1. General Principles & Basic Science MCQs

Which of the following is the primary mechanism of action for the class of medications most commonly used to reduce fracture risk in pediatric patients with Osteogenesis Imperfecta?

A newborn presents with delayed closure of the cranial sutures, wormian bones, and absent clavicles. What gene mutation is associated with this syndrome?

A newborn presents with short-limbed dwarfism, bilateral rigid clubfeet, "hitchhiker" thumbs, and cystic swelling of the pinnae. What is the primary pathophysiologic defect in this condition?

A 7-year-old girl is evaluated for delayed dental eruption and abnormal shoulder mobility, allowing her to touch her shoulders together anteriorly. Radiographs show absent clavicles and delayed closure of cranial sutures. What is the mutated gene responsible for this condition?

A 4-year-old child with recurrent fractures, blue sclerae, and dentinogenesis imperfecta is treated with intravenous pamidronate. What is the primary mechanism of action of this medication in treating this condition?

A 2-week-old neonate presents with asymmetric skin folds, pseudoparalysis of the right leg, and pain with passive hip motion.

Ultrasound confirms a large joint effusion consistent with septic arthritis. Which pathogen is most uniquely common in this specific age group compared to older children?

A 7-year-old boy with blue sclerae, dentinogenesis imperfecta, and multiple prior fractures is started on intravenous pamidronate. What is the primary mechanism of action of this medication in the treatment of Osteogenesis Imperfecta?

A patient presents with absent clavicles, delayed closure of cranial sutures, and supernumerary teeth. Which transcription factor is primarily mutated in this syndrome?

A 4-week-old infant was diagnosed with neonatal septic arthritis of the hip. Treatment was delayed for several days prior to surgical drainage. A follow-up radiograph one year later shows complete absence of the proximal femoral epiphysis and neck.

This severe structural loss is primarily the result of which of the following pathophysiologic mechanisms?

A 22-year-old man presents with chronic, non-mechanical lower back pain. Imaging shows an expansile 3 cm lytic lesion of the L4 pedicle. A biopsy is performed, and the photomicrograph is shown below.

Which of the following features is most characteristic of this lesion's microscopic appearance?

In the surgical treatment of neonatal septic arthritis of the hip, an anterior approach (Smith-Petersen) is often preferred for open arthrotomy and drainage. Which internervous plane is utilized in this surgical approach?

A 58-year-old male is undergoing a primary total hip arthroplasty via a direct anterior approach. During the superficial dissection, the surgeon develops the internervous plane and encounters a leash of vessels crossing the surgical field transversely, which requires ligation. These vessels primarily provide the blood supply to which of the following muscles?

A 65-year-old female presents with thigh pain 15 years after a primary total hip arthroplasty. Radiographs demonstrate a well-fixed femoral stem with a large, eccentric, scalloped radiolucent lesion in the greater trochanter and proximal diaphysis. Which of the following cell types is primarily responsible for phagocytosing the particulate debris and initiating the biological cascade that leads to this radiographic finding?

The manufacturing process of highly cross-linked polyethylene (HXLPE) involves irradiation to induce cross-linking, which significantly reduces adhesive and abrasive wear. However, this process generates free radicals. Which of the following thermal treatments is subsequently performed to completely eliminate these free radicals, and what is its primary biomechanical trade-off?

A surgeon is performing a primary total hip arthroplasty via the direct anterior approach. During the deep dissection, an internervous plane is utilized to expose the hip capsule. Which of the following accurately describes the innervation of the muscles defining this deep plane?

A surgeon is performing a primary total hip arthroplasty utilizing the direct anterior approach. The superficial internervous plane is developed between the tensor fasciae latae and the sartorius. During this superficial dissection, which of the following nerves is at greatest risk of iatrogenic injury, and what is its primary sensory distribution?

A 55-year-old female is undergoing a total hip arthroplasty via the direct anterior approach. The surgeon develops the internervous plane between the tensor fasciae latae and the sartorius. During the superficial dissection, a nerve is at risk of iatrogenic injury. Which of the following describes the typical anatomic course of the nerve most at risk?

A 62-year-old male presents with new-onset groin pain 7 years after a primary total hip arthroplasty. Operative records indicate he received an uncemented titanium stem, a 36-mm cobalt-chromium femoral head, and a highly cross-linked polyethylene liner. Serum metal ion testing reveals an elevated cobalt level of 8.5 ppb and a normal chromium level of 0.5 ppb. Aspiration is negative for infection. What is the most likely source of the elevated metal ions?

A surgeon is performing a primary total hip arthroplasty via the direct anterior (Smith-Petersen) approach. The internervous plane utilized for the superficial dissection is between muscles innervated by which of the following nerves?