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1. General Principles & Basic Science MCQs

Practice Set 211 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 4201

Topic: Biology, Genetics & Bone Healing

A 74-year-old woman with severe osteoporosis has been receiving denosumab injections every 6 months for the past 4 years. She missed her last two appointments and is now 12 months since her last dose. She presents to the emergency department with acute back pain, and radiographs reveal three new acute vertebral compression fractures. What underlying physiological mechanism best explains this clinical presentation?

. Paradoxical atypical fracture phenomenon from over-suppression of remodeling
. Rapid upregulation of sclerostin production leading to sudden osteoblast apoptosis
. Massive rebound increase in osteoclast number and activity due to uninhibited RANK ligand
. Accumulation of advanced glycation end-products in the collagen matrix weakening the bone
. Secondary hyperparathyroidism due to sudden profound hypocalcemia

Correct Answer & Explanation

. Massive rebound increase in osteoclast number and activity due to uninhibited RANK ligand

Explanation

Denosumab is a potent monoclonal antibody against RANK ligand (RANKL). When denosumab is discontinued, there is a well-documented 'rebound phenomenon.' As the drug clears, the uninhibited RANKL leads to a massive and rapid increase in the formation, function, and survival of osteoclasts. This results in a period of profoundly accelerated bone resorption, severe bone density loss, and a high risk of multiple spontaneous vertebral compression fractures. Patients stopping denosumab must be immediately transitioned to a bisphosphonate to prevent this rebound.

Question 4202

Topic: Biology, Genetics & Bone Healing
A 45-year-old premenopausal woman with a history of celiac disease undergoes a dual-energy x-ray absorptiometry (DXA) scan. The report indicates a lumbar spine T-score of -2.6 and a Z-score of -2.8. How should her bone density status be formally classified according to the International Society for Clinical Densitometry (ISCD) guidelines?
. Osteoporosis
. Osteopenia
. Below the expected range for age
. Within the expected range for age
. Severe osteoporosis

Correct Answer & Explanation

. Below the expected range for age

Explanation

According to the ISCD guidelines, in premenopausal women, men under the age of 50, and children, the Z-score should be used rather than the T-score. A Z-score of -2.0 or lower is defined strictly as 'below the expected range for age.' The diagnostic terminology of 'osteoporosis' based on T-score criteria (≤ -2.5) is reserved for postmenopausal women and men aged 50 and older.

Question 4203

Topic: Biology, Genetics & Bone Healing

A 70-year-old female with severe osteoporosis has been treated with denosumab for 4 years but discontinued it 8 months ago due to a dental procedure. What is the most significant skeletal risk she currently faces due to this cessation?

. Atypical subtrochanteric femur fracture
. Osteonecrosis of the jaw
. Rebound multiple vertebral fractures
. Delayed osseointegration of future implants
. Severe hypocalcemia

Correct Answer & Explanation

. Rebound multiple vertebral fractures

Explanation

Discontinuation of denosumab leads to a rapid rebound in bone turnover to above-baseline levels. This rebound phenomenon is strongly associated with a high risk of sustaining multiple rapid vertebral compression fractures.

Question 4204

Topic: Biology, Genetics & Bone Healing

A 75-year-old female with osteoporosis sustains a distal femur periprosthetic fracture. Anabolic bone therapy is considered to aid healing and improve overall bone density. Which of the following represents an absolute contraindication to the use of teriparatide?

. History of deep vein thrombosis
. Prior skeletal radiation therapy
. Renal failure (GFR < 30)
. Concurrent use of denosumab
. Peptic ulcer disease

Correct Answer & Explanation

. Prior skeletal radiation therapy

Explanation

Teriparatide (recombinant PTH) has a black box warning and is contraindicated in patients with a history of external beam or implant radiation therapy to the skeleton due to a theoretical increased risk of osteosarcoma.

Question 4205

Topic: Biology, Genetics & Bone Healing

A 68-year-old male is initiated on alendronate following a fragility fracture of the femoral neck. What is the primary intracellular molecular mechanism of action of this medication?

. Inhibition of RANKL binding to the RANK receptor
. Inhibition of farnesyl pyrophosphate (FPP) synthase
. Stimulation of osteoblast differentiation via Wnt signaling
. Binding to sclerostin to enhance bone formation
. Direct activation of the calcium-sensing receptor

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate (FPP) synthase

Explanation

Nitrogen-containing bisphosphonates (like alendronate) inhibit farnesyl pyrophosphate (FPP) synthase within the mevalonate pathway. This prevents protein prenylation, leading to osteoclast apoptosis and decreased bone resorption.

Question 4206

Topic: Biology, Genetics & Bone Healing

A 70-year-old female on oral alendronate for 8 years presents with a 3-month history of vague, non-traumatic anterior thigh pain. Radiographs reveal focal lateral cortical thickening and a transverse radiolucent line in the subtrochanteric femur. What is the most appropriate change in her medical management?

. Discontinue alendronate and begin teriparatide
. Switch from alendronate to intravenous zoledronic acid
. Switch from alendronate to denosumab
. Continue alendronate and initiate protected weight bearing
. Discontinue alendronate and begin raloxifene

Correct Answer & Explanation

. Discontinue alendronate and begin teriparatide

Explanation

Long-term bisphosphonate use increases the risk of atypical femur fractures. Management involves immediately discontinuing the bisphosphonate and starting an anabolic agent like teriparatide to stimulate bone formation and fracture healing.

Question 4207

Topic: Biology, Genetics & Bone Healing

A 65-year-old female with severe osteoporosis is initiated on denosumab therapy by her endocrinologist. What is the precise mechanism of action of this pharmacological agent?

. Binds to RANK ligand to prevent its interaction with RANK receptors
. Directly induces apoptosis of active osteoclasts
. Inhibits sclerostin to promote osteoblast-mediated bone formation
. Acts as a recombinant parathyroid hormone analog
. Selectively modulates estrogen receptors on osteoblasts

Correct Answer & Explanation

. Binds to RANK ligand to prevent its interaction with RANK receptors

Explanation

Denosumab is a human monoclonal antibody that binds directly to RANKL. This prevents RANKL from binding to the RANK receptor on osteoclast precursors, fundamentally inhibiting osteoclast maturation, function, and survival.

Question 4208

Topic: Biology, Genetics & Bone Healing

A 60-year-old female is evaluated for recurrent fragility fractures. Her DEXA T-score is -3.2. Her physician is considering starting teriparatide. Which of the following in her medical history is an absolute contraindication to this therapy?

. Prior history of unprovoked deep vein thrombosis
. History of external beam radiation therapy to the pelvis for cervical cancer
. Chronic kidney disease stage 2
. Documented allergy to sulfonamide antibiotics
. History of bleeding peptic ulcer disease

Correct Answer & Explanation

. History of external beam radiation therapy to the pelvis for cervical cancer

Explanation

Teriparatide carries a warning for the potential risk of osteosarcoma. It is strictly contraindicated in patients with a history of skeletal radiation therapy, Paget's disease, or unexplained elevations in alkaline phosphatase.

Question 4209

Topic: Biology, Genetics & Bone Healing

A 55-year-old postmenopausal female has a DEXA T-score of -1.8 at the femoral neck. Her FRAX tool assessment reveals a 10-year probability of a major osteoporotic fracture of 22% and a hip fracture probability of 4%. What is the most appropriate management according to current guidelines?

. Recommend lifestyle modifications, calcium, and Vitamin D only
. Initiate pharmacological treatment with an oral bisphosphonate
. Initiate high-dose teriparatide immediately
. Repeat DEXA scan in 3 years before making a decision
. Start systemic estrogen replacement therapy

Correct Answer & Explanation

. Initiate pharmacological treatment with an oral bisphosphonate

Explanation

Pharmacological intervention is recommended for osteopenic patients (T-score -1.0 to -2.5) if the FRAX 10-year risk for a major osteoporotic fracture is >=20% or the risk for a hip fracture is >=3%.

Question 4210

Topic: Biology, Genetics & Bone Healing

A 72-year-old female abruptly stops her osteoporosis medication prior to extensive dental surgery. Six months later, she sustains multiple spontaneous vertebral compression fractures. The abrupt cessation of which of the following medications is most notorious for causing this rapid 'rebound' fracture phenomenon?

. Alendronate
. Zoledronic acid
. Denosumab
. Raloxifene
. Calcitonin

Correct Answer & Explanation

. Zoledronic acid

Explanation

Discontinuation of denosumab leads to a rapid, profound loss of bone mineral density and a well-documented rebound increase in the risk of multiple vertebral fractures. Patients stopping denosumab must be transitioned to a bisphosphonate.

Question 4211

Topic: Biology, Genetics & Bone Healing

A 65-year-old female on long-term alendronate therapy for osteoporosis presents with atraumatic thigh pain. Radiographs reveal lateral cortical thickening and a transverse incomplete radiolucent line in the subtrochanteric region. Which of the following is considered an indication for prophylactic intramedullary nailing?

. Medial cortical flaring
. Pain with weight-bearing
. Intramedullary canal diameter < 10 mm
. Bilateral asymptomatic presentation
. Complete relief of pain with NSAIDs

Correct Answer & Explanation

. Pain with weight-bearing

Explanation

In the setting of an incomplete atypical femoral fracture (AFF) associated with bisphosphonate use, prophylactic intramedullary nailing is indicated if the patient experiences prodromal thigh pain with weight-bearing, or if the radiolucent line traverses > 50% of the cortex, as these strongly predict impending complete fracture.

Question 4212

Topic: Surgical Anatomy & Approaches

A 30-year-old female sustains a Pipkin Type IV fracture-dislocation of the hip (femoral head fracture with an associated posterior wall acetabular fracture). Which surgical approach provides optimal access to address both fractures simultaneously?

. Smith-Petersen approach
. Watson-Jones approach
. Kocher-Langenbeck approach
. Ilioinguinal approach
. Stoppa approach

Correct Answer & Explanation

. Kocher-Langenbeck approach

Explanation

A Pipkin IV injury involves a fracture of the femoral head and a posterior acetabular wall fracture. The Kocher-Langenbeck (posterior) approach is favored because it allows direct access to reduce and fix the posterior wall, and the femoral head can be accessed either through the traumatic arthrotomy, by extending the capsulotomy, or via a surgical dislocation of the hip.

Question 4213

Topic: Surgical Anatomy & Approaches

To minimize the risk of avascular necrosis during open reduction of a displaced intracapsular femoral neck fracture in a young adult, the surgeon must be meticulous to avoid damaging the predominant blood supply to the femoral head. Which artery provides this primary supply?

. Obturator artery
. Lateral femoral circumflex artery
. Medial femoral circumflex artery
. Inferior gluteal artery
. Superior gluteal artery

Correct Answer & Explanation

. Medial femoral circumflex artery

Explanation

The medial femoral circumflex artery (MFCA) gives rise to the lateral epiphyseal artery system, which provides the vast majority of the blood supply to the adult femoral head. Protecting its branches (especially posterosuperiorly) is critical during surgical approaches and reduction.

Question 4214

Topic: Surgical Anatomy & Approaches

During a primary total hip arthroplasty utilizing the direct anterior approach, the surgeon develops the superficial internervous plane. This plane lies between muscles innervated by which two nerves?

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

Correct Answer & Explanation

. Superior gluteal nerve and Femoral nerve

Explanation

The direct anterior (Smith-Petersen) approach to the hip utilizes the true internervous plane between the tensor fasciae latae (supplied by the superior gluteal nerve) and the sartorius (supplied by the femoral nerve).

Question 4215

Topic: Surgical Anatomy & Approaches

A 25-year-old male suffers a dashboard injury resulting in an irreducible posterior hip dislocation. CT imaging reveals an entrapped osteochondral fragment in the acetabular fossa preventing concentric reduction. Which of the following associated injuries is most common with this specific mechanism and direction of dislocation?

. Femoral nerve palsy
. Sciatic nerve injury
. Ipsilateral medial collateral ligament (MCL) tear
. Anterior column acetabular fracture
. Superior gluteal artery pseudoaneurysm

Correct Answer & Explanation

. Sciatic nerve injury

Explanation

Posterior hip dislocations are commonly caused by a dashboard injury (axial load on a flexed knee). The sciatic nerve (specifically the peroneal division) is the most commonly injured neurologic structure in posterior hip dislocations, occurring in approximately 10-20% of cases.

Question 4216

Topic: Surgical Anatomy & Approaches
A 38-year-old male sustains a posterior hip dislocation with an associated femoral head fracture that involves the weight-bearing surface superior to the fovea capitis. According to the Pipkin classification, what type of fracture is this, and what is the preferred surgical approach for open reduction and internal fixation?
. Pipkin Type I; Kocher-Langenbeck approach
. Pipkin Type I; Smith-Petersen approach
. Pipkin Type II; Smith-Petersen approach
. Pipkin Type III; Ilioinguinal approach
. Pipkin Type IV; Stoppa approach

Correct Answer & Explanation

. Pipkin Type II; Smith-Petersen approach

Explanation

Pipkin Type II fractures involve the femoral head superior to the fovea (the primary weight-bearing portion). For Pipkin I and II fractures requiring fixation, an anterior (Smith-Petersen) approach or a surgical hip dislocation (Ganz) is preferred to directly visualize the head, provide perpendicular access for screw fixation, and preserve the remaining posterior blood supply (MFCA).

Question 4217

Topic: 1. General Principles & Basic Science

A 45-year-old active male is undergoing a medial opening wedge high tibial osteotomy (HTO) for varus gonarthrosis. A known complication of this procedure is an unintended increase in the posterior tibial slope. Which of the following technical errors most commonly leads to this increase in slope?

. Opening the osteotomy equally at the anteromedial and posteromedial cortices
. Opening the osteotomy gap wider at the posteromedial cortex than the anteromedial cortex
. Placing the osteotomy hinge posterior to the fibular head
. Releasing the superficial medial collateral ligament
. Using a locking plate with unicortical distal screws

Correct Answer & Explanation

. Opening the osteotomy gap wider at the posteromedial cortex than the anteromedial cortex

Explanation

Because the native proximal tibia is triangular (wider posteriorly than anteriorly), opening the medial wedge equally at the anteromedial and posteromedial cortices will inadvertently increase the posterior tibial slope. To maintain the native slope, the posteromedial gap must be opened approximately twice as much as the anteromedial gap.

Question 4218

Topic: Biology, Genetics & Bone Healing

A 65-year-old female who has been taking alendronate for 10 years presents with 3 months of progressive lateral thigh pain. Radiographs reveal a transverse radiolucent line in the lateral cortex of the subtrochanteric femur with associated focal cortical thickening ('beaking'). There is no history of trauma. What is the most appropriate management?

. Discontinue the bisphosphonate, prescribe teriparatide, and allow protected weight-bearing.
. Discontinue the bisphosphonate and perform prophylactic intramedullary nailing.
. Discontinue the bisphosphonate and perform open reduction with a lateral locking plate.
. Continue the bisphosphonate, add Vitamin D supplementation, and perform core decompression.
. Perform prophylactic cerclage wiring around the focal beaking.

Correct Answer & Explanation

. Discontinue the bisphosphonate and perform prophylactic intramedullary nailing.

Explanation

This patient has an impending atypical femur fracture (AFF) associated with long-term bisphosphonate use. Hallmarks include lateral cortical beaking and a transverse radiolucent line. Because she has progressive pain (suggesting mechanical instability/microfracture propagation), prophylactic intramedullary nailing is the gold standard to prevent a complete, displaced fracture, which carries a high risk of nonunion and complication. Discontinuing the bisphosphonate is essential, but medical management alone is insufficient for a symptomatic impending AFF.

Question 4219

Topic: Surgical Anatomy & Approaches

A 25-year-old male suffers a dashboard injury resulting in a posterior hip dislocation and an associated femoral head fracture that extends superior to the fovea capitis (Pipkin II). The hip is closed reduced, but CT shows the fracture fragment is displaced 3 mm. What is the optimal surgical approach to maximize direct visualization for anatomic fixation of this specific fragment while minimizing avascular necrosis risk?

. Kocher-Langenbeck (posterior) approach.
. Smith-Petersen (anterior) approach.
. Ilioinguinal approach.
. Direct Lateral (Hardinge) approach.

Correct Answer & Explanation

. Smith-Petersen (anterior) approach.

Explanation

A Pipkin II fracture involves the femoral head superior to the fovea capitis (the weight-bearing portion). For isolated femoral head fractures requiring ORIF (Pipkin I and II), the anterior approach (Smith-Petersen) or anterolateral (Watson-Jones) approach is preferred. It provides direct visualization of the anteriorly located femoral head fragment and avoids further damage to the remaining posterior blood supply (medial circumflex femoral artery) that was not torn during the posterior dislocation. The Ganz trochanteric flip is also an excellent option but the Smith-Petersen is the classic correct answer among these choices.

Question 4220

Topic: Surgical Anatomy & Approaches

A 40-year-old male presents with a posterior hip dislocation, a displaced fracture of the femoral head, and a large displaced posterior wall acetabular fracture (Pipkin IV). Which of the following surgical approaches provides the most optimal simultaneous access for direct visualization and anatomic reduction of both fracture components?

. Anterior Smith-Petersen approach
. Ilioinguinal approach
. Kocher-Langenbeck approach with a trochanteric flip (surgical hip dislocation)
. Medial approach of Ludloff
. Direct lateral (Hardinge) approach

Correct Answer & Explanation

. Kocher-Langenbeck approach with a trochanteric flip (surgical hip dislocation)

Explanation

A Pipkin IV fracture includes both a femoral head fracture and an acetabular fracture (usually the posterior wall). The Kocher-Langenbeck approach, especially when combined with a trochanteric flip (Ganz surgical hip dislocation), provides excellent extensile exposure to anatomically reduce and fix both the posterior wall of the acetabulum and the femoral head.

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