576
Z. P. French et al.
musculoskeletal disease become more pronounced
throughout adulthood (10). In addition to altered
biomechanics, inadequate development and poor pre-
servation of muscle and bone may increase the risk of
OA. However, associations between musculoskeletal
mass and function with OA may be influenced by sex
(11, 12) and body mass index (11). Previous studies
have shown that children with CP have higher total
body (13), abdominal (14), and musculoskeletal (8) fat
compared with matched typically developing children.
While individuals with CP are at increased risk for
early development of OA, the epidemiology of OA
for this population is not well characterized. Using
medical records, recent studies in adults with CP have
reported the prevalence of any type of OA to be 5.4% in
18–30-year-olds (9, 10), and up to 34% among adults
> 50 years of age (10). The latter estimate is higher
than the 13–25% reported for the general population
of men and women > 65 years of age (15). Moreover,
middle-aged women with CP may be at greater risk for
OA than middle-aged men with CP (16).
Previous studies on CP and prevalence of OA (9, 10,
16) have significant limitations. Data were taken from a
single medical system in the Southeast region of Michi-
gan, USA, and prevalence of OA was not examined by
age and sex. Additional research is needed to determine
the prevalence of OA in adults with CP across the USA,
and to identify age and sex trajectories (16). This know-
ledge could inform clinical and rehabilitation strategies
aimed at improving health and function throughout
the adult lifespan for this population. Therefore, the
primary objective of this study was to compare the
prevalence of OA between adults with and without CP,
using a large, nationwide private insurance database. It
was hypothesized that men and women with CP would
have a higher prevalence of OA compared with those
without CP across the adult lifespan.
MATERIAL AND METHODS
Data source
Data were from the Clinformatics® Data Mart Database (Op-
tumInsight TM , Eden Prairie, MN, USA). This database is a na-
tionwide de-identified insurance claims database of beneficiaries
from a single private payer in the USA, and contains information
on beneficiaries with medical and pharmacy coverage. Data are
de-identified and patient consent was waived. The University
of Michigan Institutional Review Board approved this study
as non-regulated.
Sample selection
Data were obtained from 2016, the most recent available year.
Beneficiaries who were 18 years of age and older, had 12 full
months of continuous enrolment, and had at least one medical
www.medicaljournals.se/jrm
service utilization in 2016 (to determine any medical diagnoses)
were considered for this study. International Classification of
Diseases, Tenth Revision, Clinical Modification (ICD-10) codes
were used to identify all medical conditions. CP was identified
by at least one medical claim using the G80 family of ICD-10
codes, covering all diagnostic subtypes of CP (e.g. spastic quad-
riplegic, tetraplegic). Data regarding severity of CP using com-
mon clinical measures (e.g. gross Motor Function Classification
System) are not available in administrative claims. Furthermore,
over 70% of the cohort had “other” or “unspecified” CP, thus not
allowing us to stratify or account for the clinical subtypes of CP
(e.g. spasticity/athetoid, hemiplegic) in the current study. Using
a single medical claim to identify a paediatric-onset disability
using administrative claims data has shown approximately 80%
positive predictive value and 99% sensitivity (17). Beneficiaries
with no medical claims for CP represented the group without
CP (i.e. control subjects). Beneficiaries who had unknown or
missing data for sex were excluded (n = 991, < 0.01% of total
sample). The final sample consisted of 8,739,803 beneficiaries,
including 7,348 adults with CP.
Osteoarthritis
Any OA was defined as a single claim for the following condi-
tions (ICD-10 code): poly OA (e.g. OA in multiple joints; M15
family); hip OA (M16 family); knee OA (M17 family); first
carpometacarpal joint OA (herein referred to as “hand OA”;
M18 family); and other/unspecified OA (M19 family).
Sociodemographic and socioeconomic variables
Sociodemographic and socioeconomic variables included
age, sex, ethnic group, education level, and household annual
income. Guided by previous studies of musculoskeletal health
among adults with CP (9, 10), age was stratified into the fol-
lowing groups to reflect different stages of the adult lifespan:
18–30, 31–40, 41–50, 51–60, 61–70 and >70 years of age.
Statistical analysis
Data for the entire sample were summarized as mean (stan-
dard deviation (SD)) for continuous variables and percentage
(frequency) for categorical variables. Multivariable logistic
regression analyses were performed with each OA variable as
the outcome. CP group (reference: without CP) was included
as the primary exposure variable. Age (as continuous) and sex
were included as covariates. The interaction between CP group
with sex and CP group with age group for each OA outcome was
examined. If significant, subsequent analyses were performed
after stratifying by that variable. The main effect of CP group
was interpreted for all models. Ethnicity, education level, and
household annual income were not initially included as cova-
riates due to the extent of missingness/unknown (4.6–30.6%).
However, a sensitivity analysis was conducted by further ad-
justing the multivariable logistic regression model for ethnicity,
education level, and household annual income for participants
with complete data.
Unadjusted prevalence of any OA was also determined for
each age group and sex. We chose to examine any OA because
of the extent of “other” or “unspecified” OA, which may bias
results for prevalence of location-specific OA (e.g. hip, knee).
Unadjusted logistic regression analyses were performed for each
age group and sex, with any OA as the outcome and CP group
as the primary exposure variable.