Uncemented cups with and without screw holes in primary THA: a Swedish Hip Arthroplasty Register study with 22,725 hips

Figures & data

Figure 1. Procedures not included in the final analysis.

Figure 2. Number of operations per year.

Table 1. Baseline characteristics of the study population

	Screw holes
	No n (%)	Yes n (%)	Totals n (%)	p-value a
Sex
Male	6,916 (56)	5,405 (52)	12,321 (54)	< 0.001
Female	5,438 (44)	4,966 (48)	10,404 (46)
Age
< 45	403 (3.3)	406 (3.9)	809 (3.6)	< 0.001
45–64	7,428 (60)	6,395 (62)	13,823 (61)
65–74	3,662 (30)	2,607 (25)	6,269 (28)
≥ 75	861 (7.0)	963 (9.3)	1,824 (8.0)
Side
Right	6,550 (53)	5,572 (54)	12,122 (53)	0.3
Left	5,804 (47)	4,799 (46)	10,603 (47)
Approach^b
Posterolateral	7,769 (63)	3,252 (31)	11,021 (49)	< 0.001
Direct lateral	4,016 (33)	7,008 (68)	11,024 (49)
Other	464 (3.8)	97 (0.9)	561 (2.5)
Type of stem:
Uncemented	10,580 (86)	8,715 (84)	19,295 (85)	0.001
Cemented	1,774 (14)	1,656 (16)	3,430 (15)
Cup coating
No HA	6,662 (54)	3,483 (34)	10,145 (45)	< 0.001
HA	5,692 (46)	6,888 (66)	12,580 (55)
Head size
28 mm	1,385 (11)	2,434 (24)	3,819 (17)	< 0.001
32 mm	7,585 (61)	7,128 (69)	14,713 (65)
36 mm	3,384 (27)	809 (7.8)	4,193 (19)
Head material
Metal	9,260 (75)	9,542 (92)	18,802 (83)	< 0.001
Ceramic	3,094 (25)	828 (8.0)	3,922 (17)
Sum	12,354 (100)	10,371 (100)	22,725 (100)

Distribution of possible confounding factors between cups with and without screw holes

a Pearson’s chi-square.

b Missing data in 119 cases.

Table 2. Number of procedures included per cup design, percentage per group, and median (range) follow-up time in years

	Without screw holes		With screw holes		Total
Cup design	n (%)	follow-up a	n (%)	follow-up a	n (%)	follow-up a
Regenerex	115 (1)	4.2 (0.1–7.8)	617 (6)	3.3 (0–9.6)	732 (3)	3.6 (0–9.6)
Pinnacle	1,993 (16)	3.1 (0–10.9)	758 (7)	2.2 (0–12.0)	2,751 (12)	2.9 (0–12.0)
Pinnacle Gription	2,916 (24)	1.2 (0–6.3)	448 (4)	0.9 (0–4.8)	3,364 (15)	1.2 (0–6.3)
Trident AD	1,055 (9)	6.3 (0–13.8)	760 (7)	5.3 (0–13.7)	1,815 (8)	6.0 (0–13.8)
Trident hemi	3,092 (25)	2.4 (0–11.1)	213 (2)	2.3 (0–9.8)	3,305 (15)	2.4 (0–11.1)
Tritanium	394 (3)	4.9 (0–8.1)	153 (1)	2.7 (0.1–8.7)	547 (2)	4.2 (0–8.7)
Continuum	2,294 (19)	2.7 (0–7.2)	1,215 (12)	3.1 (0–8.2)	3,509 (15)	2.9 (0–8.2)
Trilogy	495 (4)	7.8 (0–15.6)	6,207 (60)	6.9 (0–17.7)	6,702 (29)	7.0 (0–17.7)
Total	12,354 (100)	2.6 (0–15.6)	10,371 (100)	5.2 (0–17.7)	22,725 (100)	3.4 (0–17.7)

a Median (range) follow-up time in years

There was a significant difference in follow-up time between the groups (p < 0.001, ANOVA).

Table 4. Number of cups at risk of revision in cups with and without screw holes at 2 and 10 years after primary operation

	0 years	2 years	10 years
Without screw holes	12,354	7,228	347
Regenerex	115	85	0
Pinnacle	1,993	1,272	8
Pinnacle Gription	2,916	1,008	0
Trident AD	1,055	904	216
Trident Hemi	3,092	1,758	9
Tritanium	394	330	0
Continuum	2,294	1,430	0
Trilogy	495	441	114
With screw holes	10,371	7,984	1,499
Regenerex	617	450	0
Pinnacle	758	397	34
Pinnacle Gription	448	114	0
Trident AD	760	542	106
Trident Hemi	213	123	0
Tritanium	153	99	0
Continuum	1,215	777	0
Trilogy	6,207	5,482	1,359

Table 3. Survival after 2 and 10 years and hazard ratio for revision

Endpoint	2-year survival (95% CI)	10-year survival (95% CI)	Crude HR (0–2 years) (95% CI)	p-value	Adjusted HR (0–2 years) (95% CI)	p-value	Crude HR (0–10 years) (95% CI)	p-value	Adjusted HR (0–10 years) (95% CI)	p-value
Cup revision for aseptic loosening									0.9 (0.5–1.8)	0.8
Without screw holes	99.9 (99.8–99.9)	99.1 (98.6–99.5)	0.8 (0.4–1.7)	0.6	0.6 (0.2–1.8)	0.4	1.2 (0.7–2.1)	0.5	1.0 (ref)
With screw holes	99.9 (99.8–99.9)	99.5 (99.3–99.7)	1.0 (ref)		1.0 (ref)		1.0 (ref)
Cup revision for any reason									0.7 (0.5–0.9)	0.004
Without screw holes	98.6 (98.4–98.8)	96.5 (95.8–97.2)	0.8 (0.7–1.0)	0.09	0.6 (0.5–0.8)	0.002	1.0 (0.8–1.2)	0.7	1.0 (ref)
With screw holes	98.4 (98.2–98.7)	96.8 (96.3–97.2)	1.0 (ref)		1.0 (ref)		1.0 (ref)
Revision (cup or stem) for any reason									0.7 (0.6–0.8)	< 0.001
Without screw holes	98.0 (97.7–98.2)	95.0 (94.1–95.9)	0.9 (0.7–1.0)	0.09	0.6 (0.5–0.8)	0.001	1.0 (0.8–1.1)	0.6	1.0 (ref)
With screw holes	97.7 (97.4–98.0)	95.4 (94.9–95.9)	1.0 (ref)		1.0 (ref)		1.0 (ref)

The adjusted hazard ratio was calculated based on a Cox regression model with gender, age, surgical approach, type of stem fixation, cup coating, head size, head material, and cup design as covariates.

Number of cups at risk for revision in cups without/with screw holes was 12,354/10,371 at 0 years, 7,228/7,984 at 2 years and 3,47/1,499 at 10 years after primary operation.

Table 5. Hazard ratio for cup revision within 2 years for any reason

	No. of hips	No. of revisions	Crude HR (95% CI)	Adjusted HR (95% CI)	p-value
Screw holes:
Without screw holes	12,354	140	0.8 (0.7–1.0)	0.6 (0.5–0.8)	0.002
With screw holes	10,371	153	1.0 (ref)	1.0 (ref)
Sex
Male	12,321	190	1.6 (1.2–2.0)	1.6 (1.2–2.0)	< 0.001
Female	10,404	103	1.0 (ref)	1.0 (ref)
Age
< 45	809	13	1.2 (0.7–2.1)	1.1 (0.6–2.0)	0.7
45–64	13,823	186	1.0 (ref)	1.0 (ref)
65–74	6,269	76	0.9 (0.7–1.2)	1.0 (0.7–1.3)	0.7
> 75	1,824	18	0.8 (0.5–1.2)	0.9 (0.5–1.5)	0.7
Approach
Posterolateral	11,021	130	1.0 (ref)	1.0 (ref)
Direct lateral	11,024	159	1.2 (0.9–1.5)	1.0 (0.7–1.3)	0.9
Other	561	3	0.4 (0.1–1.3)	0.5 (0.1–1.5)	0.2
Unknown	119	1	0.6 (0.1–4.6)	0.9 (0.1–6.9)	0.9
Type of stem
Uncemented	19,295	269	1.0 (ref)	1.0 (ref)
Cemented	3,430	24	0.5 (0.3–0.8)	0.6 (0.4–1.0)	0.03
Cup coating
No HA	10,145	158	1.0 (ref)	1.0 (ref)
HA	12,580	135	0.6 (0.5–0.8)	0.7 (0.5–10.2)	0.2
Head size
28 mm	3,819	42	1.0 (ref)	1.0 (ref)
32 mm	14,713	202	1.4 (1.0–1.9)	1.1 (0.8–1.6)	0.6
36 mm	4,193	49	1.2 (0.8–1.8)	1.0 (0.6–1.7)	0.9
Head material
Metal	18,802	242	1.0 (ref)	1.0 (ref)
Ceramic	3,922	51	1.1 (0.8–1.5)	1.0 (0.7–1.5)	0.8
Cup design
Regenerex	732	13	1.6 (0.9–2.8)	1.1 (0.5–2.5)	0.7
Pinnacle	2,751	38	1.3 (0.9–1.9)	1.5 (0.9–2.5)	0.2
Pinnacle Gription	3,364	36	1.2 (0.8–1.7)	1.2 (0.6–2.5)	0.6
Trident AD	1,815	18	0.9 (0.5–1.5)	1.3 (0.7–2.2)	0.4
Trident Hemi	3,305	31	0.9 (0.6–1.4)	1.5 (0.9–2.5)	0.2
Tritanium	547	7	1.1 (0.5–2.4)	1.2 (0.4–3.0)	0.8
Continuum	3,509	72	1.9 (1.4–2.6)	1.8 (1.0–3.3)	0.06
Trilogy	6,702	78	1.0 (ref)	1.0 (ref)
Hospital
Frequent user	14,985	169	1.0 (ref)	1.0 (ref)
Intermediate user	6,482	105	1.4 (1.1–1.7)	1.5 (1.2–1.8)	0.001
Low-volume user	1,258	19	1.3 (0.9–2.0))	1.4 (0.9–2.1)	0.1

The adjusted hazard ratio was calculated based a Cox regression model with the following covariates: screw holes, gender, age, surgical approach, stem fixation, cup coating, head size, head material, and cup design.