Practice Set 11 of 212
This practice set contains high-yield board review questions covering key concepts in Biology, Genetics & Bone Healing. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.
Which of the following statements best describes the mechanism of primary (direct) bone healing?
. It is mediated by cutting cones crossing the fracture site
During secondary fracture healing, the transition from a soft cartilaginous callus to a hard bony callus is primarily mediated by which of the following processes?
. Endochondral ossification
Bone formation occurs primarily via two distinct developmental pathways: endochondral ossification and intramembranous ossification. Which of the following skeletal structures forms exclusively through intramembranous ossification?
. Clavicle
Denosumab is frequently used as a neoadjuvant or primary medical management for unresectable giant cell tumors of bone. What is the precise mechanism of action of this medication?
. Monoclonal antibody against RANK ligand (RANKL)
In the process of endochondral ossification during secondary fracture healing, the cartilaginous callus is ultimately replaced by woven bone. Which of the following transcription factors is considered the master regulator strictly required for hypertrophic chondrocyte differentiation and subsequent vascular invasion in this pathway?
. RUNX2
A 12-year-old boy presents with multiple fractures and recurrent osteomyelitis of the mandible. Radiographs demonstrate diffusely sclerotic bones and a "rugger-jersey" spine. Which cellular defect is the primary cause of this condition?
. Inability of osteoclasts to acidify Howship's lacunae
A newborn infant with 46,XY karyotype but female external genitalia presents with severe bowing of the tibiae and femurs, and respiratory distress. Which genetic mutation is primarily responsible for this disorder?
. SOX9
A neonate presents with failure to thrive, severe anemia, and hepatosplenomegaly. Radiographs reveal a uniform, extreme increase in bone density with a "bone-within-a-bone" appearance in the spine. The pathogenesis of this malignant recessive disorder is primarily due to a defect in:
. Osteoclast function
A 14-year-old female presents with recurrent patellar dislocations, extreme skin hyperextensibility, and fragile tissues that bruise easily. She has wide, atrophic "cigarette paper" scars over her knees and elbows. Which of the following collagen types is most commonly defective in the classic form of this syndrome?
. Type V collagen
. Fibrillin-1
A 9-year-old boy of Ashkenazi Jewish descent presents with chronic bone pain and a pathologic fracture of the distal femur. Radiographs reveal an "Erlenmeyer flask" deformity of the distal femurs. Laboratory tests show anemia, thrombocytopenia, and hepatosplenomegaly. What is the standard medical treatment for the underlying disorder?
. Enzyme replacement therapy with imiglucerase
A 5-year-old boy presents with profound bowing of the legs and short stature. Laboratory evaluation demonstrates normal serum calcium, low serum phosphate, and elevated alkaline phosphatase. Parathyroid hormone (PTH) levels are normal. A mutation in the PHEX gene is confirmed. What is the primary mechanism of hypophosphatemia in this condition?
. Impaired renal tubular reabsorption of phosphate
A 10-month-old infant fed exclusively boiled cow's milk presents with severe irritability, bleeding gums, and pseudoparalysis of the lower extremities. Radiographs of the knee show a dense zone of provisional calcification, a radiolucent band just metaphyseal to it, and a ring of increased density around the epiphysis. The defective biochemical process is:
. Hydroxylation of proline and lysine residues
A 9-year-old boy presents with unusually wide cranial sutures, delayed closure of the fontanelles, and the ability to bring his shoulders together in the midline anteriorly. Which of the following best describes the underlying pathophysiology of his condition?
. Defective intramembranous ossification
A 6-month-old infant is evaluated for failure to thrive, hepatosplenomegaly, and cranial nerve palsies. Radiographs show a generalized, uniform increase in bone density with a "bone-within-a-bone" appearance in the spine. What is the primary cellular defect responsible for this condition?
. Absence of functional osteoclasts
A 30-year-old woman presents with a lytic epiphyseal lesion of the distal femur. Biopsy confirms a Giant Cell Tumor (GCT) of bone. Prior to surgical curettage, she is given neoadjuvant denosumab to consolidate the tumor margins. What is the mechanism of action of this medication?
. Monoclonal antibody that binds to and inhibits RANK ligand (RANKL)
A 5-year-old child presents with frequent bone fractures, cranial nerve palsies, and diffuse osteosclerosis on radiographs. A genetic defect impairing the acidification of the osteoclast resorption pit is suspected. Which of the following enzymes or proteins is most likely deficient?
. Carbonic anhydrase II
Marfan syndrome is now recognized as a defect in the following molecule:
. Fibrillin-1
. Type II collagen
. Type II