Z. P. French et al.
578
Fig. 1. Unadjusted prevalence of any osteoarthritis (i.e. poly, hip, knee,
hand, other/unspecified osteoarthritis) among (A) men and (B) women,
with and without cerebral palsy (CP).
DISCUSSION
This study found that privately-insured men and wo-
men with CP have higher prevalence of OA compared
with men and women without CP across adulthood.
The group by sex interaction for hip OA in the entire
sample suggests that, while hip OA was higher for men
and women with CP compared with men and women
without CP, there were disproportionately higher odds
in men with CP than would be expected from the
privately-insured population without CP. Furthermore,
the CP group by age group interaction revealed that,
while adults with CP across all age groups had higher
odds for OA, the younger age groups had disproportio-
nately higher odds than the older age groups for both
Table III. Unadjusted odds of osteoarthritis (OA) among adults
(≥18 years) with cerebral palsy (CP) and without CP (reference)
stratified by sex and age group
Age group Men
OR (99.5% CI) Women
OR (99.5% CI)
18–30 years
31–40 years
41–50 years
51–60 years
61–70 years
> 70 years 4.98
3.76
3.09
1.96
1.69
1.65 2.84
4.79
3.19
1.97
1.55
1.77
OR: odds ratio; CI: confidence interval.
www.medicaljournals.se/jrm
(2.87–8.65)
(2.35–6.00)
(2.23–4.27)
(1.53–2.51)
(1.34–2.15)
(1.24–2.19)
(1.21–6.68)
(3.12–7.36)
(2.31–4.40)
(1.55–2.51)
(1.24–1.95)
(1.40–2.26)
men and women, suggesting an early onset of OA for
adults with CP. These findings provide large, national-
level data to support the need for earlier preventive
and health management services for OA and its related
health and functional complications among adults with
CP. This is important because pharmacological (20),
self-management, and exercise (21) interventions have
been shown to reduce patient burden of OA in non-CP
populations. Whether such interventions would be
beneficial for adults with CP requires future research.
The hips and knees are especially debilitating lo-
cations for OA, due to weight-bearing and resulting
gross motor function limitations. In the current study,
the prevalence of hip OA for the entire sample of
adults without CP was 1.9%, which is consistent with
the Global Burden of Disease prevalence estimate of
1.6% for men and 2.1% for women in high-income
North America (5). The prevalence of knee OA for
the sample of adults without CP was 5.8%, which is
consistent with a previous population-based study in
North America (15), but slightly higher than the Global
Burden of Disease prevalence estimate of 3.1% for men
and 5.0% for women in high-income North America
(5). Differences in prevalence estimates are probably
due to differences in methodology, with the Global
Burden of Disease yielding conservative estimates (5).
Data from the current study represent the largest
known sample of claims data for adults with CP eva-
luated for prevalence of OA. It was found that adults
with CP were more likely to have all OA measures,
except for hand OA, compared with adults without CP.
When stratified by sex, it was found that the prevalence
of any OA was higher for men and women with vs
without CP throughout the adult lifespan. However,
the prevalence of any type of OA among adults with
CP from the current study is lower than we have pre-
viously published from a clinical sample of adults with
CP from the Southeast Michigan region (n = 1,395 men
and women: 18–30 years, 5.4%; 31–40 years, 13.4%;
41–50 years, 23.1%; > 50 years, 33.9%) (9, 10), which
may be due to differences in CP sample characteristics.
In our previous studies (9, 10), approximately half of
the sample had moderate-to-severe forms of CP. In the
current study, the sample of adults with CP probably
reflects a healthier and higher functioning segment of
the CP population (22), although this is speculation,
as it is not possible to determine the severity of CP
using administrative claims data. To be enrolled with
a private health plan, beneficiaries must be able to af-
ford their own insurance or be covered through their
employer, parents (up to 26 years of age), or their
spouse. Individuals with paediatric-onset disabilities,
such as CP, tend to have low employment and marriage
rates (23), which may be exacerbated with more severe