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1. General Principles & Basic Science MCQs

Practice Set 615 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 12281

Topic: Surgical Anatomy & Approaches

During an ilioinguinal approach for an anterior column acetabular fracture, significant hemorrhage occurs while dissecting near the superior pubic ramus. This bleeding is most likely from an anastomosis between which two vascular systems?

. Internal pudendal and external iliac
. Obturator and internal iliac
. External iliac and obturator
. Inferior epigastric and superficial circumflex iliac
. Superior gluteal and inferior gluteal

Correct Answer & Explanation

. Internal pudendal and external iliac

Explanation

The corona mortis is a vascular anastomosis between the external iliac (or inferior epigastric) and obturator systems. It is located on the posterior aspect of the superior pubic ramus and must be identified and ligated during ilioinguinal or Stoppa approaches.

Question 12282

Topic: Surgical Anatomy & Approaches

The Kocher approach to the radial head utilizes a true internervous plane. Which two muscles define this plane, and what are their respective innervations?

. Brachioradialis (radial n.) and Pronator teres (median n.)
. Anconeus (radial n.) and Extensor carpi ulnaris (posterior interosseous n.)
. Extensor digitorum communis (PIN) and Extensor carpi radialis brevis (radial n.)
. Flexor carpi ulnaris (ulnar n.) and Extensor carpi ulnaris (PIN)
. Triceps (radial n.) and Brachialis (musculocutaneous n.)

Correct Answer & Explanation

. Brachioradialis (radial n.) and Pronator teres (median n.)

Explanation

The Kocher approach exploits the internervous plane between the anconeus (innervated by the radial nerve) and the extensor carpi ulnaris (innervated by the posterior interosseous nerve). Distal extension is limited by the risk of injuring the PIN as it wraps around the radial neck.

Question 12283

Topic: Surgical Anatomy & Approaches

In an anterolateral approach to the distal third of the humerus, the brachialis muscle is typically split longitudinally. Why is this considered an anatomically safe maneuver?

. It has a dual blood supply from the brachial and deep brachial arteries
. It receives dual innervation from the musculocutaneous (medial) and radial (lateral) nerves
. It is innervated solely by the radial nerve, which is protected laterally
. The medial half is avascular and safe to divide
. It lacks a functional role in elbow flexion

Correct Answer & Explanation

. It has a dual blood supply from the brachial and deep brachial arteries

Explanation

The brachialis receives dual innervation; the medial portion is supplied by the musculocutaneous nerve, and the lateral portion by the radial nerve. Splitting the muscle longitudinally in its midline denervates neither half and safely protects the radial nerve laterally.

Question 12284

Topic: Surgical Anatomy & Approaches

When performing an anterolateral approach to the distal tibia and ankle joint, the internervous plane lies between the extensor digitorum longus (EDL) and the peroneus tertius. Which sensory nerve branch routinely crosses this field and must be protected?

. Sural nerve
. Deep peroneal nerve
. Intermediate dorsal cutaneous branch of the superficial peroneal nerve
. Medial dorsal cutaneous branch of the superficial peroneal nerve
. Saphenous nerve

Correct Answer & Explanation

. Sural nerve

Explanation

The intermediate dorsal cutaneous branch of the superficial peroneal nerve crosses the surgical field from medial to lateral in the distal leg and ankle. It is at significant risk during the anterolateral approach to the ankle and must be directly visualized.

Question 12285

Topic: Surgical Anatomy & Approaches

During a Kocher-Langenbeck approach to the acetabulum, the short external rotators are detached. Preserving the obturator externus tendon serves primarily to protect which vital structure?

. Sciatic nerve
. Pudendal nerve
. Medial femoral circumflex artery
. Inferior gluteal artery
. Superior gluteal nerve

Correct Answer & Explanation

. Sciatic nerve

Explanation

The medial femoral circumflex artery (MFCA) provides the primary blood supply to the femoral head and courses posterior to the obturator externus. Protecting the obturator externus helps shield the MFCA main branch from iatrogenic transection.

Question 12286

Topic: Surgical Anatomy & Approaches

The Smith-Petersen approach to the hip utilizes the internervous plane between the sartorius and the tensor fasciae latae (TFL). Which structure lies within the proximal portion of this interval and must be protected during superficial dissection?

. Femoral nerve
. Lateral femoral cutaneous nerve
. Obturator nerve
. Profunda femoris artery
. Sciatic nerve

Correct Answer & Explanation

. Femoral nerve

Explanation

The lateral femoral cutaneous nerve emerges near the anterior superior iliac spine (ASIS) and courses over or through the sartorius muscle. It is highly susceptible to stretching or transection during the proximal dissection of the Smith-Petersen approach.

Question 12287

Topic: Surgical Anatomy & Approaches

The posterior approach to the shoulder uses an internervous plane between the infraspinatus and teres minor. Which two nerves supply these muscles, respectively?

. Suprascapular nerve and Axillary nerve
. Axillary nerve and Radial nerve
. Suprascapular nerve and Subscapular nerve
. Musculocutaneous nerve and Axillary nerve
. Spinal accessory nerve and Suprascapular nerve

Correct Answer & Explanation

. Suprascapular nerve and Axillary nerve

Explanation

The infraspinatus is innervated by the suprascapular nerve, while the teres minor is innervated by the axillary nerve. This creates a true and safe internervous plane for accessing the posterior glenohumeral joint.

Question 12288

Topic: Infection, Pharmacology & VTE
A 5-year-old boy presents with a 3-day history of right hip pain, refusal to bear weight, a temperature of 38.8°C, and an ESR of 55 mm/hr. Joint aspiration yields synovial fluid with a WBC count of 85,000/mm3 (>90% PMNs). After surgical irrigation and debridement, what is the most appropriate empirical intravenous antibiotic therapy pending culture results in an area with a 20% rate of community-acquired MRSA?
. Cefazolin monotherapy
. Ceftriaxone and Clindamycin
. Ampicillin and Gentamicin
. Vancomycin or Clindamycin
. Oral Amoxicillin-Clavulanate

Correct Answer & Explanation

. Vancomycin or Clindamycin

Explanation

Staphylococcus aureus is the most common cause of septic arthritis in children >3 months. Empirical therapy must target S. aureus. In areas where community-acquired MRSA prevalence exceeds 10-15%, anti-MRSA coverage such as Clindamycin or Vancomycin should be utilized as the first-line empiric agent pending culture sensitivities.

Question 12289

Topic: Infection, Pharmacology & VTE

The Kocher criteria are used to differentiate pediatric septic arthritis from transient synovitis. Which additional laboratory marker was later added by Caird et al. to increase the predictive value of the original criteria?

. Procalcitonin > 0.5 ng/mL
. C-reactive protein (CRP) > 2.0 mg/dL
. D-dimer > 500 ng/mL
. Interleukin-6 > 10 pg/mL
. Lactate dehydrogenase (LDH) > 250 U/L

Correct Answer & Explanation

. Procalcitonin > 0.5 ng/mL

Explanation

Caird et al. added CRP > 2.0 mg/dL to the original four Kocher criteria (fever, non-weight-bearing, ESR > 40, WBC > 12,000). The presence of all five parameters predicts a >97% probability of septic arthritis.

Question 12290

Topic: 1. General Principles & Basic Science

A 6-year-old boy presents with painless snapping and popping in the lateral aspect of his knee. MRI reveals a discoid lateral meniscus that lacks normal posterior capsular attachments (coronary ligaments) and is attached only by the meniscofemoral ligament. What is this variant called?

. Incomplete variant
. Complete variant
. Wrisberg variant
. Bucket-handle variant
. Cleland variant

Correct Answer & Explanation

. Incomplete variant

Explanation

The Wrisberg variant of a discoid meniscus completely lacks posterior capsular attachments, relying solely on the meniscofemoral ligament of Wrisberg. This hypermobility leads to an unstable meniscus that subluxates into the joint, causing symptomatic snapping even without a formal tear.

Question 12291

Topic: Infection, Pharmacology & VTE

According to the Kocher criteria, which combination of clinical findings yields a 99% predictive probability for septic arthritis of the hip in a pediatric patient?

. Fever >38.5 C, inability to bear weight, ESR >40 mm/hr, WBC >12,000 cells/mm3
. Fever >38.0 C, positive blood culture, CRP >2 mg/dL, joint effusion
. Limp, night pain, morning stiffness, ESR >20 mm/hr
. Inability to bear weight, CRP >1 mg/dL, WBC >10,000 cells/mm3, recent URI
. Fever >39.0 C, refusal to walk, hip held in external rotation, negative plain films

Correct Answer & Explanation

. Fever >38.5 C, inability to bear weight, ESR >40 mm/hr, WBC >12,000 cells/mm3

Explanation

The Kocher criteria include non-weight-bearing status, temperature >38.5 C, ESR >40 mm/hr, and WBC >12,000 cells/mm3. The presence of all four criteria indicates a 99% probability of septic arthritis over transient synovitis.

Question 12292

Topic: Biology, Genetics & Bone Healing

Which transcription factor is considered the master regulator of osteoblast differentiation and is absolutely essential for both intramembranous and endochondral ossification?

. SOX9
. Runx2 (Cbfa1)
. HIF-1 alpha
. NFATc1
. MyoD

Correct Answer & Explanation

. SOX9

Explanation

Runx2 (also known as Cbfa1) is the master transcription factor for osteoblast differentiation. Mice lacking Runx2 have a complete lack of bone formation due to the arrest of osteoblast maturation. SOX9 is the master regulator for chondrogenesis. NFATc1 is essential for osteoclast differentiation.

Question 12293

Topic: Surgical Anatomy & Approaches

During the anterior ilioinguinal approach to the pelvis for an acetabular fracture, life-threatening hemorrhage is encountered from a vascular anastomosis crossing over the superior pubic ramus. This vessel represents a communication between which two vascular systems?

. Inferior epigastric artery and obturator artery
. Superior gluteal artery and inferior gluteal artery
. Internal pudendal artery and external pudendal artery
. Femoral artery and internal iliac artery directly
. Deep circumflex iliac artery and superior epigastric artery

Correct Answer & Explanation

. Inferior epigastric artery and obturator artery

Explanation

The corona mortis is a vascular anastomosis (venous, arterial, or both) between the external iliac system (via the inferior epigastric vessels) and the internal iliac system (via the obturator vessels). It lies on the posterior aspect of the superior pubic ramus and is highly vulnerable during anterior pelvic surgical exposures.

Question 12294

Topic: 1. General Principles & Basic Science

Articular cartilage is structurally divided into four distinct zones. Which of the following best describes the specific biochemical and structural characteristics of the superficial (tangential) zone?

. Lowest water content, highest proteoglycan content, collagen fibers perpendicular to the joint surface
. Highest water content, lowest proteoglycan content, collagen fibers parallel to the joint surface
. Highest proteoglycan content, collagen fibers randomly oriented, spherical chondrocytes
. Lowest cell density, highest proteoglycan content, contains the tidemark
. Highest concentration of Type X collagen, providing transition to subchondral bone

Correct Answer & Explanation

. Lowest water content, highest proteoglycan content, collagen fibers perpendicular to the joint surface

Explanation

The superficial (tangential) zone of articular cartilage is characterized by the highest water content, the lowest proteoglycan content, and densely packed collagen fibers that run parallel to the joint surface to resist shear forces. Chondrocytes in this zone are flattened.

Question 12295

Topic: Biomechanics & Biomaterials

During a fracture fixation procedure, a surgeon places a 316L stainless steel screw through a titanium alloy plate. This mixed-metal construct risks galvanic corrosion. Which of the following accurately describes the resulting electrochemical process?

. Titanium acts as the anode and corrodes rapidly.
. Stainless steel acts as the anode and undergoes accelerated corrosion.
. Both metals corrode equally due to identical galvanic potentials.
. Titanium acts as the cathode and undergoes accelerated corrosion.
. Stainless steel acts as the cathode and is protected by the sacrificial titanium.

Correct Answer & Explanation

. Titanium acts as the anode and corrodes rapidly.

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in an electrolytic solution (body fluid). The less noble metal acts as the anode and undergoes accelerated corrosion by giving up electrons, while the more noble metal acts as the cathode. Stainless steel is less noble than titanium, so the stainless steel screw acts as the anode and corrodes.

Question 12296

Topic: Biology, Genetics & Bone Healing

Which bone morphogenetic protein (BMP) is primarily associated with osteoinduction via the SMAD pathway and is currently an FDA-approved adjunct for anterior lumbar interbody fusion (ALIF)?

. BMP-2
. BMP-3
. BMP-4
. BMP-7
. TGF-beta

Correct Answer & Explanation

. BMP-2

Explanation

BMP-2 is FDA-approved for anterior lumbar interbody fusion (ALIF) and open tibial shaft fractures. It acts via the SMAD 1/5/8 signaling pathway to promote osteoinduction. BMP-7 (OP-1) was previously used under a humanitarian device exemption for nonunions but is not the FDA-approved agent for ALIF. BMP-3 is uniquely inhibitory to osteogenesis.

Question 12297

Topic: Surgical Anatomy & Approaches

During an anterior (ilioinguinal) approach for fixation of an acetabular fracture, life-threatening hemorrhage occurs while dissecting over the superior pubic ramus. This bleeding is most likely due to an unrecognized anastomosis between which two vascular systems?

. Internal iliac artery and superior gluteal artery
. External iliac artery and superior gluteal artery
. External pudendal artery and obturator artery
. Inferior epigastric artery and obturator artery
. Femoral artery and internal pudendal artery

Correct Answer & Explanation

. Internal iliac artery and superior gluteal artery

Explanation

The 'corona mortis' is a critical vascular anastomosis between the external iliac system (via the inferior epigastric artery/vein) and the internal iliac system (via the obturator artery/vein). It is located over the superior pubic ramus and is at high risk during anterior pelvic approaches.

Question 12298

Topic: 1. General Principles & Basic Science

Within the distinct layers of articular cartilage, which zone contains the highest concentration of proteoglycans, the lowest concentration of water, and thick collagen fibrils oriented perpendicular to the joint surface?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified zone
. Subchondral bone

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The deep (radial) zone of articular cartilage is responsible for resisting compressive forces. It has the highest concentration of proteoglycans, the lowest concentration of water, and collagen fibers that run perpendicular to the articular surface.

Question 12299

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with knee pain. Radiographs reveal an eccentric, lytic epiphyseal lesion in the distal femur. Biopsy confirms multinucleated giant cells in a stroma of mononuclear cells. If Denosumab is utilized, what is its primary mechanism of action?

. Inhibits osteoblast proliferation
. Monoclonal antibody that binds and inhibits RANKL
. Directly inhibits matrix metalloproteinases
. Monoclonal antibody targeting VEGF
. Directly induces apoptosis of the multinucleated giant cells

Correct Answer & Explanation

. Inhibits osteoblast proliferation

Explanation

Giant Cell Tumor (GCT) of bone is driven by neoplastic mononuclear stromal cells that express RANKL. RANKL recruits and activates reactive multinucleated giant cells (which are osteoclast-like). Denosumab is a monoclonal antibody that binds RANKL, inhibiting this process and leading to tumor calcification.

Question 12300

Topic: Biomechanics & Biomaterials

Which specific type of corrosion is most likely to occur when a 316L stainless steel screw is placed through a titanium alloy plate in an orthopaedic internal fixation construct?

. Crevice corrosion
. Fretting corrosion
. Galvanic corrosion
. Pitting corrosion
. Intergranular corrosion

Correct Answer & Explanation

. Crevice corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electrochemical potentials (such as stainless steel and titanium) are placed in direct electrical contact within an electrolytic environment (such as bodily fluids), causing the less noble metal to corrode.

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