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1. General Principles & Basic Science MCQs

Practice Set 698 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 13941

Topic: 1. General Principles & Basic Science

Which zone of articular cartilage contains the highest concentration of proteoglycans and features chondrocytes aligned perpendicular to the articular surface?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

Articular cartilage is divided into distinct zones. The deep (radial) zone has the highest proteoglycan content, the lowest water content, and chondrocytes/collagen fibers that are aligned perpendicular to the joint surface to resist compressive loads. The superficial zone has the highest water content and collagen fibers aligned parallel to the surface to resist shear stress.

Question 13942

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of bone healing, what is the maximum percentage of tissue strain that permits the direct formation of lamellar bone without an intermediate cartilaginous or fibrous phase?

. Less than 2%
. 2% to 10%
. 10% to 30%
. Greater than 30%
. Strain level does not affect the histological path of bone formation

Correct Answer & Explanation

. Less than 2%

Explanation

Perren's strain theory dictates that tissues dictate the type of healing based on the strain they can tolerate. Lamellar bone can only tolerate <2% strain. Therefore, primary (direct) bone healing requires absolute stability (strain <2%). Woven bone can tolerate up to 10% strain, while cartilage tolerates 10-30% strain, and granulation tissue tolerates up to 100% strain, which defines the secondary (callus) healing pathway under relative stability.

Question 13943

Topic: Biology, Genetics & Bone Healing

A 72-year-old female treated with alendronate for 8 years presents with a 3-month history of progressive left thigh pain. Radiographs reveal lateral cortical thickening and a transverse radiolucent line in the subtrochanteric region of the left femur. What is the most appropriate management?

. Discontinue alendronate, begin teriparatide, and restrict weight bearing
. Discontinue alendronate and perform prophylactic cephalomedullary nailing
. Continue alendronate and perform prophylactic cephalomedullary nailing
. Switch to denosumab and observe with serial radiographs
. Discontinue alendronate and perform open reduction internal fixation with a lateral plate

Correct Answer & Explanation

. Discontinue alendronate and perform prophylactic cephalomedullary nailing

Explanation

This patient has an impending atypical femur fracture (AFF) associated with long-term bisphosphonate use, characterized by lateral cortical beaking, transverse radiolucency, and thigh pain. Because she has a symptomatic impending fracture with radiographic changes, prophylactic intramedullary nailing (cephalomedullary preferred in the subtrochanteric region) is indicated. Bisphosphonates must be discontinued immediately. Plating is biomechanically inferior for AFFs.

Question 13944

Topic: Biomechanics & Biomaterials

Highly cross-linked polyethylene (HXLPE) is the standard bearing surface used in modern total hip arthroplasty due to its significantly decreased volumetric wear. However, the process of cross-linking and subsequent melting or annealing to eliminate free radicals leads to a clinically relevant decrease in which of the following mechanical properties?

. Surface hardness and scratch resistance
. Fatigue resistance and ultimate tensile strength
. Modulus of elasticity
. Oxidation resistance in vivo
. Coefficient of friction

Correct Answer & Explanation

. Fatigue resistance and ultimate tensile strength

Explanation

Irradiation of polyethylene creates cross-links that drastically reduce abrasive and adhesive volumetric wear. However, irradiation also breaks polymer chains, creating free radicals. Subsequent thermal treatments (melting or annealing) are required to eliminate these free radicals to prevent oxidation. This thermal treatment reduces the crystallinity of the polyethylene, which decreases its fatigue resistance, yield strength, ductility, and ultimate tensile strength. This is why highly cross-linked polyethylene must be used cautiously in high-stress, non-conforming joints like the knee or in very thin liners.

Question 13945

Topic: Biology, Genetics & Bone Healing

A 45-year-old male undergoes a posterolateral lumbar fusion using recombinant human bone morphogenetic protein-2 (rhBMP-2). Through which specific intracellular signaling pathway does this biologic agent primarily promote osteoblast differentiation?

. Wnt/beta-catenin pathway
. RANK/RANKL signaling
. SMAD 1/5/8 phosphorylation
. Notch signaling pathway
. Hedgehog pathway

Correct Answer & Explanation

. SMAD 1/5/8 phosphorylation

Explanation

rhBMP-2 binds to serine/threonine kinase receptors, causing phosphorylation of SMAD 1, 5, and 8. These molecules then complex with SMAD 4 to enter the nucleus and upregulate osteogenic genes like Runx2.

Question 13946

Topic: Biology, Genetics & Bone Healing

A 25-year-old female presents with a destructive, expansile lytic lesion in the distal femur. Biopsy confirms a Giant Cell Tumor of bone. If medical therapy with denosumab is initiated, what is its primary mechanism of action?

. Inhibition of vascular endothelial growth factor (VEGF)
. Monoclonal antibody targeting RANK ligand (RANKL)
. Bisphosphonate-mediated induction of osteoclast apoptosis
. Direct stimulation of osteoprotegerin (OPG) production
. Inhibition of tissue matrix metalloproteinases (MMPs)

Correct Answer & Explanation

. Monoclonal antibody targeting RANK ligand (RANKL)

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to RANKL, preventing it from activating RANK on osteoclasts and their precursors. This effectively inhibits osteoclast-mediated bone destruction characteristic of giant cell tumors.

Question 13947

Topic: Biomechanics & Biomaterials

A 55-year-old male undergoes a total hip arthroplasty. To minimize the risk of galvanic corrosion, the surgeon must be cautious about metal combinations. Which combination of stem and head materials is most strongly associated with galvanic and fretting corrosion at the trunnion?

. Titanium alloy stem with Ceramic head
. Cobalt-chromium stem with Ceramic head
. Titanium alloy stem with Cobalt-chromium head
. Stainless steel stem with Stainless steel head
. Oxinium head with Titanium alloy stem

Correct Answer & Explanation

. Titanium alloy stem with Cobalt-chromium head

Explanation

The combination of a titanium alloy stem with a cobalt-chromium head introduces dissimilar metals at the modular junction, increasing the risk of galvanic and fretting corrosion (trunnionosis). Ceramic heads are electrically insulating and do not cause galvanic corrosion.

Question 13948

Topic: Biomechanics & Biomaterials

In the context of orthopedic biomechanics and materials science, what does the "yield point" on a stress-strain curve specifically represent?

. The maximum stress a material can withstand before catastrophic failure
. The exact transition point from elastic to plastic deformation
. The point of material fatigue after repetitive cyclic loading
. The initial linear region corresponding precisely to Hooke's Law
. The total kinetic energy absorbed by the material immediately prior to fracture

Correct Answer & Explanation

. The exact transition point from elastic to plastic deformation

Explanation

The yield point marks the end of elastic deformation (where a material returns to its original shape) and the onset of plastic deformation (resulting in permanent shape change). Beyond this specific point, Hooke's Law is no longer applicable.

Question 13949

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum amount of interfragmentary strain that permits primary bone healing?

. Less than 2%
. Between 2% and 10%
. Between 10% and 15%
. Greater than 15%
. Primary bone healing is independent of strain

Correct Answer & Explanation

. Less than 2%

Explanation

Primary bone healing occurs without callus formation and requires absolute stability. According to Perren's strain theory, the interfragmentary strain must be less than 2% to allow osteoclasts to form cutting cones across the fracture site.

Question 13950

Topic: Surgical Anatomy & Approaches

The direct anterior approach (Smith-Petersen) to the hip utilizes a true internervous plane. This plane is located between muscles innervated by which of the following nerve pairs?

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

Correct Answer & Explanation

. Femoral nerve and Superior gluteal nerve

Explanation

The superficial internervous plane of the direct anterior approach is between the sartorius (femoral nerve) and the tensor fasciae latae (superior gluteal nerve). The deep plane is between the rectus femoris (femoral nerve) and gluteus medius (superior gluteal nerve).

Question 13951

Topic: Biomechanics & Biomaterials

Which of the following terms best describes the viscoelastic property where a biological material continues to slowly deform over time when subjected to a constant, sustained load?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the progressive deformation of a material over time under a constant load. Stress relaxation, conversely, is the decrease in stress over time when a material is held at a constant strain (length).

Question 13952

Topic: Biology, Genetics & Bone Healing

A 65-year-old male presents with bone pain, anemia, and hypercalcemia. Radiographs show multiple 'punched-out' lytic lesions in the skull and pelvis. The primary mechanism of bone destruction in this disease is driven by the upregulation of which of the following?

. RANK ligand (RANKL)
. Osteoprotegerin (OPG)
. Bone Morphogenetic Protein-2 (BMP-2)
. Transforming Growth Factor-beta (TGF-b)
. Fibroblast Growth Factor Receptor 3 (FGFR3)

Correct Answer & Explanation

. RANK ligand (RANKL)

Explanation

The patient has Multiple Myeloma. The myeloma cells secrete factors (like MIP-1 alpha) that upregulate RANKL and downregulate OPG, leading to massive osteoclast activation and the characteristic lytic bone lesions.

Question 13953

Topic: Biology, Genetics & Bone Healing

Which of the following bone morphogenetic proteins (BMPs) is considered to have osteo-inhibitory effects rather than osteoinductive effects?

. BMP-3
. BMP-2
. BMP-4
. BMP-6
. BMP-7

Correct Answer & Explanation

. BMP-3

Explanation

While most BMPs (such as BMP-2 and BMP-7) are strongly osteoinductive and promote bone formation, BMP-3 is unique as it acts as an antagonist to osteogenic BMPs, thereby inhibiting bone formation.

Question 13954

Topic: Surgical Anatomy & Approaches

Which of the following muscles of the posterior thigh is uniquely innervated by the common peroneal division of the sciatic nerve?

. Semimembranosus
. Short head of the biceps femoris
. Long head of the biceps femoris
. Semitendinosus
. Ischial portion of the adductor magnus

Correct Answer & Explanation

. Short head of the biceps femoris

Explanation

The short head of the biceps femoris is the only muscle in the posterior compartment of the thigh innervated by the common peroneal division of the sciatic nerve. All other hamstring muscles are innervated by the tibial division.

Question 13955

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, highly cross-linking ultra-high-molecular-weight polyethylene (UHMWPE) is performed primarily to alter its material properties. How does this manufacturing process alter the polyethylene compared to conventional UHMWPE?
. Increases wear resistance but decreases fatigue strength
. Decreases wear resistance but increases fatigue strength
. Increases both wear resistance and fracture toughness
. Decreases both wear resistance and fracture toughness
. Increases wear resistance but increases susceptibility to oxidation

Correct Answer & Explanation

. Increases wear resistance but decreases fatigue strength

Explanation

Highly cross-linked polyethylene significantly improves wear resistance, thereby reducing osteolysis in total joint arthroplasty. However, the cross-linking and subsequent thermal treatments reduce mechanical properties such as fatigue strength and fracture toughness.

Question 13956

Topic: Biomechanics & Biomaterials

When combining orthopedic implant components made of different metals, galvanic corrosion may occur. Which of the following combinations of metals carries the highest risk of clinically significant galvanic corrosion when placed in direct contact in vivo?

. Titanium and Titanium alloy
. Cobalt-Chrome and Cobalt-Chrome
. Stainless Steel and Titanium
. Ceramic and Titanium
. Highly cross-linked polyethylene and Cobalt-Chrome

Correct Answer & Explanation

. Stainless Steel and Titanium

Explanation

Galvanic corrosion occurs when two dissimilar metals with significantly different anodic indices are placed in contact in an electrolyte fluid. The coupling of stainless steel and titanium creates a strong galvanic cell, leading to rapid corrosion, and should be avoided in orthopedic constructs.

Question 13957

Topic: Biology, Genetics & Bone Healing

A 72-year-old female presents with a 3-month history of dull, aching pain in her left thigh, exacerbated by weight-bearing. She has been on alendronate for osteoporosis for 8 years. Physical examination is unremarkable. Initial X-rays of the femur are normal. What is the most appropriate next step in her diagnostic workup?

. Order a bone scan to evaluate for stress reaction.
. Prescribe NSAIDs and advise activity modification.
. Obtain an MRI of the left femur.
. Refer for a consultation with a pain management specialist.
. Discontinue alendronate immediately and observe.

Correct Answer & Explanation

. Obtain an MRI of the left femur.

Explanation

This patient's symptoms and history (long-term bisphosphonate use, thigh pain, normal initial X-rays) are highly suggestive of a prodromal or incomplete atypical femoral fracture (AFF). While a bone scan might show increased uptake, MRI is the most sensitive and specific imaging modality to detect cortical thickening, periosteal reaction, or a transverse lucency, which are characteristic findings of an impending or incomplete AFF. Early diagnosis is crucial to prevent a complete fracture. Discontinuing bisphosphonates might be part of the management but not the immediate next diagnostic step without confirming the pathology. NSAIDs and observation are inappropriate given the high suspicion for an AFF.

Question 13958

Topic: Surgical Anatomy & Approaches

A patient suffers a closed humerus fracture and subsequent radial nerve palsy. Electromyography at 4 weeks suggests an axonotmesis injury (Sunderland second-degree). Which of the following best describes the pathophysiology of this nerve injury?

. Loss of myelin with an intact axon
. Disruption of the axon with an intact endoneurium
. Disruption of the axon and endoneurium with an intact perineurium
. Disruption of the entire nerve trunk including the epineurium
. Ischemic neuropraxia without Wallerian degeneration

Correct Answer & Explanation

. Disruption of the axon with an intact endoneurium

Explanation

In an axonotmesis (Sunderland second-degree) injury, the axon is disrupted, leading to distal Wallerian degeneration, but the endoneurial tubes remain intact. These intact tubes guide the regenerating axons, allowing for a good prognosis for spontaneous recovery.

Question 13959

Topic: Biology, Genetics & Bone Healing

A 35-year-old man undergoes rigid plate fixation for a transverse radius shaft fracture. During the healing process, no fracture callus is visualized on radiographs. Which biological process dictates primary bone healing in this scenario?

. Endochondral ossification
. Cutting cone remodeling
. Fibrocartilage template formation
. Intramembranous ossification with abundant callus
. Mesenchymal cell condensation

Correct Answer & Explanation

. Cutting cone remodeling

Explanation

Primary bone healing occurs under absolute stability and relies on osteoclastic cutting cones crossing the fracture site, followed by osteoblasts depositing new lamellar bone. This process entirely bypasses the formation of a fibrocartilaginous callus.

Question 13960

Topic: Biology, Genetics & Bone Healing

A 72-year-old woman, who has been treated with alendronate for 10 years, presents with a transverse fracture of the subtrochanteric femur after simply rising from a chair. Radiographs reveal focal lateral cortical thickening and a 'beaking' appearance. What is the underlying pathophysiologic mechanism caused by her prolonged medication use?

. Inhibition of osteoclast function leading to severe suppression of bone remodeling
. Direct cytotoxic effect on mature osteoblasts preventing osteoid formation
. Overstimulation of parathyroid hormone resulting in cortical thinning
. Inhibition of lysyl oxidase causing defective collagen cross-linking
. Increased osteocyte apoptosis leading to avascular necrosis of the diaphysis

Correct Answer & Explanation

. Inhibition of osteoclast function leading to severe suppression of bone remodeling

Explanation

Prolonged bisphosphonate therapy inhibits osteoclast activity and induces their apoptosis, heavily suppressing normal bone remodeling. This failure to clear normal microdamage over time reduces bone toughness, leading to atypical subtrochanteric or diaphyseal femur fractures.

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