1. General Principles & Basic Science MCQs

A 10-year-old girl complains of severe, aching pain in her lower legs and increasing difficulty walking. Physical exam shows a wide-based waddling gait and a marked reduction in muscle mass. Radiographs demonstrate symmetric, bilateral cortical thickening of the diaphyseal regions of her femurs and tibias, sparing the metaphyses and epiphyses. Which gene is most likely mutated?

A neonate is born with severe respiratory distress, marked bowing of the tibiae with overlying skin dimples, and hypoplastic scapulae. Chromosomal analysis reveals a 46,XY karyotype, but the genitalia are phenotypically female (sex reversal). Which transcription factor is mutated in this frequently lethal dysplasia?

A 45-year-old man presents with chronic pain and stiffness in his right leg. Radiographs display irregular, dense, hyperostotic cortical bone extending along one side of the femur and tibia, resembling 'dripping candle wax'. The distribution of these lesions characteristically follows which of the following anatomical patterns?

A 10-year-old boy with a known skeletal dysplasia develops progressive, massive hyperplastic callus formation following a closed femur fracture. Radiographs also demonstrate calcification of the interosseous membranes of the forearms. What is the inheritance pattern and associated gene mutation for this specific dysplasia?

A neonate is evaluated in the NICU for micromelic short stature, severe rigid equinovarus foot deformities, and "hitchhiker" thumbs. Physical examination also reveals cystic swelling of the external ears. The genetic defect responsible for this condition affects which of the following physiological processes?

A 12-year-old girl is evaluated for a prominent forehead, hypertelorism, and delayed eruption of permanent teeth. On physical examination, she is able to approximate her shoulders anteriorly in the midline. Which of the following best describes the underlying molecular defect in this condition?

A 14-year-old boy sustains a transverse subtrochanteric femur fracture after a minor fall. Radiographs show diffusely dense, chalk-like bones with a loss of corticomedullary differentiation and a "bone-within-bone" appearance. He has a history of mild anemia and hearing loss. What is the primary cellular dysfunction resulting in this skeletal phenotype?

A neonate is born with severe respiratory distress, shortened and anterolaterally bowed tibiae with skin dimpling over the apex of the bow, and ambiguous genitalia. Chromosomal analysis reveals a 46,XY karyotype despite phenotypic female external genitalia. The mutated gene in this syndrome is crucial for which of the following processes?

A 35-year-old woman with an untreated Chiari I malformation and large cervical syringomyelia presents with rapid, painless swelling of her right shoulder, accompanied by a 'crunching' sensation during movement. Radiographs reveal severe destruction of the humeral head and glenoid with loose osseous debris. What is the underlying pathophysiology of this joint destruction?

A 10-year-old boy presents to the clinic with an isolated finding of diminished abdominal reflexes and mild hyperreflexia in the lower extremities. Further workup reveals a cervical syringomyelia. The presence of hyperreflexia in the lower extremities indicates that the syrinx has expanded to compress which structure?

In a patient diagnosed with chondroblastoma of the proximal humerus, what specific histological feature is considered pathognomonic for this lesion?

Which physical examination finding is classically associated with the expanding central cord lesion seen in advanced syringomyelia?

While chondroblastomas classically occur in the epiphysis of long bones, they can also arise in apophyseal equivalents. Which of the following is the most common apophyseal location for a chondroblastoma?

Due to a local recurrence rate of 10-20% following simple curettage of a chondroblastoma, modern surgical management routinely incorporates an extended curettage. Which of the following combinations is typically utilized in the surgical bed?

A 28-year-old male with a known cervical syrinx presents with painless burns on his hands. He has normal light touch and proprioception bilaterally. The pathophysiology of his isolated sensory deficit is due to compression of which specific spinal cord structure?

A 5-year-old girl with short-limbed dwarfism is noted to have fine, sparse, light-colored hair. Radiographs show metaphyseal flaring and irregularity. She has a history of recurrent severe respiratory infections. Which of the following is the most critical systemic manifestation to screen for in this patient?

A 3-year-old boy presents with short stature and metaphyseal dysplasia. His medical history is significant for chronic diarrhea, failure to thrive, and recurrent bacterial infections. Complete blood count reveals absolute neutropenia. Which of the following is the most likely diagnosis?

A 6-year-old child presents with bowing of the legs and a waddling gait. Radiographs show widened physes and cupped, frayed metaphyses. Laboratory investigations reveal normal serum calcium, phosphorus, alkaline phosphatase, and Vitamin D levels. Which of the following is the most appropriate next step in management?