The risk of revision due to dislocation after total hip arthroplasty depends on surgical approach, femoral head size, sex, and primary diagnosis

Figures & data

Table 1. Age at index THA

Age group	n	%
< 50	2,513	3
50–59	8,851	11
60–75	43,117	55
> 75	23,617	30

Table 2. Diagnosis at index THA

Diagnosis	n ^a	%
pOA	64,987	83
Fracture	7,785	10
FHN	2,035	3
Inflammatory	1,486	2
Pediatric	1,249	2
Other	550	1

pOA: osteoarthritis;

FHN: femoral head necrosis;

^a Missing data in 6 cases.

Table 3. Head diameters inserted at index THA

Diameter, mm	n	%
22	1,394	2
28	57,194	73
32	16,451	21
36	2,772	4
Dual-mobility	287	0.4

Table 4. Head size by diagnosis or by surgical approach

	22 mm	28 mm	32 mm	36 mm	Dual-mobility
Diagnosis
pOA	1,102	47,890	13,717	2,210	68
Inflammatory	28	1,144	226	85	3
Fracture	146	5,530	1,764	171	174
Pediatric	64	845	142	188	10
FHN	46	1,387	469	109	24
Other	8	392	133	9	8
Surgical approach
Direct lateral	1,191	25,696	6,929	1,450	194
Posterior	1,92	30,856	9,464	1,299	93
MIS	11	642	58	23	0

pOA: osteoarthritis;

FHN: femoral head necrosis;

MIS: minimally invasive approaches.

Table 5. Cup types inserted during index THA

Cup type	n	%
Lubinus	33,754	43
Hooded Duration	7,802	10
Charnley Elite	7,165	9
ZCA	6,854	9
Trilogy	4,167	5
Exeter Duration	4,088	5
Marathon	3,102	4
FAL	2,947	4
Reflection	2,241	3
Trident HA	1,705	2
Reflection XLPE	1,601	2
Charnley	1,265	2
Allofit	1,120	1
Avantage	287	0.3

Table 6. Cox regression analysis of risk factors for revision due to dislocation a

	Unadjusted		Adjusted		p-value
	RR	95% CI	RR	95% CI
Head diameter
28 mm ^b	1		1
22 mm	1.8	(1.1–2.9)	2.0	(1.2–3.3)	0.01
32 mm	0.8	(0.6–1.1)	0.8	(0.6–1.1)	0.1
36 mm	0.7	(0.3–1.3)	0.7	(0.3–1.4)	0.3
Dual-mobility	0.9	(0.1–6.1)	0.4	(0.1–2.9)	0.4
Sex
Female ^c	0.9	(0.8–1.1)	0.8	(0.7–1.0)	0.03
Diagnosis
pOA ^b, ^d	1		1
Inflammatory	1.0	(0.5–2.3)	1.0	(0.4–2.3)	1.0
Fracture	3.7	(2.9–4.7)	3.9	(3.1–5.0)	< 0.001
Pediatric	1.5	(0.7–3.1)	1.5	(0.7–3.2)	0.3
FHN ^d	3.6	(2.4–5.4)	3.7	(2.5–5.5)	< 0.001
Other	5.4	(2.7–10.9)	5.6	(2.8–11.4)	< 0.001
Age
< 50 ^b	1		1
50–59	0.9	(0.5–1.7)	1.1	(0.6–2.0)	0.8
60–75	0.8	(0.5–1.4)	0.9	(0.5–1.6)	0.7
> 75	1.2	(0.7–2.0)	1.1	(0.6–2.0)	0.6
Approach
Direct lateral ^b	1		1
Posterior	1.2	(1.0–1.4)	1.3	(1.1–1.7)	0.01
MIS ^d	3.3	(1.8–5.9)	4.2	(2.3–7.7)	< 0.001

^a Unadjusted and adjusted risk ratios (RRs) were calculated with 95% CI using a Cox proportional hazards model. p values refer to adjusted RR.

^b Reference category with RR = 1.

^c Reference category was male with RR = 1.

^d Abbreviations, see Table 4.

Figure 1. Frequency of revision surgery due to dislocation plotted against time elapsed after the index procedure.

Figure 2. Survival functions with the endpoint “revision due to dislocation” by surgical approach. A Cox proportional hazards model was used in order to calculate adjusted survival functions with 95% CI (dotted lines) for the 3 surgical approaches lateral (n = 35,460), posterior (n = 41,904), and minimally invasive (n = 734). The endpoint was revision due to dislocation. Survival functions were adjusted for the mean of the covariates gender, age, primary diagnosis, and femoral head size. The lateral approach was associated with the lowest risk of revision due to dislocation.

Figure 3. Survival functions for patients with a femoral neck fracture with the endpoint “revision due to dislocation” by femoral head size. A Cox proportional hazards model was used to calculate adjusted survival functions with 95% CI (dotted lines) for patients with a femoral head fracture, for the femoral head sizes 22 mm (n = 1,394) and 28 mm (n = 57,194), and dual-mobility cups (n = 287). The endpoint was revision due to dislocation. Survival functions were adjusted for the mean of the covariates gender, age, and surgical approach but fixed for the diagnosis femoral neck fracture. Dual-mobility cups were associated with the lowest risk of revision due to dislocation.