Effects of metal-on-metal wear on the host immune system and infection in hip arthroplasty

Figures & data

Table 1. Chemical composition and mechanical properties of CoCr28M06 alloy required by standards ASTM F75 and ISO 5832-4

	ASTM F75	ISO 5832-4
Rm ^a (MPa)	655	665
Rp 0.2% ^b (MPa)	450	450
Cobalt, Co	balance to 100%	balance to 100%
Chromium, Cr	27–30%	27–30%
Molybdenum, Mo	5.0–7.0%	4.5–7.0%
Nickel, Ni	< 0.5%	< 1%
Iron, Fe	< 0.75%	< 1%
Silicon, Si	< 1%	< 1%
Manganese, Mn	< 1%	< 1%
Carbon, C	< 0.35%	< 0.35%

^a Tensile strength is the stress at which a material breaks or permanently deforms.

^b Yield strength is the stress at which a material begins to deform plastically.

Table 2. Wear rates of MOM bearing couples defined in different units

Type of wear	Wear rate	Method	Ref.
Linear wear rate of femoral heads per year	7.6 μm (range 2.9–13) to	Explanted implant(s)	Reinisch et al. (2003)
	250 μm (range 50–810)	Radiographic analysis	Stilling et al. (2009)
First year	25 μm	Explanted implant(s)	Sieber et al. (1999)
> 3 years	5 μm	Explanted implant(s)	Sieber et al. (1999
Volumetric wear rate of femoral heads per year	2.0 mm^3 (range 0.55–3.7)	Explanted implant(s)	Reinisch et al. (2003)
	5.0 mm^3 (range 0.22–22)	Explanted implant(s)	Willert et al. (1996)
Mass wear rate per year	17 mg (range 4.6–31)	Explanted implant(s)	Reinisch et al. (2003)
No. of particles per unit volume of wear per mm^3	2.7 × 10^12 – 1.5 × 10^13	Pin-on-plate	Tipper et al. (1999)
Number of particles per 10^6 cycles	4 × 10^12 – 6 × 10^13	Pin-on-plate	Tipper et al. (1999)
Number of particles per year	6.7 × 10^12 – 2.5 × 10^14	Explanted implant(s)	Doorn et al. (1998)

Note: Retrieval study data were obtained from patients undergoing revision of THAs with MOM bearing couples. Radiographic wear analysis was performed by analysis of digitized anteroposterior (AP) radiographs using a computerized method.

Table 3. Size and morphology of wear particles generated by a hip simulator or derived from tissue samples

Size and morphology	Particle generation and type of prosthesis	Method ^a	Ref.
80 ± 40 nm, round	Hip simulator with bearing ASTM F 799 and F1357 Co-28Cr-6Mo	TEM	Catelas et al. (2001)
50–90 nm, oval or needle-shaped	Hip simulator with bearing ASTM F 799 and F1357 Co-28Cr-6Mo	SEM	Tipper et al. (1999)
25–36 nm, round	Hip simulator with bearing ASTM F 799 and F1357 Co-28Cr-6Mo	TEM	Firkins et al. (2001)
< 50 nm (range 6–834 nm), oval or round	Periprosthetic tissue samples of 2 McKee-Farrar and one McMinn prosthesis	TEM	Doorn et al. (1998)
< 50 nm, irregular	Periprosthetic tissue samples of 640 Sikomet SM21	SEM	Brown et al. (2007)
40–120 nm, needle-shaped < 90 nm, round	Periprosthetic tissue samples of one Bicon plus Ti shell with polyethylene liner, Sikomet SM21 head, and SL-Plus stem	TEM, SEM and XPS	Milosev and Remskar (2008)

^a TEM: transmission electron microscopy; SEM: scanning electron microscopy; XPS: X-ray photoelectron spectroscopy.

Schematic drawing illustrating: a. generation of wear particles; b. a metal alloy (gray scaffold) with an oxidized surface film on the upper surface (molecules marked in red); c. damage to the passive surface film (e.g. by scratching or pounding); d. occurrence of corrosion due to the lack of a protective layer; e. liberation of soluble compounds and wear particles; and f. repassivation of the surfaces including wear particles (arrows).

Table 4. Oxidation states of the elements in Co-Cr compounds

Co	Cr	Mn	Fe	Ni	Si	Mo
–1	–2	–3	–2	–1	–4 ^a	–2
+1	–1	–2	–1	+1	–3	–1
+2 ^a	+1	–1	+1	+2 ^a	–2	+1
+3 ^a	+2	+1	+2 ^a	+3	–1	+2
+4	+3 ^a	+2 ^a	+3 ^a	+4	+1	+3
+5	+4	+3	+4		+2	+4 ^a
	+5	+4 ^a	+5		+3	+5
	+6 ^a	+5	+6		+4 ^a	+6 ^a
		+6
		+7 ^a

^a represents the most common oxidation states.

Table 5. Maximum levels of Co and Cr ions in local tissues of patients with a MOM implant

Sample	Prosthesis	Cobalt (μg/L)	Chromium (μg/L)	Method ^a	Ref.
Capsule	Cemented and loose	26,000	88,000	NAA	Evans et al. (1974)
Synovial fluid	Cemented and loose	250
Capsule		22,000		NAA	Jones et al. (1975)
Femoral neck	Cemented	50,000	170,000	SES	Smethurst and Waterhouse (1977)
Acetabulum		170,000	170,000
Lining from femoral stem		130,000	1,300,000
Adjacent to articular surfaces		70,000	70,000
Acetabular pelvic lining		200,000	200,000
Capsule	Loose	6,000,000	1,500,000	AAS/NAA	Postel and Langlais (1977)
Synovial fluid	Cemented and loose	13,000	63,000	GSGSD	Dobbs and Minski (1980)
Capsule		63,000	327,000
Granuloma		193,000	323,000
Tissue (mid-femur)		6,900	5,500
Synovial fluid	Cemented and loose	155	358	AAS	Davies et al. (2005a)
Synovial fuid	Cemented	199	347	GFAAS	Dorr et al. (1990)
Capsule	(well-fixed and loose)	3,971	1,465
Fibrous membrane		2,451	1,634
Synovial fluid	Cementless	1,015	617
Capsule	(well-fixed and loose)	1,272	6,219
Fibrous membrane		3,812	20,609
Synovial fluid	Cemented and well-fixed	6	16	GFAAS	Brien et al. (1992)
Synovial fluid	Cemented and loose	152	238

^a NAA: neutron activation analysis; SES: spark emission spectroscopy; AAS: atomic absorption spectroscopy; GFAAS: graphite furnace atomic absorption spectrophotometry; GSGSD: gamma-spectroscopy with Ge-semiconductor detector.

Table 6. Maximum levels of Co and Cr ions as measured with inductively coupled plasma mass spectroscopy in hip simulator lubricant, catogorized by head size of MOM implant and number of cycles

Head size	Co (μg/L)	Cr (μg/L)	Cycles (×10^6)	Ref
55 mm	∼ 18,000	∼ 6,000	0.13	Leslie et al. (2008)
39 mm	∼ 12,000	∼ 4,000
55 mm	10,915	3,675	0.13	Leslie et al. (2009)
39 mm	9,066	3,302
36 mm	∼ 6,800,000	∼ 2,800,000	4	Williams et al. (2008a)
28 mm	∼ 12,000,000	∼ 8,000,000

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