Question 1

A 12-year-old patient with fibrous dysplasia has an increasing limp and progressive bowing in the intertrochanteric and subtrochanteric regions of his femur. Recommended treatment includes:

Explanation

The most important step in treating patients with fibrous dysplasia is to decrease the bending force on the patientâ s femur. A valgus osteotomy with a plate or a rod decreases the bending force on the patientâ s femur by decreasing the offset from the center of the patientâ s body mass. Allografting and plate or rod fixation in situ causes progressive bowing in the patient.

Question 2

Which of the following bones is the most common site for involvement with fibrous dysplasia:

Explanation

The femur and the tibia are the most common sites of fibrous dysplasia in the appendicular skeleton. Involvement of the humerus is also common. Fibrous dysplasia may also occur in the radius, ulna, and phalanges of the hand; it occurs less frequently in the femur, humerus, and pelvis.

Question 3

What is the risk of malignant transformation over the course of a lifetime in a person with fibrous dysplasia:

Explanation

Fibrous dysplasia is a relatively common disorder. The risk of malignant transformation is less than 1%. Many historic cases of malignant transformation with fibrous dysplasia occurred in patients who also received external beam irradiation.

Question 4

The most common malignancy arising from transformation of fibrous dysplasia is:

Explanation

The most common malignancies arising from transformation of fibrous dysplasia are osteosarcoma and malignant fibrous histiocytoma. However, chondrosarcoma, giant cell tumor, adamantinoma, and fibrosarcoma have been reported to result from fibrous dysplasia. Radiation increases the risk of malignant transformation of fibrous dysplasia.

Question 5

The pattern of genetic transmission of polyostotic fibrous dysplasia is best described as:

Explanation

Fibrous dysplasia is a sporadic condition. Although there are a few reports of parents and children having fibrous dysplasia, such reports are rare.

Question 6

Which of the following conditions does this computerizd tomography scan (Slide) most likely represent:

Explanation

Orthopedic Prometric Exam Chapter 3 Image

This is an osteoid osteoma of the fourth lumbar vertebra in a patient who experienced night pain and relieved the pain with nonsteroidal anti- inflammatory drugs. The location of a sclerotic nidus in the posterior elements of the vertebrae is typical for this disorder. Excision of the osteoid osteoma resulted in prompt pain relief for this patient.

Question 7

This radiograph (Slide) shows a 9-year-old boy with scoliosis. From which of the following conditions is the boyâ s scoliosis likely to have resulted:

Explanation

The patientâ s scoliosis is the result of neurofibromatosis. A sharp focal curve over few vertebrae, thinning of apical pedicles, and spindling of the ribs are symptoms of neurofibromatosis that are indicated in the radiograph.

Question 8

A 5-year-old boy presents for examination. He is diagnosed with developmental dysplasia of the hip. Recommended treatment includes:

Explanation

At age 5, traction or closed reduction is not likely to produce a stable joint. Femoral shortening is indicated to reduce pressure, reducing the likelihood of avascular necrosis or redislocation. The most likely option to produce a stable joint is open reduction with femoral and iliac osteotomy.

Question 9

The radiograph (Slide) of a 16-month-old toddler is presented. Which diagnosis is most appropriate:

Explanation

This patient has developmental dysplasia of the hip. The femoral head is delayed in ossifying because of lower contact pressure and the femur is anteverted, not retroverted.

Question 10

A 4-year-old girl sustains an injury in a motor vehicle accident. She sustained a femoral artery injury, which was repaired. Her pubic diastasis is 4.5 cm. A radiograph (Slide 1) and clinical photograph (Slide 2) are presented. Which of the following treatment options is recommended:

Explanation

This is an open-book injury due to direct frontal impact, which presumably also injured the femoral artery directly. A pubic diastasis .2.5 cm should be reduced. Open reduction and internal fixation is the preferred method to accomplish this, using either a wire or a plate. External fixation is also an acceptable option. Casts and sling are more likely to cause pressure sores or to be ineffective.

Question 11

Loeys-Dietz syndrome is caused by a mutation in:

Explanation

Loeys-Dietz syndrome is an autosomal dominant syndrome characterized by arterial tortuosity, aneurysms, hypertelorism, and bifid uvula or cleft palate. Scoliosis, foot deformities, ligamentous laxity, and other findings are often present. The aneurysms have particular risk for rupture at small diameters. This disorder is caused by mutations in genes encoding TGF-beta receptor 1 and 2.

Question 12

An 11-year-old female patient with bilateral cavus feet presents with foot pain and callosities on the plantar surface of the foot. She is diagnosed with C harcot-Marie-Tooth disease and may require surgical intervention. During a standing C olemanâ s lateral block test, the patientâ s hindfoot varus corrects bilaterally when standing on a 1-inch wooden block. Which of the following surgical options is the most appropriate:

Explanation

This patient has a typical cavovarus foot. The key in evaluating the treatment options is the standing block test. Because her hindfoot varus is corrected during this test, her hindfoot is flexible and a calcaneal osteotomy is not necessary. Osteotomy of the base of the first metatarsal is also not preferred in such a case because the growth plate becomes at risk for arrest, the procedure requires internal fixation, the second metatarsal head becomes at risk for a stress transfer lesion, and is not located at the side of the deformity. In C harcot-Marie-Tooth disease, the deformity apex generally lies in the tarsometatarsal articulations and the medial cuneiform.

Question 13

Which of the following disorders is not a cause of cavus foot:

Explanation

All of the disorders mentioned may cause cavus foot except for tarsal coalition.

Question 14

Based on the clinical photograph (Slide 1) and radiographs (Slide 2) of this 11-year-old boy, which of the following conditions is demonstrated:

Explanation

This patient has many typical features of neurofibromatosis 1: subcutaneous neurofibromas, large â coast of Californiaâ cafe-aulait spot with several others, and a dystrophic curve at a young age. Surgery is recommended.

Question 15

Which of the following factors predicts an increased risk that a child sustaining a pelvis fracture will incur an unstable fracture:

Explanation

The closure of the triradiate cartilage of the acetabulum is associated with a significant increase in the risk of an unstable pelvis fracture, as well as the need for surgical treatment. This seems to signal the change in bone plasticity from pediatric type to adult type.

Question 16

The mean age of triradiate cartilage closure in girls and boys is:

Explanation

The triradiate cartilage closes at a mean of 12.5 years in girls and 13.5 years in boys. The closure of the triradiate cartilage signals the end of the peak height velocity (growth spurt). This is important for timing of scoliosis treatment and for signaling a change in pelvic fracture patterns from pediatric to adult.

Question 17

C hildren with unstable pelvis fractures have an increased risk of late pain and dysfunction if which of the following is present:

Explanation

Pediatric pelvis fractures are associated with an increased risk of late pain and dysfunction if the asymmetry after reduction is .1.1 cm.

Question 18

Which of the following is true regarding ability to remodel after a displaced pediatric pelvic fracture:

Explanation

In pediatric pelvic fractures healing with asymmetry, no significant remodeling is seen at any age.

Question 19

According to the Delbet classification, a transphyseal fracture of the pediatric proximal femur is considered type:

Explanation

According to the Delbet classification: Type I: Transphyseal fracture Type II: Transcervical fracture Type III: Basicervical fracture Type IV: Intertrochanteric fracture

Question 20

According to the Delbet classification, the risk of avascular necrosis is least with which of the following pediatric hip fractures:

Explanation

The risk of avascular necrosis is highest with type I, followed by about equal rates for types II and III (approximately 15 %). The risk of avascular necrosis is low for type IV, intertrochanteric fractures. Type I Transphyseal Type II Transcervical Type III Basicervical Type IV Intertrochanteric

Question 21

A 9-year-old girl presents with precocious puberty, café-au-lait spots with irregular borders, and multiple lytic bone lesions with a ground-glass appearance. The pathogenesis of this condition is most directly related to a mutation in which of the following?

Explanation

McCune-Albright syndrome is caused by a sporadic, post-zygotic activating mutation in the GNAS1 gene. This leads to continuous activation of adenylyl cyclase and increased intracellular cAMP, affecting multiple endocrine and skeletal tissues.

Question 22

Which of the following histologic features best differentiates osteofibrous dysplasia from fibrous dysplasia?

Explanation

Unlike fibrous dysplasia, which lacks osteoblastic rimming around its irregular woven bone trabeculae, osteofibrous dysplasia demonstrates prominent osteoblastic rimming. Both present as fibro-osseous lesions, but this histologic distinction is critical for diagnosis.

Question 23

A 14-year-old boy with polyostotic fibrous dysplasia presents with increasing thigh pain and a severe varus deformity of the proximal femur (Shepherd's crook deformity).

What is the most appropriate surgical management?

Explanation

The standard surgical treatment for a progressive Shepherd's crook deformity in fibrous dysplasia involves a valgus-producing osteotomy stabilized with a cephalomedullary or intramedullary nail. Cortical bone grafting and plating alone have unacceptably high failure rates in these mechanically inferior bones.

Question 24

A 45-year-old woman with known fibrous dysplasia presents with a slow-growing, painless soft tissue mass in her right thigh. MRI reveals a well-circumscribed, lobulated intramuscular lesion that is hyperintense on T2-weighted images. Biopsy confirms an intramuscular myxoma. What is the diagnosis of this associated syndrome?

Explanation

Mazabraud syndrome is the rare association of single or multiple intramuscular myxomas with polyostotic fibrous dysplasia. The myxomas typically occur in the same anatomic region as the most severely affected bone.

Question 25

A 30-year-old male presents with a slowly enlarging, painful mass over the anterior crest of his left tibia. Radiographs show a distinct, eccentrically located, multiloculated lucent lesion in the anterior tibial diaphysis. Biopsy reveals a biphasic pattern of epithelial islands within a fibrous stroma. Immunohistochemistry will most likely be strongly positive for which of the following?

Explanation

The clinical and histologic picture describes an adamantinoma, a low-grade malignant bone tumor predominantly found in the anterior tibia. It is characterized by biphasic histology and positivity for epithelial markers like cytokeratin and epithelial membrane antigen (EMA).

Question 26

What is the recommended definitive management for an adult patient diagnosed with a confirmed adamantinoma of the tibia?

Explanation

Adamantinoma is a low-grade, indolent malignancy that does not respond reliably to chemotherapy or radiation. The treatment of choice is wide en bloc resection to achieve negative margins, typically followed by reconstructive procedures like osteoarticular allograft or vascularized fibula grafting.

Question 27

An 8-year-old boy presents with an asymptomatic bowing of his lower leg. Radiographs reveal a purely intracortical, expansile radiolucent lesion in the anterior diaphysis of the tibia. A biopsy confirms osteofibrous dysplasia. What is the most appropriate initial management?

Explanation

Osteofibrous dysplasia in young children is usually self-limiting and may spontaneously resolve after skeletal maturity; therefore, observation is the initial treatment of choice. Early surgery is associated with a very high recurrence rate and is reserved for severe deformity or impending fracture.

Question 28

A 65-year-old man of European descent presents with deep, aching pain in his right pelvis and thigh, accompanied by increasing head size. Laboratory studies show normal serum calcium, normal phosphorus, and markedly elevated alkaline phosphatase.

Which gene mutation is most strongly associated with the familial form of this disease?

Explanation

The patient has Paget's disease of bone, characterized by isolated elevated alkaline phosphatase and bone enlargement. Mutations in the SQSTM1 (p62) gene are present in up to 30% of familial Paget's disease cases, leading to increased osteoclast activity.

Question 29

A 70-year-old patient with long-standing polyostotic Paget's disease presents with a new, rapidly enlarging, painful mass over his proximal humerus. Radiographs show a destructive lytic lesion breaking through the cortex with an associated soft tissue mass. What is the most likely diagnosis?

Explanation

Secondary osteosarcoma is the most common malignant transformation in patients with Paget's disease, occurring in about 1% of patients. It carries a very poor prognosis and presents as a new, rapidly destructive, painful mass in a previously affected pagetic bone.

Question 30

A 55-year-old female with symptomatic Paget's disease of the femur is started on a nitrogen-containing bisphosphonate (e.g., zoledronate). What is the primary molecular mechanism of action of this medication in treating her condition?

Explanation

Nitrogen-containing bisphosphonates inhibit farnesyl pyrophosphate synthase within the osteoclast mevalonate pathway. This prevents protein prenylation, causing osteoclast apoptosis and drastically reducing the hyperactive bone resorption seen in Paget's disease.

Question 31

In Paget's disease of bone, which of the following phases is characterized by a pathognomonic "mosaic" pattern of lamellar bone with prominent cement lines upon histological examination?

Explanation

The late osteosclerotic (or burnt-out) phase of Paget's disease features dense, hypovascular bone with a disorganized "mosaic" or "jigsaw puzzle" pattern of prominent cement lines. This results from chaotic, rapid bone remodeling during the preceding mixed phase.

Question 32

A 45-year-old female presents with multiple bony lesions consistent with fibrous dysplasia. She also notes a slow-growing, painless mass in her thigh. Biopsy of the thigh mass reveals a hypocellular, abundant mucoid stroma. What is the most likely diagnosis for this syndrome?

Explanation

Mazabraud syndrome is a rare disorder characterized by the association of fibrous dysplasia with one or more intramuscular myxomas. It generally presents in adulthood and carries a slightly increased risk of malignant transformation.

Question 33

A 9-year-old girl with polyostotic fibrous dysplasia presents with precocious puberty and cafe-au-lait spots. What is the underlying genetic mechanism of her condition?

Explanation

This patient has McCune-Albright syndrome. The condition is caused by an activating somatic missense mutation in the GNAS1 gene, resulting in persistent cAMP production and widespread endocrine, cutaneous, and skeletal abnormalities.

Question 34

A biopsy of a proximal femur lesion in a 14-year-old boy shows irregular woven bone trabeculae lacking osteoblastic rimming in a fibrous stroma. What is the most likely diagnosis?

Explanation

The histologic hallmark of fibrous dysplasia is irregular, "Chinese character" trabeculae of woven bone embedded in a benign fibrous stroma without osteoblastic rimming.

Question 35

A 5-year-old boy presents with anterior bowing of the tibia. Biopsy reveals woven bone trabeculae rimmed by prominent osteoblasts within a fibrous stroma. What is the most likely diagnosis?

Explanation

Osteofibrous dysplasia occurs almost exclusively in the tibia or fibula of children. It is distinguished from fibrous dysplasia histologically by the presence of prominent osteoblastic rimming around the bone trabeculae.

Question 36

A 30-year-old patient with polyostotic fibrous dysplasia complains of intractable bone pain in the pelvis and lower extremities. Which of the following is the most appropriate initial medical therapy?

Explanation

Intravenous bisphosphonates, such as pamidronate, are considered the medical treatment of choice for alleviating bone pain and reducing the rate of osteoclastic resorption in polyostotic fibrous dysplasia.

Question 37

Although rare (less than 1%), fibrous dysplasia can undergo malignant transformation. What is the most common histologic subtype of this secondary malignancy?

Explanation

Malignant transformation in fibrous dysplasia is rare but well-documented, typically associated with prior radiation therapy. Osteosarcoma is the most common secondary malignancy, followed by fibrosarcoma.

Question 38

A 15-year-old boy presents with a prominent limp and shortening of his right leg. Radiographs demonstrate a classic "shepherd's crook" deformity of the proximal femur.

What is the preferred surgical approach for an impending fracture in this patient?

Explanation

Surgical management of a shepherd's crook deformity requires correction of the mechanical axis via valgus osteotomy and rigid internal fixation. Cortical strut grafts are preferred over cancellous grafts to prevent resorption and recurrence.

Question 39

How do the cafe-au-lait spots seen in McCune-Albright syndrome typically differ from those seen in Neurofibromatosis type 1 (NF1)?

Explanation

Cafe-au-lait macules in McCune-Albright syndrome typically have irregular, jagged borders resembling the "coast of Maine." In contrast, those in NF1 have smooth borders resembling the "coast of California."

Question 40

A 7-year-old boy has an incidentally discovered unicameral bone cyst (UBC) in the proximal humerus. Radiographs show the cyst is located immediately adjacent to the physis. Which of the following best describes this cyst?

Explanation

An active UBC is located immediately adjacent to the epiphyseal plate and has a higher risk of interfering with growth or recurring after treatment. A latent cyst has migrated away from the physis into the diaphysis.

Question 41

A 9-year-old boy presents with mild shoulder pain after throwing a baseball. Radiographs reveal a centrally located, lucent lesion in the proximal humerus with a cortical fragment resting dependently within the lesion. What is the most likely diagnosis?

Explanation

The "fallen leaf" or "fallen fragment" sign is pathognomonic for a unicameral bone cyst that has sustained a pathologic fracture. It occurs because the cyst cavity is fluid-filled, allowing the cortical fragment to settle at the base.

Question 42

An 8-year-old child sustains a mildly displaced pathologic fracture through a proximal humerus unicameral bone cyst. What is the most appropriate initial management?

Explanation

Pathologic fractures through a UBC should initially be treated non-operatively with simple immobilization (e.g., a sling) until the fracture heals. Interestingly, the cyst may sometimes heal spontaneously as the fracture calluses.

Question 43

A 14-year-old girl presents with knee pain. Radiographs reveal an expansile, eccentric lytic lesion in the distal femur. Biopsy demonstrates blood-filled spaces separated by septa containing fibroblasts, giant cells, and reactive woven bone. What is the diagnosis?

Explanation

The histologic description of blood-filled spaces devoid of an endothelial lining, separated by fibrous septa containing multinucleated giant cells and woven bone, is the classic appearance of an Aneurysmal Bone Cyst (ABC).

Question 44

Primary aneurysmal bone cysts (ABCs) are now recognized as true neoplasms. Which of the following genetic translocations is most frequently associated with primary ABCs?

Explanation

Primary ABCs are driven by the t(16;17) translocation, which fuses the promoter of the CDH11 gene to the USP6 oncogene, leading to USP6 upregulation.

Question 45

An asymptomatic 12-year-old boy has an incidental radiograph of the knee showing an eccentric, multiloculated, radiolucent lesion with a sclerotic rim in the distal femoral metaphysis. What is the expected natural history of this lesion?

Explanation

This lesion is a Non-ossifying fibroma (NOF). NOFs are common benign lesions in growing children that typically undergo spontaneous ossification and resolve completely as the child reaches skeletal maturity.

Question 46

A 16-year-old male presents with deep thigh pain that is worse at night and dramatically relieved by ibuprofen. Radiographs show a small radiolucent nidus surrounded by dense reactive sclerosis in the proximal femur. Which imaging modality is best for localizing the nidus prior to ablation?

Explanation

A thin-slice CT scan is the imaging modality of choice to clearly delineate the nidus of an osteoid osteoma and differentiate it from the surrounding reactive sclerosis. This is essential for planning surgical resection or radiofrequency ablation.

Question 47

Histological evaluation of an osteoid osteoma nidus will most likely reveal which of the following?

Explanation

The nidus of an osteoid osteoma is characterized by an interlacing network of woven bone trabeculae prominently rimmed by active osteoblasts, set within a highly vascularized fibrovascular stroma.

Question 48

In a giant cell tumor (GCT) of bone, which cell type represents the true neoplastic component driving the proliferation?

Explanation

The mononuclear stromal cells are the true neoplastic cells in a Giant Cell Tumor. They overexpress RANKL, which recruits normal macrophages and stimulates their fusion into reactive, bone-resorbing multinucleated giant cells.

Question 49

A 35-year-old female presents with an unresectable giant cell tumor of the sacrum. Which of the following targeted biologic therapies is most appropriate?

Explanation

Denosumab is a monoclonal antibody against RANKL. It is FDA-approved for adults and skeletally mature adolescents with giant cell tumors of bone that are unresectable or where surgical resection would cause severe morbidity.

Question 50

An 18-year-old presents with dull back pain not significantly relieved by NSAIDs. Imaging reveals an expansile 3.5 cm radiolucent lesion in the posterior elements of L3. Histology is identical to an osteoid osteoma. What is the most likely diagnosis?

Explanation

Osteoblastomas are histologically indistinguishable from osteoid osteomas but are larger (typically > 2 cm). They are frequently located in the posterior elements of the spine and cause pain that is less responsive to salicylates/NSAIDs.

Question 51

A 25-year-old patient undergoes a radiographic workup for right thigh pain. The femur shows an intramedullary expansile lesion with a "ground-glass" appearance, cortical thinning, and bowing.

What is the most definitive molecular feature associated with this condition?

Explanation

The "ground-glass" appearance and bowing are classic radiographic hallmarks of fibrous dysplasia. The underlying molecular defect is a somatic activating missense mutation in the GNAS gene, leading to elevated intracellular cAMP.

Question 52

A 9-year-old girl presents with a leg length discrepancy and precocious puberty. Examination reveals large, irregular hyperpigmented macules with a 'coast of Maine' border. Radiographs demonstrate polyostotic medullary lesions with a 'ground-glass' appearance.

Which of the following gene mutations is pathognomonic for this condition?

Explanation

McCune-Albright syndrome is characterized by polyostotic fibrous dysplasia, precocious puberty, and café-au-lait spots. It is caused by an activating somatic mutation in the GNAS1 gene.

Question 53

A 45-year-old female with known polyostotic fibrous dysplasia presents with a newly palpable, painless, deep soft tissue mass in her thigh. MRI shows a well-circumscribed, T2-hyperintense intramuscular mass. What is the most likely diagnosis of the soft tissue mass?

Explanation

Mazabraud syndrome is a rare condition defined by the association of fibrous dysplasia with one or more intramuscular myxomas. These soft tissue tumors are benign and typically present as painless masses.

Question 54

A 3-year-old boy presents with anterior bowing of his tibia. Radiographs show a well-circumscribed, intracortical osteolytic lesion involving the anterior tibial diaphysis. Biopsy reveals benign fibrous tissue with woven bone trabeculae lined by prominent osteoblasts. What is the most appropriate initial management?

Explanation

Osteofibrous dysplasia (Campanacci disease) typically affects the anterior cortex of the tibia in young children. Observation is the standard of care as most lesions stabilize or regress after skeletal maturity.

Question 55

Which immunohistochemical marker is essential for differentiating adamantinoma from osteofibrous dysplasia in a tibial diaphyseal lesion?

Explanation

Adamantinoma is a low-grade malignant tumor of epithelial origin, making it positive for cytokeratin, whereas osteofibrous dysplasia is negative. This differentiation is critical due to the completely different treatment protocols.

Question 56

A 16-year-old boy undergoes a biopsy of a solitary radiolucent lesion in the proximal femur with a 'ground-glass' matrix. The histological evaluation demonstrates trabeculae of woven bone in a fibrous stroma.

Which of the following classically distinguishes this lesion from normal woven bone formation?

Explanation

Fibrous dysplasia is histologically characterized by irregular trabeculae of woven bone (Chinese character shape) situated in a fibrous stroma. Notably, these bony trabeculae characteristically lack osteoblastic rimming.

Question 57

A 14-year-old male with polyostotic fibrous dysplasia presents with a progressive shepherd's crook deformity of the proximal femur and worsening hip pain. What is the most reliable surgical strategy to correct the deformity and prevent recurrence?

Explanation

In fibrous dysplasia, cortical bone grafts are frequently resorbed and replaced by dysplastic bone. The most reliable treatment for a shepherd's crook deformity involves valgus-producing osteotomies stabilized with intramedullary nails spanning the entire femur.

Question 58

A 12-year-old girl undergoes imaging after a minor knee twist. An incidental finding on the radiograph shows a 2 cm eccentric, radiolucent lesion with a sclerotic margin in the distal femoral metaphysis. She is asymptomatic. What is the most appropriate management?

Explanation

The classic presentation of a Non-Ossifying Fibroma (NOF) is an asymptomatic, eccentric, metaphyseal lesion found incidentally. Small, asymptomatic NOFs require only observation and reassurance as they typically ossify and resolve with skeletal maturity.

Question 59

Jaffe-Campanacci syndrome is characterized by the presence of multiple non-ossifying fibromas. What other clinical manifestations are classically associated with this syndrome?

Explanation

Jaffe-Campanacci syndrome is a rare disorder characterized by multiple non-ossifying fibromas, café-au-lait spots (similar to neurofibromatosis), mental retardation, hypogonadism, and cardiovascular abnormalities.

Question 60

A 9-year-old boy presents with acute arm pain after throwing a baseball. Radiographs show a centrally located, completely radiolucent metaphyseal lesion in the proximal humerus with a cortical fracture and a cortical fragment settling in the dependent portion of the lesion.

What is the most likely diagnosis?

Explanation

A Unicameral Bone Cyst (UBC) is a centrally located metaphyseal lesion that commonly presents with a pathologic fracture in the proximal humerus. The 'fallen leaf' or 'fallen fragment' sign is pathognomonic for a UBC.

Question 61

A 15-year-old female presents with progressive knee pain. MRI reveals an eccentric metaphyseal lesion in the proximal tibia demonstrating multiple fluid-fluid levels on T2-weighted images.

Histology will most likely reveal which of the following?

Explanation

The clinical and radiographic findings (fluid-fluid levels) are classic for an Aneurysmal Bone Cyst (ABC). Histologically, ABCs are characterized by cavernous, blood-filled spaces that are separated by septa and notably lack an endothelial lining.

Question 62

Which of the following cytogenetic abnormalities is most frequently identified in primary aneurysmal bone cysts?

Explanation

Primary aneurysmal bone cysts are considered true neoplasms driven by specific genetic alterations. The most common is the rearrangement of the USP6 gene on chromosome 17p13.

Question 63

A 6-year-old boy presents with back pain and a mild kyphotic deformity. Radiographs demonstrate complete collapse of the T8 vertebral body (vertebra plana) with preservation of the adjacent disc spaces. A biopsy is performed. Which of the following markers will be strongly expressed in the lesional cells?

Explanation

Vertebra plana in a young child is classically caused by Eosinophilic Granuloma (Langerhans Cell Histiocytosis). The Langerhans cells characteristically stain positive for S-100 and CD1a, and contain Birbeck granules on electron microscopy.

Question 64

A 14-year-old female presents with multiple bone lesions, irregular hyperpigmented skin macules, and a history of precocious puberty. What is the underlying genetic mechanism of her condition?

Explanation

McCune-Albright syndrome is characterized by polyostotic fibrous dysplasia, café-au-lait spots, and endocrine abnormalities. It is caused by a post-zygotic somatic activating mutation in the GNAS gene.

Question 65

Which of the following modalities is considered a strict contraindication in the management of an uncomplicated, painful fibrous dysplasia lesion?

Explanation

Radiation therapy is strongly contraindicated in the treatment of fibrous dysplasia. It dramatically increases the risk of malignant transformation, most commonly to osteosarcoma or fibrosarcoma.

Question 66

A 9-year-old boy presents with an isolated expansile, 'ground-glass' lytic lesion in the proximal femur causing a progressive deformity. If histological analysis is performed, what is the classic hallmark finding?

Explanation

The classic histological appearance of fibrous dysplasia is irregular, 'Chinese character' trabeculae of woven bone that conspicuously lack osteoblastic rimming, set in a fibrous stroma.

Question 67

A 45-year-old woman with a history of polyostotic fibrous dysplasia presents with a painless, deep soft tissue mass in her right thigh. MRI reveals an intramuscular lesion with high T2 signal. Core needle biopsy demonstrates a hypocellular, myxoid stroma without cellular atypia. What is the most likely diagnosis?

Explanation

The rare association of polyostotic fibrous dysplasia and single or multiple intramuscular myxomas is known as Mazabraud syndrome. The myxomas are benign but may cause local mechanical symptoms.

Question 68

When performing structural grafting for a pathological fracture and impending nonunion in a patient with fibrous dysplasia, which of the following graft types is most appropriate to minimize resorption and construct failure?

Explanation

Cortical allograft is preferred for structural support in fibrous dysplasia. Cancellous bone, especially autograft, is rapidly resorbed and replaced by dysplastic host bone tissue.

Question 69

A 7-year-old boy presents with anterior bowing of the tibia. Radiographs show a multi-loculated, radiolucent lesion confined to the anterior tibial cortex. Biopsy reveals woven bone trabeculae with prominent osteoblastic rimming in a fibrous stroma. What is the most likely diagnosis?

Explanation

Osteofibrous dysplasia (Campanacci lesion) classically affects the anterior tibial cortex in children under 10. Unlike fibrous dysplasia, it features prominent osteoblastic rimming on histology.

Question 70

In a 15-year-old patient with progressive Shepherd's crook deformity of the proximal femur due to fibrous dysplasia, what is the biomechanically preferred method of surgical stabilization?

Explanation

Valgus osteotomy corrects the deformity, while intramedullary nailing provides a load-sharing construct spanning the entire bone length. Plating (load-bearing) frequently fails in the weak dysplastic bone.

Question 71

Aside from precocious puberty, which of the following endocrinopathies is most frequently seen in patients with McCune-Albright syndrome?

Explanation

Hyperthyroidism is the second most common endocrine abnormality in McCune-Albright syndrome. Others include Cushing's syndrome, acromegaly, and hypophosphatemic rickets.

Question 72

A 12-year-old girl is diagnosed with polyostotic fibrous dysplasia. She presents with severe, recalcitrant bone pain in her lower extremities limiting her daily activities. Radiographs show no impending fractures. What is the most appropriate initial medical management?

Explanation

Intravenous bisphosphonates (such as pamidronate or zoledronic acid) are the mainstay of medical treatment for symptomatic bone pain in fibrous dysplasia, functioning by reducing osteoclastic bone turnover.

Question 73

A radiograph

of a 30-year-old male with long-standing fibrous dysplasia shows new cortical destruction and a soft tissue mass at the site of a previously stable lesion. He received localized therapeutic radiation in childhood. What is the most likely diagnosis?

Explanation

Malignant transformation in fibrous dysplasia is rare (<1%) but risk is markedly increased by prior radiation exposure. Osteosarcoma and fibrosarcoma are the most common secondary malignancies.

Question 74

A 4-year-old child presents with an expansile osteofibrous dysplasia lesion in the anterior tibia causing progressive bowing. What is the recommended management approach to minimize the risk of recurrence and complications?

Explanation

Osteofibrous dysplasia has a high recurrence rate if excised in young children. The preferred approach is to manage deformities conservatively with bracing until age 15, when spontaneous resolution or stabilization often occurs.

Question 75

The cutaneous lesions associated with McCune-Albright syndrome can be clinically differentiated from those seen in Neurofibromatosis type 1 by which of the following characteristics?

Explanation

The café-au-lait macules in McCune-Albright syndrome typically have irregular, jagged borders ('Coast of Maine') and often respect the midline, whereas those in NF1 have smooth ('Coast of California') borders.

Orthopedic Prometric MCQs - Chapter 3 Part 1

Orthopedic Prometric MCQs - Chapter 3 Part 13

Orthopedic Prometric MCQs - Chapter 3 Part 13

Chapter Index