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1. General Principles & Basic Science MCQs

Practice Set 249 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 4961

Topic: Biology, Genetics & Bone Healing

During secondary (indirect) fracture healing, the transition from soft callus to hard callus is mediated primarily by which of the following processes?

. Endochondral ossification
. Intramembranous ossification
. Appositional ossification
. Creeping substitution
. Haversian remodeling

Correct Answer & Explanation

. Endochondral ossification

Explanation

Secondary fracture healing involves the formation of a soft cartilaginous callus, which is subsequently mineralized and replaced by bone. This process, where bone replaces a cartilage template, is known as endochondral ossification. Intramembranous ossification (bone formation without a cartilage template) occurs during primary fracture healing and at the periosteal margins.

Question 4962

Topic: 1. General Principles & Basic Science

In articular cartilage, which structural zone has the highest concentration of water and the lowest concentration of proteoglycans?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone of articular cartilage is characterized by chondrocytes that are flattened, collagen fibers oriented parallel to the joint surface, the highest water content, and the lowest proteoglycan content. As one moves toward the deep zone, water content decreases while proteoglycan concentration increases, allowing for compressive resistance.

Question 4963

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with pain in her knee. Radiographs reveal an eccentric, lytic lesion in the distal femur that extends to the subchondral bone without a sclerotic margin. Biopsy shows multinucleated giant cells intermixed with mononuclear stromal cells. If surgical curettage is planned, which adjuvant systemic therapy can be used to downstage the tumor or treat unresectable disease?

. Imatinib
. Denosumab
. Methotrexate
. Doxorubicin
. Zoledronic acid

Correct Answer & Explanation

. Denosumab

Explanation

The diagnosis is Giant Cell Tumor (GCT) of bone. The neoplastic mononuclear stromal cells express RANKL, which recruits and activates the multinucleated osteoclast-like giant cells responsible for the aggressive bone resorption. Denosumab, a human monoclonal antibody against RANKL, halts this process, leading to tumor ossification and is highly effective as a neoadjuvant or primary treatment for aggressive or unresectable GCT.

Question 4964

Topic: Biology, Genetics & Bone Healing

Calcium phosphate ceramics are frequently used as bone graft substitutes in orthopedic surgery. Which of the following accurately describes their primary biologic property during bone healing?

. They provide both osteoinductive and osteogenic properties
. They act solely as an osteoconductive scaffold
. They contain active bone morphogenetic proteins (BMPs)
. They release live osteoblasts into the defect
. They provide immediate structural cortical strength equal to autograft

Correct Answer & Explanation

. They act solely as an osteoconductive scaffold

Explanation

Calcium phosphate ceramics (along with calcium sulfates and hydroxyapatite) are purely osteoconductive. They provide a three-dimensional scaffold for host bone cells to migrate into and deposit new bone. They do not contain living cells (therefore are not osteogenic) and do not contain proteins like BMPs that stimulate mesenchymal stem cell differentiation (therefore are not osteoinductive).

Question 4965

Topic: 1. General Principles & Basic Science

When examining the ultrastructure of mature articular cartilage, which zone is characterized by having the highest concentration of proteoglycans, the lowest water content, and collagen fibrils aligned perpendicular to the joint surface?

. 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 resisting compressive loads. It has the highest concentration of proteoglycans, the lowest concentration of water, and thick type II collagen fibrils aligned perpendicularly to the articular surface. The superficial zone, by contrast, has the highest water content, lowest proteoglycan content, and collagen fibers aligned parallel to the surface to resist shear forces.

Question 4966

Topic: Surgical Anatomy & Approaches

During an ilioinguinal approach for an anterior column acetabular fracture, significant hemorrhage is encountered behind the superior pubic ramus near the symphysis. This bleeding is most likely originating from the 'corona mortis', which represents an anastomosis between which of the following vascular systems?

. Inferior epigastric artery and external pudendal artery
. Obturator artery and external iliac or inferior epigastric artery
. Internal pudendal artery and obturator artery
. Superior gluteal artery and lateral sacral artery
. Deep circumflex iliac artery and internal pudendal artery

Correct Answer & Explanation

. Obturator artery and external iliac or inferior epigastric artery

Explanation

The corona mortis ('crown of death') is a vascular anastomosis between the obturator and external iliac or inferior epigastric systems. It courses over the superior pubic ramus and is highly susceptible to iatrogenic injury during anterior pelvic surgical approaches.

Question 4967

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is widely used in orthopedic surgery as a bone graft substitute. Which of the following best describes its innate biological properties prior to being mixed with any marrow elements?

. Osteoinductive, osteoconductive, and osteogenic
. Purely osteoconductive with no osteoinductive properties
. Osteoinductive and osteoconductive, but lacks osteogenic cells
. Purely osteoinductive with no osteoconductive properties
. Osteogenic and osteoconductive, but lacks osteoinductivity

Correct Answer & Explanation

. Osteoinductive and osteoconductive, but lacks osteogenic cells

Explanation

Demineralized bone matrix (DBM) provides a collagenous scaffold (osteoconductive) and contains bone morphogenetic proteins (BMPs) exposed by the demineralization process (osteoinductive). However, it contains no living cells, so it is not osteogenic.

Question 4968

Topic: 1. General Principles & Basic Science

Which of the following alterations to the geometric design of a cortical bone screw will most significantly increase its pullout strength?

. Increasing the inner (root) diameter
. Decreasing the outer (thread) diameter
. Increasing the outer (thread) diameter
. Decreasing the thread pitch
. Decreasing the length of thread engagement

Correct Answer & Explanation

. Increasing the outer (thread) diameter

Explanation

Screw pullout strength is directly proportional to the outer (thread) diameter, the length of thread engagement, and the shear strength of the host bone. It is inversely proportional to the thread pitch. Therefore, increasing the outer diameter will significantly increase pullout strength.

Question 4969

Topic: Surgical Anatomy & Approaches

During an ilioinguinal approach for internal fixation of an anterior column acetabular fracture, significant arterial bleeding is suddenly encountered on the posterior aspect of the superior pubic ramus near the symphysis. This vessel represents an anastomosis between which two vascular systems?

. External iliac and internal iliac
. Superior gluteal and internal pudendal
. Inferior epigastric and obturator
. Deep circumflex iliac and femoral
. Internal pudendal and obturator

Correct Answer & Explanation

. Inferior epigastric and obturator

Explanation

The corona mortis is a vascular anastomosis between the external iliac system (via the inferior epigastric artery/vein) and the internal iliac system (via the obturator artery/vein). It is classically located over the superior pubic ramus and is at high risk of iatrogenic injury during the ilioinguinal approach.

Question 4970

Topic: Biology, Genetics & Bone Healing

Which of the following Bone Morphogenetic Proteins (BMPs) is FDA-approved for use in acute, open tibial shaft 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 acute, open tibial shaft fractures treated with an intramedullary nail. rhBMP-7 was previously approved under a Humanitarian Device Exemption for recalcitrant nonunions but is no longer commercially available. BMP-3 is an antagonist to osteogenesis.

Question 4971

Topic: 1. General Principles & Basic Science

In the repair of Zone II flexor tendon lacerations, which of the following biomechanical factors most significantly increases the ultimate tensile strength of the repair, allowing for early active motion?

. Using a braided non-absorbable suture instead of monofilament
. Increasing the number of core suture strands crossing the repair site
. Placing the epitendinous suture volar rather than dorsal
. Incorporating a locking rather than grasping core suture technique
. Prolonging the period of strict immobilization post-operatively

Correct Answer & Explanation

. Increasing the number of core suture strands crossing the repair site

Explanation

The most significant factor in increasing the tensile strength of a flexor tendon repair is the number of core suture strands crossing the repair site. A 4-strand or 6-strand repair is significantly stronger than a 2-strand repair, allowing for safe early active motion protocols. While locking configurations also provide some strength benefits, the strand count is the primary determinant of ultimate strength.

Question 4972

Topic: Biology, Genetics & Bone Healing

Osteoclasts are multinucleated cells responsible for bone resorption. Which of the following signaling molecules directly binds to its receptor on the osteoclast precursor to stimulate its differentiation and activation?

. 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-b)

Correct Answer & Explanation

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

Explanation

RANKL (Receptor activator of nuclear factor kappa-B ligand) is secreted by osteoblasts and binds to the RANK receptor on osteoclast precursors, stimulating their differentiation, activation, and survival. OPG acts as a decoy receptor for RANKL, inhibiting osteoclastogenesis. M-CSF is also required for osteoclast survival but it acts on the c-fms receptor earlier in the lineage.

Question 4973

Topic: 1. General Principles & Basic Science

Articular cartilage is highly specialized and avascular. In which zone of articular cartilage are the collagen fibers oriented perpendicular to the joint surface, providing the highest resistance to compressive forces?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

In the deep (radial) zone of articular cartilage, the collagen fibers (primarily Type II) are arranged perpendicular to the articular surface. This orientation, along with a high concentration of proteoglycans, provides the greatest resistance to compressive loads. The superficial zone has fibers parallel to the surface to resist shear stress.

Question 4974

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with knee pain. Radiographs reveal an eccentric, lytic, expansile lesion in the distal femoral epiphysis extending to the articular surface without a sclerotic margin. Biopsy shows multinucleated giant cells uniformly distributed among mononuclear stromal cells. Which of the following targeted medical therapies acts by binding to RANKL and is FDA-approved for unresectable or recurrent cases of this tumor?

. Imatinib
. Denosumab
. Zoledronic acid
. Methotrexate
. Doxorubicin

Correct Answer & Explanation

. Denosumab

Explanation

The diagnosis is a Giant Cell Tumor (GCT) of bone. The mononuclear stromal cells in GCT express RANKL, which recruits and activates the osteoclast-like multinucleated giant cells responsible for the aggressive osteolysis. Denosumab is a monoclonal antibody that binds to RANKL, preventing osteoclast activation, and is highly effective in treating advanced or unresectable GCTs.

Question 4975

Topic: Surgical Anatomy & Approaches

During an extensile ilioinguinal approach for a complex acetabular fracture, massive hemorrhage occurs while dissecting over the superior pubic ramus. This bleeding is most likely originating from the 'Corona Mortis'. This structure is classically an anastomosis between which two vascular systems?

. External iliac artery and internal iliac vein
. External iliac vein and obturator artery
. External iliac (or inferior epigastric) vessels and obturator vessels
. Internal pudendal artery and obturator vein
. Superior gluteal artery and inferior epigastric vein

Correct Answer & Explanation

. External iliac (or inferior epigastric) vessels and obturator vessels

Explanation

The Corona Mortis (Crown of Death) is a critical anatomical variant defined as a vascular anastomosis between the external iliac system (or inferior epigastric vessels) and the obturator vessels. It rests on the posterior aspect of the superior pubic ramus and is highly vulnerable during the ilioinguinal approach.

Question 4976

Topic: Biomechanics & Biomaterials

A surgeon incorrectly utilizes a stainless steel plate and secures it with titanium screws for a femur fracture. The patient subsequently develops implant failure and localized reaction due to corrosion. What specific type of corrosion has predominantly occurred?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in physical contact within an electrolytic solution (like human body fluid). An electrochemical cell is created; the less noble metal (stainless steel) acts as the anode and corrodes, while the more noble metal (titanium) acts as the cathode.

Question 4977

Topic: Biology, Genetics & Bone Healing

Recombinant human bone morphogenetic protein-2 (rhBMP-2) is utilized in orthopedic surgery for its osteoinductive properties. Through which primary intracellular signaling molecules does rhBMP-2 directly transmit its signal to the nucleus to upregulate osteogenic genes?

. Beta-catenin
. JAK/STAT proteins
. Smad 1, 5, and 8
. MAP kinases
. Notch intracellular domain (NICD)

Correct Answer & Explanation

. Smad 1, 5, and 8

Explanation

Bone morphogenetic proteins (BMPs) bind to cell-surface serine/threonine kinase receptors. This binding causes phosphorylation and activation of the receptor-regulated Smads (R-Smads), specifically Smad 1, 5, and 8. These complex with the common-mediator Smad 4 and translocate to the nucleus to activate the transcription of osteogenic genes like Runx2.

Question 4978

Topic: Biomechanics & Biomaterials

A structural orthopedic implant is subjected to a constant load below its yield strength over a prolonged period. Over time, the material exhibits a gradual and continuous increase in deformation. This specific viscoelastic property is best described as:

. Stress relaxation
. Hysteresis
. Creep
. Fatigue
. Isotropy

Correct Answer & Explanation

. Creep

Explanation

Creep is a viscoelastic property defined as the progressive deformation of a material over time when subjected to a constant load or stress. Stress relaxation is the decrease in stress over time when a material is held at a constant strain (deformation). Hysteresis refers to energy lost as heat during the loading and unloading cycles of a viscoelastic material.

Question 4979

Topic: Biology, Genetics & Bone Healing

Denosumab has emerged as an effective targeted medical therapy for locally advanced or recurrent giant cell tumors of bone (GCTB). What is the specific molecular mechanism of action of this medication?

. Inhibits vascular endothelial growth factor (VEGF)
. Binds to the RANK receptor on the surface of osteoclasts
. Binds to RANK ligand (RANKL), preventing its interaction with the RANK receptor
. Stimulates osteoprotegerin (OPG) production by osteoblasts
. Inhibits matrix metalloproteinases (MMPs)

Correct Answer & Explanation

. Binds to RANK ligand (RANKL), preventing its interaction with the RANK receptor

Explanation

Denosumab is a fully human monoclonal antibody that directly binds to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By binding to RANKL, it prevents RANKL from binding to the RANK receptor on the surface of osteoclasts and their precursors, thereby inhibiting osteoclast formation, function, and survival. GCTB stromal cells express high levels of RANKL, which recruits the multinucleated giant cells.

Question 4980

Topic: Biology, Genetics & Bone Healing

Which of the following clinical and biomechanical scenarios best describes the prerequisites and process of primary bone healing?

. Endochondral ossification leading to a robust fracture callus
. Intramembranous ossification mediated by pluripotential stem cells from the periosteum
. Direct Haversian remodeling across a fracture site under conditions of absolute stability
. Cartilage template formation followed by vascular invasion and osteoblast differentiation
. Healing of a highly comminuted midshaft femur fracture treated with an intramedullary nail

Correct Answer & Explanation

. Direct Haversian remodeling across a fracture site under conditions of absolute stability

Explanation

Primary (direct) bone healing occurs only under conditions of absolute stability and anatomic reduction (e.g., rigid plate fixation with compression). It proceeds via direct Haversian remodeling (cutting cones crossing the fracture site) without the formation of a cartilaginous intermediate or visible fracture callus. Options involving callus or endochondral ossification describe secondary bone healing.

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