Repeated magnetic resonance imaging in 154 hips with large-diameter metal-on-metal hip replacement

Figures & data

Figure 1. Flow chart of the patients

Figure 2. Scatter plot of follow-up time until first MRI against time interval between MRIs in the THR group.

Table 1. Demographics of the patients

No. of patients (hips)	124 (154)
No. of males (male hips)	78 (97)
No. of females (female hips)	46 (57)
No. of implants
ASR XL THR	101
ASR hip resurfacing	53
Median femoral diameter, mm (range)
ASR XL THR	51 (41–59)
ASR hip resurfacing	51 (43–59)

Table 2. Median clinical outcome scores and whole-blood (WB) metal ion levels at the first and second clinical evaluations

	First examination	Second examination	p-value
THR patients
HHS (range)
Unilateral	98 (63–100)	94 (62–100)	0.08
Bilateral, right	96 (51–100)	86 (36–100)	0.4
Bilateral, left	98 (51–100)	86 (36–100)	0.2
WB Cr (range), ppb
Unilateral	2.1 (0.8–11)	2.6 (0.6–10)	0.06
Bilateral	3.0 (1.2–13)	3.3 (0.8–15)	0.4
WB Co (range), ppb
Unilateral	4.6 (0.8–28)	5.8 (0.8–32)	0.001
Bilateral	9.4 (1.7–29)	9.6 (1.5–30)	0.3
HR patients
HHS (range)
Unilateral	86 (59–100)	86 (59–100)	0.4
Bilateral, right	90 (66–100)	94 (84–100)	0.7
Bilateral, left	84.5 (65–100)	92 (62–100)	0.5
WB Cr (range), ppb
Unilateral	2.7 (1.0–16)	2.9 (0.6–9.3)	0.7
Bilateral	2.8 (1.4–14)	2.7 (1.0–15)	0.3
WB Co (range), ppb
Unilateral	3.2 (0.8–128)	3.3 (0.8–47)	0.8
Bilateral	2.3 (1.1–9.5)	2.5 (1.0–23)	0.1

Table 3. Indications for the repeated MR imaging and results of the primary and repeated MRIs. Other reasons included control imaging due to scheduled revision (8 hips), enchondroma (2 hips), squeaking hip (2 hips), suspicion of latent infection (2 hips), joint effusion in primary MRI (1 hip), and occurrence of palpable lump in lateral thigh (1 hip). 1 patient who had both HR and THR is not shown in the table

					Progressive change in classification
	HR patients		THR patients		HR patients		THR patients
Indication for repeated imaging	Unilateral	Bilateral	Unilateral	Bilateral	Unilateral	Bilateral	Unilateral	Bilateral
Control imaging due to elevated
Co and/or Cr	5	2	15	6	0	0	1	1
Occurrence of pain during follow-up	13	2	12	2	0	0	0	1
Control imaging to due increase
(> 5 ppb) in Co and/or Cr	2	1	22	6	1	0	4	2
Control imaging due to pseudotumor	2	1	5	1	0	0	0	1
Occurrence of pain and elevated
metal ions during follow-up	3	0	2	1	0	0	0	0
Control imaging due to presence of pain	2	3	1	1	0	0	0	0
Other	3	2	7	1	1	0	1	0
Total	30	11	64	18	2	0	6	5

Table 4. Comparison of clinical variables between patients with a significant imaging change and those without any change

	Patients with no change in MRI	Patients with a progressive change in MRI	p-value
No. of patients
Unilateral	54	6	0.1 ^a
Bilateral	13	5
Years until first MRI	^b
Unilateral	3.5 (1.5–6.4)	3.6 (2.3–6.1)	0.5
Bilateral	4.3 (1.8–6.1)	3.2 (3.0–6.8)	0.6
Months between imagings ^b
Unilateral	21 (4.8–29)	18 (13–30)	0.8
Bilateral	22 (8.2–32)	12 (12–25)	0.3
Change in WB Co, ppb ^b
Unilateral	0.95 (–7.8 to 12)	2.25 (–4.1 to 3.8)	0.4
Bilateral	0.60 (–15 to 16)	–0.35 (–0.90 to 1.2)	0.4
Change in WB Cr, ppb ^b
Unilateral	0.1 (–2.2 to 1.7)	0.35 (–0.8 to 2.3)	0.3
Bilateral	0.4 (–3.3 to 2.1)	0.15 (–0.4 to 0.30)	0.5

^a For prevalences

^b Values are median (range)

Table 5. Contingency table showing MRI findings

			Second MRI			First MRI
		0	1	2A	2B	Total
First MRI	0	109	7 ^a	1^a	2^a	119
	1	4 ^c	20	1^b	2^b	27
	2A	0	0	4	0	4
	2B	0	0	1	3	4
Second MRI	Total	113	27	7	7	154

a 10 of the 13 patients with a progressive change had a normal first scan.

b In 3 hips, a thin-walled cystic pseudotumor had developed into a thick-walled pseudotumor in the repeat MRI.

c In 4 hips with retrogressive change, an originally diagnosed pseudotumor could not be seen in the repeat MRI.

Figure 3. Scatter plot of follow-up time until first MRI against time interval between MRIs in the HR group.

Figure 4. Man aged 41 at the time of the index operation for ASR HR. Time to first MRI (left) was 7.7 years. The time elapsed between imagings was 18 months. Both times, whole-blood Co and Cr remained below 4 ppb. MRI was repeated as a control imaging in the annual follow-up visit due to joint effusion seen in the first scan. However, development of a type-2A pseudotumor was seen.

Figure 5. A man with ASR XL THR who was 69 years old at the index operation. Time to first MRI (top) was 2.3 years. The time elapsed between imagings was 2.5 years. Both times, whole-blood Cr remained below 4 ppb. Whole-blood Co increased from 7.2 ppb to 16 ppb. MRI was repeated due to increase in whole-blood Co levels and occurrence of stiffness in the operated hip. Control imaging revealed a newly formed cystic lesion (type 1).