Low-molecular-weight heparin for hip fracture patients treated with osteosynthesis: should thromboprophylaxis start before or after surgery? An observational study of 45,913 hip fractures reported to the Norwegian Hip Fracture Register

Figures & data

Figure 1. Flow chart for patients included in the study.

Figure 2. Timeline demonstrates the development in start of thromboprophylaxis from 2005 to 2016 for the patients observed in the study (n = 45,913). Hip fracture patients operated with osteosynthesis with known start of LMWH thromboprophylaxis (dalteparin or enoxaparin).

Table 1. Patients included in the study

	Start of prophylaxis
Factor	Preoperative	Postoperative
Hip fractures with osteosynthesis, n (%)	20,563 (45)	25,350 (55)
Mean duration of surgery^a	51 (33)	51 (34)
Mean age at fracture (years) (SD)	80 (12)	80 (13)
Women (%)	69	69
ASA groups, n (%)
ASA 1	1,363 (6.6)	1,857 (7.3)
ASA 2	7,015 (34)	8,793 (35)
ASA 3	10,362 (50)	12,860 (51)
ASA 4	1,475 (7)	1,520 (6)
ASA 5	34 (0.2)	27 (0.1)
Missing	314 (1.5)	293 (1.2)
Type of surgery^b
Screws, n (%)	6,781 (45)	8,204 (55)
Mean duration of surgery^a	26 (14)	26(14)
Hip compression screw, n (%)	9,939 (46)	11,825 (54)
Mean duration of surgery^a	62 (31)	61 (30)
Intramedullary nail, n (%)	3,843 (42)	5,321 (58)
Mean duration of surgery^a	66 (38)	66 (41)

a Values are minutes (SD)

b Screws include operations with Olmed screws. Hip compression screws include operations with a dynamic hip screw (DHS) with or without a support plate. Intramedullary nails include long and short nails with or without the use of an interlocking screw.

Figure 3. Postoperative mortality for hip fracture patients treated with osteosynthesis.

Table 2. Mortality and risk of reoperation 180 days postoperatively after osteosynthesis for hip fracture

		Start of prophylaxis, n (%)
	Total, n (%)	Preoperative	Postoperative	RR^a	95% CI	p-value
7 days postoperatively (n = 45,913)
Mortality	1,050 (2.3)	481 (2.3)	569 (2.2)	1.02	0.90–1.16	0.7
Reoperations	190 (0.4)	76 (0.4)	114 (0.4)	1.18	0.88–1.58	0.3
Reoperation due to infection	5 (0.0)	1 (0.0)	4 (0.0)	3.50	0.38–32.0	0.3
Reoperation due to hematoma	9 (0.0)	3 (0.0)	6 (0.0)	1.86	0.46–7.49	0.4
30days postoperatively (n = 45,913)
Mortality	3,534 (7.7)	1,606 (7.8)	1,928 (7.6)	1.05	0.98–1.12	0.2
Reoperations	627 (1.4)	275 (1.3)	352 (1.4)	1.12	0.95–1.32	0.2
Reoperation due to infection	66 (0.1)	30 (0.1)	36 (0.1)	0.88	0.54–1.44	0.6
Reoperation due to hematoma	18 (0.0)	6 (0.0)	12 (0.0)	2.04	0.71–5.82	0.2
180 days postoperatively (n = 45,913)
Mortality	8,751 (19)	4,049 (20)	4,702 (19)	1.01	0.97–1.06	0.6
Reoperations	2,067 (4.5)	966 (4.7)	1,101 (4.3)	0.99	0.90–1.08	1.0
Reoperation due to infection	115 (0.3)	49 (0.2)	66 (0.3)	1.02	0.70–1.49	0.9
Reoperation due to hematoma	19 (0.0)	6 (0.0)	13 (0.1)	2.18	0.78–6.18	0.1

a Cox relative revision risk (RR) (with preoperative start of prophylaxis as reference) is given with adjustments for possible influences of sex, ASA class, age group of the patient at surgery, duration of surgery, and year of surgery.

Figure 4. Risk of reoperation for hip fracture patients treated with osteosynthesis.

Table 3. Risk of intraoperative bleeding complications after osteosynthesis (n = 45,913) in hip fractures receiving screws (n = 14,985), hip compression screws (n = 21,764), or medullary nails (n = 9,164)

	Intraoperative bleeding, n (%)				Risk	Risk
Treatment	Preop. start	Postop. start	RR^a (95% CI)	p-value	Preop.– Postop.	difference	NNH^b
Osteosynthesis	118 (0.6)	90 (0.4)	0.67 (0.51–0.90)	0.007	0.0060 – 0.0037	0.0023	434
Screws	3 (0.0)	2 (0.0)	0.43 (0.07–2.68)	0.4	0.0004 – 0.0002	0.0002	4,940
HCS	102 (1.0)	71 (0.6)	0.64 (0.47–0.87)	0.004	0.0108 – 0.0063	0.0045	222
Intramedullary nail	13 (0.3)	17 (0.3)	1.06 (0.50–2.26)	0.9	0.0036 – 0.0034	0.0002	4,684

a See Table 2.

b NNH: Number of patients treated with preoperative start of LMWH in order to cause one intraoperative bleeding complication because of preoperative LMWH start compared with postoperative LMWH start if there is a direct causal effect. The NNH was calculated as an inverse value of the risk difference (RD) between the methods [1/(risk preoperative start–risk postoperative start)].

Table 4. Mortality and risk of reoperation 180 days postoperatively after osteosynthesis in hip fractures receiving screws, hip compression screw, or medullary nails

		Start of prophylaxis, n (%)
	Total, n (%)	Preoperative	Postoperative	RR^a	95% CI	p-value
Screws (n = 14,985)
Mortality	2,776 (19)	1,353 (21)	1,423 (18)	1.01	0.92–1.08	1.0
Reoperations	1,226 (8.2)	593 (9.1)	633 (8.0)	0.97	0.86–1.09	0.6
Reoperation due to infection	20 (0.1)	11 (0.2)	9 (0.1)	0.76	0.30–1.9	0.6
Reoperation due to hematoma	4 (0.0)	0 (0.0)	4 (0.1)	–	–	–
Hip compression screw (n = 21,764)
Mortality	4,264 (20)	1,942 (20)	2,322 (20)	1.01	0.98–1.1	0.2
Reoperations	580 (2.7)	266 (2.7)	314 (2.7)	0.97	0.82–1.2	0.7
Reoperation due to infection	77 (0.4)	35 (0.4)	42 (0.4)	0.92	0.58–1.4	0.7
Reoperation due to hematoma	11 (0.1)	4 (0.0)	7 (0.1)	1.9	0.49–7.6	0.3
Intramedullary nail (n = 9,164)
Mortality	1,711 (19)	754 (20)	957 (18)	0.96	0.87–1.1	0.4
Reoperations	261 (2.8)	107 (2.8)	154 (2.9)	1.2	0.91–1.5	0.2
Reoperation due to infection	18 (0.2)	3 (0.1)	15 (0.3)	3.7	1.04–13	0.04
Reoperation due to hematoma	4 (0.1)	2 (0.1)	2 (0.0)	1.2	0.14–9.8	0.9

a See Table 2.