Pes Anserine Bursitis

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Bulletin of the NYU Hospital for Joint Diseases 2010;68(1):46-50
Pes Anserine Bursitis
An Extra-Articular Manifestation of Gout
Raj Pal S. Grover, M.D., and Kawan S. Rakhra, M.D., F.R.C.P.C.
Abstract
While hospitalized with polymyositis, a medically complex
56-year-old male experienced an acute exacerbation of
gout. Both ultrasound and magnetic resonance imaging
cross-sectional modalities were used to detect, localize, and
characterize a soft tissue mass. The tumor was ultimately
found to be secondary to gouty inflammation of the pes
anserine bursa, a previously unrecognized manifestation
of acute gout.
T
he term “pes anserinus” (Latin for goose foot) refers
to the common insertional tendon of the sartorius,
gracilis, and semitendinosus muscles on the anteromedial surface of the proximal tibia. As the three tendons
approach the insertion, they come together to form a conjoined tendon that anatomically resembles a goose’s webbed
foot. The pes bursa is a synovial lined sac that lies deep to
the pes anserinus and superficial to the tibial attachment of
the medial collateral ligament (MCL) and the medial tibial
plateau.1-3 This bursa does not communicate with the knee
joint.1,4
Repetitive trauma or stress to the pes bursa and surrounding structures, especially in the setting of obesity, arthritis,
or anatomic dysmorphism of the knee joint, may result in
acute inflammation and fluid distension of this bursa. Patients
typically present with knee pain, which is aggravated by
climbing or descending stairs. On examination, local swelling and tenderness are noted over the proximal, anteromedial
aspect of the tibia.1-9 Anatomically, fluid distension of the pes
Raj Pal S. Grover, M.D., and Kawan S. Rakhra, M.D., are from the
Department of Diagnostic Imaging, The Ottawa Hospital, General
Campus, Ottawa, Ontario, Canada.
Correspondence: Kawan S. Rakhra, M.D., Section of Musculoskeletal Imaging, Department of Diagnostic Imaging, The Ottawa
Hospital, General Campus, 501 Smyth Road, Ottawa, Ontario,
Canada K1H 8L6; [email protected].
bursa results in its expansion proximally and posteriorly.2
To our knowledge there have been no documented cases
of gout in the pes anserine bursa. In 1984, Abeles10 described
a case of extra-articular gout, in which pain and swelling
were localized to a 1 cm area over the posteromedial aspect
of the knee. Notably, the region of the pes anserine bursa was
unremarkable on physical exam without swelling or tenderness. The swelling, in this case, may have represented a distended gastrocnemius-semimembranosus bursa, a popliteal
cyst, or a ganglion cyst. However, there was no diagnostic
imaging performed. In the case presented in this paper, pes
bursitis was confirmed anatomically by ultrasound (US) and
magnetic resonance imaging (MRI); gout was diagnosed
biochemically by polarized microscopy.
Case History
A 56-year-old male with end-stage renal disease, type 2
diabetes mellitus, hypertension, chronic hepatitis B infection, osteoarthritis, and gout (multiple previous acute gouty
attacks of the right knee and left foot) was admitted to the
hospital with polymyositis. During his admission, he developed pain and swelling on the medial aspect of his left
knee. His serum uric acid level was elevated at 592 mmol/L
(9.95 mg/dL). US of the knee was performed (Figs. 1 and 2).
Results
Ultrasound
A linear, high frequency (12 MHz) US probe (HDI 5000,
Phillips Medical Systems, Andover, Massachusetts, USA)
was used to scan the medial aspect of the knee, where a
notable soft tissue mass was found. Along the anteromedial
aspect of the left knee, a subcutaneous lobular, encapsulated, fluctuant mass measuring approximately 8x3x2 cm
was delineated. The mass was predominantly hyperechoic,
with mobile internal echoes, and demonstrated enhanced
through-transmission, consistent with complex fluid. The
Grover RPA, Rakhra KS. Pes anserine bursitis: an extra-articular manifestation of gout. Bull NYU Hosp Jt Dis. 2010;68(1):46-50.
Bulletin of the NYU Hospital for Joint Diseases 2010;68(1):46-50
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Figure 1 Ultrasound of the medial left knee, just inferior to the
joint margin, in the longitudinal axis, demonstrates a locule of the
encapsulated lobular mass, being heterogeneously hyperechoic
with enhanced through-transmission, with some dependent debris,
consistent with complex fluid. Arrows define the margin of the
collection. MC, medial condyle.
Figure 2 Ultrasound of the medial left knee, in the transverse axis,
at the level of the medial tibial plateau (MP), shows the inferior
aspect of the complex fluid collection (arrowheads). Most inferiorly,
as the tibial insertion is approached, the more echogenic pes anserine tendons (arrows) are discretely identified, separated by fluid.
structure was multiloculated with intervening septations;
no solid components were identified. Doppler interrogation
demonstrated neither peripheral nor internal vascularity. The
pes anserine tendons were intimately related to this complex
fluid collection, seen as echogenic bands coursing through
the more relatively hypoechoic fluid. The collection was
limited to the medial aspect of the knee, remaining anterior to the semimembranosus tendon. No communication
with the joint was identified. The extensor mechanism was
unremarkable. The popliteal artery and vein were normal.
A
B
Figure 3 Axial (A) and coronal (B) proton density-weighted images with fat suppression, demonstrate the traversing pes anserine tendons (arrows) encased by the fluid distended pes bursa. (SA, sartorius; GR, gracilis; ST, semitendinosus; black triangle = mesotenon of
gracilis tendon).
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Bulletin of the NYU Hospital for Joint Diseases 2010;68(1):46-50
A
B
Figure 4 Sagittal (A) and (B) intermediate-weighted images with fat suppression show a large lobular, multi-loculated fluid filled bursa
draped over the medial aspect of the knee. SA, sartorius; GR, gracilis; ST, semitendinosus.
The complex fluid collection was subsequently aspirated
under US guidance. Fluid analysis included examination
by compensated polarized light microscopy. This revealed
many aggregates of needle-like crystals, which demonstrated
negative birefringence, consistent with monosodium urate
(MSU) crystals. Calcium Pyrophosphate crystals were not
identified. A differential cell count was not available. Gram
stain, aerobic, anaerobic, fungal, and mycobacterial cultures
were all negative. These results suggested acute gout as the
cause of the patient’s knee pain and focal swelling. MRI
was recommended by the radiologist in order to characterize
further the origin of his cystic mass (Figs. 3 and 4).
Magnetic Resonance Imaging
MRI was performed 8 days after the initial US on a 1.5-T
scanner (Symphony; Siemens Medical Solutions, Erlangen,
Germany), using a quadrature extremity coil and included
the following sequences:
1. Axial, proton density-weighted, fat suppressed, turbo
spin-echo (repetition time msec/echo time, 2500/13;
turbo factor (TF) 5), 4-mm section thickness, 1-mm
spacing, 512x256 matrix, NEX 1, FOV 14 cm.
2. Sagittal, intermediate-weighted, turbo spin-echo
(2500/46; TF 7), 4-mm section thickness, 1-mm
spacing, 512x256 matrix; NEX 1, FOV 14 cm.
3. Sagittal, intermediate-weighted, fat suppressed,
turbo spin-echo (2740/46; TF 7), 4-mm section
thickness, 1-mm spacing, 512x256 matrix; NEX 1,
FOV 14 cm.
4. Sagittal, MEDIC 3.5-mm section thickness, 1-mm
spacing, 512x256 matrix; NEX 1, FOV 16 cm.
5. Coronal proton density-weighted, fat suppressed,
turbo spin-echo (2500/14, TF 5), 3.5-mm section
thickness, no spacing, 512x256 matrix; NEX 1, FOV
14 cm.
MRI demonstrated a large mass that was draped along
the anteromedial aspect of the medial joint compartment and
upper tibia. Superiorly, it started at the supracondylar level,
and, most distally, it extended to at least 5 cm below the
medial tibial plateau, although the inferior-most margin was
not included within the field of view. The visualized portion
of the lesion extended over a longitudinal distance of 10 cm,
with maximal cross-sectional dimensions of 6.2x2.1 cm.
The mass was predominantly characterized by homogeneous, very high signal on fat-suppressed intermediate
weighted images, consistent with a dominant fluid compo-
Bulletin of the NYU Hospital for Joint Diseases 2010;68(1):46-50
nent. In select areas, the signal was somewhat heterogeneous,
with multiple, irregular, intervening septations. The fluid
was contained by a thin, low signal peripheral rim. There
was no discrete solid component. Collectively, the findings
were consistent with a complex fluid collection as suggested
initially by the US.
The location and configuration were not consistent with
a Baker’s cyst, and no communication with the joint space
was identified. The epicenter was deep to the traversing
pes anserine tendons and superficial to the MCL and tibia
in the expected location of the pes anserine bursa. The pes
anserine tendons (sartorius, gracilis, and semitendinosus)
were all intact and without evidence of any acute tear. The
lower portions of the tendons were encased by the distended
pes bursa. Linear bands of low signal extended from the
medial aspect of the tendons, toward the margin of the bursa,
presumably mesotenon.
The medial meniscus, MCL, and semimembranosus and
medial gastrocnemius tendons were all intact. The regional
subcutaneous fat and upper calf musculature did not demonstrate any edema. The underlying tibial cortex was intact,
without evidence of pressure erosion or remodelling. The
tibial marrow signal was normal. The cruciate ligaments,
both menisci, lateral stabilizers, and extensor mechanism
were all intact. A mild joint effusion and mild tricompartmental degenerative cartilage changes were noted. There
was no gross synovitis or intra-articular body present.
The patient was treated with an oral corticosteroid, prednisone (10 mg daily), for both his acute gouty pes anserine
bursitis and polymyositis. Symptoms related to the patient’s
bursitis promptly resolved. He was started on Allopurinol
300 mg daily for treatment of hyperuricemia.
Discussion
Gout is a common medical condition, characterized by
hyperuricemia and the deposition of uric acid crystals, both
intra-articular and periarticular. It is a heterogeneous disorder, comprising four phases: asymptomatic hyperuricemia,
acute gouty inflammation of joints or bursae, intercritical
gout, and chronic tophaceous gout.11
Imaging Features
Acute gouty arthritis typically does not result in any radiographic musculoskeletal changes; however, nonspecific
inflammatory findings may be present. After years of episodic gouty arthritis, chronic tophaceous gout may lead to
permanent radiographic abnormalities. Periarticular, dense
nodular soft tissue masses represent tophi. Para-articular and
extra-articular “punched out” erosions, with well-defined
thin sclerotic borders and overhanging margins, result from
tophi eroding into bone. Intra-articular erosions commence
in the marginal areas of the joint and proceed centrally. The
joint space is relatively preserved until the later stages of
disease, when narrowing is common and usually uniform.12
Gout shows a marked predilection for the great toe. The
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overall distribution is usually asymmetric and polyarticular,
with random involvement of other small joints of the feet and
hands, as well as the wrists, elbows, and knees.12
As in our case, US allows characterization of soft tissue
swelling about a joint that may represent underlying bursitis.
Moreover, it is often used to guide aspiration of joint fluid
for analysis. Computed tomography (CT), MRI, and nuclear
medicine studies are not often performed to diagnose gout.
Nonetheless, CT does allow evaluation of the extent of
disease, particularly in areas that are not easily visualized
on radiographs, such as the spine and sacroiliac joints. MRI
allows visualization of the extent of soft tissue, chondral, and
bone involvement. A 99mTechnetium methylene diphosphonate bone scan may demonstrate the distribution and extent
of gouty arthritis. In acute flare-ups, increased uptake on all
three phases of a bone scan is present. On positron emission
tomography (PET) with 18-fluoro-2-deoxy-D-glucose, a
gouty tophus may demonstrate moderately increased uptake
but less than that expected of a malignancy.13,14
Differential Diagnosis
While a popliteal (Baker’s) cyst is the most common cystic
lesion about the knee, the differential diagnosis should
include meniscal, synovial, and ganglion cysts; bursitis;
hematoma; and abscess in the appropriate clinical setting.15-17
Bursitis is a nonspecific finding that may relate to a variety
of local and systemic processes, such as overuse, trauma,
infection, hemorrhage, internal joint derangement, inflammatory arthropathy, and collagen vascular disease. There are
three bursae medial to the knee: the pes anserine bursa, the
MCL bursa, and the semimembranosus MCL bursa. The pes
anserine bursa lies deep to the pes anserinus and superficial
to the tibial attachment of the MCL and the medial tibial plateau.1-3,15,16 The MCL bursa is located between the superficial
and deep portions of the MCL. The semimembranosus MCL
bursa is located between the semimembranosus tendon and
the MCL, with a deeper extension between the semimembranosus tendon and the medial tibial plateau. Finally, solid
lesions that may have cystic components include pigmented
villonodular synovitis, synovial hemangioma, and synovial
sarcoma.16,18
Conclusion
While hospitalized with suspected polymyositis, this medically complex 56-year-old male experienced an exacerbation
of his gout. Both US and MRI cross-sectional modalities
were used to detect, localize, and characterize a soft tissue
mass, ultimately found to be secondary to gouty inflammation of the pes anserine bursa, a previously unrecognized
manifestation of acute gout. This paper reviews the imaging
features of gout, including the classic radiographic findings
of longstanding gout, as well as the corresponding findings
on advanced imaging techniques, such as CT and MRI. The
differential diagnosis of a cystic soft tissue mass around
the knee is broad. Knowledge of joint, tendon, and bursal
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Bulletin of the NYU Hospital for Joint Diseases 2010;68(1):46-50
anatomy is essential in order to determine accurately the
epicenter of pathology, which, in turn, may narrow the list of
possible diagnoses. In this case, physical exam, biochemical
fluid analysis, and US and MR imaging were combined to
confirm the diagnosis of acute gout bursitis.
Disclosure Statement
None of the authors have a financial or proprietary interest
in the subject matter or materials discussed, including, but
not limited to, employment, consultancies, stock ownership,
honoraria, and paid expert testimony.
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