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1. General Principles & Basic Science MCQs

Practice Set 694 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 13861

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is widely used to supplement bone grafting in nonunions and fusions. Which of the following accurately describes its innate biological properties?

. Osteoconductive and osteoinductive
. Osteoinductive and osteogenic
. Osteoconductive and osteogenic
. Exclusively osteogenic
. Exclusively osteoconductive

Correct Answer & Explanation

. Osteoconductive and osteoinductive

Explanation

DBM is both osteoconductive (providing a structural scaffold) and osteoinductive (due to exposed bone morphogenetic proteins [BMPs] from the demineralization process). It lacks living cells, so it is not osteogenic.

Question 13862

Topic: 1. General Principles & Basic Science

Which of the following proteoglycans is primarily responsible for providing the osmotic swelling pressure and compressive resilience in healthy articular cartilage?

. Decorin
. Biglycan
. Aggrecan
. Fibromodulin
. Hyaluronan

Correct Answer & Explanation

. Aggrecan

Explanation

Aggrecan is the most abundant proteoglycan in articular cartilage matrix. Its heavily sulfated, negatively charged glycosaminoglycan chains draw water into the tissue, establishing a swelling pressure that resists compressive loads.

Question 13863

Topic: Surgical Anatomy & Approaches

During a Smith-Petersen (anterior) approach to the hip, the superficial internervous plane is developed. Which two nerves supply the specific muscles that define this superficial plane?

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

Correct Answer & Explanation

. Femoral nerve and Superior gluteal nerve

Explanation

The superficial plane of the Smith-Petersen approach lies between the sartorius (innervated by the femoral nerve) and the tensor fasciae latae (innervated by the superior gluteal nerve). This establishes a true internervous corridor.

Question 13864

Topic: Biomechanics & Biomaterials

If an orthopedic surgeon inadvertently uses a stainless steel screw through a titanium alloy locking plate, what mode of hardware failure or degradation is most likely to be accelerated?

. Crevice corrosion
. Galvanic corrosion
. Fretting corrosion
. Stress shielding
. Intergranular corrosion

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in physical contact within an electrolytic environment (such as bodily fluids). This sets up an electrochemical cell that accelerates the degradation of the more anodic metal.

Question 13865

Topic: Surgical Anatomy & Approaches

Four weeks after sustaining a closed humeral shaft fracture, a patient exhibits complete radial nerve palsy. An electromyogram (EMG) reveals fibrillation potentials in the brachioradialis but no voluntary motor unit action potentials. According to Seddon's classification, this nerve injury is best termed:

. Neuropraxia
. Axonotmesis
. Neurotmesis
. A first-degree Sunderland injury
. Wallerian regeneration

Correct Answer & Explanation

. Axonotmesis

Explanation

Fibrillation potentials confirm denervation, ruling out neuropraxia (which has preserved distal conduction and no fibrillations). Given the intact nerve sheath typically seen in closed fractures (as opposed to full transection in neurotmesis), this represents axonotmesis undergoing Wallerian degeneration.

Question 13866

Topic: Biology, Genetics & Bone Healing
The primary cellular defect in the initial active phase of Paget's disease of bone (osteitis deformans), which eventually leads to chaotic woven bone architecture, is localized to:
. Defective mineralization by osteoblasts
. Hyperactive, massive, and multinucleated osteoclasts
. Overproduction of parathyroid hormone (PTH) by adenomas
. Deficiency of tissue-nonspecific alkaline phosphatase
. Excessive production of Type III collagen fibers

Correct Answer & Explanation

. Hyperactive, massive, and multinucleated osteoclasts

Explanation

Paget's disease begins with an aggressive osteolytic phase driven by abnormally large, multinucleated osteoclasts that rapidly resorb bone. This is followed by a disorganized and frantic osteoblastic response, resulting in mechanically weak, structurally chaotic woven bone.

Question 13867

Topic: Biology, Genetics & Bone Healing
The organic extracellular matrix of normal mature lamellar bone is essential for tensile strength and ductility. Which collagen type accounts for approximately 90% of this organic matrix?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type I collagen

Explanation

Type I collagen is the overwhelmingly predominant structural protein in bone matrix, tendons, and ligaments. Type II collagen is primarily found in hyaline and articular cartilage.

Question 13868

Topic: Infection, Pharmacology & VTE
The progressive loss of articular cartilage characteristic of osteoarthritis is primarily mediated by the enzymatic cleavage of aggrecan and Type II collagen. Which class of enzymes is the primary driver of this catabolic degradation?
. Cyclooxygenases (COX-1, COX-2)
. Matrix metalloproteinases (MMPs)
. Cathepsin K
. Alkaline phosphatase
. Lipoxygenases

Correct Answer & Explanation

. Matrix metalloproteinases (MMPs)

Explanation

Matrix metalloproteinases (MMPs), specifically MMP-13 (collagenase 3) and ADAMTS-5 (an aggrecanase), are the principal enzymes that degrade the cartilage extracellular matrix in osteoarthritis.

Question 13869

Topic: 1. General Principles & Basic Science

In articular cartilage, which zone is characterized by the highest concentration of proteoglycans and collagen fibers oriented perpendicular to the joint surface?

. Superficial zone
. Transitional (middle) zone
. Deep zone
. Tidemark
. Calcified cartilage zone

Correct Answer & Explanation

. Deep zone

Explanation

The deep zone of articular cartilage contains the highest concentration of proteoglycans, the lowest water content, and collagen fibers that are oriented perpendicular to the joint surface to maximally resist compressive loads.

Question 13870

Topic: Infection, Pharmacology & VTE

A 4-year-old boy presents with a limp and refuses to bear weight on his right leg. According to the modified Kocher criteria, which of the following combinations gives the highest probability of septic arthritis of the hip?

. Fever > 38.5C, non-weight bearing, ESR > 40, WBC > 12,000
. Fever > 38.0C, limp, ESR > 20, WBC > 10,000
. Normal temperature, non-weight bearing, CRP > 1.0, WBC > 15,000
. Fever > 39.0C, non-weight bearing, ESR > 40, platelet count > 400,000
. Fever > 38.5C, limp, CRP > 2.0, WBC > 8,000

Correct Answer & Explanation

. Fever > 38.5C, non-weight bearing, ESR > 40, WBC > 12,000

Explanation

The four classic Kocher criteria for septic arthritis in a child are: non-weight bearing on the affected side, ESR > 40 mm/hr, Fever > 38.5 C (101.3 F), and WBC count > 12,000 cells/mm3. The presence of all four criteria indicates a >99% probability of septic arthritis.

Question 13871

Topic: Biology, Genetics & Bone Healing

Which type of bone healing is expected when a diaphyseal fracture is treated with a rigid plate and screws causing absolute stability, and what cell type is primarily responsible for the initial bridging?

. Secondary bone healing; chondrocytes
. Primary bone healing; osteoclasts followed by osteoblasts
. Secondary bone healing; osteoblasts
. Primary bone healing; chondrocytes
. Endochondral ossification; fibroblasts

Correct Answer & Explanation

. Primary bone healing; osteoclasts followed by osteoblasts

Explanation

Absolute stability (e.g., via a lag screw and neutralization plate) leads to primary bone healing. This occurs via cutting cones where osteoclasts bore across the fracture line, followed immediately by osteoblasts laying down new bone. There is no intermediate cartilaginous callus formation.

Question 13872

Topic: Biology, Genetics & Bone Healing

A 65-year-old female is diagnosed with osteoporosis and prescribed Alendronate. What is the primary cellular mechanism of action of this medication?

. Stimulates osteoblast differentiation
. Inhibits RANKL binding to RANK
. Inhibits farnesyl pyrophosphate synthase in osteoclasts
. Stimulates Wnt signaling pathway
. Binds to the parathyroid hormone receptor

Correct Answer & Explanation

. Inhibits farnesyl pyrophosphate synthase in osteoclasts

Explanation

Alendronate is a nitrogen-containing bisphosphonate. Its primary mechanism of action is the inhibition of farnesyl pyrophosphate (FPP) synthase in the mevalonate pathway within osteoclasts, leading to osteoclast apoptosis and decreased bone resorption.

Question 13873

Topic: 1. General Principles & Basic Science

Which of the following interventions most directly increases the statistical power of a clinical study evaluating a new orthopedic implant?

. Decreasing the alpha level from 0.05 to 0.01
. Increasing the sample size
. Increasing the variance of the data
. Decreasing the clinical effect size
. Increasing the beta error rate

Correct Answer & Explanation

. Increasing the sample size

Explanation

Statistical power (1 - Beta) is the probability of correctly rejecting the null hypothesis when it is false (avoiding a Type II error). Power is increased by increasing the sample size, increasing the expected effect size, decreasing data variance, or increasing the alpha level. Decreasing the alpha level makes it harder to find significance, thereby decreasing power.

Question 13874

Topic: Biomechanics & Biomaterials

On a stress-strain curve testing a specific orthopedic biomaterial, the concept of 'toughness' is best represented by which of the following?

. The total area under the stress-strain curve
. The slope of the linear elastic region
. The maximum stress before failure
. The point of transition from elastic to plastic deformation
. The area strictly under the linear elastic portion

Correct Answer & Explanation

. The total area under the stress-strain curve

Explanation

Toughness is the ability of a material to absorb energy and deform plastically before fracturing. It is represented by the total area under the stress-strain curve. The slope of the linear elastic region represents stiffness (Young's modulus). The maximum stress represents ultimate tensile strength. The transition point is the yield strength, and the area under the elastic portion is the resilience.

Question 13875

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in bone healing by inducing the differentiation of mesenchymal stem cells into osteoblasts. Binding of BMP to its cell surface receptor leads to direct phosphorylation and activation of which intracellular signaling proteins?

. Beta-catenin
. Notch intracellular domain (NICD)
. Hedgehog (Hh)
. Smad 1, 5, and 8
. NF-kappa B

Correct Answer & Explanation

. Smad 1, 5, and 8

Explanation

BMPs belong to the TGF-beta superfamily. When BMP binds to its heterodimeric serine/threonine kinase receptor, it phosphorylates the receptor-regulated Smads (R-Smads), specifically Smad 1, 5, and 8. These then form a complex with the co-Smad (Smad 4), which translocates to the nucleus to regulate transcription of osteogenic genes like Runx2. Beta-catenin is part of the Wnt signaling pathway.

Question 13876

Topic: 1. General Principles & Basic Science

Which of the following factors has the greatest influence on the pullout strength of a cortical screw in diaphyseal bone?

. Core diameter of the screw
. Pitch of the threads
. Insertion torque
. Outer diameter of the screw thread
. Length of the unthreaded shaft

Correct Answer & Explanation

. Outer diameter of the screw thread

Explanation

Screw pullout strength is most significantly affected by the outer diameter of the thread. Other contributing factors include thread pitch, length of thread engagement, and the shear strength of the host bone.

Question 13877

Topic: Biology, Genetics & Bone Healing
During the process of secondary bone healing, which type of collagen is initially deposited by chondrocytes in the soft callus phase?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type II collagen

Explanation

In the soft callus phase of endochondral ossification, chondrocytes lay down a cartilaginous matrix predominantly composed of Type II collagen. This is later calcified and replaced by Type I collagen as woven bone is formed.

Question 13878

Topic: Surgical Anatomy & Approaches

While performing an ilioinguinal approach for an acetabular fracture, significant hemorrhage occurs posterior to the superior pubic ramus. This is most likely due to an injury to the "corona mortis," which is an anastomosis between which two vascular systems?

. External iliac and internal pudendal
. External iliac and obturator
. Internal iliac and superior gluteal
. Femoral and obturator
. Internal pudendal and obturator

Correct Answer & Explanation

. External iliac and obturator

Explanation

The corona mortis is a critical vascular anastomosis between the external iliac (or inferior epigastric) system and the obturator system. It is classically located 5 to 7 cm laterally from the pubic symphysis.

Question 13879

Topic: Biology, Genetics & Bone Healing

Which of the following molecules binds directly to RANK on the surface of osteoclast precursors to stimulate their differentiation into mature osteoclasts?

. 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, secreted by osteoblasts, binds to RANK on osteoclast precursors to promote their differentiation and activation. Osteoprotegerin (OPG) acts as a decoy receptor for RANKL, inhibiting this bone resorption pathway.

Question 13880

Topic: Surgical Anatomy & Approaches

A patient presents with a spiral fracture of the distal third of the humeral shaft (Holstein-Lewis fracture). Which nerve is most at risk of being entrapped in the fracture site, and what clinical deficit would be expected?

. Median nerve; inability to flex the IP joint of the thumb
. Ulnar nerve; numbness of the small finger
. Radial nerve; inability to extend the wrist
. Axillary nerve; weakness of shoulder abduction
. Musculocutaneous nerve; weakness of elbow flexion

Correct Answer & Explanation

. Radial nerve; inability to extend the wrist

Explanation

The Holstein-Lewis fracture involves the distal third of the humerus, placing the radial nerve at high risk as it passes through the lateral intermuscular septum. Injury causes radial nerve palsy, which presents clinically as a wrist drop.

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