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1. General Principles & Basic Science MCQs

Practice Set 72 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 1421

Topic: 1. General Principles & Basic Science

According to current evidence-based guidelines for the management of open tibia fractures, which of the following interventions is the most critical factor in reducing the rate of deep surgical site infection?

. Early administration of appropriate intravenous antibiotics
. Copious high-pressure pulsatile lavage in the emergency department
. Immediate primary wound closure
. Application of a tourniquet prior to surgical debridement
. Use of a continuous passive motion machine postoperatively

Correct Answer & Explanation

. Early administration of appropriate intravenous antibiotics

Explanation

Early administration of intravenous antibiotics (ideally within 1 hour of injury) is the single most important factor in reducing infection rates in open tibia fractures. High-pressure lavage is discouraged as it can drive debris deeper into the tissues.

Question 1422

Topic: Infection, Pharmacology & VTE

An 82-year-old female presents after a fall with a shortened, externally rotated lower extremity. X-rays reveal a displaced femoral neck fracture. She has a history of atrial fibrillation on warfarin. Which of the following is the most appropriate initial management strategy regarding her anticoagulation?

. Continue warfarin and proceed with surgery as planned.
. Reverse warfarin immediately with Factor Xa inhibitor reversal agent and proceed with surgery within 6 hours.
. Hold warfarin, allow INR to normalize spontaneously, and delay surgery.
. Reverse warfarin with Vitamin K and Prothrombin Complex Concentrate (PCC), and proceed with surgery once INR is acceptable.
. Start bridging therapy with unfractionated heparin and proceed with surgery after 24 hours.

Correct Answer & Explanation

. Reverse warfarin with Vitamin K and Prothrombin Complex Concentrate (PCC), and proceed with surgery once INR is acceptable.

Explanation

Correct Answer: DFor displaced femoral neck fractures in elderly patients, surgical intervention is typically recommended within 24-48 hours. Patients on warfarin require rapid reversal of anticoagulation to minimize perioperative bleeding risks. The most effective and rapid reversal for significant bleeding risk is a combination of Vitamin K (for sustained effect) and Prothrombin Complex Concentrate (PCC) for immediate effect, allowing surgery once the INR is acceptable (typically <1.5). Factor Xa inhibitor reversal agents are for direct oral anticoagulants, not warfarin. Holding warfarin without rapid reversal delays surgery unnecessarily and increases DVT risk. Bridging therapy with heparin is not appropriate prior to emergency surgery for hip fracture due to bleeding risk.

Question 1423

Topic: Surgical Anatomy & Approaches

A 35-year-old male presents after a fall with a posterior hip dislocation. After successful closed reduction, he complains of weakness in ankle dorsiflexion and eversion, along with numbness over the dorsum of his foot. Which nerve is most likely injured?

. Femoral nerve
. Obturator nerve
. Sciatic nerve (common peroneal division)
. Superior gluteal nerve
. Inferior gluteal nerve

Correct Answer & Explanation

. Sciatic nerve (common peroneal division)

Explanation

Correct Answer: CPosterior hip dislocations are frequently associated with sciatic nerve injuries, particularly the common peroneal (fibular) division. This division supplies the muscles responsible for ankle dorsiflexion (e.g., tibialis anterior) and eversion (e.g., peroneus longus and brevis) and provides sensation to the dorsum of the foot. The tibial division of the sciatic nerve primarily supplies plantarflexors and foot intrinsics, and sensation to the sole. Femoral and obturator nerves are typically spared in posterior dislocations. Gluteal nerves supply gluteal muscles.

Question 1424

Topic: Biology, Genetics & Bone Healing

A 35-year-old female presents with knee pain. Imaging reveals an eccentric, purely lytic epiphyseal lesion extending to the subchondral bone of the distal femur. A core needle biopsy shows mononuclear cells interspersed with multinucleated giant cells. Which targeted medical therapy is most appropriate for a surgically unresectable recurrence of this tumor?

. Imatinib
. Denosumab
. Rituximab
. Methotrexate
. Zoledronic acid

Correct Answer & Explanation

. Denosumab

Explanation

The diagnosis is Giant Cell Tumor of bone, driven by the overexpression of RANKL by the neoplastic mononuclear cells. Denosumab is a monoclonal antibody against RANKL and is highly effective for unresectable or recurrent disease.

Question 1425

Topic: 1. General Principles & Basic Science

A 60-year-old male presents with bowel and bladder dysfunction and sacral pain. MRI reveals a large, destructive, lobulated mass arising from the midline sacrum. Histopathological examination shows nests of cells with abundant vacuolated cytoplasm. What is the classic name for these cells?

. Reed-Sternberg cells
. Physaliferous cells
. Foam cells
. Giant multinucleated cells
. Small round blue cells

Correct Answer & Explanation

. Physaliferous cells

Explanation

The clinical presentation and midline sacral location are typical for a Chordoma. Histologically, chordomas are characterized by the presence of physaliferous cells, which have abundant bubbly, vacuolated cytoplasm containing mucin.

Question 1426

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with knee pain. Radiographs demonstrate an eccentric, lytic, epiphyseal lesion in the proximal tibia. Histology shows multinucleated giant cells. Which medication can be used as a targeted neoadjuvant therapy?

. Imatinib
. Denosumab
. Methotrexate
. Doxorubicin
. Bisphosphonates

Correct Answer & Explanation

. Denosumab

Explanation

Denosumab is a monoclonal antibody against RANKL used for Giant Cell Tumors of bone. It inhibits osteoclast-like giant cells, leading to tumor consolidation and facilitating subsequent surgical curettage.

Question 1427

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with a painful lytic epiphyseal lesion in the distal femur. Biopsy reveals mononuclear cells and multinucleated giant cells. Which of the following best describes the mechanism of action of the targeted pharmacological therapy often utilized for this tumor?

. Inhibition of vascular endothelial growth factor (VEGF)
. Inhibition of Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)
. Restoration of wild-type TP53 function
. Direct tyrosine kinase inhibition
. Inhibition of the mammalian target of rapamycin (mTOR)

Correct Answer & Explanation

. Inhibition of Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)

Explanation

Denosumab is highly effective for Giant Cell Tumor of bone and acts as a monoclonal antibody that inhibits RANKL. This prevents osteoclast-like giant cell formation, thereby reducing tumor-associated bone resorption.

Question 1428

Topic: Surgical Anatomy & Approaches

A 60-year-old male undergoes an anterior lumbar interbody fusion (ALIF) at L4-L5. Postoperatively, he develops abdominal distension, absent bowel sounds, and is unable to void, requiring Foley catheterization. Which of the following is the most likely cause of his urinary retention and paralytic ileus?

. Damage to the femoral nerve during surgical approach.
. Spinal cord injury during instrumentation.
. Retrograde ejaculation due to superior hypogastric plexus injury.
. Temporary autonomic dysfunction due to surgical manipulation of the retroperitoneal structures and sympathetic plexus.
. Urinary tract infection (UTI) causing ileus.

Correct Answer & Explanation

. Temporary autonomic dysfunction due to surgical manipulation of the retroperitoneal structures and sympathetic plexus.

Explanation

Correct Answer: DAnterior lumbar interbody fusion (ALIF) involves a retroperitoneal approach, requiring mobilization of great vessels and manipulation of the anterior longitudinal ligament. This manipulation can temporarily injure or irritate the sympathetic nerve fibers and the superior hypogastric plexus, leading to transient autonomic dysfunction manifesting as paralytic ileus and urinary retention. While retrograde ejaculation is a known, more specific, and often permanent complication of superior hypogastric plexus injury during ALIF in males, generalized transient autonomic dysfunction encompassing both ileus and urinary retention is a more common immediate postoperative issue. Femoral nerve injury is less common with a proper ALIF approach. Spinal cord injury is very unlikely at the lumbar level in an ALIF. A UTI can cause urinary retention, but not typically directly cause paralytic ileus concurrently as an immediate post-op complication of this type of surgery.

Question 1429

Topic: Biology, Genetics & Bone Healing
A 70-year-old female with severe osteoporosis is prescribed denosumab. What is the primary mechanism of action of this medication in treating osteoporosis?
. Increases osteoblast activity and bone formation
. Stimulates parathyroid hormone release to increase calcium levels
. Binds directly to hydroxyapatite crystals on the bone surface
. Monoclonal antibody that targets and inhibits RANKL
. Increases intestinal absorption of calcium and phosphate

Correct Answer & Explanation

. Monoclonal antibody that targets and inhibits RANKL

Explanation

Denosumab is a human monoclonal antibody that specifically targets and inhibits Receptor Activator of Nuclear factor Kappa-Β Ligand (RANKL). RANKL is a key mediator of osteoclast formation, function, and survival. By binding to RANKL, denosumab prevents it from activating its receptor (RANK) on pre-osteoclasts and mature osteoclasts. This inhibition leads to a decrease in osteoclast numbers and activity, thereby reducing bone resorption and increasing bone mineral density.

Question 1430

Topic: Physiology & Rehabilitation

Which of the following muscles is the primary hip abductor and is crucial for maintaining pelvic stability during the single-leg stance phase of gait?

. Gluteus maximus
. Iliopsoas
. Rectus femoris
. Gluteus medius
. Adductor longus

Correct Answer & Explanation

. Gluteus medius

Explanation

Correct Answer: DThe gluteus medius is the primary hip abductor and plays a critical role in stabilizing the pelvis during the single-leg stance phase of gait. Along with the gluteus minimus, it prevents the contralateral hip from dropping (a phenomenon known as the Trendelenburg sign or gait). The gluteus maximus is a powerful hip extensor. The iliopsoas is the primary hip flexor. The rectus femoris is a hip flexor and knee extensor. The adductor longus is a hip adductor.

Question 1431

Topic: Surgical Anatomy & Approaches

A 70-year-old male undergoes a total hip arthroplasty for severe osteoarthritis. Postoperatively, he develops a foot drop and diminished sensation over the dorsum of the foot and lateral leg. Which nerve injury is most likely responsible?

. Femoral nerve
. Obturator nerve
. Sciatic nerve (common peroneal division)
. Sciatic nerve (tibial division)
. Superior gluteal nerve

Correct Answer & Explanation

. Sciatic nerve (common peroneal division)

Explanation

Correct Answer: CFoot drop and diminished sensation over the dorsum of the foot and lateral leg are classic signs of common peroneal nerve palsy. The common peroneal nerve is a division of the sciatic nerve and is particularly vulnerable during total hip arthroplasty due to traction, direct trauma, or compression, especially in cases of leg lengthening or revision surgery. Femoral nerve injury affects quadriceps strength, obturator nerve injury affects adduction, and tibial nerve injury affects plantarflexion and sensation over the sole of the foot. Superior gluteal nerve injury would affect abductor function.

Question 1432

Topic: Biology, Genetics & Bone Healing

Which type of bone healing is primarily achieved when a fracture is stabilized with absolute stability, such as with a dynamic compression plate?

. Endochondral ossification
. Primary bone healing via cutting cones
. Secondary bone healing with callus formation
. Intramembranous ossification
. Chondrogenesis

Correct Answer & Explanation

. Primary bone healing via cutting cones

Explanation

Absolute stability limits interfragmentary strain to <2%, allowing for primary bone healing via osteoclastic cutting cones and direct osteoblastic bone formation. Secondary bone healing involves cartilaginous callus formation and occurs with relative stability.

Question 1433

Topic: Biomechanics & Biomaterials

Galvanic corrosion in orthopedic implants occurs under which of the following conditions?

. Motion between two modular components of the same metal
. Implantation of two dissimilar metals in electrolytic contact
. Crevice formation in a single metal implant
. Exposure of the implant to a high-pH environment
. Fatigue loading of an intramedullary nail

Correct Answer & Explanation

. Implantation of two dissimilar metals in electrolytic contact

Explanation

Galvanic corrosion is an electrochemical process that occurs when two dissimilar metals are placed in electrical contact within an electrolytic solution like body fluids. The less noble metal acts as an anode and corrodes preferentially.

Question 1434

Topic: 1. General Principles & Basic Science

Following a Zone II flexor digitorum profundus (FDP) repair, what is the primary biomechanical advantage of using a 4-strand core suture technique over a 2-strand technique?

. Decreased work of flexion
. Improved intrinsic tendon healing
. Increased tensile strength allowing for early active motion
. Reduced risk of adhesion formation
. Elimination of the need for an epitendinous repair

Correct Answer & Explanation

. Increased tensile strength allowing for early active motion

Explanation

A 4-strand core suture repair significantly increases the tensile strength of the repair compared to a 2-strand technique. This added strength is crucial to withstand the forces generated during early active motion rehabilitation protocols.

Question 1435

Topic: Biology, Genetics & Bone Healing

A 32-year-old female presents with a painful lytic lesion in the distal radius epiphysis. Biopsy reveals mononuclear stromal cells interspersed with multinucleated giant cells. Which of the following correctly identifies the neoplastic cell in this lesion and its characteristic marker?

. Multinucleated giant cell; RANKL
. Multinucleated giant cell; RANK
. Mononuclear stromal cell; RANKL
. Mononuclear stromal cell; RANK
. Osteoblast; Runx2

Correct Answer & Explanation

. Mononuclear stromal cell; RANKL

Explanation

In giant cell tumors of bone, the mononuclear stromal cells are the actual neoplastic cells, and they express RANKL. The multinucleated giant cells are reactive osteoclast-like cells recruited by the RANKL expression.

Question 1436

Topic: 1. General Principles & Basic Science

A 45-year-old diabetic patient presents with a severe, rapidly progressive soft tissue infection of the lower extremity with crepitus. Tissue cultures grow Clostridium perfringens. What is the mechanism of action of the primary exotoxin produced by this organism?

. Inhibition of protein synthesis via EF-2
. Cleavage of SNARE proteins
. Degradation of cell membrane phospholipids
. Superantigen activation of T-cells
. Blockade of inhibitory neurotransmitter release

Correct Answer & Explanation

. Degradation of cell membrane phospholipids

Explanation

Clostridium perfringens produces alpha-toxin, a lecithinase (phospholipase C) that degrades cell membrane phospholipids. This leads to profound cell death, myonecrosis, and classic gas gangrene.

Question 1437

Topic: 1. General Principles & Basic Science

In the evaluation of a patient with a suspected peripheral nerve stretch injury, at what time point after the initial insult do fibrillation potentials and positive sharp waves (evidence of denervation) typically first appear on needle electromyography (EMG)?

. 24 to 48 hours
. 5 to 7 days
. 2 to 3 weeks
. 6 to 8 weeks
. 3 to 4 months

Correct Answer & Explanation

. 2 to 3 weeks

Explanation

Wallerian degeneration of the distal nerve segment must be complete before muscle membrane instability occurs. Therefore, fibrillation potentials and positive sharp waves typically appear 2 to 3 weeks after the initial nerve injury.

Question 1438

Topic: Biology, Genetics & Bone Healing

A 55-year-old female undergoes a DEXA scan revealing a T-score of -2.8 in the lumbar spine. She is prescribed a bisphosphonate. What is the primary cellular mechanism of action for this medication?

. Inhibition of RANKL
. Inhibition of osteoclast farnesyl pyrophosphate synthase
. Stimulation of osteoblast Wnt signaling
. Inhibition of sclerostin
. Binding to the parathyroid hormone receptor

Correct Answer & Explanation

. Inhibition of osteoclast farnesyl pyrophosphate synthase

Explanation

Nitrogen-containing bisphosphonates work by inhibiting farnesyl pyrophosphate synthase in the mevalonate pathway, leading to osteoclast apoptosis. Denosumab inhibits RANKL, and Romosozumab inhibits sclerostin.

Question 1439

Topic: Biology, Genetics & Bone Healing

In the context of fracture healing, which biomechanical environment is most conducive to promoting primary (direct) bone healing without the formation of a visible callus?

. Absolute stability with interfragmentary strain less than 2%
. Relative stability with interfragmentary strain between 2% and 10%
. Relative stability with interfragmentary strain greater than 10%
. A gap of 2 mm with micro-motion
. Dynamic compression plating with a 5 mm fracture gap

Correct Answer & Explanation

. Absolute stability with interfragmentary strain less than 2%

Explanation

Primary bone healing occurs via Haversian remodeling without callus formation and requires absolute stability (interfragmentary strain less than 2%) along with intimate bony contact. Interfragmentary strain between 2% and 10% promotes secondary bone healing characterized by callus formation.

Question 1440

Topic: Surgical Anatomy & Approaches

A 28-year-old male sustains a posterior hip dislocation after a dashboard injury in an MVC. On examination, his hip is internally rotated, adducted, and flexed. He has diminished sensation in the plantar aspect of his foot and weakness in ankle dorsiflexion and eversion. What is the most appropriate initial management step, considering the neurovascular status?

. Obtain an immediate CT scan of the hip to rule out associated fractures.
. Attempt closed reduction under conscious sedation as soon as possible.
. Perform an emergent open reduction due to neurological deficit.
. Order an MRI to assess for labral tears and capsular integrity.
. Place the patient in skeletal traction until swelling subsides.

Correct Answer & Explanation

. Attempt closed reduction under conscious sedation as soon as possible.

Explanation

Correct Answer: BPosterior hip dislocations are orthopedic emergencies due to the high risk of avascular necrosis (AVN) of the femoral head and associated sciatic nerve injury. The most critical factor is the time to reduction. A neurological deficit (like the described sciatic nerve palsy) does NOT contraindicate immediate closed reduction. In fact, prompt reduction may allow for neurological recovery. A CT scan is important AFTER successful closed reduction to assess for incarcerated fragments or occult fractures (e.g., femoral head impaction, posterior wall acetabular fracture), but it should not delay reduction. Open reduction is reserved for failed closed reduction or irreducible dislocations. MRI is not an acute management tool.

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