1. General Principles & Basic Science MCQs

Differentiating between acute Charcot arthropathy and osteomyelitis in a diabetic foot can be challenging. Which of the following imaging modalities or combinations provides the highest specificity for diagnosing superimposed osteomyelitis in a patient with an active midfoot Charcot joint?

The pathogenesis of Charcot neuroarthropathy is multifactorial, involving both neurotraumatic and neurovascular pathways. Which of the following best describes the neurovascular theory (French theory) of this disease?

Which radiographic feature is most characteristic for differentiating primary synovial chondromatosis from secondary synovial chondromatosis?

According to the neurovascular theory of Charcot arthropathy, which mechanism directly contributes to bone resorption and subsequent joint destruction?

Differentiating between acute Charcot neuroarthropathy and osteomyelitis in a diabetic foot can be challenging. Which of the following MRI findings is most specific for diagnosing osteomyelitis over acute Charcot arthropathy?

A 72-year-old man presents with severe back pain. Radiographs reveal multiple osteoblastic lesions in the lumbar spine and pelvis. Laboratory studies show elevated alkaline phosphatase. Which of the following pathophysiologic mechanisms best explains the osteoblastic nature of these specific metastatic bone lesions?

A 38-year-old woman undergoes arthroscopic removal of dozens of uniformly sized cartilaginous loose bodies from her knee for primary synovial chondromatosis. To minimize the risk of disease recurrence, which of the following additional intraoperative steps is strictly indicated?

A biopsy of a ground-glass rib lesion in a 14-year-old boy reveals fibrous stroma with irregular, woven bone trabeculae lacking osteoblastic rimming. The pathogenesis of this disease is linked to a somatic mutation leading to the substitution of arginine by histidine or cysteine. Which signaling pathway is directly upregulated by this mutation?

A 5-year-old boy presents with progressively worsening varus deformity of both knees. Lab work shows low serum phosphate, normal serum calcium, and elevated alkaline phosphatase. Genetic testing reveals a PHEX gene mutation. Which of the following laboratory values is also expected?

A 2-year-old boy presents with refusal to bear weight on the right leg and low-grade fever. Blood work shows a normal WBC count and mildly elevated CRP. Joint aspiration shows 45,000 WBCs. If the pathogen is a fastidious Gram-negative coccobacillus, what is the optimal method for isolation?

A 10-year-old boy presents with delayed eruption of secondary teeth and the ability to approximate his shoulders in the midline anteriorly. Radiographs demonstrate absent clavicles and delayed closure of cranial sutures. What bone formation process is primarily impaired in this condition?

A 7-year-old girl with a history of daily spiking fevers, an evanescent salmon-pink rash, and polyarthritis now presents with sudden onset lethargy, mucosal bleeding, and hepatosplenomegaly. Labs reveal profound thrombocytopenia, elevated ferritin, and low fibrinogen. What is the most likely life-threatening complication?

A 70-year-old man develops a chronic infection around his total hip arthroplasty, and cultures grow Staphylococcus epidermidis. Which phase of biofilm formation is characterized by the production of an extracellular polymeric substance (EPS) that creates a physical barrier against antibiotics?

A newborn is evaluated for severe micromelic dwarfism, bilateral rigid clubfeet, "hitchhiker" thumbs, and cystic swelling of the pinnae. The genetic mutation responsible for this condition directly affects which of the following cellular processes?

A 12-year-old girl presents with retained deciduous teeth and an ability to bring her shoulders together in the midline anteriorly. Radiographs demonstrate absent clavicles and delayed pubic symphysis ossification. The defective gene in this condition is an essential transcription factor for which of the following?

A 4-year-old boy has progressive varus bowing of his legs. Lab testing shows low serum phosphate, normal calcium, normal PTH, normal vitamin D, and elevated FGF23 levels. What monoclonal antibody therapy directly targets the underlying pathophysiology of this condition?

A 14-month-old exclusively breastfed infant develops widening of the wrists and bowing of the distal femurs. Laboratory evaluation reveals significantly elevated parathyroid hormone (PTH) and alkaline phosphatase. Which of the following serum calcium and phosphate profiles is most consistent with this diagnosis?

A 2-year-old boy presents with a 3-day history of right knee swelling, limp, and low-grade fever. Synovial fluid aspiration shows a WBC count of 65,000/microL. Routine cultures at 48 hours are negative. Which of the following is the most likely causative organism and the best method for its detection?

A 6-month-old infant is brought to the emergency department for irritability and refusal to move the left leg. Ultrasound reveals a left hip effusion. Which of the following features most strongly dictates the need for immediate surgical drainage of the hip joint?

A 7-year-old girl from Connecticut presents with a massive right knee effusion. Surprisingly, she bears weight with a minimal limp and has only mild discomfort with range of motion. Joint aspiration reveals 40,000 WBCs/microL with 80% neutrophils. What is the most appropriate next step in management?