Musculoskeletal Morbidity Among Adults Living With Spina Bifida and Cerebral Palsy

Abstract

Background:

Individuals living with cerebral palsy (CP) or spina bifida (SB) are at heightened risk for chronic health conditions that may develop or be influenced by the impairment and/or the process of aging.

Objectives:

The objective of this study was to compare the incidence of and adjusted hazards for musculoskeletal (MSK) morbidities among adults living with and without CP or SB.

Methods:

A retrospective, longitudinal cohort study was conducted among adults living with (n = 15,302) CP or SB and without (n = 1,935,480) CP or SB. Incidence estimates of common MSK morbidities were compared at 4 years of enrollment. Survival models were used to quantify unadjusted and adjusted hazard ratios for incident MSK morbidities. The analyses were performed in 2019 to 2020.

Results:

Adults living with CP or SB had a higher 4-year incidence of any MSK morbidity (55.3% vs. 39.0%) as compared to adults without CP or SB, and differences were to a clinically meaningful extent. Fully adjusted survival models demonstrated that adults with CP or SB had a greater hazard for all MSK disorders; this ranged from hazard ratio (HR) 1.40 (95% CI, 1.33 to 1.48) for myalgia to HR 3.23 (95% CI, 3.09 to 3.38) for sarcopenia and weakness.

Conclusion:

Adults with CP or SB have a significantly higher incidence of and risk for common MSK morbidities as compared to adults without CP or SB. Efforts are needed to facilitate the development of improved clinical screening algorithms and early interventions to reduce risk of MSK disease onset/progression in these higher risk populations.

Introduction

Spina bifida (SB) is caused by incomplete development of the spinal column in utero and includes a variety of birth defects. The prevalence of SB is 3.5 cases per 10,000 live births in the United States.¹ Cerebral palsy (CP) is a neurologic condition caused by an insult to the brain from pregnancy to early childhood and is a permanent neurologic condition. It is the most common developmental disability with a prevalence ranging from 2.6 to 3.1 cases per 1000 live births in the United States.² With both populations approaching an average adult lifespan, it is growing increasingly important to examine the long-term health outcomes in these groups. As neurologic conditions, CP and SB negatively impact accrual of muscle and bone,^3–5 leading to alterations in body composition with a relatively higher fat mass in relation to bone and muscle mass.^6,7 This alteration contributes to secondary muscle pathology⁸ and impairments in mobility, function, and independence, along with a higher risk of secondary conditions, including cardiometabolic disease and psychological morbidity.^9–11 Secondary musculoskeletal (MSK) conditions have been documented in individuals with CP and SB and include chronic pain, osteoarthritis, osteoporosis, and low-trauma and pathological fracture.^12–18 Several previous studies have evaluated the burden of MSK disease in CP and noted a high prevalence of MSK conditions and MSK multimorbidity.^19,20 MSK morbidity has been studied in individuals with spinal cord injury,²¹ but it has not been well established in adults with SB, specifically. In one of the only studies conducted to date, Trinh et al.¹⁶ demonstrated that low bone mineral density and obesity were highly prevalent in adults with SB. However, the longitudinal trends of MSK outcomes among adults living with CP or SB at the population level has not yet been determined. The purpose of this study was to examine the incidence of and hazard for developing MSK morbidities among adults living with CP and SB in the United States.

Methods

Data source

This is a cohort study of adults with CP or SB whose diagnosis could have existed across any patient care setting (inpatient or outpatient). This study used a national, private insurance claims database (Clinformatics DataMart Database; OptumInsight, Eden Prairie, MN). This is a de-identified administrative claims database of over 80 million adults and children with commercial insurance representing those on a single, large US private payer plan, who had both medical and pharmacy coverage throughout the enrollment. Enrolled beneficiaries’ emergency department, outpatient, and inpatient encounters are captured. This study was deemed exempt by the University of Michigan Institutional Review Board. Data were obtained and analyses performed in 2019–2020.

Sample selection

Individuals 18 years of age and older at the time of their enrollment, which could start from 2007 to 2017, were potentially eligible for this analysis. To obtain a sufficient claim history to identify a cohort of adults with CP or SB, we excluded individuals with less than 12 months of continuous enrollment. Medical claims excluding laboratory and outpatient pharmacy were considered to identify prevalence or treatment for these conditions during the enrollment period.

Identification of patients with CP and SB

All members with a diagnosis of CP or SB were identified using International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM; eTable 1). Members who had CP or SB prior to 2007 were excluded due to poorer coverage of diagnosis codes during 2001 to 2006 in the database. Members without a diagnosis code in any position when they were 18 years or older during enrollment were excluded. To allow adequate longitudinal follow-up for all patients with CP or SB, only those who had 4 or more continuous years of enrollment following their starting date of enrollment within the study period were included.

A comparison cohort of controls without CP or SB was also identified. Additional exclusion criteria for identifying the control cohort included removal of any individual with other physically disabling neurological disorders (e.g., paraplegia, quadriplegia, hemiplegia, traumatic spinal cord injury, and multiple sclerosis). Among remaining members without CP or SB, we obtained a 20% simple random sample of general population controls using a fixed randomization seed. We further ensured that no unintentional bias was introduced due to random sampling by conducting post hoc effect size calculations between the full general population control cohort and the 20% sample on baseline covariates such as demographics and prevalent comorbidities. We considered an unbiased random sample if post hoc effect sizes indicated no meaningful differences.

Incident MSK morbidities

Incident physician-diagnosed MSK health disorders were identified based on a single encounter that included at least one of the pertinent ICD-9 or ICD-10 codes (see eTable 1). All MSK morbidities were chosen based on established categories through the Agency for Healthcare Research and Quality (AHRQ) indicators of clinical classification software (CCS), as previously described.^22,23 The primary outcome was time in days to any incident MSK morbidity following enrollment on the plan. Secondary outcomes were component incident MSK morbidity, including (1) osteoarthritis; (2) osteoporosis; (3) pathologic fracture; (4) disorders of muscle, joint, ligament, tendons, and connective tissue (e.g., upper extremity tendonitis; synovitis and tenosynovitis; other disorders of synovium and tendon [e.g., synovial hypertrophy]; bursitis; enthesopathies–lower limb [e.g., hip tendonitis, etc.]; other enthesopathies [e.g., lateral epicondylitis]; other and unspecified soft tissue disorders, not elsewhere classified [e.g., panniculitis]; calcification and ossification of muscle); (5) sarcopenia; (6) myalgia; and (7) rheumatoid arthritis, myositis, and musculoskeletal infections.

Covariates

Explanatory covariates included age group split into three categories (18–44, 45–64, 65 or older), sex, race, educational attainment, household net worth, and a modified Elixhauser comorbidity index. The Elixhauser comorbidity index was modified to remove two conditions that would be correlated with CP/SB or incident MSK morbidity: paralysis and rheumatoid arthritis. Therefore, the revised index only considers 29 comorbidities (eTable 2).

Statistical analysis

Bivariate analyses of baseline demographic characteristics between patients with CP or SB and controls were performed. For categorical variables, column percentages were compared between both groups using effect size calculations with Cohen’s h. The Cohen’s h effect size calculation was used because, due to large sample sizes, being statistically overpowered would not provide clinically meaningful differences in proportions between groups. For continuous variables, means and standard deviations and medians with upper and lower bounds on interquartile ranges were calculated. Cohen’s d standardized mean differences (SMDs) were calculated for continuous variables to ascertain clinically meaningful differences between groups.

To capture full comorbidity history within the study period, all patients with sufficient continuous enrollment within the study period of 4 years were retained to enable sufficient follow-up. For the CP or SB cohort, the first year of enrollment was used within the 4-year enrollment to capture comorbidity history and to examine whether any prevalent MSK outcomes existed.

Enrollees in each group who had no evidence of composite MSK morbidity were plotted using Kaplan-Meier product limit survival curves for a 3-year period. To establish incidence in claims, we used a 1-year lookback period from the index date in each group to obtain evidence of any service utilization with a diagnosis of any MSK morbidity. These patients were excluded from the product-limit survival curves and other subsequent analyses.

To estimate the hazard of the composite and each MSK morbidity, a series of survival models were developed. For each MSK morbidity, all patients who had evidence of the specific MSK morbidity were excluded from the model. For example, if osteoporosis was being considered as the incident outcome, all patients with prevalent osteoporosis in the 1 year prior to the index date would be excluded from the model. Sample sizes of patients included for each outcome varied based on evidence of prevalent disease in the 1 year prior to the index date. Survival models were then used to quantify unadjusted and adjusted hazard ratios for each incident MSK morbidity. Appropriate survival models were based on distributional assumptions that included testing Weibull, lognormal, exponential, gamma, logistic, loglog, and normal distribution with respect to the follow-up in days by minimizing critical model fit statistics. Critical assessment of Akaike Information Criterion (AIC) was used as a basis for minimization amongst all candidate distributions. Use of the parametric Weibull regression for incident MSK outcome was applied stepwise. To examine the effects of incremental adjustment on the exposure variable (CP or SB), a series of models for each MSK outcome was evaluated. All patients were right censored if they did not experience the outcome in the follow-up period or disenrolled from the plan. Both unadjusted and all adjusted hazard ratios and 95% confidence intervals for the exposure to CP/SB were calculated.

All analyses were conducted using SAS 9.4 (SAS Institute, Cary, NC). Statistical testing was two-tailed with a significance level of .05. Effect sizes used a 0.2 meaningful difference cutoff.

Results

We examined common MSK disorders among adults living with CP or SB (n = 15,302), as compared to adults without CP or SB (n = 1,935,480). The median time in the plan for eligible enrollees was 7.0 (25th percentile: 5.1; 75th percentile: 9.7) and 6.7 (25th percentile: 5.0; 75th percentile: 9.3) years for patients with CP or SB versus controls, respectively (Table 1).

Table 1.

Descriptive characteristics among adults with (case) or without (control) cerebral palsy (CP) or spina bifida (SB)

	Case	Control
Overall	15,302 (100%)	1,935,480 (100%)
Full enrollment length
Mean (SD)	7.8 (3.3)	7.6 (3.3)
Median (Q1–Q3)	7.0 (5.1–9.7)	6.7 (5.0–9.3)
Years post eligibility start datea
Mean (SD)	5.8 (2.2)	5.5 (2.2)
Median (Q1–Q3)	5.3 (4.0–7.3)	5.0 (3.7–6.8)
Age group
18–44	7055 (46.1%)	798,257 (41.2%)
45–64	5255 (34.3%)	617,997 (31.9%)
65 or older	2992 (19.6%)	519,226 (26.8%)
Gender
Female	8666 (56.6%)	1,012,200 (52.3%)
Male	6636 (43.4%)	923,280 (47.7%)
Race
White	9077 (59.3%)	1,148,666 (59.3%)
Asian	300 (2.0%)	75,437 (3.9%)
Black	1496 (9.8%)	155,609 (8.0%)
Hispanic	1268 (8.3%)	175,966 (9.1%)
Unknown/Missing	3161 (20.7%)	379,802 (19.6%)
Education
<High school diploma	86 (0.6%)	10,761 (0.6%)
High school diploma	4465 (29.2%)	469,829 (24.3%)
<Bachelor’s degree	8107 (53.0%)	1,021,803 (52.8%)
Bachelor’s degree	2238 (14.6%)	371,346 (19.2%)
Unknown/Missing	406 (2.7%)	61,741 (3.2%)
Net worth
Unknown	3334 (21.8%)	346,012 (17.9%)
<$25K	3234 (21.1%)	302,790 (15.6%)
$25K-$149K	2695 (17.6%)	340,966 (17.6%)
$150K-$249K	1379 (9.0%)	196,032 (10.1%)
$250K-$499K	2088 (13.6%)	313,883 (16.2%)
≥$500K	2572 (16.8%)	435,797 (22.5%)

^aAll adults with CP and SB have their index date set the same as start of eligibility date (start of 2007, year when turned 18, or enrollment start date, whichever was the latest).

Adults living with CP or SB had a higher 4-year incidence of any MSK morbidity (55.3% vs. 39.0%) as compared to adults without CP or SB, and differences were to a clinically meaningful extent. Moreover, adults with CP or SB had significantly higher incidence of all but one of the MSK outcomes (pathologic fracture), including rheumatoid arthritis (2.6% vs. 1.5%), osteoarthritis (19.5% vs. 14.2%), osteoporosis (8.0% vs. 5.02%), other connective tissue diseases (52.7% vs. 35.7%), sarcopenia and weakness (13.4% vs. 4.0%), and myalgia (10.5% vs. 6.5%) as compared to adults without CP or SB (all ps < .01; SMD ≥ 0.2) (Table 2).

Table 2.

Incidence of any and all musculoskeletal (MSK) morbidities among adults with (case) and without (control) cerebral palsy (CP) or spina bifida (SB) with 1-year clean enrollment period

	No outcome at baselinea
	Case/Denominator	Control/Denominator
Any MSK	4946/8942 (55.3%)*	565,340/1,447,877 (39.0%)
Rheumatoid arthritis	388/14991 (2.6%)*	29,111/1,912,881 (1.5%)
Osteoarthritis	2623/13,441 (19.5%)*	252,447/1,778,059 (14.2%)
Osteoporosis	1162/14,506 (8.0%)*	92,852/1,872,442 (5.0%)
Pathological fracture	281/15,194 (1.8%)	18,820/1,929,290 (1.0%)
Other connective tissue diseases	5194/9849 (52.7%)*	553,481/1,552,040 (35.7%)
Sarcopenia and weakness	1942/14,471 (13.4%)*	76,313/1,913,796 (4.0%)
Myalgia	1503/14,309 (10.5%)*	121,275/1,871,133 (6.5%)

^*p < .01 and standard mean difference (SMD) ≥ 0.2.

^aDenominators for both cases and controls reflect a 1-year clean period during their enrollment for the specific condition.

For instance, among cases (CP/SB), there exist 13,441 patients whose first year of enrollment had no evidence of osteoarthritis; therefore, inferred incident osteoarthritis could be estimated for this subset of the full CP/SB cohort. As a result, all patient cohorts’ denominators dynamically change conditional on the incident outcome being measured to ensure a clean period in the first year of enrollment.

A Kaplan-Meier curve for the unadjusted disease-free survival for any MSK morbidity in adults with CP or SB and controls is provided in Figure 1. For the secondary analyses, unadjusted survival models demonstrated a robust hazard ratio (HR) for each of the musculoskeletal morbidities among adults with CP or SB and ranged from HR 1.42 (95% CI, 1.37 to 1.48) for osteoarthritis to HR 3.55 (95% CI, 3.39 to 3.72) for sarcopenia and weakness (all ps <.001). Fully adjusted survival models demonstrated that adults with CP or SB had a greater hazard for any MSK morbidity (HR 1.62; 95% CI, 1.58 to 1.67) (Table 3) and all MSK disorders and ranged from HR 1.40 (95% CI, 1.33 to 1.48) for myalgia to HR 3.23 (95% CI, 3.09 to 3.38) for sarcopenia and weakness (Table 4). The effect was just as strong in the fully adjusted model, indicating that the effect of CP and SB was robust and sociodemographic factors and comorbidities did not modify the model significantly.

Figure 1.

Disease-free survival and Kaplan-Meier product-limit survival curves (3-year) for adults with cerebral palsy (CP) or spina bifida (SB) (blue) and without CP or SB (red), for any musculoskeletal morbidity.

Table 3.

Fully adjusted survival model for any musculoskeletal morbidity

Parameter	Estimate	SE	HR	95% CI	p value
CP/SB	−0.508	0.015	1.620	1.58–1.67	<.001
Age (unit: 10 years)	−0.204	0.001	1.213	1.21–1.22	<.001
Female	−0.307	0.003	1.338	1.33–1.35	<.001
Race					<.001
Asian	0.241	0.008	0.796	0.78–0.81	<.001
Black	0.058	0.005	0.946	0.94–0.96	<.001
Hispanic	0.048	0.005	0.956	0.95–0.96	<.001
Unknown/Missing	−0.028	0.004	1.027	1.02–1.04	<.001
White (reference)
Division
East North Central	0.025	0.006	0.976	0.97–0.99	<.001
East South Central	−0.040	0.009	1.039	1.02–1.06	<.001
Middle Atlantic	−0.010	0.007	1.009	0.99–1.02	.138
Mountain	0.043	0.006	0.960	0.95–0.97	<.001
New England	0.010	0.008	0.991	0.98–1.01	.237
Pacific	0.038	0.005	0.965	0.96–0.97	<.001
South Atlantic	−0.021	0.005	1.021	1.01–1.03	<.001
Unknown	0.379	0.017	0.698	0.68–0.72	<.001
West North Central	0.021	0.006	0.980	0.97–0.99	<.001
West South Central (reference)
Elixhauser score (modified)	−0.156	0.001	1.159	1.16–1.16	<.001
Education
<High school diploma	0.128	0.019	0.885	0.85–0.92	<.001
High school diploma	0.027	0.004	0.974	0.97–0.98	<.001
Bachelor’s degree plus	−0.036	0.004	1.034	1.03–1.04	<.001
unknown/missing	0.518	0.010	0.611	0.60–0.62	<.001
<Bachelor’s degree (reference)
Net worth
Unknown/Missing	0.050	0.005	0.953	0.94–0.96	<.001
<$25K	0.004	0.005	0.996	0.99–1.01	.423
$25K–$149K	0.029	0.005	0.973	0.96–0.98	<.001
$150K–$249K	0.025	0.005	0.976	0.97–0.99	<.001
$250K–$499K	0.030	0.005	0.972	0.96–0.98	<.001
$500K+ (Reference)

Note: HR = hazard ratio.

Table 4.

Survival models with parametric Weibull regression was completed stepwise for each incident musculoskeletal (MSK) outcome to examine the effects of incremental adjustment on the exposure variable (cerebral palsy/spina bifida [CP/SB]) ^a

	Model 1	Model 2	Model 3	Model 4
Any MSK	1.64 (1.60, 1.69)*	1.79 (1.74, 1.84)*	1.62 (1.57, 1.66)*	1.62 (1.58, 1.67)*
Rheumatoid arthritis	1.71 (1.55, 1.89)*	1.81 (1.64, 2.00)*	1.49 (1.34, 1.64)*	1.48 (1.34, 1.64)*
Osteoarthritis	1.42 (1.37, 1.48)*	1.72 (1.65, 1.79)*	1.50 (1.44, 1.56)*	1.49 (1.43, 1.55)*
Osteoporosis	1.64 (1.55, 1.74)*	1.98 (1.87, 2.10)*	1.85 (1.74, 1.96)*	1.86 (1.76, 1.97)*
Pathological fracture	1.90 (1.69, 2.14)*	2.16 (1.92, 2.43)*	1.82 (1.61, 2.05)*	1.81 (1.61, 2.04)*
Other connective tissue disease	1.72 (1.67, 1.76)*	1.82 (1.77, 1.87)*	1.62 (1.57, 1.66)*	1.62 (1.58, 1.67)*
Sarcopenia and weakness	3.55 (3.39, 3.72)*	4.24 (4.05, 4.44)*	3.29 (3.14, 3.44)*	3.23 (3.09, 3.38)*
Myalgia	1.66 (1.58, 1.75)*	1.66 (1.57, 1.74)*	1.40 (1.33, 1.47)*	1.40 (1.33, 1.48)*

Note: Model 1: Unadjusted

Model 2: Model 1 + Demographic variables (age, sex, race, geographic region).

Model 3: Model 1 + Model 2 + Modified Elixhauser Comorbidity Index

Model 4: Model 1 + Model 2 + Model 3 + Education + Income

^aAs with incidence estimates (Table 2), all survival models used cases (CP/SB) and control cohorts are consistent with Table 2, which required a 1-year clean period with no evidence of the MSK condition being measured.

^*p < .001.

Discussion

The principal finding of this study was that adults living with CP or SB had a higher incidence of any and all MSK morbidities than adults without CP or SB. Moreover, both unadjusted and adjusted survival models revealed a significant association between the exposure of CP or SB and each of the outcomes. These findings indicate a need for clinical awareness regarding the MSK disorders experienced and the risk among adults living with CP and SB. In addition, enhancing clinical screening strategies and developing efficient referral resources for coordinated care may help reduce the burden of bone, muscle, joint, ligament, tendon, and connective tissue health disorders in these high-risk populations. These findings may also serve as an alert to clinicians treating adults living with other childhood-onset disabilities and to the caregivers, as these issues may not be specific to the diagnosis of CP or SB per se.

To date, this is the largest study to examine the longitudinal trends of MSK morbidities in a nationally representative sample of adults with CP or SB. Consistent with previous studies, this research confirms the higher risk for developing both osteoarthritis and osteoporosis in CP.^19,20 There are very few studies to have evaluated the prevalence or incidence of MSK conditions in SB. Most of these studies are small observational/cross-sectional studies, not population based, and they tend to focus on the pediatric population.^24,25 However, several small studies have also demonstrated a heightened risk of osteoporosis and fractures among adults living with SB.^16,26

This study expands on previous research by including multiple other MSK diagnoses, including pathological fracture, connective tissue diseases, sarcopenia, and myalgias, all of which demonstrated a higher incidence and HR among adults with CP or SB. Sarcopenia had the highest HR of all MSK disorders at 3.23. It is worth noting that nearly 10% of the CP or SB cohort was removed from the cohort due to baseline prevalent sarcopenia as compared to 1% from the control group (i.e., due to our exclusion criteria). It is unclear whether the higher incidence of this diagnosis represents new sarcopenia versus improved coding in more recent years; but in concert with other recent research,^7,27 it does indicate that sarcopenia in adults with CP or SB is an area of great concern. The higher risk of sarcopenia is likely a strong driver of the known progressive functional decline that has been documented across multiple prior studies in both CP and SB.^28–30 Previous small studies have evaluated muscle architecture on radiologic imaging in CP and noted fat infiltration and relative sarcopenia, but this has not been documented previously in large-scale studies.²⁷ Studies have also documented smaller muscle mass in children with CP,²⁷ and skeletal muscle composition is heavily infiltrated with adipose tissue in both children and adults with CP.^4,6 Functional loss is a common complication in both populations, with up to 75% of people with CP noting a decline in ambulation by age 25³¹ and 83% of ambulatory individuals with SB by age 40.²⁸ These are patient populations with known sedentary lifestyles,^32,33 which raises concerns for severity of functional consequences if being given a new diagnosis of sarcopenia as seen in this study. Of relevance, there is a large body of evidence in the general population linking muscular weakness, as determined by low grip strength, to a host of negative aging-related health outcomes including diabetes,^34,35 functional disability,^36–39 cognitive decline (including Alzheimer’s disease^40,41),^42,43 and early all-cause mortality.^36,44–48 Given these links, grip strength has been labeled a “biomarker of aging”⁴⁹; yet, this measure has not been incorporated into clinical screening for adults living with CP or SB. Future research is needed to examine the clinical feasibility, validity, and reliability of incorporating grip strength into physical medicine and rehabilitation or family practice clinics.

“Disorders of muscle, joint, ligament, tendons, and connective tissue” have not been evaluated on such a large scale in previous studies among adults living with CP or SB. The grouping of these diagnoses included but was not limited to muscle pain, tears, tendinopathies, enthesopathies, bursitis, and some types of muscle injury. Our findings indicate a higher incidence of tendon and muscle problems in CP and SB. These findings correlate with the known physiology of abnormal muscle and bone development leading to joint malalignment and risk for abnormal stresses on tendons and ligaments, making this population more susceptible to overuse injury. This study provides some additional insights into the need for a more careful evaluation of factors that contribute to the high burden of MSK morbidity. Small studies have noted a higher risk for development of shoulder problems in SB, but similar evaluation has not been done in CP.⁵⁰ Previous studies have documented location of MSK pain in both SB and CP, but not specific pain etiologies.^{24,28,51–53} The grouping of “disorders of muscle, joint, ligament, tendons, and connective tissue” includes tendinopathies, potentially due to overuse or injury, that can lead to worsening function. An increased risk of developing shoulder pain and rotator cuff tendinopathy has been documented in manual wheelchair uses^54,55; this can result in limited use of upper extremities and lead to difficulty with adapted mobility and eventually functional decline. MSK injuries have been shown to significantly impact quality of life in people with disabilities.⁵⁶ For instance, shoulder range of motion restrictions have been shown to cause difficulty with manual wheelchair propulsion, transfers, and self-care in people with spinal cord injury.⁵⁷ Future studies are needed to evaluate underlying MSK etiologies in more detail, which may help develop recommendations for MSK care in adults with CP and SB, similar to current guidelines for the preservation of upper extremity function in individuals with spinal cord injury.⁵⁸ Appropriate diagnosis of MSK etiology allows for targeted therapies and improved outcomes.

Limitations and Strengths

The sample with CP or SB may not be representative of the U.S. population of adults with CP or SB. We were unable to determine the severity of CP or SB through claims-based data, as patient-level characteristics pertaining to function (e.g., Gross Motor Function Classification System [GMFCS]) are not available in insurance claims-based data. However, we suspect that our sample may be more reflective of a higher functioning segment of the population with CP or SB,⁵⁹ because they had to be enrolled in private insurance. Individuals with more severe forms of CP or SB are more likely to be on federally subsidized health insurance.⁶⁰ Therefore, results and comparisons to adults without CP or SB are likely conservative estimates, and the true extent of MSK morbidity may be underestimated in this study. Moreover, in combining patients with CP and SB into a single cohort, there may be nuanced differences that we did not account for that are unique to each condition. Future studies are needed to explore the mechanisms underlying MSK morbidity in these populations across the lifespan, thus providing a better understanding of shared similarities (e.g., sedentary behaviors) and differences (e.g., endocrine) between CP and SB. Finally, we were unable to determine or account for the pathological etiologies of the CP or SB diagnoses. It is possible that the extent, severity, and compensatory mechanisms for recovery from the initial brain damage leading to CP, or extent of myelomeningocele leading to SB, may interfere with development in early life, and accelerate decline with age. Although secondary and tertiary ICD-9/10 codes may provide useful detail for type of impairment (e.g., congenital quadriplegia [343.2]), many patients lack these specific codes in the claim. Future studies are needed to disentangle the pathological features of CP and SB subtypes with the development of secondary MSK disorders in this population.

A major strength of this study is the large sample of adults with CP or SB. It can be challenging to gather data on clinical subpopulations, and very little is known about health outcomes among individuals with CP or SB as they transition into and throughout adulthood. Another strength of this study is the number of MSK morbidities from different etiologies that were investigated. Our comprehensive assessment of medically diagnosed MSK phenotypes among individuals with CP or SB throughout the adult lifespan may prompt the development of improved screening strategies and identification of individuals for risk of bone, muscle, and joint disorders. The ability to accurately identify and specifically tailor MSK and pain management/treatments by understanding etiology may also prevent early functional loss and lack of independence among adults with CP and SB.

Conclusion

Improved diagnosis of MSK conditions, particularly in persons aging with CP or SB, will allow for earlier interventions and preservation of function in a population at high risk for functional loss. Future studies are needed to examine the specific etiology of these conditions in hopes of improving treatment and prevention strategies and aiding in the development of guidelines for MSK care in individuals with CP and SB.

Funding Statement

Financial Support This research was developed in part under a grant from the National Institute on Disability, Independent Living, and Rehabilitation Research (NIDILRR #90RTHF0001-01-00).