Factors Associated With Ambulation in Myelomeningocele: A Longitudinal Study From the National Spina Bifida Patient Registry

Abstract

Objective: Evidence is limited regarding clinical factors associated with ambulation status over the lifespan of individuals with myelomeningocele. We used longitudinal data from the National Spina Bifida Patient Registry to model population-level variation in ambulation over time and hypothesized that effects of clinical factors associated with ambulation would vary by age and motor level.

Design: A population-averaged generalized estimating equation was used to estimate the probability of independent ambulation. Model predictors included time (age), race, ethnicity, sex, insurance, and interactions between time, motor level, and the number of orthopedic, noncerebral shunt neurosurgeries, and cerebral shunt neurosurgeries.

Results: The study cohort included 5371 participants with myelomeningocele. A change from sacral to low-lumbar motor level initially reduced the odds of independent ambulation (OR = 0.24, 95% CI = 0.15-0.38) but became insignificant with increasing age. Surgery count was associated with decreased odds of independent ambulation (orthopedic: OR = 0.65, 95% CI = 0.50-0.85; noncerebral shunt neurosurgery: OR = 0.65, 95% CI = 0.51-0.84; cerebral shunt: OR = 0.90, 95% CI = 0.83-0.98), with increasing effects seen at lower motor levels.

Conclusions: Our findings suggest that effects of several commonly accepted predictors of ambulation status vary with time. As the myelomeningocele population ages, it becomes increasingly important that study design account for this time-varying nature of clinical reality.

To claim cme credits: Complete the self-assessment activity and evaluation online at http://www.physiatry.org/JournalCME CME OBJECTIVES: Upon completion of this article, the reader should be able to: (1) Describe general trends in ambulation status by age in the myelomeningocele population; (2) Recognize the nuances of cause and effect underlying the relationship between surgical intervention and ambulation status; (3) Explain why variation of clinical effect over time within myelomeningocele population matters.

Level: Advanced ACCREDITATION: The Association of Academic Physiatrists is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.The Association of Academic Physiatrists designates this Journal-based CME activity for a maximum of 1.0 AMA PRA Category 1 Credit(s)™. Physicians should only claim credit commensurate with the extent of their participation in the activity.

FIGURE 1.

Community ambulators were most prevalent at younger age ranges, whereas nonambulatory participants were more prevalent in the early through mid-adulthood years. Cumulative percent for the four Hoffer categories add to 100% at each year. Ages that were of low frequency in the sample have less precise prevalence estimates.

FIGURE 2.

Increasing age reduces the odds of independent ambulation only into the late teenage years. Thereafter, further increases in age no longer significantly affect the odds of independent ambulation. Note that all effect sizes are reported in terms of the addition of one decade of life.

FIGURE 3.

By the third decade, the effect of a low-lumbar motor level on independent ambulation is not significantly different from that of a sacral motor level.

FIGURE 4.

Probability of independent ambulation varied widely over the age range of the study population.