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Fatty Muscle Atrophy: Prevalence
in the Hindfoot Muscles on MR Images
of Asymptomatic Volunteers and
Patients with Foot Pain1
Daniel T. Schmid, MD
Juerg Hodler, MD, MBA
Bernard Mengiardi, MD
Christian W. A. Pfirrmann, MD
Norman Espinosa, MD
Marco Zanetti, MD
Purpose:
To determine prevalence and degree of fatty muscle atrophy in plantar foot muscles in asymptomatic volunteers
and in patients with foot pain.
Materials and
Methods:
Institutional review board approval and informed consent
were obtained. The prevalence and degree of fatty muscle
atrophy were evaluated with magnetic resonance imaging
in the abductor digiti minimi (ADM), flexor digitorum
brevis (FDB), abductor hallucis (AH), and quadratus plantae (QP) muscles in 80 asymptomatic volunteers (mean
age, 48 years; range, 23– 84 years) and 80 patients with
foot pain (mean age, 48 years; range, 20 – 86 years). Muscles were characterized as normal (grade 0) or as having
mild (grade 1) or substantial (grade 2) fatty atrophy by two
readers separately. Results of visual grading for both readers were compared by using the Mann-Whitney test. Associations between age and degree of fatty muscle atrophy
were assessed by using the Kruskal-Wallis test.
Results:
Readers 1 and 2 found substantial fatty atrophy of the
ADM muscle in four (5%) and five (6%) volunteers, respectively, and in three (4%) and nine (11%) patients,
respectively. One reader diagnosed substantial fatty atrophy of the AH muscle in three (4%) volunteers and of the
FDB muscle in two (2%) volunteers. Prevalence for the QP
muscle varied between 0% and 1%. An association between age and degree of fatty atrophy of the ADM muscle
was found for volunteers by both readers and for patients
by reader 1 (P ⬍ .01).
Conclusion:
Prevalence of fatty muscle atrophy of the ADM muscle—
classically considered to represent entrapment neuropathy—is between 4% and 11% in both asymptomatic volunteers and patients with foot pain, and it increases with age.
娀 RSNA, 2009
1
From the Departments of Radiology (D.T.S., J.H., B.M.,
C.W.A.P., M.Z.) and Orthopedic Surgery (N.E.), Orthopedic
University Hospital Balgrist, Forchstrasse 340, CH-8008
Zurich, Switzerland. Received January 6, 2009; revision
requested March 4; revision received April 21; accepted
April 26; final version accepted May 11. Address correspondence to M.Z. (e-mail: [email protected] ).
姝 RSNA, 2009
160
radiology.rsna.org ▪ Radiology: Volume 253: Number 1—October 2009
MUSCULOSKELETAL IMAGING: Prevalence of Fatty Atrophy of Hindfoot Muscles
C
hronic pain in the hindfoot can be
caused by a variety of abnormalities, many of which can be detected
with magnetic resonance (MR) imaging.
These diagnoses include osteochondral
lesions (1), stress fractures (2,3), ligament lesions (4), tendon disorders (5),
and rheumatologic disorders (6,7).
Nerve entrapment is a cause of
chronic hindfoot pain that can easily
be overlooked on MR images. Nerve
entrapment may be the cause of heel
pain in up to 20% of patients (8–11).
The most common entrapment disorder in the hindfoot is entrapment of
the first branch of the lateral plantar
nerve, also called Baxter neuropathy
(8). The entrapment is postulated to
occur as the nerve passes between the
deep fascia of the abductor hallucis
(AH) muscle and the medial caudal
margin of the medial head of the quadratus plantae (QP) muscle or as the
nerve passes just anterior to the medial calcaneal tuberosity. Plantar spur
formation at the medial calcaneal tuberosity has been reported to be a
possible cause of entrapment (8–11).
MR imaging cannot typically be
used to prove compressive (entrapment) neuropathies by means of signal
intensity abnormalities or morphologic changes of peripheral nerves
themselves. Selective muscle edema
Advances in Knowledge
䡲 The prevalence of fatty muscle
atrophy of the abductor digiti
minimi (ADM), flexor digitorum
brevis, abductor hallucis, or quadratus plantae muscles in asymptomatic volunteers is low (⬍8%)
and is similar to that in patients
with foot or ankle pain who are
referred for MR imaging.
䡲 The prevalence of fatty atrophy of
the ADM muscle in both volunteers and patients (4%–11%) is
higher than that of the flexor digitorum brevis (0%–2%), abductor
hallucis (1%– 4%), and quadratus
plantae (0%–1%) muscles.
䡲 The prevalence of fatty atrophy of
the ADM muscle increases with
age.
and fatty atrophy are indirect signs of
entrapment neuropathy on MR images
(12). Fatty atrophy of the abductor
digiti minimi (ADM) muscle may reflect chronic compression of the inferior calcaneal nerve, which is associated with the clinical diagnosis of Baxter neuropathy. However, there is
debate as to whether selective fatty
muscle atrophy also occurs unrelated
to nerve entrapment. Recht et al (9)
found selective fatty atrophy of the ADM
muscle in 38 (6%) of 602 patients referred for foot and ankle MR imaging, but
only one patient had clinical and electrophysiologic signs of Baxter neuropathy.
Another study (13) demonstrated a significant association of ADM muscle atrophy with calcaneal spur formation, plantar fasciitis, and advancing age. Fatty atrophy of intrinsic foot muscles has also
been described (14) in patients with diabetic neuropathy.
Our hypothesis was that fatty muscle
atrophy could be found in asymptomatic
volunteers on MR images and does not
have to be related to the presence of a specific diagnosis. We evaluated the prevalence and degree of fatty replacement of the
muscles around the heel (ie, ADM, flexor
digitorum brevis [FDB], AH, and QP muscles) in an asymptomatic population and
compared the findings with those in patients with foot pain.
Materials and Methods
Volunteers
Eighty asymptomatic volunteers (38
men, 42 women; mean age, 48 years;
range, 23– 84 years) were studied. MR
images of these volunteers were acImplications for Patient Care
䡲 The clinical relevance of fatty atrophy of the ADM muscle is uncertain because its prevalence is
similar in patients with foot pain
and asymptomatic volunteers.
䡲 Radiologists should exercise caution in attributing clinical importance to fatty atrophy of the ADM
muscle when it is an incidental
finding.
Radiology: Volume 253: Number 1—October 2009 ▪ radiology.rsna.org
Schmid et al
quired between August 2003 and July
2004 for another study (15), which did
not focus on muscles. Inclusion criteria were (a) no current pain in the foot
or ankle, (b) no prior foot or ankle
surgery, (c) no visit to a physician because of foot and ankle complaints,
(d) no trauma or injury to the foot or
ankle during the previous 2 years, and
(e) no known systemic inflammatory disease. At least six men and six women were
included for each decade of life between 20
and 70 years. Three men and five women
aged between 70 and 84 years were also
included. The side imaged (right or left)
was selected randomly.
The portion of the study in asymptomatic volunteers was approved by
the institutional review board. Informed consent was obtained from
each volunteer. Our institutional review board does not require approval
for the review of patients’ records or
images; however, according to a law
protecting patients’ rights, patients
have to be asked to give permission
for anonymized review of their medical data for scientific purposes before
the examination. All patients in our
study granted permission.
Patients
Eighty patients (38 men, 42 women;
mean age, 48 years; range, 20 – 86
years) who had been referred for MR
imaging because of foot pain were in-
Published online before print
10.1148/radiol.2531090035
Radiology 2009; 253:160 –166
Abbreviations:
ADM ⫽ abductor digiti minimi
AH ⫽ abductor hallucis
FDB ⫽ flexor digitorum brevis
QP ⫽ quadratus plantae
Author contributions:
Guarantors of integrity of entire study, D.T.S., M.Z.; study
concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or
manuscript revision for important intellectual content, all
authors; approval of final version of submitted manuscript, all authors; literature research, D.T.S., J.H., N.E.,
M.Z.; clinical studies, all authors; statistical analysis,
D.T.S., M.Z.; and manuscript editing, all authors
Authors stated no financial relationship to disclose.
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MUSCULOSKELETAL IMAGING: Prevalence of Fatty Atrophy of Hindfoot Muscles
cluded. Patients were imaged between
December 2007 and June 2008. Patients were consecutively included to
match the age and sex of the volunteers. Exclusion criteria were (a) prior
foot surgery, (b) known trauma to the
foot or ankle, (c) infection (eg, skin ulceration, osteomyelitis), (d) tumors previously diagnosed with another imaging
modality or biopsy, and (e) severe congenital malformation. Patients were excluded on the basis of clinical diagnosis
and patient history, not MR imaging findings. The primary clinical indications for
MR imaging and the main MR imaging
findings are listed in Table 1.
MR Imaging
MR imaging was performed on one of
three 1.5-T systems (Magnetom Symphony [n ⫽ 110], Magnetom Espree [n ⫽
23], or Magnetom Avanto [n ⫽ 27]; Siemens Medical Solutions, Erlangen, Germany) with a circularly polarized sendreceive extremity coil (Siemens Medical
Solutions). T1-weighted (repetition time
msec/echo time msec, 572/14; section
thickness, 3–3.5 mm) and T2-weighted
Schmid et al
(4139/86; section thickness, 3–3.5 mm)
coronal images were used to assess the
degree of fatty muscle atrophy and to
measure the cross-sectional area of the
individual muscles. Volunteers and patients were imaged in the supine position
with one foot (randomly chosen in volun-
teers, painful foot in patients) in the coil
in a neutral position.
Image Interpretation
All original Digital Imaging and Communications in Medicine data sets were rendered anonymous so that the readers
Table 1
Primary Clinical Indications for and Main Findings at MR Imaging in the Patient Group
(n ⴝ 80)
Characteristic
Plantar fasciitis or thickened plantar fascia
Tendon disorder
Osteoarthritis of one or more hindfoot joints
Stress fracture
Osteochondral lesions
Neoplastic or tumorlike lesions
Lesions of ankle ligaments
Osteonecrosis
Synovitis or spondylarthritis
Tarsal tunnel syndrome
Normal MR findings
Indication*
Finding
8 (10)
26 (32)
16 (20)
8 (10)
7 (9)
3 (4)
5 (6)
5 (6)
2 (2)
2 (2)
NA
15 (19)
17 (21)
10 (12)
8 (10)
6 (8)
6 (8)†
5 (6)
2 (2)
2 (2)
0 (0)
9 (11)
Note.—Data are numbers of patients, with percentages in parentheses. NA ⫽ not applicable.
* Data do not sum to 80 because some patients had more than one indication for imaging.
†
Pigmented villonodular synovitis or scar tissue (n ⫽ 2), ganglion (n ⫽ 3), or osteochondroma (n ⫽ 1).
Figure 1
Figure 1: (a– c) Coronal T1-weighted fast spin-echo MR images illustrate different grades of fatty atrophy of ADM muscle: (a) grade 0 (52-year-old male volunteer),
(b) grade 1 (70-year-old female volunteer), and (c) grade 2 (44-year-old female patient).
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MUSCULOSKELETAL IMAGING: Prevalence of Fatty Atrophy of Hindfoot Muscles
Figure 2
Schmid et al
would be blinded to whether images belonged to a patient or to a volunteer. Image interpretation and measurements
were performed by using open-source
software (OsiriX, version 3.2.1; OsiriX
Imaging Software, Geneva, Switzerland) (16) on a computer (Mac OS X,
version 10.5.4; Apple, Cupertino,
Calif).
Table 3
Cross-sectional Areas of the Hindfoot
Muscles in Volunteers and Patients
Muscle and Group
ADM
Volunteers
Patients
FDB
Volunteers
Patients
AH
Volunteers
Patients
QP
Volunteers
Patients
Figure 2: Coronal T1-weighted fast spin-echo
MR image of a 60-year-old male volunteer at level
of cross-sectional area measurement. Osseous
insertion of tibiocalcaneal ligament (arrowheads)
is visible. Regions of interest (white boundaries)
were drawn around ADM, FDB, AH, and QP
muscles.
Cross-sectional Area (cm2)
2.5 ⫾ 0.6 (0.3–4.1)
2.3 ⫾ 0.6 (0.4–3.5)
1.5 ⫾ 0.5 (0.0–2.8)
1.5 ⫾ 0.6 (0.1–3.7)
2.1 ⫾ 0.7 (0.0–3.7)
2.0 ⫾ 0.8 (0.0–4.1)
0.8 ⫾ 0.4 (0.2–2.1)
0.8 ⫾ 0.6 (0.0–4.3)
Note.—Data are means ⫾ standard deviations, with
ranges in parentheses. By using analysis of variance, no
significant differences were found between patients and
volunteers for the area of any of the muscles.
A qualitative grading of fatty muscle
atrophy was determined by two independent readers (B.M. and J.H., with 5 and
20 years experience in musculoskeletal
radiology, respectively). Grading of fatty
atrophy was performed separately for the
ADM, FDB, AH, and QP muscles. A
three-point scale was used to grade the
degree of fatty muscle atrophy on coronal
T1-weighted images: 0 ⫽ normal muscle,
1 ⫽ mild fatty atrophy with more muscle
than fat, and 2 ⫽ substantial fatty atrophy
with more fat than muscle or equal parts
fat and muscle (Fig 1). The readers were
asked to consider the entire muscle volume for grading, not just a single section,
and to read as they would during clinical
routine. To calibrate the evaluation, each
reader had a set of reference images with
different grades of fatty muscle atrophy
available. Measurement of the crosssectional area of the ADM, FDB, AH, and
QP muscles was performed (D.T.S., a 4th
year resident) on the T1-weighted coronal MR image at the level where the bony
insertion of the tibiocalcaneal ligament at
the calcaneus was best visualized (Fig 2).
Regions of interest were defined for each
muscle at 200% zoom to minimize measurement errors. Measurements were repeated in 32 (20%) of 160 subjects to
assess variability.
Table 2
Fatty Muscle Atrophy Grading for 80 Volunteers and 80 Patients according to Reader and Interobserver Agreement
Muscle and Group
ADM
Volunteers
Patients
FDB
Volunteers
Patients
AH
Volunteers
Patients
QP
Volunteers
Patients
Reader 1*
Grade 0
Reader 2*
Age (y)†
Reader 1*
Grade 1
Reader 2*
Age (y)†
Reader 1*
Grade 2
Reader 2*
Age (y)†
␬ Value
65 (81)
57 (71)
66 (83)
56 (70)
45 ⫾ 15
45 ⫾ 15
11 (14)
20 (25)
9 (11)
15 (19)
61 ⫾ 13
58 ⫾ 16
4 (5)
3 (4)
5 (6)
9 (11)
71 ⫾ 9
61 ⫾ 18
0.679
0.556
78 (98)
75 (94)
75 (94)
76 (95)
48 ⫾ 16
48 ⫾ 17
1 (1)
5 (6)
3 (4)
4 (5)
77 ⫾ 5
51 ⫾ 20
1 (1)
0 (0)
2 (2)
0 (0)
69 ⫾ 11
...
0.560
0.412
75 (94)
69 (86)
74 (93)
73 (91)
48 ⫾ 16
47 ⫾ 16
4 (5)
10 (13)
3 (4)
6 (8)
69 ⫾ 9
59 ⫾ 18
1 (1)
1 (1)
3 (4)
1 (1)
73 ⫾ 11
86 ⫾ 0
0.329
0.386
68 (85)
61 (76)
69 (86)
64 (80)
47 ⫾ 15
47 ⫾ 16
11 (14)
19 (24)
11 (14)
15 (19)
62 ⫾ 14
55 ⫾ 18
1 (1)
0 (0)
0 (0)
1 (1)
76 ⫾ 0
24 ⫾ 0
0.496
0.421
* Data are numbers of subjects, with percentages in parentheses.
†
Data are means ⫾ standard deviations.
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163
MUSCULOSKELETAL IMAGING: Prevalence of Fatty Atrophy of Hindfoot Muscles
Schmid et al
Table 4
Findings at Secondary Review of Subjects with Substantial (Grade 2) Fatty Atrophy according to Muscle
Finding
Plantar fasciitis
Calcaneus spur
Stress fracture
Osteoarthritis or osteochondral lesion
Posterior tibial tendon partial rupture
Peroneal tendon luxation
Spring ligament insufficiency
Calcaneus avulsion fracture*
Clubfoot deformity*
Otherwise normal MR findings
ADM (n ⫽ 14)
Volunteers
Patients
FDB (n ⫽ 2)
Volunteers
Patients
AH (n ⫽ 4)
Volunteers
Patients
QP (n ⫽ 2)
Volunteers
Patients
0
0
1
0
0
1
0
0
0
3
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
1
0
0
0
1
0
0
0
0
0
0
0
0
0
0
5
1
1
1
1
0
1
1
1
1
0
0
0
1
0
0
0
0
0
0
0
0
1
1
0
0
0
0
0
0
0
0
0
1
0
0
0
1
1
0
Note.—Data are numbers of patients. Data may sum to more than the number of findings of substantial atrophy because patients could have more than one finding.
* Findings in the same patient.
Secondary Review
In subjects in whom at least one reader
diagnosed substantial fatty muscle atrophy, a secondary review of all MR images
and available clinical charts was performed in consensus by a musculoskeletal
radiologist (M.Z., 16 years experience)
and an orthopedic foot surgeon (N.E., 8
years experience). Diagnoses potentially
related to nerve entrapment (eg, masses
in or around the lateral plantar nerve,
plantar fasciitis) were noted.
Statistical Analysis
Statistical analysis was performed with
software (SPSS, version 16.0.1 for Apple
Macintosh; SPSS, Chicago, Ill). Descriptive statistics and analysis of variance
were used to evaluate and compare crosssectional areas of the ADM, FDB, AH,
and QP muscles between the volunteer
and patient groups. The Mann-Whitney
test was used to compare the grading of
fatty muscle atrophy and mean muscle
cross-sectional area between the volunteer and patient groups. The Cohen ␬ statistic was used to evaluate interobserver
agreement for the grading of fatty muscle
atrophy. According to Landis and Koch
(17), ␬ values smaller than 0.20 indicate
poor agreement; 0.21– 0.40, fair agreement; 0.41– 0.60, moderate agreement;
0.61– 0.80, good agreement; and 0.81–
1.00, very good agreement. The KruskalWallis test was used to analyze the association between age and the degree of
fatty muscle atrophy.
164
Bonferroni adjustment was applied to
adjust for multiple comparisons (age vs
fatty muscle atrophy grade and crosssectional muscle diameter vs fatty muscle
atrophy grade for two readers and comparison of the cross-sectional muscle areas between volunteers and patients). P
values less than .01 were considered to
indicate a significant difference. Intraclass
correlation coefficients were used to assess measurement variability of the crosssectional area of the ADM, FDB, AH, and
QP muscles.
Results
Substantial (grade 2) fatty muscle atrophy
of at least one of the four muscles (ADM,
AH, FDB, and QP) was observed by at
least one reader in six (8%) of 80 volunteers and in 10 (12%) of 80 patients. For
the ADM muscle, grade 2 fatty atrophy
was found in four (5%) volunteers and
three (4%) patients by reader 1 and in
five (6%) volunteers and nine (11%) patients by reader 2. For the FDB muscle,
grade 2 fatty atrophy was reported in one
(1%) volunteer by reader 1 and in two
(2%) volunteers by reader 2 but in none
of the patients by either reader. For the
AH muscle, grade 2 fatty atrophy was
reported in one (1%) volunteer and one
(1%) patient by reader 1 and in three
(4%) volunteers and one (1%) patient by
reader 2. For the QP muscle, grade 2 fatty
atrophy was seen in one (1%) volunteer
and no patients by reader 1 and in no
volunteers and one (1%) patient by
reader 2.
Interobserver agreement for grading
between readers 1 and 2 was good for the
ADM in volunteers and moderate for the
ADM in patients and for the FDB and
the QP in volunteers and patients. Only
fair agreement was reached for the AH in
volunteers and patients (Table 2). No significant differences in the degree of fatty
atrophy of the ADM, FDB, AH, and QP
muscles were found between volunteers
and patients. However, mild (grade 1)
fatty muscle atrophy was noted slightly
more frequently in patients than it was in
volunteers (Table 2).
Grade 2 fatty atrophy of the AH,
FDB, and QP muscles occurred only in
combination with grade 2 fatty atrophy of
the ADM muscle in all but one case. In
this patient, selective grade 2 fatty atrophy of the AH muscle was observed in
combination with an osteoporotic stress
fracture of the middle cuneiform bone.
A significant association between age
and degree of fatty muscle atrophy was
found for the ADM muscle in volunteers
(P ⬍ .001 for both readers) and in patients
(P ⫽ .007 for reader 1, not significant for
reader 2). For the FDB, AH, and QP muscles, P values could not be calculated because of the small number of cases (n ⬍ 5)
with grade 2 fatty muscle atrophy.
Large variability of cross-sectional
area for the ADM, FDB, AH, and QP
muscles was found between individuals in
both the volunteer and patient groups
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MUSCULOSKELETAL IMAGING: Prevalence of Fatty Atrophy of Hindfoot Muscles
Figure 3
Figure 3: Coronal (a) T1- and (b) T2-weighted
fast spin-echo and (c) sagittal short inversion time
inversion-recovery MR images of a 44-year-old female patient with substantial fatty atrophy of the ADM
muscle (arrowheads in a and b) and concomitant
plantar fasciitis (arrows in c).
(Table 3). No significant differences in the
mean cross-sectional area of the ADM,
FDB, AH, or QP muscles were found between volunteers and patients. There was
no significant correlation between the
grade of fatty atrophy and cross-sectional
area of the evaluated muscles. Measurement variability was assessed by repeated
measurements in 32 (20%) of 160 subjects. The intraclass correlation coefficients for the corresponding measurements were 0.952 for the ADM muscle,
0.967 for the FDB muscle, 0.968 for the
AH muscle, and 0.988 for the QP muscle.
The results of the secondary case re-
view of subjects with substantial (grade 2)
muscle atrophy are listed in Table 4. In
volunteers with fatty atrophy of the ADM
muscle, plantar fasciitis was not observed; however, it was the most common finding in the patient group (Fig 3).
Discussion
Our study provides information about the
prevalence of fatty atrophy of the plantar
hindfoot muscles (ADM, FDB, AH, and
QP) in asymptomatic individuals. For
readers 1 and 2 in our study, the frequencies of fatty atrophy of the ADM muscle in
Radiology: Volume 253: Number 1—October 2009 ▪ radiology.rsna.org
Schmid et al
volunteers (5% and 6%, respectively)
were similar to those in patients (4% and
11%, respectively). These rates are comparable to data in a large patient study
(6%, 38 of 602) (9). In our study, three
(50%) of six volunteers and six (67%) of
nine patients with substantial fatty atrophy of the ADM muscle were men, but in
previous studies, most of the affected patients were women (9,18). Recht et al (9)
found that 76% (29 of 38) of subjects with
fatty atrophy of the ADM muscle were
women. The higher percentage of women
in the group with fatty atrophy of the
ADM muscle cannot be solely explained
by the overall percentage of women in the
study (64%, 387 of 602) (9).
The ADM and QP muscles receive
their motor supply from branches of the
lateral plantar nerve. The AH and FDB
are innervated by the medial plantar
nerve. In neither volunteers nor patients
with grade 2 fatty muscle atrophy were
we able to detect direct external compression by a soft tissue mass on the first
branch of the lateral plantar nerve (the
Baxter nerve) (8). This finding may be
explained by the multitude of causes of
nerve compression. Clinically, entrapment of the first branch of the lateral
plantar nerve occurs mainly between the
fascia of the AH muscle and the medial
caudal margin of the QP muscle. Edema
within the AH muscle or repetitive
trauma may compromise the nerve as it
courses underneath the plantar ligament
or through the osseous canal between the
calcaneus and the flexor digitorum brevis
muscle. Another factor that may cause
injury is excessive pronation. Additionally, hypertrophy of the QP, accessory
muscles, abnormal bursae, and phlebitis
within the venous plexus have been described as potential causes of entrapment
neuropathy (19–21). The lack of a mass
lesion or signs of physical nerve compression on MR images does not exclude
nerve compression as the cause of fatty
muscle atrophy.
Fatty atrophy of the intrinsic muscles
may be similar to that seen in the rotator
cuff muscles in Parsonage-Turner syndrome (22,23) or in quadrilateral syndrome (24,25). The most likely cause of
Parsonage-Turner syndrome may be viral
or autoimmune brachial neuritis. Axillary
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MUSCULOSKELETAL IMAGING: Prevalence of Fatty Atrophy of Hindfoot Muscles
nerve damage owing to traction injuries has
also been discussed as a cause. A similar
mechanism might also be responsible for
lesions of the plantar nerves (26). In another study (13), the association between
fatty atrophy of the ADM muscle and the
presence of plantar fasciitis underlines the
possibility that mechanical entrapment may
have occurred. Our findings of plantar fasciitis in five of 14 individuals with fatty atrophy of the ADM muscle further highlight
this possible connection. In instances of
fatty atrophy of muscles with different motoric supply, a more proximal entrapment
(posterior tibial nerve), neuritis, or systemic neuropathy (eg, diabetic neuropathy)
should also be considered. In most cases of
entrapment neuropathy, the point of entrapment will not be visible on MR images.
Measurement of cross-sectional muscle
area at our reference plane revealed large
variability among individual subjects even
when no signs of fatty muscle atrophy were
present. These large interindividual differences hamper the use of such data for
quantitative muscle analysis. Quantitative
muscle analysis of the hindfoot muscles
seems to be less reliable than that in other
anatomic regions. A similar quantitative assessment of the rotator cuff muscles by using cross-sectional areas was shown to be
more reliable (27).
We acknowledge that our study had
limitations. The age- and sex-matched patient group included patients with pain of
the foot or ankle regardless of the underlying cause. Clinical information about coexisting diseases (eg, diabetes mellitus or peripheral neuropathy) was not available in
some patients and could therefore not be
included in our study. Another limitation
was that we performed a two-dimensional
cross-sectional measurement rather than a
three-dimensional volumetric measurement of the ADM, FDB, AH, and QP muscles. In addition, we used a narrow scale for
the visual grading of fatty muscle atrophy,
discriminating only normal from mild and
substantial fatty muscle atrophy. The narrow scale was used because subtle changes
in mild fatty atrophy are difficult to assess in
small muscles. Moreover, atrophy grade
may vary from one section to the next.
In conclusion, the prevalence of substantial (grade 2) fatty muscle atrophy of
166
Schmid et al
the ADM, FDB, AH, and QP muscles in
asymptomatic volunteers is low and is similar to that in patients with pain of the foot
and ankle who were referred for MR imaging. The prevalence of substantial fatty atrophy of the ADM muscle (4%–11%) is
higher than that of the FDB (0%–2%), AH
(1%–4%), and QP (0%–1%) muscles. The
relatively high prevalence of plantar fasciitis
in patients and volunteers with ADM muscle atrophy (five of 14) indicates that some
association may exist between plantar fasciitis and fatty atrophy of the ADM muscle.
Prevalence of fatty atrophy of the ADM
muscle also increases with age.
References
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radiology.rsna.org ▪ Radiology: Volume 253: Number 1—October 2009