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1. General Principles & Basic Science MCQs

Practice Set 239 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 4761

Topic: Biomechanics & Biomaterials

When analyzing the biomechanical properties of a viscoelastic orthopedic implant, the device is subjected to a constant applied load over a prolonged period. The material demonstrates a progressive, time-dependent increase in deformation. What is the correct biomechanical term for this phenomenon?

. Stress relaxation
. Hysteresis
. Fatigue
. Creep

Correct Answer & Explanation

. Creep

Explanation

Creep is defined as the progressive deformation of a viscoelastic material under a constant load over time. In contrast, stress relaxation is the time-dependent decrease in internal stress under a constant state of deformation. Hysteresis is the energy lost (usually as heat) during a loading-unloading cycle.

Question 4762

Topic: 1. General Principles & Basic Science

Articular cartilage consists of multiple distinct histologic zones, each contributing to its unique biomechanical properties. Which of the following characteristics best describes the deep zone of normal adult articular cartilage?

. Highest water content and collagen fibers oriented parallel to the joint surface.
. Lowest proteoglycan content and random orientation of collagen fibers.
. Highest proteoglycan content and collagen fibers oriented perpendicular to the joint surface.
. Primarily composed of Type I collagen and characterized by high cellularity.
. Chondrocytes arranged in horizontal clusters with high water content.

Correct Answer & Explanation

. Highest proteoglycan content and collagen fibers oriented perpendicular to the joint surface.

Explanation

The deep (radial) zone of articular cartilage contains the largest diameter collagen fibers oriented perpendicularly to the articular surface, which provides significant resistance to compressive forces. It has the lowest water content and the highest proteoglycan concentration. The superficial zone has the highest water content and collagen parallel to the surface.

Question 4763

Topic: Biology, Genetics & Bone Healing

A 30-year-old woman presents with knee pain. Radiographs show an eccentric, lytic epiphyseal lesion in the distal femur. Biopsy confirms a Giant Cell Tumor (GCT) of bone.

Denosumab is considered for neo-adjuvant treatment to consolidate the tumor rim. What is the specific cellular target of denosumab in the pathogenesis of this tumor?

. The RANK receptor on the surface of the multinucleated giant cells.
. The RANK Ligand (RANKL) produced by the neoplastic mononuclear stromal cells.
. Osteoprotegerin (OPG) produced by local osteoblasts.
. Vascular Endothelial Growth Factor (VEGF) expressed by the tumor vasculature.
. The tyrosine kinase receptor on the neoplastic giant cells.

Correct Answer & Explanation

. The RANK Ligand (RANKL) produced by the neoplastic mononuclear stromal cells.

Explanation

In Giant Cell Tumor of bone, the true neoplastic cells are the mononuclear spindle-like stromal cells, not the giant cells. These stromal cells secrete large amounts of RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). The RANKL recruits and activates normal osteoclast precursors to fuse into the characteristic reactive, bone-destroying multinucleated giant cells. Denosumab is a monoclonal antibody that specifically binds to and inhibits RANKL.

Question 4764

Topic: Biomechanics & Biomaterials

In orthopedic implant manufacturing, the mechanical properties of an alloy dictate its behavior within the host bone. Which of the following standard solid metallic biomaterials exhibits the lowest modulus of elasticity, thereby minimizing stress shielding when utilized as a diaphyseal stem?

. Cobalt-Chromium-Molybdenum (CoCrMo) alloy
. 316L Stainless Steel
. Titanium alloy (Ti-6Al-4V)
. Zirconia toughened Alumina (ZTA)
. Commercially pure Iron

Correct Answer & Explanation

. Titanium alloy (Ti-6Al-4V)

Explanation

The modulus of elasticity (Young's modulus) is a measure of material stiffness. Cortical bone has a modulus of roughly 15-20 GPa. Titanium alloys (like Ti-6Al-4V) have a modulus of about 110 GPa, which is much closer to bone than 316L Stainless Steel (~200 GPa) or CoCrMo alloys (~210-240 GPa). The closer the implant's modulus is to cortical bone, the less load it shields from the bone, thereby reducing periprosthetic bone resorption (stress shielding).

Question 4765

Topic: Surgical Anatomy & Approaches

During a Kocher-Langenbeck approach for an acetabular fracture, the surgeon must be mindful of protecting the sciatic nerve. What is the optimal positioning of the lower extremity to minimize tension on the sciatic nerve during retraction?

. Hip flexed and knee extended
. Hip extended and knee flexed
. Hip and knee both extended
. Hip and knee both flexed
. Hip internally rotated and knee extended

Correct Answer & Explanation

. Hip extended and knee flexed

Explanation

Extending the hip and flexing the knee relaxes the sciatic nerve. This minimizes the risk of iatrogenic traction injury during posterior retractor placement.

Question 4766

Topic: Surgical Anatomy & Approaches

A 24-year-old rugby player undergoes a Latarjet procedure for recurrent anterior shoulder instability with 25% glenoid bone loss. During the transfer of the coracoid process, which of the following nerves is at greatest risk of injury and must be carefully protected?

. Axillary nerve
. Suprascapular nerve
. Musculocutaneous nerve
. Radial nerve
. Median nerve

Correct Answer & Explanation

. Musculocutaneous nerve

Explanation

The musculocutaneous nerve enters the coracobrachialis approximately 5 cm distal to the coracoid tip. It is at significant risk during coracoid osteotomy and mobilization of the conjoint tendon.

Question 4767

Topic: Biology, Genetics & Bone Healing

Which of the following statements correctly describes the cellular pathophysiology of a Giant Cell Tumor (GCT) of bone?

. Multinucleated giant cells are the primary neoplastic cells and express RANK.
. Mononuclear stromal cells are the primary neoplastic cells and express RANKL.
. Multinucleated giant cells express RANKL to recruit reactive mononuclear cells.
. The tumor is driven by an overproduction of osteoprotegerin (OPG).
. Denosumab directly induces apoptosis in the multinucleated giant cells.

Correct Answer & Explanation

. Mononuclear stromal cells are the primary neoplastic cells and express RANKL.

Explanation

In Giant Cell Tumor of bone, the mononuclear stromal cells are the true neoplastic cells. They express Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL), which recruits and activates the reactive multinucleated osteoclast-like giant cells that cause bone destruction.

Question 4768

Topic: Infection, Pharmacology & VTE

During the posteromedial approach for fixation of a split-depression medial tibial plateau fracture, the optimal surgical interval to expose the posterior aspect of the medial tibial condyle is between the medial head of the gastrocnemius and which anterior structure?

. Semimembranosus
. Popliteus
. Pes anserinus
. Medial collateral ligament (MCL)
. Soleus

Correct Answer & Explanation

. Pes anserinus

Explanation

The posteromedial approach to the proximal tibia utilizes the interval between the medial head of the gastrocnemius (retracted posteriorly) and the pes anserinus tendons (retracted anteriorly) to safely place a buttress plate.

Question 4769

Topic: Biology, Genetics & Bone Healing

A patient sustains an isolated, closed transverse fracture of the humeral shaft. During non-operative management with a functional brace, primary healing occurs via endochondral ossification. If rigid internal fixation with a compression plate had been used instead, bone healing would primarily depend on which of the following cellular processes?

. Formation of a soft cartilage callus
. Osteoclastic cutting cones crossing the fracture site
. Proliferation of periosteal stem cells without osteoclasts
. Differentiation of mesenchymal cells into chondrocytes
. Secretion of matrix metalloproteinases by macrophages

Correct Answer & Explanation

. Osteoclastic cutting cones crossing the fracture site

Explanation

Rigid internal fixation with absolute stability (such as a compression plate for a transverse fracture) promotes primary bone healing. This occurs via direct Haversian remodeling driven by osteoclastic cutting cones, bypassing the formation of a cartilaginous soft callus seen in secondary healing.

Question 4770

Topic: Biology, Genetics & Bone Healing



A 28-year-old female presents with a lytic lesion in her distal femur abutting the joint. Biopsy confirms a Giant Cell Tumor of bone. She is treated with Denosumab prior to surgery. What is the mechanism of action of Denosumab, and what is the characteristic histological change seen after treatment?

. Inhibits RANK; increases osteoclast apoptosis.
. Binds RANKL; elimination of multinucleated giant cells and formation of woven bone.
. Binds osteoprotegerin; increased calcification of tumor matrix.
. Tyrosine kinase inhibitor; central necrosis of the tumor.
. Binds RANKL; proliferation of mononuclear spindle cells.

Correct Answer & Explanation

. Binds RANKL; elimination of multinucleated giant cells and formation of woven bone.

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, preventing it from interacting with RANK on osteoclasts and osteoclast-like giant cells. In Giant Cell Tumor of bone, it leads to a dramatic depletion of the multinucleated giant cells, leaving behind a fibrous stroma and resulting in dense woven bone formation and peripheral rimming.

Question 4771

Topic: 1. General Principles & Basic Science

Articular cartilage is divided into four structural zones. Which zone is characterized by the highest concentration of proteoglycans, lowest concentration of water, and collagen fibers oriented perpendicular to the articular surface?

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

Correct Answer & Explanation

. Deep (radial) zone.

Explanation

The deep (radial) zone of articular cartilage contains collagen fibers that are oriented perpendicular to the articular surface, anchoring the cartilage to the tidemark. This zone possesses the highest concentration of proteoglycans and the lowest water content, optimizing it for compressive load resistance. The superficial zone has collagen parallel to the joint, highest water content, and lowest proteoglycan content.

Question 4772

Topic: 1. General Principles & Basic Science

A 45-year-old female with a BMI of 35 presents with acute medial knee pain after a deep knee flexion maneuver. MRI confirms a complete radial tear at the medial meniscus posterior root footprint. What is the primary biomechanical consequence of this specific injury pattern if left untreated?

. Increased anterior tibial translation during the Lachman test
. Loss of hoop stresses resulting in contact pressures equivalent to a total meniscectomy
. Isolated increased peak contact pressures in the lateral compartment
. Medial patellar subluxation during knee flexion
. Accelerated varus morphologic bowing of the proximal tibia

Correct Answer & Explanation

. Loss of hoop stresses resulting in contact pressures equivalent to a total meniscectomy

Explanation

A posterior root tear disrupts the meniscal hoop stresses, causing the meniscus to extrude. Biomechanically, this results in peak contact pressures identical to a complete meniscectomy, predisposing to rapid cartilage degradation.

Question 4773

Topic: Infection, Pharmacology & VTE

Intravenous Vancomycin is frequently used as prophylaxis or treatment in orthopedic surgery for MRSA infections. What is the specific cellular mechanism of action of this antibiotic?

. Inhibiting DNA gyrase to prevent bacterial replication
. Binding to the 30S ribosomal subunit to inhibit protein synthesis
. Binding to the D-alanyl-D-alanine terminus of cell wall precursor peptides
. Inhibiting beta-lactamase enzymes directly
. Disrupting the bacterial cell membrane by binding to phospholipids

Correct Answer & Explanation

. Binding to the D-alanyl-D-alanine terminus of cell wall precursor peptides

Explanation

Vancomycin is a glycopeptide antibiotic that inhibits cell wall synthesis by binding tightly to the D-alanyl-D-alanine portion of the peptidoglycan precursor, preventing cross-linking.

Question 4774

Topic: Biology, Genetics & Bone Healing

Recombinant human bone morphogenetic proteins (rhBMPs) are commonly used to enhance bone healing. Which specific intracellular signaling molecules are directly phosphorylated by the BMP receptor complex to translocate to the nucleus and activate osteogenic gene transcription?

. JAK/STAT
. Smad 1, 5, and 8
. Wnt/beta-catenin
. MAPK/ERK
. NFATc1

Correct Answer & Explanation

. Smad 1, 5, and 8

Explanation

BMPs bind to serine/threonine kinase receptors that phosphorylate receptor-regulated Smads (Smad 1, 5, and 8). These then form a complex with Smad 4, which translocates to the nucleus to regulate transcription of osteogenic genes.

Question 4775

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) is subjected to irradiation to improve wear resistance. However, irradiation creates free radicals that can cause oxidative degradation. Which post-irradiation thermal treatment completely eliminates free radicals but significantly reduces the mechanical properties (e.g., yield strength) of the polyethylene?
. Annealing
. Remelting
. Vitamin E blending
. Cold drawing
. Ethylene oxide sterilization

Correct Answer & Explanation

. Remelting

Explanation

Remelting (heating above the melting point of ~135 degrees C) completely extinguishes residual free radicals, enhancing oxidation resistance, but it decreases crystallinity, thereby reducing yield strength and fatigue resistance. Annealing heats below the melting point, preserving mechanical properties but leaving some free radicals.

Question 4776

Topic: Biology, Genetics & Bone Healing

Denosumab is increasingly used as a targeted medical therapy for the treatment of giant cell tumor of bone. By which specific mechanism does this monoclonal antibody halt tumor progression?

. Inhibiting the Wnt/beta-catenin pathway in osteoblasts
. Binding to RANK ligand to prevent osteoclast activation
. Directly inducing apoptosis of the neoplastic stromal cells
. Blocking vascular endothelial growth factor (VEGF) receptors
. Antagonizing parathyroid hormone-related peptide (PTHrP)

Correct Answer & Explanation

. Binding to RANK ligand to prevent osteoclast activation

Explanation

Denosumab binds directly to RANKL, preventing it from interacting with RANK on the surface of osteoclast precursors. In giant cell tumors, this stops the neoplastic stromal cells from recruiting and activating the destructive multinucleated giant cells.

Question 4777

Topic: Biomechanics & Biomaterials
In the manufacturing of ultra-high molecular weight polyethylene (UHMWPE) for total joint arthroplasty, highly cross-linked polyethylene is utilized to reduce volumetric wear. However, the cross-linking process introduces free radicals. Which secondary process is most commonly used to extinguish these free radicals and prevent long-term oxidative degradation?
. Cold irradiation
. Ethylene oxide sterilization
. Remelting or annealing
. Calcium hydroxyapatite coating
. Addition of barium sulfate

Correct Answer & Explanation

. Remelting or annealing

Explanation

Gamma irradiation is used to cross-link UHMWPE to reduce wear, but it inherently creates free radicals that cause long-term oxidative degradation. Thermal treatments, such as remelting or annealing, are utilized to extinguish these free radicals and stabilize the polyethylene.

Question 4778

Topic: Infection, Pharmacology & VTE

A 50-year-old female presents with acute pain and swelling in her right shoulder. She is febrile and reports a history of intravenous drug use. On examination, the shoulder is exquisitely tender, erythematous, and warm. She resists all attempts at passive range of motion. Joint aspiration yields purulent fluid. Which of the following is the MOST critical initial step in management, after obtaining cultures?

. Initiate oral antibiotics immediately
. Perform a CT scan to assess bone involvement
. Refer for urgent surgical irrigation and debridement
. Apply ice and immobilize the shoulder
. Start NSAIDs for pain and inflammation

Correct Answer & Explanation

. Refer for urgent surgical irrigation and debridement

Explanation

This clinical picture is highly suggestive of septic arthritis of the shoulder. After obtaining Gram stain and cultures from the aspirated fluid, urgent surgical irrigation and debridement is paramount to remove pus and necrotic tissue, reduce bacterial load, and prevent cartilage destruction. This should be combined with appropriate intravenous antibiotics. Oral antibiotics alone are insufficient for septic arthritis. A CT scan may be useful later for osteomyelitis assessment but is not the immediate priority for acute septic arthritis. Ice and immobilization are palliative and do not address the infection. NSAIDs will mask symptoms and do not treat the underlying pathology.

Question 4779

Topic: Surgical Anatomy & Approaches

A 55-year-old patient undergoes an open Bankart repair for recurrent anterior shoulder instability. Post-operatively, he develops difficulty with elbow flexion and sensation along the lateral forearm. What nerve is MOST likely injured?

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

Correct Answer & Explanation

. Musculocutaneous nerve

Explanation

The musculocutaneous nerve innervates the biceps brachii and brachialis muscles (primary elbow flexors) and provides sensory innervation to the lateral forearm (lateral cutaneous nerve of the forearm). It is at risk during anterior shoulder approaches, particularly with excessive retraction of the conjoined tendon (coracobrachialis and short head of biceps), which lies close to this nerve. Axillary nerve injury would affect deltoid and teres minor. Radial nerve affects wrist/finger extensors. Ulnar nerve affects intrinsic hand muscles and medial forearm sensation. Median nerve affects forearm pronation, thumb, and index/middle finger flexion, and sensation to the thumb/index/middle fingers.

Question 4780

Topic: Biomechanics & Biomaterials

A 21-year-old collegiate baseball pitcher undergoes ulnar collateral ligament (UCL) reconstruction via the docking technique after failing nonoperative management for a full-thickness anterior bundle tear. What is the most critical anatomical consideration when creating the ulnar tunnel to ensure proper biomechanics?

. Recreating the isometric footprint on the anteroinferior medial epicondyle
. Positioning the tunnel at the level of the radial head articulation
. Recreating the eccentric attachment on the sublimis tubercle
. Ensuring the tunnel penetrates the intra-articular capsular reflection
. Placing the graft deep to the flexor pronator mass for dynamic compression

Correct Answer & Explanation

. Recreating the isometric footprint on the anteroinferior medial epicondyle

Explanation

The anterior bundle of the UCL is the primary restraint to valgus stress at the elbow. Recreating its nearly isometric origin on the anteroinferior surface of the medial epicondyle is the most critical technical step to restore stable, physiologic elbow kinematics throughout the arc of motion.

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