SYMPOSIUM: PAPERS PRESENTED AT THE ANNUAL MEETINGS OF THE HIP SOCIETY
MRI Predicts ALVAL and Tissue Damage in Metal-on-Metal Hip
Danyal H. Nawabi MD, FRCS(Orth), Stephanie Gold BA,
Steven Lyman PhD, Kara Fields MS, Douglas E. Padgett MD,
Hollis G. Potter MD
Published online: 26 January 2013
? The Association of Bone and Joint Surgeons1 2013
around metal-on-metal (MOM) hip arthroplasties are
increasingly being recognized as a cause of failure. These
reactions may be associated with intraoperative tissue
damage and complication rates as high as 50% after revi-
sion. Although MRI can identify ALTR in MOM hips, it is
unclear whether the MRI findings predict those at revision
Adverse local tissue reactions (ALTR)
MRI characteristics correlated with histologically con-
firmed ALTR (using the aseptic lymphocytic vasculitis-
associated lesions [ALVAL] score) and intraoperative
tissue damage and (2) developed a predictive model using
modified MRI to detect ALVAL and quantify intraopera-
tive tissue damage.
MethodsWe retrospectively reviewed 68 patients with
failed MOM hip arthroplasties who underwent preoperative
MRI and subsequent revision surgery. Images were ana-
lyzed to determine synovial volume, osteolysis, and
synovial thickness. The ALVAL score was used to grade
tissue samples, thus identifying a subset of patients with
ALTR. Intraoperative tissue damage was graded using a
four-point scale. Random forest analysis determined the
sensitivity and specificity of MRI characteristics in
detecting ALVAL (score C 5) and intraoperative tissue
ResultsMaximal synovial thicknesses and synovial vol-
umes as determined on MRI correlated with the ALVAL
score and were higher in cases of severe intraoperative
tissue damage. Our MRI predictive model showed sensi-
tivity and specificity of 94% and 87%, respectively, for
detecting ALVAL and 90% and 86%, respectively, for
quantifying intraoperative tissue damage.
We therefore (1) identified which
The institution of one or more of the authors (HGP) has received,
during the study period, funding from General Electric Healthcare
(Waukesha, WI, USA). One of the authors certifies that he (DEP), or a
member of his or her immediate family, has or may receive payments
or benefits, during the study period, an amount less than $10,000 from
Stryker (Mahwah, NJ, USA), and an amount of $10,000–$100,000
from Mako (Fort Lauderdale, FL, USA).
All ICMJE Conflict of Interest Forms for authors and Clinical
Orthopaedics and Related Research editors and board members are
on file with the publication and can be viewed on request.
Clinical Orthopaedics and Related Research neither advocates nor
endorses the use of any treatment, drug, or device. Readers are
encouraged to always seek additional information, including FDA-
approval status, of any drug or device prior to clinical use.
Each author certifies that his or her institution approved the human
protocol for this investigation, that all investigations were conducted
in conformity with ethical principles of research, and that informed
consent for participation in the study was obtained.
This work was performed at Hospital for Special Surgery, New York,
D. H. Nawabi, D. E. Padgett
Adult Reconstruction and Joint Replacement Division Surgery,
Hospital for Special Surgery, New York, NY, USA
S. Gold, H. G. Potter (&)
Department of Radiology and Imaging, Hospital for Special
Surgery, 535 East 70th Street, New York, NY 10021, USA
S. Lyman, K. Fields
Epidemiology and Biostatistics Core, Hospital for Special
Surgery, New York, NY, USA
S. Lyman, D. E. Padgett, H. G. Potter
Weill Cornell Medical College of Cornell University, New York,
Clin Orthop Relat Res (2014) 472:471–481
and Related Research®
A Publication of The Association of Bone and Joint Surgeons®
ALVAL and tissue damage in patients with MOM hip
implants. MRI can be used as a screening tool to guide
surgeons toward timely revision surgery.
Level of EvidenceLevel III, diagnostic study. See
Guidelines for Authors for a complete description of levels
MRI is sensitive and specific in detecting
The current generation of metal-on-metal (MOM) cobalt-
chromium-molybdenum bearings in hip arthroplasty have
shown overall survivorship rates at 5 and 10 years of 98%
and 94% [3, 4, 13, 18, 31] respectively. However, reports
have emerged describing the presence of periprosthetic soft
tissue lesions, which have been described interchangeably
as adverse local tissue reactions (ALTR) , adverse
reactions to metal debris (ARMD) , aseptic lympho-
metallosis , and pseudotumors . Although these
soft tissue masses are not malignant or infectious, they can
be associated with catastrophic local tissue destruction 
and complication rates of 50% after revision arthroplasty
. The importance of early detection and prompt revision
therefore is paramount.
Histologically, the soft tissue lesions are characterized
by lymphocytes, histiocytes, and necrosis  but also may
exhibit metallic deposits and corrosion products .
Campbell et al.  proposed a histologic scoring system
which predicts the presence of a lymphocyte-predominant
reaction in the soft tissues, known as ALVAL. This is
believed to reflect a type IV hypersensitivity reaction 
that typically is either absent or low grade in patients with
excess metal wear [2, 17]. Schmalzried  first proposed
the term ALTR to include all adverse responses resulting
from wear-related and biologic causes. ALTR has since
been used by others  and we have also used ALTR as an
encompassing term to describe all failures secondary to
periprosthetic soft tissue lesions, regardless whether
attributable to excess metal wear.
Several recent studies suggest ALTR can occur in
asymptomatic, well-functioning MOM hip arthroplasties
[15, 22, 34] and that its prevalence is similar in patients
who are asymptomatic and patients with painful MOM hip
implants . These studies used either ultrasonography or
metal artifact reduction sequence (MARS) MRI to detect
ALTR but did not find objective differences in the MRI
characteristics between well-functioning and failing hips.
With the emphasis on early revision surgery in cases of
ALTR, the use of MRI in identifying a failing MOM hip
implant warrants investigation. MARS MRI is recognized
as a useful modality in the assessment of ALTR around
MOM hip implants, showing characteristics such as size,
shape, and contents of lesions [10, 11, 27]. Newer proto-
observation of soft tissue around MOM hip implants .
However, it is unclear whether these MRI characteristics
correspond to ALTR that may result in substantial intra-
operative tissue damage. We sought to use this technology
to study the potential of modified MRI to detect a specific
subset of ALTR and intraoperative tissue damage as early
We therefore (1) identified which MRI characteristics
correlated with a histologically proven ALTR (using the
ALVAL score) and intraoperative tissue damage and
(2) developed a predictive model using modified MRI to
detect ALVAL and quantify intraoperative tissue damage.
Patients and Methods
From an institutional database we identified 68 patients
(70 hips) who had undergone preoperative modified MRI
followed by revision surgery for a failed MOM hip
arthroplasty. As part of an ongoing institutional initiative,
all patients with a MOM hip arthroplasty presenting with
pain and/or functional impairment were recommended to
undergo modified MRI. There were 31 males and 37
females with a median age of 52 and 57 years, respectively,
at the time of primary surgery. The median time to revision
was 36 months (range, 11–103 months). All methods were
approved by our institutional review board and informed
consent was obtained from all patients before enrollment in
The hips were revised by 13 surgeons at our institution.
Twenty-one (30%) of the primary hip arthroplasties were
performed at our institution and the remainder were per-
formed in other centers. The reasons for revision were
determined according to the categories used by the
National Joint Registry for England and Wales [7, 19].
These included aseptic acetabular loosening (n = 8), aseptic
femoral loosening (n = 3), component malalignment
(n = 4), infection (n = 1), and unexplained pain (n = 54). An
infection workup was performed on every patient in this
study which included serum C-reactive protein level and if
elevated, fluoroscopically guided aspiration of the hip with
fluid tested for microbiologic culture and sensitivities. A
primary diagnosis was established for all patients with a
history, physical examination, and radiographs, except for
the patients with component loosening and unexplained
pain. Acetabular and femoral loosening was suggested on
radiographs but confirmed intraoperatively. Patients with
unexplained pain were further investigated with modified
MRI. The decision to revise was based primarily on the
472Nawabi et al. Clinical Orthopaedics and Related Research1
presence of pain originating from the hip and/or the pres-
ence of a functional impairment. Most recently (since
acquisition of the data reported in our study), the presence
of an adverse synovial reaction on MRI is taken into
consideration when making a decision regarding revision
surgery. Forty-six of the 70 hips had large-diameter
([ 38 mm) MOM THA implants with monoblock cups.
These included 24 ASR (DePuy, Leeds, UK), eight BHR
(Smith & Nephew, Memphis, TN, USA), seven M2a-
Magnum (Biomet, Warsaw, IN, USA), four Durom (Zim-
mer, Warsaw, IN, USA), and three Conserve Plus (Wright
Medical Technology, Memphis, TN, USA) implants. The
remaining 24 hips had hip resurfacings, which included 19
BHR (Smith & Nephew), two Cormet (Corin, Cirencester,
UK), one ReCap (Biomet), and two Conserve Plus (Wright
Medical Technology) implants.
Intraoperative tissue damage was subjectively graded by
the operating surgeon using a four-point scale devised after
consultation with two experienced arthroplasty surgeons
± mild synovial reaction ± pseudocapsular dehiscence;
Grade 2=Grade1+moderate toseveresynovialreaction±
metallosis; or Grade 3 = Grade 2 + abductor damage and/or
bone loss. A damage score of 2 or greater was considered
indicative of severe soft tissue damage. Operative reports
were not available for two patients and therefore no intra-
operative score could be calculated; these patients were
excluded from the final analysis.
All patients underwent preoperative MRI using a stan-
dard protocol optimized to reduce metallic susceptibility
artifact . Scanning was performed using 1.5-T clinical
scanners (GE Healthcare, Waukesha, WI, USA) using
either an eight-channel cardiac coil (GE Healthcare) or a
three-channel shoulder coil (MedRad, Indianola, PA,
USA). Two-dimensional fast spin echo (FSE) images were
obtained in three planes using modifications to the pulse
parameters to reduce susceptibility artifact. A wider
receiver bandwidth and oversampling in the frequency
encoding axis were used to increase the strength of the
readout gradient ; the voxel size was reduced, thereby
improving spatial resolution; and the number of signals
averaged was increased to increase the signal-to-noise ratio
. Multiacquisition variable-resonance image combina-
tion (MAVRIC) was used in the coronal plane to reduce
susceptibility artifact by combining multiple data sets
acquired at frequency bands offset from the center proton
frequency  (Fig. 1). The specific parameters used are
summarized (Table 1). Compared with other MARS tech-
niques, our institutional MARS protocol differs greatly, as
instead of T1- or T2-weighted sequences, a moderate echo
time proton density sequence is used that is fluid sensitive
and can delineate very low signal intensity metallic
deposits without the loss of signal-to-noise ratio (SNR). In
addition, we add the MAVRIC sequence, typically in the
coronal plane. MAVRIC is currently under FDA review
and we hope it will be available to all orthopaedic surgeons
in the near future.
MR images were evaluated by two musculoskeletal
radiologists (HGP, AB) through consensus agreement. One
is a senior musculoskeletal radiologist with more than 10
(AB). MR images were evaluated for the presence and vol-
presence of fluid signal intensity material or solid debris,
either contained by the pseudocapsule or communicating
with the disrupted pseudocapsule. The synovitis was char-
acterized as (1) solid; (2) fluid; or (3) mixed (solid and fluid)
in appearance and the maximal thickness of the synovial
lining was measured on axial FSE images. Solid synovitis
was denoted by intermediate signal intensity material while
pure fluid collections had a signal intensity of free water and
mixed synovitis had characteristics of both. Any decom-
pression of synovitis into the trochanteric or iliopsoas bursa
also was noted (Fig. 2). Osteolysis was defined by the
presence of areas of osseous resorption, appearing as inter-
(Fig. 3). The volumes of synovitis and osteolysis were cal-
culated using a previously validated method of manual
segmentation from the coronal MAVRIC or axial FSE
images [26, 32]. The pseudocapsule was evaluated for
dehiscence, which was characterized by either anterior or
posterior capsular detachment. The presence of extracapsular
femoral and acetabular components as denoted by circum-
ferential bone resorption surrounding the arthroplasty. The
distension of the pseudocapsule (Fig. 4) Preexisting abductor
tears were denoted by abnormal signal and morphologic fea-
reaction did not impinge or abut the tendon. Additionally, the
obturator, sciatic, and femoral nerves were assessed for neu-
rovascular compression, defined by the loss of normal fat
planes surrounding the nerve (Fig. 5). Enlarged lymph nodes
were denoted by intermediate signal intensity foci in the
corresponding anatomic distributions around the implant.
Data were collected on a standard form (Appendix 1).
All tissue samples excised at revision surgery were
submitted for histologic examination and were reviewed by
one musculoskeletal pathologist (GP). The revision sur-
geons routinely and consistently sampled tissue from the
posterior capsule and inferior neck of the femur. The tissue
samples were processed routinely: serially cut to maximize
information obtained and stained with hematoxylin and
Volume 472, Number 2, February 2014MRI of Metal-on-metal Hip Arthroplasty473
Fig. 1A–B (A) The FSE pulse
sequence for a 29-year-old man
after a right hip resurfacing arthro-
artifact (white arrowheads) aris-
ing from the cobalt-chromium
implant, precluding observation
of the synovial lining. (B) A coro-
nal MAVRIC sequence shows
marked reduction in susceptibility
artifact, unmasking right hip syno-
vitis (white arrows).
Fig. 2A–C (A) An axial FSE image for a 51-year-old woman after
right hip resurfacing arthroplasty shows mixed- (fluid and solid) type
synovitis (white arrow). (B) The coronal MAVRIC prototype
sequence for a 57-year-old man after a MOM THA shows marked
synovial thickening (white arrow). (C) The axial FSE image for a
65-year-old man after his THA shows decompression of synovitis into
the greater trochanteric bursa (white arrowhead). There is lateral
dehiscence of the posterior pseudocapsule (white arrow). The overlaid
graphics show the segmentation method used to quantify the volume
Table 1. Imaging parameters of the hip at 1.5 T in the presence of metal
ParameterSTIRAxial FSE Sagittal FSE Coronal FSECoronal MAVRIC
TR (ms) 45004500–50005500–65004500–5500 4000–6000
TE (ms)18 24–3025–3024–3421–43
RBW (kHz) 83–100 83–10083–100 83–100±125
NEX2 4–54–5 4–5 .5
FOV (cm)Inter-tro 17–1918–20 18–2420–24
Matrix 256 9 192512 9 256 512 9 352512 9 384320–512 9 256–384
Slice thickness (mm)/gap 5/04/0 3–4/0 4/03–4.5/0
STIR = short-tau fast inversion recovery; FSE = fast spin echo; MAVRIC = multiacquisition variable-resonance image combination TR =
repetition time; TE = echo time; TI = time to inversion; RBW = receiver bandwidth; NEX = number of excitations FOV = field of view.
474Nawabi et al. Clinical Orthopaedics and Related Research1
eosin. Samples were examined under light microscopy
without knowledge of MRI findings. Sections were evalu-
ated for the presence of fibrinous exudates, necrosis,
inflammatory cells, metallic deposits, and corrosion prod-
ucts. The status of the synovial lining, inflammatory
infiltrate, and tissue organization was recorded to give an
ALVAL score from 0 to 10 as proposed by Campbell et al.
. In the circumstance where these features could not be
delineated reliably owing to widespread necrosis, no score
was given. There were four such cases. An ALVAL score
of 5 or greater was consistent with a diagnosis of moderate
to severe ALVAL . There were four histology samples
in which only necrosis was observed, and these therefore
were noncontributory to the final analysis.
The first dependent variable considered in this study was
whether the patients had ALVAL (ALVAL score C 5). The
independent (predictor) variables considered were the MRI
was whether the patients had severe intraoperative tissue
damage (damage score C 2). This also was compared with
the MRI characteristics (Appendix 1). For both analyses,
Fisher’s exact test was used to compare categorical inde-
pendent variables between outcome groups and the
Wilcoxon rank-sum test was used to compare continuous
independent variables. The Spearman rank correlation
coefficient was used to identify correlations between MRI
characteristics and the ALVAL and tissue damage scores.
Random forest analysis was used to determine which MRI
characteristics were most predictive of detecting ALVAL
(ALVALscoreC 5)and intraoperative tissue damage andto
identify the sensitivity and specificity of selected MRI
quantifying intraoperative tissue damage as none to mild
(Grades 0–1) or severe (Grades 2–3). A random forest is an
ensemble (set) of decision trees, each built from a bootstrap
sample of observations. Each decision tree is constructed by
random subset of variables) that allows for the best segre-
gation of outcome groups. The outcome of each observation
is predicted by the majority assignment of the ensemble of
predictive ability is reflected by its calculated importance
were pooled over 10 forests of 10,000 trees for each of the
previously in MRI research . All inferential analyses
were performed using the SAS System for Windows 9.2
(SAS Institute Inc, Cary, NC, USA). The R party package
(R Foundation for Statistical Computing, Vienna, Austria)
was used to perform the random forest analysis.
When comparing patients with ALVAL (score C 5) with
patients with a low probability of ALVAL (score\5), the
mixed pattern of synovitis (solid and fluid) with higher
Fig. 3 A coronal MAVRIC prototype pulse sequence for a 52-year-
old woman obtained after right hip resurfacing arthroplasty shows
extensive replacement of the normal periacetabular marrow fat by low
signal intensity (white arrowheads), consistent with osteolysis. There
is an adjacent large extracapsular low signal intensity deposit (white
arrow) abutting the sciatic nerve.
Fig. 4 A coronal FSE image obtained after a left MOM THA in a
62-year-old man shows decompression of the synovitis into the
greater trochanteric bursa with associated disruption of the hip
abductors and retraction of the torn tendons (white arrow). Atrophy of
the muscle bellies also is evident (black arrow).
Volume 472, Number 2, February 2014MRI of Metal-on-metal Hip Arthroplasty475
Decompression of synovitis (Fig. 8), low signal intensity
deposits, soft tissue edema, pseudocapsular dehiscence,
abductor disruption, and neurovascular compression were
more likely to be present on MRI in patients with ALVAL
(Table 2). Patients with ALVAL were not more likely to
have implant loosening as detected by MRI. Patients with
severe tissue damage were more likely (p\0.001) to have a
mixed pattern of synovitis with higher (p\0.001) maximal
synovial thicknesses and higher (p\0.001) synovial vol-
umes as determined on MRI. Decompression of synovitis,
low signal intensity deposits, soft tissue edema, pseudocap-
sular dehiscence, abductor disruption, and neurovascular
in patients with severe tissue damage (Fig. 9). These patients
of nodes on MRI. Maximal synovial thickness on MRI cor-
Synovialvolume onMRI alsocorrelatedwith(q = 0.74; 95%
CI, 0.61–0.84) the ALVAL score.
In our model, maximal synovial thickness was the stron-
gest predictor for the diagnosis of ALVAL. The type and
volume of synovitis also were strong predictors of ALVAL.
nodes was not indicative of ALVAL (Fig. 10). The presence
of pseudocapsular dehiscence, extracapsular synovial
decompression, and the type of synovitis were the three
strongest predictors of severe intraoperative tissue damage
(Fig. 11). Neurovascular compression, soft tissue edema,
and the presence of nodes were not suggestive of severe
tissue damage. Our MRI predictive model found sensitivity
and specificity of 94% and 87%, respectively, for detecting
ALVAL and 90% and 86%, respectively, for quantifying
intraoperative tissue damage.
Periprosthetic soft tissue lesions around MOM hip implants
have been reported by numerous authors using various
terms including ALTR, ARMD, ALVAL, metallosis, and
pseudotumor [1, 17, 23, 24, 33]. These soft tissue masses
can be associated with major tissue destruction  and
therefore early recognition and prompt revision are critical.
Our aims were to identify which MRI characteristics cor-
related with the ALVAL score and intraoperative tissue
Fig. 5A–B (A) An axial FSE
image obtained after a right hip
resurfacing arthroplasty in a 51-
year-old woman shows marked
(white arrow) impinging the fem-
oral nerve (white arrowhead).
(B) The coronal FSE image for a
57-year-old man obtained after a
right THA shows marked poster-
ior synovial expansion (white
arrow) abutting the adjacent sci-
atic nerve (white arrowheads).
Fig. 6 A box plot shows the interquartile range (box edges represent-
ing 25thand 75thpercentiles), median (dark bar inside box), and mean
(circle) for synovial thickness by the presence of ALVAL. The error
bars represent the minimum and maximum observed values within 1.5
indicates a major difference in medians between outcome groups.
476 Nawabi et al.Clinical Orthopaedics and Related Research1
damage and to develop a predictive model using modified
MRI to detect ALVAL as confirmed by histology and to
quantify intraoperative tissue damage.
We acknowledge several limitations to our study. First,
although we chose the term ALTR to encompass all
periprosthetic soft tissue lesions, we only studied a specific
subset, namely patients with ALVAL. This was because
ALVAL can be confirmed histologically. Therefore, our
conclusions on the predictive value of MRI can be applied
only to an ALTR occurring secondary to ALVAL. Further-
more, adverse tissue responses secondary to excessive metal
wear [14, 16] tend to be histiocyte-dominant with low
ALVAL scores [2, 17] and therefore our study design would
have clustered these cases in the low-probability ALVAL
group. Second, the operating surgeons were blinded to MRI
findings and not given any guidance regarding which tissue
four samples in which only necrosis was observed, and these
ALVAL score has been reported to have interobserver and
intraobserver variabilities of 0.71 and 0.68, respectively .
Our scores are limited by this variability. We addressed this
is subject to less variability. Fourth, we analyzed MOM hip
implants from various manufacturers. This could not be
avoided because we are a tertiary referral center and 70% of
the hips in this study were referred from outside centers.
Finally, the intraoperative tissue damage score is subjective
and not validated. The association between quantifiable MRI
characteristics and macroscopic tissue damage at revision
surgery has not been studied and therefore we believed it
Fig. 7 A box plot shows the interquartile range (box edges represent-
ing 25thand 75thpercentiles), median (band inside box), and mean
(circle) for synovial volume by the presence of ALVAL. The error bars
the interquartile range values. Outliers are not shown. The asterisk
indicates a major difference in medians between outcome groups.
Fig. 8A–B (A) An axial (A) FSE image obtained after MOM THA in
a 57-year-old man shows marked synovial expansion and thickening
(white arrows) with anterior and posterior decompression. (B) The
patient’s coronal FSE image shows a large volume of synovitis
decompressing inferiorly (white arrows) and superiorly into the
subiliacus bursa (black arrowheads). The high volume of mixed-
(fluid and solid) type synovitis combined with the greatly thickened
synovial lining and disruption of the abductors resulting from
distention of the pseudocapsule is suggestive of a high ALVAL
score. This was confirmed at revision surgery with subsequent
histologic analysis showing an ALVAL score of 9.
Volume 472, Number 2, February 2014 MRI of Metal-on-metal Hip Arthroplasty 477
on intraoperative tissue damage, however, are weakened by
We found that maximal synovial thickness and synovial
volume on MRI correlated with the ALVAL score. We also
found that patients with an ALVAL score of 5 or greater
were more likely to have a mixed pattern of synovitis (solid
and fluid) with higher maximal synovial thicknesses and
synovial volumes. These patients also were more likely to
have decompression of synovitis, low signal intensity
deposits, soft tissue edema, and pseudocapsule dehiscence.
Finally, abductor disruption and neurovascular compres-
sion were more likely to be present on MRI in patients
diagnosed with ALVAL. These findings are in contrast to
recent MRI studies [10, 27] which found no distinguishing
features between symptomatic and asymptomatic tissue
lesions. A recent ultrasound study, however, did find that
joint expansion and cystic and mass patterns on ultrasound
were associated with symptomatic MOM hips .
Regarding tissue damage, we found that when compar-
ing patients with a damage score of 2 or greater with
patients with no or mild damage, the patients with severe
tissue damage were more likely to have pseudocapsular
dehiscence and a mixed pattern of synovitis with higher
maximal synovial thickness and volume. The association
between MRI characteristics and intraoperative tissue
damage has not been studied previously. Our findings can
provide the revision surgeon with vital preoperative clues
regarding tissue damage and aid in formulating a plan in
the presence of massive soft tissue defects.
The random forest predictive model used in this study
provides us with an algorithm by which we can predict the
outcomes for specific patients based on of the various MRI
characteristics. This has advantages over a traditional
scoring system in that the weights applied to each char-
acteristic are dynamic. If a traditional MR scoring system
was published, these scores would become static. There-
screening tool such that the results of our random forest
analysis can be updated in real time as new patients are
added to the cohort. Our predictive model showed that
maximal synovial thickness and a mixed synovial pattern
were the two strongest predictors for detection of ALVAL.
It also showed that pseudocapsule dehiscence, mixed
Table 2. Results of the comparison of MRI characteristics in patients
with and without ALVAL
(ALVAL C 5)
(N = 32 hips)
(N = 34 hips)
Presence of synovitis
synovitis (% yes)
85% 41% 0.002
deposits (% yes)
Soft tissue edema
dehiscence (% yes)
Presence of osteolysis
Presence of nodes
Table 3. Results of the comparison of MRI characteristics in patients
with severe versus none-mild tissue damage
score C 2)
(N = 40 hips)
(N = 30 hips)
synovitis (% yes)
synovitis (% yes)
deposits (% yes)
Soft tissue edema
dehiscence (% yes)
osteolysis (% yes)
compression (% yes)
Presence of nodes
478Nawabi et al. Clinical Orthopaedics and Related Research1
pattern of synovitis, and decompression of synovitis were
the strongest predictors of severe intraoperative tissue
damage. These findings are in agreement with a recent
study which concluded that consistency rather than the size
of the pseudotumor is useful when predicting the likelihood
for revision . We found sensitivity and specificity of
94% and 87%, respectively, for detecting ALVAL and 90%
and 86%, respectively, for quantifying tissue damage.
These values are a major improvement on the predictive
ability of blood cobalt and chromium ion levels for
identifying a failing hip implant, which have sensitivity
and specificity of 63% and 86%, respectively .
Other groups have used MRI to study soft tissue lesions
around MOM hip implants, but none has used quantitative,
reproducible MRI features and none has compared findings
30, 35]. In a retrospectivestudy, Toms etal.  qualitatively
graded adverse reactions as mild, moderate, or severe and
of the lesions. Hart et al.  proposed an MRI classification
Fig. 9A–B (A) The axial FSE image obtained after a left MOM THA
in a 46-year-old man shows synovial expansion and thickening with
decompression of synovitis into the greater trochanteric bursa (white
arrows) through a lateral dehiscence in the pseudocapsule. (B) The
patient’s coronal FSE image shows synovial expansion (white
arrowheads) undermining the hip abductors with resulting disruption
of the anterolateral fibers of the gluteus medius (small white arrow).
The mixed-type synovial expansion with associated pseudocapsular
dehiscence and extensive decompression of synovitis suggests
substantial intraoperative damage. This is further supported by the
large volume of synovitis and thick synovial lining. These findings
were confirmed at revision surgery, when substantial soft tissue
damage was seen and the patient received an intraoperative damage
score of 3.
Fig. 10 A random forest analysis shows the normalized importance
of MRI characteristics in predicting the presence of ALVAL.
Importance is normalized to the best predictor, assigned the value
Fig. 11 A random forest analysis shows the normalized importance
of MRI characteristics in predicting the presence of intraoperative
tissue damage. Importance is normalized to the best predictor,
assigned the value of 1.
Volume 472, Number 2, February 2014 MRI of Metal-on-metal Hip Arthroplasty479
undergoing revision surgery and therefore correlation of MRI
characteristics with histologic findings was not possible.
Modified MRI is a reproducible, noninvasive method to
assess patients with a MOM hip implant. It has a strong
predictive value in being able to detect an adverse tissue
response in the form of ALVAL around a failed MOM hip
arthroplasty and is also predictive of severe tissue damage.
Maximal synovial thickness and synovial volume are
quantifiable parameters that can be calculated on modified
MRI and may be effective markers for surveillance of
MOM hip arthroplasties. Further longitudinal study of
asymptomatic hips is required to propose appropriate cut-
off values beyond which revision surgery should be
considered. Our observations suggest a mixed pattern of
synovitis, with pseudocapsule dehiscence and decompres-
sion of synovitis, in the setting of large synovial volumes
and synovial thicknesses may be an indication for early
intervention in a MOM hip arthroplasty.
the MRI analysis, Matthew Koff PhD for help with the statistical
analysis, and Giorgio Perino MD for grading the histologic samples.
We thank Alissa Burge MD for assistance with
Appendix 1. Scoring sheet used to evaluate patients with a metal-on-metal hip arthroplasty
480Nawabi et al.Clinical Orthopaedics and Related Research1
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Volume 472, Number 2, February 2014MRI of Metal-on-metal Hip Arthroplasty481