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1. General Principles & Basic Science MCQs

Practice Set 382 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 7621

Topic: 1. General Principles & Basic Science

Tranexamic acid (TXA) has become a standard pharmacological adjunct in joint arthroplasty to minimize perioperative blood loss and reduce transfusion requirements. Which of the following describes the fundamental mechanism of action of TXA?

. Irreversible inhibition of the cyclooxygenase-1 (COX-1) enzyme
. Direct inhibition of Factor Xa in the common coagulation cascade
. Competitive inhibition of the activation of plasminogen to plasmin
. Enhancement of antithrombin III binding to thrombin
. Promotion of von Willebrand factor release from the vascular endothelium

Correct Answer & Explanation

. Irreversible inhibition of the cyclooxygenase-1 (COX-1) enzyme

Explanation

Tranexamic acid (TXA) is a synthetic analog of the amino acid lysine. It acts as an antifibrinolytic agent by reversibly and competitively binding to the lysine-binding sites on plasminogen. This prevents plasminogen from binding to fibrin and being activated into plasmin, thereby inhibiting the degradation of established fibrin clots and reducing surgical bleeding.

Question 7622

Topic: Biology, Genetics & Bone Healing

A 55-year-old patient with end-stage renal disease presents with diffuse bone pain and an increased risk of fragility fractures. Laboratory tests reveal hypocalcemia, hyperphosphatemia, and significantly elevated parathyroid hormone (PTH) levels. Which of the following enzymes is primarily deficient in this patient, driving the pathogenesis of their metabolic bone disease?

. 25-hydroxylase
. 1-alpha-hydroxylase
. 24,25-hydroxylase
. Alkaline phosphatase
. Cathepsin K

Correct Answer & Explanation

. 25-hydroxylase

Explanation

In chronic kidney disease, the loss of functional renal parenchyma leads to a deficiency in 1-alpha-hydroxylase. This enzyme is responsible for converting 25-hydroxyvitamin D (calcidiol) into 1,25-dihydroxyvitamin D (calcitriol), the physiologically active form of vitamin D. The resulting deficiency of calcitriol impairs intestinal calcium absorption, leading to hypocalcemia and a compensatory, often severe, secondary hyperparathyroidism (renal osteodystrophy).

Question 7623

Topic: Biology, Genetics & Bone Healing

During a posterolateral lumbar fusion, a surgeon uses a commercially prepared demineralized bone matrix (DBM) to supplement local autograft. Based on the fundamental properties of bone grafting materials, which of the following biological properties does DBM inherently provide?

. Osteoconduction and osteogenesis
. Osteoinduction and osteogenesis
. Osteoconduction and osteoinduction
. Osteogenesis only
. Osteoinduction only

Correct Answer & Explanation

. Osteoconduction and osteogenesis

Explanation

Demineralized bone matrix (DBM) is an allograft product prepared by the acid extraction of the mineralized phase of bone, leaving behind the structural collagen matrix and noncollagenous proteins. The remaining matrix provides a physical scaffold for new bone growth (osteoconduction), while retained growth factors, primarily bone morphogenetic proteins (BMPs), stimulate host mesenchymal stem cells to differentiate into osteoblasts (osteoinduction). Because DBM is processed and sterilized, it contains no viable cells and thus possesses no intrinsic osteogenic potential.

Question 7624

Topic: 1. General Principles & Basic Science

A researcher is studying the structural and mechanical properties of articular cartilage. She evaluates a specific layer where chondrocytes are flattened and collagen fibers are oriented parallel to the joint surface. Which of the following is the primary mechanical function of this specific cartilage layer?

. Resisting high-impact compressive forces during axial loading
. Resisting shear and tensile stresses during joint articulation
. Anchoring the cartilage to the underlying subchondral bone
. Providing a high concentration of proteoglycans to maintain hydration
. Regulating the calcification of the extracellular matrix

Correct Answer & Explanation

. Resisting high-impact compressive forces during axial loading

Explanation

The superficial (tangential) zone of articular cartilage is characterized by flattened chondrocytes and collagen fibers that are oriented parallel to the joint surface. This zone has the lowest concentration of proteoglycans and the highest concentration of water. Its unique structural arrangement makes its primary mechanical function to resist shear and tensile stresses. Compressive forces are primarily resisted by the middle and deep zones, where the proteoglycan concentration is higher and collagen fibers are oriented obliquely or perpendicularly.

Question 7625

Topic: Biomechanics & Biomaterials

A study evaluates the mechanical properties of the anterior cruciate ligament (ACL) under cyclic loading. The investigators observe that when the ACL is subjected to a constant displacement (strain), the corresponding holding force required to maintain that displacement progressively decreases over time. This viscoelastic phenomenon is best described as:

. Creep
. Load to failure
. Stress relaxation
. Hysteresis
. Fatigue failure

Correct Answer & Explanation

. Creep

Explanation

Stress relaxation is a viscoelastic property defined as the decrease in applied stress (or force) over time when a material is held at a constant strain (or displacement). Creep, another viscoelastic property, is the progressive deformation (strain) of a material over time when it is subjected to a constant load (stress). Hysteresis is the energy lost (usually as heat) during the loading and unloading cycle of a viscoelastic material.

Question 7626

Topic: Infection, Pharmacology & VTE

In the pathogenesis of prosthetic joint infections (PJI), biofilm formation protects bacteria from host immune clearance and antimicrobial therapy. During biofilm development, which of the following phases is characterized by cell proliferation and the extensive production of an extracellular polymeric substance (EPS) matrix?

. Planktonic phase
. Initial reversible attachment
. Maturation phase
. Dispersal phase
. Quorum sensing phase

Correct Answer & Explanation

. Planktonic phase

Explanation

Biofilm formation occurs in several distinct stages: (1) Reversible attachment of planktonic bacteria to a surface, (2) Irreversible attachment mediated by adhesins, (3) Maturation phase, which is characterized by bacterial proliferation, three-dimensional growth, and the production of a protective extracellular polymeric substance (EPS) matrix, and (4) Dispersal phase, where bacteria detach to colonize new sites. The EPS matrix is heavily responsible for antibiotic resistance.

Question 7627

Topic: Biology, Genetics & Bone Healing

A 35-year-old male undergoes open reduction and internal fixation of a diaphyseal femur fracture. The surgeon utilizes an absolute stability construct achieved via compression plating. Which of the following best describes the primary mode of bone healing expected and the corresponding mechanical strain environment at the fracture site?

. Endochondral ossification, strain < 2%
. Endochondral ossification, strain between 2% and 10%
. Intramembranous ossification, strain < 2%
. Primary (Haversian) bone healing, strain < 2%
. Primary (Haversian) bone healing, strain between 2% and 10%

Correct Answer & Explanation

. Endochondral ossification, strain < 2%

Explanation

Absolute stability constructs, such as compression plating, aim to achieve a strain environment of less than 2% across the fracture gap. Under these highly rigid conditions, secondary (callus) formation is suppressed, and the bone heals via primary (Haversian) bone healing. This process involves osteoclasts creating cutting cones across the fracture site, directly followed by osteoblasts laying down new lamellar bone. Strain environments between 2% and 10% (relative stability) promote secondary bone healing via endochondral ossification.

Question 7628

Topic: 1. General Principles & Basic Science

Following a severe, complete peripheral nerve transection injury, the affected muscle undergoes progressive denervation changes. If surgical repair is not performed and reinnervation does not occur, what is the most likely histological state of the denervated muscle 18 to 24 months post-injury?

. Hypertrophy of type 1 fibers and preferential atrophy of type 2 fibers
. Targetoid fiber formation and extensive fiber type grouping
. Severe myofiber atrophy with predominant replacement by fibroadipose connective tissue
. Increased number of centralized nuclei and prolific fiber splitting
. Massive accumulation of glycogen and lipid droplets within the remaining sarcolemma

Correct Answer & Explanation

. Hypertrophy of type 1 fibers and preferential atrophy of type 2 fibers

Explanation

After a complete denervation injury without subsequent reinnervation, skeletal muscle fibers undergo progressive, irreversible atrophy. By 12 to 24 months, the atrophied myofibers undergo apoptosis and are extensively replaced by fatty and fibrous connective tissue. Fiber type grouping (Option B) is a classic histological sign of successful reinnervation, where collateral sprouting from intact axons innervates adjacent denervated fibers, converting them to the same histochemical type.

Question 7629

Topic: Biology, Genetics & Bone Healing

A 72-year-old woman is prescribed teriparatide for the treatment of severe osteoporosis complicated by multiple vertebral compression fractures. The primary cellular mechanism by which teriparatide increases total bone mass is by:

. Inhibiting the RANKL/RANK interaction, thereby preventing osteoclast activation
. Directly stimulating osteoblast differentiation and lifespan via intermittent PTH receptor activation
. Inhibiting the enzyme farnesyl pyrophosphate synthase in the mevalonate pathway
. Binding firmly to hydroxyapatite crystals and inducing osteoclast apoptosis
. Acting as a selective estrogen receptor modulator to decrease osteoclast-mediated bone resorption

Correct Answer & Explanation

. Inhibiting the RANKL/RANK interaction, thereby preventing osteoclast activation

Explanation

Teriparatide is a recombinant human parathyroid hormone (PTH 1-34) analog. When administered intermittently (e.g., as a daily subcutaneous injection), it has an anabolic effect on bone by stimulating osteoblast differentiation, activity, and lifespan, leading to a net increase in bone formation. Denosumab inhibits RANKL (Option A). Bisphosphonates inhibit farnesyl pyrophosphate synthase and promote osteoclast apoptosis (Options C and D). Raloxifene is a selective estrogen receptor modulator (Option E).

Question 7630

Topic: Biology, Genetics & Bone Healing

A surgeon elects to use a locking compression plate (LCP) for the fixation of a highly comminuted metaphyseal fracture in osteoporotic bone. Compared to a conventional non-locking plate, which of the following biomechanical principles represents the primary advantage of the locking plate construct in this scenario?

. It relies heavily on friction between the plate and the underlying cortex to maintain fracture reduction.
. It functions as a fixed-angle, single-beam construct that does not require compression against the bone.
. It requires strict bicortical screw purchase in every hole to achieve adequate angular stability.
. It relies entirely on the pull-out strength of individual screws rather than the overall construct stability.
. It induces primary (Haversian) bone healing by achieving absolute stability across the comminuted gap.

Correct Answer & Explanation

. It relies heavily on friction between the plate and the underlying cortex to maintain fracture reduction.

Explanation

Locking plates act as fixed-angle devices where the screw heads thread directly into the plate, creating a single-beam construct. This design provides stability independent of the friction between the plate and the bone, preserving periosteal blood supply. Because the screws are fixed to the plate, the construct relies on the aggregate pull-out strength rather than individual screw purchase, making it ideal for osteoporotic bone. Bridging a comminuted fracture with a locking plate typically provides relative stability, leading to secondary (callus) bone healing, not primary healing.

Question 7631

Topic: Biology, Genetics & Bone Healing

A 45-year-old man undergoes an open reduction and internal fixation of a diaphyseal radial fracture using dynamic compression plating. The goal is to achieve primary (direct) bone healing. Which of the following conditions is most critical for achieving this type of healing without callous formation?

. Interfragmentary strain between 2% and 10%
. Gap size of less than 1 mm and absolute stability
. Presence of intramembranous ossification mediators exclusively
. Micromotion at the fracture site to stimulate osteoblast activity
. Preservation of the fracture hematoma

Correct Answer & Explanation

. Interfragmentary strain between 2% and 10%

Explanation

Primary (direct) bone healing occurs without callus formation and requires absolute stability (interfragmentary strain < 2%) and direct cortical contact or a gap of less than 1 mm. This allows osteoclasts to create cutting cones across the fracture line, followed immediately by osteoblasts depositing lamellar bone. Interfragmentary strain between 2% and 10% or micromotion leads to secondary bone healing via endochondral ossification and callus formation.

Question 7632

Topic: Biology, Genetics & Bone Healing

Recombinant human bone morphogenetic proteins (rhBMPs) are commonly used in orthopedic surgery to promote osteoinduction. Which of the following bone morphogenetic proteins is FDA-approved as an adjunct for use in acute, open tibial shaft fractures treated with an intramedullary nail?

. BMP-2
. BMP-3
. BMP-4
. BMP-7
. BMP-9

Correct Answer & Explanation

. BMP-2

Explanation

Bone morphogenetic proteins (BMPs) are members of the TGF-beta superfamily that promote osteoinduction by stimulating the differentiation of mesenchymal stem cells into osteoblasts. rhBMP-2 is FDA-approved for use in acute, open tibial shaft fractures treated with an intramedullary nail, as well as for anterior lumbar interbody fusion (ALIF). BMP-7 (OP-1) was previously approved under a humanitarian device exemption for recalcitrant long-bone nonunions but has had limited application. BMP-3 acts as an antagonist to osteogenesis.

Question 7633

Topic: 1. General Principles & Basic Science

A patient undergoes surgical exploration for a possible gluteal nerve injury. The surgeon identifies the sciatic nerve emerging from the greater sciatic foramen, inferior to the piriformis muscle. Which nerve typically emerges superior to the piriformis muscle, making it vulnerable in superior gluteal region trauma?

. Inferior gluteal nerve
. Pudendal nerve
. Posterior cutaneous nerve of the thigh
. Superior gluteal nerve
. Nerve to obturator internus

Correct Answer & Explanation

. Inferior gluteal nerve

Explanation

The superior gluteal nerve exits the pelvis through the greater sciatic foramen, superior to the piriformis muscle. It innervates the gluteus medius, gluteus minimus, and tensor fasciae latae, and its injury results in a Trendelenburg gait. All other listed nerves (inferior gluteal nerve, pudendal nerve, posterior cutaneous nerve of the thigh, and nerve to obturator internus) typically exit the greater sciatic forameninferiorto the piriformis muscle.

Question 7634

Topic: Surgical Anatomy & Approaches

A patient complains of sciatica-like symptoms, particularly pain radiating down the posterior thigh, exacerbated by prolonged sitting and internal rotation of the hip. Examination reveals tenderness in the buttock. Which anatomical variation involving the piriformis muscle and the sciatic nerve is most commonly associated with piriformis syndrome?

. Sciatic nerve passing anterior to piriformis
. Common peroneal division passing through piriformis, tibial division passing anterior
. Common peroneal division passing through piriformis, tibial division passing inferior
. Sciatic nerve bifurcating proximal to piriformis, with both divisions passing inferior
. Sciatic nerve passing superior to piriformis

Correct Answer & Explanation

. Sciatic nerve passing anterior to piriformis

Explanation

Piriformis syndrome involves compression of the sciatic nerve by the piriformis muscle. The most common anatomical variation associated with this syndrome is when the common peroneal (fibular) division of the sciatic nerve passesthroughthe piriformis muscle, while the tibial division passesinferiorto it. This configuration makes the peroneal division particularly vulnerable to compression by muscle spasm or hypertrophy. Other variations exist, but this specific arrangement is the most frequently cited cause of neurogenic symptoms in piriformis syndrome. The sciatic nerveneverpasses anterior to the piriformis; it always passes posterior or through it from an anterior perspective within the pelvis. Passing superior to piriformis is for the superior gluteal nerve.

Question 7635

Topic: Surgical Anatomy & Approaches

Which of the following ligaments is considered the strongest ligament in the human body, preventing hyperextension of the hip joint?

. Pubofemoral ligament
. Ischiofemoral ligament
. Ligamentum teres
. Iliofemoral ligament
. Sacrotuberous ligament

Correct Answer & Explanation

. Pubofemoral ligament

Explanation

The iliofemoral ligament, also known as the Y-ligament of Bigelow, is considered the strongest ligament in the human body. It originates from the anterior inferior iliac spine (AIIS) and acetabular rim and inserts into the intertrochanteric line of the femur. Its primary function is to prevent hyperextension of the hip joint. The pubofemoral ligament limits abduction and extension, while the ischiofemoral ligament limits extension and internal rotation. The ligamentum teres stabilizes the femoral head but is not the primary restraint to hyperextension. The sacrotuberous ligament is a pelvic ligament, not directly related to hip joint stability in this context.

Question 7636

Topic: Surgical Anatomy & Approaches

A patient sustains a shoulder injury resulting in weakness of deltoid and teres minor muscles. Sensation over the 'regimental badge' area is diminished. The axillary nerve is implicated. Through which anatomical space does the axillary nerve typically pass?

. Triangular space (medial axillary space)
. Quadrangular space
. Triangular interval (lateral axillary space)
. Coracoacromial arch
. Rotator cuff interval

Correct Answer & Explanation

. Triangular space (medial axillary space)

Explanation

The axillary nerve, along with the posterior circumflex humeral artery, passes through the quadrangular space. The boundaries of the quadrangular space are: superiorly, the teres minor muscle (or inferior border of subscapularis); inferiorly, the teres major muscle; medially, the long head of the triceps brachii; and laterally, the surgical neck of the humerus. Compression or injury within this space can lead to deltoid and teres minor weakness and sensory loss over the lateral shoulder. The triangular space contains the circumflex scapular artery. The triangular interval contains the radial nerve and profunda brachii artery.

Question 7637

Topic: Surgical Anatomy & Approaches

During total hip arthroplasty, the surgeon is concerned about potential damage to the obturator nerve. This nerve innervates which primary group of muscles?

. Gluteus medius and minimus
. Hamstring muscles
. Quadriceps femoris muscles
. Adductor muscles of the thigh
. Peroneal group of muscles

Correct Answer & Explanation

. Gluteus medius and minimus

Explanation

The obturator nerve (L2-L4) exits the pelvis via the obturator foramen and supplies the medial compartment of the thigh. This compartment primarily consists of the adductor muscles: adductor longus, adductor brevis, adductor magnus (adductor portion), gracilis, and obturator externus. Damage to this nerve during hip surgery can lead to weakness in adduction and sensory loss over the medial thigh. The gluteal muscles are supplied by gluteal nerves, hamstrings by the sciatic nerve, quadriceps by the femoral nerve, and peroneal muscles by the common peroneal nerve.

Question 7638

Topic: 1. General Principles & Basic Science

During surgical repair of the hip abductor mechanism, the surgeon must be aware of the different trochanteric bursae. Which bursa is located between the gluteus maximus tendon and the greater trochanter, and is commonly implicated in 'trochanteric bursitis'?

. Ischiogluteal bursa
. Iliopsoas bursa
. Gluteus medius bursa
. Subgluteus maximus bursa (superficial trochanteric bursa)
. Deep trochanteric bursa

Correct Answer & Explanation

. Ischiogluteal bursa

Explanation

There are several bursae around the greater trochanter. The subgluteus maximus bursa, often referred to as the superficial trochanteric bursa, is located between the greater trochanter and the overlying gluteus maximus muscle/iliotibial band. This bursa is the most commonly inflamed bursa in cases of 'trochanteric bursitis.' The gluteus medius bursa is located between the gluteus medius and the greater trochanter. The ischiogluteal bursa is near the ischial tuberosity. The iliopsoas bursa is anterior to the hip joint. The term 'deep trochanteric bursa' can be used somewhat generically, but 'subgluteus maximus' precisely describes the superficial bursa implicated.

Question 7639

Topic: 1. General Principles & Basic Science

A patient presents with a Trendelenburg gait. This indicates weakness of the hip abductors, which are primarily innervated by which nerve?

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

Correct Answer & Explanation

. Inferior gluteal nerve

Explanation

The superior gluteal nerve (L4-S1) innervates the gluteus medius, gluteus minimus, and tensor fasciae latae muscles. These muscles are the primary abductors of the hip and are crucial for stabilizing the pelvis during gait. Damage to the superior gluteal nerve or weakness of these muscles results in a Trendelenburg gait, where the pelvis drops on the unsupported side during the stance phase of the opposite limb. The inferior gluteal nerve innervates the gluteus maximus (hip extensor). Obturator nerve innervates adductors. Femoral nerve innervates quadriceps. Sciatic nerve innervates hamstrings and all muscles below the knee.

Question 7640

Topic: 1. General Principles & Basic Science

The pes anserinus is a common insertion site for three distinct muscles on the anteromedial aspect of the proximal tibia. Which of the following muscles is not a component of the pes anserinus?

. Sartorius
. Gracilis
. Semitendinosus
. Semimembranosus
. All of the above are components

Correct Answer & Explanation

. Sartorius

Explanation

The pes anserinus (goose's foot) is the conjoined tendinous insertion of three muscles on the anteromedial aspect of the proximal tibia, distal to the medial tibial condyle. These three muscles are the Sartorius (femoral nerve), Gracilis (obturator nerve), and Semitendinosus (tibial division of sciatic nerve). The Semimembranosus tendon inserts more deeply and proximally on the posteromedial aspect of the medial tibial condyle, separate from the pes anserinus. Therefore, Semimembranosus is not a component of the pes anserinus.

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