Monoblock all-polyethylene tibial components have a lower risk of early revision than metal-backed modular components

Figures & data

Table 1. Study sample characteristics by component modularity, 2001–2010

	Total sample		Metal-backed modular		Monoblock all-polyethylene
	n	(%)	n	(%)	n	(%)	p-value
No.	27,657	100	25,351	91.7	2,306	8.3
Mean age, years	68.4	9.1	68.1	9.1	71.8	9.0	< 0.001
Age category, years
< 65	9,215	33.3	8,737	34.8	478	20.7	< 0.001
≥ 65	18,439	66.7	16,611	65.5	1,828	79.3
Sex
Female	17,614	63.7	16,170	63.8	1,444	62.6	0.3
Male	10,042	36.3	9,180	36.2	862	37.4
Race
White	17,393	62.9	15,716	62.0	1,677	72.7	< 0.001
Hispanic	4,516	16.3	4,206	16.6	310	13.4
Black	2,154	7.8	2,087	8.2	67	2.9
Asian	1,407	5.1	1,314	5.2	93	4.0
Other/Multi	541	2.0	510	2.0	31	1.3
Unknown	1,646	6.0	1,518	6.0	128	5.6
Diabetes	7,658	27.7	7,017	27.7	641	27.8	0.9
Mean BMI (mean, SD)	31.4	6.2	31.6	6.3	30.1	5.4	< 0.001
Unknown	515	1.9	463	1.8	52	2.3
ASA score
1 & 2	15,861	57.4	14,493	57.2	1,368	59.3	0.003
≥ 3	11,224	40.6	10,314	40.7	910	39.5
Unknown	572	2.1	544	2.2	28	1.2
Osteoarthritis	26,880	97.2	24,630	97.2	2,250	97.6	0.2
Osteonecrosis	137	0.5	123	0.5	14	0.6	0.4
Posttraumatic arthritis	250	0.9	237	0.9	13	0.6	0.07
Rheumatoid arthritis	579	2.1	530	2.1	49	2.1	0.91

^a Missing data: age (n = 3, 0.1%), sex (n = 1, 0.0%).

Table 2. Surgeon, hospital, procedure, and implant characteristics according to component modularity, 2001–2010

	Total sample		Metal-backed modular		Monoblock all-polyethylene
	n	(%)	n	(%)	n	(%)	p-value
Total no.	27,657	100	25,351	91.7	2,306	8.3
Fellowship training	11,644	42.1	10,780	42.5	864	37.5	< 0.001
Surgeon, average annual volume
< 20	1,639	5.9	1,613	6.4	26	1.1	< 0.001
20–49	9,031	32.7	8,375	33.0	656	28.5
≥ 50	16,987	61.4	15,363	60.6	1,624	70.4
Hospitals	40	100.0	40	100.0	13	32.5
Hospital, average yearly volume
< 100	558	2.0	558	2.2	0	0.0	< 0.001
100–199	3,358	12.1	3,358	13.3	0	0.0
≥ 200	23,741	85.8	21,435	84.6	2,306	100
Implant stability
CR	9,408	34.0	8,897	35.1	511	22.2	< 0.001
PS	18,223	65.9	16,430	64.8	1,793	77.8
Unknown	26	0.1	24	0.1	2	0.1
Fixation
Cemented	24,987	90.4	22,810	90	2,177	94.4	< 0.001
Hybrid	1,267	4.6	1,244	4.9	23	1.0
Uncemented	114	0.4	106	0.4	8	0.4
Unknown	1,289	4.7	1,191	4.7	98	4.3
Patella not resurfaced	631	2.3	603	2.4	28	1.2	< 0.001
Bilateral procedures	2,821	10.2	2,587	10.2	234	10.2	0.9
Operative time (min), (mean, SD)	92.3	32.4	92.7	32.7	87.4	28.4	< 0.001

CR: cruciate retaining; PS: posterior stabilized.

Table 3. Crude revision rate and revision rate/100 years of observation for all-cause revision and aseptic revision, for the overall cohort and according to component modularity

	Total sample		Metal-backed modular		Monoblock all-polyethylene		p-value
Crude revision rate	n	(%)	n	(%)	n	(%)
All-cause	572	2.07	550	2.17	22	0.95	< 0.001
Aseptic	313	1.13	300	1.18	13	0.56	0.007
Revision rate/100 y
of observation	Total y	Rate/100 y	Total y	Rate/100 y	Total y	Rate/100 y
All-cause	92,273	0.62	84,971	0.65	7,302	0.30
Aseptic		0.34		0.35		0.18

Table 4. Adjusted risk of all-cause and aseptic revision for all-polyethylene monoblocks compared to metal-backed modular tibial components. Cox proportional hazard models

	HR	95% CI	p-value
All-cause revision models
Overall	0.51	0.33–0.78	0.002
Patients ≥ 65 years old	0.59	0.35–0.99	0.05
Patients < 65 years old	0.26	0.10–0.72	0.01
Aseptic revision models
Overall	0.59	0.29–1.19	0.1
Patients ≥ 65 years old	0.75	0.32–1.76	0.5
Patients < 65 years old	0.27	0.11–0.65	0.003