High body mass index is associated with increased risk of implant dislocation following primary total hip replacement: 2,106 patients followed for up to 8 years

Figures & data

Time to an event of implant dislocation from 0 to 3 years after primary THR, by BMI and smoking status.

Table 1.  Characteristics of 2,106 patients who underwent total hip replacement. Distribution of variables by survival status as of December 31, 2004

	All subjects in the cohort	Implant dislocation	Reoperation	Hip fracture or THR in the contralateral hip	Death or emigration	Still at risk
No. (% ^a) in the cohort	2,106 (100)	53 (2.5)	39 (1.8)	294 (14)	120 (5.7)	1,600 (76)
Body mass index category
18.5–24.9	681 (100)	8 (1.2)	10 (1.5)	91 (13)	35 (5.1)	537 (79)
25–29.9	1,132 (100)	32 (2.8)	20 (1.8)	159 (14)	71 (6.3)	850 (75)
30+^b	272 (100)	11 (4.0)	9 (2.9)	43 (16)	14 (5.2)	196 (72)
Missing data	21 (100)	2 (10)	1 (5)	1 (5)	0 (0.0)	17 (81)
Age category
30–54	239 (100)	3 (1.3)	4 (1.7)	36 (15)	4 (1.7)	192 (80)
55–59	324 (100)	9 (2.8)	6 (1.9)	61 (19)	5 (1.5)	243 (75)
60–64	387 (100)	10 (2.6)	7 (1.8)	52 (13)	9 (2.3)	309 (80)
65–69	391 (100)	9 (2.3)	5 (1.3)	49 (13)	21 (5.4)	307 (79)
70–74	370 (100)	9 (2.2)	7 (1.9)	50 (14)	26 (7.0)	279 (75)
75–79	244 (100)	7 (2.9)	6 (2.5)	30 (12)	25 (10)	176 (72)
80+	151 (100)	7 (4.6)	4 (2.7)	16 (11)	30 (20)	94 (62)
Calendar period
1997–1999	659 (100)	20 (3.0)	18 (2.7)	125 (19)	73 (11)	423 (64)
2000–2004	1,447 (100)	33 (2.3)	21 (1.5)	169 (12)	47 ( 3.2)	1,177 (81)
Overall tobacco smoking status
Never- smokers	833 (100)	20 (2.4)	13 (1.5)	13 (1.5)	34 (4.1)	642 (77)
Previous smokers	567 (100)	9 (1.6)	17 (3.0)	69 (12)	39 (6.9)	433 (77)
Current smokers	706 (100)	24 (3.4)	9 (1.3)	101 (14)	47 (6.6)	525 (74)
Pack years of tobacco use
Never-smokers	833 (100)	20 (2.4)	13 (1.5)	13 (1.5)	34 (4.1)	642 (77)
0–19.9	887 (100)	23 (2.6)	16 (1.8)	122 (14)	49 (5.5)	677 (76)
20+^c	303 (100)	10 (3.3)	10 (3.3)	40 (13)	31 (10)	212 (70)
Missing data	83 (100)	0 (0.0)	0 (0.0)	8 (10)	6 (7.2)	69 (83)
Fixation principle
Non-cemented or hybrid	310 (100)	5 (1.6)	4 (1.3)	29 (9.3)	4 (1.3)	268 (87)
Cemented	1,796 (100)	48 (2.7)	35 (1.9)	265 (15)	116 (6.5)	1,332 (74)

^a All percentages are row percentages.

^b Maximum BMI was 42.

^c Maximum pack years of tobacco smoking was 61.5.

Table 2.  Hazard ratios for implant dislocation from 0 to 3 years following primary THR, adjusted for age at time of surgery

	Hazard ratio	95 %CI	P-value
Body mass index category
<18.5–24.9	1	Ref	Ref
25–29.9	2.4	1.1–5.2	0.03
30+	3.6	1.4–8.9	0.006
Tobacco smoking status
Never-smokers	1	Ref	Ref
Previous smokers	0.72	0.32–1.6	0.4
Current smokers	1.7	0.89–3.1	0.1
Pack years of tobacco use
Never-smokers	1	Ref	Ref
0–19.9	1.2	0.66–2.3	0.5
20+	1.5	0.68–3.2	0.3

Table 3.  BMI, smoking status and the risk of implant dislocation from 0 to 3 years following primary THR. Multi-variable proportional hazards model

	Hazard ratio	95 %CI	P-value
Body mass index category ^a
<18.5–24.9	1	Ref	Ref
25–29.9	2.5	1.1–5.5	0.02
30+	3.7	1.5–9.3	0.005
Tobacco smoking status ^b
Never-smokers	1	Ref	Ref
Previous smokers	0.70	0.31–1.6	0.4
Current smokers	1.69	0.90–3.2	0.1
Pack years of tobacco use ^b
Never-smokers	1	Ref	Ref
0–19.9	1.22	0.65–2.3	0.5
20+	1.44	0.66–3.2	0.4

^aThe final model for BMI was adjusted for age, calendar period, smoking status, and fixation principle.

^b Each tobacco-related exposure variable was fitted separately. All final models were adjusted for age, calendar period, BMI, and fixation principle.