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1. General Principles & Basic Science MCQs

Practice Set 606 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 12101

Topic: Biology, Genetics & Bone Healing

A 35-year-old female presents with an expansile, eccentric, lytic lesion in the epiphysis of the distal femur. A biopsy confirms the diagnosis of giant cell tumor (GCT) of bone. If she requires systemic medical therapy for unresectable disease, she may be treated with Denosumab. What is the mechanism of action of this drug?

. It binds to the RANK receptor directly on osteoclasts
. It is a monoclonal antibody that binds and inhibits RANKL
. It inhibits Vascular Endothelial Growth Factor (VEGF)
. It stimulates the production of Osteoprotegerin (OPG)
. It inhibits tyrosine kinase receptors on neoplastic stromal cells

Correct Answer & Explanation

. It binds to the RANK receptor directly on osteoclasts

Explanation

Giant cell tumor of bone consists of neoplastic stromal cells that express high levels of RANKL, which recruits and activates the reactive multinucleated giant cells (osteoclasts) responsible for the bone destruction. Denosumab is a human monoclonal antibody that binds to RANKL, preventing it from activating the RANK receptor on osteoclasts, thereby halting tumor-associated osteolysis.

Question 12102

Topic: 1. General Principles & Basic Science

Articular cartilage is a highly specialized tissue divided into distinct structural zones. Which zone contains the highest concentration of proteoglycans, the lowest water content, and collagen fibrils oriented strictly perpendicular to the articular surface?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The deep (radial) zone of articular cartilage is characterized by thick type II collagen fibrils oriented perpendicularly to the joint surface to resist compressive loads. It has the highest concentration of proteoglycans and the lowest water content compared to the more superficial zones.

Question 12103

Topic: Biomechanics & Biomaterials

Manufacturers have introduced Vitamin E-blended highly cross-linked polyethylene for total joint arthroplasty components. The primary biomechanical purpose of incorporating Vitamin E is to prevent which of the following processes?

. Adhesive wear
. Abrasive wear
. Oxidative degradation
. Cold flow (creep)
. Third-body wear

Correct Answer & Explanation

. Adhesive wear

Explanation

Vitamin E acts as a potent antioxidant. It neutralizes free radicals introduced during the irradiation cross-linking process, thereby preventing long-term oxidative degradation of the polyethylene component.

Question 12104

Topic: Surgical Anatomy & Approaches

A surgeon utilizes the volar (Henry) approach to the forearm for fixation of a proximal radius fracture. The proximal internervous plane of this surgical approach lies between the brachioradialis and which other muscle?

. Flexor carpi radialis
. Pronator teres
. Flexor digitorum superficialis
. Extensor carpi radialis longus
. Supinator

Correct Answer & Explanation

. Flexor carpi radialis

Explanation

The proximal internervous plane for the volar (Henry) approach to the radius lies between the brachioradialis (radial nerve) and the pronator teres (median nerve). Distally, the plane is between the brachioradialis and the flexor carpi radialis.

Question 12105

Topic: 1. General Principles & Basic Science

According to the Seddon classification of peripheral nerve injuries, which of the following accurately describes the histopathology of an axonotmesis?

. Complete transection of the nerve including the epineurium
. Disruption of the axon and myelin sheath with an intact endoneurium
. Localized physiologic conduction block with intact axonal continuity
. Demyelination without any axonal disruption
. Disruption of the epineurium with completely intact perineurium

Correct Answer & Explanation

. Complete transection of the nerve including the epineurium

Explanation

Axonotmesis involves loss of axonal continuity and subsequent Wallerian degeneration, but the connective tissue framework (endoneurium, perineurium, and epineurium) remains completely or partially intact. This intact framework allows for potential spontaneous axonal regeneration.

Question 12106

Topic: Biomechanics & Biomaterials

A 45-year-old active female sustains a medial meniscus posterior root tear. From a biomechanical perspective, how does this injury alter the knee joint kinematics and contact pressures?

. Normalizes contact pressure across the medial compartment
. Decreases peak contact pressure by 50%
. Increases the inherent hoop stresses within the remaining meniscus
. It is biomechanically equivalent to a total meniscectomy
. Shifts the mechanical axis to a valgus alignment

Correct Answer & Explanation

. Normalizes contact pressure across the medial compartment

Explanation

A medial meniscus posterior root tear severely compromises the meniscal hoop tension. Biomechanically, the loss of hoop stress containment results in peak contact pressures equivalent to a complete meniscectomy, predisposing the joint to rapid arthrosis.

Question 12107

Topic: Biology, Genetics & Bone Healing
During secondary bone healing via endochondral ossification, a soft cartilaginous callus is formed and subsequently replaced by woven bone. Which type of collagen predominates in the soft cartilaginous callus prior to its replacement?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IX collagen
. Type X collagen

Correct Answer & Explanation

. Type II collagen

Explanation

During endochondral ossification, the initial soft callus is composed primarily of cartilage, which is characterized by Type II collagen. As mineralization occurs and the hard callus forms, Type II collagen is replaced by Type I collagen.

Question 12108

Topic: Biology, Genetics & Bone Healing

A 35-year-old female is diagnosed with an aggressive giant cell tumor of the proximal tibia. She is started on denosumab therapy prior to surgery. What is the precise mechanism of action of this medication?

. Monoclonal antibody against the RANK receptor on osteoblasts
. Monoclonal antibody against RANKL, preventing osteoclast activation
. Direct inhibition of matrix metalloproteinases
. Stimulation of osteoblast apoptosis via the Wnt pathway
. Inhibition of the bisphosphonate-sensitive farnesyl pyrophosphate synthase

Correct Answer & Explanation

. Monoclonal antibody against the RANK receptor on osteoblasts

Explanation

Denosumab is a monoclonal antibody that binds to RANK Ligand (RANKL), preventing it from interacting with the RANK receptor on osteoclasts and giant cells. This effectively halts osteoclast-mediated bone resorption and promotes tumor consolidation.

Question 12109

Topic: 1. General Principles & Basic Science

A 28-year-old carpenter sustains a laceration to his index finger volar surface, resulting in a Zone II flexor digitorum profundus (FDP) and superficialis (FDS) transection. Following primary repair, early active mobilization is prescribed. What is the primary biologic advantage of this protocol?

. It accelerates the conversion of tenocytes to chondrocytes
. It decreases adhesion formation and improves tendon excursion
. It eliminates the need for an intact flexor sheath
. It prevents immediate rupture of the core suture
. It bypasses the inflammatory phase of tendon healing

Correct Answer & Explanation

. It accelerates the conversion of tenocytes to chondrocytes

Explanation

Early active mobilization following flexor tendon repair in Zone II enhances intrinsic tendon healing. It significantly decreases peritendinous adhesion formation and improves final tendon glide and excursion without unacceptably increasing the rupture rate.

Question 12110

Topic: Biology, Genetics & Bone Healing

Bone Morphogenetic Proteins (BMP-2 and BMP-7) are potent osteoinductive agents utilized in spine fusion and fracture nonunions. Following binding to cell surface receptors, which intracellular signaling proteins do BMPs primarily phosphorylate to induce osteoblastic gene transcription?

. JAK/STAT proteins
. Wnt/beta-catenin complex
. SMAD 1, 5, and 8 proteins
. MAP kinase extracellular signaling regulated kinases
. Notch/Hes intracellular domains

Correct Answer & Explanation

. JAK/STAT proteins

Explanation

Bone Morphogenetic Proteins (BMPs) bind to serine/threonine kinase receptors on the mesenchymal stem cell surface. This binding phosphorylates and activates downstream receptor-regulated SMAD proteins (specifically SMAD 1, 5, and 8), which translocate to the nucleus to promote osteoblast differentiation.

Question 12111

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic protein-2 (BMP-2) has potent osteoinductive properties and is utilized in various orthopedic fusion procedures. The intracellular signaling cascade initiated by BMP-2 binding to its cell surface serine/threonine kinase receptors relies primarily on the phosphorylation and activation of which of the following molecules?

. JAK and STAT proteins
. Smad 1, 5, and 8
. Beta-catenin
. NF-kappaB
. Erk and p38 MAPK

Correct Answer & Explanation

. JAK and STAT proteins

Explanation

Bone morphogenetic proteins (BMPs) belong to the TGF-beta superfamily. When BMP-2 binds to its heterodimeric serine/threonine kinase receptors (Type I and Type II), it phosphorylates intracellular receptor-regulated Smad proteins (R-Smads), specifically Smad 1, 5, and 8. These phosphorylated R-Smads then form a complex with the common-partner Smad (co-Smad), Smad 4, which translocates to the nucleus to regulate the transcription of osteogenic genes (e.g., Runx2, Osterix). Wnt signaling relies on beta-catenin, while RANKL utilizes the NF-kappaB pathway.

Question 12112

Topic: Biomechanics & Biomaterials

Orthopedic implants and connective tissues exhibit viscoelastic properties. Which of the following statements provides the most accurate biomechanical definition of 'stress relaxation'?

. A decrease in stress within a material over time when it is subjected to a constant strain
. An increase in strain within a material over time when it is subjected to a constant stress
. The energy lost as heat during the loading and unloading cycles of a material
. The point at which a material transitions from elastic to plastic deformation
. The gradual increase in microcracks leading to failure under repetitive cyclic loading

Correct Answer & Explanation

. A decrease in stress within a material over time when it is subjected to a constant strain

Explanation

Viscoelastic materials exhibit time-dependent responses to loading. 'Stress relaxation' is defined as the progressive decrease in internal stress over time when the material is held at a constant strain (deformation). An example is the decreasing tension in a tightened ligament graft over time. Option 1 defines 'creep', which is the progressive increase in strain (deformation) over time when subjected to a constant stress (load). Option 2 defines 'hysteresis'. Option 3 describes the yield point. Option 4 describes fatigue failure.

Question 12113

Topic: Biology, Genetics & Bone Healing

During fracture healing, bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction by directing mesenchymal stem cells to differentiate into osteoblasts. Which of the following BMPs is FDA-approved for use in acute open tibial shaft fractures treated with an intramedullary nail?

. BMP-2
. BMP-4
. BMP-7
. BMP-9
. BMP-14

Correct Answer & Explanation

. BMP-2

Explanation

Recombinant human BMP-2 (rhBMP-2, commercial name Infuse) is currently FDA-approved for the treatment of acute, open tibial shaft fractures stabilized with an intramedullary nail, as well as for anterior lumbar interbody fusions (ALIF). rhBMP-7 (OP-1) previously had a humanitarian device exemption for recalcitrant tibial nonunions.

Question 12114

Topic: Biomechanics & Biomaterials
In the manufacturing of modern highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) for total joint arthroplasty, what is the primary biomechanical and chemical purpose of adding vitamin E (alpha-tocopherol) to the polymer?
. To increase the melting temperature of the polymer allowing for easier machining
. To improve the initial yield strength of the polyethylene under heavy loads
. To scavenge free radicals generated during irradiation and prevent in vivo oxidation
. To facilitate more rapid bony ingrowth into the porous metal backing
. To increase the overall degree of cross-linking without needing gamma irradiation

Correct Answer & Explanation

. To scavenge free radicals generated during irradiation and prevent in vivo oxidation

Explanation

Irradiation is used to heavily cross-link UHMWPE to reduce wear, but it leaves behind free radicals. Over time, these free radicals can react with oxygen in vivo, leading to oxidative degradation, embrittlement, and failure. Vitamin E (alpha-tocopherol) is a potent antioxidant added to scavenge these free radicals, neutralizing them without needing secondary thermal treatments (like remelting) which can reduce mechanical strength.

Question 12115

Topic: Surgical Anatomy & Approaches

During the harvest of a hamstring autograft for an anterior cruciate ligament (ACL) reconstruction, care must be taken to avoid injury to a cutaneous nerve that supplies sensation to the anteromedial aspect of the lower leg. This nerve is a direct terminal branch of which of the following nerves?

. Obturator nerve
. Sciatic nerve
. Femoral nerve
. Tibial nerve
. Common peroneal nerve

Correct Answer & Explanation

. Obturator nerve

Explanation

The saphenous nerve is at high risk of iatrogenic injury during hamstring graft harvest, which can result in anteromedial leg numbness or a painful neuroma. The saphenous nerve is the largest and longest cutaneous terminal branch of the femoral nerve.

Question 12116

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of bone healing, what is the maximum interfragmentary strain environment that will permit primary (contact) bone healing to occur via osteoclast cutting cones?

. Less than 2%
. Between 2% and 10%
. Between 10% and 30%
. Greater than 30%
. Strain has no direct effect on primary bone healing

Correct Answer & Explanation

. Less than 2%

Explanation

Perren's strain theory dictates that primary (direct) bone healing, characterized by Haversian remodeling and osteoclast cutting cones without intermediate cartilage formation, requires absolute stability. This corresponds to an interfragmentary strain of less than 2%. Strains between 2% and 10% permit secondary healing (endochondral ossification/callus), while strains greater than 10% result in fibrous nonunion.

Question 12117

Topic: Surgical Anatomy & Approaches

During an anterior (ilioinguinal) surgical approach to the pelvic ring for an acetabular fracture, life-threatening hemorrhage can occur if a vascular structure known as the 'corona mortis' is inadvertently lacerated. This vascular anomaly represents an anastomosis between which two vascular systems?

. Internal pudendal and obturator
. External iliac (or inferior epigastric) and obturator
. Superior gluteal and external iliac
. Internal iliac and femoral
. Inferior gluteal and pudendal

Correct Answer & Explanation

. Internal pudendal and obturator

Explanation

The corona mortis ('crown of death') is an important vascular anastomosis (arterial, venous, or both) connecting the external iliac system (commonly via the inferior epigastric vessels) with the obturator system (internal iliac). It is located on the posterior aspect of the superior pubic ramus and is highly susceptible to injury during anterior approaches to the acetabulum.

Question 12118

Topic: Biomechanics & Biomaterials

In orthopedic biomechanics, stress shielding around an implant is largely determined by the mismatch in stiffness between the implant material and the host bone. Which of the following values best approximates the modulus of elasticity (Young's modulus) of normal human cortical bone?

. 0.5 - 1 GPa
. 15 - 20 GPa
. 100 - 110 GPa
. 200 - 220 GPa
. 500 - 550 GPa

Correct Answer & Explanation

. 0.5 - 1 GPa

Explanation

The modulus of elasticity (stiffness) of cortical bone is approximately 15-20 GPa. For comparison, cancellous bone is much more flexible (0.1-2 GPa). Titanium alloys used in orthopedics have a modulus around 110 GPa, and Stainless Steel/Cobalt-Chrome alloys are around 200-220 GPa. The large difference between metal implants and cortical bone is the primary driver of stress shielding.

Question 12119

Topic: Biology, Genetics & Bone Healing

Giant cell tumor of bone (GCTB) is a locally aggressive benign tumor. In cases where surgery is morbid and systemic therapy with Denosumab is utilized, what specific molecular interaction is being targeted by this medication?

. Inhibition of VEGF receptors on vascular endothelial cells
. Binding to RANKL to prevent activation of the RANK receptor
. Inhibition of the mTOR pathway within the neoplastic stromal cells
. Direct induction of apoptosis in the multinucleated giant cells via p53
. Inhibition of matrix metalloproteinases (MMPs) in the extracellular matrix

Correct Answer & Explanation

. Inhibition of VEGF receptors on vascular endothelial cells

Explanation

Denosumab is a fully human monoclonal antibody that specifically binds to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). In GCTB, the neoplastic mononuclear stromal cells overexpress RANKL, which recruits and activates the reactive, bone-resorbing multinucleated giant cells. By inhibiting RANKL, Denosumab breaks this cycle, preventing giant cell formation and halting osteolysis.

Question 12120

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is widely utilized in orthopedic surgery to minimize perioperative blood loss. What is its primary mechanism of action?
. Irreversible inhibition of cyclooxygenase
. Direct inhibition of Factor Xa
. Reversible blockade of lysine binding sites on plasminogen
. Activation of antithrombin III
. Enhancement of platelet aggregation via ADP receptors

Correct Answer & Explanation

. Reversible blockade of lysine binding sites on plasminogen

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It acts as an antifibrinolytic by reversibly binding to the lysine binding sites on plasminogen molecules. This prevents plasminogen from binding to fibrin, thereby inhibiting its activation into plasmin and preventing the breakdown of existing blood clots.

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