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1. General Principles & Basic Science MCQs

Practice Set 538 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 10741

Topic: 1. General Principles & Basic Science

A patient sustains a severe compressive radial nerve injury. According to Sunderland's classification, which grade of nerve injury is characterized by complete disruption of the axon and myelin sheath but complete preservation of the endoneurium, perineurium, and epineurium?

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

Correct Answer & Explanation

. Second-degree

Explanation

A second-degree nerve injury (equivalent to Seddon's axonotmesis) involves complete axonal disruption and Wallerian degeneration, but the endoneurial tubes and supporting connective tissue strictly remain intact. This anatomy allows for predictable and complete nerve regeneration at roughly 1 mm/day.

Question 10742

Topic: Biology, Genetics & Bone Healing

A 4-month-old infant presents with recurrent fractures, cranial nerve palsies, and diffuse skeletal sclerosis on radiographs. Genetic testing reveals a mutation in the TCIRG1 gene. Which of the following is the primary pathophysiologic mechanism responsible for this condition?

. Defective ruffled border formation in osteoclasts
. Impaired osteoblast differentiation via Wnt signaling
. Defective collagen type I alpha-1 chain synthesis
. Lack of carbonic anhydrase II enzyme
. Overexpression of fibroblast growth factor receptor 3

Correct Answer & Explanation

. Defective ruffled border formation in osteoclasts

Explanation

TCIRG1 mutation is the most common cause of infantile malignant osteopetrosis. It encodes the a3 subunit of the V-ATPase, which is essential for acidifying the resorption lacuna. Defective ruffled border and proton pump function prevents bone resorption, leading to dense but brittle bone.

Question 10743

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, which of the following modifications to ultra-high molecular weight polyethylene (UHMWPE) most effectively increases its resistance to adhesive and abrasive wear?
. Sterilization in an oxygen-rich environment
. Increasing the crystalline lamellar thickness
. Highly cross-linking the polyethylene via irradiation
. Addition of barium sulfate
. Gamma irradiation at extremely low doses

Correct Answer & Explanation

. Highly cross-linking the polyethylene via irradiation

Explanation

Highly cross-linked polyethylene (HXLPE) is created by exposing UHMWPE to ionizing radiation, which creates free radicals that recombine to form strong cross-links. This significantly increases wear resistance and reduces particulate debris, though it necessitates subsequent thermal treatment to extinguish residual free radicals.

Question 10744

Topic: Biology, Genetics & Bone Healing

A 65-year-old female presents with persistent, dull, aching back pain. Radiographs show a compressive fracture of L4 and multiple 'punched-out' lytic lesions in her skull. Serum protein electrophoresis reveals a monoclonal spike. Which of the following factors is primarily responsible for the osteolytic bone destruction seen in this disease process?

. Overproduction of Osteoprotegerin (OPG)
. Upregulation of RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand)
. Direct destruction of bone by tumor cells
. Excessive production of parathyroid hormone (PTH)
. Downregulation of Macrophage Colony-Stimulating Factor (M-CSF)

Correct Answer & Explanation

. Upregulation of RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand)

Explanation

Multiple myeloma cells secrete various factors (such as MIP-1 alpha and IL-6) that upregulate RANKL expression by marrow stromal cells and downregulate OPG. This leads to profound osteoclast activation and the characteristic lytic bone lesions. The myeloma cells do not directly resorb bone.

Question 10745

Topic: Biology, Genetics & Bone Healing

A 35-year-old female presents with knee pain. Radiographs reveal an eccentrically located, lytic epiphyseal lesion extending to the subchondral bone in the proximal tibia. Biopsy shows multinucleated giant cells interspersed with mononuclear stromal cells. Treatment with Denosumab is considered. Denosumab targets which of the following to arrest tumor progression?

. RANK receptor on the multinucleated giant cells
. RANKL produced by the mononuclear stromal cells
. Osteoprotegerin (OPG) produced by the multinucleated giant cells
. Vascular endothelial growth factor (VEGF) in the tumor stroma
. Macrophage colony-stimulating factor (M-CSF) receptor on osteoclasts

Correct Answer & Explanation

. RANKL produced by the mononuclear stromal cells

Explanation

Giant Cell Tumor of Bone consists of neoplastic mononuclear stromal cells and reactive multinucleated giant cells. The neoplastic stromal cells produce excessive RANKL, which recruits and activates the osteoclast-like giant cells. Denosumab is a monoclonal antibody that binds to RANKL, preventing it from activating the RANK receptor on the giant cells.

Question 10746

Topic: Biomechanics & Biomaterials

Which of the following metal combinations represents the highest risk for galvanic corrosion when used together in an orthopaedic implant construct?

. Cobalt-chromium and Titanium
. Stainless steel and Titanium
. Cobalt-chromium and Tantalum
. Titanium and Tantalum
. Cobalt-chromium and Zirconium

Correct Answer & Explanation

. Stainless steel and Titanium

Explanation

Mixing stainless steel with either titanium or cobalt-chromium alloys is contraindicated due to a high risk of galvanic corrosion. Because stainless steel is significantly less noble (more anodic) than titanium, the stainless steel component will undergo rapid and severe corrosion when coupled with titanium in the body's electrolytic environment. Titanium and cobalt-chromium are more compatible with each other due to similar nobility profiles, though mixing them is still generally minimized.

Question 10747

Topic: Biomechanics & Biomaterials

In the biomechanical evaluation of viscoelastic materials such as ligaments and tendons, which of the following best defines the phenomenon of 'creep'?

. Decreasing peak force over time under a constant deformation
. Increasing deformation over time under a constant load
. Energy lost as heat during a loading and unloading cycle
. Rate-dependent increase in stiffness during rapid loading
. Microfailure of collagen fibers prior to macroscopic failure

Correct Answer & Explanation

. Increasing deformation over time under a constant load

Explanation

Creep is the progressive deformation of a viscoelastic material over time when it is subjected to a constant load. Stress relaxation (Option A) is the gradual decrease in stress over time when the material is held at a constant deformation. Hysteresis (Option C) is the energy lost during the loading and unloading cycle.

Question 10748

Topic: 1. General Principles & Basic Science

Which zone of articular cartilage is characterized by the highest concentration of water, the lowest concentration of proteoglycans, and collagen fibers aligned parallel to the joint surface?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone of articular cartilage has the highest water content and the lowest proteoglycan concentration. Its collagen fibers (primarily Type II) are oriented parallel to the articular surface to strongly resist shear forces.

Question 10749

Topic: Surgical Anatomy & Approaches

During the ilioinguinal approach to the pelvis, the surgeon must carefully identify and ligate the 'corona mortis' to prevent catastrophic hemorrhage. This structure typically represents an anastomosis between which two vascular systems?

. External iliac and internal pudendal vessels
. Inferior epigastric and obturator vessels
. Superior gluteal and inferior gluteal vessels
. Internal iliac and median sacral vessels
. External pudendal and obturator vessels

Correct Answer & Explanation

. Inferior epigastric and obturator vessels

Explanation

The corona mortis ('crown of death') is a retropubic vascular anastomosis between the obturator vessels and the external iliac or inferior epigastric vessels. It is located over the superior pubic ramus and is at high risk of injury during anterior pelvic approaches.

Question 10750

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is widely used in orthopedic surgery to reduce perioperative blood loss. Which of the following best describes its mechanism of action?
. Directly inhibits factor Xa in the coagulation cascade
. Prevents the activation of prothrombin to thrombin
. Acts as a synthetic analog of lysine to reversibly block plasminogen activation
. Cross-links fibrin strands by activating factor XIII
. Promotes the release of von Willebrand factor from endothelial cells

Correct Answer & Explanation

. Acts as a synthetic analog of lysine to reversibly block plasminogen activation

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It functions as an antifibrinolytic by reversibly binding to the lysine-binding sites on plasminogen, which prevents its activation into plasmin. This stabilizes existing fibrin clots and reduces bleeding.

Question 10751

Topic: Infection, Pharmacology & VTE

A 7-year-old boy from an endemic area presents with an acute, massive effusion of his right knee. He is afebrile and tolerating weight-bearing. Joint aspiration yields 45,000 WBCs/mm3 with 80% neutrophils. Serology for Borrelia burgdorferi is positive. What is the most appropriate initial treatment?

. Emergent arthroscopic irrigation and debridement
. Oral amoxicillin or doxycycline for 28 days
. Intravenous ceftriaxone for 14 days
. Intra-articular corticosteroid injection
. Serial daily aspirations until the effusion resolves

Correct Answer & Explanation

. Oral amoxicillin or doxycycline for 28 days

Explanation

The clinical presentation describes Lyme arthritis. Despite high synovial fluid cell counts that mimic septic arthritis, a patient who is systemically well and positive for Lyme in an endemic area should be treated initially with a 28-day course of oral antibiotics (amoxicillin for young children, doxycycline for adults/older children). Operative intervention is not initially indicated.

Question 10752

Topic: Biology, Genetics & Bone Healing

Which of the following conditions is an absolute requirement for primary (direct) bone healing to occur without the formation of a cartilaginous callus?

. Relative stability with micro-motion
. An intramedullary environment free of endosteal blood supply
. An interfragmentary gap greater than 2 mm
. Absolute fracture stability with anatomic reduction
. Application of low-intensity pulsed ultrasound

Correct Answer & Explanation

. Absolute fracture stability with anatomic reduction

Explanation

Primary (direct) bone healing bypasses endochondral ossification (callus formation) and requires absolute mechanical stability (strain < 2%) alongside anatomic reduction (gap < 0.1 mm). It occurs via osteonal cutting cones directly crossing the fracture line. Relative stability results in secondary bone healing via callus formation.

Question 10753

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with knee pain and swelling. Radiographs show an eccentric, lytic epiphyseal lesion in the distal femur without a sclerotic rim. Biopsy confirms a giant cell tumor of bone. If medical therapy is considered, which of the following describes the mechanism of the most appropriate targeted agent?

. Inhibition of vascular endothelial growth factor (VEGF)
. Direct binding to RANK receptors on multinucleated giant cells
. Monoclonal antibody binding to RANK ligand (RANKL)
. Inhibition of the mammalian target of rapamycin (mTOR)
. Tyrosine kinase inhibition targeting the c-kit mutation

Correct Answer & Explanation

. Monoclonal antibody binding to RANK ligand (RANKL)

Explanation

Giant cell tumor of bone is driven by neoplastic stromal cells that express high levels of RANKL, which recruits and activates reactive multinucleated osteoclast-like giant cells. Denosumab is a monoclonal antibody that binds directly to RANKL, inhibiting this process and reducing tumor-related bone destruction.

Question 10754

Topic: 1. General Principles & Basic Science

A 45-year-old male undergoes a spinal fusion using a structural cortical freeze-dried allograft. Which of the following best describes the predominant mechanism of initial graft incorporation?

. Osteoconduction with rapid complete replacement
. Osteogenesis and early revascularization
. Osteoinduction via BMPs
. Osteoconduction via creeping substitution
. Direct intramembranous ossification

Correct Answer & Explanation

. Osteoconduction via creeping substitution

Explanation

Cortical allografts incorporate primarily through osteoconduction and creeping substitution. The graft acts as a scaffold, but incorporation is slow and often remains incomplete centrally.

Question 10755

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) are osteoinductive growth factors belonging to the TGF-beta superfamily. Which of the following BMPs is an FDA-approved biologically active protein used as an adjunct in acute open tibia fractures?

. 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 use in acute open tibial shaft fractures and anterior lumbar interbody fusions. BMP-3 actually acts as an antagonist to osteogenesis.

Question 10756

Topic: 1. General Principles & Basic Science

Regarding the ultrastructure of hyaline articular cartilage, which zone contains the highest concentration of proteoglycans, the lowest concentration of water, and chondrocytes arranged in columns?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage is responsible for providing the greatest resistance to compressive forces. It contains the highest concentration of proteoglycans, the lowest water content, and vertically aligned chondrocytes.

Question 10757

Topic: Biology, Genetics & Bone Healing

Which cytokine is secreted by osteoblasts to directly stimulate osteoclast differentiation by binding to its specific receptor on the surface of osteoclast precursors?

. Osteoprotegerin (OPG)
. Macrophage colony-stimulating factor (M-CSF)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Interleukin-1 (IL-1)
. Transforming growth factor-beta (TGF-beta)

Correct Answer & Explanation

. Receptor activator of nuclear factor kappa-B ligand (RANKL)

Explanation

RANKL is secreted by osteoblasts and binds to RANK on osteoclast precursors, stimulating their differentiation and activation. OPG acts as a decoy receptor to inhibit this process.

Question 10758

Topic: 1. General Principles & Basic Science

Which zone of articular cartilage is characterized by the highest concentration of water and collagen fibers that are oriented parallel to the articular surface?

. Superficial zone
. Transitional zone
. Deep zone
. Calcified zone
. Subchondral bone

Correct Answer & Explanation

. Superficial zone

Explanation

The superficial zone of articular cartilage contains the highest water content and has collagen fibers oriented parallel to the joint surface to resist shear forces. Deep zone fibers are perpendicular to resist compressive loads.

Question 10759

Topic: Biology, Genetics & Bone Healing

A 55-year-old female with short bowel syndrome presents with diffuse bone pain and symmetric Looser zones on radiographs. What is the expected laboratory profile for her condition?

. Normal Calcium, normal Phosphate, normal PTH, normal ALP
. Low Calcium, low Phosphate, high PTH, high ALP
. High Calcium, low Phosphate, high PTH, high ALP
. Normal Calcium, low Phosphate, low PTH, high ALP
. Low Calcium, high Phosphate, low PTH, normal ALP

Correct Answer & Explanation

. Low Calcium, low Phosphate, high PTH, high ALP

Explanation

The patient has osteomalacia secondary to malabsorption. This causes poor vitamin D absorption, leading to low calcium and phosphate, which triggers secondary hyperparathyroidism (high PTH) and elevated alkaline phosphatase (ALP).

Question 10760

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, providing absolute fracture stability with less than 2% interfragmentary strain will promote which specific type of bone healing?

. Endochondral ossification
. Primary cortical healing via cutting cones
. Intramembranous ossification
. Robust cartilaginous callus formation
. Fibrous nonunion

Correct Answer & Explanation

. Primary cortical healing via cutting cones

Explanation

Absolute stability (strain less than 2%) allows for primary bone healing without callus formation. This is achieved via Haversian remodeling where osteoclasts create cutting cones followed immediately by osteoblast bone deposition.

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