Master ABOS Orthopedic Board Review: Tumors & Fractures

Question 1

A 16-year-old boy presents with severe right anterior thigh pain that is predictably worse at night and dramatically relieved by NSAIDs. Imaging reveals the following characteristic finding.

What is the most characteristic biochemical feature of the central nidus in this lesion?

Explanation

Osteoid osteomas contain a central nidus that characteristically secretes high levels of Prostaglandin E2 (PGE2), causing nocturnal pain that responds to NSAIDs. The surrounding reactive sclerosis is a hallmark radiographic finding.

Question 2

A 55-year-old woman is evaluated for severe burning pain, stiffness, and skin color changes in her right hand following a distal radius fracture treated with a cast 8 weeks ago. Which of the following prophylactic measures has been shown to reduce the incidence of this condition following conservative or surgical management of distal radius fractures?

Explanation

Complex Regional Pain Syndrome (CRPS) can complicate distal radius fractures. Prophylactic administration of Vitamin C (500 mg daily for 50 days) has been demonstrated to significantly reduce the risk of developing CRPS in these patients.

Question 3

A 10-year-old boy with severe hemophilia A is scheduled for an elective total knee arthroplasty due to advanced hemophilic arthropathy. To prevent catastrophic bleeding, what is the optimal management of his Factor VIII levels during the perioperative period?

Explanation

For major orthopedic surgery in patients with hemophilia A, Factor VIII levels should be raised to 100% prior to surgery. Levels should be maintained at >50% for the initial 10-14 postoperative days to ensure adequate hemostasis and wound healing.

Question 4

A 6-year-old child presents with a waddling gait, short stature, and joint pain. Radiographs demonstrate delayed, irregular ossification of multiple epiphyses and a 'double-layer' patella. A mutation in which of the following genes is most strongly associated with this phenotype?

Explanation

Multiple Epiphyseal Dysplasia (MED) is frequently associated with mutations in the COMP (Cartilage Oligomeric Matrix Protein) gene. The 'double-layer' patella is a classic radiographic sign associated with this dysplasia.

Question 5

A 14-year-old girl is diagnosed with osteosarcoma of the distal femur. Histological examination shows anaplastic spindle cells producing osteoid matrix. Which of the following genetic alterations is most commonly implicated in the pathogenesis of conventional osteosarcoma?

Explanation

Conventional osteosarcoma is strongly linked to mutations or deletions in the p53 and Retinoblastoma (Rb) tumor suppressor genes. Inactivation of these pathways allows unregulated cellular proliferation and osteoid production by malignant cells.

Question 6

A 13-year-old adolescent presents with a painful, rigid scoliotic curve. Imaging identifies a lesion with a radiolucent nidus on the concavity of the curve.

If surgical management is planned, what is the primary goal of the intervention?

Explanation

In spinal osteoid osteomas causing painful scoliosis, the lesion is typically found on the concavity. Successful excision or radiofrequency ablation of the nidus alone generally results in rapid relief of pain and spontaneous resolution of the scoliotic curve.

Question 7

A 40-year-old female presents with an atypical subtrochanteric femur fracture characterized by transverse orientation, lateral cortical thickening, and a medial spike. Which of the following medications is most directly associated with the pathogenesis of this fracture pattern?

Explanation

Atypical femur fractures are a recognized complication of long-term bisphosphonate therapy due to severe suppression of bone turnover. They classically present in the subtrochanteric or diaphyseal region with lateral cortical beaking and a transverse fracture line.

Question 8

A 3-month-old infant is evaluated for short limbs, a normal-sized trunk, frontal bossing, and midface hypoplasia. What is the primary pathophysiologic mechanism resulting from the mutated gene responsible for this condition?

Explanation

Achondroplasia is caused by a gain-of-function mutation in FGFR3, which prematurely inhibits chondrocyte proliferation in the proliferative zone of the physis. This results in the characteristic rhizomelic dwarfism.

Question 9

A 22-year-old male with a history of Multiple Hereditary Exostoses (MHE) reports rapid enlargement and pain in a previously asymptomatic lesion on his proximal tibia. An MRI shows a cartilage cap measuring 2.5 cm in thickness. What is the most likely diagnosis?

Explanation

Malignant transformation of an osteochondroma into a secondary chondrosarcoma should be highly suspected if the cartilage cap is thicker than 2 cm in an adult, or if the lesion becomes painful or rapidly enlarges.

Question 10

A 45-year-old man exhibits extreme hyperalgesia, allodynia, and trophic changes in his foot following a crush injury 4 months prior. A triple-phase bone scan is performed to support the diagnosis of CRPS.

What is the classic finding on phase III (delayed phase) of a bone scan in patients with early/active Complex Regional Pain Syndrome?

Explanation

In the early or active stages of CRPS, the classic finding on the delayed phase (Phase III) of a technetium-99m bone scan is diffuse, increased periarticular uptake in the affected extremity compared to the contralateral side.

Question 11

A newborn is noted to have severe micromelic dwarfism, 'hitchhiker' thumbs, clubfeet, and cystic swelling of the external ears (cauliflower ears). Which of the following inheritance patterns and gene mutations corresponds to this clinical picture?

Explanation

Diastrophic dysplasia is characterized by hitchhiker thumbs, cauliflower ears, and severe clubfeet. It is an autosomal recessive disorder caused by mutations in the SLC26A2 gene, resulting in defective sulfate transport in cartilage.

Question 12

A 12-year-old boy presents with fever, weight loss, and localized thigh pain. Radiographs demonstrate a permeative destructive lesion in the femoral diaphysis with an 'onion-skin' periosteal reaction. A biopsy reveals small round blue cells. Which chromosomal translocation is pathognomonic for this tumor?

Explanation

Ewing sarcoma is a small round blue cell tumor classically presenting in the diaphysis of long bones. It is driven by the t(11;22) translocation, creating the EWS-FLI1 fusion protein in approximately 85-90% of cases.

Question 13

A 35-year-old male with severe Hemophilia B presents with an expanding, painless, expansile lytic mass in his ilium. Imaging suggests complete cortical destruction with a well-encapsulated soft-tissue component. What is the most appropriate initial management for this hemophilic pseudotumor?

Explanation

A hemophilic pseudotumor is an encapsulated hematoma that can cause massive bone destruction. Biopsy or aspiration is strictly contraindicated due to the risk of uncontrollable hemorrhage or fistula formation; initial management must focus on replacing the deficient factor (Factor IX in Hemophilia B) prior to any surgical intervention.

Question 14

A 30-year-old patient presents with a 9-month-old tibial shaft fracture that has not healed. Radiographs show abundant callus formation with a persistent radiolucent fracture line and implant failure (broken intramedullary nail). Which of the following accurately describes the pathology and ideal treatment?

Explanation

Hypertrophic nonunions display abundant callus, indicating adequate biology but inadequate mechanical stability. The ideal treatment is improving mechanical stability (e.g., larger IM nail or plate fixation) to allow the biological process to bridge the fracture; bone grafting is typically unnecessary.

Question 15

A 28-year-old woman presents with knee pain. Radiographs show an eccentric, expansile, purely lytic lesion in the distal femoral epiphysis extending to the subchondral bone. Histology reveals mononuclear cells and multinucleated osteoclast-like giant cells. What targeted medical therapy has been FDA-approved for unresectable cases of this tumor?

Explanation

Giant Cell Tumor of bone (GCT) classically occurs in the epiphysis of skeletally mature patients. Denosumab, a monoclonal antibody against RANKL, prevents the recruitment and activation of the osteoclast-like giant cells and is used for unresectable or recurrent GCTs.

Question 16

A 22-year-old male with Hemophilia A has developed high-titer inhibitors (>5 Bethesda Units) to Factor VIII. He sustains a closed, displaced femur fracture requiring operative fixation. What is the agent of choice to provide hemostasis for surgery?

Explanation

Patients with high-titer inhibitors to Factor VIII cannot be managed with standard Factor VIII replacement because the antibodies neutralize it. Bypassing agents, such as recombinant Factor VIIa (rFVIIa) or activated prothrombin complex concentrate (aPCC/FEIBA), are required to initiate the clotting cascade.

Question 17

A 5-year-old boy presents with an ability to touch his shoulders together anteriorly. He has a wide, flat skull, delayed fontanelle closure, and a wide pubic symphysis on radiographs. This condition is caused by a mutation in a gene crucial for the differentiation of which cell type?

Explanation

Cleidocranial dysplasia is caused by a mutation in the RUNX2 (CBFA1) gene, which is a master transcription factor essential for osteoblast differentiation. It is characterized by absent or hypoplastic clavicles, delayed cranial suture closure, and dental anomalies.

Question 18

A 45-year-old farm worker sustains an open tibia fracture highly contaminated with soil and manure. According to the current trauma guidelines, which antibiotic regimen provides the most appropriate coverage for this Type IIIA open fracture?

Explanation

For severe open fractures (Type III) contaminated with farm soil or feces, broad-spectrum coverage is required. This typically includes a first- or third-generation cephalosporin, an aminoglycoside for Gram-negatives, and Penicillin to cover anaerobes like Clostridium species.

Question 19

A 17-year-old female presents with diffuse, severe burning pain in her hand and hypersensitivity to light touch 3 months after a wrist sprain.

According to the Budapest Criteria, which of the following symptom categories is NOT strictly required to make the clinical diagnosis of Complex Regional Pain Syndrome?

Explanation

The Budapest criteria for CRPS are purely clinical, requiring the presence of symptoms and signs in categories such as sensory, vasomotor, sudomotor/edema, and motor/trophic. While a bone scan can support the diagnosis, it is not a strictly required criterion.

Question 20

A 10-year-old boy presents with progressive knee pain. Imaging reveals a subchondral lucency in the proximal tibial epiphysis. A biopsy demonstrates sheets of mononuclear cells with a 'coffee bean' nucleus and longitudinal grooving, alongside eosinophils. Which immunohistochemical marker is characteristically positive in this lesion?

Explanation

Langerhans Cell Histiocytosis (LCH) typically presents with eosinophilic infiltration and Langerhans cells having characteristic 'coffee bean' nuclei with longitudinal grooves. These cells are characteristically positive for S-100 and CD1a.

Question 21

A 15-year-old boy presents with progressive right thigh pain that is notably worse at night and rapidly relieved by ibuprofen. Imaging shows a cortical lesion with a central lucent nidus and surrounding sclerosis. What is the most appropriate definitive, minimally invasive treatment for this condition?

Explanation

The clinical and radiographic presentation is classic for an osteoid osteoma. Radiofrequency ablation (RFA) under CT guidance is the gold standard minimally invasive treatment, offering high success rates and minimal morbidity.

Question 22

A 65-year-old woman sustains a displaced distal radius fracture. To reduce the risk of developing the painful condition shown in the radiograph, which is characterized by periarticular patchy osteopenia, which of the following prophylactic measures is recommended?

Explanation

The image demonstrates Sudeck's atrophy (CRPS). Vitamin C (500 mg daily for 50 days) has been shown in some studies to significantly reduce the incidence of CRPS following distal radius fractures.

Question 23

A 14-year-old boy with severe Hemophilia A requires an elective orthopedic procedure. Preoperative laboratory testing reveals a high-titer Factor VIII inhibitor (>5 Bethesda Units). Which of the following is the most appropriate management to ensure perioperative hemostasis?

Explanation

Patients with high-titer inhibitors (>5 BU) fail to respond to standard Factor VIII replacement due to rapid neutralization. Bypassing agents, such as recombinant Factor VIIa or aPCC (FEIBA), are required to achieve hemostasis.

Question 24

A 6-year-old boy presents with short stature, a waddling gait, and bilateral knee pain. Radiographs reveal delayed ossification and fragmentation of multiple epiphyses, but the spine demonstrates normal vertebral body height and morphology. A mutation in which of the following genes is most likely responsible?

Explanation

The clinical picture describes Multiple Epiphyseal Dysplasia (MED), which typically spares the spine, distinguishing it from Spondyloepiphyseal Dysplasia (SED). MED is most commonly associated with mutations in the COMP (Cartilage Oligomeric Matrix Protein) gene.

Question 25

The lesion shown in the radiograph typically produces severe nocturnal pain. The central nidus of this tumor is known to produce highly elevated levels of which of the following inflammatory mediators?

Explanation

Osteoid osteomas produce extremely high levels of Prostaglandin E2 (PGE2), which causes the characteristic intense night pain. This is the physiologic basis for why NSAIDs provide rapid and dramatic pain relief.

Question 26

A 45-year-old man develops severe, burning left hand pain 6 weeks after a crush injury. He exhibits skin color asymmetry, hyperhidrosis, and allodynia. According to the Budapest criteria for diagnosing Complex Regional Pain Syndrome (CRPS), which of the following conditions must be met?

Explanation

The Budapest criteria are purely clinical for diagnosing CRPS. A fundamental requirement of the criteria is that no other diagnosis can better explain the patient's signs and symptoms.

Question 27

A 9-year-old girl is evaluated for precocious puberty and a recent pathologic proximal femur fracture. Radiographs show a 'ground-glass' expansile lesion with a 'shepherd's crook' deformity. A post-zygotic somatic mutation in which of the following genes is responsible for this condition?

Explanation

The patient has McCune-Albright syndrome, characterized by polyostotic fibrous dysplasia, precocious puberty, and café-au-lait spots. This syndrome is caused by a somatic activating mutation in the GNAS1 gene, leading to increased cAMP.

Question 28

In a patient with severe hemophilia, recurrent hemarthroses inevitably lead to end-stage hemophilic arthropathy. What is the primary mediator of the initial synovial hypertrophy and subsequent cartilage destruction in this disease process?

Explanation

Recurrent bleeding into the joint leads to the accumulation of iron/hemosiderin from red blood cell breakdown. Iron accumulation induces marked synovial hypertrophy, chronic inflammation, and direct chondrocyte toxicity.

Question 29

A 16-year-old boy undergoes neoadjuvant chemotherapy followed by wide surgical resection for a conventional osteosarcoma of the distal femur. Which of the following histologic findings in the resected specimen is the single most important prognostic factor for long-term survival?

Explanation

The degree of tumor necrosis following neoadjuvant chemotherapy (evaluated by the Huvos grading system) is the most critical prognostic indicator. Greater than 90% necrosis indicates a favorable response and better long-term survival.

Question 30

A patient develops early-stage CRPS of the upper extremity following a distal radius fracture, presenting with severe sympathetically maintained pain. If conservative management fails, what is the primary sympathetic ganglion targeted for diagnostic and therapeutic nerve blocks?

Explanation

The stellate ganglion provides sympathetic innervation to the upper extremity. Stellate ganglion blocks are utilized both diagnostically and therapeutically for sympathetically maintained pain in upper extremity CRPS.

Question 31

A 12-year-old boy presents with a diaphyseal femur lesion exhibiting a 'moth-eaten' appearance and periosteal 'onion-skinning'. Biopsy reveals sheets of uniform small round blue cells. Which of the following chromosomal translocations is diagnostic for this malignancy?

Explanation

The clinical and histologic description is classic for Ewing sarcoma. The t(11;22)(q24;q12) translocation, resulting in the EWS-FLI1 fusion protein, is found in approximately 85% of Ewing sarcoma cases.

Question 32

A 72-year-old woman who has taken alendronate for 8 years sustains a low-energy transverse subtrochanteric femur fracture. Radiographs show lateral cortical thickening and a medial spike. Along with surgical fixation, what is the most appropriate long-term management of her bone health?

Explanation

The patient sustained an atypical femur fracture (AFF) due to severe suppression of bone turnover from long-term bisphosphonate use. Bisphosphonates must be stopped, and an anabolic agent like teriparatide (recombinant PTH) should be initiated to stimulate bone formation.

Question 33

A 3-year-old boy with blue sclerae and a history of multiple low-energy fractures is diagnosed with Osteogenesis Imperfecta (OI) Type I. The pathogenesis of this condition is primarily related to a defect involving which of the following?

Explanation

OI Type I is the mildest and most common form, caused by a quantitative defect (decreased production) of otherwise structurally normal Type I collagen. OI Types II, III, and IV generally involve qualitative structural defects.

Question 34

A 35-year-old man with severe Hemophilia A is scheduled for a total knee arthroplasty for end-stage arthropathy. To prevent catastrophic perioperative bleeding complications, what is the required target factor VIII activity level immediately prior to surgical incision?

Explanation

For major orthopedic surgery in a patient with severe hemophilia, the factor level must be replaced to 100% activity immediately prior to surgery and maintained near this level in the acute postoperative period.

Question 35

A 30-year-old woman presents with an expansile, lytic, epiphyseal lesion of the proximal tibia. Biopsy confirms Giant Cell Tumor (GCT) of bone. Denosumab is planned to aid in joint preservation. Denosumab acts primarily by inhibiting which of the following?

Explanation

Denosumab is a monoclonal antibody that binds to and inhibits RANKL. In GCT, the neoplastic stromal cells express RANKL, which recruits and activates the reactive osteoclast-like giant cells that cause bone destruction.

Question 36

The radiograph demonstrates a typical osteoid osteoma. If a histopathologically identical lesion presented in the posterior elements of the spine, measured 3.0 cm in diameter, and caused progressive non-structural scoliosis without classic nocturnal pain, what would be the most likely diagnosis?

Explanation

Osteoblastomas are histologically indistinguishable from osteoid osteomas but are distinguished clinically by their larger size (>2 cm), predilection for the posterior elements of the spine, and less predictable response to NSAIDs.

Question 37

A 10-year-old boy with severe hemophilia A experiences recurrent hemarthrosis of the right knee despite being on a strict prophylactic factor replacement regimen. Radiographs show early but mild joint space narrowing. Which of the following is the most appropriate next step in management to preserve joint function?

Explanation

Radiosynovectomy is the preferred initial treatment for recurrent hemarthrosis in hemophilic patients who fail medical prophylaxis. It is minimally invasive, highly effective at reducing bleeding episodes, and avoids the surgical morbidity associated with arthroscopic or open synovectomy.

Question 38

A 15-year-old male presents with dull, aching thigh pain that is predictably worse at night and dramatically relieved by NSAIDs.

Based on the typical clinical and radiographic presentation shown, what is the most likely diagnosis?

Explanation

The classic presentation of night pain relieved by NSAIDs combined with an imaging finding of a radiolucent nidus surrounded by dense reactive sclerosis is diagnostic for osteoid osteoma. Prostaglandin production by the nidus is responsible for the characteristic pain pattern.

Question 39

A 12-year-old boy presents with short stature, waddling gait, and early-onset osteoarthritis of the hips. Radiographs demonstrate irregular, delayed ossification of the capital femoral epiphyses and a double-layered patella. A mutation in which of the following genes is most likely responsible?

Explanation

Multiple Epiphyseal Dysplasia (MED) is characterized by delayed epiphyseal ossification and double-layered patellae. The most common autosomal dominant form is caused by a mutation in the Cartilage Oligomeric Matrix Protein (COMP) gene.

Question 40

A 14-year-old male is diagnosed with high-grade conventional osteosarcoma of the distal femur. After completing neoadjuvant chemotherapy, he undergoes wide surgical resection. Which of the following histological findings in the resected specimen is the most critical prognostic factor for his overall survival?

Explanation

The percentage of tumor necrosis in response to neoadjuvant chemotherapy (typically using the Huvos grading system) is the single most important histologic prognostic indicator for osteosarcoma. Greater than 90% necrosis indicates a good response and correlates with improved survival.

Question 41

A 45-year-old female sustains a minimally displaced distal radius fracture treated in a cast. Six weeks later, she presents with severe, burning pain out of proportion to her injury, alongside swelling, stiffness, and shiny skin.

Which of the following interventions at the time of injury has been shown to reduce the risk of developing this condition?

Explanation

This patient has Complex Regional Pain Syndrome (CRPS) Type I (algodystrophy/Sudeck's atrophy). Administration of Vitamin C (500mg daily for 50 days) starting at the time of injury has been shown in studies to significantly reduce the incidence of CRPS following distal radius fractures.

Question 42

A patient with severe hemophilia A requires urgent orthopedic surgery for an open fracture. Preoperative testing reveals the presence of high-titer factor VIII inhibitors (>5 Bethesda units). Which of the following is the most appropriate hemostatic agent to administer before surgery?

Explanation

Patients with high-titer inhibitors to Factor VIII cannot be effectively treated with Factor VIII concentrates because the antibodies neutralize the factor. Bypassing agents, such as recombinant Factor VIIa or activated prothrombin complex concentrate (aPCC), are required to achieve hemostasis.

Question 43

An infant is diagnosed with achondroplasia, exhibiting rhizomelic short stature, frontal bossing, and midface hypoplasia. During the first two years of life, which of the following spinal complications warrants the most vigilant screening due to its potential for sudden mortality?

Explanation

Foramen magnum stenosis is a critical and potentially fatal complication in infants with achondroplasia, leading to cervicomedullary compression, central apnea, and sudden death. Screening with sleep studies and MRI is essential, whereas lumbar stenosis typically becomes problematic in adulthood.

Question 44

A 30-year-old female presents with knee pain. Radiographs reveal an eccentric, lytic epiphyseal lesion in the proximal tibia extending to the subchondral bone. Biopsy confirms Giant Cell Tumor of Bone (GCTB). Prior to planned intralesional curettage, the multidisciplinary tumor board recommends medical therapy to consolidate the tumor margins. Which agent is most appropriate?

Explanation

Denosumab, a monoclonal antibody against RANKL, inhibits osteoclast-like giant cell formation, leading to tumor necrosis and peripheral ossification of the tumor margin. It is widely used to facilitate joint-sparing curettage in challenging or aggressive GCTB cases.

Question 45

A 60-year-old male with a history of renal cell carcinoma presents with impending pathologic fracture of the subtrochanteric femur (Mirels score 10). Surgical stabilization with an intramedullary nail is planned. What critical preoperative intervention must be performed to minimize catastrophic intraoperative complications?

Explanation

Renal cell carcinoma and thyroid carcinoma bone metastases are notoriously hypervascular. Preoperative angiographic embolization (typically within 24-48 hours prior to surgery) is essential to minimize the risk of massive, uncontrollable intraoperative hemorrhage.

Question 46

A 6-year-old girl is evaluated for delayed dental eruption and abnormal shoulder mobility. Physical examination reveals the ability to approximate her shoulders anteriorly to the midline. Cranial sutures are widened. A defect in which of the following transcription factors is responsible for this condition?

Explanation

Cleidocranial dysplasia is characterized by hypoplastic or absent clavicles, delayed cranial suture closure, and dental anomalies. It is caused by an autosomal dominant mutation in the RUNX2 (CBFA1) gene, which is a master transcription factor for osteoblast differentiation.

Question 47

A 55-year-old male presents with deep pelvic pain. Imaging reveals a large, lobulated soft tissue mass arising from the ilium with internal "ring and arc" calcifications and cortical breakthrough. Biopsy confirms Grade II conventional chondrosarcoma. What is the treatment of choice?

Explanation

Conventional chondrosarcoma is notably resistant to both chemotherapy and radiation therapy due to its poor vascularity and slow growth fraction. The mainstay of treatment is wide surgical resection with negative margins.

Question 48

A 40-year-old male with severe hemophilia B presents with an enlarging, painless mass in his right ilium. Radiographs show a large, expansile lytic lesion destroying the cortex, with an associated soft-tissue mass. Biopsy is contraindicated. What is the most likely diagnosis?

Explanation

A hemophilic pseudotumor is an encapsulated hematoma caused by repeated intraosseous or subperiosteal bleeding, often presenting as a destructive, expansile lytic lesion on imaging. Biopsy can lead to uncontrollable hemorrhage or chronic fistulae and must be avoided.

Question 49

An 18-year-old male presents with a painful scoliosis. Imaging reveals a small sclerotic lesion in the pedicle of a lumbar vertebra.

In patients with an osteoid osteoma of the spine causing scoliosis, where is the lesion typically located relative to the scoliotic curve?

Explanation

Osteoid osteoma of the spine causes asymmetric muscle spasm due to local inflammation, leading to a scoliotic deformity. The lesion is characteristically located on the concavity of the curve at the apex of the deformity.

Question 50

A 25-year-old healthy male sustains a high-energy Pauwels Type III (vertical) femoral neck fracture. Closed reduction and internal fixation are planned. Which of the following factors is the strongest predictor of fracture nonunion in this scenario?

Explanation

In young adults with high-energy femoral neck fractures, initial fracture displacement is the strongest predictor of both nonunion and osteonecrosis. While a highly vertical angle (Pauwels III) increases shear stress, initial displacement represents the degree of vascular insult and mechanical instability.

Question 51

A 4-year-old child with blue sclerae, dentinogenesis imperfecta, and multiple long bone fractures is diagnosed with Osteogenesis Imperfecta (OI). Intravenous bisphosphonate therapy is initiated to reduce fracture burden. What is the primary cellular mechanism of action of this medication?

Explanation

Bisphosphonates, such as pamidronate or zoledronic acid, reduce fracture rates in OI by inhibiting osteoclast-mediated bone resorption. This increases cortical thickness and bone mass, despite the underlying defect in Type I collagen synthesis.

Question 52

An 11-year-old girl presents with fever, elevated ESR, and a painful thigh. Radiographs demonstrate a permeative, diaphyseal lytic lesion in the femur with a multilamellated ("onion skin") periosteal reaction. Cytogenetic testing reveals a t(11;22) translocation. Which fusion protein is produced by this translocation?

Explanation

Ewing sarcoma is characterized by the t(11;22)(q24;q12) chromosomal translocation in >85% of cases. This results in the EWS-FLI1 fusion protein, which acts as an aberrant transcription factor driving oncogenesis.

Question 53

A 35-year-old male sustains a gunshot wound to the posterolateral leg resulting in a partial transection of the common peroneal nerve. Weeks later, he develops severe, burning pain in the foot, hyperalgesia, and trophic skin changes.

Which of the following features specifically distinguishes his condition as Complex Regional Pain Syndrome (CRPS) Type II rather than Type I?

Explanation

CRPS Type II (formerly known as causalgia) is distinguished from CRPS Type I (algodystrophy/RSD) exclusively by the presence of a definable peripheral nerve injury. Both types share the same clinical symptoms of burning pain, allodynia, and autonomic/trophic changes.

Question 54

A 50-year-old male with severe hemophilia A and end-stage hemophilic arthropathy of the knee is scheduled for a total knee arthroplasty (TKA). To minimize perioperative bleeding, what should the target peak level of Factor VIII be maintained at for the first 1-3 days postoperatively?

Explanation

For major orthopedic surgery such as TKA in a patient with hemophilia A, the target Factor VIII level should be 100% preoperatively and maintained at 80-100% of normal for the first 1-3 days postoperatively to ensure adequate hemostasis.

Question 55

A neonate is born with disproportionate short-trunk dwarfism, a barrel chest, and cleft palate. Radiographs show severe coxa vara and delayed ossification of the epiphyses. An ophthalmologic exam reveals severe myopia. This clinical picture is most consistent with Spondyloepiphyseal Dysplasia Congenita (SEDC). Which structural protein is primarily defective?

Explanation

SEDC is a type II collagenopathy caused by mutations in the COL2A1 gene. Since type II collagen is the primary structural protein in articular cartilage and the vitreous humor of the eye, patients present with epiphyseal dysplasia, short trunk, and severe visual problems like myopia or retinal detachment.

Question 56

A 22-year-old male presents with progressive, dull back pain that is not completely relieved by NSAIDs. Imaging reveals an expansile, 2.5 cm lytic lesion involving the posterior elements of the L4 vertebra with cortical thinning. Biopsy shows interconnected woven bone trabeculae lined by prominent osteoblasts in a vascular stroma. What distinguishes this lesion from an osteoid osteoma?

Explanation

Osteoblastomas are histologically identical to osteoid osteomas but are distinguished clinically by their larger size (>2 cm) and lack of dramatic pain relief with NSAIDs. They most commonly occur in the posterior elements of the spine and can be locally aggressive.

Question 57

An 18-year-old male presents with persistent mid-thigh night pain that is reliably relieved by ibuprofen. Imaging shows a radiolucent nidus surrounded by reactive sclerosis.

If conservative management fails, what is the best next step in management?

Explanation

Osteoid osteoma classically presents with night pain relieved by NSAIDs. Radiofrequency ablation is the gold standard minimally invasive surgical treatment when symptomatic management fails.

Question 58

A 55-year-old female presents with severe pain, swelling, and stiffness of the hand 6 weeks after a distal radius fracture.

Which of the following prophylactic treatments has been shown to reduce the incidence of this complication if initiated acutely following the fracture?

Explanation

The patient has Complex Regional Pain Syndrome (CRPS). Vitamin C (500 mg daily) has been shown to decrease the risk of developing CRPS when given early following a distal radius fracture.

Question 59

A 28-year-old male with severe Hemophilia A (Factor VIII level <1%) requires a total knee arthroplasty for end-stage hemophilic arthropathy. What is the target Factor VIII level recommended immediately prior to the surgical incision?

Explanation

For major orthopedic surgeries such as total joint arthroplasty in severe hemophilia A, the target Factor VIII level must be restored to 100% immediately preoperatively. It should be maintained at high levels postoperatively to prevent catastrophic bleeding.

Question 60

A 4-year-old boy presents with disproportionate short stature, rhizomelic shortening, and frontal bossing. Which of the following genetic mutations is responsible for his condition?

Explanation

Achondroplasia is caused by an activating mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. This mutation leads to an abnormal inhibition of chondrocyte proliferation in the proliferative zone of the physis.

Question 61

A 22-year-old male undergoes excision of a cortical bone lesion in his proximal femur. Histology reveals a highly vascularized nidus of woven bone surrounded by sclerotic cortical bone.

The central nidus typically produces high levels of which substance?

Explanation

Osteoid osteomas have a central nidus that produces high levels of Prostaglandin E2 (PGE2). This excess PGE2 production is the mechanism responsible for the intense local pain that is classically relieved by NSAIDs.

Question 62

A patient with suspected Type 1 CRPS following a tibial shaft fracture fails conservative management, including physical therapy and neuropathic pain modulators. What is the next most appropriate diagnostic and potentially therapeutic intervention?

Explanation

In cases of lower extremity CRPS failing conservative management, a lumbar sympathetic ganglion block is the next step. It can confirm sympathetically mediated pain and provide significant therapeutic relief.

Question 63

A 15-year-old boy with Hemophilia B presents with recurrent hemarthroses of the right knee despite adequate factor prophylaxis. Radiographs show early joint space narrowing without significant subchondral collapse. Which of the following is the most appropriate next step?

Explanation

Radiosynovectomy (using isotopes like Phosphorus-32 or Yttrium-90) is highly effective for decreasing the frequency of hemarthroses in patients with refractory hemophilic synovitis but minimal cartilaginous damage.

Question 64

A 10-year-old girl is able to bring her shoulders together anteriorly in the midline and exhibits delayed eruption of secondary teeth. What is the expected inheritance pattern and affected gene for this condition?

Explanation

Cleidocranial dysplasia is an autosomal dominant condition caused by a mutation in the CBFA1 (RUNX2) gene, crucial for osteoblast differentiation. It classically features hypoplastic clavicles and delayed dental eruption.

Question 65

A 14-year-old boy presents with a permeative lytic lesion in the femoral diaphysis with an associated onion-skin periosteal reaction. Biopsy shows uniform small round blue cells. Which chromosomal translocation is most characteristic of this diagnosis?

Explanation

Ewing sarcoma is characterized by the t(11;22)(q24;q12) translocation in 85% of cases. This results in the formation of the EWS-FLI1 fusion protein.

Question 66

Which of the following is the single most important prognostic factor for overall survival in a patient presenting with a high-grade intramedullary osteosarcoma?

Explanation

The presence of distant metastasis at the time of diagnosis is the most critical prognostic factor for overall survival in osteosarcoma patients. The lungs are the most common site of metastasis.

Question 67

A 25-year-old female sustains a subtrochanteric femur fracture through a benign-appearing ground-glass cystic lesion. She has a history of precocious puberty and large café-au-lait spots. Which of the following best describes the underlying pathophysiology?

Explanation

McCune-Albright syndrome consists of polyostotic fibrous dysplasia, precocious puberty, and café-au-lait spots. It is caused by a somatic activating mutation in the GNAS gene, leading to increased intracellular cAMP via the Gs-alpha protein.

Question 68

A 40-year-old male with severe Hemophilia A presents with an expanding, painless mass in the pelvis accompanied by osteolytic destruction of the ilium. What is the most appropriate initial management of this lesion?

Explanation

Hemophilic pseudotumors are encapsulated hematomas causing pressure necrosis of adjacent bone. Initial management is prolonged factor replacement and immobilization; biopsy is strictly contraindicated due to bleeding risk.

Question 69

A 65-year-old male presents with deep thigh pain. Radiographs reveal a lytic lesion in the proximal femur with endosteal scalloping >2/3 of cortical thickness and intralesional popcorn calcifications. What is the most appropriate definitive treatment for a conventional grade II lesion?

Explanation

Conventional high-grade (Grade II or III) chondrosarcomas are largely resistant to chemotherapy and radiation. Wide surgical resection is the mainstay of treatment to prevent local recurrence.

Question 70

A 60-year-old female presents with glossy skin, joint stiffness, and severe allodynia in her foot 3 months after a treated ankle fracture.

Which of the following findings is most likely to be seen on a triple-phase bone scan in the late stages (Stage 3) of this condition?

Explanation

In the late (atrophic) stage of CRPS, a triple-phase bone scan typically shows normal or decreased flow and blood pool phases with decreased uptake on the delayed phase, contrasting the diffuse increased uptake of earlier stages.

Question 71

A child presents with frequent fractures, cranial nerve palsies, and hepatosplenomegaly. Radiographs show a generalized bone-in-bone appearance. The pathophysiology of this disease is primarily related to a defect in which of the following?

Explanation

Osteopetrosis is caused by defective osteoclastic bone resorption, often due to a failure to form the ruffled border or a defect in carbonic anhydrase II. This leads to excessively dense but highly brittle bone.

Question 72

A 30-year-old female presents with knee pain. Radiographs show an eccentric, purely lytic epiphyseal lesion extending to the subchondral bone without a sclerotic rim. Biopsy confirms Giant Cell Tumor. Which medication targets the underlying molecular driver of the neoplastic cells?

Explanation

In Giant Cell Tumor of bone, the neoplastic stromal cells express RANKL, which recruits bone-resorbing osteoclast-like giant cells. Denosumab, a monoclonal antibody against RANKL, inhibits this process.

Question 73

A 14-year-old boy presents with worsening right thigh pain, typically at night, relieved by NSAIDs. An image is shown.

What is the classic radiolucent nidus size limit for this diagnosis?

Explanation

Osteoid osteoma typically presents with nocturnal pain relieved by NSAIDs. The nidus is radiolucent and classically less than 1.5 cm in diameter. Lesions larger than this are considered osteoblastomas.

Question 74

A 9-year-old boy with severe Hemophilia A presents with a warm, swollen knee after minimal trauma. He has had 4 similar episodes this year. What is the primary pathophysiologic mechanism for the progressive joint destruction seen in this condition?

Explanation

Repeated hemarthroses in hemophilia cause iron deposition (hemosiderin) in the synovium. This leads to synovial hypertrophy, chronic inflammation, and direct cartilage apoptosis mediated by iron and inflammatory cytokines.

Question 75

A 12-year-old girl is evaluated for multiple bony prominences around her knees and wrists. Genetic testing reveals a mutation in the EXT1 gene. She is at highest risk for developing which of the following malignant tumors?

Explanation

Multiple Hereditary Exostoses (MHE) is an autosomal dominant condition linked to EXT1, EXT2, and EXT3 genes. Patients have a 1-5% lifetime risk of malignant transformation to a secondary chondrosarcoma, typically in adulthood.

Question 76

A 45-year-old woman presents with severe burning pain, swelling, and altered skin color in her right hand 6 weeks following a distal radius fracture. An image is provided.

According to the Budapest criteria, which of the following must be present for a clinical diagnosis of Complex Regional Pain Syndrome (CRPS)?

Explanation

The Budapest criteria for CRPS require continuing pain that is disproportionate to any inciting event. It also requires at least one symptom in three of four categories: sensory, vasomotor, sudomotor/edema, and motor/trophic.

Question 77

A 32-year-old woman presents with knee pain. Radiographs reveal an eccentric, lytic lesion in the distal femur extending to the subchondral bone without a sclerotic margin. A biopsy confirms multinucleated giant cells. Which medication is an FDA-approved targeted therapy for unresectable or recurrent cases of this tumor?

Explanation

Giant Cell Tumor of bone consists of neoplastic stromal cells that express RANKL, stimulating the recruitment of osteoclast-like giant cells. Denosumab, a monoclonal antibody against RANKL, is an effective treatment for unresectable or recurrent GCT.

Question 78

A 65-year-old man with a known history of Paget's disease of bone sustains a subtrochanteric femur fracture after a minor fall. What is the most common underlying cause of increased bone turnover in this disease?

Explanation

Paget's disease is characterized by an initial phase of excessive and chaotic osteoclastic bone resorption. This is followed by a compensatory, disorganized osteoblastic bone formation resulting in structurally weak woven bone prone to fractures.

Question 79

A 28-year-old man with Hemophilia B requires a total knee arthroplasty for end-stage hemophilic arthropathy. To safely perform this surgery, what is the target factor IX activity level for the perioperative period (surgery day to post-op day 3)?

Explanation

For major orthopedic surgeries like TKA in hemophilia patients, factor levels should be corrected to 80-100% immediately preoperatively. It should be maintained near that level for the first 3-5 postoperative days to prevent catastrophic bleeding.

Question 80

A 9-year-old girl is found to have a "shepherd's crook" deformity of her proximal femur, café-au-lait spots with irregular "coast of Maine" borders, and precocious puberty. What is the underlying genetic mutation responsible for this triad?

Explanation

The clinical presentation is classic for McCune-Albright syndrome, which consists of polyostotic fibrous dysplasia, café-au-lait macules, and endocrine abnormalities. It is caused by a somatic, post-zygotic activating mutation in the GNAS1 gene.

Question 81

A 16-year-old boy has an osteoid osteoma of the proximal tibia confirmed by imaging.

He has failed conservative management with NSAIDs. What is the current gold standard minimally invasive treatment for this lesion?

Explanation

Radiofrequency ablation (RFA) under CT guidance has become the gold standard treatment for osteoid osteoma when medical management fails. It offers a high success rate, minimal morbidity, and rapid recovery compared to open surgical excision.

Question 82

A 55-year-old woman is scheduled for closed reduction and casting of a Colles fracture.

What pharmacological agent, when given daily for 50 days post-injury, has been shown in some trials to reduce the incidence of CRPS in distal radius fractures?

Explanation

Vitamin C (ascorbic acid) at a dose of 500 mg daily for 50 days has been demonstrated in multiple studies to significantly decrease the incidence of Complex Regional Pain Syndrome following distal radius fractures.

Question 83

A 15-year-old boy presents with knee pain and a palpable mass. Radiographs show a "sunburst" periosteal reaction in the distal femur. Biopsy reveals malignant spindle cells producing osteoid. What is the most important prognostic factor for his long-term survival?

Explanation

In conventional high-grade osteosarcoma, the degree of tumor necrosis (>90% indicates a good response) following neoadjuvant chemotherapy is the most critical prognostic factor for long-term survival.

Question 84

A 72-year-old woman on long-term alendronate therapy for osteoporosis presents with atraumatic thigh pain. Radiographs reveal focal cortical thickening and a transverse radiolucent line on the lateral cortex of the subtrochanteric femur. What is the recommended management?

Explanation

Atypical femur fractures are associated with prolonged bisphosphonate use. Patients with an impending fracture (lateral cortical 'beaking' and pain) should undergo prophylactic intramedullary nailing, and anabolic agents like teriparatide may be initiated.

Question 85

A 60-year-old man presents with dull pelvic pain. Pelvic radiograph reveals a large, ill-defined lytic lesion in the ilium with "popcorn" calcifications. Biopsy shows atypical chondrocytes in a hyaline cartilage matrix. What is the primary treatment for this condition?

Explanation

Conventional chondrosarcomas are characteristically resistant to both chemotherapy and radiotherapy. Therefore, wide surgical resection with negative margins is the primary and most effective treatment modality.

Question 86

A 35-year-old man with severe Hemophilia A presents with a slowly enlarging, painless mass in his right thigh over the past two years. Imaging reveals an encapsulated cystic mass with intramural calcification eroding into the femur. What is the most likely diagnosis?

Explanation

Hemophilic pseudotumors are encapsulated hematomas that progressively expand due to recurrent bleeding. They can cause pressure necrosis, erode adjacent bone, and become massive, requiring complex multidisciplinary surgical management.

Question 87

A 3-year-old boy presents with his third fracture of the year, blue sclerae, and early hearing loss. A defect in which of the following is most likely responsible for his condition?

Explanation

Osteogenesis imperfecta is most commonly caused by autosomal dominant mutations in the COL1A1 or COL1A2 genes, causing defects in Type I collagen. This results in bone fragility, blue sclerae, and dentinogenesis imperfecta.

Question 88

A 40-year-old man with refractory CRPS type 1 of the right upper extremity continues to have severe pain despite aggressive physical therapy.

What is the most appropriate next step in interventional management?

Explanation

For patients with CRPS type 1 that is refractory to conservative measures, a stellate ganglion (cervical sympathetic) block can be both diagnostic and therapeutic for sympathetically maintained upper extremity pain.

Question 89

A 10-year-old boy presents with fever, weight loss, and mid-shaft femur pain. Radiographs show an "onion-skin" periosteal reaction. Molecular testing of the biopsy specimen is expected to reveal which of the following chromosomal translocations?

Explanation

Ewing sarcoma is a small round blue cell tumor that classically occurs in the diaphysis of long bones in children. It is characterized by the t(11;22)(q24;q12) translocation, which results in the EWS-FLI1 fusion protein.

Question 90

A 16-year-old boy has a painless, firm mass at the proximal medial tibia. Radiographs reveal a sessile bony outgrowth that is continuous with the medullary cavity of the underlying bone. When would surgical excision be definitively indicated?

Explanation

Osteochondromas are the most common benign bone tumors. Excision is indicated for mechanical symptoms, neurovascular compromise, or rapid growth/new pain after skeletal maturity, suggesting malignant transformation to chondrosarcoma.

Question 91

A 12-year-old boy is brought in after twisting his ankle. Radiographs show a 2-cm eccentrically located, radiolucent, multi-loculated lesion with a sclerotic margin in the distal tibial metaphysis. There is no fracture. What is the recommended management for this lesion?

Explanation

Non-ossifying fibromas (NOF) are common, benign, and self-limiting fibrous defects. Unless they are very large (>50% of the bone diameter) posing a risk for pathologic fracture, they require only observation and typically ossify by adulthood.

Question 92

A 20-year-old man underwent excision of a small bone lesion causing severe night pain.

Which of the following substances is produced in excess by the nidus, explaining the dramatic response to aspirin?

Explanation

The nidus of an osteoid osteoma produces high levels of Prostaglandin E2 (PGE2) due to increased COX-2 expression. This mediates the intense pain and explains the characteristic relief provided by NSAIDs and aspirin.

Skeletal Dysplasias of the Spine - Arab Board MCQ Prep

Master ABOS Orthopedic Board Review: Dysplasias, Tumors, Hemophilia, Fractures | Part 13

Key Takeaway

Master ABOS Orthopedic Board Review: Dysplasias, Tumors, Hemophilia, Fractures | Part 13

Chapter Index