Metal release and metal allergy after total hip replacement with resurfacing versus conventional hybrid prosthesis

Figures & data

Table 1. Patient demographics and characteristics

Patient demographics	MOM	MOP/COP	p-value
n	19	25
Sex (M/F)	9/10	7/18
Mean age at surgery, years	64 (56–70)	64 (57–70)
Mean BMI	26 (19–33)	27 (21–32)
Implant positioning:
Mean cup inclination angle	66 (59–86)	60 (35–75)
Mean cup anteversion angle	8 (2–17)	9 (2–25)
Neutral stem	13	23
Valgus stem	5	2
Varus stem	1	0
Heterotopic ossifications, n	10	14
Metal allergy-related questions (Yes/No):
Have your ears ever been pierced?	7	13
Have you ever experienced dermatitis following skin exposure to jewellery, buttons, or watches?	4	6	0.9
Postoperative redness around the operated hip?	0	1	1
Postoperative progress in hypersensitivity?	0	1	1

Table 2. MOM vs. MOP. Urine metal levels normalized to creatinine concentration

Ratios	Preoperatively	Postoperatively	3 months	1 year	2 years	5 years
Cobalt/creatinine
MOM	0.02 (0.02–0.04)	0.40 (0.40–0.60) ^a	0.03 (0.02–0.06)	0.50 (0.30–0.80) ^a	0.40 (0.38–0.75) ^a	0.56 (0.31–0.89) ^a
MOP	0.02 (0.02–0.04)	0.03 (0.02–0.05)	0.02 (0.02–0.04)	0.03 (0.02–0.05)	0.03 (0.02–0.05)	0.04 (0.03–0.06)
Chromium/creatinine
MOM	0.0 (0.0–0.0)	0.1 (0.1–0.1)	0.0 (0.0–0.0)	0.2 (0.1–0.3) ^a*	0.2 (0.2–0.4) ^a	0.3 (0.2–0.4)^a
MOP	0.0 (0.0–0.0)	0.0 (0.0–0.0)	0.0 (0.0–0.0)	0.0 (0.0–0.0)	0.0 (0.0–0.0)	0.0 (0.0–0.0)
Molybdenum/creatinine
MOM	2.1 (1.0–3.1)	0.9 (0.3–2.3)	3.1 (1.6–6.6)	1.8 (1.2–3.8)	3.0 (1.8–4.9)	4.1 (2.4–6.9)
MOP	2.6 (1.8–3.6)	0.7 (0.4–2.3)	2.7 (1.7–5.1)	2.6 (2.2–4.4)	3.3 (2.5–6.2)	6.1 (4.0–8.1)
Nickel/creatinine
MOM	0.2 (0.1–0.3)	0.1 (0.1–0.1)	0.2 (0.1–0.3)	0.1 (0.1–0.2)	0.1 (0.1–0.2)	0.1 (0.0–0.4)
MOP	0.2 (0.1–0.2)	0.1 (0.1–0.3)	0.1 (0.1–0.1)	0.1 (0.1–0.2)	0.1 (0.1–0.1)	0.2 (0.1–0.3)

The data did not follow a Gaussian distribution and are presented as median with interquartile range.

^a p < 0.01.

Table 3. MOP vs. COP. Urine metal levels normalized to creatinine concentration

Ratios	Preoperatively	Postoperatively	3 months	1 year	2 year	5 year
Cobalt/creatinine
MOP	0.02 (0.02–0.03)	0.03 (0.02–0.04)	0.04 (0.04–0.07)	0.03 (0.02–0.06)	0.03 (0.02–0.04)	0.04 (0.03–0.07)
COP	0.02 (0.01–0.04)	0.04 (0.02–0.05)	0.03 (0.02–0.08)	0.02 (0.02–0.04)	0.03 (0.02–0.04)	0.04 (0.02–0.06)
Chromium/creatinine
MOP	0.0 (0.0–0.0)	0.0 (0.0–0.0)	0.0 (0.0–0.0)	0.0 (0.0–0.0)	0.0 (0.0–0.0)	0.0 (0.0–0.0)
COP	0.0 (0.0–0.0)	0.0 (0.0–0.0)	0.0 (0.0–0.0)	0.0 (0.0–0.0)	0.0 (0.0–0.0)	0.0 (0.0–0.0)
Molybdenum/creatinine
MOP	2.4 (1.7–3.6)	1.8 (0.6–3.0)	3.4 (1.9–5.3)	2.9 (2.3–4.9)	3.5 (2.3–5.7)	5.3 (3.9–8.0)
COP	2.6 (2.0–3.4)	0.4 (0.3–1.3)	2.1 (1.7–3.1)	2.3 (2.0–3.4)	3.2 (2.6–6.5)	6.3 (4.7–9.5)
Nickel/creatinine
MOP	0.1 (0.1–0.1)	0.1 (0.1–0.1)	0.1 (0.1–0.2)	0.1 (0.1–0.2)	0.2 (0.1–0.3)	0.2 (0.2–0.5)
COP	0.1 (0.0–0.1)	0.1 (0.1–0.2)	0.1 (0.1–0.1)	0.1 (0.1–0.2)	0.1 (0.1–0.2)	0.1 (0.1–0.3)

The data did not follow a Gaussian distribution and are presented as median with interquartile range.

Table 4. Hypersensitivity evaluated by patch test. The number of positive patch tests for each hapten in the MOM group and the MOP/COP group

Hapten	MOM (n = 19)	MOP/COP (n = 24)	p-value
Cobalt, Co	4	5	1.0
Chromium, Cr	1	2	0.7
Molybdenum, Mo	2	2	1.0
Nickel, Ni	4	7	0.7
Ferric, Fe	1	3	0.6
Manganese, Mn	5	6	1.0
Vanadium, Va	3	5	1.0
Titanium, Ti	2	0	0.2
Zirconium, Zr	1	0	0.4
Aluminum, Al	0	0	1.0
Overall prevalence of metals present	12 (n 76)	25 (n 216)	0.4

Table 5. Lymphocyte transformation assay. The number with positive metal reactivity (SI) > 2.0 in each patient group (the MOM group and the MOP/COP group)

Hapten	MOM (n = 8)	MOP/COP (n = 15)	p-value
Chromium, Cr	2	1	0.3
Cobalt, Co	0	1	0.7
Nickel, Ni	4	8	0.6
Overall prevalence of metals present	6 (24)	9 (45)	0.8