Increased risk of revision of acetabular cups coated with hydroxyapatite

Figures & data

Table 1.  Characteristics of the patients studied (n = 6,646) from the Swedish Hip Arthroplasty Register (1992–2007)

	n	%
Sex
Male	3,367	51
Female	3,279	49
Age (years)
0–49	1,705	26
50–59	2,614	39
60–75	2,142	32
> 75	185	3
Primary diagnosis
Primary OA	5,037	77
Inflammatory disease	324	5
Fracture	257	4
Pediatric hip disease	599	9
Idiopathic femoral head necrosis	210	3
Secondary posttraumatic OA	37	0.6
Tumor	7	0.1
Other	50	0.8
Total	6,646	100

Table 2.  Acetabular components in the hips studied

	+ HA		– HA		Total
	n	%	n	%
Trilogy	4,501	86	1,035	37	5,536
Romanus	440	9	1,091	38	1,531
Harris-Galante	272	5	704	25	976
Total	5,213	100	2,830	100	8,043

Table 3.  Distribution of cemented and uncemented stems

Uncemented cups:	+ HA		– HA		Total
	n	%	n	%	n	%
Cemented stem	2,919	56	1,495	53	4,414	55
Uncemented stem	2,287	44	1,331	47	3,618	45

Table 4.  Relative risk (RR) of cup revision due to aseptic loosening. 8,043 hips in 6,646 patients.

Endpoint: aseptic loosening	No. of patients	No. of revisions	Crude RR (95% CI)	Adjusted RR (95% CI)
Coating
– HA	2,830	257	1.0 (ref) ^a	1.0 (ref)
+ HA	5,213	180	1.12 (0.98–1.46)	1.65 (1.32–2.06)
Sex
Female	4,048	232	1.0 (ref)	1.0 (ref)
Male	3,995	205	1.10 (0.91–1.33)	1.06 (0.87–1.28)
Primary diagnosis
Primary OA	6,152	309	1.0 (ref)	1.0 (ref)
Inflammatory disease	421	34	1.19 (0.83–1.69)	0.80 (0.55–1.15)
Fracture	266	7	0.84 (0.40–1.78)	0.71 (0.34–1.51)
Pediatric hip disease	722	53	1.96 (1.47–2.63)	1.57 (1.15–2.13)
Idiopathic femoral head necrosis	249	13	1.23 (0.71–2.14)	1.06 (0.61–1.86)
Secondary posttraumatic OA	39	5	1.83 (0.76–4.43)	1.40 (0.57–3.41)
Tumor	7	0	0.00 (0.00–∞)	0.00 (0.00–∞)
Other	52	8	1.13 (0.56–2.28)	0.90 (0.44–1.82)
Age
0–49	1,992	179	1.0 (ref)	1.0 (ref)
50–59	3,147	173	0.59 (0.48–0.73)	0.59 (0.47–0.74)
60–75	2,677	82	0.42 (0.32–0.54)	0.42 (0.31–0.56)
> 75	227	3	0.54 (0.17–1.69)	0.61 (0.19–1.92)
Cup design
Trilogy	5,536	70	1.0 (ref)	1.0 (ref)
Romanus	1,531	213	1.93 (1.45–2.56)	2.62 (1.90–3.63)
Harris-Galante	976	154	1.86 (1.37–2.51)	2.44 (1.77–3.37)
Stem fixation
Cemented stem	4,414	290	1.0 (ref)	1.0 (ref)
Uncemented stem	3,618	147	1.11 (0.91–1.35)	0.76 (0.61–0.95)

^a ref: reference group.

A Cox regression analysis was performed where covariates (age, sex, primary diagnosis, HA coating, cup design, and stem fixation) were initially entered as singular variables, and a crude risk ratio was calculated for each variable. Thereafter, all covariates mentioned above were entered in the regression model and risk ratios were mutually adjusted for all covariates. Crude and adjusted risk ratios (RRs) were calculated for revision due to aseptic loosening.

Table 5.  Relative risk (RR) of cup revision for any reason. 8,043 hips in 6,646 patients.

Endpoint: any reason	No. of patients	No. of revisions	Crude RR (95% CI)	Adjusted RR (95% CI)
Coating
– HA	2,830	331	1.0 (ref) ^a	1.0 (ref)
+ HA	5,213	245	1.11 (0.93–1.32)	1.44 (1.18–1.75)
Sex
Female	4,048	265	1.0 (ref)	1.0 (ref)
Male	3,995	311	1.14 (0.97–1.35)	1.12 (0.94–1.32)
Primary diagnosis
Primary OA	6,152	410	1.0 (ref)	1.0 (ref)
Inflammatory disease	421	42	1.13 (0.83–1.56)	0.80 (0.57–1.11)
Fracture	266	12	1.03 (0.58–1.83)	0.91 (0.51–1.62)
Pediatric hip disease	722	65	1.75 (1.34–2.27)	1.42 (1.08–1.87)
Idiopathic femoral head necrosis	249	17	1.19 (0.73–1.93)	1.06 (0.65–1.73)
Secondary posttraumatic OA	39	8	2.28 (1.13–4.59)	1.78 (0.87–3.61)
Tumor	7	1	6.29 (0.88–∞)	4.77 (0.67–∞)
Other	52	10	1.14 (0.61–2.14)	0.93 (0.50–1.76)
Age
0–49	1,992	222	1.0 (ref)	1.0 (ref)
50–59	3,147	232	0.64 (0.53–0.77)	0.65 (0.53–0.79)
60–75	2,677	117	0.47 (0.38–0.59)	0.47 (0.37–0.60)
> 75	227	5	0.58 (0.24–1.41)	0.64 (0.26–1.57)
Cup design
Trilogy	5,536	123	1.0 (ref)	1.0 (ref)
Romanus	1,531	254	1.69 (1.34–2.13)	2.04 (1.57–3.66)
Harris-Galante	976	199	1.78 (1.39–2.28)	2.16 (1.66–2.82)
Stem fixation
Cemented stem	4,414	377	1.0 (ref)	1.0 (ref)
Uncemented stem	3,618	199	1.09 (0.92–1.29)	0.84 (0.69–1.02)

^a ref: reference group.

A Cox regression analysis was performed where covariates (age, sex, primary diagnosis, HA coating, cup design, and stem fixation) were initially entered as singular variables, and a crude risk ratio was calculated for each variable. Thereafter, all covariates mentioned above were entered in the regression model and risk ratios were mutually adjusted for all covariates. Crude and adjusted risk ratios (RRs) were calculated for revision for any reason.

Table 6.  Distribution of stems combined with the cup types Romanus (A), Trilogy (B), and Harris-Galante (C)

	+ HA		– HA
	n	%	n	%
A. Romanus Cup
Bimetric + HA	262	60	141	13
Bimetric – HA	67	15	251	23
Bimetric cemented	15	3	359	33
Others	96	22	340	31
	440	100	1,091	100
B. Trilogy Cup
Spectron EF primary	1,215	27	28	3
Lubinus SPII	1,026	23	70	7
CLS	942	21	479	46
Others	1,318	29	458	44
	4,501	100	1,035	100
C. Harris-Galante Cup
Spectron EF	114	42	172	24
Lubinus SPII	26	10	245	35
Charnley	14	5	144	21
Others	118	43	143	20
	272	100	704	100