Infection after primary hip arthroplasty

Figures & data

Number of primary THAs and HAs (red squares) included in the NOIS, the NAR, and the NHFR, including number of arthroplasties with missing data on the confounders and incomplete 30–day and 1–year follow–up.

Table 1. Distribution of the assessed risk factors in the registers: THAs and HAs included from the Norwegian Surveillance System for Healthcare Associated Infections (NOIS), THAs included from in the Norwegian Arthroplasty Register (NAR) and HAs included from in the Norwegian Hip Fracture Register (NHFR).

	Total hip arthroplasty		Hemiarthroplasty
Register	NOIS	NAR	NOIS	NHFR
Number of procedures	5,540	31,086	1,416	10,972
Risk factor %
Agegroup (years)
<60	19	20	2	1
60–69	31	30	4	5
70–79	34	34	22	24
80–89	15	15	56	54
≥90	1	1	16	15
Sex
female	66	67	74	74
male	34	33	26	26
ASA score
1	18	29	2	5
2	65	52	42	35
≥3	17	19	56	60
Duration of surgery (Min)
<60	6	7	19	22
60–89	41	40	50	47
90–119	33	35	22	24
≥120	19	19	8	8
Type of surgery
emergency	3	2	74	86
planned	97	98	26	14
Method of fixation
cemented	64	65	81	81
uncemented	16	16	19	19
hybrid	20	18
NNIS index
0	63	64	32	31
1	32	31	54	56
≥2	5	5	14	13

Table 2. 1-year incidence of SSI and reoperation after primary arthroplasties as reported to the Norwegian Surveillance System for Healthcare Associated Infections (NOIS) and 1-year incidence of revisions due to infection after THAs as reported to the Norwegian Arthroplasty Register (NAR) and after HAs as reported to the Norwegian Hip Fracture Register (NHFR)

Total hip arthroplasty 1–year incidence	Hemiarthroplasty 1–year incidence	Register^a Endpoint
NOIS
Sugical Site Infection	3.0% (167/5,540)	7.3% (103/1,416)
Superficial SSI	1.7% (94/5,540)	2.2% (31/1,416)
Deep SSI	1.3% (73/5,540)	5.1% (72/1,415)
SSI reoperated	1.0% (58/5,540)	3.6% (51/1.416)
NAR / NHFR
Revision due to infection	0.7% (182/24,512)	1.5% (128/8,262)

^a The NOIS and the NAR/NHFR represents different selections of cases

Table 3. Risk factors for infection after THA: Adjusted risk of surgical site infection (SSI) after primary THAs in the Norwegian Surveillance System for Healthcare Associated Infections (NOIS), and adjusted risk of revision due to infection in the Norwegian Arthroplasty Register (NAR) for different risk factors. Each risk factor was adjusted for the other risk factors in the table except NNIS index

Total hip arthroplasty
Register: Number infected / included:	NOIS 167 / 5,540 (3.0%)						NAR 236 / 31,086 (0.8%)
Risk factor	A	B	C	D	E	F	G	H	I	J	K	L
Age group (years)
< 60	1,067	23	1			2.4	6,114	34	1			0.4
60–69	1,740	46	1.2	0.7–2.1	0.5	2.7	9,320	61	1.3	0.8–1.9	0.3	0.4
70–79	1,882	59	1.4	0.8–2.4	0.2	3.3	10,703	95	1.7	1.1–2.6	0.02	0.6
80–89	816	36	1.9	1.1–3.5	0.03	4.2	4,766	45	1.8	1.1–3.0	0.02	0.8
≥90	35	3	3.8	1.1–13	0.04	7.4	183	1	1.0	0.1–7.4	1.0	0.5
Sex
female	3,676	103	1			2.7	20,922	113	1			0.4
male	1,864	64	1.3	0.9–1.8	0.1	3.6	10,164	123	2.4	1.8–3.1	<0.001	1.0
ASA score
1	1,010	18	1			2.1	8,964	46	1			0.4
2	3,608	109	1.5	0.9–2.5	0.1	3.1	16,148	125	1.5	1.1–2.2	0.02	0.6
≥3	922	40	1.9	1.0–3.4	0.04	4.1	5,974	65	2.0	1.3–2.9	0.001	0.7
Duration of surgery (min)
<60	357	20	2.4	1.4–4.0	0.001	6.8	2,045	15	1.0	0.6–1.8	0.9	0.6
60–89	2,294	56	1			2.4	12,427	84	1			0.5
90–119	1,822	59	1.3	0.9–1.9	0.1	3.2	10,745	84	1.1	0.8–1.5	0.5	0.5
≥120	1,067	32	1.2	0.8–1.9	0.4	3.2	5,869	53	1.3	0.9–1.8	0.2	0.5
Type of surgery
emergency	183	10	1.8	0.9–3.4	0.08	6.6	609	9	2.2	1.1–4.3	0.02	1.3
planned	5,357	157	1			2.9	30,477	227	1			0.5
Method of fixation
cemented	3,547	111	1			2.9	20,308	159	1			0.5
unemented	902	25	1.0	0.7–1.7	0.8	3.5	5,110	43	1.5	1.0–2.2	0.03	0.8
hybrid	1,091	31	1.1	0.7–1.7	0.7	3.4	5,668	34	1.1	0.7–1.6	0.7	0.6
NNIS index ^a
0	3,480	94	1			2.8	19,729	129	1			0.5
1	1,784	64	1.3	0.9–1.7	0.2	3.8	9,760	87	1.3	1.0–1.7	0.08	0.6
≥2	267	9	1.0	0.5–2.0	1.0	3.5	1,597	20	1.7	1.1–4.4	0.02	0.6

A Number of primary arthroplasties included

B Number of SSIs

C Adjusted risk of SSI

D 95% CI

E P-value

F Adjusted 1–year SSI percent

G Number of primary THAs included

H Number of revisions due to infection

I Adjusted risk of revision due to infection

J 95% CI

K P-value

L Adjusted 1–year revision percent

^a Adjusted for sex, age, type of surgery and method of fixation

Table 4. Risk factors for infection after HA: Adjusted risk of surgical site infection (SSI) after primary HAs in the Norwegian Surveillance System for Healthcare Associated Infections (NOIS), and adjusted risk of revision due to infection in the Norwegian Hip Fracture Register (NHFR) for different risk factors. Each risk factor was adjusted for the other risk factors in the table except NNIS index

Hemiarthroplasty
Register: Number infected / included:	NOIS 103 / 1,416 (7.3%)						NHFR 167 / 10,972 (1.5%)
Risk factor	A	B	C	D	E	F	G	H	I	J	K	L
Age group (years)
<60	22	1	0.8	0.1–5.8	0.8	4.0	145	7	3.6	1.6–7.8	0.001	5.1
60–69	51	4	1.2	0.4–3.4	0.7	6.7	566	8	1.0	0.5–2.1	1.0	1.4
70–79	318	19	1.0	0.6–1.6	0.9	6.0	2,634	41	1.1	0.8–1.7	0.5	1.6
80–89	796	54	1			6.2	5,946	80	1			1.4
≥90	229	25	1.6	1.0–2.6	0.06	8.7	1,681	31	1.4	1.0–2.2	0.08	2.1
Sex
Female	1,053	82	1			7.0	8,085	115	1			1.5
Male	363	21	0.8	0.5–1.3	0.3	4.8	2,887	52	1.3	1.0–1.9	0.08	2.0
ASA score
1	25	0					523	7	1			1.3
2	592	43	1			7.3	3,854	58	1.2	0.5–2.6	0.6	1.5
≥3	799	60	1.1	0.7–1.6	0.8	8.2	6,595	102	1.3	0.6–2.8	0.5	1.6
Duration of surgery (min)
<60	271	26	1.9	1.0–3.9	0.06	7.8	2,371	47	1.4	0.9–2.0	0.1	2.2
60–89	709	53	1.7	0.9–3.2	0.08	7.2	5,152	77	1			1.6
90–119	317	13	1			3.7	2,598	30	0.8	0.5–1.2	0.2	1.2
≥120	119	11	2.2	1.0–4.9	0.06	8.0	851	13	0.9	0.5–1.7	0.7	1.4
Type of surgery
Emergency	1,041	81	1.3	0.8–2.0	0.8	6.9	9,459	137	0.8	0.5–1.1	0.2	1.5
Planned	375	22	1			5.4	1,513	30	1			2.0
Method of fixation
Cemented	1,141	74	1			6.0	8,849	127	1			1.5
Unemented	275	29	1.4	0.9–2.3	0.1	8.5	2,123	40	1.2	0.8–1.7	0.4	1.8
NNIS index ^a
0	452	32	1			7.2	3,436	54	1			1.6
1	759	56	1.1	0.7–1.7	0.7	8.2	6.113	92	1.0	0.7–1.4	1.0	1.6
≥2	190	15	1.2	0.6–2.2	0.6	7.9	1.423	21	0.9	0.6–1.6	0.8	1.5

A–L: See table 3.

^a Adjusted for sex, age, type of surgery and method of fixation