Effects of hydroxyapatite coating of cups used in hip revision arthroplasty

Figures & data

Table 1. Type of diagnosis at primary THA within the 2 groups of patients with HA-coated and uncoated revision cups

Primary diagnosis ^b	Revision cups				p-value ^a
	+ HA		− HA
	n	%	n	%	0.03
Primary OA	949	75	360	71
Inflammatory disease	99	8	38	8
Pediatric hip disease	82	7	59	12
Fracture	81	6	25	5
Other diagnoses ^c	47	5	26	5
Total	1,258	100	508	100

^a Chi-square test.

^b Missing data in 14 cases.

^c Including secondary posttraumatic OA, idiopathic femoral head necrosis, tumor, and other type of secondary OA.

Table 2. Characteristics of the study population

	+ HA		– HA		p-value ^a
	n	%	n	%
Sex					0.7
Male	593	47	244	48
Female	677	53	266	52
Age					< 0.001
< 50	53	4	65	13
50–59	125	10	93	18
60–75	576	45	270	53
> 75	516	41	82	16
Cause of index revision					0.03
Aseptic loosening	1,084	85	456	89
Infection	13	1	4	1
Dislocation	84	7	16	3
Other ^b	89	7	34	7

^a Chi-square test.

^b Including fracture, technical reasons, pain only, implant fracture.

Table 3. Use of bone graft at index cup revision within the 2 groups (HA-coated and uncoated revision cups)

	+ HA		− HA
	n	%	n	%	p-value ^a
Bone graft at index operation ^b					0.6
Yes	599	49	238	48
No	625	51	261	52
Total	1,224	100	499	100

^a Chi-square test.

^b Missing data in 57 cases.

Table 4. Relative risk (RR) for cup re-revision for any reason

Endpoint: any reason	No. of hips	No. of re-revisions	Crude RR (95% CI)	Adjusted RR (95% CI)	p-value
Coating
– HA	510	80	1.0 (ref) ^a	1.0 (ref)
+ HA	1,270	79	1.0 (0.7–1.4)	1.4 (0.9–2.0)	0.1
Age at index revision
0–49	118	31	2.6 (1.4–5.0)	3.5 (2.0–6.2)	0.003
50–59	218	34	2.4 (1.4–4.1)	1.9 (1.0–3.5)	0.04
60–75	846	73	1.5 (0.9–2.5)	1.3 (0.8–2.2)	0.3
> 75	598	21	1.0 (ref)	1.0 (ref)
Sex
Male	837	68	1.0 (ref)	1.0 (ref)
Female	943	91	1.1 (0.8–1.6)	0.9 (0.7–1.3)	0.6
Cause for index revision
Aseptic loosening	1,540	129	1.0 (ref)	1.0 (ref)
Infection	17	1	1.5 (0.2–10.7)	1.7 (0.2–12.5)	0.6
Dislocation	100	18	4.4 (2.6–7.2)	3.8 (2.2–6.6)	< 0.001
Other	123	11	1.3 (0.7–2.4)	1.3 (0.7–2.5)	0.4
Cup fixation at primary arthroplasty ^b
Cemented	1,424	106	1.0 (ref)	1.0 (ref)
Uncemented	339	53	1.9 (1.3–2.6)	1.4 (0.97–2.1)	0.07
Cup design
Trilogy	1,440	76	1.0 (ref)	1.0 (ref)
Harris-Galante	340	83	1.6 (1.1–2.3)	1.6 (1.0–2.5)	0.03
Bone graft at index revision ^c
No use of bone graft	886	74	1.0 (ref)	1.0 (ref)
Use of bone graft	837	78	0.9 (0.6–1.2)	0.9 (0.7–1.3)	0.7

^a ref: reference group.

^b Missing data in 17 cases.

^c Missing data in 57 cases.

A Cox regression analysis was performed where covariates (HA coating, age at index revision, sex, cause of index cup revision, cup design, use of bone grafting at index cup revision, and cup fixation at primary arthroplasty) were initially entered as singular variables, and a crude risk ratio (RR) was calculated for each variable. Then all covariates mentioned above were entered in the regression model and risk ratios were mutually adjusted for all covariates. Crude and adjusted RRs were calculated for revision for any reason.

Figure 1. Unadjusted Kaplan-Meier survival with hydroxyapatite (HA) coating as the independent factor and cup re-revision due to any reason as the endpoint. 10-year survival was 88.7% (CI: 85.5–92.0) for the HA-coated cups (red) and 87.2% (CI: 83.8–90.7) for the uncoated cups (blue). The dashed lines represent 95% confidence intervals for the 2 groups of cups.

Table 5. Relative risk (RR) for cup re-revision due to aseptic loosening

Endpoint: aseptic loosening	No. of hips	No. of re-revisions	Crude RR (95% CI)	Adjusted RR (95% CI)	p-value
Coating
– HA	510	55	1.0 (ref) ^a	1.0 (ref)
+ HA	1,270	26	0.7 (0.4–1.1)	1.1 (0.6–1.9)	0.9
Age at index revision
0–49	118	21	8.6 (2.9–25.3)	4.3 (1.4–13.3)	0.01
50–59	218	23	5.8 (2.0–17.0)	3.1 (1.0–9.4)	0.05
60–75	846	33	2.6 (0.9–7.3)	1.9 (0.7–5.5)	0.2
>75	598	4	1.0 (ref)	1.0 (ref)
Sex
Male	837	31	1.0 (ref)	1.0 (ref)
Female	943	50	1.4 (0.9–2.1)	1.1 (0.7–1.7)	0.8
Cause for index revision
Aseptic loosening	1,540	75	1.0 (ref)	1.0 (ref)
Infection	17	0	0.0 (0.0–∞)	0.0 (0.0–∞)	1.0
Dislocation	100	1	0.6 (0.1–4.3)	0.6 (0.1–4.6)	0.6
Other	123	5	1.1 (0.4–2.6)	1.4 (0.6–3.6)	0.5
Cup fixation at primary arthroplasty ^b
Cemented	1,424	45	1.0 (ref)	1.0 (ref)
Uncemented	339	36	2.9 (1.9–4.6)	2.2 (1.4–3.6)	0.02
Cup design
Trilogy	1,440	19	1.0 (ref)	1.0 (ref)
Harris-Galante	340	62	3.3 (1.9–5.9)	2.7 (1.4–5.2)	0.02
Bone graft at index revision ^c
No use of bone graft	886	25	1.0 (ref)	1.0 (ref)
Use of bone graft	837	52	1.6 (1.0–2.6)	1.5 (0.9–2.5)	0.09

^a ref: reference group.

^b Missing data in 17 cases.

^c Missing data in 57 cases.

Cox regression analysis: See Table 4.

Figure 2. Unadjusted Kaplan-Meier survival with hydroxyapatite (HA) coating as the independent factor and cup re-revision due to aseptic loosening as the endpoint. 10-year survival was 94.7% (CI: 91.9–97.5) for the HA-coated cups (red) and 91.9% (CI: 89.1–94.8) for the uncoated cups (blue). The dashed lines represent 95% confidence intervals for the 2 groups of cups.

Table 6. Exploratory analyses using putatively relevant covariates. Adjusted relative risk (RR) for cup re-revision for any reason

Endpoint: any reason	Adjusted RR (95% CI)	p-value
Type of hospital at primary arthroplasty
University hospital	1.0 (ref) ^a
Regional hospital	1.2 (0.8–1.8)	0.3
Local hospital	1.9 (1.1–3.1)	0.02
Private hospital	1.3 (0.5–3.2)	0.6
Hospital abroad	1.4 (0.2–10.6)	0.7
Type of hospital at index cup revision
University hospital	1.0 (ref) ^a
Regional hospital	1.2 (0.9–1.8)	0.3
Local hospital	2.1 (0.9–4.9)	0.09
Private hospital	1.5 (0.2–11.4)	0.7
Age at primary arthroplasty
0–49	1.0 (ref) ^a
50–59	1.6 (0.9–3.1)	0.2
60–75	2.0 (0.9–4.4)	0.09
>75	3.6 (0.9–13.5)	0.06
Diagnosis at primary arthroplasty
OA	1.0 (ref) ^a
Other diagnosis	1.4 (0.98–2.1)	0.07
Stem fixation at index revision
Cemented	1.0 (ref) a ^a
Uncemented	0.6 (0.3–1.2)	0.2

^a ref: reference group.

For each covariate, the adjusted RR with the endpoint cup re-revision for any reason was calculated. Each covariate was entered in the Cox regression model and the risk ratio was adjusted for the covariates: sex, HA coating, age at index revision, cause of index cup revision, cup design, use of bone grafting at index cup revision, and cup fixation at primary arthroplasty.

Table 7. Distribution of the 3 most commonly used stems combined with the cup types Trilogy (A) and Harris-Galante (B)

	+ HA		– HA
	n	%	n	%
A. Trilogy cup
Lubinus SPII	238	20	23	9
Exeter polished	118	10	25	10
Wagner SL rev. lateral	32	3	36	15
Others	804	67	164	66
	1,192	100	248	100
B. Harris-Galante cup
Lubinus SPII	13	17	31	12
Charnley	9	12	35	13
Spectron EF	12	15	16	6
Others	44	56	180	69
	78	100	262	100