The effect of hospital volume on length of stay, re-admissions, and complications of total hip arthroplasty

Figures & data

Table 1. Number of patients and annual number of hospitals in different hospital volume groups, with annual number of private hospitals in parentheses

Group	No. of patients 1998–2005	Annual no. of hospitals
		1998	1999	2000	2001	2002	2003	2004	2005
1	2,759	15 (7)	18 (8)	23 (8)	25 (9)	23 (10)	19 (11)	19 (10)	18 (9)
2	11,591	29 (2)	32 (2)	26 (2)	26 (3)	28 (2)	22 (2)	21 (2)	23 (4)
3	8,134	2 (0)	9 (0)	9 (0)	8 (0)	10 (1)	9 (0)	10 (0)	8 (0)
4	7,782	1 (1)	2 (1)	4 (1)	5 (1)	3 (1)	7 (2)	6 (2)	9 (2)
Total	30,266	57 (10)	61 (11)	62 (11)	64 (13)	64 (14)	57 (15)	56 (14)	58 (15)

See Material and Methods for explanation of groups

Table 2. Number (N_a) and percentage of replacements in cohorts when analyzing length of stay and unscheduled re-admissions, and number (N_b) and percentage of replacements in cohorts when analyzing dislocations, re-operations, and infections

Cohort	No. (Na) of hips (%)	No. (Nb) of hips (%)
1998	2,863 (10)	1,906 (9)
1999	3,083 (10)	2,025 (10)
2000	3,360 (11)	2,178 (11)
2001	3,554 (12)	2,389 (12)
2002	3,877 (13)	2,639 (13)
2003	4,336 (14)	3,056 (15)
2004	4,113 (14)	2,963 (14)
2005	5,080 (17)	3,658 (18)
Total	30,266 (100)	20,814 (100)

Table 4. Related diseases used in the adjustment of the study population

Hypertension (ICD-10: I10*-I15*, ICD-9: 40*, Social Insurance Institutions entitlement to reimbursement: 205, use and cost of drugs ATC: C03*, C07* (if there is no coronary disease or atrial fibrillation), C09A*, C09B*, C09C*, C09D*, C08*)

Coronary disease (ICD-10: I20*-I25*, ICD-9: 410*-414*, Social Insurance Institutions entitlement to reimbursement: 206, 213, 280)

Atrial fibrillation (ICD-10: I48*, ICD-9: 4273*, Social Insurance Institutions entitlement to reimbursement: 207, use and cost of drugs ATC: B01AA03)

Heart insufficiency (ICD-10: I50*, ICD-9: 428*, Social Insurance Institutions entitlement to reimbursement: 201)

Diabetes (ICD-10: E10*-E14*, ICD-9: 250*, Social Insurance Institutions entitlement to reimbursement: 103 use and cost of drugs ATC-DDD: A10A*, A10B*)

Cancer (ICD-10: C00*-C99*, D00*-D09*, ICD-9: 140*-208*, Social Insurance Institutions entitlement to reimbursement: 115, 116, 117, 128, 130, 180, 184, 185, 189, 311, 312, 316, use and cost of drugs ATC L01* except L01BA01)

COPD and asthma (ICD-10: J44*-J46*, ICD-9: 4912*, 496*, 493*, Social Insurance Institutions entitlement to reimbursement: 203, use and cost of drugs ATC: R03*)

Depression (ICD-10: F32*-F34*, ICD-9: 2960*, 2961*, 2069*, use and cost of drugs ATC: N06A*)

Parkinson's disease (ICD-10: G20*, ICD-9: 332*, Social Insurance Institutions entitlement to reimbursement: 110, use and cost of drugs ATC: N04B*)

Dementia (ICD-10: F00*-F03*, G30*, ICD-9: 290*, 3310*, Social Insurance Institutions entitlement to reimbursement: 307, use and cost of drugs ATC: N06D*)

Kidney insufficiency (ICD-10: N18*, ICD-9: 585*, Social Insurance Institutions entitlement to reimbursement: 137)

Mental disorders (ICD-10: F20*-F31*, ICD-9: 295*-298*, except 2960*, 2961*, Social Insurance Institutions entitlement to reimbursement: N05A* except N05AB04 and N05AB01 and there is no dementia)

Table 5. The average length of stay and the number of days saved if patients were treated in hospitals with the shortest length of stay

Year	Group	LOS	N	Difference in LOS	Days saved
1998	1	10.06	233	0.35	82
	2	10.52	1,395	0.81	1,130
	3	9.05	1,145	-0.66	-756
	4	9.71	90	–	–
	In total		2,863		456
1999	1	9.80	227	0.59	134
	2	10.01	1,664	0.8	1,331
	3	8.85	953	-0.36	-343
	4	9.21	239	–	–
	In total		3,083		1,122
2000	1	9.37	388	1.50	582
	2	9.81	1,452	1.94	2,817
	3	8.82	932	0.95	885
	4	7.87	588	–	–
	In total		3,360		4,284
2001	1	8.65	493	0.92	454
	2	9.66	1,386	1.93	2,675
	3	8.57	899	0.84	755
	4	7.73	776	–	–
	In total		3,554		3,884
2002	1	8.34	449	1.21	543
	2	9.15	1,647	2.02	3,327
	3	7.76	1,207	0.63	760
	4	7.13	574	–	–
	In total		3,877		4,630
2003	1	7.17	315	1.08	340
	2	8.58	1,358	2.49	3,381
	3	7.93	988	1.84	1,818
	4	6.09	1,675	–	–
	In total		4,336		5,539
2004	1	7.22	346	1.34	464
	2	8.46	1,181	2.58	3047
	3	7.38	1,059	1.50	1,589
	4	5.88	1,527	–	–
	In total		4,113		5,100
2005	1	6.84	308	1.35	416
	2	7.63	1,508	2.14	3,227
	3	6.65	951	1.16	1,103
	4	5.49	2,313	–	–
	In total		5,080		4,746
1998–2005					29,761

LOS: annual mean length of stay (surgical treatment period) in days; N: number of patients; Difference in LOS: difference between the shortest length of stay and that of other hospital groups in days; Days saved: number of days saved if patients were operated in hospitals with the shortest length of stay (days saved = difference in LOS multiplied by N). In 1998 and 1999, the average LOS was shorter in group 3 than in group 4. This is why “Difference in LOS” and “Days saved” have negative values in the Table.

Table 6a. Unadjusted odds ratios for unscheduled re-admissions within 14 and 42 days, and for dislocations, reoperations, and infections

	Re-admsissions 14 days		Re-admsissions 42 days		Dislocations		Reoperations		Infections
Groups	OR	95% WCI	OR	95% WCI	OR	95% WCI	OR	95% WCI	OR	95% WCI
2 vs. 1	0.9	0.8–1.1	0.9	0.8–1.0	0.9	0.7–1.2	1.1	0.9–1.3	1.0	0.7–1.6
3 vs. 1	1.0	0.9–1.2	1.0	0.8–1.1	0.7	0.6–0.9	1.0	0.8–1.2	0.9	0.6–1.5
4 vs. 1	1.2	1.0–1.4	1.1	1.0–1.3	0.8	0.6–1.0	0.7	0.5–0.9	0.8	0.5–1.3

OR: odds ratio; 95% WCI: 95% Wald confidence interval.

See Methods for explanation of groups.

Table 6b. Adjusted odds ratios for unscheduled re-admissions within 14 and 42 days, and for dislocations, reoperations, and infections

	Re-admsissions 14 days		Re-admsissions 42 days		Dislocations		Reoperations		Infections
Groups	OR	95% WCI	OR	95% WCI	OR	95% WCI	OR	95% WCI	OR	95% WCI
2 vs. 1	0.9	0.8–1.1	0.9	0.8–1.0	0.9	0.7–1.1	1.0	0.8–1.3	1.0	0.6–1.6
3 vs. 1	1.0	0.9–1.2	0.9	0.8–1.1	0.7	0.6–0.9	0.9	0.8–1.2	0.9	0.6–1.4
4 vs. 1	1.2	1.0–1.4	1.1	1.0–1.2	1.1	0.9–1.4	0.9	0.7–1.1	0.8	0.5–1.4

OR: odds ratio; 95% WCI: 95% Wald confidence interval.

See Methods for explanation of groups.