DOI:10.2214/AJR.04.1481
AJR 2006; 186:948-955
© American Roentgen Ray Society
Sonography of Plantar Plates in Cadavers: Correlation with MRI and Histology
Julie M. Gregg1,2,
Morry Silberstein2,
Timothy Schneider3,
Jeffrey B. Kerr4 and
Paul Marks1,2
1 Department of Diagnostic Imaging, Symbion Healthcare, The Avenue Hospital, 40
The Avenue, Windsor, Victoria 3181, Australia.
2 Department of Medicine, Monash University, Clayton, Victoria, Australia.
3 Melbourne Orthopaedic Group, Windsor, Victoria, Australia.
4 Department of Anatomy and Cell Biology, Monash University, Clayton, Victoria,
Australia.
Received September 20, 2004;
accepted after revision February 23, 2005.
Address correspondence to J. M. Gregg
(jmgre8{at}optusnet.com.au).
Abstract
OBJECTIVE. The purpose of our study was to describe the sonographic
appearance of the lesser metatarsal plantar plates in cadavers and to
correlate these findings with MRI and histology.
MATERIALS AND METHODS. Six soft-embalmed cadaveric feet (74–92
years old; two male, one female) were imaged with sonography and MRI. Tear
dimensions of the plantar plate were recorded in the long and short axes.
Orthopedic surgeons directly inspected the plantar plates before removing
samples for histologic correlation. One young fresh cadaver was imaged with
sonography before histologic assessment.
RESULTS. The normal plantar plate appearance on sonography was a
slightly echoic, homogeneous, curved structure. At direct inspection, a tear
was present in 23 (96%) of 24 of the lesser plantar plates in the
soft-embalmed feet. This direct inspection correlated with sonography
detecting 23 tears correctly and MRI, 22 tears. Both sonography and MRI
falsely reported one tear, but MRI also failed to detect one tear.
Histologically, the abnormal plantar plate showed loss of the normal dense
regular tissue and replacement with vessels, hydropic tissue, and a mixture of
loose connective tissue and dense irregular connective tissue.
CONCLUSION. Sonography, being noninvasive, shows promise as an
imaging tool of the plantar plate. With ongoing research in this area we hope
to determine the reliability and significance of such a technique in the
evaluation of the plantar plate.
Keywords: fibrocartilage • foot • instability • metatarsophalangeal • MRI • musculoskeletal imaging • plantar plate • sonography
Introduction
The normal function of the plantar plate has been widely reported,
indicating that rupture may be central to instability of the
metatarsophalangeal joint
[1–6].
Dysfunction of the plantar plate can lead to significant morbidity.
Arthrography and MRI have been used previously to assess the plantar plate
[7–9].
To our knowledge, the role of sonography is yet to be described. We aim to
describe the sonographic appearance of the lesser (second through fifth)
metatarsal plantar plates in cadavers, and to correlate these findings with
MRI and histology. We will show that sonography is a promising technique for
assessing the integrity of the plantar plate.
The metatarsophalangeal joints consist of a joint capsule reinforced on
each side by collateral ligaments, dorsally by the extensor expansions, and
ventrally by the plantar plate
[10]. Between the heads of the
metatarsals runs the deep transverse metatarsal ligament
[11]. The plantar plate is a
firm, flexible structure, with an articular surface on its dorsal aspect. The
plate has been extensively studied at the level of the second
metatarsophalangeal joint where it is, on average, 20 mm long, 9 mm wide, and
2 mm deep [1,
2,
9]. Other than the collateral
ligaments, the plate itself has no strong fibrous insertion onto the
metatarsal. The proximal origin of the plantar plate attaches loosely to the
periosteum of the metatarsal shaft, just proximal to the metaphysis of the
metatarsal head. Distally, the plantar plate inserts firmly and directly into
the bone on the plantar surface of the proximal phalanx, just distal to the
articular surface [2].
The plantar plate is centrally located, with multiple important attachments
that include the proper and accessory collateral ligaments, plantar fascia,
intermetatarsal ligaments, interosseous tendons, and fibrous sheath of the
flexor tendons, thereby serving as a central stabilizing structure. The
fibrocartilaginous composition of the plate suggests that it withstands
compressive loads, acting as a supportive articular surface for the metatarsal
head [1].
Materials and Methods
Cadavers
The approval of our hospital ethics committee was obtained for this
project. Three soft-embalmed cadavers (74–92 years old; 2 male, 1
female) were provided at random through the related university anatomy
department. Only cadavers with evidence of previous lower leg surgery were
excluded.
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Fig. 1A —Sonograms of normal plantar plate in 19-year-old fresh cadaver.
Longitudinal image of third plantar plate of right foot shows mildly echoic
plantar plate (short arrows) is homogeneous and lies deep in relation
to flexor tendon (arrowhead). Plantar plate is superficial to
metatarsal head and hypoechoic line of hyaline cartilage (long
arrows) inserting onto proximal phalanx (asterisk).
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Fig. 1B —Sonograms of normal plantar plate in 19-year-old fresh cadaver. In
transverse image of second plantar plate of left foot at level of metatarsal
head, calipers delineate width of homogeneous plantar plate (arrows),
which is seen lying superficial to metatarsal head and deep in relation to
rounded flexor tendon (asterisk). Thin hypoechoic hyaline cartilage
(arrowheads) is seen against bright line of skeletal cortex.
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Fig. 2A —74-year-old male soft-embalmed cadaver with full-thickness tear of
second plantar plate of left foot. Sagittal proton density–weighted
image lateral to flexor tendon has been rotated to correspond directly to
sonogram in Figs. 1A and
1B (plantar surface is at top).
Low-signal-intensity fibers of fifth plantar plate are seen to insert onto
proximal phalanx (arrow), contrasting with increased signal intensity
of articular cartilage (arrowheads).
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Fig. 2B —74-year-old male soft-embalmed cadaver with full-thickness tear of
second plantar plate of left foot. Coronal proton density–weighted image
shows normal plantar plate (white arrows) to be C-shaped band of low
signal intensity. On plantar surface, central groove accommodates flexor
tendon (arrowhead). Collateral ligaments (asterisks) blend
with plantar plate. Incidentally, intermetatarsal fibrosis is seen in first
and third web spaces (black arrows) and fibrosis is also present in
fat pad directly beneath second and third metatarsal heads.
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Fig. 2C —74-year-old male soft-embalmed cadaver with full-thickness tear of
second plantar plate of left foot. Coronal T2-weighted fat-suppressed image of
normal plantar plate shows thin band of hyaline cartilage as high signal
intensity on articular surface (arrowheads). Low-signal-intensity
circular flexor tendon abuts plantar surface of plantar plate (arrow)
centrally.
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Fig. 2D —74-year-old male soft-embalmed cadaver with full-thickness tear of
second plantar plate of left foot. Sagittal proton density–weighted
image of second plantar plate shows hyperintense focus (arrow) that
replaces normal hypointense fibrocartilage of plantar plate. Arrowhead
indicates intact plantar plate.
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Fig. 2E —74-year-old male soft-embalmed cadaver with full-thickness tear of
second plantar plate of left foot. Coronal T2-weighted fat-suppressed image at
level of insertion of second and third plantar plates onto proximal phalanx.
Ill-defined focus of increased signal intensity represents plantar plate tear
(white arrow). Normal plantar plate fibers are seen laterally.
Plantar plate tear is also seen in third plantar plate (arrowhead).
Adventitial bursitis is seen as hyperintense regions in fat pad adjacent to
second through fourth metatarsal heads (black arrows).
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Fig. 2F —74-year-old male soft-embalmed cadaver with full-thickness tear of
second plantar plate of left foot. Corresponding axial proton
density–weighted image shows plantar plate disruption (white
arrow) located centrally. Lateral collateral ligaments (black
arrow) remain intact.
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Fig. 2G —74-year-old male soft-embalmed cadaver with full-thickness tear of
second plantar plate of left foot. Sagittal paraffin section shows dense
fibrocartilage is disrupted proximal to its insertion onto proximal phalanx.
This results in abrupt border between fibrocartilage (white arrows)
and replacement cellular structures, including vacuoles (asterisks)
and vessels (black arrows). Remnant fibrocartilage inserts into bone
(B). (Masson's trichrome stain, x5)
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After the soft-embalmed cadavers were imaged and dissected, it became
evident that most (96%) of the plantar plates were either torn or
degenerative. Sonography and histology correlation required normal tissue for
a baseline, so another cadaver was requested.
A young fresh cadaver, with neither a history of foot surgery nor a history
of a high level of sporting activity was requested from the local forensics
department. After forensics ethics committee approval and consent from next of
kin were obtained, a 19-year-old male donor was imaged with sonography before
dissection of the lesser plantar plates (MRI was not approved).
The study was a blinded study. The sonographer (the principal researcher),
performed the sonography and wrote the report; the MRI examination on the
soft-embalmed cadavers was performed by medical imaging technologists and then
reported by the musculoskeletal radiologist. The sonographer and radiologist
were blinded to one another's findings and operated independently of one
another.
Dissections were performed by an orthopedic foot surgeon, histology was
prepared by the related university histology department technician, and
histologic assessment was conducted by the senior anatomist and
histologist.
Sonographic Technique
Sonography was performed using a 13–5-MHz linear probe (Antares,
Siemens Medical Solutions) and superficial musculoskeletal settings (11.4 MHz;
2 cm depth; dynamic range, 60 dB; 1 focal zone). Plantar assessment was
achieved with the lower leg supine and the toes pointing anteriorly. The
sonographic appearances of the plantar plate have not previously been
documented. Similarities in composition to the palmar (volar) plate of the
hand suggest that the plantar plate will possess similar sonographic
characteristics. It is expected that the normal plantar plate will be a
slightly echoic, homogeneous structure with tears being represented as
hypoechoic or echogenic defects in the fibrocartilage
[12].
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Fig. 3A —Photomicrographs of histopathology specimens from plantar plate of
right foot in 19-year-old fresh cadaver. Sagittal paraffin section of third
plantar plate shows densely interwoven connective fibers (long
arrows) and dense connective septa (arrowheads). Hyaline
cartilage (small arrow) undercuts plantar plate at insertion.
Tidemark (asterisk) represents interdigitations between calcified
fibrocartilage and subchondral bone. B indicates bone. (Masson's trichrome
stain, x5 magnification)
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Fig. 3B —Photomicrographs of histopathology specimens from plantar plate of
right foot in 19-year-old fresh cadaver. Fibrocartilage (F) of plantar plate
is tightly compacted with collagen, with intermittent connective tissue septa
(black arrows) and blood vessels (white arrow). (Masson's
trichrome stain, x33 magnification)
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The plantar plates were assessed at each lesser metatarsophalangeal joint,
and images in the longitudinal and transverse planes were obtained. Extending
the toe back by 15° at each metatarsophalangeal joint whenever possible
aided in the delineation of tears and the plantar plate margins, especially in
the longitudinal plane. Tears were described in relation to their location
(medial, central, or lateral) and to their proximity to the proximal phalanx.
Full plantar plate tears were measured in the transverse and sagittal planes;
the depth of partial tears was also recorded.
MRI Technique
MRI was conducted using a 1.5-T unit (Signa HighSpeed Plus, GE Healthcare).
A surface coil, the Med Advances Quadrature wrist coil, was placed on the
forefoot and provided high-resolution capability. Proton
density–weighted fast spin-echo sequences (TR range/TE,
2,800–3,000/35) and T2-weighted fat-suppressed fast spin-echo sequences
(3,000–4,000/55) were used. All scanning was performed using a 10-cm
field of view, flip angle of 90°, and 2-mm thickness with 0-mm gap.
Sagittal, axial, and coronal planes of the plantar plate were obtained using
both techniques.
The MRI appearance of the normal plantar plate has previously been reported
as a smooth, curvilinear, low-signal structure abutting the plantar aspect of
the metatarsal head and attaching to the proximal phalangeal base adjacent to
the joint surface
[7–9].
The MRI findings of a plantar plate tear are plate discontinuity and an area
of increased signal intensity in its attachment to the base of the proximal
phalanx
[7–9].
Tears were described in relation to their location and to their proximity to
the proximal phalanx. Plantar plate tears were measured in the sagittal and
coronal planes.
Dissection and Histology Technique
After imaging, the soft-embalmed feet were dissected and the lesser
metatarsal plantar plates were inspected with a blunt probe to identify
deficiencies in the plantar plates. The measurement and location of tears were
documented with the use of a micrometer (Wernier Gauge, Rostfrei). Eight of
the 24 lesser metatarsal plantar plates (a random sample) were removed for
histology assessment and placed in 10% neutral-buffered formalin. These
samples consisted of the first centimeter of the proximal phalanx and the
entire plantar plate. The samples were decalcified by immersion in formic acid
and ethylenediamine tetraacetic acid, disodium salt-2-hydrate (EDTA). Sagittal
paraffin sections measuring 10 µm were stained with Masson's trichrome
stain.
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Fig. 4 —92-year-old female soft-embalmed cadaver, third plantar plate of
left foot. Longitudinal sonogram of plantar plate shows partial tear
represented as hypoechoic change (white arrows) extending from
articular surface to very near plantar surface. Normal plantar plate fibers
are seen proximally (arrowhead) and at insertion (black
arrow), where a flap of remnant tissue is visible.
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Fig. 5A —74-year-old male soft-embalmed cadaver, second plantar plate of left
foot. Sonogram shows full-thickness tear (white arrows) of
insertional fibers of plantar plate represented as hypoechoic defect extending
from articular surface to plantar surface. Remaining plantar plate
(arrowhead) is homogeneous. Flexor tendon (black arrow) is
seen overlying plantar plate.
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Fig. 5B —74-year-old male soft-embalmed cadaver, second plantar plate of left
foot. Transverse sonogram shows torn plantar plate. Calipers delineate
location and width of tear, which is centrolateral and hypoechoic (white
arrow) to normal plantar plate tissue seen medially. Flexor tendon
(black arrow) remains centrally located, and some subcutaneous fluid
(arrowhead) is present adjacent to flexor tendon.
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The young cadaver was imaged with sonography 48 hr after death, and the
dissection occurred at 72 hr after death. The donor was fresh and had only
been refrigerated before imaging. Each lesser metatarsal plantar plate was
retrieved and then placed in 10% neutral-buffered formalin and decalcified
with EDTA and formic acid. Sagittal paraffin sections measuring 10 µm were
placed on slides and stained with Masson's trichrome stain.
A quantitative histologic analysis was performed using morphologic volume
density analysis [13]. One
slide per soft-embalmed plantar plate specimen (n = 8) was selected,
representing the central fibers of the plantar plate. Comparison was made with
the central fibers from the young fresh cadaver (n = 2). Volume
density calculations were performed on digitized Masson's
trichrome–stained histology samples (x4 magnification and zoom at
200%). A 10 x 10 square lattice with 121 intersection test points was
placed at random over the insertional fibers of the plantar plate using the
software program Microsoft Publisher 2000 (SR-1). Each field size was 7.5
mm2. The number of test points superimposed over a structure of
interest was counted and expressed as a percentage of 121, and means were
expressed as volume densities.
Statistical Analysis
Descriptive analysis (mean ± SD) of tear dimensions was performed
with software (Microsoft Excel 2000, SR-1). Sensitivity, specificity,
predictive values, and accuracy were calculated for both MRI and sonography in
determining the presence of a tear using direct inspection as the gold
standard. Because ours was a pilot project, the number of cadavers imaged was
small. Our capacity to examine the results statistically was limited.
Results
Normal Sonographic Appearance
In the longitudinal plane (Fig.
1A), the normal plantar plate is a slightly echoic, homogeneous,
labral-like structure curving over the metatarsal head to insert into the
proximal phalanx [12]. The
flexor tendon is seen lying centrally over the plantar plate. The proximal
edge of the plantar plate is visible with dynamic scanning wrapping loosely
over the metaphysis of the metatarsal head. Distally, the plantar plate
structure is clearly visualized inserting onto the plantar surface of the
proximal phalanx. The hyaline cartilage of the metatarsal head is seen as a
thin hypoechoic line against the bright line of the skeletal cortex.
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Fig. 6 —92-year-old female soft-embalmed cadaver. Sagittal proton
density–weighted MR image of third plantar plate of left foot shows
replacement of normal plantar plate fibers with a hyperintense focus (long
arrow) on articular surface. Thin section of low-signal-intensity plantar
plate persists on plantar surface, suggestive of partial-thickness tear of
plantar plate. Short arrow indicates intact plantar plate fibers. Arrowhead
indicates proximal plantar plate, which is completely intact.
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The evaluation of the plantar plate in the transverse plane similarly
reveals a curved, slightly echoic structure overlying the metatarsal head. A
shallow groove centrally houses the flexor tendon on its plantar surface
(Fig. 1B).
Normal MRI Findings
In the sagittal plane, proton density–weighted sequences depict the
normal plantar plate as a uniform hypointense triangular structure inserting
onto the proximal phalanx. The plantar plate appears to cradle the metatarsal
head, providing a matching articular surface. The hypointense flexor tendon
overlying the plantar plate appears to blend with it, making the cleavage
plane indiscernible (Fig. 2A).
The origin of the plantar plate at the level of the metatarsal shaft just
proximal to the flare of the metatarsal head is poorly delineated from the
flexor tendon. The insertional fibers are well delineated against the
articular cortex of the proximal phalanx.
Coronal proton density–weighted and T2-weighted fat-suppressed images
of the plantar plate reveal a C-shaped low-signal-intensity band centrally
under the metatarsal heads (Figs.
2B and
2C). On the plantar surface a
central groove on the plantar plate accommodates the flexor tendons.
Collateral ligaments blend with the plantar plate at the base of the proximal
phalanx. On T2-weighted fat-suppressed images, the plantar plate appears as a
uniformly hypointense structure. The insertional fibers are also hypointense
adjacent to the articular cortex of the proximal phalanx. This latter finding
is important in deciphering the normal plantar plate.
Axial images of the plantar plate have limited diagnostic value except when
metatarsal alignment makes coronal assessment difficult. The major benefit of
the axial imaging comes when assessing the bone marrow, phalangeal alignment,
extent of soft-tissue masses, and fluid.
Normal Histology
Histologically, the normal plantar plate is seen as densely interwoven
connective fibers dorsally and linear striations inferiorly
(Fig. 3A). The fibrocartilage
has a tightly compacted appearance, numerous isogeneous chondrocytes aligned
in rows, and a high collagen content (Fig.
3B). The fibrocartilage forms a tidemark as it inserts into the
proximal phalanx. The tidemark describes a relatively linear area that under
high magnification reveals the interdigitations between the calcified
fibrocartilage and subchondral bone. The insertion of the plantar plate into
the bone is generally termed the "enthesis," which is any region
where a tendon, ligament, or joint capsule attaches to bone
[14].
Histology analysis of the central fibers of the fresh cadaver plantar
plates was performed on those that were reported sonographically to be normal
(only two of the eight lesser plantar plates were normal). From these two
plantar plates, the normal histology volume density was calculated. Regular
dense connective tissue had a volume density of 64%; blood vessels, 7%;
irregular dense connective tissue, 9%; and loose cellular tissue (excluding
fat cells), 20% (Table 1).
Sonographic Appearances of the Abnormal Plantar Plate
A tear of the plantar plate is diagnosed when a hypoechoic or heterogeneous
focus replaces the normally homogeneously echoic insertion. Isoechoic change
has also been seen, in which the echogenicity is slightly echoic but the
direction of the fibers appears disorganized. The retraction of the tear is
best assessed on the longitudinal plane. The transverse images assist in
demarcating the location of the tear in relation to the metatarsal head,
flexor tendon, and to a lesser extent, the collateral ligaments. The location
of the tear is described as either medial, central, or lateral.
Partial-thickness tears involve the articular surface fibers and spare the
plantar surface (Fig. 4).
Full-thickness tears extend from the articular surface to the plantar surface
(Figs. 5A and
5B). Partial-versus
full-thickness tears can be assessed in both the sagittal and transverse
planes. In the transverse plane, the fibers may be displayed with the flexor
tendon subluxing into the tear. Osteophyte formation may be seen in chronic
disease. Osteophytes appear as highly echoic foci similar in echogenicity to
bone.
In the 24 lesser plantar plates of the soft-embalmed cadavers, the abnormal
plate varied in appearance from hypoechoic (67%; n = 16) to isoechoic
(17%; n = 4) to heterogeneous (17%; n = 4). Osteophyte
formation was presumed to be identified in 21% (n = 5) of the plantar
plates. Sonography detected 100% (n = 24) of the full-thickness
tears. The tears were all located at the insertion onto the proximal phalanx.
Sonographically, the mean length of tears was 3.8 mm (range, 2–6
± 0.9 [SD] mm). The mean width of the abnormality was 3.6 mm (range,
1.6–6.3 ± 1.2 mm). All tears were found to occur centrally and
also included the medial fibers (17%; n = 4) and lateral fibers (63%;
n = 15).
MRI Appearance of the Abnormal Plantar Plate
A tear of the plantar plate is diagnosed when a hyperintense focus replaces
the normally hypointense insertion. Tears appear hyperintense on both proton
density–weighted and T2-weighted fat-suppressed images. The retraction
of the tear is best assessed on the sagittal images. The coronal images assist
in demarcating its location in relation to the collateral ligaments and the
flexor tendon. Partial-versus full-thickness tears can be assessed in both the
sagittal and coronal planes. Partial-thickness tears involve the articular
surface fibers and spare the plantar surface
(Fig. 6). Full-thickness tears
extend from the articular surface to the plantar surface (Figs.
2D,
2E, and
2F).
In the 24 lesser plantar plates of the soft-embalmed cadavers, MRI detected
71% (n = 17) of the full-thickness tears and 25% (n = 6) of
the partial-thickness tears occurring at the insertion onto the proximal
phalangeal base. MRI determined the mean length of tears to be 3 mm (range,
2–5 ± 0.8 mm) and the mean width of tears to be 3.3 mm (range,
2–5 ± 1.1 mm). MRI determined that tears were centrally located
88% (n = 21) of the time, but they also included the medial fibers in
17% (n = 4). MRI determined that solitary tears medially were seen in
8% (n = 2) and laterally in 4% (n = 1) of cases.
Histology Appearance of the Abnormal Plantar Plate
Histologically, degenerative or torn plantar plate appearances meant the
replacement of dense fibrocartilage and collagen bundles with a variety of
tissues (Fig. 2G). The volume
densities of these tissues were calculated in the soft-embalmed cadavers as an
average volume (performed on the eight randomly removed lesser plantar
plates): 6% fat cells, 10% hydropic tubules (watery fluid), 18% blood vessels,
26% loose cellular tissue (excluding fat cells), 23% dense irregular tissue,
and 18% dense regular tissue was present (see
Table 1). Plantar plate tears
were found to occur at the insertion onto the proximal phalanx but did not
include the tidemark.
Direct Inspection
Direct inspection of the plantar plate revealed that most (96%) were torn
and were filled with soft loose connective tissue. The mean length of plantar
plate tears was 2.2 mm (range, 1–4 ± 0.8 mm), and the mean width,
4 mm (2–7 ± 1.5 mm). The depth of a partial tear could not be
accurately estimated by direct view. Tears were found to involve the central
fibers of the plantar plate insertion 100% of the time, but also included
medial fibers in 61% (14/23) and lateral fibers in 9% (2/23) of cases.
Statistical Analysis
The sensitivity and specificity of sonography and MRI in detecting a tear
(partial or full thickness) in the plantar plate were determined using direct
inspection as the gold standard. MRI, with 22 true-positive findings, no
true-negatives, one false-positive, and one false-negative, had a sensitivity
of 96% and a specificity of 0%. Sonography, with 23 true-positives, no
true-negatives, one false-positive, and no false-negatives, had a sensitivity
of 100% and 0% specificity. Both imaging techniques had a positive predictive
value of 96% and negative predictive value of 0%. Accuracies for MRI and
sonography were 92% and 96%, respectively.
Discussion
To our knowledge, this is the first prospective pilot study evaluating the
potential of sonography to image the plantar plate. The main limitations of
the research plan were the small number and the advanced age of the
soft-embalmed cadavers. The soft-embalmed cadavers were 74–92 years old,
and 96% of their plates were torn. Sonographic penetration was hindered by
overlying tissue where tough, callused skin or a thickened fat pad diminished
image quality. Other difficulties encountered included the stiffness and
inflexibility of the metatarsophalangeal joint of the soft-embalmed feet as
compared with our experience with living patients. The younger fresh cadaver
also showed early signs of plantar plate damage, with partial tears seen in
six of the eight lesser metatarsophalangeal joint plantar plates. Baseline
histology for the normal plantar plate was obtained from the two normal
plantar plates. The young cadaver had no history of elite sports activity but
was found subsequently to have worked as a garbage collector, which is
physically demanding, especially on the feet. Therefore, we believe that this
was not a true representation of the average young man.
Boutry et al. [12] reported
the volar plate to be composed of vascularized connective tissue, in contrast
with previous reports [15]
that stated it was composed of fibrocartilage, which contains a very small
proportion of blood vessels. In our histologic assessment, we concur with the
earlier reports and have endeavored to extend this finding using detailed
histologic analysis, although the small sample size limits its reliability.
The normal plantar plate was found to possess only a relatively small number
of blood vessels (7%). The abnormal plate showed a diminishment in the
quantity of regular dense connective tissue (a reduction from 64% to 18%),
whereas the average number of blood vessels was more than doubled (18%).
Sonographically, areas of degeneration were often subtle, with the contour
often appearing to be intact. The normal fibrillary appearance was lost and
replaced with hypoechoic, heterogeneous, or isoechoic tissue. Deposition of
bone at the fibrocartilaginous entheses may occur at any
fibrocartilage–bone interface
[14].
Sonography identified osteophyte formation (n = 5), but this could
not be confirmed histologically or by MRI because both were unable to
visualize osteophytes. The histology specimens were decalcified to allow
slicing, and the decalcification process also likely destroyed or rendered
invisible any osteophytes that may have been present. MRI cannot clearly
identify small osteophytes because they have similar signal intensity
characteristics to fibrocartilage. All tears were located centrally in the
insertional fibers of the plantar plate with a varying degree of medial and
lateral involvement.
The accuracies of sonography and MRI were both high, although they were
poor in specificity. The obvious difference between sonography and MRI is the
resolution; when images of the plantar plate of identical frame size are
compared, the sonography image better illustrates this tiny structure. The
other advantage of sonography is the dynamic nature of the technique. For
distorted toes, sonography can readily modify the scanning plane to achieve
true longitudinal and short-axis imaging.
In conclusion, although the age range of the cadavers and the small sample
size limited this study, we were able to image the plantar plate with
sonography and to describe normal and abnormal characteristics. Sonography
assessment of tears is comparable to that using MRI and to what is seen at
dissection. A broader study is planned to further evaluate sonography as a
diagnostic tool for plantar plate assessment.
Acknowledgments
We thank the Department of Anatomy and Cell Biology at Monash University
Clayton and the Victorian Institute of Forensic Medicine for providing the
cadavers for examination in this study.
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Abstract
Introduction
