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    Medical Imaging 33

    2 Medical Imaging

    Randy E. Cohen, DP M

    C o n t e n t s

    2.1 Computed Tomography (CT) . . . . . . . . . . . . . . 34

    2.2 Magnetic Resonance Imaging (MRI) . . . . . . . . 34

    2.3 Bone Scan . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

    2.4 Bone Tumors . . . . . . . . . . . . . . . . . . . . . . . . . 35

    2.5 Osteomyelitis . . . . . . . . . . . . . . . . . . . . . . . . . 44

    2.6 Rheumatology . . . . . . . . . . . . . . . . . . . . . . . . 44

    2.7 Osteochondrosis. . . . . . . . . . . . . . . . . . . . . . . 46

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    2.1 Computed Tomography (CT)

    Advantages over Conventional Radiology

    Cross sectional display

    Excellent density resolution

    CT Numbers (Hounsfield Units HU) Bone < 1000 white (radiodense)

    Air -1000 black (radiolucent)

    Window Width and Window Level

    Window width is the variations in gray

    Window level is the mid point in gray

    For evaluating bone pathology we use window widths of 400 or more and window levels of 50 or more. For

    evaluating soft tissue pathology we use narrower window widths of 100-200 and lower window levels of 20-50.

    To enhance contrast in soft tissue pathology iodine based dye is used. CT is superior to MRI in evaluating ossi-

    fication, calcification and cortical bone. It is useful in evaluating articular disorders but not as accurate as MRI. CT

    is excellent to evaluate osseous coalitions. It can be used to evaluate the extent of soft tissue and osseous involvementin infections, but it is not tissue specific. For neoplasms it adds additional information that improves diagnostic

    accuracy.

    2.2 Magnetic Resonance Imaging (MRI)

    There is no ionizing radiation. A strong magnetic field and radio waves are used to produce the image.

    Spin density = hydrogen concentration

    TR = repetition time

    TE = time to echo

    T1 = short TR and short TE good for anatomy

    T2 = long TR and long TE good for pathology

    Increased signal intensity means bright or white. Decreased signal intensity means dark or black. STIR scans orfat suppression scans turn the fat black enhancing contrast in the bone marrow and soft tissue. Gadolinium is a

    paramagnetic contrast enhancing agent.

    Advantages of MRI

    Cortical bone is invisible

    Bone marrow visualizes well

    Better soft tissue contrast than CT

    Moving blood acts as a contrast medium

    Disadvantages of MRI

    Exam takes a long time

    Large magnets take up space and are expensive

    Requires wide area free of metallic material

    Magnetic materials in the body preclude scanning

    Cardiac pacemakers preclude scanning

    Claustrophobia precludes scanning

    Tissue appearance on MRI

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    Medical Imaging 35

    Molecules with strong molecular bonds such as ossification or calcification will not image well on MR giving a

    low signal intensity. Molecules with low water content such as ligaments will also give a low signal intensity.

    MR imaging provides superior soft tissue contrast without ionizing radiation. It is the most tissue specific diag-

    nostic modality we have short of biopsy.

    2.3 Bone Scan

    A bone scan is highly sensitive but non-specific. It can detect osteogenesis well before it will show up on an x-

    ray. A bone scan is useful and effective for early detection of stress fractures and osteomyelitis. It can accurately eval-

    uate delayed and non-union.

    In atrophic non-union of fractures there is diminished uptake at both ends of the fracture site as well as a gap

    in between. In hypertrophic non-union there is increased uptake at both ends of the fracture site with a clear gap in

    between. Delayed union will show up as diminished uptake.

    Pagets disease has a characteristic appearance on bone scans. Pagets has 3 stages: lytic, blastic, and quiescent. Inthe lytic stage the bone scan shows no increased uptake. In stage two, the blastic stage, there is confluent uptake

    starting at the end of the bone. Focal uptake is rare. In the third stage there is no increased uptake. Metastatic CA

    usually presents with focal uptake.

    2.4 Bone Tumors

    Unicameral Bone Cyst (Solitary)

    A membrane lined cavity containing a clear yellow fluid

    Occurs most often in children 4-10 years of age

    Lesions remain asymptomatic unless complicated by fracture

    They enlarge during skeletal growth and become inactive, or latent, after skeletal maturity

    Active Type

    Develops in patients under 10 years of age

    Cyst arises adjacent to growth plate and may grow to fill most of metaphysis

    Bone may be slightly expanded within cortical shell

    May cause pathologic fracture

    Tissue Appearance on MRITissue T1weighted T2weighted

    Cortical Bone dark dark

    Calcification dark dark

    Ligaments dark dark

    Large Vessels dark darkFibrosis dark dark

    Chronic Hemorrhage white white

    Fat white gray

    Muscle gray dark

    Acute Hemorrhage gray black

    Hemosiderin black black

    Exudate gray white

    Edema gray white

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    36 The 2005 Podiatry Study Guide

    Passive Type

    Patients are usually over 12 years of age

    Cysts cease to expand

    Have thicker bony wall than active lesions

    May show evidence of healing or ossification

    Less likely to result in fracture

    Predilection for the Metaphysis of Long Bones

    Proximal humerus (50% of cases)

    Proximal tibia

    Proximal femur (40%)

    Radiographic

    Show a central, well marginated and symmetric radiolucent defect in metaphysis

    Usually no bony separations or loculations

    Thin rim of non-reactive bone borders the unicameral bone cyst

    Treatment

    Goal of treatment is prevention of pathologic fracture

    Simple cysts are treated with curettage and bone grafting Recurrence is high for active cysts (50%) and low for latent cysts (10%)

    Conventional teaching is that the cyst will heal and resolve if a fracture occurs through the cyst

    Steroids:

    80=200 mg of rnethylprednisolone infused into cavity

    The failure in weight-bearing bones was high

    Autologous bone marrow injection multiple drill holes

    Aneurysmal Bone Cyst

    An uncommon expansile osteolytic lesion of bone consisting of a proliferation of vascular tissue that forms a

    lining around blood filled cystic lesion

    Develops in metaphyseal region of long bones, pelvis, vertebral body Most aneurysmal bone cysts occur in patients under 20 years of age, and it is uncommon after 30 years of age

    Grows rapidly and may attain considerable size

    Commonly involves the proximal humerus, femur, tibia, and pelvis

    Can cause paraplegia when it involves the vertebrae

    Radiographic

    Radiolucent lesion with expanded cortex arising in the medullary canal of the metaphysis

    Aneurysmal expanded appearance of cortex is contained by periosteum and thin shell of bone

    Marked cortical thinning and erosion and periosteal elevation

    Lesion rarely penetrates the articular surface or growth plate

    Diagnostic

    CT scan

    Has a density of about 20 Hounsfield units

    Spine: CT scan shows a cystic lesion not appreciated on the radiograph

    Bone Scan

    Shows intense uptake in the margin of the lesion with normal background or decreased uptake in its center

    Treatment

    Curettage and bone grafting has a 20%-40% recurrence rate

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    Recurrence can be managed with more aggressive curettage or excision

    Marginal excision or wide excision with bone grafting is preferable

    With pathologic fracture, successful resection may be difficult

    Osteoid Osteoma

    Benign osseous tumor usually less than 1.5 cm in diameter

    Comprising 11% of all benign hone tumors

    Occurs primarily in adolescents and less often in children

    Is rare in patients over 40 years of age

    Presenting symptom is well localized pain, which may be more severe at night and is relieved by aspirin or

    other prostaglandin inhibitors

    Because osteoid osteoma is a vascular tumor, substances that cause vasodilitation such as alcohol may

    precipitate an acute pain crisis

    Most common site is proximal femur and diaphysis of long bones

    Less often: foot (talus, navicular, or calcaneus) and in posterior spine

    Radiographic

    Intense bony reaction to small nidus is hallmark of osteoid osteoma, however, may be difficult to see on

    x-rays

    Look for oval radiolucent nidus only 3-5 mm in diameter that is surrounded by disproportionally large

    dense reactive zone

    Although usually located in cortex, nidus may occur subperiosteal and endosteal regions

    Radiographic Differential Diagnosis

    Garres osteomyelitis (chronic sclerosing osteomyelitis)

    Brodies abscess

    Stress fracture

    Bone Scan

    Bone scans usually shows moderate or intense radioisotope uptake

    Treatment When nidus is located in a low stress area such as metaphysis, treatment should consist of en bloc excision

    with surrounding small block of reactive bone

    Tetracycline localization:

    Using tetracycline at a dosage of 4 mg/kg, four times daily, two days preoperatively, the nidus will have a

    golden yellow fluorescence; the OR must be dark in order to see it

    Percutaneous radiofrequency coagulation

    Involves percutaneous insertion of a biopsy needle under CT scan guidance

    A tissue biopsy is taken in order to prove that the needle is properly located

    Then a radiofrequency electrode with a 5 mm exposed tip is introduced through the cannula

    The electrode is connected to a radiofrequency generator which raises the temperature of the tip to 90C

    (which is maintained for 6 minutes)

    Osteoblastoma

    Unusual benign osseous tumor

    It resembles osteoid osteoma but is usually larger (>2 cm)

    Occurs in older adolescents and young adults

    Usually does not cause localized night pain, and when pain occurs, pain is usually not relieved by ASA

    Intense bony reaction that is seen with osteoid osteoma, does not occur with osteoblastoma

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    More often located in the posterior elements of vertebra

    Will not resolve spontaneously

    Sites of involvement: spine, femur, bones of the foot

    An associated soft tissue mass may be seen in about 25% of patients

    Malignant transformation is possible (rare)

    Radiographic Show radiolucent lesion which is surrounded by a thin margin of reactive bone that may have expanded

    (aneurysmal appearance)

    Appear as a radiolucent defect with a central density due to ossification

    Treatment

    En bloc marginal excision is treatment of choice

    Active tumors are more likely to recur if intracapsular resection is performed

    Fibrous Dysplasia

    Clinical Presentation;

    Lesions may occur in one bone (monostotic) or in many (polyostotic)

    Occasionally, a child may present with pathologic fracture or angular deformity

    Polyostotic Fibrous Dysplasia:

    Children present around 10 years of age

    Findings include pain, pathologic fracture, limp, or limb deformity

    In general osseous abnormalities present before 20 years of age

    Lesion of bone that results in a haphazard mixture of immature fibrous tissue and small fragments of

    immature irabecular bone

    Angular deformities may result from defective mineralization of immature dysplastic bone

    Affected bone becomes widened and adjacent cortical bone becomes thin

    Radiographic

    Appearance of lesions is variable but most often will show:

    Intramedullary diaphyseal lesion that blends with thinned, bulged cortex Hazy or ground glass lesion which may occur with angular deformity

    Angular deformity in bone is often present at the level of lesion

    Sites of Involvement

    Rib is involved most often but any bone can be involved; also seen in proximal femur, proximal tibia,

    and mandible

    Bone becomes deformed by multiple stress fracture which may eventually lead to pathologic fracture

    Cystic type of lesion: radiolucent with a reactive rim, no trabeculae, and normal cortical thickness

    Pagetoid type of lesion: trabecular pattern which is more dense than normal bone

    Shepards crook deformity: extensive involvement of proximal femur results in a characteristic varus

    deformity which resembles a Shepards crook

    Nonossifying Fibroma

    Also known as fibrous cortical defect

    Most common bone lesion (40% children)

    Results from defect of periosteal cortical bone development which leads to a failure of ossification

    Lesion typically develops in childhood and adolescence

    During adolescence, nonossifying fibroma is an active Stage two lesion that persists or enlarges throughout

    childhood

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    With skeletal maturation, it becomes latent and either regresses or ultimately ossifies

    When tumor occupies > 50% of diameter of bone, it is prone to fracture

    Radiographic

    Well marginated radiolucent lesion, with a distinct multilocular appearance

    Is usually irregular and is surrounded by reactive rim of bone

    Benign cortical thinning, erosion, slight expansion There are two subtypes:

    Fibrous Cortical Defect (more common lesion), is small < 0.5 cm radiolucency within cortex with

    sharply defined cortex

    Metaphyseal Defect (lesion commonly develops in metaphysis of distal femur, in 90% of cases, or the

    distal tibia and is eccentrically located). The cortex may bulge over the lesion, as lack of remodeling and

    may be surrounded by a well-defined thin rim of reactive bone. No periosteal reaction is seen unless

    there has been a fracture.

    Nonossifying fibroma can act as a stress riser in bone, which can lead to stress fracture with heavy running and

    this will result in pain and increase uptake on bone scan. In children, closed treatment is the treatment of choice in

    most cases.

    Enchondroma

    Benign and asymptomatic cartilaginous tumor of bone, which most often occurs in adolescents or young

    adults

    Is an intramedullary cartilage lesion located in central metaphysis

    Intramedullary tumor develops in adjacent metaphysis and may eventually penetrate the diaphysis

    Results from failure of normal endochondral ossification below the growth plate and represents a dysplasia of

    the central growth plate

    If dysplastic process occurs in lateral growth plate, resulting tumor is called osteochondroma

    Most often affects small tubular bones of hands or feet (40%-65%)

    Frequent cause of pathologic fracture

    Most frequently involves the proximal phalanx, followed by the middle phalanx and the metacarpals

    Transformation

    Enchondroma usually become latent in adulthood and < 2% of asymptomatic solitary enchondromas will

    transform to chondrosarcoma

    Enchondromas of long bones have higher chance for malignant transformation

    In enchondromatosis, risk of malignant transformation is about 10%-25%

    In Maffucci disease (multiple enchondromas and hemangiomas) risk is near 100%

    Radiographic

    Central radiolucent lesion with well defined minimally thickened bony margin

    During active phase in adolescence, the lesion may slowly enlarge

    In children, cortex is usually thin and the lesion is radiolucent

    As lesion matures, it develops a reactive marginBone Scans

    Demonstrate radioisotope uptake in margin, related to activity of lesion

    While there is moderate uptake in the active phase there will also be some activity in latent phase

    Treatment

    Asymptomatic solitary enchondromas may be followed non-operatively with serial radiographs prognosis

    for benign enchondroma is excellent

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    Giant Cell Tumor

    A common benign but locally aggressive lesion of unknown etiology

    Occurs chiefly in men between 20 and 50 years of age (after epiphyseal closure);

    Tumor is an expansile, lytic lesion that involves the epiphysis and metaphysis

    Tumor may erode & penetrate subchondral bone, articular cartilage and cruciate ligaments

    Radiographic Large radiolucent lesion surrounded by distinct margin of reactive bone

    Often the lesion is eccentric

    Cortical thinning, endosteal erosion, and trabecularization or bony septation, of the cavity are associated

    findings

    Lesion will aggressively destroy medullary and cortical bone

    Scalloping and ridges in the wall of the tumor give it a soap bubble appearance on the radiograph

    Treatment

    Due to proximity to articular cartilage, excision of GCT of bone is difficult

    Because intra-lesional excision of GCT tends to leave tumor cells behind, past attempts of excision had

    been associated with a high recurrence rate (40%)

    Stage 1 or 2 lesions Intra-lesional excision is treatment of choice

    Use of phenol, polymethacrylate, and liquid nitrogen

    Phenol can be extremely toxic and, if used at all, its concentration should be limited to 5%

    Recurrent or stage 3 lesions

    En bloc excision with wide margin along with appropriate reconstruction

    5% of patients will have pulmonary metastases

    Tumor is considered benign-ii if pulmonary lesions are histologically benign

    Pulmonary lesions may be cured with surgical resection

    Osteochondroma

    A developmental dysplasia of peripheral growth plate, which forms a cartilage capped projection of bonefound near metaphyses of long bones

    It is the most common benign bone tumor

    Usually occurs in long bones, but may occur in any bone that is preformed in cartilage

    Tumor will continue to enlarge during skeletal growth, but will become latent at skeletal maturity

    The lesion may continue to grow into the third decade

    Occasionally a lesion grows more rapidly than expected

    Most common locations are proximal or distal femur, proximal humerus, proximal tibia, pelvis, and scapula

    In areas other than the knee, more likely to undergo malignant degeneration

    Risk of sarcomatous transformation in solitary exostosis is about 1%, but in multiple hereditary exostoses,

    the risk approaches 10%

    Clinical presentation Firm, non-tender, immovable mass arising near end of the long bone

    A symptomatic lesion may be caused by irritation of overlying soft tissues which may go on to form a fluid

    filled bursa

    Bursal fluid may be mistaken for a soft tissue mass

    Radiographic

    Exostosis is either fiat, sessile lesion, or pedunculated

    pedunculated osteochondromas are oriented in proximal direction

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    X-ray hallmark is blending of tumor into underlying metaphysis

    Cartilaginous cap displays irregular areas of calcification

    Treatment

    No treatment is required if the diagnosis is not in doubt and if the patient is relatively asymptomatic

    Surgical resection is indicated for persistent irritation (from bursitis) or for neurovascular compromise

    Surgical resection is also indicated for continued osteochondroma growth after skeletal maturity

    Chondroblastoma

    Most common primary epiphyseal tumor in children

    The adults counterpart of chondroblastoma is giant cell tumor

    Most common location is proximal tibial epiphysis and proximal humeral epiphysis

    Differential Diagnosis

    Only three tumors may invade physis:

    Chondroblastoma

    Giant cell tumor

    Clear cell chondrosarcoma

    Clinical Presentation Painful: motion limiting, benign tumor arising during adolescence

    Majority are active Stage 2 lesions

    Most lesions occur in the proximal part of the tibia (17%) and the proximal part of the humerus (15%)

    The hands and feet are the sites of 10% of chondroblastoma with the tumors having a particular

    predilection for the talus and calcaneus

    Chondroblastoma is the most common tumor affecting the patella, followed by giant cell tumor

    Radiographic

    Epiphyseal radiolucent lesion with fine punctate calcifications

    Oval osteolysis located eccentrically in the epiphysis

    Tumor is usually bordered by a well defined margin of reactive bone

    Stage 3 chondroblastoma may extend through growth plate into metaphysis or through articular cartilageinto the joint

    Treatment

    Stage 2

    Wide excision is the treatment of choice, if technically possible

    It is important to avoid joint penetration because chondroblastoma cells will grow in joint fluid

    Addition of methylmethacrylate to defect may be added to curettage to prevent recurrence

    Stage 3

    Stage 3 will require en bloc excision

    These may metastasize to the lungs

    Patients with lesions around the hip (proximal femur, greater trochanter, and pelvis) are significantly more

    likely to develop recurrences as well as metastatic lesions

    Chondromyxoid Fibroma

    Locally painful benign cartilaginous lesion of bone

    Occurs in adolescents

    Located in metaphysis of major long bones

    This lesion most often presents as an active Stage 2 lesion that is are locally destructive and has a high

    recurrence rate (up to 25%)

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    Does not undergo malignant transformation

    Eccentric radiolucent defect with NO calcification

    Adjacent cortex may be expanded, thinned or even absent

    Look for sclerotic and scalloped rim

    Typically located in the metaphyseal region of long bones and in some cases it is possible for it to invade the

    epiphyseal plate

    Treatment

    Curettage is indicated for well encapsulated Stage 2 lesions

    Stage 3 lesions, most often seen in the pelvis, require wide excision to prevent recurrence.

    Chondromyxoid Fibroma Chondrosarcoma

    Malignant cartilaginous tumor of bone

    It is less common and less aggressive than osteosarcoma

    Chondrosarcoma

    Primary

    Most often presents as a low grade - intracompartmental lesion

    They are slow to metastasize and may grow to immense proportions

    Tumor tends to destroy bone and to extend into the soft tissues

    Tumor may invade blood vessels and produce a long intravascular tumor that may extend into heart and

    pulmonary arteries

    Long-term survival rate of patients with treated chondrosarcoma is between 50%-75%

    Primary form occurs most often in men between 50 and 60 years of age whereas osteosarcoma occurs

    between 20 and 30 years of age

    Most common locations are the pelvis, proximal femur and shoulder girdle, whereas osteosarcoma occurs

    most often around the knee

    When chondrosarcoma occurs in the pelvis, it is often large, high grade, diagnosed late, and has a poor

    prognosis

    Secondary

    Secondary form occurs in about 25% of cases

    Malignant transformation from preexisting enchondroma or osteochondroma Variants of chondrosarcoma: (based on histology and location)

    Clear cell (intermediate grade) extraosseous

    Atypical enchondroma (juxtacortical chondroma)

    Clinical Presentation

    Persistent, dull, aching pain

    Found in an older age group peaking at 45 years of age

    Majority of chondrosarcomas occur about the hip and pelvis

    Radiographic

    Subtle, radiolucent, permeative lesion

    May have hazy or speckled calcifications with either a diffuse salt and pepperpattern or a more discrete

    popcorn pattern

    Pattern of calcification is usually diagnostic of cartilaginous tumor

    Treatment

    Tumor does not respond to x-ray therapy nor to currently available antineoplastic drugs

    Low grade tumors:

    Rarely metastasize

    Rarely recurs after wide limb salvaging excision

    The involved bone is resected along with a small cuff of surrounding muscle

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    High grade tumors

    Have higher rate of recurrence after limb salvage (requires amputation)

    Are prone to pulmonary metastases

    Osteosarcoma

    Malignant tumor of bone in which neoplastic osteoid is produced by a proliferating spindle cell stroma

    Most common primary malignant bone tumor of mesenchymal derivation

    Arises in adolescents and affects males slightly more often than females

    Locations

    Occurs in region of knee (distal femur or proximal tibia) in 50% of patients

    Other sites include proximal humerus, proximal femur, and pelvis

    Most osteosarcomas occur in the metaphysis

    Infrequently occurs in the spine

    Clinical Presentation

    Initial symptom is a painful bony mass

    Significant number of osteosarcomas in adults occur in association with Pagets disease

    PrognosisAt time of diagnosis, most osteosarcomas are Stage 2b lesions that have infiltrated the soft tissue in 50% of

    adolescent patients; the tumor penetrates growth plate into epiphysis

    Metastasis

    Osteosarcoma tends to have early hematogenous metastasis

    Pulmonary or lymph node metastases are detected at presentation in about 10% of patients

    Pulmonary metastases are usually detected within and year after diagnosis

    Undetectable micrometastases are probably present in lungs of most patients at time they first seek

    medical attention

    Without control of micrometastatic disease, there will be x-ray evidence of lung metastases in up to 80%

    of patients after 1-2 years; following surgical resection, skip metastases are found in 25% of patients.

    Survival

    In the past survival rate was around 15%, but with adjunctive therapy survival is greater than 50%.

    Metastatic disease evident at presentation also indicates presence of more aggressive disease and poor

    prognosis

    Treatment

    Surgery alone as a treatment yields only a 20% survival rate; with adjuvant chemotherapy, the 5 year

    survival rate is > 50%

    Some surgeons insist on preoperative chemotherapy in the management of osteosarcoma

    Commonly used agents include doxorubicin, cisplatin, high-dose methotrexate, ifosfamide, and cy-

    clophosphamide

    Limb Salvage versus Amputation

    Limb salvage surgery does not seem to have a higher local recurrence rate than amputation.

    Surgical resection of osteosarcoma pulmonary metastases

    Aggressive surgical resection will improve 5-year survival rate.

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    2.5 Osteomyelitis

    Initially we see soft tissue swelling with obliteration of fascial planes. Bony changes appear on x-ray in 10-14

    days. Initial changes include decreased bone density or localized osteoporosis. Periosteal reaction with absence of

    Sharpys fibers is noted. Indistinct changes in bony appearance can occur such as a break in the cortex and a lack of

    bony definition.

    Sequestra involucrum and cloaca are relatively late changes seen in osteomyelitis. Sequestra is dead avascularbone that the body tries to wall off. Initially sequestra appears as the same density as normal bone. Due to hyper-

    emia, the surrounding live viable bone will become diminished in density and the sequestra will appear relatively

    more dense. If involucrum (granulation tissue) is lied down over the sequestra, we will see an absolute increase in

    bone density. Involucrum is granulation tissue that appears radiolucent. As it consolidates and ossifies, it takes on

    the density of bone.

    Cloaca is a hole in the bone caused by proteolytic enzymes and pressure. It is more commonly seen in

    hematogenous OM than direct extension osteomyelitis.

    Diagnosing OM

    It takes 10-14 days for osteomyelitis to show up on x-ray. A technesium bone scan becomes positive for

    osteomyelitis 24-48 hours after symptoms appear.A triphasic technesium scan is useful in differentiating an acute cellulitis from acute OM. The three phases are

    the blood flow, blood pooling, and the delayed. The first two stages measure blood, the third stage measures osteo-

    genesis. Acute cellulitis is hot in the first two stages and cool in the third stage. Acute OM is hot in all three stages,

    getting hotter in the third stage.

    Gallium, a soft tissue-scanning agent is often used in conjunction with a technesium scan. Gallium binds with

    the ferroproteins in white blood cells. It is better for chronic infections because it stays hot for a long time. Focal gal-

    lium uptake in bone is characteristic of OM.

    Indium is a soft tissue-scanning agent that is better for acute infections. Indium does not localize to bone well.

    The most sensitive nuclear medicine scan for osteomyelitis is a technesium labeled lymphocyte scan. Uptake in

    bone is highly suggestive for OM.

    The most reliable magnetic resonance study is a fat suppression (STIR), gadolinium-enhanced scan. Increasedsignal intensity in bone is highly suggestive of OM.

    2.6 Rheumatology

    Osteoarthritis

    Osteoarthritis is an insidious disease related to aging, although not all old people get it. It is associated with

    weight-bearing joints but is common in the shoulder.

    It is primarily a disease of the cartilage, which becomes soft and frayed. The primary radiographic changes are

    hypertrophic.

    Initially we see non-uniform joint space narrowing. There is subchondral sclerosis. Abnormal pressure in the

    joint results in subchondral cyst formation, which does not erode the cortex. Abnormal forces at the joint cause the

    capsule and ligaments to pull forming osteophytes and exostoses.

    Because OA is not an inflammatory arthritity, osteoporosis is not a primary part of the disease. However, if the

    patient stops ambulating because of the pain, disuse osteoporosis can occur. Joint fusions are not a primary part of

    the disease, although exostosis can impinge and inhibit range of motion.

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    Rheumatoid Arthritis

    Rheumatoid is a T-cell mediated collagen vascular disease, which affects joints. Although the full-blown disease

    is bilaterally symmetrica1, the initial onset can be unilateral. There is a predilection for young women 3:1 over

    young men.

    Rheumatoid is primarily an atrophic arthritity. There appears to be a predilection for the metatarsals before it

    affects the phalanges. Fusiform swelling of the digits is common.Initially effusion of the joints is noted giving uniform joint space widening. Periarticular osteoporosis is a com-

    mon early radiographic feature. Uniform joint space narrowing due to consolidation of panus is a relatively late

    finding.

    Joint fusions are uncommon but possible. Periarticular erosions in the area of the synovium are common.

    Subluxations and dislocations are possible with fibula deviations. Subchondral cysts, which can erode through the

    cortex, are present.

    Seronegative Arthritis

    Ankylosing Spondylitis

    Ankylosing Spondylitis primarily affects the sacroiliac joints and the spine. The peripheral joints may also be

    involved. A high incidence of the HLA-B27 antigen is present. There is a predilection for young males 3:1 overfemales.

    Back pain is usually the first clinical manifestation. Bilateral sacroiliitis is common. Complete bony ankylosis is

    possible. Syndesmophyte formation can occur. Fusion of the vertebral column resulting in bamboo spine is an end

    result.

    Bony erosions at tendon insertions and synovium are possible, as in the other seronegative arthritities.

    Psoriatic Arthritis

    In 10% of the cases the arthritic lesions precede the skin lesions. A diagnosis of psoriatic arthritis cannot defini-

    tively be made without the skin lesions. There is an increased incidence of the HLA-B27 antigen in psoriatic arthritic

    patients.

    Entheseopathy is common especially of the tendoachilles and plantar fascia. In two-thirds of the patients mono

    or oligoarticular arthritis is present similar to that seen in the other sero negative arthritities. In one-third to one-half of the patients, the disease will evolve into a symmetrical distribution similar to that of rheumatoid.

    Psoriatic arthritis characteristically has both atrophic and hypertrophic changes with a lack of osteoporosis.

    Pauciarticular erosions are present. Joint space widening with well-demarcated articular borders are characteristic.

    There are intraarticular erosions. Joint fusions are common.

    Saucer-in-cup or pencil-in-cup deformities are associated with psoriatic arthritis but occur less than 3% of the

    time. Hypertrophic changes of the base of one phalanx with atrophic changes of the head of the adjoining phalanx

    give this appearance.

    There is a predilection for the interphalangeal joints with lack of fibula deviation. There is no significant

    osteoporosis.

    Reiters Reactive Arthritis

    There is a marked increase in the presence of the HLA-B27 antigen. Young men have the highest incidence ofthe disease. The classic triad of symptoms is non-gonococcal urethritis, conjunctivitis, and arthritis. Keratoderma

    blennorrhagicum, a dermatological lesion of the palms and soles, can also occur.

    Dactylitis, or sausage-like soft tissue swelling of the digits, occurs. The lower extremity is affected more than the

    upper. Periarticular osteoporosis with intraarticular erosions are present. Erosions are also present at synovial and

    tendinous insertions.

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    46 The 2005 Podiatry Study Guide

    Gout

    Gout is the symptomatic deposition of uric acid crystals in the joint. It has its highest incidence in older males.

    Females with gout are usually post-menopausal.

    Gout has a predilection for the smaller joints with the highest incidence at the first metatarsal phalangeal joint.

    It takes many years and multiple attacks for gouty erosions to show up on x-ray. The classic lesion is an erosion

    with overhanging cortical margin (Martels Sign) with a rat bite-like appearance. Martels Sign appears less than

    10% of the time.

    Urate tophi may calcify, giving it a cloudy amorphous appearance in the soft tissue.

    Pseudogout (Calcium Pyrophosphate Dihydrate Deposition)

    Pseudogout is the symptomatic deposition of calcium pyrophosphate dihydrate crystals. Pseudogout has a

    predilection for the knee and other large joints.

    The classic radiographic appearance is calcification in articular cartilage, as well as in articular capsule liga-

    ments and tendons.

    2.7 Osteochondrosis

    An osteochondrosis is an aseptic necrosis-like process at a growth center (epiphysis or apophysis). A true osteo-

    chondrosis will undergo a sequence of events characteristic of an infarct. Initially there will be an infarct followed byreabsorption, revascularization, and remodeling. All true osteochondrosis undergo this sequence of events and show

    characteristic radiographic changes.

    An early diagnostic sign in a true osteochondritity is a crescent sign. This is a crescent or triangular shape radio-

    density in the subchondral bone that is an early indicator of infarct.

    Immobilization is required to prevent joint destruction and allow healing with minimal sequela. Sequela result

    in joint flattening, neck broadening, and degenerative joint disease.

    True Osteochondrosis

    Legg-Calve-Perthes Disease

    This is an osteochondrosis of the proximal femoral epiphysis. It is more common in males than females with a

    peak incidence of about 5 yrs of age.

    Freibergs DiseaseThis is an osteochondrosis of the metatarsal head seen in young females between the age of 10 and 15 yrs of

    age. It is most common in the second metatarsal bead. Studies show this is likely a stress fracture of the epiphy-

    seal plate. This results in a flattening of the metatarsal head with an S-shaped joint and degenerative joint

    disease.

    Osteochondrosis of the Sesamoids

    Radiographically, we see cystic erosions in the sesamoids.

    Abnormalities in Osteogenesis and Chondrogenesis

    Osgood Schlatters Disease (Osteochondrosis of the Tibial Tuberosity)

    This is a tendonitis of the patella tendon with bone formation in the tendon. A normal tibial tubercle may be

    fragmented and teardrop-shaped. This is not an x-ray diagnosis. This is most commonly seen in young boys with

    pain on palpation of the tibial tuberosity. There is pain upon squatting and going up and down steps.

    Blounts Disease (Osteochondrosis of the Medial Tibial Condyle)

    This is an abnormality of chondrogenesis of the proximal medial tibial epiphysis. This is most likely seen in

    young black males. The infantile form of the disease is much more severe than the juvenile. Significant tibial bowing

    may result.

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    Medical Imaging 47

    Anatomical Variants

    Kohlers Disease

    This is associated with delayed ossification of the navicular. We see a disk-shaped navicular narrowed in its

    A/P diameter. It may be fragmented, sclerotic, hazy, and out of focus. It will eventually ossify normally.

    There is no real pathology.

    Islins Disease

    This is a normally fragmented or multi-partite apophysis at the base of the fifth metatarsal.

    Severs Disease

    The calcaneal apophysis is the most sclerotic apophysis in the body. Irregularity, fragmentation, and new

    bone formation is normal. There are no reported cases of long-term deformity associated with this disor-

    der. The three most common etiologies of heel pain in children are plantar fasciitis, Achilles tendonitis, and

    Haglund's deformity. The heel pain is not caused by the fragmented calcaneus but usually by one of these

    pathologies.

    Osteochondritis Dissecans

    This is a localized ischemic necrosis that occurs more frequently in young men and boys often following

    injury. It is an osteochondral fracture that results in a button of necrotic bone separating from the joint

    surface. It is seen most commonly in the knee.