumed that the impact of age on functional outcome is the same across the spectrum of injury severity. PURPOSE: To test this assumption, we evaluated age as a potential effect moderator governing the relationship between acute neurologic status and long-term functional outcome. STUDY DESIGN/SETTING: Combined analysis of two prospective SCI datasets enrolling patients from North American trauma centers over the last decade. PATIENT SAMPLE: Adult patients (≥16 years old) with traumatic SCI and a standardized American Spinal Injury Association (ASIA) neurologic examination performed within 3 days of injury. OUTCOME MEASURES: Functional independence measure (FIM) motor score at the 1-year follow-up was the primary outcome of interest. METHODS: To define older and younger age groups, age was dichotomized at a threshold of 65 years old. A sensitivity analysis was also performed by dichotomizing age at 60 years. Multivariable linear regression was used to investigate the moderating effects of age on the relationship between acute ASIA Impairment Scale (AIS) grade and follow-up FIM motor score. An interaction plot was generated to understand how the effect of age on functional outcome changed depending on the acute AIS grade. A second linear regression model investigating the moderating effects of age was produced that adjusted for additional relevant predictor variables. RESULTS: Of 729 patients, 376 met the eligibility criteria. The mean age was 43.2 (±16.9), with a total of 41 patients (10.9%) older than 65 years. In the univariable analysis there was no age-related difference in motor recovery or AIS grade conversion at follow-up; however, there was a significantly lower mean FIM motor score observed among the older group at 1 year (p=.03). In the multivariable analysis, age was found to have a significant moderating effect on the relationship between acute AIS grade and future functional status (p<.05). The interaction plot revealed that, although older patients had decreased follow-up FIM motor scores overall, this effect was greatest for AIS B and AIS C patients and lesser for AIS A and AIS D patients. After adjustment for additional covariates in the second linear model, these results remained unchanged. CONCLUSIONS: Overall, advanced age is associated with worse functional outcome after SCI; however, this effect varies across the spectrum of injury severity. These results will help to facilitate enhanced clinical communication as well as potentially aid in the development of customized treatment and rehabilitation protocols.