AJR 2001; 176:1535-1539
© American Roentgen Ray Society
Sonography of the Patellar Tendon and Adjacent Structures in Pediatric and Adult Patients
James C. Carr1,2,
Sinead Hanly1,
James Griffin1 and
Robin Gibney1
1
Department of Diagnostic Imaging, St. Vincent's Hospital, Elm Park, Dublin 4,
Ireland.
2
Present address: Department of Radiology, Northwestern University Medical
School, Ste. 700, 448 E. Ontario St., Chicago, IL 60611.
Received June 26, 2000;
accepted after revision October 24, 2000.
Address correspondence to J. C. Carr.
Introduction
The patellar tendon and its adjacent soft tissue and bony structures may be
affected by a number of conditions, most of which are thought to be related to
trauma. The patellar tendon is readily seen on sonography because of its
superficial location. Patellar tendon abnormalities have been given a number
of different labels with a confusing overlap in terminology.
This pictorial essay illustrates both normal and abnormal appearances of
the patellar tendon on sonography and describes the more common conditions
affecting it.
Sonographic Technique
The patellar tendon is readily examined on sonography with high-frequency
linear array transducers. Transducers up to 20 MHz are now available and may
be desirable to achieve high spatial resolution. However, acoustic penetration
may be limited, and these transducers are expensive and not widely available.
In practice, excellent patellar tendon sonography can be performed with 7- to
10-MHz transducers. The knee is examined in a flexed or semiflexed position,
and comparison may be made with the contralateral side. Longitudinal and
transverse images of the tendon are obtained with electronic focusing at the
appropriate depth [1]. An
acoustic standoff pad can be used to help visualize more superficial
structures in greater detail and can also facilitate direct palpation during
real-time scanning. Power Doppler sonography can be used to examine for
increased tissue blood flow associated with patellar tendon abnormality
[2].
Normal Appearances
The patellar tendon appears on sonography as a cylindric structure passing
from the inferior pole of the patella to the tibial tuberosity (Fig.
1A,1B,1C).
The normal tendon measures 4-5 mm in anteroposterior thickness and broadens at
both insertions.
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Fig. 1A. —Normal patellar tendon in 18-year-old man. Sonogram shows
normal patellar tendon (arrow) as linear structure arising from
inferior pole of patella (solid arrowhead). Normal tendon has
well-defined echogenic margins anteriorly (open arrowhead) and
posteriorly (open arrowhead) with low-to-moderate longitudinal echoes
internally.
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Fig. 1B. —Normal patellar tendon in 18-year-old man. Sonogram shows mid
portion of normal patellar tendon (arrow) with well-defined echogenic
margins anteriorly (arrowhead) and posteriorly
(arrowhead).
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Fig. 1C. —Normal patellar tendon in 18-year-old man. Sonogram shows
normal patellar tendon (solid arrow) attaching distally to tibial
tuberosity (open arrow). Anterior (arrowhead) and posterior
(arrowhead) margins of tendon are shown.
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Because of anisotropy, the sonographic appearance of the tendon may vary as
the angle of insonation changes. This variation can be counteracted somewhat
by ensuring that the transducer remains directly perpendicular to the tendon
in both the transverse and longitudinal planes. Loss of anisotropy in tissues
typically denotes underlying abnormality.
There are several bursae immediately adjacent to the patellar tendon. The
prepatellar bursa lies anterior to the lower patella and upper patellar tendon
and deep in relation to the subcutaneous tissues. The deep infrapatellar bursa
lies between the anterior aspect of the tibia and the inferior patellar
tendon. It is separated from the synovial cavity of the knee joint by the
infrapatellar fat pad. A small superficial infrapatellar bursa lies
subcutaneously anterior to the insertion of the patellar tendon. The deep
infrapatellar bursa may be visible normally as a flattened 2- to 3-mm anechoic
fluid-containing structure. The normal prepatellar bursa and superficial
infrapatellar bursa are not commonly visualized.
Patellar Tendon and Abnormal Sonographic Appearances
Jumper's Knee
Jumper's knee is a clinical syndrome affecting adults, usually athletes,
who are involved in sports that require repetitive violent contraction of the
quadriceps muscle. Such sports include running, jumping, and kicking. The
syndrome is characterized by chronic recurrent anterior knee pain and
tenderness of the patellar tendon near its insertion to the patella. Initially
the pain is present only after activity. Later, it may become persistent until
finally the tendon ruptures
[3].
The pathologic process that gives rise to jumper's knee has been given a
number of different names including "patellar tendinopathy,"
"patellar tendinitis," "patellar tendinosis," and
"patellar tendon degeneration." This variation has created some
confusion when an attempt is made to classify the abnormality on the basis of
imaging findings. Use of the clinical term "jumper's knee" avoids
this confusing overlap in terminology.
Histologic analysis of tendons from patients with jumper's knee reveals
microtears with chronic inflammatory changes and areas of regeneration
[3,
4]. The histopathologic changes
reflect an ongoing repair process that may be the result of repeated minor
trauma.
On sonography, the proximal patellar tendon is thickened. A central area of
low echogenicity is visible posteriorly in the tendon close to the patellar
apex (Fig.
2A,2B)
and suggests a primary abnormality of the osteotendinous junction. The
posterior patellar tendon fibers are attached directly to the patella, whereas
the anterior fibers originate from the quadriceps tendon, making them less
susceptible to injury [5]. More
discrete focal hypoechoic areas may represent small partial tears.
Calcification or dystrophic ossification
[4,
6] can occur within an area of
chronically inflamed or damaged tendon. In addition, rarefaction and
fragmentation of the inferior pole of the patella can occur in long-standing
disease, most likely as a result of chronic avulsion injury
[3].
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Fig. 2A. —Jumper's knee. Longitudinal sonogram of 28-year-old male
football player with persistent knee pain shows marked thickening of proximal
patellar tendon (open arrow). Note focal area of low echogenicity in
posterior portion of tendon (solid arrow). Anterior (white open
arrowhead) and posterior (black open arrowhead) margins of
patellar tendon are visible. Normal anterior surface of patella is seen as
thin echogenic line (solid arrowhead).
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Fig. 2B. —Jumper's knee. Longitudinal sonogram of 29-year-old female
athlete shows thickening of proximal patellar tendon (open arrow)
that contains posterior hypoechoic focus (solid arrow). Inferior
patellar bony surface is irregular and fragmented (solid arrowhead)
and is suggestive of long-standing disease. Anterior (white open
arrowhead) and posterior (black open arrowhead) margins of
patellar tendon are shown.
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Sinding-Larsen-Johansson Disease and Osgood-Schlatter Disease
Sinding-Larsen-Johansson disease and Osgood-Schlatter disease are clinical
syndromes that occur in adolescence and are thought to be related to traction
trauma at the immature osteotendinous junctions. Sinding-Larsen-Johansson
disease affects the proximal tendon at its insertion to the patella, whereas
Osgood-Schlatter disease affects the distal tendon at its insertion into the
tibial tuberosity.
Sinding-Larsen-Johansson disease is a syndrome that occurs in adolescence
between 10 and 14 years old and consists of point tenderness and soft-tissue
swelling at the inferior pole of the patella, accompanied by abnormal findings
on radiography [7]. There is
bony irregularity and fragmentation of the inferior pole of the patella at the
site of insertion of the patellar tendon. The proximal tendon is enlarged and
hypoechoic and may contain bony ossicles (Fig.
3A,3B).
In addition, there is overlying soft-tissue swelling. The sonographic
appearances of Sinding-Larsen-Johansson disease and jumper's knee are similar.
The original description of Sinding-Larsen-Johansson disease was of a
condition that occurred in adolescence, whereas jumper's knee can occur at any
age. It is believed that Sinding-Larsen-Johansson disease is a specific type
of jumper's knee [7].
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Fig. 3A. —Sinding-Larsen-Johansson disease. Longitudinal sonogram of
14-year-old boy with anterior knee discomfort shows thickening of proximal
patellar tendon (open arrow). Upper patellar surface is smooth
(solid arrowhead), whereas distally it is irregular (open
arrowhead). Detached bony fragment is visible in tendon (solid
arrow).
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Fig. 3B. —Sinding-Larsen-Johansson disease. Longitudinal sonogram of
10-year-old boy with persistent knee pain and swelling shows swollen proximal
patellar tendon (open arrow) and fragmentation of lower patella
(solid arrow). Upper patellar surface appears normal
(arrowhead).
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"Osgood-Schlatter disease" occurs in adolescence between 11 and
15 years old [8]. Boys are
affected more frequently than girls, and there is usually a history of
participation in sports and a rapid growth spurt. The condition is bilateral
in 25% of patients. The cause of the condition is thought to be traumatic in
origin, resulting in avulsion of fragments of cartilage and bone from the
tibial tuberosity [8].
Clinically, there is pain, tenderness, and soft-tissue swelling over the
tibial tuberosity at the site of insertion of the patellar tendon. The
findings are more clearly shown on sonography than on radiography. The
sonographic appearances in Osgood-Schlatter disease (Fig.
4A,4B)
include swelling of the unossified cartilage and overlying soft tissues,
fragmentation, and irregularity of the ossification center with reduced
internal echogenicity, thickening of the tendon, and infrapatellar
bursitis.
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Fig. 4A. —Osgood-Schlatter disease. Longitudinal sonogram of
12-year-old girl with focal tenderness over tibial tuberosity shows swollen
hypoechoic distal patellar tendon (arrow) with bony irregularity of
anterior tibial surface (arrowheads).
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Fig. 4B. —Osgood-Schlatter disease. Longitudinal sonogram of
13-year-old boy with anterior knee discomfort shows marked fragmentation of
tibial tuberosity (arrowheads) with slight swelling of patellar
tendon (arrow).
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Tendon Tears or Ruptures
As mentioned previously, we believe recurrent partial tears to be one of
the major factors causing jumper's knee, which typically presents as chronic
pain. An acute tendon tear usually presents with sudden pain, typically after
a sports injury, and can be partial or complete. A discrete hypoechoic focus
is visible within the tendon, representing intratendinous hematoma and edema
(Fig. 5A). Although rare,
complete tendon rupture (Fig.
5B) appears as a full-thickness discontinuity of the tendon.
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Fig. 5A. —Tendon tears. Longitudinal sonogram of 25-year-old male
football player with acute knee pain. Proximal patellar tendon is diffusely
swollen (open arrow). Linear crescent-shaped area of low echogenicity
is seen centrally in swollen tendon (solid arrow), indicating
incomplete tear. Normal anterior patellar surface (arrowhead) is
clearly visible.
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Fig. 5B. —Tendon tears. Longitudinal sonogram of 30-year-old female
athlete with knee discomfort shows no evidence of normal patellar tendon.
Surrounding soft tissues are swollen and edematous (arrow). Findings
are consistent with complete rupture of patellar tendon, which was confirmed
at surgery. Normal anterior surface of tibia is seen as thin echogenic line
(arrowhead).
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Foreign Bodies
The anterior knee is a common site for puncture wounds and soft-tissue
foreign bodies. Sonography readily shows foreign bodies in the soft tissues
and is particularly useful for nonradioopaque foreign bodies that do not show
on conventional radiographs.
Foreign bodies appear as hyperechoic foci within soft tissues (Fig.
6A,6B).
They are more readily seen if they have been present for some time and will be
conspicuous within a surrounding hypoechoic abscess or granulomatous reaction.
Acoustic shadowing deep in relation to foreign bodies depends primarily on
their surface attributes and not on their composition. A small radius of
curvature or rough surface produces a clean shadow. Smooth surfaces with large
radii of curvature (e.g., metal or glass) produce dirty shadows or
reverberations [9].
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Fig. 6A. —Foreign body. Longitudinal sonogram of 12-year-old girl with
knee pain but no history of injury reveals linear-shaped echogenic foreign
body (arrow) in soft tissues of anterior knee. Adjacent soft tissues
are hypoechoic (arrowhead), and this appearance may be due to
surrounding edema, granulation tissue, or hemorrhage.
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Fig. 6B. —Foreign body. Axial sonogram of same patient as in A
shows foreign body (arrow) with surrounding area of low echogenicity
(arrowhead). Small wooden splinter was removed surgically with the
administration of local anesthetic.
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Peritendon Hematoma
Trauma to the knee can result in hemorrhage into the peritendinous soft
tissues or into a bursa. Acute hematoma will typically appear on sonography as
an echogenic collection. Subsequent appearances will vary with the age of the
collection (Fig. 7).
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Fig. 7. —Longitudinal sonogram of 42-year-old woman with knee swelling
after fall. Elliptic-shaped mixed echogenic mass (open arrow) is
located anterior to distal patellar tendon (solid arrow). Arrowhead
indicates anterior surface of tibia. Appearances are consistent with hematoma,
most likely located in superficial infrapatellar bursa.
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Bursitis
Bursitis is commonly idiopathic but may be the result of trauma, repetitive
injury, infection, or an underlying arthropathy.
Bursitis adjacent to the patellar tendon involves the prepatellar or
infrapatellar bursae (Fig.
8A,8B,8C).
Infrapatellar bursitis, "clergyman's knee," is due to kneeling in
the upright posture. Prepatellar bursitis, housemaid's knee, results from
friction due to prolonged kneeling. Bursitis can produce thickening of the
bursal wall with an associated effusion. In addition, the presence of
increased flow on color or power Doppler imaging or pain during transducer
palpation are indicative of an inflammatory state consistent with true
bursitis [10].
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Fig. 8A. —Bursitis. Longitudinal sonogram shows 30-year-old man with
knee pain. Fluid is visible in deep infrapatellar bursa (solid
arrow), indicating deep infrapatellar bursitis. Patellar tendon is normal
(open arrow), but overlying soft tissues appear swollen
(arrowhead).
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Fig. 8B. —Bursitis. Longitudinal sonogram shows 40-year-old woman with
knee discomfort. Superficial infrapatellar bursa is visible as hypoechoic
linear structure (solid arrow), indicating superficial infrapatellar
bursitis. Underlying patellar tendon (open arrow) appears normal.
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Fig. 8C. —Bursitis. Longitudinal sonogram shows 60-year-old man with
painless swelling of anterior knee. Prepatellar bursa is distended with
anechoic fluid (open arrow), and synovial wall is thickened
(arrowhead). Underlying patellar tendon appears normall (solid
arrow). Findings are consistent with chronic prepatellar bursitis.
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Soft-Tissue Masses
A large number of soft-tissue tumors and tumorlike lesions can be
identified on sonography of the knee joint. These lesions may present as a
clinically obvious mass or as nonspecific infrapatellar discomfort. Most
soft-tissue masses have a completely nonspecific appearance on sonography,
presenting as well-defined solid or complex solid and cystic masses.
Occasionally, some lesions display sonographic features that point to a
particular cause. Increased echogenicity within a lesion may represent fat,
suggestive of a lipoma. Tortuous tubular structures within a lesion, with
associated calcifications, are suggestive of a vascular lesion such as a
hemangioma [6] (Fig.
9A,9B).
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Fig. 9A. —Soft-tissue mass. Longitudinal sonogram of 14-year-old girl
with mild knee discomfort shows serpiginous-shaped hypoechoic mass (solid
arrow) deep in relation to distal patellar tendon (open arrow)
and anterior to superior surface of tibia (arrowhead).
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Fig. 9B. —Soft-tissue mass. Sagittal proton density-weighted MR image
of knee in same patient as A shows hyperintense mass (arrow)
superficial to anterior surface of tibia. Normal patellar tendon is seen
superiorly as hypointense linear structure (arrowhead). Mass was
removed surgically, and pathology revealed angiolipoma containing multiple
venous vascular channels.
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Conclusion
Sonography is useful in the assessment of abnormalities of the patellar
tendon and adjacent structures. It helps to accurately identify the anatomic
structures involved and to detect and classify patellar tendon abnormality.
Sonography is also useful in assessing abnormalities adjacent to the patellar
tendon, such as soft-tissue foreign bodies, bursitis, and peritendon hematomas
and tumors. Sonography is a relatively inexpensive diagnostic tool that is
widely available. The real-time nature of sonography allows joints and
soft-tissue structures to be examined in a dynamic manner so that imaging can
be correlated directly with the site of clinical abnormality. Sonography,
however, is operator-dependent, and this feature has the potential to lead to
inconsistent results.
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Introduction
Sonographic Technique
