Regional variation in incidence of primary total hip arthroplasties and revisions in Denmark, 1996–2002

Figures & data

Table 1.  Characteristics of the total hip arthroplasty (THA) patients registered in the Danish Hip Arthroplasty Registry, 1996–2002

Characteristic	1996	1997	1998	1999	2000	2001	2002
Primary THA, n (%)	4,633 (84.0)	4,897 (84.4)	5,044 (85.0)	5,280 (85.3)	5,431 (85.7)	5,557 (85.2)	6,302 (86.4)
Revision, n (%)	883 (16.0)	905 (15.6)	889 (15.0)	911 (14.7)	904 (14.3)	966 (14.8)	988 (13.6)
Hospital type, n (%)
Primary THA
University hospitals	813 (17.5)	760 (15.5)	765 (15.2)	854 (16.2)	860 (15.8)	791 (14.2)	935 (14.8)
Other hospitals	3,820 (82.5)	4,137 (84.4)	4,277 (84.8)	4,426 (83.8)	4,571 (84.2)	4,766 (85.8)	5,367 (85.2)
Revision
University hospitals	331 (37.5)	343 (37.9)	327 (36.8)	305 (33.5)	305 (33.7)	277 (28.7)	264 (26.7)
Other hospitals	552 (62.5)	562 (62.1)	562 (63.2)	606 (66.5)	599 (66.3)	689 (71.3)	724 (73.3)
Total number of inhabitants at risk in Denmark	4,608,491	4,618,164	4,626,797	4,638,703	4,653,478	4,669,518	4,689,729

Table 2.  Hospital-specific incidence rates (IR) of primary total hip arthroplasty (THA) and revision per 100,000 person years, standardized according to the European Standard Population, 1996–2002

Hospital type	1996	1997	1998	1999	2000	2001	2002
University hospitals
Primary THA	15.0	13.9	13.8	15.7	15.4	14.1	16.5
Revision	6.2	6.3	6.0	5.6	5.5	4.9	4.5
Other hospitals
Primary THA	71.6	76.5	78.9	81.7	83.6	86.2	96.9
Revision	10.1	10.2	10.3	11.0	10.8	12.2	12.8

Table 3.  Incidence rate ratio (IRR) of primary total hip arthroplasty (THA) and revision for each Danish county com-pared with Copenhagen Hospital Cooperation (H:S) (Poisson regression)

			Primary THA			Revision
			Crude IRR	Adjusted IRR ^b		Crude IRR	Adjusted IRR
Counties	Person years	THA (n)	(95% CI ^a)	(95% CI ^a)	Revision (n)	(95% CI ^a)	(95% CI ^a)
H:S	3,644,182	3,163	1.0 (ref.)	1.0 (ref.)	796	1.0 (ref.)	1.0 (ref.)
Copenhagen county	3,725,886	4,072	1.3 (1.2–1.3)	1.1 (1.1–1.2)	667	0.8 (0.7–0.9)	0.8 (0.7–0.8)
Frederiksborg	2,199,387	2,526	1.3 (1.3–1.4)	1.3 (1.2–1.3)	547	1.1 (1.0–1.3)	1.2 (1.1–1.3)
Roskilde	1,394,380	1,475	1.2 (1.1–1.3)	1.3 (1.2–1.4)	237	0.8 (0.8–0.9)	0.8 (0.7–1.0)
West Zealand	1,801,941	2,294	1.5 (1.4–1.5)	1.3 (1.2–1.4)	390	1.0 (0.9–1.1)	0.9 (0.8–1.0)
Great Stream	1,597,433	2,346	1.7 (1.6–1.8)	1.4 (1.3–1.4)	389	1.1 (1.0–1.3)	0.9 (0.8–1.1)
Bornholm	276,087	431	1.8 (1.6–2.0)	1.4 (1.3–1.6)	83	1.4 (1.1–1.7)	1.1 (0.9–1.4)
Funen	2,891,186	3,766	1.5 (1.4–1.6)	1.3 (1.3–1.4)	497	0.8 (0.7–0.9)	0.7 (0.6–0.8)
South Jutland	1,545,866	2,174	1.6 (1.5–1.7)	1.4 (1.3–1.5)	272	0.8 (0.7–0.9)	0.7 (0.6–0.8)
Ribe	1,354,561	1,652	1.4 (1.3–1.5)	1.3 (1.3–1.4)	425	1.4 (1.3–1.6)	1.4 (1.2–1.6)
Vejle	2,106,678	2,342	1.3 (1.2–1.4)	1.2 (1.0–1.3)	417	0.9 (0.8–1.0)	0.9 (0.8–1.0)
Rinkjøbing	1,651,990	1,887	1.3 (1.2–1.4)	1.3 (1.2–1.3)	376	1.0 (0.9–1.2)	1.0 (0.9–1.2)
Aarhus	3,865,611	3,594	1.1 (1.0–1.1)	1.1 (1.0–1.1)	584	0.9 (0.8–1.0)	0.8 (0.7–0.8)
Viborg	1,419,522	1,690	1.4 (1.3–1.5)	1.2 (1.1–1.3)	218	0.7 (0.6–0.8)	0.6 (0.5–0.7)
North Jutland	3,020,018	3,557	1.4 (1.3–1.4)	1.2 (1.1–1.3)	485	0.7 (0.6–0.8)	0.8 (0.6–0.8)

^a 95% confidence interval

^bAdjusted for age and sex.

Table 4.  Characteristics of the possible factors associated with regional variation (factors are expressed on average between 1995 and 2002 per county)

Factor	Mean (range)	Coefficient of variation (%)	Unadjusted regression coefficient (95 % CI) ^b	Adjusted regression coefficient(95 % CI) ^c
The number of orthopedic surgeons per 100,000 inhabitants	8.2 (4.9–12)	20	−4.13 (−7.52; −0.75)	−3.09 (−8.82; 2.64)
Harris Hip Score	42 (23–45)	10	−0.837 (−2.04; 0.366)	−0.041 (−1.51; 1.42)
Proportion of patients with primary arthrosis	78 (68–84)	5	1.55 (−0.015; 3.12)	0.927 (−1.16; 3.009)
Population density ^a	640 (56–6944)	275	−0.004 (−0.007; −0.001)	0.003 (−0.006; 0.012)
Gross domestic product per capita	210 (160–364)	25	−0.16 (−0.252; −0.076)	−0.157 (−0.390; 0.076)
Hospitals costs per capita	6,860 (6,463–7,272)	4	0.024 (−0.0005;0.048)	0.005 (−0.021; 0.031)

^a Number of inhabitants per square meter.

^b Based on univariate linear regression, with age- and gender-standardized incidence rates of primary total hip arthroplasty as the dependent variable.

^c Based on multiple linear regression.