Question 1

Platelet calmodulin levels correlate with which of the following phenomena:

Explanation

Platelets contain actin and myosin and, therefore, have some features similar to skeletal muscle. C almodulin is a calcium-binding receptor protein that regulates intracellular calcium. Platelet calmodulin levels are increased in progressive adolescent idiopathic scoliosis.

Question 2

The proximal humerus is the most common location of unicameral bone cysts. Which of the following is the second most common location:

Explanation

The proximal femur is the second most common location for unicameral bone cysts. All other locations are distinctly less common.

Question 3

An 8-year old patient presents with pain in a unicameral bone cyst of the proximal femur. Which of the following treatments is most likely to prevent fracture:

Explanation

Injection of any substance has a risk of recurrence, even if the injection is repeated. Bone graft has a risk as well, but internal fixation decreases the risk of fracture.

Question 4

All of the following are common in McC une-Albright syndrome except:

Explanation

McCune-Albright syndrome consists of polyostotic fibrous dysplasia, precocious puberty, and cafa-au-lait spots. Long bone deformity is almost universal. Multiple osteocartilaginous exostoses are not part of this syndrome.

Question 5

Which of the following is most likely to minimize bowing of the femora over the long term in a young patient with polyostotic fibrous dysplasia:

Explanation

Bowing of the femora is a major problem for patients with polyostotic fibrous dysplasia. Bisphosphonates can decrease bone pain and increase bone density somewhat, but they do not prevent bowing. Allograft, autograft, and demineralized matrix are rapidly resorbed in most cases. Internal fixation with metal provides the best long-term protection.

Question 6

The phenomenon of spinal cord injury without radiographic abnormality in children may be due to any one of the following except:

Explanation

In most cases, spinal cord injury without radiographic abnormality, or SC IWORA, is due to the greater elasticity or translation of the skeletal elements. Apophyseal or transverse ligament injuries are other explanations. Myelination of the cord is complete after birth so this is not an explanation.

Question 7

A 6-year-old girl is seriously injured in an automobile accident. She remains unconscious and intubated 6 days after the injury due to head and pulmonary injuries. She is expected to survive. A firm cervical collar was placed on her neck at the time of rescue and remains in place. Plain radiographs show no cervical abnormalities. At this time, recommended treatment includes:

Explanation

Spinal cord injury without radiographic abnormality (SC IWORA) may occur in children. Motor vehicle accidents and head injury are two risk factors for this. The neck collar cannot be left on indefinitely or it may cause pressure sores. Therefore, it is most prudent to evaluate the cervical spine with magentic resonance imaging if the patientâ s neck cannot be cleared by physical exam. Passive range of the neck is risky, and ultrasound is not used for this purpose.

Question 8

Which of the following properties is the same for both botulinum toxin types A and B:

Explanation

There are seven serologic subtypes of botulinum toxin, and only two are approved for clinical use. The duration of action of type A is slightly longer and it is less antigenic. Both type A and B have different structures. The dose of type A is lower in absolute units. Both have the same site of action they inhibit the release of acetylcholine from the neuromuscular junction, although they act on different proteins inside the cell.

Question 9

Stickler syndrome is caused by a mutation in the gene for which of the following:

Explanation

Stickler syndrome is characterized by premature osteoarthritis in multiple joints, visual complications, auditory defects, and cleft palate. Stickler syndrome is caused by a defect in the genes for type 2 or type 11 collagen.

Question 10

Stickler syndrome is characterized by all of the following features except:

Explanation

Stickler syndrome, also known as hereditary arthro-ophthalmopathy, is characterized by visual problems, progressive hearing loss, and malar or mandibular hypoplasia. In terms of orthopedic complications, most patients develop premature degenerative joint disease and disk abnormalities, including narrow and irregular endplates. Significant short stature is not common in patients with Stickler syndrome.

Question 11

The majority of pediatric pedestrian-vehicle injuries occur in which time period:

Explanation

The majority (54%) of pediatric pedestrian-vehicle accidents occur from 3 pm to 8 pm. This time period may coincide with walks home from school, after-school play, and high traffic volume.

Question 12

Which of the following demographic factors places a child at increased risk of pedestrian vs vehicle trauma:

Explanation

Male gender and age 5 to 9 years old are factors that place children at increased risk of being struck by a vehicle.

Question 13

Before any intervention, which of the following statements is true regarding the walking gait of a diplegic patient who has an equinus gait:

Explanation

In patients with spastic diplegia, ankle plantarflexion increases during single-limb stance, contrary to the normal pattern.

Question 14

Which of the following complications is the most common in anterior iliac crest graft harvesting:

Explanation

Transient or permanent sensory disturbance is the most common complication (13% of patients) of anterior iliac crest graft harvesting.

Question 15

Which of the following is the most common site for primary epiphyseal osteomyelitis:

Explanation

Osteomyelitis of the epiphysis is less common than osteomyelitis of the metaphysis. Osteomyelitis of the epiphysis may occur from spread across transphyseal vessels or primary hematogenous seeding. The most common location is the distal femoral epiphysis, and it most commonly affects infants and young children.

Question 16

A normal (negative) result is used to rule out septic arthritis of the hip on which of the following tests:

Explanation

False-negative results may occur with each of the tests. C ulture results may be negative in up to a quarter of patients. Ultrasound may be false-negative in up to 20% of patients with septic arthritis of the hip. C-reactive protein may be normal early in the course of disease. The diagnosis is based upon a constellation of findings, including clinical examination.Correct Answer: None of the above

Question 17

Which of the following structures is the primary stabilizer of the atlantoaxial segment against anterior atlantal translation:

Explanation

The transverse ligament is the primary stabilizer of the atlantoaxial segment against anterior atlantal translation. The transverse ligament runs between the lateral masses of C1 and behind the odontoid process. The apical ligament is attached to the tip of the odontoid and the occiput, but not C1. The paired alar ligaments run obliquely and are secondary restraints, as is the anterior atlantodental ligament. The ligamentum nuchae is a strong condensation of fibers extending from the external occipital protuberance to the tips of the spinous processes C2-C 7.

Question 18

The radiographic line delimiting the foramen magnum that is used in determining basilar invagination is the:

Explanation

The McRae line is from the anterior to the posterior lip of the foramen magnum. Protrusion of the odontoid above this line indicates basilar invagination. The McGregor and Ranawat lines are also used to evaluate basilar invagination. The Swischuk line is from the posterior cortex of C1 to C3 lamina and is used in evaluating pseudosubluxation.

Question 19

Which of the following factors determines the treatment for a child with tibial hemimelia:

Explanation

When treating a child with tibial hemimelia, the surgeon must decide whether to attempt to reconstruct the knee or perform a disarticulation. The determining factor is whether there is a proximal tibial remnant.

Question 20

Which of the following is a contraindication to the use of vacuum assisted closure (VAC ):

Explanation

Vacuum assisted closure (VAC ) should be applied to infected or damaged tissue after debridement. All of the other possible answer choices are conditions for which VAC is appropriate.

Question 21

Which of the following genetic translocations is most characteristically associated with primary aneurysmal bone cysts?

Explanation

Primary aneurysmal bone cysts are characterized by the t(16;17) translocation, which results in the upregulation of the USP6 gene. The t(11;22) translocation is associated with Ewing sarcoma, and t(X;18) is associated with synovial sarcoma.

Question 22

The classic nocturnal pain associated with an osteoid osteoma is primarily mediated by the high local concentration of which of the following substances?

Explanation

Osteoid osteomas produce high levels of Prostaglandin E2 due to robust COX-2 expression within the nidus. This local PGE2 production explains the characteristic severe nocturnal pain and its dramatic relief with nonsteroidal anti-inflammatory drugs.

Question 23

A 12-year-old girl presents with a shepherd's crook deformity of the femur and café-au-lait spots with irregular borders. This condition is caused by a somatic mutation affecting which of the following genes?

Explanation

McCune-Albright syndrome, characterized by polyostotic fibrous dysplasia, endocrinopathy, and café-au-lait spots, is caused by a somatic activating mutation in the GNAS1 gene. This mutation impairs the GTPase activity of the alpha subunit of the Gs protein, leading to increased cAMP.

Question 24

Following neoadjuvant chemotherapy and surgical resection for conventional high-grade osteosarcoma, which of the following represents the most significant prognostic factor for overall patient survival?

Explanation

The degree of tumor necrosis after neoadjuvant chemotherapy, quantified by Huvos grading, is the most critical prognostic indicator in conventional osteosarcoma. Greater than 90% tumor necrosis indicates a favorable response to chemotherapy and significantly improves overall survival.

Question 25

A 14-year-old boy presents with a permeative diaphyseal lesion of the femur with a periosteal "onion-skin" reaction. Immunohistochemical staining of a biopsy specimen is most likely to be strongly positive for which of the following?

Explanation

Ewing sarcoma is a small round blue cell tumor that typically exhibits strong, diffuse membranous staining for CD99 (MIC2). S-100 is typically used to identify neural tumors and melanoma.

Question 26

A 55-year-old man presents with a painful shoulder. Radiographs reveal a lytic lesion with "ring and arc" calcifications in the proximal humerus, and MRI shows endosteal scalloping greater than 2/3 of the cortical thickness. What is the most likely diagnosis?

Explanation

"Ring and arc" calcifications suggest a cartilaginous matrix. The presence of pain and deep endosteal scalloping (greater than 2/3 of the cortical thickness) are highly concerning imaging features for a low-grade chondrosarcoma rather than a benign enchondroma.

Question 27

A 30-year-old female presents with an expansile, purely lytic lesion in the distal femur epiphysis extending to the subchondral bone. Which of the following systemic medications serves as a targeted adjunct to surgical treatment for this specific pathology?

Explanation

Giant cell tumors of bone consist of neoplastic stromal cells that express RANKL, which recruits normal osteoclast-like giant cells. Denosumab, a monoclonal antibody against RANKL, is an effective adjunctive treatment to halt bone destruction.

Question 28

A 25-year-old male presents with a slow-growing, deep soft tissue mass near the knee joint. Biopsy reveals a biphasic tumor with both epithelial and spindle cell components. Which of the following translocations is diagnostic for this tumor?

Explanation

Synovial sarcoma is characterized by the t(X;18) chromosomal translocation, resulting in the SYT-SSX fusion gene. It often presents as a deep, calcified soft tissue mass in the extremities of young adults.

Question 29

A 10-year-old boy has an incidentally discovered eccentrically located, multi-loculated radiolucent lesion with a sclerotic margin in the distal tibial metaphysis. He is entirely asymptomatic. What is the most appropriate management?

Explanation

This classic presentation represents a non-ossifying fibroma (NOF), a benign "do-not-touch" lesion. NOFs are typically asymptomatic and resolve spontaneously through progressive ossification as the child reaches skeletal maturity, requiring only observation.

Question 30

A 15-year-old male presents with chronic knee pain. Radiographs reveal a 2 cm eccentric, radiolucent lesion with a fine sclerotic margin and central calcifications situated entirely within the proximal tibial epiphysis. What is the most likely diagnosis?

Explanation

Chondroblastoma is a rare, benign cartilaginous tumor that characteristically arises in the epiphysis or apophysis of skeletally immature patients. Histology typically reveals "chicken-wire" calcifications surrounding chondroblasts.

Question 31

A 65-year-old woman presents with back pain and generalized fatigue. Radiographs show multiple punched-out lytic lesions in her skull and pelvis. Laboratory tests show hypercalcemia and elevated creatinine. Which diagnostic test is most essential for confirming the underlying diagnosis?

Explanation

The clinical picture strongly suggests multiple myeloma, characterized by the CRAB criteria (HyperCalcemia, Renal failure, Anemia, Bone lesions). Serum protein electrophoresis (SPEP) is critical to identify the monoclonal M-protein spike associated with this plasma cell dyscrasia.

Question 32

A 20-year-old patient with Multiple Hereditary Exostoses reports recent rapid growth and pain in a previously stable lesion on his proximal humerus. What is the most important imaging parameter to evaluate for malignant transformation?

Explanation

Malignant transformation of an osteochondroma to a secondary chondrosarcoma is best evaluated by measuring the cartilage cap thickness on T2-weighted MRI. A cartilage cap thicker than 1.5 to 2.0 cm in a skeletally mature patient is highly concerning for malignancy.

Question 33

Which of the following primary bone tumors characteristically arises in the diaphyseal region of long bones?

Explanation

Adamantinoma is a rare, low-grade malignant bone tumor that classically occurs in the anterior cortex of the tibial diaphysis. In contrast, giant cell tumors and chondroblastomas are epiphyseal, and osteosarcoma is typically metaphyseal.

Question 34

A 10-year-old child presents with a severe skeletal deformity characterized by multiple enchondromas combined with multiple superficial soft tissue hemangiomas. What is the proper eponym for this syndrome?

Explanation

Maffucci syndrome is defined by the concurrent presence of multiple enchondromatosis and soft tissue hemangiomas. Patients with Maffucci syndrome carry a significantly higher lifetime risk of malignant transformation (e.g., to chondrosarcoma) compared to those with Ollier disease.

Question 35

Mazabraud syndrome is a rare genetic disorder characterized by the presence of polyostotic fibrous dysplasia in association with which of the following soft tissue lesions?

Explanation

Mazabraud syndrome is characterized by the synchronous presentation of fibrous dysplasia of bone and intramuscular myxomas. The soft tissue myxomas frequently develop in the same anatomic regions as the most severely affected bones.

Question 36

A 60-year-old female undergoes prophylactic fixation for an impending pathologic fracture of the femur secondary to metastatic thyroid carcinoma. Which of the following describes the classic radiographic appearance of this lesion?

Explanation

Bone metastases arising from thyroid and renal cell carcinomas are classically purely osteolytic, destructive, and notoriously hypervascular. Pre-operative embolization is routinely recommended before surgical stabilization to mitigate catastrophic intraoperative blood loss.

Question 37

Which of the following bone tumors is histologically identical to soft tissue fibromatosis and is considered its intraosseous counterpart?

Explanation

Desmoplastic fibroma of bone is a rare, locally aggressive benign tumor that is histologically indistinguishable from extra-abdominal soft tissue desmoid tumors. It lacks metastatic potential but exhibits a high rate of local recurrence if managed with simple curettage alone.

Question 38

Percutaneous CT-guided radiofrequency ablation (RFA) is currently considered the gold standard, first-line intervention for which of the following symptomatic lesions?

Explanation

CT-guided radiofrequency ablation (RFA) provides excellent clinical success rates for symptomatic osteoid osteomas. It has largely replaced traditional surgical en bloc resection due to lower morbidity and faster patient recovery.

Question 39

A 55-year-old male presents with a large, destructive sacral mass causing bowel and bladder dysfunction. Biopsy reveals large cells with prominent intracytoplasmic vacuoles. Which immunohistochemical marker is highly specific for confirming the suspected diagnosis?

Explanation

Chordomas arise from embryonic notochord remnants and contain characteristic physaliferous cells with large vacuoles. Brachyury is a transcription factor crucial for notochord development and acts as a highly sensitive and specific diagnostic marker for chordoma.

Question 40

A 14-year-old boy presents with an expansile, eccentric lytic lesion in the proximal tibia. Biopsy reveals blood-filled spaces separated by fibrous septa. Which of the following genetic translocations is most characteristic of this lesion?

Explanation

Primary aneurysmal bone cysts are characterized by a t(16;17) translocation, resulting in the upregulation of USP6. t(11;22) is seen in Ewing sarcoma, while t(X;18) is associated with synovial sarcoma.

Question 41

A 16-year-old girl is undergoing surgical resection of a conventional osteosarcoma of the distal femur following neoadjuvant chemotherapy. Which of the following is the most important prognostic factor for her long-term survival?

Explanation

The percentage of tumor necrosis following neoadjuvant chemotherapy is the most reliable prognostic indicator for long-term survival in conventional osteosarcoma. Greater than 90% necrosis is considered a good histologic response.

Question 42

A 32-year-old woman presents with a recurrent giant cell tumor of the distal radius. She is started on denosumab therapy. What is the precise mechanism of action of this medication?

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, preventing it from activating RANK on the surface of osteoclasts and giant cells. This arrests the osteolytic activity characteristic of giant cell tumors of bone.

Question 43

A 9-year-old girl is diagnosed with polyostotic fibrous dysplasia, precocious puberty, and cafe-au-lait spots. The pathophysiology of her condition is directly related to a mutation in which of the following?

Explanation

McCune-Albright syndrome features polyostotic fibrous dysplasia, endocrine abnormalities, and cafe-au-lait spots. It is caused by a somatic, post-zygotic activating mutation in the GNAS1 gene, resulting in elevated intracellular cAMP.

Question 44

A 65-year-old man presents with a rapidly enlarging mass in his proximal femur. Radiographs demonstrate a pre-existing lesion with rings-and-arcs calcification and a new, large, aggressive unmineralized soft tissue mass. Which of the following is the most likely diagnosis?

Explanation

A bimorphic radiographic appearance (a low-grade cartilaginous lesion adjacent to a high-grade, unmineralized soft-tissue mass) is pathognomonic for dedifferentiated chondrosarcoma. This transformation carries a very poor prognosis.

Question 45

A 12-year-old boy presents with multiple enchondromas and multiple soft-tissue hemangiomas. Which of the following complications is he at the highest risk of developing over his lifetime?

Explanation

Maffucci syndrome is characterized by multiple enchondromas and soft-tissue hemangiomas. Patients have a nearly 100% lifetime risk of malignant transformation, most commonly to chondrosarcoma, but also visceral malignancies.

Question 46

In which of the following clinical scenarios is prophylactic in situ pinning of the contralateral hip most strongly indicated in a patient presenting with a unilateral slipped capital femoral epiphysis (SCFE)?

Explanation

Prophylactic contralateral pinning is highly recommended for patients with an endocrine disorder (like hypothyroidism or renal osteodystrophy) or those who are very young (<10 years), due to the high risk of contralateral slip.

Question 47

According to the Herring Lateral Pillar classification for Legg-Calve-Perthes disease, which of the following radiographic findings defines a Group C hip?

Explanation

The Herring classification assesses the height of the lateral pillar on the AP pelvis radiograph during the fragmentation stage. Group C is defined by the lateral pillar maintaining less than 50% of its original height, indicating a poor prognosis.

Question 48

A 3-month-old infant is being treated with a Pavlik harness for developmental dysplasia of the hip (DDH). At the follow-up visit, the infant exhibits an absence of active knee extension. Which of the following is the most appropriate next step in management?

Explanation

Absence of active knee extension indicates a femoral nerve palsy, a known complication of excessive hip flexion in a Pavlik harness. The harness must be discontinued or significantly adjusted immediately to prevent permanent damage.

Question 49

When utilizing the Ponseti method for the correction of idiopathic clubfoot, which deformity should be addressed first?

Explanation

The Ponseti method follows the CAVE sequence: Cavus, Adductus, Varus, Equinus. Cavus is corrected first by elevating the first ray to supinate the forefoot, aligning it with the midfoot.

Question 50

A 6-year-old child sustains a displaced extension-type supracondylar humerus fracture. After closed reduction and percutaneous pinning, the hand remains pink and warm, but the radial pulse is absent on Doppler. What is the most appropriate management?

Explanation

A "pulseless, pink hand" following adequate reduction and stabilization of a supracondylar humerus fracture is generally observed closely. Collateral circulation is sufficient for viability, and the pulse often returns within days.

Question 51

A 13-year-old boy sustains a juvenile Tillaux fracture. Which of the following ligaments is primarily responsible for the avulsion of this specific fracture fragment?

Explanation

A juvenile Tillaux fracture is a Salter-Harris III fracture of the anterolateral distal tibial epiphysis. It is caused by an avulsion force from the anterior inferior tibiofibular ligament (AITFL) as the medial physis closes before the lateral physis.

Question 52

A neonate is diagnosed with Osteogenesis Imperfecta Type II. This lethal condition is most commonly caused by a mutation resulting in the substitution of which of the following amino acids in the collagen triple helix?

Explanation

Osteogenesis Imperfecta is typically caused by mutations in the COL1A1 or COL1A2 genes. The most severe forms involve a substitution for glycine, the smallest amino acid, which disrupts the tight coiling of the collagen type I triple helix.

Question 53

A 10-year-old boy presents with an aggressive diaphyseal lesion of the femur with an "onion skin" periosteal reaction. Immunohistochemical staining of the biopsy specimen is most likely to be positive for which of the following markers?

Explanation

Ewing sarcoma is a small round blue cell tumor typically found in the diaphysis of long bones in children. It strongly stains positive for CD99 (MIC2) and usually harbors a t(11;22) translocation.

Question 54

A 14-year-old male with multiple hereditary exostoses (MHE) is evaluated. The genetic mutation associated with his condition leads to a deficiency in the synthesis of which of the following?

Explanation

MHE is an autosomal dominant condition caused by mutations in the EXT1 or EXT2 genes. These genes encode glycosyltransferases essential for the synthesis of heparan sulfate, leading to abnormal physeal signaling and osteochondroma formation.

Question 55

A 5-year-old child with spastic quadriplegic cerebral palsy is found to have a migration percentage of 45% on a screening AP pelvis radiograph. Which of the following is the most appropriate surgical intervention?

Explanation

In cerebral palsy, a migration percentage >40% typically indicates a progressive hip subluxation that will not resolve with soft tissue releases alone. Bony reconstruction with a VDRO, often combined with a pelvic osteotomy, is the standard of care.

Question 56

A 4-year-old girl with achondroplasia presents with progressively worsening lower extremity weakness and hyperreflexia. What is the most likely anatomic site of neurologic compression in this patient?

Explanation

Children with achondroplasia are at high risk for foramen magnum stenosis, which can cause cervicomedullary compression leading to hyperreflexia, weakness, central apnea, or even sudden death. Urgent decompression is required if symptomatic.

Question 57

A 12-year-old boy presents with a rapidly expanding, painful lytic lesion in the distal femur. Biopsy reveals blood-filled cystic spaces lacking an endothelial lining. Which of the following genetic translocations is most characteristic of this primary lesion?

Explanation

Primary aneurysmal bone cysts (ABCs) are neoplastic and characterized by the t(16;17) translocation involving the USP6 gene. The other translocations are associated with Ewing sarcoma, Synovial sarcoma, Myxoid liposarcoma, and Dermatofibrosarcoma protuberans, respectively.

Question 58

A 15-year-old male presents with a painful, permeative diaphyseal lesion in the femur with a laminated periosteal reaction. Histopathology shows small, round blue cells. Which of the following fusion genes is responsible for the pathogenesis of this condition?

Explanation

The patient has Ewing sarcoma, which is characterized by an onionskin periosteal reaction and small round blue cells. Approximately 85% to 90% of Ewing sarcomas express the t(11;22) translocation resulting in the EWS-FLI1 fusion protein.

Question 59

A 14-year-old boy complains of chronic knee pain. Radiographs demonstrate a 2-cm lucent lesion with a sclerotic rim located exclusively within the proximal tibial epiphysis. Histological analysis reveals mononuclear cells and "chicken-wire" calcification. What is the location of this tumor relative to the physis?

Explanation

Chondroblastoma is a rare benign cartilage tumor that almost exclusively arises in the epiphysis or apophysis of growing children. The pathognomonic histological finding is pericellular "chicken-wire" calcification.

Question 60

An 18-year-old male presents with severe proximal focal tibial pain that worsens at night and is completely relieved by ibuprofen. Imaging reveals a cortically based radiolucent nidus surrounded by dense reactive sclerosis. The pain in this condition is primarily mediated by excessive production of which of the following?

Explanation

Osteoid osteoma causes severe night pain due to a 100- to 1000-fold increase in local prostaglandin E2 (PGE2) production by the nidus cells. This explains the dramatic clinical response to cyclooxygenase inhibitors like NSAIDs.

Question 61

A 30-year-old female presents with an eccentric, lytic epiphyseal-metaphyseal lesion of the distal femur. Biopsy confirms a giant cell tumor of bone. If medical therapy is considered, which of the following molecular targets is specifically inhibited to reduce osteoclast-mediated bone resorption?

Explanation

The neoplastic stromal cells in a giant cell tumor of bone express high levels of RANKL, which recruits and activates the reactive multinucleated giant cells. Denosumab, a monoclonal antibody against RANKL, is utilized as targeted medical therapy for advanced or unresectable cases.

Question 62

An 8-year-old girl is evaluated for precocious puberty, café-au-lait macules with irregular "coast of Maine" borders, and a "shepherd's crook" deformity of the proximal femur. This syndrome is caused by a somatic activating mutation in which of the following genes?

Explanation

McCune-Albright syndrome consists of polyostotic fibrous dysplasia, café-au-lait spots, and endocrinopathies. It is caused by a somatic, post-zygotic activating mutation in the GNAS gene, leading to overproduction of intracellular cAMP.

Question 63

A 10-year-old boy is diagnosed with Maffucci syndrome after presenting with multiple enchondromas and soft tissue hemangiomas. Which of the following gene mutations is most strongly associated with this condition?

Explanation

Maffucci syndrome and Ollier disease are associated with somatic mosaic mutations in the isocitrate dehydrogenase 1 or 2 (IDH1 or IDH2) genes. Maffucci syndrome carries a significantly higher risk of malignant transformation to chondrosarcoma compared to Ollier disease.

Question 64

A 6-year-old child sustains a Gartland type III extension-type supracondylar humerus fracture. On physical examination, the child is unable to flex the interphalangeal joint of the thumb and the distal interphalangeal joint of the index finger. Which nerve is most likely injured?

Explanation

The anterior interosseous nerve (AIN) is the most commonly injured nerve in extension-type supracondylar humerus fractures. Injury presents with an inability to form the "OK" sign due to weakness of the flexor pollicis longus and the flexor digitorum profundus to the index finger.

Question 65

An orthopedic surgeon is utilizing the Ponseti method to correct an idiopathic clubfoot in a 2-week-old infant. According to this protocol, which component of the deformity must be corrected last?

Explanation

In the Ponseti method, the components of the clubfoot deformity are corrected in a specific sequence summarized by the acronym CAVE: Cavus, Adductus, Varus, and finally Equinus. Equinus is typically corrected last, often requiring a percutaneous Achilles tenotomy.

Question 66

A 13-year-old obese boy presents with a 3-week history of vaguely localized knee pain and a limp. Examination reveals obligatory external rotation of the hip during passive hip flexion. What is the most appropriate initial management?

Explanation

The presentation is classic for a slipped capital femoral epiphysis (SCFE), characterized by obligatory external rotation with hip flexion. The gold standard initial treatment for a stable SCFE is in situ fixation with a single cannulated screw.

Question 67

A 6-year-old boy with a painless limp is diagnosed with Legg-Calvé-Perthes disease. Radiographs show fragmentation of the femoral head. According to the Herring lateral pillar classification, a Group C classification is defined by what degree of lateral pillar height loss?

Explanation

The Herring lateral pillar classification determines prognosis in Legg-Calvé-Perthes disease based on the height of the lateral pillar during the fragmentation stage. Group C indicates greater than 50% loss of lateral pillar height and carries the poorest prognosis.

Question 68

A 3-month-old infant is being treated with a Pavlik harness for developmental dysplasia of the hip (DDH). During follow-up, the parents note the infant is no longer actively extending the knee on the affected side. What is the most appropriate next step in management?

Explanation

Decreased active knee extension in a Pavlik harness indicates a femoral nerve palsy, typically caused by hyperflexion. The correct management is immediate removal of the harness to allow for nerve recovery before reassessing treatment options.

Question 69

A 7-year-old child with Gross Motor Function Classification System (GMFCS) Level V cerebral palsy is being evaluated. Which of the following radiographic parameters is most critical for routine screening to assess the risk of hip subluxation and dislocation in this patient?

Explanation

Children with severe cerebral palsy (GMFCS levels IV and V) have a high risk of progressive spastic hip displacement. The Reimers migration percentage on an AP pelvis radiograph is the standard screening metric, with values >30% typically warranting surgical consideration.

Question 70

A 4-year-old girl with blue sclerae, dentinogenesis imperfecta, and multiple prior fractures is diagnosed with Osteogenesis Imperfecta. This condition is primarily caused by an inherited defect in the synthesis of which of the following?

Explanation

Osteogenesis Imperfecta (OI) is a genetic disorder of connective tissue caused primarily by mutations in the COL1A1 or COL1A2 genes, which encode the chains of Type I collagen. This leads to bone fragility, blue sclerae, and hearing loss.

Question 71

A newborn is noted to have rhizomelic short stature, frontal bossing, and midface hypoplasia. Radiographs reveal narrowing of the interpedicular distances in the lumbar spine. Which genetic mutation is responsible for this condition?

Explanation

Achondroplasia is the most common form of skeletal dysplasia and disproportionate short stature. It is caused by an autosomal dominant, gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene, which inhibits chondrocyte proliferation at the growth plate.

Question 72

A 4-year-old child presents with progressive genu varum. Radiographs demonstrate focal depression and a bony beak at the medial metaphysis of the proximal tibia, consistent with Langenskiöld stage III Blount disease. What is the primary pathoanatomic location of the growth disturbance?

Explanation

Blount disease (tibia vara) is a developmental disorder characterized by abnormal endochondral ossification and growth suppression at the medial proximal tibial physis. This results in progressive varus, internal rotation, and procurvatum deformities of the tibia.

Question 73

A 10-year-old boy sustains a minor ankle sprain. Radiographs reveal an incidental 2-cm eccentric, cortically based, radiolucent lesion with a thin sclerotic margin in the distal tibial metaphysis. He has no pain at the site. What is the most appropriate management?

Explanation

The radiographic description is classic for a non-ossifying fibroma (NOF) or fibrous cortical defect. Since it is small, asymptomatic, and incidental, the standard of care is observation, as the vast majority undergo spontaneous ossification and resolve by adulthood.

Question 74

A patient with multiple bony protuberances around the knees and shoulders is diagnosed with Multiple Hereditary Exostoses (MHE). Genetic testing confirms a mutation in the EXT1 gene. This mutation directly impairs the synthesis of which of the following cell surface molecules?

Explanation

The EXT1 and EXT2 genes encode glycosyltransferases essential for the biosynthesis of heparan sulfate. Defective heparan sulfate synthesis alters chondrocyte signaling (such as Indian Hedgehog and PTHrP pathways), leading to the formation of osteochondromas.

Question 75

A 16-year-old male is diagnosed with high-grade conventional intramedullary osteosarcoma of the distal femur. Staging studies are performed. What is the single most important prognostic factor for overall survival at the time of initial presentation?

Explanation

In osteosarcoma, the presence of detectable metastatic disease (most commonly to the lungs) at the time of presentation is the most significant adverse prognostic factor. While tumor necrosis following neoadjuvant chemotherapy is an important prognostic factor later, initial staging relies heavily on metastatic status.

Question 76

A 12-year-old girl is evaluated for Adolescent Idiopathic Scoliosis (AIS). She has not yet reached menarche. Radiographs show a right thoracic curve of 35 degrees. Her Risser stage is 1. What is the most appropriate recommendation regarding treatment?

Explanation

Indications for bracing in AIS include a curve between 25 and 45 degrees in a patient with significant remaining growth (typically Risser 0-2 and pre-menarchal). A full-time TLSO brace is recommended to prevent further progression in this high-risk scenario.

Question 77

Which of the following genetic translocations is highly characteristic of a primary aneurysmal bone cyst (ABC)?

Explanation

Primary aneurysmal bone cysts are characterized by the t(16;17) translocation which upregulates the USP6 oncogene. In contrast, Ewing sarcoma is associated with t(11;22) and synovial sarcoma with t(X;18).

Question 78

A 14-year-old boy presents with knee pain. Radiographs reveal a lytic lesion in the proximal tibial epiphysis. Biopsy shows mononuclear cells with grooved nuclei and areas of pericellular calcification. Which of the following is the most likely diagnosis?

Explanation

Chondroblastoma typically occurs in the epiphysis of skeletally immature patients. Histology demonstrates chondroblasts with "coffee-bean" (grooved) nuclei and characteristic "chicken-wire" pericellular calcification.

Question 79

Which of the following clinical or radiographic features most reliably differentiates an osteoblastoma from an osteoid osteoma?

Explanation

Osteoblastomas are typically larger than 2 cm and lack the dramatic pain relief with NSAIDs seen in osteoid osteomas. Osteoid osteomas classically present with night pain relieved by NSAIDs and a nidus less than 1.5 to 2 cm.

Question 80

A 10-year-old girl is diagnosed with a polyostotic bone lesion demonstrating a "ground-glass" appearance. This condition is most commonly associated with a somatic activating mutation in which of the following?

Explanation

Fibrous dysplasia is caused by a somatic activating mutation in the GNAS1 gene, resulting in increased intracellular cAMP. This leads to abnormal differentiation of osteoblasts and replacement of normal medullary bone with fibrous tissue.

Question 81

Denosumab is frequently used in the management of unresectable or recurrent giant cell tumors of bone. Which of the following is the specific molecular target of this medication?

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, inhibiting its interaction with RANK on osteoclasts and osteoclast precursors. In giant cell tumors, the neoplastic stromal cells overexpress RANKL, which recruits the destructive reactive multinucleated giant cells.

Question 82

A patient with multiple hereditary exostoses (MHE) undergoes genetic testing. The most common mutated genes in this condition are directly responsible for the synthesis of which of the following?

Explanation

MHE is associated with mutations in the EXT1 and EXT2 genes, which are tumor suppressors involved in the biosynthesis of heparan sulfate. Decreased heparan sulfate alters normal chondrocyte signaling, leading to osteochondroma formation.

Question 83

A 6-year-old boy presents with a solitary lytic lesion of the skull. Biopsy reveals histiocytes with folded nuclei and numerous eosinophils. Electron microscopy would most likely reveal which of the following structures?

Explanation

The diagnosis is Langerhans cell histiocytosis (eosinophilic granuloma). The pathognomonic electron microscopy finding is Birbeck granules, which have a characteristic "tennis racket" appearance.

Question 84

A 25-year-old male presents with a slow-growing, multi-loculated lytic lesion in the anterior cortex of the tibial diaphysis. Histological examination shows islands of epithelial cells in a fibrous stroma. Immunohistochemistry will likely be positive for which of the following markers?

Explanation

Adamantinoma is a low-grade malignant bone tumor that almost exclusively occurs in the tibial diaphysis. It is characterized by a biphasic histological pattern of epithelial cells (which stain strongly positive for cytokeratin) within an osteofibrous stroma.

Question 85

In a patient newly diagnosed with Ewing sarcoma of the femur, which of the following factors is associated with the worst overall prognosis?

Explanation

The most significant adverse prognostic factor in Ewing sarcoma is the presence of distant metastases at presentation. Specifically, bone or bone marrow metastases confer a significantly worse prognosis than isolated lung metastases.

Question 86

A 60-year-old man presents with bowel and bladder dysfunction. Imaging reveals a destructive midline sacral mass. Biopsy demonstrates physaliferous cells. This tumor originates from remnants of which of the following embryonic structures?

Explanation

Chordomas are rare, slow-growing, locally aggressive neoplasms that arise from remnants of the embryonic notochord. They typically occur in the sacrum or clivus and are characterized histologically by vacuolated physaliferous cells.

Question 87

Which of the following radiographic findings is most suggestive of the malignant transformation of an enchondroma to a secondary chondrosarcoma?

Explanation

Signs of malignant transformation of an enchondroma to a chondrosarcoma include new onset of pain, cortical destruction, deep endosteal scalloping (greater than two-thirds of the cortex), and the presence of a soft tissue mass. Enchondromas typically have benign intralesional calcifications and only minor scalloping.

Question 88

A 9-year-old boy presents with a pathologic fracture through a unicameral bone cyst (UBC) in the proximal humerus. What is the most appropriate initial management for this patient?

Explanation

The initial management for a pathologic fracture through a proximal humerus UBC is typically non-operative immobilization to allow the fracture to heal. Definitive cyst treatments, such as steroid injections or curettage, are reserved for cysts that persist after the fracture has united.

Question 89

Following neoadjuvant chemotherapy and surgical resection for conventional osteosarcoma, a patient's tumor specimen is evaluated for histologic necrosis. According to the Huvos grading system, a "good response" indicating improved survival is defined by at least what percentage of tumor necrosis?

Explanation

A good histologic response to neoadjuvant chemotherapy in osteosarcoma is generally defined as greater than or equal to 90% tumor necrosis (Huvos Grade III or IV). This degree of necrosis is the single most important prognostic factor for long-term survival.

Question 90

A 15-year-old girl is found to have multiple enchondromas localized primarily to one side of her body, alongside multiple soft tissue hemangiomas. Which of the following complications is she at the highest risk for compared to a patient with multiple enchondromas alone?

Explanation

The presentation describes Maffucci syndrome, distinguished from Ollier disease by the presence of soft tissue hemangiomas. Patients with Maffucci syndrome have a significantly higher risk of developing concurrent visceral malignancies (e.g., astrocytoma, GI tract) in addition to their chondrosarcoma risk.

Question 91

Multiple myeloma bone disease is characterized by uncoupled bone remodeling resulting in severe osteolytic lesions. Which of the following best describes the molecular mechanism responsible for osteoblast suppression in this condition?

Explanation

In multiple myeloma, osteoblast activity is severely suppressed primarily through the secretion of Dickkopf-1 (DKK-1) by myeloma cells, which inhibits the Wnt/beta-catenin signaling pathway. While RANKL drives osteoclast overactivity, DKK-1 is the key suppressor of bone formation.

Question 92

A 30-year-old woman presents with a slow-growing, hard mass on the posterior aspect of the distal femur. Radiographs show a heavily ossified, broad-based mass attached to the cortex. Histology shows low-grade spindle cells and woven bone. What is the most characteristic genetic alteration in this tumor?

Explanation

Parosteal osteosarcoma is a low-grade surface osteosarcoma typically arising on the posterior distal femur. It is characterized molecularly by supernumerary ring chromosomes leading to the amplification of the MDM2 and CDK4 genes.

Question 93

A 28-year-old male presents with a painless soft tissue mass near the knee joint. Biopsy reveals a biphasic tumor with both epithelial and spindle cell components. Cytogenetic testing confirms a t(X;18)(p11;q11) translocation. This translocation results in which of the following fusion genes?

Explanation

Synovial sarcoma is characterized by the t(X;18)(p11;q11) translocation, which fuses the SYT gene on chromosome 18 with one of the SSX genes on the X chromosome. The resulting SYT-SSX fusion protein acts as an aberrant transcriptional regulator.

Orthopedic Prometric MCQs - Chapter 3 Part 1

Orthopedic Prometric MCQs - Chapter 3 Part 3

Orthopedic Prometric MCQs - Chapter 3 Part 3

Chapter Index