Risk factors for prosthetic joint infections following total hip arthroplasty based on 33,337 hips in the Finnish Arthroplasty Register from 2014 to 2018

Figures & data

Table 2. Univariable analysis of possible risk factors for revision for PJI

Variable	Hazard ratio (95% CI)
Sex (reference male)
Female	0.6 (0.5–0.7)
ASA class (reference ASA I)
ASA II	1.7 (1.1–2.7)
ASA III–IV	2.5 (1.6–3.9)
BMI (reference BMI 21–25)
≤ 20	0.7 (0.2–2.1)
26–30	1.3 (0.9–1.8)
31–35	2.3 (1.7–3.3)
> 35	5.0 (3.5–7.1)
Preoperative diagnosis (reference primary osteoarthritis)
Fracture	1.0 (0.6–1.7)
Inflammatory arthritis	1.3 (0.7–2.7)
Other	1.6 (1.1–2.2)
Intraoperative bleeding (reference < 500 mL)
> 500 mL	1.5 (1.2–1.9)
Anesthesia (spinal)(reference no)
Yes	0.6 (0.4–0.8)
Anesthesia (epidural)(reference no)
Yes	2.2 (1.4–3.5)
Anesthesia (general)(reference no)
Yes	1.7 (1.2–2.3)
Antithrombotic prophylaxis (reference enoxaparin)
Warfarin	2.7 (0.9–8.4)
Rivaroxaban	0.8 (0.6–1.0)
Tinzaparin	0.6 (0.3–1.2)
Not used	2.8 (1.5–5.3)
Other	0.6 (0.3–1.2)
Bearing couple (reference metal-on-UHXLPE)
Ceramic-on-ceramic	0.4 (0.2–0.7)
Ceramic-on-UHXLPE	0.9 (0.6–1.1)
Ceramized metal-on-UHXLPE	0.9 (0.5–1.5)
Other	0.1 (0.0–0.6)
Femoral head size (reference 32 mm)
28 mm	2.8 (1.2–6.5)
36 mm	1.9 (1.4–2.6)
> 36 mm	2.1 (0.7–5.7)

UHXLPE = ultra-highly crosslinked polyethylene.

Figure 1. A directed acyclic graph (DAG) was constructed under the following assumptions:

1. THA “revision for infection” is dependent on “patient age,” “sex,” ‘bilaterality,” “ASA class,” “BMI,” “diagnosis,” “hospital volume,” “education of surgery,” “bleeding,” “duration,” “intraoperative complications,” “previous operations,” “antimicrobial incise drape,” “anesthesia,” “antibiotic prophylaxis,” and type of THA “fixation.” Choice of “side,” “education of assistant,” “surgical approach,” “bearing couple,” antithrombotic prophylaxis,” “anticoagulant medications,” and “femoral head size” are not expected to affect “revision for infection” due to clinical suspicion.

2. “Fixation” is dependent on “age” and “sex” because older and female patients have probably received a cemented or hybrid THA due to their poorer bone quality. “Bearing couple” may be dependent on age because surgeons have probably chosen ceramic-on-ceramic bearing couple in younger patients. “Bearing couple” may also be dependent on ASA class for the same reason. ASA class is partly dependent on age by definition. “Bilaterality” is dependent on “age” and “ASA class” because both hips are seldom operated on in elderly or high ASA class patients.

3. “BMI” may be affected by “duration” and “intraoperative complications” due to more difficult operation with high BMI. “Duration” may be dependent on “education of surgery” due to experience factor. “Bleeding,” “duration,” and “previous operations” may be dependent on clinical basis.

4.“Anesthesia” is dependent on “ASA class” and “age” because general anesthesia is usually avoided in elderly patients.

Table 4. Multivariable analysis for revision for PJI

Variable	Hazard ratio (95% CI)
ASA class (reference ASA I)
ASA II	2.0 (1.3–3.2)
ASA III–IV	3.2 (2.0–5.1)
Intraoperative bleeding (reference < 500 mL)
> 500 mL	1.4 (1.1–1.7)
Anesthesia (spinal)(reference no)
Yes	0.6 (0.4–0.8)
Anesthesia (epidural)(reference no)
Yes	2.1 (1.3–3.4)
Anesthesia (general)(reference no)
Yes	1.6 (1.2–2.3)
Bearing couple (reference metal-on-UHXLPE)
Ceramic-on-ceramic	0.4 (0.2–0.7)
Ceramic-on-UHXLPE	0.9 (0.7–1.2)
Ceramized metal-on-UHXLPE	0.9 (0.5–1.6)
Other	0.1 (0.0–0.6)
Fixation (reference cementless)
Cemented	1.1 (0.7–1.7)
Hybrid	1.3 (0.9–1.7)
Reverse hybrid	0.9 (0.5–1.5)

UHXLPE = ultra-highly crosslinked polyethylene.

ASA class was adjusted for age. Intraoperative bleeding was adjusted for BMI, previous contributing operations, complications during surgery, and level of education (surgeon). Spinal, epidural, and general anesthesia and bearing couples were adjusted for age and ASA class. Fixation was adjusted for sex and age.

Table 5. Uni- and multivariable analyses divided to suitable time intervals for the duration, simultaneous bilateral operation, anesthesia (LIA), and complications during surgery (fracture) due to not fulfilling the assumption of proportional hazards

	Univariable hazard ratio (95% CI)	Multivariable hazard ratio (95% CI)
Duration (minutes)(reference 45–59)
Time interval 0–3 weeks
< 45	1.0 (0.5–2.3)	1.1 (0.5–2.5)
60–89	1.4 (0.8–2.3)	1.3 (0.8–2.2)
90–120	1.4 (0.8–2.5)	1.3 (0.7–2.3)
> 120	3.3 (1.8–6.0)	3.0 (1.6–5.6)
Time interval > 3 weeks
< 45	1.2 (0.4–3.7)	1.1 (0.3–3.4)
60–89	1.1 (0.5–2.2)	1.0 (0.5–2.2)
90–120	1.4 (0.6–3.1)	1.4 (0.6–3.1)
> 120	0.6 (0.2–1.5)	0.5 (0.2–1.4)
Simultaneous bilateral operation
Time interval
0–3 weeks	2.2 (1.2–4.2)	2.6 (1.4–4.9)
> 3 weeks	0.3 (0.07–1.0)	0.3 (0.07–1.0)
Anesthesia (LIA)
Time interval
0–3 weeks	0.7 (0.5–1.1)	0.7 (0.5–1.1)
> 3 weeks	1.5 (0.9–2.6)	1.5 (0.8–2.5)
Complications during surgery (fracture)
Time interval
0–5 weeks	0.3 (0.04–2.2)	0.4 (0.05–2.6)
> 5 weeks	8.8 (0.9–86.2)	8.6 (0.9–84)

In the multivariable analysis simultaneous bilateral operations and local infiltrative anesthesia were adjusted for age and ASA classification. Complication during surgery (fracture) was adjusted for BMI. Duration was adjusted for previous contributing operations, level of education (surgeon), intraoperative bleeding, BMI, and complications during surgery.