1. General Principles & Basic Science MCQs

A 10-year-old boy presents to the orthopedic clinic with a wide waddling gait and the unusual ability to appose his shoulders anteriorly across his chest. Radiographs show widening of the symphysis pubis and coxa vara. Which transcription factor is primarily mutated in this syndrome?

An infant presents with failure to thrive, hepatosplenomegaly, and severe anemia. Radiographs demonstrate diffusely dense bones with a "bone-within-a-bone" appearance and loss of medullary canals. Which of the following represents the primary cellular mechanism defective in this severe condition?

A newborn presents with severe respiratory distress, shortened and anteriorly bowed lower extremities, and skin dimpling over the tibial bows. Karyotype analysis reveals a 46,XY genotype, but the external genitalia appear female. A mutation in which of the following genes is the definitive cause?

A 9-year-old boy presents with severe knock-knees, platyspondyly, and corneal clouding. Laboratory tests reveal increased urinary excretion of keratan sulfate. This patient's condition is an autosomal recessive lysosomal storage disease caused by a deficiency in which enzyme?

A 10-year-old boy with blue sclerae, dentinogenesis imperfecta, and multiple prior fractures is scheduled for rodding of his tibiae. His condition is caused by a dominant mutation in COL1A1. Which of the following best describes the fundamental defect in his bone collagen?

A 4-year-old boy presents with short stature, waddling gait, and progressive bowing of the lower extremities. Laboratory studies demonstrate normal calcium, phosphorus, and alkaline phosphatase levels. Radiographs show coxa vara and flared, irregular metaphyses, but the epiphyses are normal. A defect in which collagen type is most likely responsible?

A 5-year-old child presents with recurrent fractures, severe anemia, and hepatosplenomegaly. Radiographs exhibit a generalized increased bone density with a classic "bone-within-bone" appearance. What is the primary cellular defect responsible for this condition?

A 10-year-old boy presents to the orthopedic clinic with the ability to touch his shoulders together anteriorly across his chest. Examination reveals delayed closure of the fontanelles and multiple supernumerary teeth. Which transcription factor is mutated in this condition?

A 5-year-old boy presents with normal intelligence, corneal clouding, genu valgum, and a prominent pectus carinatum. Urine spot tests show elevated keratan sulfate. Deficiency of which of the following enzymes is the cause of this syndrome?

A newborn with phenotypic female genitalia is found to have a 46,XY karyotype. The infant exhibits marked anterolateral bowing of the tibiae and femora, hypoplastic scapulae, and severe respiratory distress. A mutation in which gene is responsible for this condition?

A 4-year-old child presents with short stature, severe bowing of the legs, and a waddling gait. Radiographs demonstrate flaring and irregularity of the metaphyses with widened physes mimicking rickets, but serum calcium and phosphorus are normal. Mutation in the gene encoding which collagen type is responsible?

A 12-year-old girl presents with a chronic limp and mild thigh pain. Radiographs reveal a ground-glass expansile lesion in the proximal femur with a characteristic shepherd's crook deformity. What is the underlying molecular pathogenesis of this condition?

The neurovascular theory of Charcot arthropathy suggests that autonomic neuropathy leads to which of the following physiological changes?

Fibrous dysplasia is caused by a somatic activating mutation in which of the following genes?

Which imaging modality or technique is most specific for differentiating an acute Charcot neuroarthropathy from pedal osteomyelitis in a diabetic foot with an overlying ulcer?

Which pharmacological agent has shown efficacy in reducing bone pain and potentially decreasing the rate of abnormal bone turnover in patients with polyostotic fibrous dysplasia?

A 72-year-old male presents with severe back pain. Radiographs show multiple dense, blastic lesions in the lumbar spine and pelvis.

Which of the following combinations of tumor marker and primary cellular mechanism is characteristic of this malignancy?

Which of the following best describes the underlying molecular pathophysiology of fibrous dysplasia?

A 55-year-old female with a history of breast cancer presents with severe thoracic back pain. Imaging demonstrates a blastic and lytic lesion at T8 with posterior element involvement but no spinal cord compression. In addition to localized radiation, what pharmacological agent is indicated to reduce skeletal-related events?