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1. General Principles & Basic Science MCQs

Practice Set 73 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 1441

Topic: Infection, Pharmacology & VTE

A 48-year-old female presents after a motor vehicle accident with a comminuted fracture of the distal tibia extending into the ankle joint (pilon fracture). There is significant soft tissue swelling and blistering. What is the primary goal of immediate non-operative management?

. Achieve anatomical reduction and maintain it with external splinting.
. Aggressive pain control and early mobilization.
. Reduction of soft tissue swelling to prepare for definitive surgery.
. Prevention of deep vein thrombosis (DVT).
. Immediate weight-bearing to promote bone healing.

Correct Answer & Explanation

. Reduction of soft tissue swelling to prepare for definitive surgery.

Explanation

Correct Answer: CPilon fractures are challenging due to their articular involvement and often severe soft tissue injury. Significant soft tissue swelling and blistering indicate a compromised soft tissue envelope that is not ready for definitive surgical intervention. The primary goal of immediate non-operative management (often with a spanning external fixator for provisional stability) is to allow the soft tissues to recover, reduce swelling, and improve the skin condition. This 'waiting game' is crucial to minimize the high risk of wound complications (dehiscence, infection) associated with early surgery on inflamed tissues. Anatomical reduction is the ultimate goal, but it must be achieved when the soft tissues allow. Early weight-bearing is contraindicated. DVT prophylaxis is important but not the primary goal of local fracture management in this context.

Question 1442

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with knee pain. Radiographs show an eccentric, lytic lesion in the distal femoral epiphysis extending to the articular surface. Biopsy reveals multinucleated giant cells in a background of mononuclear cells. Which medication targets the underlying pathophysiology of this tumor?

. Bisphosphonates
. Denosumab
. Imatinib
. Doxorubicin
. Methotrexate

Correct Answer & Explanation

. Denosumab

Explanation

Giant cell tumors of bone consist of neoplastic mononuclear cells that express RANKL, recruiting reactive osteoclast-like giant cells. Denosumab is a monoclonal antibody against RANKL used for inoperable or recurrent GCTs.

Question 1443

Topic: Biology, Genetics & Bone Healing

An 8-year-old boy sustains a minor fall and presents with arm pain. X-rays show a centrally located, completely lytic metaphyseal lesion in the proximal humerus with a "fallen leaf" sign. What is the accepted pathophysiology of this lesion?

. Venous outflow obstruction
. Neoplastic proliferation of RANKL-expressing cells
. Defect in metaphyseal remodeling
. Benign overgrowth of cartilage
. Fibroblastic replacement of spongiosa

Correct Answer & Explanation

. Venous outflow obstruction

Explanation

Unicameral (simple) bone cysts are believed to result from localized venous outflow obstruction leading to increased intraosseous pressure and fluid accumulation. The "fallen leaf" sign indicates a pathologic fracture through the cyst wall.

Question 1444

Topic: Infection, Pharmacology & VTE

A 40-year-old farmer sustains a severe open tibia fracture heavily contaminated with soil and manure. According to current guidelines, what is the most appropriate initial intravenous antibiotic regimen?

. Cefazolin alone
. Cefazolin and gentamicin
. Cefazolin and clindamycin
. Ceftriaxone and vancomycin
. Cefazolin, gentamicin, and penicillin

Correct Answer & Explanation

. Cefazolin, gentamicin, and penicillin

Explanation

Farm injuries or wounds heavily contaminated with soil have a high risk of clostridial infection. The addition of high-dose penicillin is recommended alongside a first-generation cephalosporin and an aminoglycoside.

Question 1445

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with wrist pain. Radiographs reveal an eccentric, lytic, expansile lesion in the epiphysis of the distal radius extending to the subchondral bone, without a sclerotic rim. Biopsy confirms multinucleated giant cells. If the patient is treated with a targeted pharmacological agent prior to surgery, what is the mechanism of action of this drug?

. Inhibition of vascular endothelial growth factor (VEGF)
. Inhibition of the RANK ligand (RANKL)
. Direct cytotoxicity to osteoclasts via bisphosphonate accumulation
. Inhibition of tyrosine kinase
. Inhibition of mammalian target of rapamycin (mTOR)

Correct Answer & Explanation

. Inhibition of the RANK ligand (RANKL)

Explanation

The patient has a Giant Cell Tumor (GCT) of bone. Denosumab is frequently used for large or unresectable GCTs and works by binding to RANKL, thereby inhibiting osteoclast-like giant cell formation and reducing tumor-associated osteolysis.

Question 1446

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with a large, lytic lesion in the distal femur extending to the subchondral bone. Biopsy confirms Giant Cell Tumor of bone. She is treated with denosumab pre-operatively. What is the specific mechanism of action of denosumab?

. Binds directly to RANK on osteoclasts to induce apoptosis
. Binds to RANKL, preventing interaction with RANK on osteoclast precursors
. Inhibits farnesyl pyrophosphate synthase in the mevalonate pathway
. Inhibits vascular endothelial growth factor (VEGF) to reduce tumor angiogenesis
. Directly binds to the neoplastic mononuclear cells, inducing apoptosis

Correct Answer & Explanation

. Binds to RANKL, preventing interaction with RANK on osteoclast precursors

Explanation

Denosumab is a monoclonal antibody that binds to RANKL (secreted by the neoplastic stromal cells), preventing it from activating RANK on osteoclast precursors. This inhibits osteoclast-mediated bone resorption.

Question 1447

Topic: Surgical Anatomy & Approaches

A 25-year-old unrestrained driver suffers a posterior hip dislocation in a motor vehicle collision. Following closed reduction, the patient exhibits a foot drop and inability to extend the toes. Which nerve division is most likely injured?

. Tibial division of the sciatic nerve
. Peroneal division of the sciatic nerve
. Femoral nerve
. Obturator nerve
. Superior gluteal nerve

Correct Answer & Explanation

. Peroneal division of the sciatic nerve

Explanation

The common peroneal division of the sciatic nerve is most susceptible to injury during a posterior hip dislocation. This is due to its lateral position and secure tethering at the sciatic notch and fibular neck.

Question 1448

Topic: Biology, Genetics & Bone Healing

A 28-year-old female presents with a destructive, eccentric lytic lesion in the distal femur. Biopsy reveals numerous multinucleated giant cells in a stroma of mononuclear cells. Preoperative treatment with denosumab is planned to facilitate joint-salvage surgery. What is the mechanism of action of this medication?

. It binds directly to RANKL, preventing it from activating the RANK receptor on osteoclasts.
. It binds to the RANK receptor, competitively inhibiting osteoclast activation.
. It induces osteoblast apoptosis, thereby reducing tumor matrix formation.
. It is a synthetic analog of osteoprotegerin that permanently destroys osteoclast precursors.
. It acts as a bisphosphonate by directly inhibiting the farnesyl pyrophosphate synthase pathway.

Correct Answer & Explanation

. It binds directly to RANKL, preventing it from activating the RANK receptor on osteoclasts.

Explanation

Denosumab is a monoclonal antibody that binds to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). By binding RANKL, it prevents the activation of the RANK receptor on the surface of osteoclasts and their precursors, effectively halting osteoclast-mediated bone destruction in giant cell tumors.

Question 1449

Topic: 1. General Principles & Basic Science

A 35-year-old male sustains a severe open tibia fracture with a 6 cm segmental bone defect. The surgeon utilizes the Masquelet technique, placing a PMMA cement spacer during the first stage. What is the primary biological function of this PMMA spacer?

. It provides definitive rigid internal fixation across the fracture gap.
. It releases high doses of systemic antibiotics to treat deep osteomyelitis.
. It induces the formation of a pseudo-synovial membrane rich in VEGF and BMP-2.
. It acts as a permanent structural graft to bear weight.
. It directly stimulates osteoclast activity to debride necrotic bone ends.

Correct Answer & Explanation

. It induces the formation of a pseudo-synovial membrane rich in VEGF and BMP-2.

Explanation

The PMMA spacer in the Masquelet technique induces a foreign body reaction that forms a highly vascularized biomembrane. This membrane secretes vital growth factors like VEGF, BMP-2, and TGF-beta, which create an optimal environment for the autologous bone graft placed in the second stage.

Question 1450

Topic: Surgical Anatomy & Approaches

A 14-year-old female with a high-grade osteosarcoma of the proximal humerus has completed neoadjuvant chemotherapy. Post-chemotherapy MRI shows a good response with significant tumor shrinkage. The surgical plan is for limb salvage. Which of the following nerves is at highest risk of injury during the surgical approach to the proximal humerus, particularly when dissecting around the surgical neck and deltoid?

. Radial nerve
. Ulnar nerve
. Median nerve
. Axillary nerve
. Musculocutaneous nerve

Correct Answer & Explanation

. Axillary nerve

Explanation

Correct Answer: DExplanation:Theaxillary nerveis the nerve at highest risk of injury during surgical approaches to the proximal humerus, especially when the dissection involves the surgical neck and the deltoid muscle. The axillary nerve originates from the posterior cord of the brachial plexus (C5, C6), passes posteriorly around the surgical neck of the humerus, and innervates the deltoid and teres minor muscles. Damage to this nerve results in paralysis of the deltoid, leading to significant impairment of shoulder abduction and external rotation, and sensory loss over the lateral shoulder.A. Radial nerve:The radial nerve also originates from the posterior cord and spirals around the posterior aspect of the humerus in the radial groove, making it vulnerable in mid-shaft humeral fractures or approaches to the posterior humerus, but less so in the immediate proximal humeral surgical neck region compared to the axillary nerve.B. Ulnar nerve:The ulnar nerve runs medially in the arm and is typically not at high risk during proximal humeral approaches unless dissection extends significantly medially or distally.C. Median nerve:The median nerve runs with the brachial artery in the anterior compartment of the arm and is generally not at high risk during standard proximal humeral approaches.E. Musculocutaneous nerve:This nerve innervates the anterior compartment muscles of the arm (biceps, brachialis) and is typically more anterior and distal to the immediate surgical neck area.

Question 1451

Topic: Biology, Genetics & Bone Healing

An asymptomatic 12-year-old boy undergoes a radiograph for minor knee trauma, revealing a 2 cm eccentric, bubbly, cortically based metaphyseal radiolucency in the distal femur. If a biopsy were to be performed, which of the following histological patterns would be expected?

. Mononuclear cells with longitudinal nuclear grooves (coffee bean appearance)
. Spindle cells arranged in a storiform pattern with scattered lipid-laden macrophages
. Sheets of small round blue cells with scant cytoplasm
. Plump stromal cells with interspersed chicken-wire calcification
. Biphasic population of osteoclast-like giant cells and mononuclear cells with identical nuclei

Correct Answer & Explanation

. Spindle cells arranged in a storiform pattern with scattered lipid-laden macrophages

Explanation

The radiographic description is classic for a non-ossifying fibroma (NOF) or fibrous cortical defect. Histologically, these lesions exhibit a background of bland spindle cells in a storiform (pinwheel) arrangement, accompanied by multinucleated giant cells, hemosiderin, and lipid-laden (foamy) macrophages.

Question 1452

Topic: Biology, Genetics & Bone Healing

Which of the following histologic features is most characteristic of a non-ossifying fibroma (NOF)?

. Spindle cells arranged in a storiform pattern with multinucleated giant cells and foam cells
. Bland spindle cells producing woven bone with a 'Chinese letter' pattern
. Sheets of uniform mononuclear cells with interspersed multinucleated giant cells
. Lobules of hyaline cartilage separated by fibrous septa
. Atypical spindle cells producing delicate, lace-like osteoid

Correct Answer & Explanation

. Spindle cells arranged in a storiform pattern with multinucleated giant cells and foam cells

Explanation

The classic histology of a non-ossifying fibroma consists of bland fibroblasts arranged in a storiform (cartwheel) pattern, intermixed with multinucleated giant cells and lipid-laden macrophages (foam cells).

Question 1453

Topic: 1. General Principles & Basic Science

A 42-year-old patient is undergoing surgical repair of a proper digital nerve laceration in the middle finger. The surgeon is preparing for the repair under an operating microscope. According to the surgical technique described in the case, which of the following is the most appropriate suture material and technique for a primary epineurial repair of a proper digital nerve?

. 4-0 absorbable chromic gut sutures with a simple interrupted technique.
. 7-0 non-absorbable polypropylene sutures with a running locked technique.
. 9-0 or 10-0 non-absorbable monofilament nylon sutures with an interrupted technique.
. 11-0 absorbable polyglactin sutures with a group fascicular repair technique.
. Heavy braided silk sutures with a mattress technique to ensure strong coaptation.

Correct Answer & Explanation

. 9-0 or 10-0 non-absorbable monofilament nylon sutures with an interrupted technique.

Explanation

Correct Answer: CThe 'Surgical Technique - Nerve Repair' section, under 'Repair Technique - Epineurial Repair,' states: 'Using 9-0 or 10-0 non-absorbable monofilament nylon sutures, 3-6 sutures are placed through the epineurium to approximate the nerve ends meticulously.' This directly matches option C.Option A is incorrectbecause 4-0 sutures are too large for digital nerve repair, and absorbable sutures are not typically used for primary nerve repair where long-term coaptation is desired.Option B is incorrectbecause 7-0 sutures are generally too large for proper digital nerves, and a running locked technique is not the standard for epineurial repair, which typically uses interrupted sutures for precise alignment.Option D is incorrectbecause 11-0 sutures might be too fine for epineurial repair (more common for fascicular repair, which is rarely indicated for digital nerves), and absorbable sutures are not preferred. Group fascicular repair is also rarely indicated for digital nerves.Option E is incorrectbecause heavy braided silk sutures are too traumatic and reactive for delicate nerve repair, and a mattress technique is not the standard for epineurial coaptation.

Question 1454

Topic: 1. General Principles & Basic Science

During a Zone II flexor tendon repair, the surgeon adds a running epitendinous suture to the core suture construct. What is the primary biomechanical benefit of adding this epitendinous suture?

. It prevents immediate rupture during passive flexion
. It decreases the overall bulk of the repair and increases strength by 20-30%
. It stimulates intrinsic healing pathways via synovial diffusion
. It replaces the need for a multi-strand core suture
. It prevents the formation of adhesions to the flexor sheath

Correct Answer & Explanation

. It decreases the overall bulk of the repair and increases strength by 20-30%

Explanation

Adding a running epitendinous suture to a flexor tendon repair smooths the repair site (decreasing bulk/friction) and significantly increases the tensile strength of the construct by 10% to 30%, while minimizing gap formation.

Question 1455

Topic: 1. General Principles & Basic Science

A 28-year-old carpenter sustains a deep laceration to the volar aspect of his index finger in Zone II. During surgical exploration and repair of the flexor digitorum profundus (FDP) and superficialis (FDS) tendons, maintaining the integrity of the flexor pulley system is critical. Which of the following pulley combinations is most essential to preserve in order to prevent bowstringing of the flexor tendons?

. A1 and A3 pulleys
. A2 and A4 pulleys
. A1 and A5 pulleys
. A3 and C1 pulleys
. A2 and C2 pulleys

Correct Answer & Explanation

. A2 and A4 pulleys

Explanation

The A2 and A4 pulleys are the major biomechanical pulleys essential for preventing bowstringing of the flexor tendons during digit flexion. They arise from the rigid periosteum of the proximal and middle phalanges, respectively.

Question 1456

Topic: Physiology & Rehabilitation
A 65-year-old male with pre-existing cervical spondylotic stenosis falls forward and strikes his chin on a table, sustaining a severe hyperextension injury to his neck. He arrives at the trauma bay with significant bilateral motor weakness that is noticeably more profound in his upper extremities than his lower extremities, particularly affecting his hands. Proprioception and perianal sensation remain largely intact. What is the most likely diagnosis?
. Anterior cord syndrome
. Brown-Séquard syndrome
. Central cord syndrome
. Posterior cord syndrome
. Conus medullaris syndrome

Correct Answer & Explanation

. Central cord syndrome

Explanation

Central cord syndrome frequently occurs in elderly patients with pre-existing cervical spondylosis who sustain hyperextension injuries. It is classically characterized by disproportionate motor impairment in the upper extremities compared to the lower extremities, often with varied sensory sparing.

Question 1457

Topic: Biology, Genetics & Bone Healing

When reviewing the shoulder X-ray of an 84-year-old female, which radiographic finding is most indicative of severe osteoporosis, beyond just fracture presence?

. Subchondral cysts
. Joint space narrowing
. Trabecular thinning and cortical attenuation
. Osteophyte formation
. Acromial erosion

Correct Answer & Explanation

. Trabecular thinning and cortical attenuation

Explanation

Correct Answer: CTrabecular thinning and cortical attenuation (thinning of the outer bone layer) are direct radiographic signs of reduced bone mineral density characteristic of osteoporosis. While osteoporosis predisposes to fractures, the other options are signs of degenerative joint disease (subchondral cysts, joint space narrowing, osteophyte formation) or rotator cuff arthropathy (acromial erosion), not direct indicators of systemic bone density loss.

Question 1458

Topic: 1. General Principles & Basic Science

Regarding the collagenous architecture of the menisci, which of the following statements most accurately describes the predominant fiber orientation in the main body of the meniscal substance, critical for its biomechanical function?

. Primarily radial fibers resisting compressive loads.
. Predominantly longitudinal (circumferential) fibers resisting hoop stresses.
. Anisotropic arrangement with equal distribution of radial and circumferential fibers.
. Randomized, interwoven network providing multi-directional strength.
. Mainly oblique fibers acting as primary stabilizers.

Correct Answer & Explanation

. Predominantly longitudinal (circumferential) fibers resisting hoop stresses.

Explanation

Correct Answer: BThe menisci are primarily composed of type I collagen, with the vast majority (90-95%) of the fibers arranged circumferentially. These longitudinal fibers are crucial for converting vertical compressive loads into 'hoop stresses,' which are then resisted by the integrity of the circumferential fibers, allowing the meniscus to transmit load efficiently and protect articular cartilage. Radial fibers, though fewer, act as 'tie-ropes' to prevent extrusion of the circumferential fibers.

Question 1459

Topic: 1. General Principles & Basic Science

Which meniscal structure is considered a secondary stabilizer to anterior tibial translation, particularly in the ACL-deficient knee?

. Posterior horn of the medial meniscus.
. Anterior horn of the lateral meniscus.
. Body of the medial meniscus.
. Posterior horn of the lateral meniscus.
. Anterior horn of the medial meniscus.

Correct Answer & Explanation

. Posterior horn of the medial meniscus.

Explanation

Correct Answer: AThe posterior horn of the medial meniscus plays a significant role as a secondary stabilizer to anterior tibial translation. Its posterior root attachment resists anterior displacement of the meniscus itself, and its intact structure prevents excessive anterior translation of the tibia relative to the femur, especially when the ACL is deficient. The posterior horn of the lateral meniscus also contributes but to a lesser degree than the medial.

Question 1460

Topic: 1. General Principles & Basic Science

The primary blood supply to the menisci in adults is derived from which arterial network?

. Inferior genicular artery branches.
. Superior genicular artery branches.
. Popliteal artery direct branches.
. Circumflex femoral artery.
. Femoral artery direct perforators.

Correct Answer & Explanation

. Inferior genicular artery branches.

Explanation

Correct Answer: AThe primary blood supply to the menisci in adults originates from branches of the inferior genicular arteries (medial and lateral), which form a perimeniscal plexus. This plexus supplies the outer 10-30% of the meniscal tissue, creating the well-known 'red-red' (vascular), 'red-white' (partially vascular), and 'white-white' (avascular) zones.

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