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1. General Principles & Basic Science MCQs

Practice Set 662 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 13221

Topic: 1. General Principles & Basic Science

A patient reports that he felt a pop and immediate pain over the MP joint of his finger. Examination reveals tenderness on the dorsum of the joint and subluxation of the extensor tendon. Which of the following is the most common defect:

. C entral slip
. Lateral bands
. Triangular ligament
. Sagittal fibers
. Extensor tendon

Correct Answer & Explanation

. Sagittal fibers

Explanation

Tears of the sagittal fibers of the dorsal aponeurosis result in subluxation of the extensor tendon. This usually occurs on the long finger with subluxation to the ulnar side. Treatment for acute injuries requires immobilization of the metacarpophalangeal joint in extension for 6 weeks. Treatment for chronic injuries includes repair of the torn radial sagittal fibers.

Question 13222

Topic: Biology, Genetics & Bone Healing

A 35-year-old male undergoes open reduction and internal fixation of a simple transverse radial shaft fracture using a dynamic compression plate to achieve absolute stability. By which mechanism will this fracture primarily heal?

. Endochondral ossification
. Primary (direct) bone healing via cutting cones
. Secondary bone healing with robust cartilaginous callus
. Intramembranous ossification with bridging fibrous tissue
. Chondrocyte hypertrophy followed by calcification

Correct Answer & Explanation

. Primary (direct) bone healing via cutting cones

Explanation

Rigid internal fixation that achieves absolute stability (e.g., dynamic compression plating) eliminates interfragmentary motion, leading to primary bone healing. This occurs directly via osteoclastic cutting cones and osteoblastic bone formation without a callus phase.

Question 13223

Topic: 1. General Principles & Basic Science

A 30-year-old carpenter sustained a sharp laceration to his volar index finger, resulting in a Zone II flexor digitorum profundus rupture. During surgical repair, which technical factor contributes most significantly to the ultimate tensile strength of the tendon repair, allowing for safe early active mobilization?

. The number of core suture strands crossing the repair site
. The use of a braided, non-absorbable suture material
. The addition of a running epitendinous suture
. The specific geometry of the grasping knot
. The angle of the core suture purchase

Correct Answer & Explanation

. The number of core suture strands crossing the repair site

Explanation

The tensile strength of a flexor tendon repair is directly proportional to the number of core suture strands crossing the coaptation site. A minimum of a 4-strand core repair is generally required to withstand the forces of early active motion protocols.

Question 13224

Topic: 1. General Principles & Basic Science
A 55-year-old diabetic male presents with severe erythema, swelling, and pain out of proportion in his right calf. You are calculating a LRINEC (Laboratory Risk Indicator for Necrotizing Fasciitis) score to help guide your decision for operative debridement. Which of the following laboratory values is NOT a component of the LRINEC score?
. C-reactive protein
. White blood cell count
. Serum sodium
. Serum potassium
. Serum creatinine

Correct Answer & Explanation

. Serum potassium

Explanation

The LRINEC score uses six laboratory parameters: C-reactive protein, white blood cell count, hemoglobin, serum sodium, serum creatinine, and serum glucose. Serum potassium is not a component of this predictive model.

Question 13225

Topic: Biology, Genetics & Bone Healing

A researcher is studying the biomechanical properties of human hyaline articular cartilage. The tensile stiffness and structural framework of this tissue are primarily provided by which of the following macromolecular components?

. Type I collagen
. Type II collagen
. Aggrecan
. Hyaluronic acid
. Chondroitin sulfate

Correct Answer & Explanation

. Type II collagen

Explanation

Type II collagen comprises 90-95% of the collagen in normal articular cartilage and is primarily responsible for its tensile strength. Proteoglycans like aggrecan provide compressive stiffness through osmotic tissue swelling.

Question 13226

Topic: 1. General Principles & Basic Science

A 25-year-old man sustains a laceration to the volar aspect of his index finger in Zone II. He undergoes primary flexor tendon repair. To optimize tendon gliding and minimize adhesion formation postoperatively, which rehabilitation protocol is currently most favored?

. Absolute immobilization in a cast for 6 weeks
. Early active extension and passive flexion
. Immediate active unrestricted flexion
. Dynamic extension splinting with static flexion
. Six weeks of static extension splinting

Correct Answer & Explanation

. Early active extension and passive flexion

Explanation

Early active extension with passive flexion (e.g., modified Kleinert or Duran protocols) is standard after Zone II flexor tendon repairs. It stimulates intrinsic tendon healing while minimizing restrictive peritendinous adhesions.

Question 13227

Topic: Surgical Anatomy & Approaches
A 30-year-old restrained driver presents after a head-on motor vehicle collision. He has a shortened, internally rotated, and adducted right lower extremity. Radiographs confirm a posterior hip dislocation. Which of the following neurologic structures is at highest risk of injury in this scenario?
. Femoral nerve
. Obturator nerve
. Peroneal division of the sciatic nerve
. Tibial division of the sciatic nerve
. Superior gluteal nerve

Correct Answer & Explanation

. Peroneal division of the sciatic nerve

Explanation

Posterior hip dislocations place the sciatic nerve at risk of stretch or compression. The peroneal division is more commonly and severely injured than the tibial division due to its lateral position and secure tethering at the sciatic notch and fibular head.

Question 13228

Topic: 1. General Principles & Basic Science

In the physiological structure of normal articular cartilage, which zone is characterized by the highest concentration of proteoglycans and the lowest water content?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified cartilage zone
. Tidemark

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage has the highest concentration of proteoglycans and the lowest concentration of water. The superficial zone has the highest water content and highest collagen content, with collagen fibers oriented parallel to the joint surface to resist shear forces.

Question 13229

Topic: 1. General Principles & Basic Science

A surgeon performs a primary total hip arthroplasty using a direct lateral (Hardinge) approach. Postoperatively, the patient demonstrates a significant Trendelenburg gait. Injury to which of the following nerves is the most likely cause if the proximal split in the abductor mechanism was extended too far?

. Superior gluteal nerve
. Inferior gluteal nerve
. Sciatic nerve
. Femoral nerve
. Obturator nerve

Correct Answer & Explanation

. Superior gluteal nerve

Explanation

The superior gluteal nerve innervates the gluteus medius, gluteus minimus, and tensor fasciae latae. In the direct lateral approach to the hip, proximal splitting of the gluteus medius greater than 3 to 5 cm from the tip of the greater trochanter risks transecting the branches of the superior gluteal nerve, leading to abductor weakness and a Trendelenburg gait.

Question 13230

Topic: Biology, Genetics & Bone Healing

Which of the following growth factors is primarily responsible for inducing the differentiation of mesenchymal stem cells into osteoblasts during the early phases of fracture healing?

. Transforming growth factor-beta (TGF-beta)
. Platelet-derived growth factor (PDGF)
. Bone morphogenetic protein-2 (BMP-2)
. Vascular endothelial growth factor (VEGF)
. Insulin-like growth factor-1 (IGF-1)

Correct Answer & Explanation

. Bone morphogenetic protein-2 (BMP-2)

Explanation

Bone morphogenetic proteins (specifically BMP-2 and BMP-7) are potent osteoinductive growth factors of the TGF-beta superfamily. They play a critical role in bone healing by inducing the differentiation of pluripotential mesenchymal stem cells into osteoblasts.

Question 13231

Topic: Biomechanics & Biomaterials

When preparing antibiotic-loaded polymethylmethacrylate (PMMA) bone cement for the treatment of a periprosthetic joint infection, which of the following pharmacological characteristics is absolutely essential for the selected antibiotic?

. Heat lability
. High protein binding affinity
. A purely bacteriostatic mechanism of action
. Thermostability
. High lipophilicity

Correct Answer & Explanation

. Thermostability

Explanation

The polymerization of PMMA is a highly exothermic reaction, often reaching temperatures in excess of 80°C to 100°C in vivo. Therefore, any antibiotic mixed into the cement must be thermostable to retain its bactericidal properties. Common examples include Vancomycin, Tobramycin, and Gentamicin.

Question 13232

Topic: Biomechanics & Biomaterials

A resident is performing serial casting for an infant with clubfoot. When stretching the foot into dorsiflexion, the resident holds the cast in a constant deformed position and notes that the force required to maintain this position decreases over time. Which biomechanical property of ligaments and tendons does this describe?

. Creep
. Stress relaxation
. Hysteresis
. Fatigue failure
. Anisotropy

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is the decrease in stress (force) over time when a viscoelastic material is held at a constant strain (deformation). Creep, in contrast, is the gradual increase in deformation when a constant force is applied.

Question 13233

Topic: Biomechanics & Biomaterials

A surgeon decides to use a titanium plate with stainless steel screws to fix a femur fracture. Which type of corrosion is most likely to occur at the interface between these two different metals?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in contact within a conductive fluid (like body tissue), causing the less noble metal to act as an anode and corrode. To prevent this, implants made of different metals are generally not mixed.

Question 13234

Topic: Biology, Genetics & Bone Healing

A midshaft radius fracture is treated with rigid plate osteosynthesis resulting in absolute stability and anatomic reduction. This construct promotes bone healing primarily via which of the following mechanisms?

. Endochondral ossification
. Intramembranous ossification
. Primary bone healing via osteoclast cutting cones
. Secondary bone healing with robust callus formation
. Appositional periosteal growth

Correct Answer & Explanation

. Primary bone healing via osteoclast cutting cones

Explanation

Rigid internal fixation with absolute stability (strain < 2%) suppresses callus formation and promotes primary (direct) bone healing. This occurs via Haversian remodeling where osteoclast cutting cones cross the fracture site followed by osteoblasts.

Question 13235

Topic: Biology, Genetics & Bone Healing

A 30-year-old female with an unresectable recurrent Giant Cell Tumor (GCT) of the sacrum is started on denosumab therapy. What is the precise mechanism of action of this medication?

. Monoclonal antibody that binds and inhibits RANKL
. Bisphosphonate that induces osteoclast apoptosis
. Tyrosine kinase inhibitor targeting VEGF
. Monoclonal antibody against TNF-alpha
. Selective estrogen receptor modulator

Correct Answer & Explanation

. Monoclonal antibody that binds and inhibits RANKL

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANKL, preventing it from activating RANK on the surface of osteoclasts. In GCT, it targets the reactive osteoclast-like giant cells, halting bone destruction.

Question 13236

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction during bone healing. Once a BMP binds to its cell surface receptor, it primarily initiates osteogenic gene expression through which intracellular signaling pathway?

. Wnt / beta-catenin pathway
. JAK / STAT pathway
. Smad 1/5/8 pathway
. MAP kinase pathway
. cAMP / PKA pathway

Correct Answer & Explanation

. Smad 1/5/8 pathway

Explanation

BMPs are members of the TGF-beta superfamily. They bind to serine/threonine kinase receptors and primarily transduce their osteoinductive signals intracellularly via phosphorylation of Smad 1, 5, and 8.

Question 13237

Topic: Biology, Genetics & Bone Healing

A 35-year-old male sustains a midshaft transverse humerus fracture treated with dynamic compression plating. Which of the following best describes the fundamental mechanical principle allowing primary bone healing in this scenario?

. Absolute stability with strain less than 2%
. Relative stability with strain between 2% and 10%
. Callus formation driven by fracture site hypoxia
. Endochondral ossification mediated by micromotion
. High micromotion promoting robust osteoblast proliferation

Correct Answer & Explanation

. Absolute stability with strain less than 2%

Explanation

Primary bone healing occurs only under absolute stability, requiring strain less than 2%. It proceeds via cutting cones directly bridging the fracture gap without intermediate cartilaginous callus formation.

Question 13238

Topic: Biology, Genetics & Bone Healing

Denosumab is utilized in the treatment of osteoporosis and giant cell tumor of bone. What is the specific cellular target and mechanism of action of this biologic medication?

. Inhibits osteoclast ruffled border formation via integrin blockade
. Binds directly to RANK on osteoclasts to induce apoptosis
. Acts as a monoclonal antibody against RANKL, preventing osteoclast activation
. Inhibits farnesyl pyrophosphate synthase, disrupting osteoclast function
. Stimulates Wnt signaling pathway to increase osteoblast activity

Correct Answer & Explanation

. Acts as a monoclonal antibody against RANKL, preventing osteoclast activation

Explanation

Denosumab is a human monoclonal antibody that binds to RANKL, preventing its interaction with the RANK receptor on osteoclasts. This effectively inhibits osteoclast formation, function, and survival.

Question 13239

Topic: Biomechanics & Biomaterials

A surgeon uses a stainless steel screw to secure a titanium plate during an internal fixation procedure. Which type of corrosion is most likely to occur at the interface of these two different metals?

. Fretting corrosion
. Crevice corrosion
. Galvanic corrosion
. Pitting corrosion
. Stress corrosion cracking

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electrochemical potentials are placed in contact within an electrolytic environment, such as body fluids. The less noble metal undergoes accelerated corrosion due to electron transfer.

Question 13240

Topic: Surgical Anatomy & Approaches

A patient sustains a closed humerus fracture with a concomitant radial nerve palsy. EMG at 4 weeks shows fibrillation potentials, but ultrasound reveals the nerve remains in continuity with intact perineurium and epineurium. According to Sunderland's classification, what is the grade of this nerve injury?

. First degree
. Second degree
. Third degree
. Fourth degree
. Fifth degree

Correct Answer & Explanation

. Second degree

Explanation

A second-degree injury (axonotmesis) involves disruption of the axon with intact endoneurium, perineurium, and epineurium. Wallerian degeneration occurs distal to the injury, but the intact endoneurial tubes allow for highly predictable regeneration.

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