Menu

1. General Principles & Basic Science MCQs

Practice Set 251 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 5001

Topic: Biology, Genetics & Bone Healing

Which of the following processes characterizes primary (direct) bone healing, such as that achieved through anatomical reduction and absolute stability with a dynamic compression plate?

. Endochondral ossification
. Intramembranous ossification
. Osteoclastic cutting cones crossing the fracture site
. Robust callus formation bridging the fracture gap
. Chondroid bone formation

Correct Answer & Explanation

. Osteoclastic cutting cones crossing the fracture site

Explanation

Primary (direct) bone healing occurs under conditions of absolute stability and anatomical reduction. It bypasses the intermediate stages of callus formation and relies directly on osteoclastic 'cutting cones' that bore across the fracture line, followed immediately by osteoblasts that lay down lamellar bone. Secondary bone healing involves callus formation and endochondral ossification.

Question 5002

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with distal femur pain. Radiographs reveal an eccentric, purely lytic lesion in the epiphysis extending to the subchondral bone. Biopsy confirms a Giant Cell Tumor (GCT) of bone. In cases where neoadjuvant treatment is indicated, Denosumab is often utilized. What is the precise mechanism of action of this medication in treating GCT?

. It inhibits vascular endothelial growth factor (VEGF) to starve the tumor
. It acts as a competitive antagonist of estrogen receptors in the stroma
. It is a monoclonal antibody that binds to RANKL, preventing the recruitment and activation of osteoclast-like giant cells
. It binds directly to the RANK receptor on the neoplastic mononuclear stromal cells to induce apoptosis
. It is a potent bisphosphonate that binds to hydroxyapatite and poisons osteoclasts

Correct Answer & Explanation

. It is a monoclonal antibody that binds to RANKL, preventing the recruitment and activation of osteoclast-like giant cells

Explanation

Giant Cell Tumor of bone is composed of neoplastic mononuclear stromal cells that overexpress RANK Ligand (RANKL). This RANKL binds to RANK receptors on normal circulating monocytes, recruiting them and causing them to fuse into massive, bone-destroying osteoclast-like giant cells. Denosumab is a monoclonal antibody that binds directly to RANKL (not the RANK receptor), intercepting the signal and halting the bone destruction caused by the giant cells.

Question 5003

Topic: Surgical Anatomy & Approaches
A 35-year-old male sustains an APC-III pelvic ring injury. During the anterior surgical approach (ilioinguinal), massive hemorrhage occurs near the superior pubic ramus. Which vascular structures most likely represent the 'corona mortis' that was injured?
. An anastomosis between the internal pudendal and external iliac systems
. An anastomosis between the obturator and the external iliac or inferior epigastric systems
. An anastomosis between the superior gluteal artery and the external iliac vein
. The main branch of the internal iliac artery bifurcating prematurely
. An aberrant deep circumflex iliac artery inserting into the obturator vein

Correct Answer & Explanation

. An anastomosis between the obturator and the external iliac or inferior epigastric systems

Explanation

The corona mortis ('crown of death') is an anatomical variant representing an anastomosis between the obturator vessels (internal iliac system) and the external iliac or inferior epigastric vessels. It crosses the superior pubic ramus and is highly susceptible to injury during anterior pelvic approaches (e.g., ilioinguinal or Stoppa approaches), which can result in life-threatening hemorrhage.

Question 5004

Topic: Biology, Genetics & Bone Healing

A 65-year-old male presents with back pain and hypercalcemia. Radiographs show multiple 'punched-out' lytic lesions in the skull and vertebrae. Serum protein electrophoresis reveals an M-spike. Which of the following laboratory findings is most characteristic of this disease's specific effect on bone turnover?

. Markedly elevated serum alkaline phosphatase
. Decreased serum calcium levels
. Normal serum alkaline phosphatase with elevated urinary N-telopeptide
. Elevated parathyroid hormone (PTH) levels
. Elevated serum osteocalcin

Correct Answer & Explanation

. Normal serum alkaline phosphatase with elevated urinary N-telopeptide

Explanation

In multiple myeloma, malignant plasma cells secrete factors (like DKK1, MIP-1 alpha) that stimulate osteoclasts but heavily inhibit osteoblast differentiation and activity. Therefore, despite massive bone destruction (high N-telopeptide, high calcium), osteoblast-specific markers like alkaline phosphatase and osteocalcin remain surprisingly normal or low.

Question 5005

Topic: 1. General Principles & Basic Science

In the structural anatomy of normal articular hyaline cartilage, which zone contains the highest concentration of proteoglycans, the lowest water content, and chondrocytes that are arranged in vertical columns?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage is characterized by chondrocytes arranged in vertical columns perpendicular to the joint surface. It has the largest diameter collagen fibrils, the highest concentration of proteoglycans, and the lowest water content, providing high resistance to compressive forces.

Question 5006

Topic: Biology, Genetics & Bone Healing

In the treatment of open tibial shaft fractures, the use of recombinant human bone morphogenetic protein-2 (rhBMP-2) has been shown to decrease the need for secondary bone grafting. Which of the following intracellular signaling pathways is primarily activated by rhBMP-2?

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

Correct Answer & Explanation

. Smad 1/5/8 pathway

Explanation

Bone morphogenetic proteins (BMPs), particularly BMP-2 and BMP-7, bind to cell surface serine/threonine kinase receptors. This receptor activation leads to the intracellular phosphorylation of Smad 1, 5, and 8, which then form a complex with Smad 4 and translocate into the nucleus to regulate transcription of osteogenic genes.

Question 5007

Topic: 1. General Principles & Basic Science

During a Zone II flexor tendon repair, a surgeon decides to place an epitendinous suture around the primary core suture repair. Which of the following is the primary biomechanical benefit of adding the epitendinous suture?

. Increases gap resistance and overall construct strength
. Decreases gliding resistance but reduces overall construct strength
. Eliminates the need for a multi-strand core suture
. Increases the intrinsic vascularity to the repair site
. Prevents intrinsic healing of the tendon to limit adhesions

Correct Answer & Explanation

. Increases gap resistance and overall construct strength

Explanation

The addition of a running epitendinous suture increases the tensile strength of the repair by 10% to 50%, improves resistance to gap formation, and decreases gliding resistance by smoothing out the bulky core suture knots.

Question 5008

Topic: 1. General Principles & Basic Science
The biomechanical properties of articular cartilage are determined by its extracellular matrix components. Which of the following best describes the primary collagen type in articular cartilage and its primary mechanical function?
. Type I collagen; provides tensile strength
. Type II collagen; provides tensile strength
. Type I collagen; provides compressive strength
. Type II collagen; provides compressive strength
. Type III collagen; facilitates shear stress resistance

Correct Answer & Explanation

. Type II collagen; provides tensile strength

Explanation

Articular cartilage is composed primarily of Type II collagen (90-95% of the collagen content), which is responsible for the tissue's tensile strength and stiffness. Proteoglycans, primarily aggrecan, attract water and provide the tissue's resistance to compressive forces.

Question 5009

Topic: Biology, Genetics & Bone Healing

During fracture healing and normal bone development, osteogenesis occurs via two distinct pathways. Intramembranous ossification differs from endochondral ossification fundamentally by the absence of which of the following during the process?

. Osteoblast differentiation
. Mesenchymal stem cell proliferation
. A cartilaginous intermediate template
. Woven bone formation
. Vascularization

Correct Answer & Explanation

. A cartilaginous intermediate template

Explanation

Intramembranous ossification (seen in flat bones like the clavicle, skull, and during distraction osteogenesis) involves the direct differentiation of mesenchymal cells into osteoblasts without a preceding cartilaginous anlage (template). Endochondral ossification (long bone fracture callus) requires a cartilage intermediate that is subsequently mineralized and replaced by bone.

Question 5010

Topic: 1. General Principles & Basic Science

A 22-year-old soccer player sustains a knee injury and an MRI demonstrates a tear of the medial meniscus. When determining the indication for meniscal repair versus meniscectomy, healing potential relies heavily on vascularity. Which zone of the meniscus has the highest healing potential due to robust blood supply?

. Red-red zone (peripheral 10-30%)
. Red-white zone (middle third)
. White-white zone (inner third)
. Anterior horn central margin
. Posterior horn central margin

Correct Answer & Explanation

. Red-red zone (peripheral 10-30%)

Explanation

The vascular supply to the menisci originates from the perimeniscal capillary plexus, which is supplied by the medial and lateral geniculate arteries. This blood supply only penetrates the peripheral 10% to 30% of the meniscus (the red-red zone), giving this region the highest potential for healing after surgical repair.

Question 5011

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) initiate intracellular signaling leading to osteoblast differentiation. Which of the following best describes the specific intracellular mediators that translocate to the nucleus upon BMP receptor activation?

. STAT proteins
. Smad 1, 5, and 8
. Smad 2 and 3
. Beta-catenin
. NF-kappaB

Correct Answer & Explanation

. Smad 1, 5, and 8

Explanation

BMPs bind to serine/threonine kinase receptors on the cell surface, which phosphorylate receptor-regulated Smad 1, 5, and 8. These form a complex with the co-Smad (Smad 4) and translocate to the nucleus to regulate transcription of osteogenic genes like Runx2. Smad 2/3 are activated by TGF-beta.

Question 5012

Topic: 1. General Principles & Basic Science

Boundary lubrication in native articular cartilage is primarily mediated by a superficial layer of molecules that reduce friction under high-load conditions. Which specific glycoprotein is the main contributor to this mechanism?

. Aggrecan
. Hyaluronic acid
. Lubricin (PRG4)
. Type II collagen
. Chondroitin sulfate

Correct Answer & Explanation

. Lubricin (PRG4)

Explanation

Lubricin (proteoglycan 4 or PRG4) is synthesized by superficial zone chondrocytes and synoviocytes. It binds to the articular surface and provides boundary lubrication, critical for reducing friction under high loads. Hyaluronic acid primarily contributes to fluid-film (hydrodynamic) lubrication.

Question 5013

Topic: 1. General Principles & Basic Science

The vincula tendinum provide segmental blood supply to the flexor tendons within the digital sheath. Which of the following vessels provides the primary direct blood supply to the vinculum breve of the flexor digitorum profundus (FDP)?

. Proper digital artery
. Common digital artery
. Superficial palmar arch
. Deep palmar arch
. Princeps pollicis artery

Correct Answer & Explanation

. Proper digital artery

Explanation

Within the flexor sheath, the flexor tendons receive nutrition via diffusion from synovial fluid and via direct vascular perfusion through the vincula. The vincula (longa and brevia) are supplied by transverse communicating branches arising directly from the proper digital arteries.

Question 5014

Topic: Surgical Anatomy & Approaches

Which internervous plane is utilized superficially during the direct anterior (Smith-Petersen) approach to the hip?

. Between the tensor fasciae latae and gluteus medius
. Between the sartorius and tensor fasciae latae
. Between the rectus femoris and vastus lateralis
. Between the gluteus maximus and gluteus medius
. Between the adductor longus and gracilis

Correct Answer & Explanation

. Between the sartorius and tensor fasciae latae

Explanation

The direct anterior (Smith-Petersen) approach utilizes a true superficial internervous plane between the sartorius (innervated by the femoral nerve) and the tensor fasciae latae (innervated by the superior gluteal nerve). The deep plane is between the rectus femoris (femoral nerve) and gluteus medius (superior gluteal nerve).

Question 5015

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) stimulate osteoblast differentiation. Upon binding to their cell surface serine/threonine kinase receptors, which family of intracellular signaling molecules is directly phosphorylated to translocate to the nucleus and regulate gene transcription?

. STAT proteins
. Smad proteins
. MAP kinases
. Wnt proteins
. Beta-catenin

Correct Answer & Explanation

. Smad proteins

Explanation

BMPs belong to the TGF-beta superfamily. When they bind to their specific serine/threonine kinase receptors, the activated receptor directly phosphorylates intracellular receptor-regulated Smad proteins (R-Smads, typically Smad1, 5, and 8). These form a complex with Co-Smad (Smad4), which translocates to the nucleus to induce transcription of osteogenic genes like Runx2.

Question 5016

Topic: 1. General Principles & Basic Science

During skeletal muscle contraction, action potentials travel down the T-tubules to trigger the release of calcium. Which specific receptor complex physically facilitates the release of calcium from the sarcoplasmic reticulum into the cytosol?

. Dihydropyridine (DHP) and Ryanodine receptors
. Nicotinic acetylcholine receptors
. Voltage-gated sodium channels
. SERCA pumps
. Tropomyosin-troponin complex

Correct Answer & Explanation

. Dihydropyridine (DHP) and Ryanodine receptors

Explanation

Depolarization of the T-tubule membrane causes conformational changes in voltage-sensitive dihydropyridine (DHP) receptors. These are physically coupled to ryanodine receptors (RyR1) on the terminal cisternae of the sarcoplasmic reticulum. Activation of this DHP-RyR complex opens calcium channels, causing a massive efflux of Ca2+ into the sarcoplasm to initiate contraction.

Question 5017

Topic: Biology, Genetics & Bone Healing

During the process of creeping substitution in a structural cortical bone allograft, which of the following sequences best describes the biologic incorporation?

. Osteoblast proliferation followed by osteoclast resorption
. Osteoclast resorption followed by osteoblast deposition
. Simultaneous osteoclast and osteoblast activity at the graft surface only
. Chondrocyte proliferation, calcification, and replacement by osteoblasts
. Woven bone formation followed by direct cartilaginous conversion

Correct Answer & Explanation

. Osteoclast resorption followed by osteoblast deposition

Explanation

Cortical bone grafts incorporate via creeping substitution, which is strictly initiated by osteoclastic resorption (cutting cones) of the necrotic graft bone, followed directly by osteoblastic deposition of new viable bone within the newly created vascular channels. This transient porosity weakens the graft before it reaches its final mechanical strength.

Question 5018

Topic: Biology, Genetics & Bone Healing

When using a locked plate construct for a comminuted diaphyseal fracture, increasing the 'working length' of the plate achieves which of the following biomechanical effects?

. Decreases the construct flexibility, leading to absolute stability
. Increases the construct flexibility, promoting secondary bone healing
. Increases the stress on the screw-plate interface, increasing failure risk
. Decreases interfragmentary motion to zero
. Promotes primary bone healing via direct Haversian remodeling

Correct Answer & Explanation

. Increases the construct flexibility, promoting secondary bone healing

Explanation

In locked plating of comminuted fractures, the goal is relative stability to promote secondary (callus) bone healing. The 'working length' is the longitudinal distance between the two innermost screws spanning the fracture. Increasing the working length increases the overall flexibility of the construct, which allows beneficial interfragmentary micromotion and stimulates robust callus formation.

Question 5019

Topic: Biology, Genetics & Bone Healing

Lubricin (PRG4) is a critical glycoprotein responsible for boundary lubrication in human articular joints. Which cells are the primary producers of lubricin within the joint environment?

. Synovial fibroblasts and superficial zone chondrocytes
. Middle zone chondrocytes
. Deep zone chondrocytes
. Calcified zone chondrocytes
. Subchondral osteoblasts

Correct Answer & Explanation

. Synovial fibroblasts and superficial zone chondrocytes

Explanation

Lubricin is primarily synthesized by synovial fibroblasts and chondrocytes in the superficial zone of articular cartilage. It localizes to the cartilage surface and provides boundary lubrication, which reduces friction during joint motion and protects the articular surface from wear.

Question 5020

Topic: Surgical Anatomy & Approaches

During the anterior approach to the pelvis for acetabular fracture fixation, significant hemorrhage can occur due to an anastomotic vessel known as the 'corona mortis'. This structure typically represents a vascular communication between which two systems?

. Internal pudendal and inferior gluteal vessels
. Superior gluteal and lateral sacral vessels
. Inferior epigastric and obturator vessels
. Internal iliac and external iliac arteries directly
. Deep circumflex iliac and internal pudendal vessels

Correct Answer & Explanation

. Inferior epigastric and obturator vessels

Explanation

The corona mortis ('crown of death') is a high-risk vascular anastomosis between the external iliac system (typically the inferior epigastric artery or vein) and the internal iliac system (obturator artery or vein). It crosses the superior pubic ramus and must be carefully identified and ligated during an ilioinguinal or modified Stoppa approach.

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page