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132
J. Day and B. Adams
untreated tumor with wide resection of the entire
surgical bed in conjunction with radiation and
possibly chemotherapy depending on the underlying histologic subtype.
Outcomes
Outcomes for soft tissue sarcomas vary by subtype. Poor prognostic factors include large size,
high-grade tumors, deep tumors, and metastatic
disease. Patients receiving an unplanned excision
have increased local morbidity including additional surgical procedures, a greater need for
plastic surgery reconstruction, and a higher rate
of amputation. Notably, an adverse effect on survival has not been shown.
Undierentiated Pleomorphic
Sarcoma (UPS)
Undifferentiated pleomorphic sarcoma (UPS),
formerly known as malignant brous histiocytoma (MFH), is the most common soft tissue
sarcoma in adults. It is a high-grade tumor that
lacks differentiation into a more specic subtype. Histologically, it is composed of pleomorphic spindle cells arranged in a storiform pattern
with frequent mitosis. It follows the typical pattern of presentation of a painless mass in the
lower extremity. Other common sites include
the upper extremity and then the retroperitoneum.
Prognosis depends on the factors listed above.
The 5-year overall survival is approximately
60%.
Liposarcoma
Liposarcoma is the second most common soft
tissue sarcoma and comprises a wide range of
malignant potential dependent on the individual
grade of the tumor. Tumors range from welldifferentiated liposarcoma (termed atypical
lipomatous tumor in the extremities) with essentially no metastatic potential to a pleomorphic
liposarcoma that has a similar outcome to
UPS.The common feature among all liposarcomas is the presence of immature lipoblasts seen
on histology. Fat can be easily seen on MRI in
low-grade lesions, while high-grade lesions
share the typical appearance of a high-grade sarcoma. Atypical lipomatous tumors are sometimes indistinguishable from benign lipomas on
imaging with diagnosis made by the presence of
MDM2 staining.
Myxoid Liposarcoma
Myxoid liposarcoma is the most common subtype of liposarcoma and has some notable features. They are typically low-grade but can be
high-grade lesions which are usually associated
with a large round cell component. Myxoid liposarcoma is associated with translocation t(12;16).
Radiographically, it contains components that
are relatively dark on T1 sequences and bright on
T2 sequences owing to the high myxoid component. Myxoid liposarcoma has an unusual pattern of spread for a sarcoma. In addition to the
lungs and bone, it can spread to sites including
the retroperitoneum and liver. Bone lesions are
difcult to detect by CT, technetium bone scan,
or PET, making whole body MRI the imaging
modality of choice to screen for extrapulmonary
disease. Myxoid liposarcoma is also notable for
its signicant response to radiation, even with
relatively low doses.
Leiomyosarcoma
As its name suggests, leiomyosarcoma classically
arises from smooth muscle cells, particularly
from those of the abdominopelvic organs. They
occur most commonly in the uterus and are therefore more common in females. They also occur in
the extremities and comprise about 10–15% of all
extremity-associated sarcomas, with the thigh
being the most common location [25]. In the
extremities, lesions most often arise from a vessel
wall. Histologically, leiomyosarcoma is characterized by intersecting fascicles of spindle cells
containing elongated nuclei within an abundance
of eosinophilic cytoplasm [26].
6 Tumors oftheMusculoskeletal System
133
While treatment is similar to other soft tissue
sarcomas, leiomyosarcoma is considered to be
more sensitive the chemotherapy than other sarcomas. Overall survival at 5years is close to 70% [27].
Fibrosarcoma
Fibrosarcoma is a malignant soft tissue tumor
composed of broblasts with varying amounts of
collagen bers organized in a classic “herringbone” pattern [28]. While commonly discussed,
brosarcoma is not a particularly common type
of soft tissue sarcoma [29]. It is most commonly
a disease of older age, and often occurs as a
dedifferentiated component of a lower grade
tumor. Treatment and prognosis are similar to
other high-grade soft tissue sarcomas [30].
Synovial Sarcoma
Synovial sarcoma is a soft tissue sarcoma that
usually occurs in young adults. It has a characteristic translocation t(X;18) producing a fusion
protein SYT-SSX1, 2, or 4. Patients with the
SYT:SSX1 fusion protein have a worse prognosis. Contrary to what the name would suggest,
synovial sarcoma does not arise from the
synovium or a synovial cell. The cell of origin is
unknown. Synovial sarcoma can be found
throughout the body but is the most common soft
tissue sarcoma of the foot.
MRI appearance of synovial sarcoma is similar to other soft tissue sarcomas. It does have a
high rate of calcication that can be seen on
X-ray. Synovial sarcoma classically has a biphasic appearance histologically with both spindle
cell and epithelial cell components.
Metastatic disease develops in up to 50% of
patients with synovial sarcoma. Synovial sarcoma has long been thought to have a higher incidence of lymph node metastasis, although more
recent data would suggest the incidence is similar
to other soft tissue sarcomas. Chemotherapy, particularly regimens containing ifosfamide, has
been shown to improve overall survival. Overall
survival remains poor with 50% 5-year survival.
Epithelioid Sarcoma
Epithelioid sarcoma is a low-grade sarcoma that
occurs most commonly in the upper extremity. It
is the most common soft tissue sarcoma in the
hand and occurs more commonly in males than
females. Clinically, masses often appear similar
to a hypertrophic scar and because of this and
their slow growth, diagnosis is often delayed.
Epithelioid sarcomas are also histologically
challenging to diagnose, and they are often mistaken for necrotizing granulomas. The lungs are
the most common site of metastasis, but epithelioid sarcoma has a high rate of lymph node
metastasis [31]. Regional metastasis in addition
to other atypical sites of metastatic disease are
also relatively common. Because of this, a sentinel node biopsy and a PET scan should be
included in staging. The disease course is characterized by a high rate of late local recurrence
and regional metastasis. Five-year survival is
close to 80%, but it is not uncommon for patients
to have multiple metastatic lesions removed in
an extremity before eventually developing pulmonary disease [32].
Benign Soft Tissue Tumors
All mesenchymal tissue can give rise to benign
lesions. They may occasionally be confused with
malignant lesions, or they may become symptomatic because of their size, anatomic location,
or both. Benign lesions are much more common
than their malignant counterparts. Imaging features are often similar. It is important to differentiate between benign and malignant lesions to
avoid over- and undertreating, respectively.
Lipomas
Lipomas are the most commonly occurring mesenchymal tumor, and primarily form in adults.
They can occur essentially anywhere in the body.
The majority are in the subcutaneous tissue, but
lipomas also occur deep to the fascia. While most
lipomas are solitary occurrences, approximately
134
J. Day and B. Adams
5–10% of patients with lipomas will have multiple lesions. Intramuscular lipomas can grow
quite large with masses in the thigh reaching
40cm. This large size does not infer malignancy,
although a large lipoma may be mistaken for a
sarcoma prior to imaging (Fig. 6.23). Lipomas
develop from histologically normal fat cells and
consist of monotonous sheets of mature fat cells
that are ovoid to round and usually contain a single fat droplet that compresses the nucleus.
Occasionally myxoid changes, dense trabeculae,
and interdigitating capillary vessels can be seen
on histological examination. Lipomas probably
have no potential of malignant transformation.
MRI is diagnostic in the vast majority of cases. A
tumor with signal equal to the subcutaneous fat
on all sequences with an internal complexity
equal to or less than the complexity of the subcutaneous fat is a lipoma. No biopsy is necessary in
this instance. Treatment for most lipomas is
observation. Large intramuscular lipomas are
often removed as they become symptomatic,
a
while supercial lesions typically are removed
only for cosmetic reasons.
Benign Tumors ofPeripheral Nerves
Schwannoma
Schwannomas, or neurilemmomas, are benign
tumors of the peripheral nerve sheath. Their progenitor cells are Schwann cells, giving rise to the
name. They are encapsulated—which is a dening feature when compared to the other predominant benign peripheral nerve tumor,
neurobromas, which are unencapsulated. On
histological examination, schwannomas are comprised of Antoni A (cellular) and Antoni B (loose
myxoid) components. They typically occur in isolation but may occur with other peripheral lesions
(Schwannomatosis) or in conjunction with lesions
in the vestibular nerves (Neurobromatosis type
2). Schwannomas can be painful or present with
paresthesias, but often are asymptomatic. Imaging shows a fusiform lesion that is bright on T2
sequence sometimes a string sign is evident
(Fig. 6.24). Surgical treatment involves simple
excision of the mass after splitting the nerve bers
and opening the capsule.
b
Fig. 6.23 T1 weight MRI (a) and clinical picture (b) of
an intramuscular lipoma of the thigh
Neurobroma
Neurobromas are another common benign tumor
of peripheral nerves. They can be solitary or multiple. Lesions may be cutaneous, subcutaneous, or
plexiform. Most lesions are asymptomatic, but
plexiform lesions may be painful. On histological
examination, neurobromas are comprised of
Schwann cells associated with collagen brils and
myxoid material. Imaging can be similar to
schwannoma. A target sign may be seen on an
axial view of the lesion, a thin rim of normal intermuscular fat often surrounds the lesion (a split fat
sign). Neurobromas can be part of neurobromatosis type 1 (NF1), which can have a constellation of additional symptoms including Café-au-lait
spots, axillary and inguinal freckling, optic gliomas, and Lisch nodules. Plexiform neurobromas
6 Tumors oftheMusculoskeletal System
Fig. 6.24 Schwannoma arising from the tibial nerve with
nerve evident along mass or string sign (arrow)
carry a risk for malignant transformation into a
malignant peripheral nerve sheath tumor
(MPNST), which is heralded by an enlarging
mass and change in pain. Patients with NF1 have
an approximately 10% risk of malignant transformation. Treatment for a neurobroma is typically
observation. Lesions can be removed, but excision of a lesion from a large nerve can result in
loss of function. Treatment of MPNST is the same
as other soft tissue sarcomas.
135
Fig. 6.25 Fibromatosis involving the gluteus maximus.
Fibromatosis often has an inltrative border as seen on the
medial aspect of the mass as well as areas of dark signal
on all sequences because of dense brous tissue
ies into multiple anatomic compartments. Signs
of this inltrative irregular border can be seen on
MRI.The other dening imaging feature is areas
of dark signal on both T1 and T2 sequences
because of the dense brous tissue (Fig. 6.25).
Treatment historically has been wide excision.
Because of the inltrative border, recurrence
rates are as high as 50%. This can lead to multiple surgeries and in the retroperitoneum can lead
to death. Multiple treatment modalities including
NSAIDs, tamoxifen, low-dose chemotherapy,
and radiation have all been used in the treatment
of bromatosis. When left untreated, many
tumors stop growing approximately 1year after
presentation. This, along with the poor outcomes
of active treatment strategies, has led to observation with serial MRIs being the preferred initial
treatment strategy.
Fibromatosis
Fibromatosis, also known as a desmoid tumor, is
a benign brous tumor that can be very locally
aggressive. Fibromatosis can be associated with
familial adenomatous polyposis (FAP). Tumors
are “rock hard” on examination and may be tender. The tumor has an inltrative border allowing
it to invade beyond its easily recognized boundar-
Benign Vascular Lesions
Vascular malformations can be categorized in a
number of ways and include capillary, cavernous,
venous, or arteriovenous lesions (Fig. 6.26).
While there is differing terminology, a hemangioma is commonly viewed as a type of vascular
malformation. Capillary hemangiomas are the
most common subtype. Vascular malformations
or hemangiomas are not neoplastic. Patients
136
Fig. 6.26 CT of the abdomen showing a vascular malformation of the left ank extending into the abdominal wall
musculature
often present with a mass that uctuates in size
and may be painful. On MRI, serpiginous vessels
that are bright on T2 sequences are intermixed
with areas of normal looking fat. Well-dened
calcications, called phleboliths, may be seen on
plain radiographs. When classic imaging features
are present, no biopsy is necessary. Treatment is
typically observation with symptomatic management. Symptomatic lesions can be treated with
sclerotherapy or excision, although the recurrence rate is high.
Tumors Originating fromtheJoint
The list of tumors that arise from the synovium or
occur intraarticularly is short. While a malignancy can arise intraarticularly, this is exceedingly rare. In general, treatment decisions can be
made from clinical examination and imaging
without biopsy. The primary differential for
intraarticular lesions is typically inammatory
arthropathies.
Tenosynovial Giant Cell Tumor
Tenosynovial giant cell tumor (TSGCT) can
occur both intra- and extraarticularly.
Intraarticular disease is more commonly known
as pigmented villonodular synovitis (PVNS) and
has a nodular and diffuse form. The nodular, or
J. Day and B. Adams
Fig. 6.27 Diffuse tenosynovial giant cell tumor with
extensive involvement of anterior and posterior knee.
There are many areas of low signal within the lesion on
this T2 weighted sequence corresponding to hemosiderin
deposition. Patient was treated with staged anterior and
posterior synovectomy followed by low-dose external
beam radiation
localized, form has an indolent course with
symptoms caused primarily by mass effect.
Diffuse TSGCT is an aggressive disease of
synovium characterized by prominent synovial
proliferation with formation of villi and nodules
caused by overexpression of colony stimulating
factor 1 (CSF1). The knee joint is classically
involved in a majority of cases, followed by hip
and ankle joints.
Diffuse TSGCT commonly occurs between
the second and fth decades of life. Patients
complain of pain, joint swelling, and recurrent
effusion. Arthrocentesis of the involved joint
reveals bloody or brownish synovial uid. MRI
shows nodular thickening of the synovium that
enhances with contrast administration. Masses
can extend outside of the joint capsule. There are
typically punctate areas that are dark on both T1
and T2 sequences corresponding to areas of
hemosiderin deposition (Fig.6.27). Histological
ndings are nonspecic, and usually reveal a
heterogeneous population of cells within the
6 Tumors oftheMusculoskeletal System
137
synovium, including histiocytes, xanthoma cells,
hemosiderin- laden macrophages, and multinucleated giant cells.
Treatment for nodular or localized disease is
simple excision. Diffuse disease requires complete synovectomy. Postoperative radiation of
30–35Gy reduces the risk of local recurrence. In
patients with extensive or recurrent disease a
CSF1 inhibitor is available, although its role in
the treatment of TSGCT is not well-dened at
this time.
Ganglia
Ganglia, or ganglion cysts, are cystic structures
arising from the joint lining or tendon sheath and
are common. They are very common in the hand
and wrist and predominantly affect women in the
second to fth decade of life. Ganglia most often
form in the wrist, but other sites include the metatarsophalangeal joints, ankle, and knee. Ganglia
are not neoplastic, but the etiology of their formation remains uncertain; two predominant theories
include the extrusion of synovial uid from a
capsule and degeneration of connective tissue
secondary to repetitive injury. MRI reveals a
homogenous lesion that is dark on T1 sequences
and bright on T2 sequences that communicates
with a joint or tendon sheath. Biopsy is typically
not indicated. Histopathologic examination
should demonstrate mucin-lled synovial cell
lined sac. Treatment is based on severity of symptoms, and options include observation, aspiration, and excision. Notably, care should be taken
with apparent ganglia that have an unusual
appearance or are distant from any joint or tendon sheath. These, along with apparent atraumatic hematomas, are common sources of
misdiagnosis for soft tissue sarcomas.
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Pediatric Orthopedics
DenverB.Kraft, JohnN.Delahay,
andRyanS.Murray
7
Biological Dierences
Growth
As mentioned, the fact that the child’s skeleton
is growing, both longitudinally and latitudinally, positions it uniquely for damage from the
adverse effects of trauma and disease. The
extent of this damage is a reection of the rate
of growth and the immaturity of the skeleton.
Hence, an insult will have a greater impact, if
applied at the time of more rapid growth (a
growth spurt) or when the skeleton is very
young (neonate).
Remodeling
The immature skeleton can remodel to a much
greater degree than that of the adult. Due to the
presence and activity of multiple cell populations, damage to the skeleton can be repaired
more extensively than one should anticipate in
D. B. Kraft · J. N. Delahay · R. S. Murray (*)
Department of Orthopaedic Surgery, MedStar
Georgetown Univeristy Hospital, Washington, DC,
USA
e-mail: Ryan.S.Murray@gunet.georgetown.edu
the adult. The challenge for the physician is to
recognize the limitations of this remodeling process and work within the boundaries of this
potential.
Specic Anatomic Structures
Bone
Although a child’s bone is historically lamellar
in pattern, there remains enough exibility in
the skeleton to permit what has been called
“biological plasticity,” a phenomenon not
nearly as extensive in adult bone. Essentially,
this allows a bone to “bend without breaking”
and is responsible for some of the unique types
of fractures seen in the pediatric age groups,
specically buckle and greenstick fractures
(Figs.7.1 and 7.2).
In addition, the mechanical properties of a
child’s bone vary from those of the adult. Such
characteristics as modulus of elasticity, ultimate tensile strength, and yield point all reect
the increased elasticity and plasticity unique in
this age group. However, the overall “strength”
tends to be less than that of the adult in certain
modes of loading, such as tension and shear.
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2024
W. F. Postma et al. (eds.), Essentials of Orthopedic Surgery,
https://doi.org/10.1007/978-3-031-66215-7_7
139
140
ab
Fig. 7.1 (a) Lateral radiograph of a greenstick forearm
fracture of both bones. The dorsal cortex angles without
completely fracturing (plastic deformation). (b) Lateral
radiograph obtained after reduction. (From Tachdjian
MO. Pediatric Orthopedics, 6th ed. Philadelphia, PA:
Herring; 2022. Reprinted with permission)
Ligament
As a tissue, ligament is one of the most ageresistant tissues in the human body. The tensile
strength in the child and the adult is virtually the
same. Therefore, these structures remain constant
in the musculoskeletal system. While the strength
of bone, cartilage, and muscle tends to change,
the ligamentous structures remain unchanged
with growth and development.
Periosteum
The outer covering of the bone is a dense brous
layer, which in the child is signicantly thicker
than that of the adult. The periosteum of the child
has an outer brous layer and an inner cambial or
osteogenic layer. Hence, the child’s periosteum
confers both mechanical strength and biologic
activity. The effect of these biologic differences
is far reaching when one discusses fractures in
children. Due to this thickened periosteum, fractures do not tend to displace to the degree seen in
D. B. Kraft et al.
Fig. 7.2 Lateral radiograph of the distal radius showing a
buckle fracture of the dorsal cortex. The volar cortex is
uninvolved, and the dorsal cortex is not completely fractured. (From Tachdjian MO. Pediatric Orthopedics, 6th
ed. Philadelphia, PA: Herring; 2022. Reprinted with
permission)
adults, and the intact periosteum can be used as
an aid in fracture reduction and maintenance. In
addition, fractures will heal signicantly faster
than similar injuries in adults due to all the cellular precursors that are already present.
The osteogenic layer supplies active osteoblasts, ready to make bone for the fracture callus.
There are some injuries where the periosteum
can be torn or entrapped in the fracture site, creating a block to reduction or source of future
growth disturbance.
Cartilage
The skeleton is developed embryologically
within a cartilage model. At birth, large portions
of any given bone remain largely cartilaginous.
Cartilage is not seen on standard radiographs.
7 Pediatric Orthopedics
141
The cartilage anlage is very labile and dramatically affected by external inuences such as
mechanical loading. It is important to realize
that, in examining an X-ray, one should not be
lulled into a false sense of security if all appears
well; what you do not see (i.e., the cartilage) is
more important than what you do! Aberrant cartilaginous growth will drastically affect the ultimate shape of bones and, more importantly,
joints. The best example is the proximal femur
where most of the upper end is cartilaginous.
Adverse inuences due to eccentric loading seen
in developmental dysplasia of the hip can have
far-reaching effects when applied to the immature cartilage of the neonatal hip.
The Growth Plate
Far and away, the most unique characteristic of
the immature skeleton—indeed, what is the
dening component of the immature skeleton—
is the growth plate, or the “physis” (Fig.7.3). The
physis is a cartilaginous plate interposed between
the epiphysis (the secondary ossication center)
and the metaphysis. It is essential for long-bone
growth to occur. The downside is that this ana-
tomic structure creates a point of mechanical
weakness. The physis historically has four zones,
each with its own physiologic role:
• Resting zone: The top layer of attened cells is
germinal and metabolically stores materials for
later use, since they will ultimately “move their
way” down the plate toward the metaphysis.
The chondrocytes in this zone also are synthetic,
as they fabricate the matrix in which they lie.
• Proliferating zone: The cells in this region are
actively replicating and extending the plate.
Their appearance has been described as a
“stack of plates.” In this region, the cells use
the materials that they have previously stored
for their “trip to the metaphysis.”
• Hypertrophic zone: Having extended the plate
in the former zone, the cells now swell and
switch over to a catabolic state. They prepare
the matrix for calcication and ultimately for
conversion to bone. Due to large swollen cells
and the disorganized matrix, this zone has
been cited as being the weakest mechanically;
hence, it is here that failure tends to occur.
Most, however, would agree that fracture
propagation can be seen throughout all zones
in the case of trauma.
Fig. 7.3 Anatomy of a
physis. Most injuries
occur just above the area
of provisional
calcication within the
hypertrophic zone.
Subsequently the
germinal layer
frequently remains intact
and attached to the
epiphysis. (From
Tachdjian MO.Pediatric
Orthopedics, 6th ed.
Philadelphia, PA:
Herring; 2022.
Reprinted with
permission)
Epiphyseal
artery
Ring of
LaCroix
Zone of
Ranvier
Metaphyseal
artery
Secondary
ossification
center
Germinal zone
Proliferative zone
Hypertrophic zone
Zone of
enchondral
ossification
Periosteal
sleeve