1. General Principles & Basic Science MCQs

A patient presents with a swollen, painful right knee. Aspiration reveals 80,000 WBC/mcL with 90% neutrophils. Gram stain is negative. The patient recently completed oral antibiotics for a presumed skin infection. The surgeon performs arthroscopic irrigation and debridement. Which component of the biofilm matrix is primarily responsible for protecting residual bacteria from antibiotic penetration?

An 8-year-old child presents with multiple fractures and disproportionate short stature. Radiographs show a "bone within a bone" appearance in the spine and Erlenmeyer flask deformities of the distal femora. Labs reveal severe anemia and thrombocytopenia. What is the most likely defective mechanism?

A 55-year-old woman is evaluated for atraumatic osteolysis of the distal clavicle and diffuse joint pains. Laboratory results show markedly elevated serum calcium, low phosphorus, and elevated parathyroid hormone (PTH) levels. Dual-energy X-ray absorptiometry (DEXA) reveals severe cortical bone loss. What is the primary skeletal manifestation of this disease?

A 5-year-old boy presents with progressive limb bowing, waddling gait, and premature loss of primary teeth. Laboratory testing shows hypercalcemia, normal parathyroid hormone, and markedly low serum alkaline phosphatase. Elevated levels of urine phosphoethanolamine are noted. What is the most likely diagnosis?

A 65-year-old man presents with progressive bowing of his right tibia and dull, aching bone pain. Labs show isolated markedly elevated alkaline phosphatase with normal calcium and phosphorus. Radiographs reveal cortical thickening and coarsened trabeculae. What is the primary cellular pathophysiology initiating this disease process?

A 12-year-old boy is evaluated for retained deciduous teeth and an unusual ability to bring his shoulders together anteriorly. Radiographs demonstrate a widened symphysis pubis and hypoplastic clavicles. The mutated gene responsible for this condition primarily affects which of the following cellular processes?

A 4-year-old boy presents with a femur fracture after a minor fall. His medical history is significant for severe anemia, hepatosplenomegaly, and bilateral hearing loss. Radiographs reveal diffusely sclerotic bones with absent medullary canals and an "Erlenmeyer flask" deformity of the distal femora. What is the fundamental cellular defect in this condition?

A 45-year-old immigrant presents with months of insidious midthoracic back pain, low-grade fevers, and progressive lower extremity weakness. MRI demonstrates destruction of the T8 and T9 vertebral bodies with relative early sparing of the intervertebral disc, along with a large paraspinal abscess. What is the most characteristic histopathologic finding of the causative organism's infection?

A 3-year-old boy with autism spectrum disorder and a highly restricted diet presents with refusal to walk, irritability, and swollen, bleeding gums. Radiographs of the lower extremities reveal a dense zone of provisional calcification, a radiolucent band directly metaphyseal to it, and marginal spurring. The patient's condition is caused by a deficiency in a co-factor required for which of the following biochemical steps?

A 35-year-old male sustained a severe traumatic brain injury 8 months ago and developed massive heterotopic ossification around his right hip. Which of the following is considered the most reliable radiographic indicator of heterotopic ossification maturity prior to surgical excision?

A 5-year-old boy presents with short trunk dwarfism, a barrel chest, a waddling gait, and high myopia. Radiographs show delayed ossification of the femoral heads and flattening of the vertebral bodies. A mutation in which collagen type is associated with this condition?

A 12-year-old girl is noted to have excessive mobility of her shoulders, allowing her to touch them together anteriorly. Radiographs show hypoplastic clavicles and delayed closure of the cranial sutures. What transcription factor is mutated in this disorder?

A 45-year-old female presents with progressive osteolysis of her left hemipelvis and proximal femur, diagnosed as Gorham-Stout disease.

Alongside surgical stabilization, which pharmacological agent has shown the most efficacy in slowing the osteolytic process?

A 12-year-old boy presents with delayed tooth eruption, hypermobility of the shoulders allowing them to meet in the midline, and a wide, flat skull. Which transcription factor is mutated in this condition?

A 32-year-old male with confirmed Gorham-Stout disease of the left femur is experiencing progressive, massive osteolysis despite conservative care.

Which of the following medical treatments has shown efficacy in slowing the osteolytic process in this disease?

A 4-year-old child presents with short stature, bowlegs, and a waddling gait. Radiographs reveal flared, irregular metaphyses but normal epiphyses and spine. Laboratory studies show normal calcium, phosphorus, and alkaline phosphatase. Which collagen gene is typically mutated?

A 5-year-old male presents with short trunk dwarfism, a barrel chest, and coxa vara. He has normal intelligence and normal-sized hands and feet. Radiographs show flattened vertebral bodies and delayed ossification of the epiphyses. Which structure's underlying defect is responsible for this condition?

What is the primary histological feature driving the massive osteolysis seen in Gorham-Stout disease?

A 15-year-old male presents with progressive osteolysis of his clavicle and ribs consistent with Gorham's disease. What is the most common life-threatening complication associated with this specific anatomic involvement?

A 24-year-old patient presents with genu valgum. Radiographs reveal widening of the metaphyses of the long bones, yielding an 'Erlenmeyer flask' deformity, while the diaphyses are of normal thickness. Which of the following is true regarding this condition?