DOI:10.2214/AJR.05.1466
AJR 2007; 188:W355-W358
© American Roentgen Ray Society
The Prepatellar Bursa: Cadaveric Investigation of Regional Anatomy with MRI After Sonographically Guided Bursography
Rodrigo O. Aguiar1,2,3,
Flavio C. Viegas1,
Rodrigo Y. Fernandez1,
Debra Trudell1,
Parviz Haghighi4 and
Donald Resnick1
1 Department of Radiology, Veterans Affairs Medical Center, University of
California, San Diego, CA.
2 Present Address: Department of Radiology, Federal University of Rio de
Janeiro, Rio de Janeiro, Brazil.
3 Present Address: Av. Brasilia 5474, ap 83 bl B, Curitiba, Brazil
80240-240.
4 Department of Pathology, Veterans Affairs Medical Center, University of
California, San Diego, CA.
Received August 20, 2005;
accepted after revision December 7, 2005.
Address correspondence to R. O. Aguiar
(aguiar.rodrigo{at}gmail.com).
WEB This is a Web exclusive article.
Abstract
OBJECTIVE. The purpose of this study was to use MRI and anatomic
correlation in cadavers to show the macroscopic anatomic configuration of the
prepatellar bursa.
MATERIALS AND METHODS. MRI of the prepatellar bursa of nine
cadaveric knees was performed after sonographically guided bursography. The
images were compared with those seen on anatomic sectioning. Histologic
analysis was obtained in two specimens.
RESULTS. Mean dimensions of the prepatellar bursa in the
craniocaudal, lateromedial, and anteroposterior planes were 39.7, 40.5, and
3.2 mm, respectively. A trilaminar aspect of the bursa was shown in seven of
the nine knees (78%) and a bilaminar appearance in two of the nine knees
(22%). Lateral extension of the bursa over the patella was observed in three
knees (33%) and medial extension in one knee (11%). On histopathologic
analysis, three potential bursal spaces were found.
CONCLUSION. The prepatellar bursa is most commonly a trilaminar
structure, and variation in its relation to the patella can occur.
Keywords: anatomy • knee • MRI • prepatellar bursa
Introduction
The prepatellar bursa is described in standard textbooks of anatomy
as a unicompartmental structure situated in the subcutaneous tissue anterior
to the patella
[1-3].
Diseases of this structure have been described mainly through a series of case
reports, some of them including cross-sectional imaging findings
[4-8].
Accurate knowledge of prepatellar bursal anatomy is important to orthopedic
surgeons so that they can protect or repair the bursa during surgery
[9] and to radiologists so that
they can correctly diagnose diseases that affect this bursa.
The surgical anatomy of the prepatellar bursa has been addressed
[10,
11] with documentation of a
tricompartmental structure separated by two thin septa oriented in the coronal
plane. The compartments are a superficial compartment, designated the
prepatellar subcutaneous bursal space, localized between the subcutaneous
tissue and an extension of the fascia lata, called the transverse superficial
fascia, which is the structure classically described in the anatomic
literature; an intermediate compartment, the prepatellar subfascial bursal
space, situated between the transverse superficial fascia and an intermediate
oblique fascia formed by fascial extension of the vastus lateralis and vastus
medialis muscles; and a deep compartment, the prepatellar subapone urotic
bursal space, localized between the intermediate oblique fascia and the deep
longitudinal fibers of the rectus femoris tendon, which insert directly in the
patella (Fig. 1). To the best
of our knowledge, no reports have detailed the imaging features of the normal
prepatellar bursa. The main objective of this study was to use MRI after
sonographically guided bursography to describe the qualitative and
quantitative anatomic characteristics of the prepatellar bursa.
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Fig. 1 —Diagram shows compartmentalization of prepatellar bursa. SCCT =
subcutaneous cellular tissue; QT = quadriceps tendon; PT = patellar tendon; F
= femur; 1 = superficial compartment, or prepatellar subcutaneous bursal
space, between subcutaneous tissue and transverse superficial fascia; 2 =
intermediate compartment, or prepatellar subfascial bursal space, situated
between transverse superficial fascia and intermediate oblique fascia; 3 =
deepest compartment, or prepatellar subaponeurotic bursal space, between
intermediate oblique fascia and deep longitudinal fibers of rectus femoris
tendon, which inserts directly in patella (P).
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Materials and Methods
Cadaver and Specimen Preparation
Nine knee specimens were harvested from eight unembalmed cadavers (five
women, four men; age range at death, 59-92 years; mean age at death, 76
years). The specimens were derived from legs cut through the distal portion of
the femur and proximal portions of the tibia and fibula. Routine radiographs
were obtained to exclude the presence of gross abnormalities such as fracture
and calcifications. The specimens were immediately deep-frozen at -40°C
(Bio-Freezer, Forma Scientific). All specimens were allowed to thaw for 30
hours at room temperature before sonographically guided bursography and
MRI.
Sonographically Guided Bursography
Bursography was performed with a dilute gad-olinium solution, two parts of
4 mmol/L gadopen-tetate dimeglumine (Magnevist, Schering), one part of
iodinated contrast material (Omnipaque 350 [iohexol], Nycomed Imaging A.S.),
and one part of 15% concentrated solution of gelatin. Sonographic guidance
(Sequoia 512, Acuson) with an 8- to 14-MHz probe (Acuson 8L5) was used to
localize the anatomic landmarks of the prepatellar bursa. From a superior to
inferior approach with the needle oriented parallel to the dorsal patellar
surface, a needle was inserted between the subcutaneous tissue and the
patellar tendon at the level of the center of the patella, and 1-3 mL of
solution was instilled in the bursa. The injection was stopped when the fluid
returned into the syringe with release of pressure from the plunger. The
criteria used to identify the prepatellar bursa were its smooth contour and
anechoic lenticular appearance on sonographic scans. MRI was performed within
30-60 minutes after each injection.
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Fig. 2 —Cadaver of 79-year-old woman. Lateral extension of prepatellar
bursa. Fat-suppressed axial T1-weighted spin-echo MR image (TR/TE, 500/13)
shows lateral margin (straight arrow) of patella (P) and lateral
margin of prepatellar bursa (curved arrow). Septum compartmentalizing
bursa is evident (arrowheads).
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MRI
MRI was performed with a 1.5-T MRI unit (Signa, GE Healthcare). MR images
of the knee were acquired with a single receiver, 3-inch gradient coil
centered over the patella. T1-weighted spin-echo MR images with and without
fat suppression and frequency-selective fat-suppressed T2-weighted fast
spin-echo images were acquired in the sagittal and axial planes. Sequence
parameters chosen to optimize visualization of the prepatellar space were as
follows: TR/TE for T1-weighted images, 500/13; for T2-weighted images,
2,500/63; echo-train length, 12; field of view, 8 x 8 cm; section
thickness, 2.5 mm; gap, 0.5 mm; number of excitations, 4; matrix size, 256
x 224.
MRI and Anatomic Comparison
After imaging, all cadaveric knees were immediately positioned in the
extended position, frozen at -40°C for at least 24 hours, and sectioned in
the sagittal (seven knees) or transverse (two knees) plane with a band saw
(model B12, Butcher) into 3-mm-thick sections that corresponded approximately
to the thickness and orientation of the MR images. The anatomic slices were
cleaned with running water for macroscopic inspection. Digital photography was
performed for all specimen slices. Radiographs (Faxitron, Hewlett Packard) of
each slice were obtained to depict the iohexol component of the solution.
After water irrigation, however, it was not possible to differentiate this
component of the solution, and these data were not used.
After anatomic inspection, histopathologic analysis of bursae from two
specimens was performed in the sagittal plane. The samples were suspended in
10% formalin solution, embedded in paraffin, and sectioned further into
5-µm-thick specimens. The histopathologic sections were stained with
hematoxylin-eosin and then analyzed with a light microscope (magnification,
x2 to x100) by an experienced musculoskeletal pathologist (PH).
The characteristics of the bursae were reported.
Results
The prepatellar bursa was located anterior to the patella and oriented in
the coronal plane in all cases. The mean measurements after distention in the
craniocaudal, lateromedial, and anteroposterior directions were 39.7, 40.5,
and 3.2 mm. Extension of the bursa beyond the lateral margin of the patella
was found in three knees (Fig.
2), the extension varying between 3.0 and 8.2 mm in maximum
diameter. Medial extension 7.5 mm beyond the medial margin of the patella was
found in one case (Table 1).
Inferior leakage or extravasation of contrast medium was visualized as an
irregular margin of the bursa in three specimens, and superior or medial
extravasation was found in one specimen each. These borders were discarded for
calculation of the bursal dimensions.
A trilaminar bursa was found in seven (78%) of the knees (Figs.
3A,
3B,
3C,
3D and
4A,
4B,
4C) and a bilaminar bursa in
two (22%) of the knees. A single-layer bursa was not found. In the coronal
plane, septa with a thickness less than 2 mm were identified
compartmentalizing the bursa. When a trilaminar pattern was depicted, the
deepest septum was slightly thicker than the superficial one. In the specimens
with three layers (n = 7), the deepest compartment was the largest in
four (57%) of the knees. The intermediate compartment was the largest in one
(14%) of the knees. In the other two specimens, the amount of contrast
material injected was equal in all three compartments.
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Fig. 3A —Cadaver of 69-year-old man. Sagittal T1-weighted spin-echo MR image
(TR/TE, 500/13) without fat suppression. Image shows patella (P), transverse
superficial fascia (arrows), and intermediate oblique fascia
(arrowheads).
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Fig. 3B —Cadaver of 69-year-old man. Sagittal T1-weighted spin-echo MR image
(500/13) with fat suppression. Image shows patella (P), transverse superficial
fascia (arrows), and intermediate oblique fascia
(arrowheads).
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Fig. 3D —Cadaver of 69-year-old man. Photomicrograph shows transverse
superficial fascia (arrows), intermediate oblique fascia
(arrowheads), subcutaneous cellular tissue (SCCT), and rectus femoris
tendon fibers (TF). (H and E, x10)
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Fig. 4A —Cadaver of 65-year-old woman. T1-weighted spin-echo MR image (TR/TE,
500/13) without fat suppression. Image shows tricompartmental patellar bursa
in axial plane, patella (P), transverse superficial fascia (arrows),
and intermediate oblique fascia (arrowheads).
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Fig. 4B —Cadaver of 65-year-old woman. T1-weighted spin-echo MR image
(500/13) with fat suppression. Image shows tricompartmental patellar bursa in
axial plane, patella (P), transverse superficial fascia (arrows), and
intermediate oblique fascia (arrowheads).
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Fig. 4C —Cadaver of 65-year-old woman. Anatomic photograph shows two thin
layers compartmentalizing prepatellar bursa. Image shows tricompartmental
patellar bursa in axial plane, patella (P), transverse superficial fascia
(arrows), and intermediate oblique fascia (arrowheads).
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At histopathologic analysis of the prepatellar space, three potential
bursal spaces between the subcutaneous tissue and the patella were found with
two thin longitudinal fibrous layers separating them. Endothelial synovial
lining cells covering the bursal spaces were not detected.
Discussion
Standard anatomic medical books describe the prepatellar bursa as a
unicompartmental bursa situated symmetrically anterior to the patella
[1-3].
Occasional texts describe a bilaminar bursa with the existence of an
intermediate aponeurotic layer with oblique fibers separating two compartments
[11]. Dye et al.
[10] in a cadaveric study
found a trilaminar prepatellar bursa oriented in the coronal plane in 93% of
61 knees. In 7% of the cases, only two compartments were seen, and they did
not have oblique intermediate fascia. In our study, a trilaminar nature of the
prepatellar bursa was found in 78% of cases. In 22% of cases, a bilaminar
pattern was found. In the Nomina Anatomica
[12], the possibility of three
spaces is considered, but the deepest space is called the prepatellar
subtendinous bursa rather than the subaponeurotic bursa, and the space lies
between the fibers of the rectus femoris tendon and the patella. Dye et al.
[10] did not find a space in
this area, and our findings corroborate theirs.
Histologic analysis of two of our specimens revealed three compartments
separated by two fascia. The oblique intermediate fascia was slightly thicker
than the superficial fascia, and the synovial membrane was not visualized. The
same histologic finding has been described in the literature
[10].
Although some publications report measurements of the prepatellar bursa,
such measurements have always related to analysis of abnormal bursae, which
can reach 150-160 mm in largest axis
[4,
5]. To our knowledge, our
analysis is the first to show quantitative imaging findings of a normal
prepatellar bursa. We found this bursa was generally centered at the patella,
but we identified lateral extension of the bursa in three cases and medial
extension of one bursa. These findings can be useful in clinical practice,
serving as an anatomic guide with respect to the normal landmarks of this
bursa.
Limitations of this study included the absence of clinical history and the
advanced age (mean, 76 years) of the persons from whom the specimens were
acquired, which might have increased the incidence of degenerative changes.
All specimens, however, were screened with radiographic studies. Another
limitation was that instillation of contrast agent in the deepest portion of
the prepatellar region and the pressure used to inject the contrast medium may
have caused opacification of two rather than all three bursal compartments and
extravasation of contrast medium. Despite these limitations, however, the main
aim of this work was achieved, which was to use MRI to show the normal
anatomic configuration of the prepatellar bursa. The trilaminar appearance of
the bursa was found to be most common, and variation of bursal location with
respect to the patella was documented.
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Abstract
Introduction
