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1. General Principles & Basic Science MCQs

Practice Set 569 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 11361

Topic: Biomechanics & Biomaterials

In orthopaedic internal fixation, why is it generally contraindicated to use a stainless steel screw in direct combination with a titanium plate?

. Mismatch in elastic modulus will cause early plate fatigue
. It predisposes the hardware construct to galvanic corrosion
. It significantly increases the risk of a severe local foreign body giant cell reaction
. Titanium induces a local osteolytic reaction when adjacent to steel
. Stainless steel has a lower yield strength than titanium leading to screw breakage

Correct Answer & Explanation

. Mismatch in elastic modulus will cause early plate fatigue

Explanation

Mixing dissimilar metals (such as stainless steel and titanium) in a continuous electrolytic environment (such as human body fluids) creates an electrochemical cell. This leads to galvanic corrosion, where the less noble metal (stainless steel in this pairing) undergoes accelerated degradation. This can compromise implant integrity and release metallic debris.

Question 11362

Topic: Biomechanics & Biomaterials

A 72-year-old patient presents with an acutely painful, swollen knee. Joint aspiration yields synovial fluid with a white blood cell count of 25,000 cells/mcL. Microscopic examination under polarized light reveals rhomboid-shaped crystals with weakly positive birefringence. What is the predominant composition of these crystals?

. Monosodium urate
. Calcium pyrophosphate dihydrate
. Calcium hydroxyapatite
. Cholesterol
. Basic calcium phosphate

Correct Answer & Explanation

. Monosodium urate

Explanation

The presence of rhomboid-shaped, weakly positively birefringent crystals on polarized light microscopy is the hallmark finding for pseudogout, which is caused by the deposition of Calcium Pyrophosphate Dihydrate (CPPD) crystals. In contrast, monosodium urate crystals (seen in gout) are needle-shaped and exhibit strong negative birefringence.

Question 11363

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of fracture healing, primary (direct) bone healing without the formation of an intermediate callus requires the absolute interfragmentary strain to be kept below what threshold?

. 2%
. 10%
. 15%
. 25%
. 50%

Correct Answer & Explanation

. 2%

Explanation

Perren's strain theory postulates that the type of tissue that can form in a fracture gap is dictated by the level of interfragmentary strain. Granulation tissue can form at high strain (up to 100%), cartilage up to 10%, and woven/lamellar bone can only form if the strain is less than 2%. Therefore, for primary (direct) bone healing (which bypasses the cartilaginous callus phase), absolute stability must be achieved to keep strain below 2%.

Question 11364

Topic: 1. General Principles & Basic Science

In the neurophysiology of the musculoskeletal system, which sensory receptor is primarily responsible for detecting the rate of change in muscle length and mediating the classic myotatic (stretch) reflex?

. Golgi tendon organ
. Muscle spindle
. Pacinian corpuscle
. Ruffini ending
. Free nerve ending

Correct Answer & Explanation

. Golgi tendon organ

Explanation

Muscle spindles are specialized sensory receptors located within the belly of muscles (intrafusal fibers). They detect changes in the length of the muscle and the velocity of that change, mediating the myotatic reflex (deep tendon reflex) to prevent overstretching. Golgi tendon organs are located at the musculotendinous junction and sense changes in muscle tension, mediating autogenic inhibition.

Question 11365

Topic: Biomechanics & Biomaterials
Which sterilization method for ultra-high-molecular-weight polyethylene (UHMWPE) creates free radicals that most significantly increase the risk of oxidative degradation and accelerated wear in total joint arthroplasty?
. Gamma irradiation in air
. Gamma irradiation in a vacuum
. Ethylene oxide gas
. Gas plasma
. Electron beam irradiation in an inert gas

Correct Answer & Explanation

. Gamma irradiation in air

Explanation

Gamma irradiation in air introduces free radicals that combine with oxygen, leading to chain scission and oxidative degradation over time. This severely compromises the mechanical properties and increases wear rates of the polyethylene.

Question 11366

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic protein-2 (BMP-2) primarily induces bone formation and osteoblast differentiation through which intracellular signaling pathway?

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

Correct Answer & Explanation

. Wnt/beta-catenin pathway

Explanation

BMP-2 binds to cell surface receptors to activate the intracellular Smad 1/5/8 pathway. These activated Smad proteins complex with Smad 4 and translocate to the nucleus to regulate the transcription of osteogenic genes.

Question 11367

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

Correct Answer & Explanation

. BMP-2

Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA approved for acute open tibial shaft fractures stabilized with intramedullary nailing. BMP-7 (rhBMP-7/OP-1) was previously approved for recalcitrant tibial nonunions under a humanitarian device exemption.

Question 11368

Topic: 1. General Principles & Basic Science

Which of the following factors has the greatest mathematical influence on the pull-out strength of a cortical screw?

. Inner root diameter
. Thread pitch
. Outer thread diameter
. Length of thread engagement
. Core diameter

Correct Answer & Explanation

. Inner root diameter

Explanation

Screw pull-out strength is directly proportional to the outer thread diameter, making it the primary determinant. Other critical factors include the length of thread engagement and the shear strength of the surrounding bone.

Question 11369

Topic: Infection, Pharmacology & VTE

During the pathogenesis of orthopedic implant infections, Staphylococcus aureus forms a biofilm. Which of the following host-pathogen interactions mediates the initial irreversible adhesion phase to the implant surface?

. Planktonic dispersion driven by physical forces
. Exopolysaccharide matrix secretion
. Microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) binding to host proteins
. Quorum-sensing molecule diffusion
. Teichoic acid degradation

Correct Answer & Explanation

. Planktonic dispersion driven by physical forces

Explanation

MSCRAMMs mediate the initial irreversible adhesion of bacteria to the host-protein coated implant surface. Following this attachment, the bacteria multiply and secrete an exopolysaccharide matrix to develop a mature biofilm.

Question 11370

Topic: 1. General Principles & Basic Science

A 45-year-old patient sustained a traumatic below-knee amputation. Compared to a non-amputee baseline, what is the expected approximate increase in energy expenditure required for ambulation?

. 10%
. 25%
. 65%
. 100%
. 200%

Correct Answer & Explanation

. 10%

Explanation

A traumatic below-knee amputation (BKA) increases walking energy expenditure by approximately 25%. A traumatic above-knee amputation (AKA) increases it by about 65%, while vascular AKA increases it by up to 100%.

Question 11371

Topic: 1. General Principles & Basic Science

A patient sustains an isolated nerve injury classified as a Sunderland third-degree injury. Which of the following best describes the anatomical disruption?

. Myelin disruption only, intact axon
. Axon and myelin disrupted, intact endoneurium
. Axon, myelin, and endoneurium disrupted, intact perineurium
. Disruption of perineurium, intact epineurium
. Complete nerve transection

Correct Answer & Explanation

. Myelin disruption only, intact axon

Explanation

A Sunderland third-degree injury involves disruption of the axon, myelin, and endoneurium, but the perineurium and epineurium remain intact. Recovery is variable and often incomplete due to intrafascicular scarring.

Question 11372

Topic: Biomechanics & Biomaterials

In the setting of a total hip arthroplasty, assembling a cobalt-chromium femoral head onto a titanium femoral stem can lead to which type of corrosion at the trunnion?

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

Correct Answer & Explanation

. Fretting corrosion only

Explanation

Mixing two dissimilar metals, such as cobalt-chromium and titanium, exposes them to body fluids acting as an electrolyte, creating an electrochemical gradient that leads to galvanic corrosion. Mechanically induced fretting corrosion often occurs concurrently at this modular junction.

Question 11373

Topic: Biology, Genetics & Bone Healing

A 55-year-old male with end-stage renal disease presents with bilateral spontaneous quadriceps tendon ruptures. Which of the following underlying physiological mechanisms most directly contributes to this condition?

. Vitamin D toxicity
. Secondary hyperparathyroidism
. Primary hypoparathyroidism
. Excessive calcitonin secretion
. Osteopetrosis

Correct Answer & Explanation

. Vitamin D toxicity

Explanation

Patients with end-stage renal disease frequently develop secondary hyperparathyroidism due to hyperphosphatemia and decreased active vitamin D. The resulting excess PTH causes bone resorption and weakens the osteotendinous junction, predisposing to spontaneous tendon ruptures.

Question 11374

Topic: 1. General Principles & Basic Science
Which of the following is the primary mechanism of action of low-molecular-weight heparin (LMWH) used for deep vein thrombosis prophylaxis in orthopedic surgery?
. Direct inhibition of thrombin (Factor IIa)
. Vitamin K antagonism via epoxide reductase inhibition
. Binding to antithrombin III to predominantly inhibit Factor Xa
. Inhibition of cyclooxygenase-1 (COX-1)
. Activation of plasminogen to plasmin

Correct Answer & Explanation

. Binding to antithrombin III to predominantly inhibit Factor Xa

Explanation

LMWH exerts its anticoagulant effect by binding to antithrombin III, which significantly accelerates its interaction to predominantly inhibit Factor Xa. It has a much lower affinity for inhibiting thrombin (Factor IIa) compared to unfractionated heparin.

Question 11375

Topic: 1. General Principles & Basic Science

During fracture healing by secondary intention, non-steroidal anti-inflammatory drugs (NSAIDs) are often cautioned against. What is the primary theoretical mechanism by which NSAIDs impair bone healing?

. Inhibition of the Wnt/beta-catenin pathway
. Suppression of cyclooxygenase-2 (COX-2) which delays endochondral ossification
. Direct cellular toxicity to osteoblasts
. Upregulation of osteoclast apoptosis
. Inhibition of angiogenesis via VEGF suppression

Correct Answer & Explanation

. Inhibition of the Wnt/beta-catenin pathway

Explanation

NSAIDs inhibit COX-2, an enzyme essential for prostaglandin synthesis during the early inflammatory phase of fracture healing. Suppression of this pathway has been shown in animal models to delay endochondral ossification and potentially lead to nonunion.

Question 11376

Topic: Surgical Anatomy & Approaches

The direct anterior (Smith-Petersen) approach to the hip is increasingly popular for THA. This approach utilizes a superficial internervous plane between which of the following muscles?

. Tensor fasciae latae and gluteus medius
. Sartorius and tensor fasciae latae
. Gluteus maximus and gluteus medius
. Rectus femoris and vastus lateralis
. Pectineus and adductor longus

Correct Answer & Explanation

. Tensor fasciae latae and gluteus medius

Explanation

The direct anterior approach utilizes the internervous plane between the sartorius (innervated by the femoral nerve) and the tensor fasciae latae (innervated by the superior gluteal nerve) superficially. The deep plane is between the rectus femoris (femoral n.) and gluteus medius (superior gluteal n.).

Question 11377

Topic: Biomechanics & Biomaterials

What is the primary mechanism by which polymethylmethacrylate (PMMA) bone cement secures a total joint arthroplasty component to the host bone?

. Chemical bonding to the hydroxyapatite of the bone matrix
. Biological osteointegration directly into the cement surface
. Covalent chemical bonding to the metal prosthesis
. Mechanical interlock with the interstices of cancellous bone
. Formation of a dense fibrocartilaginous anchoring layer

Correct Answer & Explanation

. Chemical bonding to the hydroxyapatite of the bone matrix

Explanation

PMMA acts as a grout, not an adhesive glue. It provides initial rigid fixation by penetrating the trabecular interstices of cancellous bone and creating a robust mechanical interlock once it polymerizes and hardens.

Question 11378

Topic: Physiology & Rehabilitation

Which of the following best describes the normal 'screw-home' kinematic mechanism of the knee as it moves from active flexion into terminal extension in an open kinetic chain?

. The tibia internally rotates relative to the femur
. The tibia externally rotates relative to the femur
. The femur externally rotates relative to the tibia
. The patella translates forcefully medial to the trochlear groove
. The posterior cruciate ligament completely relaxes

Correct Answer & Explanation

. The tibia internally rotates relative to the femur

Explanation

The 'screw-home' mechanism provides stability to the knee in full extension. Due to the asymmetry of the femoral condyles (the medial articular surface is longer than the lateral), as the knee reaches terminal extension in an open kinetic chain, the tibia externally rotates on the femur. In a closed kinetic chain, the femur internally rotates on the fixed tibia.

Question 11379

Topic: 1. General Principles & Basic Science

A 45-year-old active male is undergoing an opening-wedge high tibial osteotomy (HTO) for isolated medial compartment osteoarthritis. Compared to a closing-wedge HTO, which of the following postoperative changes in knee geometry is most reliably anticipated with an opening-wedge technique?

. Decreased posterior tibial slope and patella alta
. Increased posterior tibial slope and patella baja
. Decreased posterior tibial slope and patella baja
. Increased posterior tibial slope and patella alta
. No change in tibial slope or patellar height

Correct Answer & Explanation

. Decreased posterior tibial slope and patella alta

Explanation

An opening-wedge HTO inherently tends to increase the posterior tibial slope (due to the triangular shape of the proximal tibia and soft tissue tethers like the MCL) and results in relative patella baja (inferior displacement of the patella relative to the joint line) because the osteotomy is proximal to the tibial tubercle, effectively elevating the joint line away from the tubercle.

Question 11380

Topic: Infection, Pharmacology & VTE

In correcting a severe varus deformity during a primary total knee arthroplasty, after resection of osteophytes, the medial side remains tight in both flexion and extension. According to standard medial release algorithms, which structure is typically released first?

. Superficial medial collateral ligament
. Pes anserinus tendons
. Deep medial collateral ligament
. Semimembranosus tendon
. Posterior cruciate ligament

Correct Answer & Explanation

. Superficial medial collateral ligament

Explanation

In a varus knee, the deep MCL and medial capsule are typically released first along with comprehensive osteophyte removal. If further balancing is needed, the superficial MCL and pes anserinus can be sequentially addressed.

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