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Published by hip.taiwan, 2017-01-26 05:09:09

201702_02

201702_02

中文摘要

背景:
金屬對聚乙烯(MoP)全髖關節置換術(THA)中,金屬頭與股骨柄連接介面問題
(trunnionosis)和血中金屬離子濃度升高的前置因子目前不明。
方法:
本回溯性世代研究納入連續80名無其他金屬植入物的無症狀MoP THA病患(男性
43人),經過2-5年追蹤。採集血清鈷(Co)和鉻(Cr)濃度,並進行關於人口
統計學、植入物和手術特性的回溯分析。手術時的平均年齡為65.7歲(範圍35.6-
85.9歲),平均術後追蹤期為28.7個月(範圍24.4-58.9個月)。
結果:
在評估的因素中,唯一表現出與血清鈷離子濃度升高大於世代內基線有相關性的是
股骨頭偏心距。高偏心距和低偏心距植入物的鈷濃度,平均差為0.58 ppb(95%
信心區間 [CI] = 0.05-1.11 ppb;P = .03),鉻濃度平均差為0.19 ppb(95%
CI = -0.23 到 0.60 ppb;P = .37)。小頭和大頭的鈷濃度,平均差為0.20 ppb
(95% CI = -0.41 到 0.81 ppb;P = .59),鉻濃度的平均差為0.28 ppb(95%
CI = -0.18 到 0.74 ppb;P = .06)。年齡、性別、Harris髖關節評分、和植入
時間長短,都與金屬離子濃度變化無關。

結論:
股骨頭偏心距似乎是MoP THA之中,金屬離子濃度升高的一項重要來源因素。需要
進一步試驗來瞭解股骨頭偏心距增加,是否與後續的局部組織不良反應相關。

The Journal of Arthroplasty 31 (2016) 2814e2818

Contents lists available at ScienceDirect

The Journal of Arthroplasty

journal homepage: www.arthroplastyjournal.org

Primary Arthroplasty

Increased Femoral Head Offset is Associated With Elevated Metal Ions
in Asymptomatic Patients With Metal-on-Polyethylene Total Hip
Arthroplasty

John R. Martin, MD, Christopher L. Camp, MD, Cody C. Wyles, MD, Michael J. Taunton, MD,
Robert T. Trousdale, MD, David G. Lewallen, MD *

Department of Orthopedic Surgery, Mayo Clinic, Rochester, Minnesota

article info abstract

Article history: Background: Predisposing factors for trunnionosis and elevated metal ion levels in metal-on-
Received 1 February 2016 polyethylene (MOP) total hip arthroplasty (THA) are currently unknown.
Received in revised form Methods: This retrospective cohort study enrolled 80 consecutive patients (43 males) with an asymp-
26 April 2016 tomatic MOP THA at 2- to 5-year follow-up and no other metal implants. Serum cobalt (Co) and
Accepted 23 May 2016 chromium (Cr) levels were collected at the time of enrollment, and retrospective review was performed
Available online 1 June 2016 regarding demographic, implant, and surgical characteristics. Mean age at the time of surgery was 65.7
years (range 35.6-85.9 years), and mean postoperative follow-up was 28.7 months (range 24.4-58.9
Level of Evidence: months).
Level IV Results: Femoral head offset was the only evaluated factor shown to increase serum Co ion levels above
Therapeutic study baseline within the cohort. Mean difference in Co level for high and low offset implants was 0.58 ppb
(95% confidence interval [CI] ¼ 0.05-1.11 ppb; P ¼ .03). Mean difference in Cr level for high and low offset
Keywords: implants was 0.19 ppb (95% CI ¼ À0.23 to 0.60 ppb; P ¼ .37). Mean difference in Co level for small and
total hip arthroplasty large femoral heads was 0.20 ppb (95% CI ¼ À0.41 to 0.81 ppb; P ¼ .59). Mean difference in Cr level for
metal ions small and large femoral heads was 0.28 ppb (95% CI ¼ À0.18 to 0.74 ppb; P ¼ .06). Age, gender, Harris Hip
cobalt Score, and implant duration were not associated with changes in metal ion levels.
chrome Conclusion: Femoral head offset appears to be an important source of elevated metal ion levels in MOP
head size THA. Further studies will be needed to understand if increasing femoral head offset is associated with
offset subsequent adverse local tissue reactions.

© 2016 Elsevier Inc. All rights reserved.

Femoral head modularity allows surgeons the ability to quickly as well as pseudotumors similar to previously described ALTRs in
and efficiently change femoral length and offset intraoperatively. metal-on-metal THA [5].
However, there have been concerns about femoral corrosion at the
modular junction secondary to multiple modes of corrosion [1-3]. Elevated serum Co and Cr levels have been attributed to
Recently, a series of 10 patients were identified with adverse local excessive corrosion at the modular junction in patients with MOP
tissue reactions (ALTRs) secondary to metal-on-polyethylene THA [6,7]. Femoral heads composed of cobaltechromium alloy
(MOP) total hip arthroplasty (THA) [4]. Patients presented with were used in all reported cases of ALTR in patients with MOP THA.
elevated serum levels of cobalt (Co) and chromium (Cr) metal ions However, there is little information available on predisposing risk
factors for developing elevated metal ion levels and subsequent
One or more of the authors of this paper have disclosed potential or pertinent ALTR in MOP THA [8]. Femoral head size has been speculated to
conflicts of interest, which may include receipt of payment, either direct or indirect, increased metal ion levels, but this has not been proven clinically
institutional support, or association with an entity in the biomedical field which [9]. In addition, femoral head offset and femoral stem offset may
may be perceived to have potential conflict of interest with this work. For full predispose to ALTR secondary to increased stress placed on the
disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2016.05.047. trunnion. Furthermore, normal laboratory values for patients with
asymptomatic MOP THA have yet to be established. The purpose of
* Reprint requests: David G. Lewallen, MD, Mayo Clinic, 200 First St., SW, this investigation was to identify normal baseline serum metal
Rochester, MN 55905. ion levels in MOP THA patients and determine implant- or

http://dx.doi.org/10.1016/j.arth.2016.05.047
0883-5403/© 2016 Elsevier Inc. All rights reserved.

J.R. Martin et al. / The Journal of Arthroplasty 31 (2016) 2814e2818 2815

Table 1
Summary of Individual Patient, Implant, and Serum Metal Ion Characteristics.

Age (y) Follow-Up Sex Femoral Component Stem Size Head Head Cup Poly Liner HHS @ Final Cobalt Chromium
(mo) Offset Size Size Thickness Offset
(mm) (mm) (mm) (mm) (mm) Follow-Up (ppb) (ppb)

52 25 M Summit ha hi 6 À2 40 60 40 Â 60 4 100 0.2 0.1
56 27 À2 40 60 40 Â 60 4 100 0.2 0.2
54 30 M Summit ha hi 4 À2 36 52 36 Â 52 4 100 0.2 0.1
78 27 À2 40 56 40 Â 56 4
77 25 F Corail ha 10 À2 36 54 36 Â 54 4 96 0.2 0.2
83 26 À2 36 56 36 Â 56 4 86 0.3 0.5
50 25 M Summit ha hi 4 À2 36 56 36 Â 56 0 100 0.2 0.2
58 26 À2 36 62 36 Â 62 0 96 0.2 0.5
64 58 F Summit ha 4 À2 36 54 36 Â 54 4 96 0.2 0.1
55 30 À2 36 54 36 Â 54 0 d 0.2 0.1
53 26 M Corail high offset ha 11 À2 36 62 36 Â 62 0 93 0.3 0.1
59 24 À2 36 58 36 Â 58 0 d 0.2 0.3
73 27 F Summit ha hi 3 À2 40 58 40 Â 58 4 100 1.2 0.1
49 28 À2 40 58 40 Â 58 4 d 0.2 0.2
47 30 M Summit ha hi 7 À2 40 60 40 Â 60 4 96 0.2 0.1
75 27 À2 40 60 40 Â 60 0 100 0.2 0.1
78 28 F Summit ha 5 À2 40 56 40 Â 56 4 71 0.2 0.1
53 31 À2 44 62 44 Â 62 4 96 0.3 0.1
63 26 F Summit hi ha 7 40 62 40 Â 62 0 96 0.2 0.1
84 52 0 32 52 32 Â 52 0 88 0.4 0.1
55 28 M Summit hi ha 7 0 36 58 36 Â 58 0 100 1.3 1
64 28 0 36 62 36 Â 62 0 d 0.5 0.1
70 28 M Summit hi ha 6 0 36 56 36 Â 56 0 100 0.2 0.3
61 27 0 32 50 32 Â 50 0 d 0.2 0.2
37 27 M Summit hi ha 7 1 32 52 32 Â 52 0 97 0.2 0.4
50 27 1 32 52 32 Â 52 0 100 0.3 0.1
36 59 M Summit hi ha 6 1 32 50 32 Â 50 0 100 0.2 0.1
44 29 1 32 54 32 Â 54 0 d 0.2 0.2
77 27 M Corail high offset ha 16 1 32 54 32 Â 50 0 100 0.2 0.2
73 29 1 32 54 32 Â 54 0 85 0.2 0.1
67 27 M Summit hi ha 7 1 32 50 32 Â 50 0 100 0.2 0.1
57 25 1 32 48 32 Â 48 0 96 0.3 0.1
78 27 M Summit hi ha 5 1 32 54 32 Â 54 0 100 0.2 0.2
77 27 1 32 48 32 Â 48 4 d 0.2 0.2
65 27 M Summit hi ha 5 1 36 58 36 Â 58 0 100 0.2 0.1
68 36 1.5 36 54 36 Â 54 4 100 0.2 0.1
70 27 F Restoration modular 17 Â 155 1.5 40 58 40 Â 58 4 96 0.4 6.4
64 27 1.5 36 56 36 Â 56 4 94 0.2 0.1
73 27 F SROM 18 Â 10 Â 160 1.5 36 54 36 Â 54 0 100 0.2 0.1
72 28 1.5 36 50 36 Â 50 0 97 0.2 0.4
63 28 F Fitmore stem B/6 1.5 36 56 36 Â 56 0 79 0.9 0.1
69 27 1.5 40 58 40 Â 58 4 100 0.2 0.3
72 27 M Secur-fit 12 1.5 36 56 36 Â 56 0 100 0.2 0.1
65 26 1.5 36 54 36 Â 54 4 100 0.2 0.4
64 25 M Secur-fit 10 1.5 44 66 44 Â 66 4 100 0.2 0.1
70 28 1.5 36 60 36 Â 60 0 d 0.2 0.3
65 27 F Corail ha 9 1.5 36 58 36 Â 58 0 96 0.2 0.2
84 28 1.5 40 58 40 Â 58 4 100 0.3 0.1
65 26 F Summit hi ha 3 1.5 36 60 36 Â 60 0 100 0.2 0.2
62 27 1.5 36 56 36 Â 56 0 100 0.2 0.1
65 26 F Summit hi ha 1 2.5 36 52 36 Â 50 0 100 0.4 0.7
75 26 3 32 54 32 Â 54 0 87 0.2 0.1
65 27 M Summit ha 2 3.5 36 58 36 Â 58 0 d 0.4 0.2
67 36 3.5 40 64 40 Â 62 0 d 0.3 0.8
80 27 F Summit hi ha 2 5 32 52 32 Â 52 0 97 0.2 0.4
56 26 5 36 58 36 Â 58 0 d 0.2 0.1
67 29 M Summit ha 7 5 36 60 36 Â 60 0 100 0.2 0.1
85 28 5 44 64 44 Â 64 4 100 0.2 0.1
68 27 F Corail ha 12 5 32 50 32 Â 50 0 94 8.4 0.4
64 26 5 32 52 32 Â 52 0 88 0.4 0.5
73 24 F Corail high offset HA 10 5 36 60 36 Â 60 0 d 0.3 1.1
64 29 5 36 60 36 Â 60 0 100 0.2 0.1
72 28 F Corail HA 11 5 36 62 36 Â 62 0 96 1.3 0.1
61 31 5 36 60 36 Â 60 0 100 0.2 0.1
66 26 F Corail HA 11 5 36 54 36 Â 54 0 100 0.9 0.3
76 27 5 36 52 36 Â 52 4 d 0.3 0.3
61 24 F Summit hi ha 4 5 36 54 36 Â 54 0 73 0.2 0.1
73 30 5 36 58 36 Â 58 0 100 0.2 0.1
69 25 M Corail ha 13 5 36 56 36 Â 56 0 100 0.4 0.1
62 28 5 40 56 40 Â 56 4 100 0.3 0.5
86 26 F Summit hi ha 3 5 32 50 32 Â 50 4 100 0.2 0.1
61 28 5 44 74 44 Â 74 0 84 0.4 0.1
M Summit hi ha 7 5 92 0.6 0.5

M Summit hi ha 6 (continued on next page)

F Corail ha 10

F Corail ha 11

F Corail ha 10

M Summit hi ha 7

F Summit hi ha 6

F Corail ha 11

M Summit hi ha 6

M Corail ha 14

M Corail ha 12

M Summit hi ha 4

M Summit hi ha 8

M Secur-fit 10

F SROM 18 Â 13 Â 160þ4L

F Fitmore stem B/6

F Fitmore stem B7

M Depuy AML 19.5

F Corail high offset ha 11

M Corail high offset ha 12

M Summit hi ha 6

M Summit ha 5

F Corail ha 11

F Corail ha 11

M Corail ha 15

M Corail ha 13

M Corail ha 12

M Summit hi ha 7

F Summit hi ha 3

F Corail ha 12

F Summit hi ha 4

M Summit hi ha 8

F Summit ha 5

M Corail ha 16

F Accolade 4

M Reclaim 27 Â 240

2816 J.R. Martin et al. / The Journal of Arthroplasty 31 (2016) 2814e2818

Table 1 (continued ) Head Head Cup Poly Liner HHS @ Final Cobalt Chromium
Offset Size Size Thickness Offset Follow-Up (ppb) (ppb)
Age (y) Follow-Up Sex Femoral Component Stem Size (mm) (mm) (mm) (mm) (mm)
(mo) d 7 4.6
7 32 58 32 Â 58 0 d 0.2 0.3
72 32 F Fitmore stem B/7 7 36 58 36 Â 58 0 100 0.2 2.6
60 27 7 32 54 32 Â 54 0 d 0.4 0.3
63 26 M Fitmore stem 7 8.5 40 100 0.7 0.2
70 35 8.5 36 d d d 0.5 0.6
61 28 F Fitmore stem 5 8.5 36 60 36 Â 60 0 92 0.9 0.1
75 29 8.5 36 56 36 Â 56 0 96 0.5 0.1
80 27 M Solution stem 8 Â 18 9 32 58 36 Â 58 4 100
61 26 50 32 Â 50 0
M Corail high offset ha 16

M Corail high offset ha 11

M Summit ha 7

F Summit ha 4

AML, anatomic medullary locking; HHS, Harris Hip Score.

patient-specific factors associated with increased serum metal ion having a 36 mm or larger femoral head). To determine the impact of
levels in this patient population. femoral head offset on metal ions patients were similarly dichot-
omized into a low offset cohort (femoral heads with an offset
Methods of þ1.5 mm or less) and a high offset cohort (femoral heads with an
offset of þ2 mm or greater). We used the manufacturers' implant
This retrospective cohort study was performed at a single ter- information for each implant type to determine femoral head offset
tiary care institution from 2013 to 2015. Enrollment took place instead of relying on a radiographic calculation that would be less
during this period until 80 consecutive eligible patients were accurate. A comparison of metal ions was also performed on the
identified and subsequently consented for participation. following factors: age, sex, HSS, and implant duration to assess for
potential confounders.
Following institutional review board approval, our Institutional
Joint Registry was used to identify patients who were returning for When means of continuous, normally distributed variables were
clinical follow-up 2- to 5-year status after MOP THA. Patient charts compared between 2 groups (Co and Cr serum metal ion levels
were screened for the following inclusion criteria: (1) cobalte between the small and large metal head cohorts and the low and
chromium modular femoral head on highly crosslinked high offset cohorts), a student t test was used. P values <.05 were
polyethylene, (2) absence of additional metal implants, (3) considered statistically significant. In addition, serum metal ion
asymptomatic and well-functioning THA, and (4) Titanium femoral levels were plotted based on femoral head offset. Spearman cor-
stem. Patients were excluded if they had known renal dysfunction. relation coefficients were used to determine the strength of asso-
Patients that met the above criteria were screened by a study ciation between patient implant duration and HHS to metal ion
coordinator at the time of their routine follow-up. They were levels. All analysis was conducted using SAS, version 9.3 (SAS
subsequently consented to participate in the study. Patients un- Institute Inc, Cary, NC).
derwent a standard 2- or 5-year recheck with physical examina-
tion, radiographic evaluation, and then had serum Co and Cr levels Eighty patients were enrolled in the study from 2013 to 2015.
measured. The study included 43 males and 37 females with a mean age of
65.7 years (range 35.6-85.9 years). Femoral head sizes ranged from
Patient demographic data including sex, age, side of surgery, 32 to 44 mm, with a median of 36 mm. The mean HHS for the
date of THA, and primary diagnosis were recorded. Surgical data cohort was 96.1 (range 71-100). Patient demographic data are
were also recorded including femoral head size and offset per the summarized in Tables 1 and 2. The most common preoperative
manufacturer. Metal ion levels and Harris Hip Scores (HHS) were diagnosis was osteoarthritis (n ¼ 68, 85%). Mean duration from
also recorded on each patient. Levels of serum Co and Cr were surgery to obtaining metal ion levels was 28.7 months (range 24.4-
drawn at the time of enrollment. Impact of femoral head size on 58.9 months).
metal ion levels was determined by sensitivity analyses. Following
this, patients were divided into a small head cohort (consisting of The 3 most common acetabular cup designs were 66 DePuy, 7
patients with a head of 32 mm) and a large head cohort (patients Zimmer, and 6 Stryker. Mean cup size was 56 mm (range 48-74). All
femoral components were uncemented; the 3 most common

Table 2
Patient Demographic Summary.

Entire Cohort Head Sizea Head Offsetb

Small Large P Low High P

Patients (N) 80 20 60 d 49 31 d
Age (y) 65.7 (35.6-85.9) 65.4 ± 14.8 65.8 ± 8.9 .9 64.0 ± 11.7 68.4 ± 7.6 .06
Females (%) 46 90 32 47 42 .82
Time with implant (mo) 28.7 (24.4-58.9) 30.0 ± 8.9 28.2 ± 4.6 <.01 29.2 ± 7.4 27.9 ± 2.7 .35
Osteoarthritis (%) 85 75 90 .25 81 88 .76
Head size (mm) 32 37.5 (36-44) .13 .89
Head offset (mm) 36 (32-44) 36 ± 3 36 ± 3
Harris Hip Score 2 (À2 to 9) 2.9 ± 2.6 1.9 ± 3.3 <.01 À0.1 ± 1.5 5.5 ± 1.6 <.01
Cobalt level (ppb) 96 ± 6 95 ± 7 .22 96 ± 6.8 .63
Chromium level (ppb) 96 (71-100) 0.7 ± 1.5 0.5 ± 1.1 .67 96 ± 6.2 0.87 ± 1.85 .03
0.5 (0.2-8.4) 0.6 ± 1.3 0.2 ± 0.2 .59 0.28 ± 0.23 0.51 ± 0.90 .37
0.4 (0.1-6.4) .06 0.32 ± 0.90

Comparative data are presented as means with standard deviations or means with ranges.

P values in bold are statistically significant (P < .05).
a Small femoral head size ¼ 32 mm; large femoral head size !36 mm.
b Low femoral head offset þ1.5 mm or less; high femoral head offset ! þ2mm.

J.R. Martin et al. / The Journal of Arthroplasty 31 (2016) 2814e2818 2817

Table 3
Serum Metal Ion Levels Stratified by Demographic Variables.

Cobalt (ppb) P Chromium (ppb) P

Age

Young 0.33 ± 0.26 .17 0.69 ± 0.43 .31
0.50 ± 1.18 .12
Old 0.29 ± 1.63 .55
.94 0.20 ± 1.27 .24
Gender 0.45 ± 0.14

Male 0.52 ± 1.10 .22 0.41 ± 1.11
0.28 ± 0.47
Female 0.50 ± 1.25
.10 0.27 ± 0.43
Harris Hip Score (HHS) 0.51 ± 1.20

Low 0.63 ± 1.45

High 0.30 ± 0.24

Implant duration

Low 0.29 ± 0.20

High 0.73 ± 1.65

Fig. 1. Serum cobalt ion level (ppb) on the y-axis is plotted against femoral head offset Data for cobalt and chromium are presented as means with standard deviations.
(mm) on the x-axis. A sharp increase is noted in serum cobalt ion levels with each Age, HSS, and implant duration were all stratified into a group of the highest 40
subsequent increase in femoral head offset greater than þ1.5 mm. patients and a group of the lowest 40 patients as indicated by variable; there were
43 males and 37 females.

femoral stem designs were 37 Summit, 23 Corail, and 6 Fitmore. difference in Cr level for high and low offset implants was 0.19 ppb
The following surgical approaches were used for these primary THA (95% CI ¼ À0.23 to 0.60 ppb; P ¼ .37; Table 2 and Fig. 2).
procedures: 56 posterior, 17 direct anterior, and 7 anterolateral. All
patients in the study had no history of any other metal implant Following sensitivity analyses, patients were also divided post
devices. Summary characteristics of all patients in the study are hoc by femoral head size into a small (32 mm) and large (!36 mm)
detailed in Table 1. femoral head cohort. There were 20 patients with a small femoral
head and 60 patients with large femoral heads. There were no
Results statistically significant differences in age, preoperative diagnosis, or
average follow-up between these 2 cohorts (Table 2). Mean dif-
Mean serum Co ion level was 0.51 ppb (range 0.2-8.4 ppb), and ference in Co level for small and large femoral heads was 0.20 ppb
mean serum Cr ion level was 0.39 ppb (range 0.1-6.4 ppb; Table 2). (95% CI ¼ À0.41 to 0.81 ppb; P ¼ .59; Table 2). Mean difference in Cr
However, after stratifying the data by low and high femoral head level for small and large femoral heads was 0.28 ppb (95%
offset (below, the only variable shown to correlate with differential CI ¼ À0.18 to 0.74 ppb; P ¼ .06; Table 2).
ion levels), the low offset group had a mean Co ion level of 0.28 ppb
(standard deviation ¼ 0.23 ppb) and mean Cr ion level of 0.32 ppb Four variables were assessed for potential confounders
(standard deviation ¼ 0.90 ppb; Table 2). including age, gender, HHS, and implant duration (Table 3). Metal
ion levels were then compared by dividing the patient populations
Following sensitivity analyses, patients were divided post hoc into 2 patient cohorts of 40 after stratifying by increasing age, HHS,
into either low ( þ1.5 mm) or high (!þ2 mm) femoral head offset and implant duration. In addition, metal ion levels were compared
groups. There were 49 patients in the low offset cohort and 31 in between males and females. No significant differences were noted
the high offset cohort. There were no statistically significant dif- in Co and Cr levels with increasing age (P ¼ .17 and .31, respectively),
ferences in age, gender, preoperative diagnosis, or follow-up HHS (P ¼ .22 and .55, respectively), and implant duration (P ¼ .10
duration between these 2 groups (Table 2). Mean difference in Co and 0.24, respectively; Table 3). Likewise, there was no significant
level for high and low offset groups was 0.58 ppb (95% confidence difference in Co and Cr levels between males and females (P ¼ .94
interval [CI] ¼ 0.05-1.11 ppb; P ¼ .03; Table 2 and Fig. 1). Mean and .12, respectively; Table 3). We performed additional explor-
atory analysis on the relationship between implant duration and
HHS with serum metal ion levels. This was performed by deter-
mining the Spearman coefficient for relatedness for the entire
cohort. The Spearman coefficient between implant duration and Co
and Cr was R2 ¼ 0.00415 and 0.02791, respectively. The Spearman
coefficient between HHS and Co and Cr was R2 ¼ 0.00296 and
0.00859, respectively. All 4 of these coefficients indicate a weak
relationship with no correlation.

Fig. 2. Serum chromium ion level (ppb) on the y-axis is plotted against femoral head Discussion
offset (mm) on the x-axis. A sharp increase is noted in serum chromium ion levels with
each subsequent increase in femoral head offset greater than þ5.0 mm. Modular femoral heads have been associated with several
benefits including efficiency in altering femoral length and offset
intraoperatively, decreased implant inventory, and ease of removal
at the time of revision surgery [10,11]. Recently, there have been
increasing reports of ALTR associated with modular femoral heads
in MOP THA [4,12-15]. This study attempted to answer the
following: (1) what are the typical baseline serum Co and Cr metal
ion values for asymptomatic patients with MOP THA and (2) what
implant- or patient-specific factors are associated with elevated
metal ion levels? In this cohort, we found that baseline serum Co
and Cr levels were approximately 0.3 ppb after stratifying by

2818 J.R. Martin et al. / The Journal of Arthroplasty 31 (2016) 2814e2818

identified risk factors and that increasing femoral head offset is well the combined offset of the femoral stem and the femoral head.
most strongly associated with increasing Co levels. However, we noted no significant differences in metal ions with
either of these variables. We speculate that increasing femoral head
There are several limitations to this study. First, the number of offset leads to more torsional stresses on the trunnion by increasing
patients with small femoral heads (32 mm) was limited (n ¼ 20). In the lever arm on the trunnion as the center of rotation medializes
addition, we did not associate metal ion levels with cross-sectional with increasing femoral head offset.
imaging. Because patients were asymptomatic and metal ion levels
were not drastically elevated, we did not obtain ultrasounds or When using cobaltechromium femoral heads with increased
magnetic resonance image studies to evaluate for an ALTR. We also offset, caution should be exercised. To avoid increasing femoral
have a relatively small patient population with average follow-up of head offset, preoperative templating can be performed to identify
28 months; however, this time point correlates closely with the patients that may require a femoral stem with increased offset. If
time course where many ALTR are observed clinically. In addition, femoral stem offset has been maximized with instability present
there are several trunnion issues that were not addressed in this and it appears that a femoral head offset of >1.5 is necessary, one
study. Specifically, we did not assess trunnion length, trunnion could consider alternative bearing surfaces, such as a ceramic
shape, or how the femoral head was impacted onto the trunnion. It femoral head. Ceramic femoral heads eliminate the modular metal
is possible that each could contribute to trunnion corrosion. Finally, femoral head altogether, and to our knowledge have not been
patients in this cohort all remain asymptomatic; therefore, we associated with an ALTR to date in the absence of a cobaltechrome
cannot comment at this point on the clinical significance of the femoral component. Modular femoral heads have been associated
differences in serum metal ion levels noted between patients with with increasing reports of ALTR and elevated metal ion levels. We
high and low offset femoral heads. have identified typical baseline values for asymptomatic patients
with MOP THA to be approximately 0.3 ppb for both Co and Cr.
Currently, there is minimal information available on the normal Furthermore, we noted no significant association with increasing
serum Co and Cr levels in asymptomatic patients with MOP THA. femoral head size. Femoral head offset >1.5 mm appears to be the
One study defined normal laboratory values for MOP THA as a major source for elevated metal ion levels in asymptomatic patients
serum Co of 0.16 and Cr of 0.24 ppb [4]. The patient population in with MOP THA. As a result, surgeons should exercise caution when
which these data were derived is unknown, but the laboratory using high offset cobalt chromium femoral heads during THA.
values appear to be similar to what was identified in this study. In Further study will be mandatory to determine the clinical signifi-
this population of asymptomatic MOP THA patients, mean Co and cance of this association and whether these relationships are
Cr levels were 0.51 and 0.39 ppb, respectively. However, we have maintained in a symptomatic population.
identified a significant increase in metal ion levels with increasing
femoral head offset. Utilizing the values of lower femoral head References
offset, we noted Co and Cr levels of ~0.3 ppb (Table 2).
1. Collier JP, Surprenant VA, Jensen RE, et al. Corrosion at the interface of cobalt-
Recently, increasing femoral head size was shown to increase alloy heads on titanium-alloy stems. Clin Orthop Relat Res 1991;(271):305.
stresses at the trunnion in a finite element analysis [9]. The authors
speculated that this would clinically lead to tribocorrosion with 2. Kawalec JS, Brown SA, Payer JH, et al. Mixed-metal fretting corrosion of Ti6Al4V
associated elevation of metal ion levels. Interestingly, the small and wrought cobalt alloy. J Biomed Mater Res 1995;29(7):867.
head cohort in our study demonstrated higher metal ion levels;
however, we noted no significant difference between small and 3. Goldberg JR, Gilbert JL. In vitro corrosion testing of modular hip tapers. J Biomed
large femoral heads. On further evaluation of the 2 cohorts, we Mater Res B Appl Biomater 2003;64(2):78.
noted a nonstatistically significant increase in femoral head offset
in the small head cohort. This was likely the reason for elevated 4. Cooper HJ, Della Valle CJ, Berger RA, et al. Corrosion at the head-neck taper as a
metal ion levels in this group. Some surgeons have speculated that cause for adverse local tissue reactions after total hip arthroplasty. J Bone Joint
femoral head offset may be associated with increased metal ions. Surg Am 2012;94(18):1655.
The increased femoral head offset directly increases torque on the
trunnion; however, to date, increased femoral head offset has never 5. Campbell P, Ebramzadeh E, Nelson S, et al. Histological features of
been associated with increased metal ion levels. We noted a sig- pseudotumor-like tissues from metal-on-metal hips. Clin Orthop Relat Res
nificant increase in serum Co levels in patients with increased 2010;468(9):2321.
femoral head offset. Increased Cr level was also shown in patients
with higher femoral head offset, but this did not reach significance 6. Porter DA, Urban RM, Jacobs JJ, et al. Modern trunnions are more flexible: a
until we compared a low offset cohort with a Cr level of 0.2 ppb mechanical analysis of THA taper designs. Clin Orthop Relat Res 2014;472(12):
(including À2 to 1 mm offset) to a very high femoral head offset 3963.
cohort with a Cr level of 1.1 (þ7 to 9 mm offset; P ¼ .002). In
addition, we noted metal ion levels of approximately 0.2 ppb with 7. Goldberg JR, Gilbert JL, Jacobs JJ, et al. A multicenter retrieval study of the taper
increasing femoral offset up to 1.5 mm. However, above a femoral interfaces of modular hip prostheses. Clin Orthop Relat Res 2002;401:149.
head offset of 1.5 mm, the metal ion levels increase significantly.
8. Levine BR, Hsu AR, Skipor AK, et al. Ten-year outcome of serum metal ion levels
We analyzed 4 variables for potential confounders including after primary total hip arthroplasty: a concise follow-up of a previous report*.
age, gender, HHS, and implant duration. No significant difference in J Bone Joint Surg Am 2013;95(6):512.
serum metal ion levels was noted with any of these factors. In
addition, sex was not associated with serum metal ion levels. It 9. Lavernia CJ, Iacobelli DA, Villa JM, et al. Trunnion-head stresses in THA: are big
appears that increasing femoral head offset is the most important heads trouble? J Arthroplasty 2015;30(6):1085.
factor in increased metal ion levels using our current data. We also
performed a separate analysis evaluating the femoral stem offset as 10. Jacobs JJ, Urban RM, Gilbert JL, et al. Local and distant products from modularity.
Clin Orthop Relat Res 1995;319:94.

11. Collier JP, Mayor MB, Williams IR, et al. The tradeoffs associated with modular
hip prostheses. Clin Orthop Relat Res 1995;311:91.

12. Wassef AJ, Schmalzried TP. Femoral taperosis: an accident waiting to happen?
Bone Joint J 2013;95B(11 Suppl A):3.

13. Craig P, Bancroft G, Burton A, et al. Raised levels of metal ions in the blood in
patients who have undergone uncemented metal-on-polyethylene Trident-
Accolade total hip replacement. Bone Joint J 2014;96B(1):43.

14. Esposito CI, Wright TM, Goodman SB, et al. What is the trouble with trunnions?
Clin Orthop Relat Res 2014;472(12):3652.

15. McGrory BJ, MacKenzie J, Babikian G. A high prevalence of corrosion at the
head-neck taper with contemporary Zimmer non-cemented femoral hip com-
ponents. J Arthroplasty 2015;30(7):1265.


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