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1. General Principles & Basic Science MCQs

Practice Set 608 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 12141

Topic: Biology, Genetics & Bone Healing

Which of the following stages of fracture healing is most reliant on the presence of transforming growth factor-beta (TGF-beta) and platelet-derived growth factor (PDGF) released from degranulating platelets?

. Soft callus formation
. Inflammatory phase
. Hard callus formation
. Remodeling phase
. Woven bone formation

Correct Answer & Explanation

. Soft callus formation

Explanation

Following a fracture, hematoma formation and the inflammatory phase occur first. Degranulating platelets within the fracture hematoma release key cytokines, including PDGF and TGF-beta, which recruit mesenchymal stem cells and initiate the early cascade of the inflammatory phase of bone healing.

Question 12142

Topic: Biomechanics & Biomaterials

Galvanic corrosion in orthopedic implants is most likely to occur when which of the following conditions is met?

. Two identical metals are subjected to repeated cyclic loading
. A stainless steel plate is used with a titanium screw in a fluid medium
. A titanium implant is placed in a highly oxygenated environment
. Polyethylene debris accumulates around a cobalt-chrome femoral head
. Ceramic implants undergo micro-fractures under compression

Correct Answer & Explanation

. Two identical metals are subjected to repeated cyclic loading

Explanation

Galvanic corrosion occurs when two dissimilar metals (such as stainless steel and titanium) are in physical contact within an electrolytic solution (like bodily fluids). The difference in their electrochemical potentials drives an electron transfer, causing the more anodic metal to corrode.

Question 12143

Topic: 1. General Principles & Basic Science

Following a Zone II flexor digitorum profundus (FDP) and flexor digitorum superficialis (FDS) repair, a patient undergoes early active motion rehabilitation. At 6 weeks post-op, the patient demonstrates an inability to actively flex the distal interphalangeal (DIP) joint, despite full passive range of motion. What is the most likely cause?

. Adhesion formation
. Intact FDS with FDP rupture
. Intact FDP with FDS rupture
. Lumbrical plus finger
. Quadrigia effect

Correct Answer & Explanation

. Adhesion formation

Explanation

The inability to actively flex the DIP joint with fully preserved passive motion indicates a mechanical failure of the FDP tendon. Given that the patient is moving the finger but specifically lacks active DIP flexion, the most likely diagnosis is an intact FDS repair with a ruptured FDP repair.

Question 12144

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, which of the following wear mechanisms is primarily responsible for the generation of submicron polyethylene particles that lead to macrophage-mediated osteolysis?
. Adhesive wear
. Abrasive wear
. Fatigue wear
. Third-body wear
. Fretting wear

Correct Answer & Explanation

. Adhesive wear

Explanation

Adhesive wear is the primary mechanism generating submicron ultra-high-molecular-weight polyethylene (UHMWPE) wear debris in total joint arthroplasty, which initiates the macrophage-mediated osteolytic cascade.

Question 12145

Topic: Biology, Genetics & Bone Healing

Which Bone Morphogenetic Protein (BMP) is FDA approved as an alternative to autograft for anterior lumbar interbody fusion (ALIF)?

. BMP-2
. BMP-3
. BMP-4
. BMP-7
. BMP-9

Correct Answer & Explanation

. BMP-2

Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA approved for single-level anterior lumbar interbody fusion (ALIF) within a specific carrier. BMP-7 (also known as OP-1) was previously approved under a humanitarian device exemption for recalcitrant long bone nonunions.

Question 12146

Topic: Surgical Anatomy & Approaches

A 28-year-old man sustains an anterior shoulder dislocation. Post-reduction, he has weakness in shoulder abduction and decreased sensation over the lateral deltoid. EMG confirms an isolated axillary nerve injury. Through which anatomical space does this nerve normally exit the axilla?

. Triangular space
. Quadrangular space
. Triangular interval
. Suprascapular notch
. Spinoglenoid notch

Correct Answer & Explanation

. Triangular space

Explanation

The axillary nerve and posterior circumflex humeral artery exit the axilla posteriorly through the quadrangular space. The boundaries are the teres minor (superior), teres major (inferior), long head of the triceps (medial), and the surgical neck of the humerus (lateral).

Question 12147

Topic: 1. General Principles & Basic Science
A 21-year-old football player sustains a valgus blow to the knee. Exam reveals medial joint line tenderness and 5 mm of opening to valgus stress at 30 degrees of flexion with a firm endpoint. Valgus stress at 0 degrees is stable. What is the severity of the injury?
. Grade I superficial MCL
. Grade II superficial MCL
. Grade III superficial MCL
. Grade II deep MCL
. Grade III posteromedial corner

Correct Answer & Explanation

. Grade II superficial MCL

Explanation

Opening to valgus at 30 degrees with a firm endpoint indicates a Grade II sprain (partial tear) of the superficial medial collateral ligament (sMCL), which is the primary restraint to valgus stress at 30 degrees of flexion. Complete tears (Grade III) lack a firm endpoint.

Question 12148

Topic: Biomechanics & Biomaterials

A total hip arthroplasty with a cobalt-chromium (CoCr) femoral head and a titanium alloy stem is revised for aseptic loosening. Black debris is noted at the modular head-neck junction. Which type of corrosion initiates the mechanically assisted crevice corrosion (MACC) at this modular interface?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Fretting corrosion initiates mechanically assisted crevice corrosion (MACC) at the modular head-neck junction (trunnionosis) of a THA. Fretting (micromotion) continuously breaks the protective oxide passivation layer, allowing subsequent crevice and galvanic corrosion to proceed.

Question 12149

Topic: Biomechanics & Biomaterials

A 65-year-old man undergoes revision total hip arthroplasty where a cobalt-chromium femoral head is placed onto a titanium alloy femoral stem. Which of the following types of corrosion is most likely to occur at the head-neck junction?

. Pitting corrosion
. Crevice corrosion
. Galvanic corrosion
. Fretting corrosion
. Uniform corrosion

Correct Answer & Explanation

. Pitting corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (such as cobalt-chromium and titanium alloy) are placed in physical contact within an electrolytic solution like body fluid. The less noble metal undergoes accelerated corrosion. Fretting corrosion can also occur at modular junctions due to micromotion, but the presence of dissimilar metals specifically defines galvanic corrosion.

Question 12150

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) induce bone formation primarily through which of the following mechanisms?

. Osteoconduction
. Osteoinduction
. Osteogenesis
. Chemotaxis
. Angiogenesis

Correct Answer & Explanation

. Osteoconduction

Explanation

BMPs act via osteoinduction, which is the process of stimulating undifferentiated mesenchymal stem cells to differentiate into osteoprogenitor cells and eventually osteoblasts. Osteoconduction provides a scaffold, while osteogenesis requires the transfer of live cells.

Question 12151

Topic: 1. General Principles & Basic Science

Which zone of the meniscus has the best potential for healing following surgical repair?

. Red-red zone
. Red-white zone
. White-white zone
. Inner third
. Central core

Correct Answer & Explanation

. Red-red zone

Explanation

The red-red zone is the peripheral outer third of the meniscus, which receives abundant vascularity from the perimeniscal capillary plexus. This robust blood supply provides the highest healing potential for meniscal repairs.

Question 12152

Topic: 1. General Principles & Basic Science
What is the predominant type of collagen found in healthy adult articular cartilage?
. Type I
. Type II
. Type III
. Type IV
. Type X

Correct Answer & Explanation

. Type II

Explanation

Type II collagen makes up 90-95% of the collagen found in normal, healthy articular (hyaline) cartilage. Type I collagen is predominant in bone, tendon, meniscus, and fibrocartilage (which forms after cartilage injury).

Question 12153

Topic: 1. General Principles & Basic Science

Which of the following best describes the biological process of 'intrinsic' healing in a primarily repaired Zone II flexor tendon?

. It relies primarily on fibrovascular ingrowth from the surrounding flexor sheath.
. It is driven by tenocytes originating from the epitenon and endotenon.
. It results in dense adhesion formation limiting tendon glide.
. It is completely independent of synovial fluid diffusion.
. It peaks exclusively during the initial inflammatory phase of wound healing.

Correct Answer & Explanation

. It relies primarily on fibrovascular ingrowth from the surrounding flexor sheath.

Explanation

Flexor tendon healing occurs via both intrinsic and extrinsic mechanisms. Intrinsic healing relies on the proliferation and migration of tenocytes from the epitenon and endotenon within the tendon itself, nourished heavily by synovial fluid diffusion. Extrinsic healing relies on cells and vascular ingrowth from the surrounding sheath, which forms adhesions. Modern early active motion protocols favor intrinsic healing to minimize adhesions.

Question 12154

Topic: Biology, Genetics & Bone Healing

A 65-year-old man presents with dull aching pain in his right thigh and an increasing hat size. Radiographs of his femur demonstrate cortical thickening, increased trabecular markings, and a 'blade of grass' lucency. A bone biopsy would most likely reveal which of the following cellular abnormalities?

. Malignant spindle cells producing unmineralized osteoid
. Multinucleated osteoclasts with paramyxovirus-like inclusion bodies
. Sheets of uniform plasma cells with eccentric nuclei and clock-face chromatin
. Histiocytes with grooved coffee-bean nuclei and abundant eosinophils
. Enlarged hyperchromatic osteoblasts with clear perinuclear halos

Correct Answer & Explanation

. Malignant spindle cells producing unmineralized osteoid

Explanation

The clinical picture is classic for Paget's disease of bone (osteitis deformans). The primary cellular defect is hyperactive, enlarged, multinucleated osteoclasts (sometimes with up to 100 nuclei per cell). Ultrastructural studies often show paramyxovirus-like (e.g., measles, RSV) inclusion bodies within both the cytoplasm and nuclei of these osteoclasts, pointing to a possible viral etiology.

Question 12155

Topic: Biomechanics & Biomaterials

Articular cartilage exhibits highly predictable viscoelastic properties. When a constant compressive load is applied to cartilage, it deforms rapidly at first, followed by a slow, progressive increase in deformation until an equilibrium is reached. This time-dependent biomechanical phenomenon is known as:

. Stress relaxation
. Creep
. Hysteresis
. Anisotropy
. Boundary lubrication

Correct Answer & Explanation

. Stress relaxation

Explanation

'Creep' is defined as the progressive deformation of a viscoelastic material under a constant load over time. In articular cartilage, this is primarily due to the exudation of interstitial fluid from the extracellular matrix. 'Stress relaxation', by contrast, is the decrease in stress over time when a material is held at a constant strain (constant deformation).

Question 12156

Topic: Biomechanics & Biomaterials

Which type of corrosion occurs in modular junctions of orthopedic implants, such as the head-neck taper of a total hip arthroplasty, primarily due to micromotion that mechanically disrupts the protective passive oxide layer?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Fretting corrosion occurs at contact sites between materials under load subject to minute relative motion (micromotion). This micromotion constantly disrupts the protective passive oxide film on the metal surface, exposing the underlying metal and leading to accelerated localized corrosion. This is the primary mechanism of trunnionosis in the modular head-neck taper of a THA.

Question 12157

Topic: Biology, Genetics & Bone Healing

A 30-year-old female is diagnosed with a giant cell tumor (GCT) of the distal femur. Because the tumor is marginally resectable, she is treated with denosumab to downstage the lesion. Denosumab exerts its therapeutic effect by binding directly to which of the following targets?

. RANK receptor on the surface of osteoclasts
. RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand)
. Osteoprotegerin (OPG)
. Macrophage colony-stimulating factor (M-CSF)
. Vascular endothelial growth factor (VEGF)

Correct Answer & Explanation

. RANK receptor on the surface of osteoclasts

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand), thereby preventing it from interacting with the RANK receptor on the surface of osteoclasts and their precursors. In GCT, neoplastic stromal cells overexpress RANKL, recruiting destructive osteoclast-like giant cells. Denosumab halts this osteolysis.

Question 12158

Topic: 1. General Principles & Basic Science

In the primary repair of a Zone II flexor digitorum profundus (FDP) tendon laceration, which of the following biomechanical variables contributes most significantly to the ultimate tensile strength of the repair?

. The use of a running epitenon suture
. The thickness (caliber) of the core suture material
. The number of core suture strands crossing the repair site
. The placement of core sutures in the volar half of the tendon
. The use of a locking knot configuration rather than a grasping configuration

Correct Answer & Explanation

. The use of a running epitenon suture

Explanation

According to Strickland's principles of flexor tendon repair, the ultimate tensile strength of the repair is directly proportional to the number of core suture strands crossing the repair site. For example, a 4-strand repair is significantly stronger than a 2-strand repair. While locking knots, heavier suture caliber, and epitenon sutures (which add about 20% to the strength and smooth the repair) all contribute, the number of core strands is the single most critical factor for early active motion protocols.

Question 12159

Topic: Surgical Anatomy & Approaches

During the ilioinguinal approach for open reduction and internal fixation of an anterior column acetabular fracture, life-threatening hemorrhage occurs while dissecting along the posterior aspect of the superior pubic ramus. Which of the following vascular structures, which represents an anastomosis between the external iliac and obturator systems, is most likely injured?

. Superior gluteal artery
. Inferior epigastric artery
. Corona mortis
. Internal pudendal artery
. Deep circumflex iliac artery

Correct Answer & Explanation

. Superior gluteal artery

Explanation

The 'corona mortis' (crown of death) is a highly variable vascular anastomosis between the external iliac (or inferior epigastric) vessels and the obturator vessels. It is classically located retropubically, approximately 5-7 cm from the pubic symphysis, crossing the superior pubic ramus. Injury to this structure during the ilioinguinal or Stoppa approach can lead to massive, difficult-to-control hemorrhage.

Question 12160

Topic: Biology, Genetics & Bone Healing

According to Perrenโ€™s strain theory of bone healing, the type of tissue that forms in a fracture gap is determined by the local mechanical strain environment. Which of the following biological tissues can tolerate the highest degree of strain before mechanical failure?

. Woven bone
. Lamellar bone
. Fibrocartilage
. Granulation tissue
. Hyaline cartilage

Correct Answer & Explanation

. Woven bone

Explanation

Perren's strain theory dictates that a tissue can only be formed in a fracture gap if the strain in that gap does not exceed the strain tolerance of the tissue. Granulation tissue can tolerate up to 100% strain without rupturing. As the fracture stabilizes and strain decreases, tissues with lower strain tolerance form: fibrocartilage tolerates 10-15% strain, woven bone tolerates about 5-10% strain, and lamellar bone tolerates only about 2% strain.

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