Health care costs in US patients with and without a diagnosis of osteoarthritis

Figures & data

Table 1 Study sample selection

	n	Percentage
• Patients with at least one OA diagnosis from January 1, 2007 through December 31, 2007	1,010,071	100%
• Age 18 years or older at first OA diagnosis	1,007,532	99.7%
• Continuous enrollment and pharmacy benefits ≥12 months before first OA diagnosis	471,205	46.7%
• Continuous enrollment and pharmacy benefits ≥12 months after first OA diagnosis	470,416	46.6%
• Mental health benefits ≥12 months before first OA diagnosis	421,627	41.7%
• Mental health benefits ≥12 months after first OA diagnosis	420,889	41.7%
• Second OA diagnosis on/between 15 and 365 days pre- and post-index	259,886	25.7%
Total number of eligible patients for OA cohort	259,886	25.7%
Total number of matched OA patients	258,237	25.6%
Total number of non-OA controls	258,237

Notes: OA patients were directly matched 1:1 to control patients with no evidence of OA on the basis of age group, gender, geographic region, health plan type, and Medicare eligibility. OA patients for whom a match could not be located were dropped from the sample.

Abbreviation: OA, osteoarthritis.

Table 2 Demographic characteristics

	OA patients n = 258,237		Controls n = 258,237		P value
Age (mean, SD)	67.0	12.9	66.3	12.9	<0.05
Age group (n, %)					0.999
18–34	1563	0.6%	1563	0.6%
35–44	7380	2.9%	7380	2.9%
45–54	34,950	13.5%	34,950	13.5%
55–64	81,007	31.4%	81,007	31.4%
65–74	50,405	19.5%	50,405	19.5%
75+	82,932	32.1%	82,932	32.1%
Gender (n, %)					0.999
Male	92,345	35.8%	92,345	35.8%
Female	165,892	64.2%	165,892	64.2%
Geographic region (n, %)					0.999
North Central	90,412	35.0%	90,412	35.0%
Northeast	25,255	9.8%	25,255	9.8%
South	95,361	36.9%	95,361	36.9%
West	46,343	17.9%	46,343	17.9%
Unknown	866	0.3%	866	0.3%
Health plan type (n, %)					0.999
Comprehensive	103,499	40.1%	103,499	40.1%
Exclusive provider organization	444	0.2%	444	0.2%
Health maintenance organization	34,097	13.2%	34,097	13.2%
Preferred provider organization	18,705	7.2%	18,705	7.2%
Point of service	96,714	37.5%	96,714	37.5%
Point of service with capitation	1118	0.4%	1118	0.4%
Consumer driven health plan	1647	0.6%	1647	0.6%
Unknown	2013	0.8%	2013	0.8%
Medicare coverage (n, %)	129,292	50.1%	129,292	50.1%	0.999

Abbreviations: OA, osteoarthritis; SD, standard deviation.

Table 3 Comorbidities over the 12 month pre-index period

	OA patients n = 258,237		Controls n = 258,237
CCIa (mean, SD)	0.87	1.34	0.61	1.19
Medical conditionsb (n, %)
Hypertension	115,572	44.8%	83,826	32.5%
Cardiovascular disease	74,930	29.0%	52,585	20.4%
Diabetes	43,812	17.0%	32,450	12.6%
Peptic ulcer or gastritis	9177	3.6%	4,723	1.8%
Obesity	5049	2.0%	1539	0.6%
Insomnia	4947	1.9%	2561	1.0%
Kidney disease	4176	1.6%	2893	1.1%
Liver disease	3707	1.4%	2511	1.0%
Seizure or epilepsy	2729	1.1%	1984	0.8%
Psychiatric conditions (n, %)
Depression	16,413	6.4%	8851	3.4%
Alcohol use disorder	532	0.2%	289	0.1%
Pain conditionsb (n, %)
Joint pain/arthralgia	96,410	37.3%	18,504	7.2%
Injuries	76,984	29.8%	36,399	14.1%
Low back pain	45,749	17.7%	17,891	6.9%
Neuropathic pain	11,061	4.3%	3682	1.4%
Inflammatory arthritisc	11,593	4.5%	3019	1.2%
Fibromyalgia	10,183	3.9%	3025	1.2%
Migraine	4757	1.8%	2778	1.1%

Notes: All comparisons were statistically significant with a P value < 0.05.

a Charlson Comorbidity Index, Deyo adaptation, calculated over 12 months pre-index;

b presence of ≥one claim with a diagnosis code indicative of the condition in the 12 months pre-index;

c includes rheumatoid arthritis, ankylosing spondylitis or psoriatic arthropathy.

Abbreviations: CCI, Charlson Comorbidity Index; OA, osteoarthritis; SD, standard deviation.

Table 4 Health care utilization over the 12-month post-index period

	OA patients n = 258,237		Controls n = 258,237
Patients with services (n, %)
Hospitalizations	84,010	32.5%	22,133	8.6%
Emergency department	72,147	27.9%	50,133	19.4%
Office visit, primary care	229,001	88.7%	167,442	64.8%
Office visit, specialist	220,734	85.5%	125,457	48.6%
Physical/occupational therapy	112,650	43.6%	30,105	11.7%
All medications	248,594	96.3%	223,969	86.7%
Pain-related medicationsa	224,427	86.9%	135,924	52.6%
Number of services (mean, SD)
Hospitalizations	0.4	0.7	0.1	0.4
Emergency department	0.5	1.2	0.3	1.0
Office visit, primary care	5.5	5.3	2.4	3.2
Office visit, specialist	5.3	5.4	1.9	3.5
Physical/occupational therapy	5.0	9.7	1.0	4.6
All medications	36.2	30.0	22.0	24.1
Pain-related medicationsa	11.9	14.1	4.3	8.1

Notes: All comparisons were statistically significant with a P value < 0.05.

a Includes the following medications that may be used to treat osteoarthritis symptoms: opioids, tramadol, nonsteroidal anti-inflammatory drugs, topical analgesics, other analgesics not elsewhere classified, cyclooxygenase-2 (COX-2) inhibitors, proton pump inhibitors/H2 blockers (may be prescribed for gastroprotection), intra-articular injections, muscle relaxants, anticonvulsants, antidepressants, benzodiazepines, and nonbenzodiazepine sedative hypnotics. These mediations may have other indications as well. Medications not resulting in an outpatient claim (eg, over-the-counter products) were not counted.

Abbreviations: OA, osteoarthritis; SD, standard deviation.

Table 5 Generalized linear model regression of all-cause total health care costs

	Coefficienta	Standard error
Key independent variable
Controls (reference)
OA patients	0.900	0.005*
Age
Gender	0.010	0.000*
Male (reference)
Female	−0.053	0.005*
Urbanicity
Rural or unknown (reference)
Urban	0.003	0.006
Region
South (reference)
Northeast	−0.020	0.009*
North Central	−0.022	0.006*
West	0.044	0.008*
Unknown	−0.232	0.043*
Health plan type
Comprehensive (reference)
Exclusive provider organization	0.071	0.060
Health maintenance organization	−0.042	0.010*
Point of service	−0.018	0.011
Preferred provider organization	0.031	0.007*
Point of service with capitation	−0.189	0.040*
Consumer driven health plan	0.011	0.032
Unknown	0.150	0.029*
Capitation status
Not capitated (reference)
Capitated	0.165	0.013*
Medicare	−0.217	0.009*
Charlson Comorbidity Index	0.175	0.003*
Preperiod comorbidities
Peptic ulcer/gastritis	0.161	0.015*
Kidney disease	0.372	0.022*
Liver disease	0.327	0.023*
Hypertension	0.131	0.005*
Obesity	0.183	0.022*
Insomnia	0.112	0.021*
Diabetes	0.097	0.008*
Cardiovascular disease	0.259	0.006*
Seizure or epilepsy	0.301	0.026*
Depression	0.306	0.012*
Alcohol use disorder	0.168	0.063*
Neuropathic pain	0.166	0.015*
Lower back pain	0.224	0.008*
Migraine	0.281	0.021*
Inflammatory arthritis	0.282	0.015*
Injuries	0.122	0.006*
Joint pain/arthralgia	0.138	0.006*
Constant	7.871	0.023*

* Notes: Significant with P < 0.05;

a Positive coefficient indicates increase in cost, while negative coefficient indicates decrease in cost.

Table 6 Regression-adjusted health care costs over the 12 month post-index period

	OA patients			Controls
	Mean	95% CI		Mean	95% CI
Inpatient costs	$6668	$6587	$6744	$1756	$1717	$1794
Outpatient costs	$7840	$7786	$7902	$3675	$3637	$3711
Rx costs	$3213	$3195	$3233	$2245	$2229	$2262
Total costs	$18,435	$18,318	$18,560	$7494	$7425	$7557

Notes: Nonoverlapping confidence intervals indicate that the means are significantly different. All amounts are in US dollars.

Abbreviations: CI, confidence interval; OA, osteoarthritis.