Menu

1. General Principles & Basic Science MCQs

Practice Set 481 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 9601

Topic: 1. General Principles & Basic Science

Which screw characteristic is most crucial for maintaining reduction of an osteotomy in cancellous bone without causing bone resorption around the threads?

. Larger core diameter and finer thread pitch.
. Larger outer diameter and coarser thread pitch.
. Self-tapping flutes on the tip.
. Cannulated design for precise placement.
. Differential thread pitch for dynamic compression.

Correct Answer & Explanation

. Larger outer diameter and coarser thread pitch.

Explanation

For optimal purchase and stability in cancellous bone, screws are designed with a larger outer diameter and a coarser thread pitch (fewer threads per unit length). This design maximizes the surface area of bone engaged by the threads, distributing forces over a larger area and providing superior pullout strength in soft bone, thereby minimizing the risk of bone resorption due to localized stress or micromotion around the threads. A finer pitch is for cortical bone, and a smaller core implies a larger thread height relative to core, good for cortical bone.

Question 9602

Topic: 1. General Principles & Basic Science

What is the primary disadvantage of using stainless steel screws compared to titanium screws in situations where magnetic resonance imaging (MRI) may be required post-operatively?

. Lower fatigue strength of stainless steel.
. Increased cost of stainless steel implants.
. Greater artifact on MRI scans, obscuring anatomical detail.
. Higher risk of allergic reactions to stainless steel.
. Reduced long-term biocompatibility.

Correct Answer & Explanation

. Greater artifact on MRI scans, obscuring anatomical detail.

Explanation

Stainless steel (specifically 316L stainless steel, a commonly used orthopedic alloy) is ferromagnetic, meaning it can create significant artifacts on MRI scans. These artifacts appear as large signal voids or distortions, which can obscure critical anatomical details and hinder diagnostic interpretation of soft tissues or bone healing around the implant. Titanium, being paramagnetic or diamagnetic depending on the alloy, produces significantly less artifact on MRI, making it the preferred material if post-operative MRI is anticipated.

Question 9603

Topic: 1. General Principles & Basic Science

What is the consequence if the drill bit used for the pilot hole for a self-tapping cortical screw is significantly smaller than the screw's core diameter?

. Increased interfragmentary compression.
. Easier screw insertion due to less resistance.
. Higher risk of screw breakage and/or stripping of bone threads.
. Reduced pullout strength due to inadequate bone engagement.
. Enhanced self-tapping capability.

Correct Answer & Explanation

. Higher risk of screw breakage and/or stripping of bone threads.

Explanation

If the pilot hole is significantly smaller than the core diameter of the screw, the screw will encounter excessive resistance during insertion. This dramatically increases the insertion torque required. Such high torque can lead to several problems: the screw itself might break, the drill bit could break during tapping, or the bone threads could strip due to the excessive force trying to cut into insufficient space. This compromises the stability of the fixation and can damage the bone. Proper pilot hole sizing, matching the core diameter, is crucial.

Question 9604

Topic: Biology, Genetics & Bone Healing

Bone Morphogenetic Proteins (BMPs) act primarily by binding to which type of cellular receptor?

. G-protein coupled receptor
. Tyrosine kinase receptor
. Serine/threonine kinase receptor
. Intracellular nuclear receptor
. Ligand-gated ion channel

Correct Answer & Explanation

. Serine/threonine kinase receptor

Explanation

BMPs are part of the TGF-beta superfamily. They bind to transmembrane serine/threonine kinase receptors, leading to phosphorylation of intracellular Smad proteins, which then translocate to the nucleus to regulate gene transcription for osteoblastic differentiation.

Question 9605

Topic: Biomechanics & Biomaterials

In biomechanics, the phenomenon where a tissue maintains a constant deformation (strain) over time while the applied force (stress) gradually decreases is known as:

. Creep
. Stress relaxation
. Hysteresis
. Fatigue failure
. Anisotropy

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a viscoelastic property defined as the decrease in stress over time when a material is held at a constant strain. Creep is the opposite: increasing strain over time under a constant stress.

Question 9606

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with a destructive, eccentrically located lytic lesion in the distal femur epiphysis extending to the subchondral bone. Histology reveals neoplastic mononuclear cells and abundant reactive multinucleated giant cells. Which of the following is an appropriate targeted medical therapy for advanced or unresectable cases of this tumor?

. Imatinib
. Denosumab
. Zoledronic acid
. Rituximab
. Methotrexate

Correct Answer & Explanation

. Denosumab

Explanation

The clinical and histologic description is classic for a Giant Cell Tumor (GCT) of bone. The neoplastic mononuclear cells express RANKL, which recruits and activates the multinucleated giant cells (osteoclast-like cells) responsible for bone destruction. Denosumab is a monoclonal antibody that targets and binds RANKL, inhibiting this process, and is an FDA-approved treatment for advanced or unresectable GCTs.

Question 9607

Topic: 1. General Principles & Basic Science

Which zone of articular cartilage contains the largest diameter collagen fibrils, the highest concentration of proteoglycans, and chondrocytes arranged in vertical columns?

. Superficial (tangential) zone
. Transitional (middle) 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 parallel to the collagen fibers, which are themselves oriented vertically (perpendicular to the joint surface). This zone has the largest diameter collagen fibrils and the highest concentration of proteoglycans, providing maximal resistance to compressive forces.

Question 9608

Topic: Infection, Pharmacology & VTE

A 4-year-old boy presents with a 2-day history of right hip pain, a limp, and a tactile fever. Which of the following is NOT a parameter included in the classic Kocher criteria used to differentiate septic arthritis from transient synovitis of the pediatric hip?

. Non-weight-bearing on the affected side
. Erythrocyte sedimentation rate (ESR) > 40 mm/hr
. Serum white blood cell (WBC) count > 12,000/mm3
. Temperature > 38.5 degrees C
. Presence of a joint effusion on ultrasound

Correct Answer & Explanation

. Presence of a joint effusion on ultrasound

Explanation

The classic Kocher criteria for predicting septic arthritis of the hip in children include four parameters: Non-weight-bearing status, ESR > 40 mm/hr, WBC count > 12,000/mm3, and Temperature > 38.5°C. C-reactive protein (CRP) > 20 mg/L was later identified by Caird et al. as an excellent independent predictor. The presence of a joint effusion on ultrasound confirms fluid but does not differentiate between transient synovitis and septic arthritis, and is not a Kocher criterion.

Question 9609

Topic: Biology, Genetics & Bone Healing

A 68-year-old man presents with progressive aching pain in his right thigh and diminished hearing over the past year. Radiographs of his femur show cortical thickening, coarse trabeculae, and anterior bowing. Alkaline phosphatase is markedly elevated, but serum calcium and phosphate are normal. What is the primary cellular defect initiating this disease process?

. Defective mineralization of osteoid by osteoblasts
. Excessive, uncoordinated osteoclastic bone resorption
. Impaired synthesis of type I collagen
. Overproduction of parathyroid hormone
. Deficient osteoprotegerin (OPG) production

Correct Answer & Explanation

. Excessive, uncoordinated osteoclastic bone resorption

Explanation

The patient has Paget's disease of bone, characterized by elevated alkaline phosphatase, normal calcium/phosphate, and classic radiographic findings (cortical thickening, coarse trabeculae). The disease is initiated by an initial phase of excessive, uncoordinated bone resorption by abnormal, large, multinucleated osteoclasts. This is followed by a mixed phase and eventually a sclerotic phase of disorganized, woven bone formation by osteoblasts.

Question 9610

Topic: 1. General Principles & Basic Science

When optimizing a screw for fixation in poor-quality osteoporotic bone, which of the following structural alterations will yield the greatest increase in the screw's pullout strength?

. Increasing the outer diameter
. Increasing the inner (root) diameter
. Increasing the thread pitch
. Decreasing the length of screw engagement
. Utilizing a core-tapered screw design

Correct Answer & Explanation

. Increasing the outer diameter

Explanation

Pullout strength of a screw is primarily determined by the volume of bone caught between the threads. The formula for pullout strength is proportional to the outer diameter, the length of engagement, and the shear strength of the bone material. Increasing the outer diameter increases the thread volume and has the most significant impact on pullout strength. Conversely, increasing the inner (root) diameter decreases the thread depth, which would lower pullout strength.

Question 9611

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in bone healing by stimulating the differentiation of mesenchymal stem cells into osteoblasts. Which of the following BMPs is an FDA-approved osteoinductive agent commonly used in spinal fusion and the treatment of open tibia fractures?

. BMP-1
. BMP-2
. BMP-3
. BMP-6
. BMP-13

Correct Answer & Explanation

. BMP-2

Explanation

Recombinant human BMP-2 (rhBMP-2) is heavily utilized and FDA-approved for anterior lumbar interbody fusion (ALIF) and acute open tibial shaft fractures. BMP-7 (also known as Osteogenic Protein-1 or OP-1) was previously approved for recalcitrant tibial nonunions. Notably, BMP-1 is not actually a member of the TGF-beta superfamily (it is a metalloproteinase), and BMP-3 has an inhibitory effect on bone formation.

Question 9612

Topic: Biology, Genetics & Bone Healing

A 45-year-old female with a history of severe celiac disease presents with diffuse, dull bone pain and proximal muscle weakness. Radiographs demonstrate bilateral radiolucent bands perpendicular to the cortex in the medial femoral necks (Looser zones). Which of the following laboratory profiles is most characteristic of her underlying metabolic bone disease?

. High calcium, low phosphorus, high parathyroid hormone (PTH)
. Normal calcium, normal phosphorus, normal alkaline phosphatase (ALP)
. Low or normal calcium, low phosphorus, high PTH, high ALP
. High calcium, high phosphorus, low PTH, low ALP
. Normal calcium, high phosphorus, normal PTH

Correct Answer & Explanation

. Low or normal calcium, low phosphorus, high PTH, high ALP

Explanation

The patient has osteomalacia secondary to vitamin D malabsorption (celiac disease). Looser zones (pseudofractures) are pathognomonic radiographic findings. Deficient Vitamin D leads to decreased intestinal calcium absorption, triggering secondary hyperparathyroidism (high PTH). High PTH maintains serum calcium at low-normal or low levels but causes renal phosphate wasting (low phosphorus). Alkaline phosphatase (ALP) is elevated due to increased osteoblast activity attempting to mineralize the abundant unmineralized osteoid.

Question 9613

Topic: 1. General Principles & Basic Science

Which factor has the most significant positive impact on the pull-out strength of a non-locking screw in bone?

. Increased screw length.
. Increased thread pitch.
. Decreased core diameter relative to outer diameter.
. Increased bone mineral density.
. Self-tapping design.

Correct Answer & Explanation

. Increased bone mineral density.

Explanation

Bone mineral density (D) is the most critical factor influencing screw pull-out strength. Screws derive their purchase from the quality and quantity of bone they engage. In osteoporotic bone, all screw designs will have significantly reduced pull-out strength regardless of other factors. While increased screw length (A) (up to a point in cortical bone, or engaging more cancellous bone) and decreased core diameter (C) (meaning a larger thread depth) improve pull-out strength, these are secondary to the fundamental quality of the bone itself. Increased thread pitch (B) (coarser) is for cancellous bone, not necessarily increasing strength in all bone types. Self-tapping design (E) is a convenience factor and generally does notincreasepull-out strength compared to pre-tapped holes, and can sometimes even reduce it by creating more bone damage.

Question 9614

Topic: 1. General Principles & Basic Science

Assuming all other factors are constant, increasing the diameter of a screw has the greatest positive impact on its resistance to which type of force?

. Axial pull-out force.
. Bending moment.
. Torsional moment.
. Shear force.
. Compressive force.

Correct Answer & Explanation

. Bending moment.

Explanation

The resistance of a cylindrical object (like a screw) to bending is proportional to the cube of its radius (or diameter). Therefore, even a small increase in diameter significantly increases the screw's resistance to bending moments. While diameter also affects pull-out (A), torsional (C), and shear (D) strength, the effect on bending is the most pronounced due to this cubic relationship. Compressive force (E) is less relevant to a screw's structural integrity in most fixation scenarios where bending or shear are more common failure modes.

Question 9615

Topic: 1. General Principles & Basic Science

Proper maintenance of surgical drill bits is crucial. What is the most important reason for discarding a dull or damaged drill bit?

. It increases the risk of thermal necrosis of the bone.
. It can lead to screw stripping during insertion.
. It makes the drill hole too large, compromising screw purchase.
. It increases surgical time and patient anesthesia exposure.
. It dulls the tap more quickly.

Correct Answer & Explanation

. It increases the risk of thermal necrosis of the bone.

Explanation

A dull or damaged drill bit generates significantly more friction and heat during drilling. This excessive heat can cause thermal necrosis (death) of the bone around the drill hole, which can compromise screw purchase, lead to loosening, or even create a focus for infection. While it might increase surgical time (D), the biological damage (A) is paramount. It would make the holesmallerif it deflects, or might chatter, not necessarily too large (C). Stripping (B) is more related to tapping or screw insertion technique. Dulling the tap (E) is a secondary issue.

Question 9616

Topic: 1. General Principles & Basic Science

When measuring for screw length in a standard bicortical fixation, which of the following is the most appropriate technique?

. Measure the depth to the far cortex, then subtract 5mm.
. Measure the depth to the near cortex, then add 5mm.
. Use a depth gauge to measure through both cortices, then choose the next shortest screw.
. Use a depth gauge to measure through both cortices, then choose the screw length that allows 1-2mm protrusion past the far cortex.
. Always use the longest screw possible for maximum purchase.

Correct Answer & Explanation

. Use a depth gauge to measure through both cortices, then choose the screw length that allows 1-2mm protrusion past the far cortex.

Explanation

For bicortical fixation, the depth gauge is passed through both cortices. The ideal screw length is typically measured to allow the tip of the screw to just engage or protrude 1-2 mm beyond the far cortex. This ensures maximum purchase in both cortices without being excessively prominent, which could irritate soft tissues or compromise adjacent structures. Subtracting 5mm (A) risks losing far cortical purchase. Measuring to near cortex (B) is insufficient. Choosing the next shortest (C) might lose critical far cortical purchase. The longest screw possible (E) can be dangerous due to nerve/vessel impingement or soft tissue irritation.

Question 9617

Topic: 1. General Principles & Basic Science

Which characteristic of a cancellous screw thread design is crucial for maximizing purchase in soft, spongy bone?

. Small core diameter.
. Fine thread pitch.
. Large outer diameter.
. Deep and coarse threads.
. Self-drilling tip.

Correct Answer & Explanation

. Deep and coarse threads.

Explanation

Cancellous bone is soft and porous. To get good purchase, the screw needs to engage a large volume of bone. Deep and coarse threads (D) maximize the contact area between the screw and the cancellous bone, much like a wood screw. A small core diameter (A) (relative to outer diameter) contributes to larger thread depth. Fine thread pitch (B) is for cortical bone. Large outer diameter (C) helps, but the threadmorphology(deep and coarse) is the defining factor for purchase in cancellous bone. Self-drilling tip (E) is for convenience, not maximizing purchase itself.

Question 9618

Topic: Biology, Genetics & Bone Healing

In bridging osteosynthesis for a comminuted fracture, what is the primary biomechanical function of the screws?

. To provide absolute stability at the primary fracture site.
. To compress the comminuted fragments together.
. To secure the plate to the main bone fragments, acting as anchors for the plate-bone construct.
. To lag the individual comminuted fragments to each other.
. To promote primary bone healing across the zone of comminution.

Correct Answer & Explanation

. To secure the plate to the main bone fragments, acting as anchors for the plate-bone construct.

Explanation

In bridging osteosynthesis, the plate spans the comminuted zone without direct contact with the intermediate fragments. The plate acts as the load-bearing implant, maintaining length and alignment. The screws' primary role is to securely attach the plate to the healthy bone segments proximally and distally, thereby anchoring the plate and forming a stable plate-bone construct. The goal isrelativestability to promote secondary healing (callus). Absolute stability (A), compression (B), or lagging fragments (D) are not the primary goals in bridging osteosynthesis. Primary bone healing (E) is not the goal across a comminuted zone with bridging.

Question 9619

Topic: 1. General Principles & Basic Science

A screw has broken flush with the bone surface during an attempted removal. What is the most appropriate initial approach for removing the retained fragment?

. Leave the fragment in situ if the patient is asymptomatic.
. Attempt to grasp the fragment with pointed rongeurs.
. Use a high-speed burr to create a trough around the screw head for extraction tools.
. Utilize a small osteotome to lever out the fragment.
. Drill out the center of the screw fragment.

Correct Answer & Explanation

. Use a high-speed burr to create a trough around the screw head for extraction tools.

Explanation

When a screw breaks flush, the first step is often to expose the fragment sufficiently to allow specialized extraction tools to engage. This typically involves using a small, high-speed burr or fine osteotome to carefully create a trough of bone around the remaining screw fragment, thus exposing enough of its circumference or the top of the head for a screw extractor, reverse tap, or small vice-grip to gain purchase. Leaving it (A) is an option if asymptomatic and not causing issues, but the question asks for removal. Rongeurs (B) are usually not precise or strong enough. Levering (D) can cause bone damage. Drilling out the center (E) may weaken the bone further or cause iatrogenic damage.

Question 9620

Topic: Biomechanics & Biomaterials

Which screw component is most susceptible to fatigue fracture in a long-standing, inadequately stabilized construct?

. The screw head.
. The threaded tip.
. The core of the screw at the bone-plate interface.
. The driver recess.
. The unthreaded shaft.

Correct Answer & Explanation

. The core of the screw at the bone-plate interface.

Explanation

The junction where the screw passes from the relatively rigid plate into the bone (the bone-plate interface) is a stress riser. If the fracture is inadequately stabilized or the construct is subjected to repetitive cyclic loading, this area experiences concentrated bending stresses. The core diameter of the screw at this point, where the threads begin or end at the interface, is the narrowest and therefore most vulnerable to fatigue failure and fracture. The head (A), tip (B), recess (D), and unthreaded shaft (E) are generally stronger or experience less concentrated stress in this scenario.

Test Yourself

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

On this Page