ABOS Orthopedic Board Review: Paget's Disease, Gout, Hyperparathyroidism, Septic Coxitis | Part 5

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ABOS Orthopedic Board Review: Paget's Disease, Gout, Hyperparathyroidism, Septic Coxitis | Part 5

Key Takeaway

Orthopedic Board Review Pathology covers Paget's disease (bone remodeling, fragility, diagnosis), Gout (urate crystals, tophi, diagnosis), Hyperparathyroidism (PTH, bone resorption, kidney stones, brown tumors), and Newborn Septic Coxitis (S. aureus, hip position, ultrasound). This section provides essential knowledge for ABOS exam preparation.

ABOS Orthopedic Board Review: Paget's Disease, Gout, Hyperparathyroidism, Septic Coxitis | Part 5

Comprehensive 100-Question Exam

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Question 1

A 70-year-old male with a known history of Paget's disease presents with a 2-month history of new, severe, and unrelenting pain in his right thigh. Radiographs reveal a mixed lytic and sclerotic lesion in the mid-diaphysis of the femur with cortical destruction and a soft tissue mass. What is the most likely diagnosis?

Explanation

The most feared complication of Paget's disease is malignant transformation, which occurs in about 1% of patients and is most commonly osteosarcoma. This typically presents with new, progressive pain in a previously asymptomatic or stable pagetic bone.

Question 2

A 55-year-old female with end-stage renal disease presents with diffuse bone pain. Radiographs of her hands are obtained to evaluate for secondary hyperparathyroidism. What is the classic and earliest radiographic hallmark of this condition in the hand?

Explanation

Secondary hyperparathyroidism classically presents with subperiosteal bone resorption. The earliest and most sensitive radiographic location for this finding is the radial aspect of the middle phalanges of the index and middle fingers.

Question 3

A 45-year-old male presents with an acutely swollen, red, and painful knee. Aspiration yields turbid fluid. Synovial fluid analysis confirms the diagnosis of gout. Which of the following describes the characteristic microscopic findings under polarized light?

Explanation

Gout is caused by the deposition of monosodium urate crystals in the joint. Under polarized light microscopy, these crystals classically appear negatively birefringent and needle-shaped.

Question 4

A 4-year-old boy refuses to bear weight on his right leg. His temperature is 38.8°C, WBC is 13,500/mm3, and ESR is 45 mm/hr. An ultrasound of the right hip demonstrates a significant joint effusion. What is the most appropriate next step in management?

Explanation

This child meets all four Kocher criteria (fever, inability to bear weight, ESR >40, WBC >12,000) for a septic hip, predicting a >99% probability of the disease. The standard of care is emergent aspiration and surgical washout to prevent devastating cartilage destruction and osteonecrosis.

Question 5

A patient with symptomatic Paget's disease of the tibia is prescribed the first-line pharmacologic treatment to reduce bone pain and turnover. What is the primary cellular mechanism of action of this medication class?

Explanation

Bisphosphonates are the first-line treatment for symptomatic Paget's disease. Nitrogen-containing bisphosphonates inhibit farnesyl pyrophosphate synthase, which disrupts the mevalonate pathway and ultimately causes osteoclast apoptosis.

Question 6

A 40-year-old female with a history of recurrent nephrolithiasis presents with a well-circumscribed lytic lesion in her distal femur. Biopsy reveals localized accumulations of giant cells, hemosiderin-laden macrophages, and spindle cells. Laboratory workup shows elevated serum calcium and low serum phosphorus. What is the most likely diagnosis of the bone lesion?

Explanation

Brown tumors are non-neoplastic, reactive bone lesions caused by primary or secondary hyperparathyroidism, histologically characterized by giant cells and hemosiderin. The laboratory findings of hypercalcemia and hypophosphatemia point to primary hyperparathyroidism as the underlying cause.

Question 7

A neonate in the NICU develops irritability, fever, and pseudoparalysis of the left lower extremity. Physical examination reveals the left hip is held in a specific resting posture to minimize intracapsular pressure. Which position is most characteristic of a hip joint effusion in septic coxitis?

Explanation

A septic hip effusion increases intracapsular pressure, leading to severe pain. The joint capsule accommodates the maximum volume of fluid when the hip is placed in flexion, abduction, and external rotation (FABER), which is the classic position of comfort.

Question 8

A 60-year-old male with a history of recurrent painful joint attacks presents with chronic deformities of his toes. Radiographs are obtained. What is the radiologic hallmark of this condition?

Explanation

Chronic tophaceous gout classically presents on radiographs with punched-out lytic lesions and overhanging sclerotic margins, often referred to as 'rat bite' erosions. Unlike rheumatoid arthritis, joint spaces are typically preserved until very late in the disease process, and periarticular osteopenia is absent.

Question 9

Routine laboratory testing in an asymptomatic 65-year-old male reveals an isolated, marked elevation of serum alkaline phosphatase. Calcium, phosphorus, and GGT levels are completely normal. Radiographs of the pelvis show coarse trabeculations and cortical thickening. What phase of Paget's disease does this presentation most likely represent?

Explanation

Paget's disease progresses through lytic, mixed, and sclerotic phases. The mixed lytic and sclerotic phase is characterized by markedly elevated alkaline phosphatase due to exuberant osteoblastic activity attempting to keep pace with chaotic osteoclastic resorption.

Question 10

A 60-year-old male on long-term hemodialysis presents with diffuse bone pain. Radiographs demonstrate a 'rugger jersey' appearance of the spine. His labs show elevated PTH, low calcium, and high phosphorus. What is the primary pathophysiologic trigger for his skeletal disease?

Explanation

Secondary hyperparathyroidism in chronic kidney disease is primarily driven by phosphate retention and decreased renal 1-alpha-hydroxylase activity, which reduces active Vitamin D. This leads to chronic hypocalcemia, stimulating compensatory PTH hypersecretion.

Question 11

A 5-year-old child presents with a severe limp and a 3 cm limb length discrepancy. History reveals a prolonged NICU stay for sepsis as a neonate. Radiographs show complete absence of the femoral head and neck with proximal migration of the femoral shaft. This severe deformity is a known sequela of delayed treatment for which of the following?

Explanation

Neonatal septic coxitis can rapidly and completely destroy the unossified cartilaginous femoral head due to proteolytic enzymes. Delayed diagnosis often results in permanent loss of the proximal femur, classified as Tomich type IV sequelae.

Question 12

A 72-year-old male with a long history of polyostotic Paget's disease presents with progressive bilateral lower extremity weakness, numbness, and neurogenic claudication. What is the most likely cause of his neurologic symptoms?

Explanation

Paget's disease frequently involves the axial skeleton, leading to chaotic osseous overgrowth of the vertebral bodies and neural elements. This enlargement frequently causes symptomatic central or foraminal spinal stenosis.

Question 13

A 55-year-old male presents with an acute gout flare in his first metatarsophalangeal joint. He has a history of a recent severe upper gastrointestinal bleed and end-stage renal disease on dialysis. Which of the following is the most appropriate acute pharmacologic treatment?

Explanation

NSAIDs (indomethacin, naproxen) are contraindicated due to his recent GI bleed and ESRD. Colchicine must be dose-adjusted or avoided in severe renal failure due to toxicity. Corticosteroids are the safest and most effective acute treatment in this patient.

Question 14

A 2-year-old, fully immunized child is brought to the emergency department with a 2-day history of fever, refusal to walk, and left hip pain. Joint aspiration yields purulent fluid with a WBC count of 85,000/mm3. What is the most common causative organism overall for this condition?

Explanation

Staphylococcus aureus remains the most common overall cause of septic arthritis in children. While Kingella kingae is increasingly recognized as a common pathogen in children aged 6 months to 4 years, S. aureus is still universally considered the most prevalent pathogen.

Question 15

Which of the following laboratory profiles most accurately differentiates primary hyperparathyroidism from secondary hyperparathyroidism?

Explanation

Primary hyperparathyroidism involves autonomous overproduction of PTH, leading to hypercalcemia. Secondary hyperparathyroidism is a normal physiologic response to chronic hypocalcemia (often from renal failure or vitamin D deficiency), resulting in elevated PTH but low or normal serum calcium.

Question 16

A bone biopsy from the thickened, bowed tibia of a patient with Paget's disease demonstrates a characteristic mosaic pattern of lamellar bone with prominent, disorganized cement lines. What is the underlying primary cellular abnormality driving this disease process?

Explanation

The primary pathophysiologic defect in Paget's disease is the presence of hyperactive, massively enlarged osteoclasts with an excessive number of nuclei (often up to 100). The pathognomonic mosaic pattern of cement lines results from the subsequent chaotic, rapid bone formation by osteoblasts.

Question 17

A 65-year-old male presents with massive, ulcerated, chalky white tophaceous deposits over his olecranon and PIP joints, causing severe mechanical restriction and recurrent secondary infections. Initial surgical management of these symptomatic lesions primarily involves:

Explanation

Surgical indications for gouty tophi include infection, intractable pain, ulceration, severe nerve compression, and mechanical block to motion. The primary surgical approach is careful debulking and excision of the tophi while rigorously preserving adjacent functional tendons, nerves, and skin.

Question 18

A 58-year-old male with a history of prolonged hemodialysis followed by a successful renal transplant 3 years ago presents to the clinic. Routine labs show persistent, severe hypercalcemia and markedly elevated PTH levels despite normal renal graft function. What is the most likely diagnosis?

Explanation

Tertiary hyperparathyroidism occurs when the parathyroid glands become completely autonomous and secrete excessive PTH irrespective of serum calcium levels. This typically occurs after a long period of secondary hyperparathyroidism, such as in a dialysis patient who subsequently receives a kidney transplant.

Question 19

A 55-year-old man presents with a swollen, erythematous first metatarsophalangeal joint. Joint aspiration is performed to confirm the diagnosis of acute gout.

Which of the following describes the characteristic crystal findings under polarized light microscopy?

Explanation

Gout is characterized by monosodium urate crystals that appear needle-shaped and strongly negatively birefringent under polarized light. Under parallel polarized light, they appear yellow. Calcium pyrophosphate crystals (pseudogout) are positively birefringent and rhomboid-shaped.

Question 20

What is the primary cellular defect that initiates the pathogenesis of Paget's disease of bone?

Explanation

Paget's disease begins with an initial osteolytic phase driven by overactive, massive multinucleated osteoclasts, often linked to SQSTM1 gene mutations. This is followed by a compensatory but disorganized mixed osteoblastic/osteoclastic phase, leading to weak, woven bone formation.

Question 21

A 62-year-old woman with chronic kidney disease presents with diffuse bone pain. Radiographs of her hands show subperiosteal bone resorption on the radial aspect of the middle phalanges.

What is the most likely primary driving mechanism for these osseous changes?

Explanation

Subperiosteal bone resorption on the radial aspect of the middle phalanges is the pathognomonic radiographic sign of hyperparathyroidism. In the context of chronic kidney disease, secondary hyperparathyroidism results in sustained PTH elevation leading to osteitis fibrosa cystica.

Question 22

A 10-day-old neonate presents with irritability, fever, and asymmetric active leg movement. The affected hip is held in flexion, abduction, and external rotation.

What is the physiologic reason for this classic posture?

Explanation

In septic coxitis, the hip joint is typically held in flexion, abduction, and external rotation (FABER). This specific position maximizes the intra-articular capsular volume, which minimizes pain and prevents ischemia from the high-pressure distension caused by a purulent effusion.

Question 23

A 70-year-old man with a long-standing history of enlarged skull and bowed tibias presents with a sudden onset of severe, unrelenting pain in his right proximal femur, which was previously asymptomatic. His serum alkaline phosphatase is notably higher than his baseline.

What is the most likely diagnosis?

Explanation

A sudden increase in localized pain, swelling, and a massive spike in alkaline phosphatase in a patient with Paget's disease is highly suspicious for malignant transformation. Osteosarcoma is the most common and aggressive malignancy arising in Pagetic bone.

Question 24

A 45-year-old man with a history of recurrent acute podagra and visible tophi on his elbows is started on long-term medical therapy to lower his serum uric acid. He is prescribed a medication that inhibits xanthine oxidase. Which of the following drugs fits this mechanism?

Explanation

Allopurinol is a xanthine oxidase inhibitor used for the chronic management of gout to decrease uric acid production. Colchicine inhibits microtubule polymerization, while Probenecid is a uricosuric agent that increases renal excretion of uric acid.

Question 25

Which of the following laboratory profiles is most characteristic of an untreated patient with primary hyperparathyroidism?

Explanation

Primary hyperparathyroidism is typically caused by a solitary parathyroid adenoma, resulting in autonomously elevated PTH, hypercalcemia, and hypophosphatemia. In contrast, secondary hyperparathyroidism from chronic kidney disease features low or normal calcium and high phosphorus.

Question 26

A 68-year-old woman with active Paget's disease of the right hemipelvis and femur is scheduled for a total hip arthroplasty due to severe secondary osteoarthritis. Which preoperative pharmacological intervention is highly recommended to reduce intraoperative blood loss?

Explanation

Pagetic bone is highly vascular during the active mixed phases, which can lead to life-threatening intraoperative hemorrhage during orthopedic procedures. Preoperative administration of bisphosphonates reduces bone turnover and vascularity, thereby significantly decreasing surgical blood loss.

Question 27

A 4-year-old boy presents with right hip pain and a limp. He refuses to bear weight. His temperature is 38.8°C (101.8°F), ESR is 45 mm/hr, and peripheral WBC count is 14,000/mm³. According to the Kocher criteria, what is the approximate probability that this child has septic arthritis of the hip?

Explanation

The Kocher criteria for pediatric septic arthritis of the hip include non-weight-bearing, fever > 38.5°C, ESR > 40 mm/hr, and WBC > 12,000/mm³. The presence of all four predictors indicates an approximate 99% probability of septic arthritis.

Question 28

A 68-year-old male presents with a painful, swollen great toe. Radiographs demonstrate punched-out periarticular erosions with overhanging edges.

Synovial fluid analysis of the affected joint is most likely to reveal which of the following?

Explanation

The clinical and radiographic presentation is classic for gout. Synovial fluid analysis in gout reveals monosodium urate crystals, which are needle-shaped and strongly negatively birefringent under polarized light.

Question 29

A 74-year-old male with a long-standing history of bone pain and enlarging skull size presents with a new, severe, and unrelenting pain in his right thigh. Radiographs reveal a destructive, lytic lesion with cortical breakthrough in the diaphysis of the femur.

What is the most likely diagnosis?

Explanation

The patient has a history consistent with Paget's disease. The most dreaded complication of Paget's disease is malignant transformation, most commonly to secondary osteosarcoma, which typically presents with new unrelenting pain and a destructive lytic lesion.

Question 30

A 45-year-old female presents with diffuse bone pain and a history of recurrent nephrolithiasis. Radiographs demonstrate a lytic lesion in her proximal femur. Biopsy of the lesion reveals spindle cells, multinucleated giant cells, and abundant hemosiderin deposits. Which of the following laboratory profiles is most consistent with her diagnosis?

Explanation

The biopsy findings and clinical history (stones, bones) are classic for a Brown tumor associated with primary hyperparathyroidism. Typical laboratory findings include elevated serum calcium, elevated PTH, and low serum phosphorus.

Question 31

A 2-week-old neonate is brought to the emergency department for irritability and decreased spontaneous movement of the right lower extremity. Ultrasound reveals a significant hip effusion.

What is the most appropriate next step in management?

Explanation

The neonate presents with pseudoparalysis and an effusion, highly suspicious for septic coxitis. Urgent aspiration and surgical drainage (arthrotomy) are required to prevent catastrophic destruction of the cartilaginous femoral head.

Question 32

A 65-year-old male presents with enlarging hat size, hearing loss, and bowing of the tibiae. Laboratory evaluation reveals an isolated, markedly elevated alkaline phosphatase with normal serum calcium and phosphorus. What is the primary cellular abnormality initiating this disease process?

Explanation

Paget's disease is initiated by intense, disorganized osteoclastic bone resorption, often linked to SQSTM1 (p62) mutations. This is followed by a compensatory but chaotic increase in osteoblastic bone formation.

Question 33

A 72-year-old male with a known history of Paget's disease presents with new-onset, severe, and unrelenting left thigh pain. Radiographs demonstrate a destructive lytic lesion in the femur with cortical breakthrough and soft tissue extension.

What is the most likely diagnosis?

Explanation

Malignant transformation in Paget's disease occurs in about 1% of patients, presenting with new, unrelenting pain. Secondary osteosarcoma is the most common and carries a poor prognosis.

Question 34

A 68-year-old male with symptomatic Paget's disease of the right hip is scheduled for a total hip arthroplasty due to severe secondary osteoarthritis. To minimize severe intraoperative hemorrhage, which medical management is recommended prior to surgery?

Explanation

Preoperative administration of bisphosphonates (like zoledronic acid) is recommended prior to elective surgery in Pagetoid bone. This effectively decreases the intense vascularity of the bone and reduces intraoperative blood loss.

Question 35

In a patient diagnosed with asymptomatic Paget's disease incidentally on radiographs, which of the following represents an absolute indication for initiating bisphosphonate therapy?

Explanation

Treatment for asymptomatic Paget's disease is generally reserved for patients preparing for orthopedic surgery at involved sites to decrease vascularity. It is also indicated if there is involvement of weight-bearing bones at high risk of fracture or skull involvement threatening hearing.

Question 36

A 55-year-old male presents with acute, severe pain, swelling, and erythema of the first metatarsophalangeal joint. Joint aspiration is performed. What is the expected crystal analysis result under polarized light microscopy?

Explanation

Acute gout is characterized by the deposition of monosodium urate crystals in the joint. Under polarized light microscopy, these appear as negatively birefringent, needle-shaped crystals.

Question 37

A 60-year-old male has a history of recurrent joint pain. Radiographs of his hands demonstrate periarticular erosions with overhanging sclerotic margins and preserved joint spaces.

What is the primary etiology of this disease process?

Explanation

The radiographic findings of "rat-bite" erosions with overhanging margins and relatively preserved joint spaces are hallmark signs of chronic tophaceous gout. This is caused by prolonged monosodium urate deposition.

Question 38

A patient with an acute gout flare is evaluated in the emergency department. He has a history of severe chronic kidney disease (Stage IV). Which of the following is the most appropriate initial treatment for his acute flare?

Explanation

In patients with severe chronic kidney disease, NSAIDs and colchicine are generally contraindicated due to toxicity risks. Corticosteroids (intra-articular or systemic) are the safest and most effective option for acute flares in this population.

Question 39

A 45-year-old female with chronic renal failure complains of diffuse bone pain. Laboratory evaluation shows elevated parathyroid hormone (PTH), low serum calcium, and high serum phosphate. Radiographs show subperiosteal resorption in the phalanges. What is the most likely diagnosis?

Explanation

Secondary hyperparathyroidism is common in chronic kidney disease and is characterized by elevated PTH in response to hypocalcemia and hyperphosphatemia. Subperiosteal resorption on the radial aspect of the middle phalanges is pathognomonic.

Question 40

A 50-year-old female presents with a pathological fracture of the humerus. Radiographs show a well-defined, expansile, lytic lesion. Labs reveal hypercalcemia, hypophosphatemia, and elevated PTH.

Biopsy of the lesion would most likely show:

Explanation

The clinical picture describes primary hyperparathyroidism presenting with a Brown tumor (osteitis fibrosa cystica). Histologically, Brown tumors consist of multinucleated giant cells and mononuclear cells in a highly vascular, hemorrhagic, fibroblastic stroma.

Question 41

A 4-year-old boy presents with a sudden onset limp and refuses to bear weight on his right leg. He has a temperature of 38.8 C. Labs show an ESR of 45 mm/h and a WBC count of 13,500/mm3. According to the Kocher criteria, what is the probability that he has septic arthritis of the hip?

Explanation

The Kocher criteria for pediatric septic hip include: non-weight-bearing, temperature >38.5 C, ESR >40 mm/h, and WBC >12,000/mm3. The presence of all 4 criteria yields a 99% predicted probability of septic arthritis.

Question 42

A 3-week-old neonate in the NICU develops swelling of the left thigh and pseudoparalysis of the left leg. The hip is held in flexion, abduction, and external rotation.

What is the most common causative organism for this condition in this age group?

Explanation

Staphylococcus aureus is the most common cause of pediatric septic arthritis across all age groups, including neonates. Group B Streptococcus and Gram-negative bacilli are also important pathogens in the neonatal period.

Question 43

A delay in the surgical drainage of septic coxitis in an infant can lead to devastating sequelae due to increased intra-articular pressure and bacterial chondrolysis. Which of the following structures is at highest immediate risk of irreversible ischemic necrosis?

Explanation

The hip joint is entirely intra-articular, and increased purulent effusion raises intra-articular pressure, compromising the delicate retinacular vessels. This leads to avascular necrosis of the capital femoral epiphysis and profound joint destruction.

Question 44

A 55-year-old patient on hemodialysis presents with mechanical back pain. Lateral radiographs of the lumbar spine demonstrate alternating bands of dense sclerosis at the superior and inferior vertebral body endplates with central lucency.

What is this characteristic radiographic sign called?

Explanation

The "rugger jersey spine" appearance consists of prominent sclerotic bands at the endplates of the vertebral bodies. It is a classic radiographic manifestation of renal osteodystrophy secondary to hyperparathyroidism.

Question 45

A 70-year-old female with active Paget's disease is treated with zoledronic acid. What is the primary cellular mechanism of action of this medication?

Explanation

Nitrogen-containing bisphosphonates (like zoledronic acid) act by inhibiting farnesyl pyrophosphate synthase in the mevalonate pathway. This disrupts osteoclast function and promotes osteoclast apoptosis.

Question 46

A 62-year-old male with a history of gout undergoes an elective total knee arthroplasty. On postoperative day 3, he develops acute, severe pain, swelling, and erythema of the operated knee. Aspiration yields cloudy fluid with 35,000 WBCs/mm3 and negatively birefringent crystals. Gram stain is negative. What is the most appropriate next step?

Explanation

Acute postoperative gout flares can closely mimic acute periprosthetic joint infection. The presence of negatively birefringent crystals and a negative Gram stain supports acute gout, which is initially managed medically with NSAIDs or corticosteroids, avoiding unnecessary surgery.

Question 47

A 6-year-old child presents with atraumatic hip pain and fever. An ultrasound is performed, which reveals an asymmetry in the anterior capsular distance of 3 mm compared to the contralateral hip. Which of the following is the most appropriate next step to confirm the diagnosis?

Explanation

An anterior capsular distance asymmetry of >2 mm on ultrasound indicates a significant hip effusion. Ultrasound-guided aspiration is the definitive diagnostic step to differentiate septic arthritis from transient synovitis via cell count, Gram stain, and culture.

Question 48

A patient with refractory secondary hyperparathyroidism due to end-stage renal disease requires medical optimization. Which of the following medications functions as a calcimimetic to directly lower PTH levels?

Explanation

Cinacalcet is a calcimimetic agent that increases the sensitivity of the calcium-sensing receptors on the parathyroid gland. This tricks the gland into detecting higher serum calcium levels, thereby reducing PTH secretion.

Question 49

An 70-year-old man with a long-standing history of Paget's disease presents with a sudden, progressive increase in thigh pain and swelling. Radiographs show a destructive, permeative lesion in the proximal femur with cortical breakthrough. What is the most common malignant transformation in this patient population?

Explanation

Osteosarcoma is the most common malignant transformation in Paget's disease, occurring in about 1% of patients. It typically presents with a sudden increase in pain and a destructive bone lesion.

Question 50

A 3-week-old neonate presents with fever, irritability, and decreased spontaneous movement of the right lower extremity. Clinical examination reveals pain upon passive range of motion of the right hip. Ultrasound shows a joint effusion. What is the most appropriate next step in management?

Explanation

Septic coxitis in a neonate is an orthopedic emergency presenting as pseudoparalysis. Immediate ultrasound-guided aspiration followed by urgent surgical debridement is required to prevent rapid femoral head destruction.

Question 51

A 55-year-old man presents with an acute, exquisitely tender, swollen first metatarsophalangeal joint. Joint aspiration yields cloudy fluid. Which of the following best describes the microscopic appearance of the crystals pathognomonic for this condition?

Explanation

Gout is characterized by monosodium urate crystals, which appear as strongly negatively birefringent, needle-shaped crystals under polarized light microscopy. Positively birefringent rhomboid crystals are indicative of pseudogout.

Question 52

A 48-year-old woman with end-stage renal disease presents with diffuse bone pain. Radiographs of her hands reveal pathognomonic subperiosteal bone resorption on the radial aspect of the middle phalanges. What are the expected serum laboratory findings in this patient?

Explanation

This patient has secondary hyperparathyroidism due to renal osteodystrophy. The kidneys fail to excrete phosphorus and activate Vitamin D, leading to hyperphosphatemia, hypocalcemia, and a compensatory hypersecretion of PTH.

Question 53

A 65-year-old man is incidentally diagnosed with a thickened calvarium and bowing of the tibia. His serum alkaline phosphatase is significantly elevated, but calcium and phosphate are normal. If a biopsy of the affected bone were performed, what would be the characteristic histological finding?

Explanation

The hallmark histological feature of the mixed and sclerotic phases of Paget's disease is a "mosaic" or "jigsaw puzzle" pattern of lamellar bone. This is caused by rapid, haphazard bone resorption and formation, leaving prominent cement lines.

Question 54

A 62-year-old man with a history of recurrent monoarticular arthritis presents with chronic pain and deformity in his foot. Radiographs display well-defined, "punched-out" erosions with sclerotic margins and overhanging edges in the first metatarsophalangeal joint. What is the underlying pathophysiology of this condition?

Explanation

The clinical and radiographic findings are classic for chronic tophaceous gout. It is caused by hyperuricemia, most commonly due to renal underexcretion (90%), or less commonly, overproduction of uric acid.

Question 55

A 35-year-old woman presents with a pathological fracture of the proximal humerus. Radiographs reveal a large, purely lytic lesion. Laboratory tests demonstrate elevated serum calcium and elevated parathyroid hormone levels. A biopsy of the lesion shows abundant multinucleated giant cells in a fibrovascular stroma with hemosiderin deposition. What is the most appropriate definitive management for the underlying cause of this bone lesion?

Explanation

The patient has a Brown tumor resulting from primary hyperparathyroidism. Definitive treatment involves parathyroidectomy to normalize parathyroid hormone levels, which usually allows the bone lesion to heal spontaneously.

Question 56

A 72-year-old man with symptomatic Paget's disease involving the pelvis and femur is scheduled for a total hip arthroplasty due to severe secondary osteoarthritis. Which preoperative medication should be considered to reduce intraoperative blood loss and disease activity?

Explanation

Preoperative administration of bisphosphonates is recommended in patients with active Paget's disease undergoing elective orthopedic surgery. It reduces the hypervascularity of the pagetic bone, thereby significantly decreasing intraoperative blood loss.

Question 57

A 4-year-old child presents with a severe limp and limb length discrepancy. His mother reports he had a severe febrile illness requiring an operation on his hip shortly after birth. Radiographs show a completely absent femoral head and neck with proximal migration of the femoral shaft. What was the most likely diagnosis during the neonatal period?

Explanation

Delay in diagnosis and treatment of neonatal septic arthritis of the hip (septic coxitis) leads to rapid destruction of the cartilaginous femoral head by proteolytic enzymes. This results in severe, permanent deformity and joint subluxation.

Question 58

A 50-year-old man presents with an acute flare of gout in his knee. He is prescribed colchicine. What is the mechanism of action of this medication in the treatment of acute gout?

Explanation

Colchicine works by binding to tubulin and inhibiting microtubule polymerization. This impairs neutrophil chemotaxis and degranulation, effectively reducing the acute inflammatory response to monosodium urate crystals.

Question 59

A 55-year-old man on hemodialysis presents with chronic back pain. Lateral radiographs of the lumbar spine demonstrate dense sclerotic bands at the superior and inferior endplates of the vertebral bodies, with central radiolucency. What is this classic radiographic sign called?

Explanation

The "rugger jersey spine" is characterized by sclerotic endplates and is a classic sign of secondary hyperparathyroidism (renal osteodystrophy). "Picture frame vertebra" is seen in Paget's disease, and "Bamboo spine" in ankylosing spondylitis.

Question 60

An 80-year-old woman with advanced Paget's disease of the skull presents with gradual hearing loss and tinnitus. What is the primary cause of hearing loss in this patient?

Explanation

Hearing loss in Paget's disease of the skull (osteitis deformans) is the most common neurologic complication. It is primarily caused by bony overgrowth narrowing the cranial foramina, leading to compression of the vestibulocochlear nerve (CN VIII).

Question 61

A patient with a chronic history of gouty arthritis presents with multiple, painless, firm, yellowish nodules over the olecranon bursa and Achilles tendon. Chalky white material is extruded from one of the nodules. Which of the following conditions is most strongly associated with this disease process?

Explanation

The patient has tophaceous gout. Gout and hyperuricemia are strongly associated with metabolic syndrome, which includes a constellation of hypertension, central obesity, insulin resistance, and dyslipidemia.

Question 62

A 65-year-old man with Paget's disease presents for a routine follow-up complaining of progressive hearing loss. Which of the following is the primary mechanism of action of the first-line medication used to treat the symptomatic manifestations of this condition?

Explanation

First-line treatment for symptomatic Paget's disease, including cranial nerve entrapment causing hearing loss, is a nitrogen-containing bisphosphonate. These drugs inhibit farnesyl pyrophosphate synthase, leading to osteoclast apoptosis and decreased bone resorption.

Question 63

A 52-year-old male with a history of recurrent podagra presents with a painful, nodular mass on his first metatarsophalangeal joint.

Radiographs are obtained. Which of the following radiographic features is most characteristic of chronic tophaceous gout?

Explanation

Chronic gout is classically associated with punched-out juxta-articular erosions featuring sclerotic, overhanging margins known as Martel's sign. Joint space is often preserved until late in the disease process.

Question 64

A 48-year-old female with chronic kidney disease presents with diffuse back pain. Spine radiographs reveal alternating bands of radiolucency and radiodensity in the vertebral bodies. Which of the following underlying pathophysiologic processes is most directly responsible for this radiographic finding?

Explanation

The radiograph describes a Rugger-Jersey spine, characteristic of secondary hyperparathyroidism in renal osteodystrophy. It results from chronic parathyroid hormone (PTH) stimulation leading to endplate sclerosis and central vertebral lucency.

Question 65

A 4-year-old boy presents with a limp, a temperature of 38.8°C, and refusal to bear weight on his right leg. Lab work shows a WBC of 13,000/mm³ and an ESR of 55 mm/hr. Which of the following represents the most appropriate next step in management?

Explanation

The patient meets all four Kocher criteria (non-weight-bearing, fever >38.5°C, ESR >40 mm/hr, WBC >12,000/mm³), indicating a 99% probability of septic arthritis. Ultrasound-guided aspiration is the most appropriate next step for definitive diagnosis before surgical washout.

Question 66

A 72-year-old man undergoes a biopsy of a thickened, enlarged tibia exhibiting a bowing deformity. Histological examination of the bone reveals a mosaic pattern of lamellar bone with prominent cement lines. Which of the following cell types is initially responsible for the pathogenesis of this disease?

Explanation

Paget's disease initiates with an intensely osteolytic phase driven by large, overactive, multinucleated osteoclasts. This is followed by a mixed phase and a sclerotic phase, resulting in disorganized lamellar bone with characteristic cement lines.

Question 67

A 60-year-old man with a history of severe peptic ulcer disease and chronic kidney disease (eGFR 25 mL/min) presents with an acute gout flare in his left knee. Which of the following is the most appropriate initial pharmacological treatment for this acute flare?

Explanation

NSAIDs are contraindicated in patients with severe peptic ulcer disease and poor renal function. Intra-articular corticosteroids are the safest and most effective option for managing an acute monoarticular gout flare in this specific patient.

Question 68

A 50-year-old woman is found to have an expansive, lytic lesion in her distal femur.

Serum calcium is 11.5 mg/dL (Normal: 8.5-10.5) and PTH is significantly elevated. Biopsy reveals highly vascular fibroblastic stroma containing numerous multinucleated giant cells and hemosiderin. What is the most appropriate definitive management for the bone lesion?

Explanation

The lesion is a Brown tumor (osteitis fibrosa cystica) caused by hyperparathyroidism. These lesions typically regress and remineralize following the treatment of the underlying endocrine disorder, which is primarily achieved through parathyroidectomy.

Question 69

A 2-week-old neonate presents with irritability, poor feeding, and pseudoparalysis of the left lower extremity.

Examination shows pain with passive range of motion of the left hip. If left untreated, which of the following is the most likely catastrophic complication specific to this joint in this age group?

Explanation

Septic arthritis of the hip in a neonate is a surgical emergency. Delayed treatment rapidly leads to complete destruction of the cartilaginous femoral anlage (femoral head and neck) due to proteolytic enzymes and compromised intracapsular blood supply.

Question 70

A 75-year-old male with long-standing polyostotic Paget's disease is scheduled for an elective total hip arthroplasty. To minimize perioperative blood loss associated with the hypervascular pagetic bone, which of the following preoperative interventions is most appropriate?

Explanation

Pagetic bone is highly vascular during active phases, leading to a significant risk of intraoperative hemorrhage during orthopedic surgery. Pretreatment with bisphosphonates for 2-3 months reduces disease activity and bone vascularity, thereby minimizing blood loss.

Question 71

A 45-year-old male with chronic tophaceous gout is started on long-term urate-lowering therapy. Six weeks later, his serum uric acid levels are significantly reduced. What is the mechanism of action of the most commonly prescribed first-line medication for this purpose?

Explanation

Allopurinol is the first-line urate-lowering therapy for chronic gout. It functions as a competitive inhibitor of xanthine oxidase, preventing the conversion of hypoxanthine to xanthine, and xanthine to uric acid.

Question 72

A 55-year-old male with chronic renal failure presents with knee pain. Labs reveal hypocalcemia, hyperphosphatemia, and an extremely high PTH level. Radiographs show subperiosteal resorption. Which of the following combinations of laboratory findings is most characteristic of primary hyperparathyroidism, distinguishing it from this patient's condition?

Explanation

Primary hyperparathyroidism is typically caused by a parathyroid adenoma, resulting in elevated PTH, elevated serum calcium, and decreased serum phosphate. This contrasts with secondary hyperparathyroidism from renal failure, which presents with low or normal calcium and high phosphate.

Question 73

A 3-week-old infant in the NICU develops an acutely swollen and erythematous right hip. Aspiration of the joint reveals purulent fluid. While Staphylococcus aureus is the most common pathogen overall, which of the following organisms is particularly unique to this age group and must be covered empirically?

Explanation

In neonates (age < 1 month), Group B Streptococcus (S. agalactiae) and Gram-negative bacilli are common causes of septic arthritis, in addition to S. aureus. Empirical antibiotic coverage must include agents effective against these organisms.

Question 74

A 68-year-old male with known Paget's disease presents with slowly progressive bilateral lower extremity weakness, numbness, and difficulty walking. Radiographs of the lumbar spine show an enlarged, dense vertebral body (ivory vertebra). What is the most likely cause of his neurological symptoms?

Explanation

Paget's disease causes cortical thickening and osseous enlargement of the affected bones. In the spine, this expansion can lead to central canal or foraminal stenosis, compressing the spinal cord or nerve roots and causing progressive neurological deficits.

Question 75

A mass is excised from the olecranon bursa of a 55-year-old male. Gross examination reveals chalky white deposits. Histological examination using H&E staining shows large amorphous granular pink material surrounded by macrophages and multinucleated giant cells, but no distinct crystals are seen. Why are the crystals not visible on standard H&E preparation?

Explanation

Monosodium urate crystals are water-soluble and dissolve in the aqueous formalin fixatives used for standard H&E processing. To visualize the actual crystals histologically, tissue must be fixed in absolute alcohol.

Question 76

A 65-year-old man undergoes a biopsy for an expansile diaphyseal tibial lesion. Pathology shows a chaotic pattern of woven and lamellar bone with prominent and irregular cement lines. Based on this histological description, what is the most likely diagnosis?

Explanation

Paget's disease is characterized histologically by a "mosaic" pattern of lamellar bone. This pattern is created by chaotic, rapid bone remodeling with prominent, irregular cement lines marking previous sites of bone resorption.

Question 77

A 54-year-old woman with chronic kidney disease presents with diffuse skeletal pain. Radiographs of her hand show characteristic lesions

. Where is the classic earliest location of the subperiosteal resorption associated with this condition?

Explanation

The earliest and most classic radiographic finding in hyperparathyroidism is subperiosteal bone resorption. This typically occurs on the radial aspect of the middle phalanges of the index and middle fingers.

Question 78

A 3-year-old child presents with a limp, refusal to bear weight, a temperature of 38.8 C, an ESR of 45 mm/hr, and a peripheral WBC of 13,000/mm^3. According to the Kocher criteria, what is the probability that this child has septic arthritis of the hip?

Explanation

The Kocher criteria include non-weight-bearing, temperature > 38.5 C, ESR > 40 mm/hr, and WBC > 12,000/mm^3. The presence of all four criteria yields a 99% predictive probability for septic arthritis of the hip.

Question 79

A 50-year-old man presents with a painful, swollen first MTP joint. Joint aspirate reveals needle-shaped crystals. When aligned parallel to the axis of the compensator under polarized light microscopy, what color do these crystals typically appear?

Explanation

Gout is caused by monosodium urate crystals, which are strongly negatively birefringent. They appear yellow when aligned parallel to the axis of the compensator and blue when perpendicular.

Question 80

A 72-year-old man with active Paget's disease of the proximal femur is scheduled for an elective total hip arthroplasty due to severe secondary osteoarthritis. His alkaline phosphatase is markedly elevated. Which preoperative intervention is most appropriate to reduce surgical complications?

Explanation

Pagetoid bone is highly vascular, posing a significant risk of massive intraoperative hemorrhage. Preoperative treatment with bisphosphonates (1 to 3 months prior) reduces disease activity, normalizing vascularity and decreasing surgical blood loss.

Question 81

A 48-year-old woman presents with a lytic lesion in her distal radius. Biopsy reveals sheets of osteoclast-like multinucleated giant cells in a background of spindle cells and abundant hemosiderin. Lab evaluation shows elevated serum calcium and intact PTH. What is the underlying pathogenesis of this bone lesion?

Explanation

The lesion is a brown tumor of hyperparathyroidism (osteitis fibrosa cystica). It arises from intense osteoclastic activity leading to bone resorption, microhemorrhages, and subsequent hemosiderin deposition, which gives it a brown color.

Question 82

A 4-week-old infant is diagnosed with a delayed presentation of septic coxitis

. Which of the following is the most devastating, yet common, complication of delayed surgical decompression in this specific age group?

Explanation

Septic arthritis of the hip in infants is a surgical emergency. Delayed decompression leads to rapid proteolytic destruction of the largely cartilaginous capital femoral epiphysis, causing irreversible joint damage and catastrophic growth disturbances.

Question 83

A 60-year-old man presents with chronic foot pain and the following radiographic findings

. What is the classic radiographic description of the erosions associated with this disease process?

Explanation

Chronic tophaceous gout is classically characterized by juxta-articular "punched-out" bony erosions. These often feature overhanging cortical edges, also known as Martel's sign, with preservation of the joint space until late in the disease.

Question 84

First-line medical therapy for symptomatic Paget's disease involves a class of drugs that potently inhibit bone resorption. What is the primary molecular target of the nitrogen-containing agents in this class?

Explanation

Nitrogen-containing bisphosphonates (e.g., zoledronic acid) are the first-line treatment for active Paget's disease. They work by inhibiting farnesyl pyrophosphate synthase within the mevalonate pathway, ultimately leading to osteoclast apoptosis.

Question 85

A 42-year-old male with end-stage renal disease presents with chronic back pain. Radiographs of the lumbar spine demonstrate dense sclerotic bands at the superior and inferior endplates of the vertebral bodies. This "Rugger-Jersey" spine appearance is a hallmark of which condition?

Explanation

The "Rugger-Jersey" spine is characterized by horizontal sclerotic bands adjacent to the vertebral endplates. It is a classic radiographic manifestation of osteosclerosis associated with secondary hyperparathyroidism (renal osteodystrophy).

Question 86

Septic arthritis of the hip in infants is frequently complicated by concurrent osteomyelitis of the proximal femur. What anatomical feature of the infant hip uniquely predisposes to this rapid contiguous spread?

Explanation

In infants, the metaphysis of the proximal femur lies entirely within the joint capsule. Consequently, hematogenous metaphyseal osteomyelitis can easily rupture through the thin cortex directly into the joint, resulting in septic arthritis.

Question 87

A 78-year-old patient with longstanding polyostotic Paget's disease notes rapid enlargement and extreme pain over his right humerus. Radiographs show a destructive lytic lesion with cortical breakthrough

. What is the generally accepted prognosis for this complication?

Explanation

Secondary osteosarcoma occurs in approximately 1% of patients with Paget's disease. It represents a highly aggressive malignancy with a dismal prognosis, typically having a 5-year survival rate of less than 20% despite aggressive intervention.

Question 88

A patient undergoes surgical excision of a large chalky mass over the olecranon bursa

. To optimally preserve the diagnostic crystals for histological examination, which specific processing method must the pathologist utilize?

Explanation

Monosodium urate crystals are water-soluble and will dissolve if placed in routine aqueous formalin. To properly preserve gouty tophi for histologic analysis, the tissue must be fixed in a non-aqueous solution, such as absolute alcohol.

Question 89

Which of the following serum laboratory profiles is most characteristic of PRIMARY hyperparathyroidism?

Explanation

Primary hyperparathyroidism is typically caused by an autonomously functioning parathyroid adenoma. This results in an elevated PTH, which drives hypercalcemia (via bone resorption and renal retention) and hypophosphatemia (via renal phosphate wasting).

Question 90

A 2-week-old premature infant in the neonatal intensive care unit develops an acutely swollen left thigh and holds the hip in a flexed and externally rotated position. In addition to Staphylococcus aureus, which organism is a leading cause of septic coxitis in this age group and requires empirical coverage?

Explanation

In neonates (infants less than 4 weeks old), the most common causative organisms for septic arthritis are Staphylococcus aureus, Group B Streptococcus, and Gram-negative bacilli. Empiric antibiotic therapy must broadly cover these pathogens.

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