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1. General Principles & Basic Science MCQs

Practice Set 560 of 789

This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 11181

Topic: Surgical Anatomy & Approaches

The Kocher-Langenbeck approach for fixation of a posterior wall acetabular fracture places which of the following nervous structures at highest iatrogenic risk during deep dissection and retractor placement?

. Superior gluteal nerve
. Sciatic nerve
. Lateral femoral cutaneous nerve
. Femoral nerve
. Obturator nerve

Correct Answer & Explanation

. Superior gluteal nerve

Explanation

During the Kocher-Langenbeck approach to the posterior column and posterior wall of the acetabulum, the sciatic nerve is at high risk and must be carefully protected. Retractors placed in the greater sciatic notch or excessive traction on the nerve (especially with the hip extended and knee extended) can cause an iatrogenic sciatic nerve palsy. The knee should be flexed and hip extended to relax the nerve during the procedure.

Question 11182

Topic: Biology, Genetics & Bone Healing

Nine months after operative fixation of a midshaft femur fracture, a patient presents with persistent thigh pain. Radiographs demonstrate an atrophic nonunion with a 'pencil-point' appearance of the bone ends and no bridging callus. What principle dictates the surgical management of this condition?

. Improving mechanical stability alone, as the biological environment is highly active
. Surgical debridement, autologous bone grafting to provide biology, and rigid internal fixation
. Exchange nailing with a smaller diameter nail to increase interfragmentary strain
. Pulsed electromagnetic field therapy alone as a non-invasive biological enhancer
. Administration of systemic bisphosphonates to inhibit osteoclast activity at the nonunion site

Correct Answer & Explanation

. Improving mechanical stability alone, as the biological environment is highly active

Explanation

An atrophic nonunion is fundamentally a biological failure. Unlike hypertrophic nonunions, which have adequate biology ('elephant foot' appearance) but lack stability, atrophic nonunions lack both osteogenic potential and stability. Treatment mandates establishing a healthy biological environment (typically via autologous bone grafting, which provides osteoinduction, osteoconduction, and osteogenesis) combined with stable internal fixation.

Question 11183

Topic: 1. General Principles & Basic Science

A 3-year-old girl presents with progressive bowing of her left leg. The standing radiograph is shown:

Which of the following radiographic parameters best differentiates infantile Blount disease from physiologic bowing?

. Metaphyseal-diaphyseal angle > 16 degrees
. Tibiofemoral angle > 15 degrees
. Epiphyseal-metaphyseal angle > 20 degrees
. Valgus alignment of the knee
. Anterior bowing of the tibia

Correct Answer & Explanation

. Metaphyseal-diaphyseal angle > 16 degrees

Explanation

The Levine-Drennan metaphyseal-diaphyseal angle (MDA) is used to differentiate physiologic bowing from infantile tibia vara (Blount disease). An MDA > 16 degrees indicates a high likelihood of progression to true Blount disease, whereas < 10 degrees is typical for physiologic bowing.

Question 11184

Topic: Biology, Genetics & Bone Healing

Intravenous bisphosphonates are a mainstay of medical management for children with moderate to severe Osteogenesis Imperfecta (OI). What is the primary molecular target of nitrogen-containing bisphosphonates?

. Type 1 collagen gene transcription
. Osteoprotegerin activation
. RANK ligand binding
. Farnesyl pyrophosphate synthase in the mevalonate pathway
. Cathepsin K activity

Correct Answer & Explanation

. Type 1 collagen gene transcription

Explanation

Nitrogen-containing bisphosphonates (e.g., pamidronate, zoledronic acid) inhibit farnesyl pyrophosphate (FPP) synthase in the mevalonate pathway. This prevents the prenylation of small GTPases essential for osteoclast function and survival, leading to osteoclast apoptosis and decreased bone resorption.

Question 11185

Topic: Infection, Pharmacology & VTE

In the original Kocher criteria for differentiating pediatric septic arthritis from transient synovitis of the hip, which of the following laboratory/clinical parameters was NOT one of the four factors used?

. White blood cell count > 12,000 cells/mm3
. Erythrocyte sedimentation rate (ESR) > 40 mm/hr
. Temperature > 38.5 degrees Celsius
. Serum C-reactive protein (CRP) > 2.0 mg/dL
. Inability to bear weight

Correct Answer & Explanation

. White blood cell count > 12,000 cells/mm3

Explanation

The original four Kocher criteria are: non-weight bearing, temperature > 38.5 C, ESR > 40 mm/hr, and WBC > 12,000 cells/mm3. CRP > 2.0 mg/dL was later validated and added by Caird et al., creating a 5-factor model, but it was not part of the original 4 criteria.

Question 11186

Topic: Infection, Pharmacology & VTE
A 2-year-old child presents with a limp, fever of 38.5°C, and refusal to bear weight on the left leg. Aspiration of the hip yields purulent fluid. Which of the following organisms is the most common cause of joint infections in this specific age group and often requires specialized culture techniques (e.g., BACTEC blood culture bottles) for detection?
. Staphylococcus aureus
. Kingella kingae
. Streptococcus pneumoniae
. Haemophilus influenzae type b
. Neisseria gonorrhoeae

Correct Answer & Explanation

. Kingella kingae

Explanation

Kingella kingae is a fastidious Gram-negative coccobacillus that has surpassed S. aureus as the most common cause of septic arthritis and osteomyelitis in children under the age of 4. It is notoriously difficult to grow on standard solid media, and its detection rate increases significantly when synovial fluid is inoculated directly into blood culture vials.

Question 11187

Topic: Biology, Genetics & Bone Healing
An 18-month-old boy presents with anterolateral bowing of the tibia and a recent fracture through the apex of the bow that shows no signs of healing. He has multiple café-au-lait spots. What is the most definitive surgical strategy to achieve union in this condition?
. Simple cast immobilization for 12 weeks
. Percutaneous drilling and injection of bone marrow aspirate
. Excision of the pseudarthrosis, placement of an intramedullary rod, and copious autogenous bone grafting
. Open reduction and internal fixation with a dynamic compression plate only
. Amputation below the knee without attempted reconstruction

Correct Answer & Explanation

. Excision of the pseudarthrosis, placement of an intramedullary rod, and copious autogenous bone grafting

Explanation

Congenital pseudarthrosis of the tibia (CPT) is strongly associated with Neurofibromatosis Type 1 (NF1). It is notoriously difficult to heal. Plating alone almost uniformly fails. The standard of care involves excision of the hamartomatous tissue, intramedullary rodding (often spanning the ankle), and robust bone grafting (often utilizing BMP or vascularized fibula grafts).

Question 11188

Topic: Biology, Genetics & Bone Healing
A 4-year-old boy presents with a history of multiple recurrent long bone fractures, blue sclerae, and early hearing loss. Radiographs show osteopenia and multiple healed fractures in various stages of healing. This condition is primarily caused by a genetic mutation affecting the synthesis of which type of collagen?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type I collagen

Explanation

Osteogenesis imperfecta is most commonly caused by mutations in the COL1A1 or COL1A2 genes, leading to defective or deficient Type I collagen. This collagen is the major structural protein in bone, sclerae, and teeth.

Question 11189

Topic: Infection, Pharmacology & VTE
A 5-year-old boy presents with acute right hip pain, inability to bear weight, a temperature of 38.8°C (101.8°F), a WBC count of 14,000/mm³, and an ESR of 55 mm/hr. According to the Kocher criteria, what is the most appropriate next step in management?
. Observation and administration of NSAIDs
. MRI of the bilateral hips with contrast
. Immediate open arthrotomy without aspiration
. Ultrasound-guided hip aspiration
. Bone scan of the lower extremities

Correct Answer & Explanation

. Ultrasound-guided hip aspiration

Explanation

This patient meets all four Kocher criteria (non-weight bearing, fever, ESR > 40, WBC > 12k), predicting a 99% probability of septic arthritis. The next best step is an ultrasound-guided aspiration of the hip to confirm the diagnosis and identify the organism before surgical washout.

Question 11190

Topic: 1. General Principles & Basic Science

A 6-year-old girl presents with a painless "clunking" sound in her lateral knee during flexion and extension. MRI reveals a discoid lateral meniscus. In the Wrisberg variant of a discoid meniscus, which stabilizing anatomical structure is characteristically absent?

. Anterior horn attachment
. Transverse intermeniscal ligament
. Ligament of Wrisberg
. Posterior meniscotibial (coronary) ligament
. Meniscofemoral ligament

Correct Answer & Explanation

. Anterior horn attachment

Explanation

The Wrisberg variant of a discoid meniscus lacks the normal posterior meniscotibial (coronary) ligament attachments. Its only posterior tether is the meniscofemoral ligament (of Wrisberg), resulting in a hypermobile meniscus that snaps during knee motion.

Question 11191

Topic: 1. General Principles & Basic Science

An 8-year-old boy presents with a painless, snapping sensation in his lateral knee during extension. MRI confirms a discoid lateral meniscus. According to the Watanabe classification, which type lacks posterior capsular attachments and is highly hypermobile?

. Incomplete type
. Complete type
. Wrisberg variant
. Ring-shaped variant

Correct Answer & Explanation

. Incomplete type

Explanation

The Wrisberg variant of a discoid meniscus lacks normal posterior meniscotibial attachments (coronary ligaments). It is attached posteriorly only by the meniscofemoral ligament of Wrisberg, leading to hypermobility and a clinical snapping knee.

Question 11192

Topic: Infection, Pharmacology & VTE
A 4-year-old child presents with an acute onset of an inability to bear weight on the right leg, a temperature of 38.8°C, an ESR of 50 mm/hr, and a WBC count of 13,000/mm³. According to the Kocher criteria, what is the probability that this child has septic arthritis of the hip?
. < 10%
. 25-35%
. 50-60%
. 70-80%
. > 90%

Correct Answer & Explanation

. > 90%

Explanation

This patient meets all four Kocher criteria: non-weight bearing, temperature >38.5°C, ESR >40 mm/hr, and WBC >12,000/mm³. The presence of all four criteria correlates with a 99% predictive probability of septic arthritis.

Question 11193

Topic: Biology, Genetics & Bone Healing

A 5-year-old boy with a history of multiple low-energy fractures, blue sclerae, and dentinogenesis imperfecta is treated with intravenous bisphosphonates. What is the primary mechanism of action of this medication in treating his condition?

. Stimulating osteoblast proliferation
. Inhibiting osteoclast-mediated bone resorption
. Increasing renal calcium reabsorption
. Enhancing intestinal calcium absorption
. Promoting type I collagen synthesis

Correct Answer & Explanation

. Stimulating osteoblast proliferation

Explanation

Osteogenesis imperfecta is a genetic defect in type I collagen. Bisphosphonates do not correct the collagen defect but inhibit osteoclast-mediated bone resorption, increasing overall bone density and decreasing the incidence of fractures.

Question 11194

Topic: 1. General Principles & Basic Science

A surgeon is planning a posterior C1-C2 fusion using transarticular screws. Preoperative CTA is obtained to evaluate the vertebral artery. Anatomically, the vertebral artery typically enters the transverse foramen at which cervical level, and what percentage of the population has an anomalous entry?

. C7; anomalous in 5%
. C6; anomalous in 5-10%
. C5; anomalous in 20%
. C4; anomalous in 15%
. C2; anomalous in 1%

Correct Answer & Explanation

. C7; anomalous in 5%

Explanation

The vertebral artery typically arises from the subclavian artery and enters the transverse foramen of C6 in about 90-95% of individuals. In 5-10% of people, it has an anomalous entry, most commonly entering higher up at C5, C4, or occasionally C7.

Question 11195

Topic: Surgical Anatomy & Approaches

A 30-year-old bodybuilder presents with poorly localized posterior shoulder pain and paresthesias over the lateral deltoid. He is diagnosed with quadrilateral space syndrome. Which vascular structure passes through this anatomical space alongside the axillary nerve?

. Anterior circumflex humeral artery
. Posterior circumflex humeral artery
. Circumflex scapular artery
. Profunda brachii artery
. Suprascapular artery

Correct Answer & Explanation

. Anterior circumflex humeral artery

Explanation

The quadrilateral space is bordered by the teres minor (superior), teres major (inferior), long head of the triceps (medial), and surgical neck of the humerus (lateral). It transmits the axillary nerve and the posterior circumflex humeral artery.

Question 11196

Topic: Surgical Anatomy & Approaches

During the anterior intrapelvic (modified Stoppa) approach for an acetabular fracture, an aberrant vascular anastomosis known as the 'corona mortis' is encountered draped over the superior pubic ramus. This vessel represents an anastomosis between the obturator vessels and which of the following?

. Internal iliac vessels
. Superior gluteal vessels
. External iliac or deep inferior epigastric vessels
. Internal pudendal vessels
. Femoral vessels

Correct Answer & Explanation

. Internal iliac vessels

Explanation

The corona mortis ('crown of death') is a vascular anastomosis between the external iliac system (specifically the deep inferior epigastric artery/vein or the external iliac itself) and the obturator system. It crosses over the superior pubic ramus and is highly susceptible to iatrogenic injury.

Question 11197

Topic: Surgical Anatomy & Approaches

A 35-year-old male sustains a spiral fracture of the middle third of the humerus (Holstein-Lewis fracture). He presents with a wrist drop. The radial nerve is closely associated with the posterior humerus. Approximately how far proximal to the lateral epicondyle does the radial nerve pierce the lateral intermuscular septum to enter the anterior compartment of the arm?

. 5 cm
. 10 cm
. 15 cm
. 20 cm
. 2 cm

Correct Answer & Explanation

. 5 cm

Explanation

The radial nerve runs in the spiral groove of the posterior humerus and pierces the lateral intermuscular septum to enter the anterior compartment approximately 10 cm (range, 10-12 cm) proximal to the lateral epicondyle. This anatomical landmark is crucial during surgical approaches to the humerus.

Question 11198

Topic: Surgical Anatomy & Approaches

A patient presents with classic signs of piriformis syndrome, including buttock pain and sciatic radiculopathy that worsens with prolonged sitting. Anatomical variations in the relationship between the sciatic nerve and the piriformis muscle can predispose to this condition. According to Beaton and Anson classification, what is the most common variant (excluding the normal anatomy)?

. The entire sciatic nerve passes superior to the piriformis.
. The entire sciatic nerve pierces the piriformis belly.
. The common peroneal division pierces the piriformis, and the tibial division passes inferiorly.
. The common peroneal division passes superior to the piriformis, and the tibial division passes inferiorly.
. The tibial division pierces the piriformis, and the common peroneal division passes superiorly.

Correct Answer & Explanation

. The entire sciatic nerve passes superior to the piriformis.

Explanation

Normally (Type A, ~85%), the entire sciatic nerve exits the greater sciatic foramen inferior to the piriformis muscle. The most common variation (Type B, ~10%) occurs when the common peroneal nerve division pierces the piriformis muscle, while the tibial division passes inferior to it.

Question 11199

Topic: Surgical Anatomy & Approaches

A spine surgeon is performing a lateral lumbar interbody fusion (LLIF) at L4-L5. The retractor must be passed through the psoas major muscle. Which of the following best describes the anatomical location of the lumbar plexus, specifically the femoral nerve, within the psoas major at the L4-L5 disc space level?

. Anterior third of the psoas muscle
. Middle third of the psoas muscle
. Posterior third of the psoas muscle
. It lies entirely anterior to the psoas fascia
. It passes entirely medial to the psoas muscle alongside the aorta

Correct Answer & Explanation

. Anterior third of the psoas muscle

Explanation

As the lumbar plexus descends, its nerves migrate from medial to lateral and from anterior to posterior within the psoas major muscle. At the L4-L5 disc space, the femoral nerve is generally located in the posterior third of the psoas major, making the anterior/middle aspect the safest zone for retractor placement during lateral transpsoas approaches.

Question 11200

Topic: Surgical Anatomy & Approaches

In the ilioinguinal approach to the acetabulum, three distinct 'windows' are utilized for access. Which of the following anatomic structures must be incised to gain access to the true pelvis and strictly divides the lateral window from the middle window?

. Inguinal ligament
. Conjoint tendon
. Iliopectineal fascia
. Rectus sheath
. Transversalis fascia

Correct Answer & Explanation

. Inguinal ligament

Explanation

The iliopectineal fascia separates the lateral window (containing the iliacus and the iliopsoas muscle with the femoral nerve) from the middle window (containing the external iliac vessels). Incising the iliopectineal fascia down to the pelvic brim is a critical step in the ilioinguinal approach to allow access to the true pelvis and the quadrilateral plate.

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