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1. General Principles & Basic Science MCQs

Practice Set 100 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 1981

Topic: Biology, Genetics & Bone Healing

A 70-year-old male with severe osteoporosis (T-score -3.0) sustains a subtrochanteric femur fracture. He is medically optimized for surgery. The orthopedic surgeon plans for intramedullary nailing. During the procedure, the surgeon encounters difficulty achieving adequate purchase with standard cortical screws for distal locking, noting the bone feels 'crunchy' and prone to stripping. This observation is consistent with the biomechanical properties of osteoporotic bone. Which of the following statements best describes the microarchitectural changes contributing to this challenge?

. A. Increased bone mineral density leading to excessive rigidity.
. B. Expansion of Haversian canals and heightened intracortical remodeling in cortical bone.
. C. Pathological conversion of rod-like trabeculae to plate-like structures in cancellous bone.
. D. Increased collagen cross-linking leading to enhanced bone toughness.
. E. Reduced porosity of cortical bone, making it denser but more brittle.

Correct Answer & Explanation

. B. Expansion of Haversian canals and heightened intracortical remodeling in cortical bone.

Explanation

Correct Answer: BThe case describes that cortical bone in osteoporotic patients undergoes significant thinning, with increased porosity secondary to the expansion of Haversian canals and heightened intracortical remodeling. This geometric alteration drastically reduces the area moment of inertia, leading to diminished bending and torsional strength. This microarchitectural degradation directly contributes to the 'crunchy' feel and susceptibility to stripping during screw insertion, as the thin, porous cortices cannot withstand the torque required for adequate purchase.Option A (Increased bone mineral density leading to excessive rigidity)is incorrect. Osteoporosis is characterized by decreased bone mineral density, not increased, leading to fragility rather than excessive rigidity.Option C (Pathological conversion of rod-like trabeculae to plate-like structures in cancellous bone)is incorrect. The case states the opposite: there is a pathological conversion of plate-like trabeculae to mechanically inferior rod-like structures, leading to a critical loss of connectivity and reduced ability to resist compressive and shear loads.Option D (Increased collagen cross-linking leading to enhanced bone toughness)is incorrect. The case states that alterations in collagen cross-linking and mineral crystal size lead to increased brittleness and reduced toughness, making the bone more susceptible to comminution.Option E (Reduced porosity of cortical bone, making it denser but more brittle)is incorrect. Cortical bone in osteoporosis exhibitsincreasedporosity, not reduced, due to Haversian canal expansion, which makes it weaker and more prone to stripping, not denser.

Question 1982

Topic: Biology, Genetics & Bone Healing

A 75-year-old female with known osteoporosis presents with severe, intractable back pain after a fall, diagnosed with an L1 vertebral compression fracture. She has developed progressive neurological deficits, including lower extremity weakness and bowel/bladder dysfunction. Her pain has failed to respond to four weeks of medical management and bracing. Based on the case, which of the following interventions is most indicated for this patient?

. A. Continued non-operative management with increased analgesia and physical therapy.
. B. Vertebroplasty or kyphoplasty for cement augmentation.
. C. Referral to a pain management specialist for nerve blocks.
. D. Surgical decompression and stabilization.
. E. Initiation of anabolic agents for bone formation.

Correct Answer & Explanation

. D. Surgical decompression and stabilization.

Explanation

Correct Answer: DThe case explicitly lists 'Progressive neurological deficit' as an operative indication for vertebral compression fractures. While cement augmentation (vertebroplasty/kyphoplasty) is indicated for severe, intractable pain failing medical management, the presence of progressive neurological deficits necessitates surgical decompression and stabilization to address the spinal cord or nerve root compression. This is a critical distinction, as cement augmentation alone does not decompress neural elements.Option A (Continued non-operative management with increased analgesia and physical therapy)is inappropriate given the progressive neurological deficit and intractable pain that has failed four weeks of medical management. This patient requires more aggressive intervention.Option B (Vertebroplasty or kyphoplasty for cement augmentation)is indicated for severe, intractable pain failing medical management, but it does not address neurological deficits. Cement augmentation primarily stabilizes the vertebral body and reduces pain, but it does not decompress the spinal canal.Option C (Referral to a pain management specialist for nerve blocks)might be considered for pain management in stable fractures, but it does not address the underlying mechanical instability or the progressive neurological deficit, which requires surgical intervention.Option E (Initiation of anabolic agents for bone formation)is part of secondary fracture prevention and long-term osteoporosis management. While important, it is not an acute treatment for a symptomatic vertebral compression fracture with neurological compromise.

Question 1983

Topic: Biology, Genetics & Bone Healing

A 76-year-old female with a T-score of -3.2 undergoes bridge plating for a comminuted distal tibia fracture. The surgeon elects to use far cortical locking (FCL) screws. What is the primary biomechanical advantage of this construct in osteoporotic bone?

. It provides absolute stability for primary bone healing.
. It increases the axial stiffness of the construct.
. It provides symmetric micromotion to promote robust callus formation.
. It relies on high insertion torque for stability.
. It prevents en masse pullout by locking to the near cortex only.

Correct Answer & Explanation

. It provides symmetric micromotion to promote robust callus formation.

Explanation

Far cortical locking (FCL) screws allow for a controlled reduction in construct stiffness by bypassing the near cortex and engaging only the far cortex. This permits symmetric biphasic micromotion at the fracture site, which stimulates secondary bone healing via callus formation.

Question 1984

Topic: Biology, Genetics & Bone Healing

A 70-year-old female presents with a highly comminuted, osteoporotic proximal tibia fracture. A standard non-locked plate relies on friction between the plate and bone for stability. In contrast, how does a locked plate construct primarily fail in osteoporotic bone?

. Sequential screw toggle
. Loss of friction at the plate-bone interface
. En masse pullout of the entire construct
. Plate breakage at the most proximal screw hole
. Stress fracture of the diaphyseal bone

Correct Answer & Explanation

. En masse pullout of the entire construct

Explanation

Locked plate constructs function as fixed-angle devices that do not rely on friction against the bone. In severe osteoporosis, because the screws are fixed to the plate, the entire construct tends to fail via "en masse" pullout rather than individual screw toggle.

Question 1985

Topic: 1. General Principles & Basic Science

When placing distal interlocking screws during an antegrade tibial nail insertion, which screw trajectory is generally preferred to minimize the risk of iatrogenic injury to the superficial peroneal nerve?

. Lateral to medial
. Anterior to posterior
. Posterior to anterior
. Inferior to superior
. Medial to lateral

Correct Answer & Explanation

. Anterior to posterior

Explanation

Anterior to posterior (AP) locking screws in the distal tibia are preferred because lateral to medial screws place the superficial peroneal nerve at significant risk. The nerve courses anteriorly and laterally over the distal third of the leg.

Question 1986

Topic: Biology, Genetics & Bone Healing

A 45-year-old male sustains a high-energy closed tibia pilon fracture (OTA 43-C). A spanning external fixator is placed on the day of injury. What clinical parameter strictly dictates the appropriate timing for definitive open reduction and internal fixation?

. Wait exactly 14 days from the time of injury
. Resolution of soft tissue edema indicated by the appearance of skin wrinkles
. Normalization of systemic inflammatory markers (CRP/ESR)
. Formation of visible soft callus on plain radiographs
. Clearance from the infectious disease specialist

Correct Answer & Explanation

. Resolution of soft tissue edema indicated by the appearance of skin wrinkles

Explanation

Staged management of pilon fractures is standard. Definitive fixation is delayed until the soft tissue envelope has adequately recovered, reliably indicated by the resolution of edema and the return of normal skin lines (the 'wrinkle sign').

Question 1987

Topic: Biology, Genetics & Bone Healing

Far cortical locking (FCL) technology is sometimes used in the plate fixation of osteoporotic tibia fractures. What is the intended biomechanical advantage of FCL screws over standard locking screws?

. They increase the rigidity of the near cortex, preventing hardware pullout.
. They decrease construct stiffness at the near cortex, promoting parallel interfragmentary motion and symmetric callus.
. They dynamically compress the fracture upon weight-bearing.
. They rely solely on near-cortex threads, sparing the far cortex.
. They eliminate the need for bicortical screw purchase.

Correct Answer & Explanation

. They decrease construct stiffness at the near cortex, promoting parallel interfragmentary motion and symmetric callus.

Explanation

Far cortical locking screws have a smooth shaft at the near cortex and lock only into the far cortex and the plate. This reduces near-cortex construct stiffness, allowing symmetric, biphasic interfragmentary motion to stimulate robust callus formation.

Question 1988

Topic: Biology, Genetics & Bone Healing

An elderly patient with severe osteoporosis sustains a distal tibia spiral fracture managed with a lateral locking plate.

If mechanical failure occurs due to poor bone quality, which mechanism is most characteristic of a fully locked construct?

. En bloc pullout of the entire fixed-angle hardware construct
. Progressive varus deformity due to sequential screw back-out
. Fatigue fracture of the plate at the metadiaphyseal junction
. Shearing of the screw threads within the medullary canal
. Immediate nonunion with hypertrophic callus

Correct Answer & Explanation

. En bloc pullout of the entire fixed-angle hardware construct

Explanation

Because locking screws thread directly into the plate, the construct acts as a single fixed-angle device. In osteoporotic bone with poor purchase, the construct typically fails all at once (en bloc pullout) rather than individual screws backing out.

Question 1989

Topic: Biology, Genetics & Bone Healing

A 74-year-old female presents with atraumatic anterior leg pain. She has been on oral alendronate for 12 years. Radiographs reveal focal lateral cortical thickening of the tibial diaphysis with a transverse radiolucent line. What is the most appropriate management?

. Cessation of alendronate and observation
. Prophylactic intramedullary nailing
. Open reduction and internal fixation with a locking plate
. Teriparatide therapy alone
. Calcium and Vitamin D supplementation

Correct Answer & Explanation

. Prophylactic intramedullary nailing

Explanation

Atypical tibial fractures can occur with prolonged bisphosphonate use, presenting with lateral cortical thickening and a transverse fracture line. Prophylactic intramedullary nailing is recommended for impending fractures to prevent completion and promote healing.

Question 1990

Topic: 1. General Principles & Basic Science

Which of the following screw modifications will most significantly increase the pull-out strength of a cortical screw in osteoporotic bone?

. Decreasing the outer (thread) diameter
. Increasing the inner (core) diameter
. Decreasing the thread pitch
. Increasing the length of the unthreaded shank
. Utilizing a self-tapping flute

Correct Answer & Explanation

. Decreasing the thread pitch

Explanation

Pull-out strength is directly proportional to the volume of bone caught between the threads. Decreasing the thread pitch (increasing the number of threads per unit length) and increasing the outer diameter maximize purchase in osteoporotic bone.

Question 1991

Topic: Biology, Genetics & Bone Healing

A surgeon is using a bridging locking plate construct for a comminuted tibial shaft fracture in a 70-year-old osteoporotic patient. What is the biomechanical rationale for using "far cortical locking" screws instead of standard locking screws?

. To increase construct stiffness
. To allow parallel interfragmentary motion and promote callus formation
. To rely on plate-to-bone friction for stability
. To increase the pullout strength in the near cortex
. To prevent cold welding of the screw heads

Correct Answer & Explanation

. To allow parallel interfragmentary motion and promote callus formation

Explanation

Standard locking constructs can be too rigid, suppressing secondary bone healing. Far cortical locking screws engage only the far cortex, allowing controlled, parallel interfragmentary micromotion at the near cortex to stimulate robust callus formation.

Question 1992

Topic: Biology, Genetics & Bone Healing

A 75-year-old male with severe osteoporosis sustains a distal tibia spiral fracture. The fibula is intact. The decision is made to manage the patient non-operatively in a cast. What is the most likely deformity to develop due to the intact fibula?

. Valgus
. Varus
. Procurvatum
. Recurvatum
. External rotation

Correct Answer & Explanation

. Varus

Explanation

In the presence of a distal tibia fracture, an intact fibula acts as a strut. As the tibia settles and shortens, the intact fibula typically drives the distal tibia into varus angulation.

Question 1993

Topic: 1. General Principles & Basic Science

A 70-year-old female sustains a depressed lateral tibial plateau fracture. During ORIF, the osteoporotic metaphyseal void is filled. What is the primary advantage of using injectable calcium phosphate cement over polymethylmethacrylate (PMMA) for this purpose?

. Calcium phosphate provides immediate definitive rigid fixation allowing for immediate weight-bearing.
. Calcium phosphate undergoes an exothermic reaction that stimulates local osteoblasts.
. Calcium phosphate is completely radiolucent, allowing better postoperative assessment of the articular surface.
. Calcium phosphate is osteoconductive and sets isothermally, avoiding thermal necrosis.
. Calcium phosphate has superior tensile strength compared to PMMA.

Correct Answer & Explanation

. Calcium phosphate is osteoconductive and sets isothermally, avoiding thermal necrosis.

Explanation

Calcium phosphate is a bioceramic that sets without significant heat generation (isothermal) and is highly osteoconductive, eventually being remodeled into bone. PMMA undergoes an exothermic reaction that can cause thermal necrosis and does not remodel.

Question 1994

Topic: 1. General Principles & Basic Science

A 69-year-old patient with osteoporosis is being treated for a distal tibia fracture. The surgeon elects to use a locked plate. If the plate is positioned 5 mm off the surface of the bone, what is the biomechanical consequence compared to placing it flush?

. It decreases the working length of the screws.
. It provides absolute stability and promotes primary bone healing.
. It increases the bending moment on the screws, increasing the risk of fatigue failure.
. It significantly improves the pull-out strength of the locking screws.
. It decreases the risk of soft tissue irritation.

Correct Answer & Explanation

. It increases the bending moment on the screws, increasing the risk of fatigue failure.

Explanation

Placing a locked plate away from the bone increases the distance from the screw-plate interface to the cis-cortex. This effectively increases the bending moment on the screws, predisposing them to fatigue failure and breakage.

Question 1995

Topic: Biomechanics & Biomaterials

A 65-year-old female presents with an open, highly comminuted tibia shaft fracture and severe osteopenia. A circular external fixator (Ilizarov frame) is applied. What specific modification to the external fixator pins will most significantly increase their pull-out strength in this osteoporotic bone?

. Using fully threaded cortical screws instead of half-pins.
. Decreasing the pin diameter to preserve bone stock.
. Placing the pins perfectly parallel to the joint line.
. Applying pre-tension to all half-pins.
. Using hydroxyapatite-coated half-pins.

Correct Answer & Explanation

. Using hydroxyapatite-coated half-pins.

Explanation

In osteoporotic bone, external fixation pin loosening is a major complication. Using hydroxyapatite-coated half-pins enhances osteointegration at the pin-bone interface, significantly increasing pull-out strength and reducing the incidence of pin tract infections.

Question 1996

Topic: Biology, Genetics & Bone Healing

Reviewing an osteoporotic tibial shaft nonunion case, a 78-year-old female on chronic bisphosphonate therapy presents 9 months after IM nailing. X-rays demonstrate a hypertrophic nonunion. What is the characteristic effect of prolonged bisphosphonate use on fracture healing?

. It prevents the formation of a soft callus entirely.
. It accelerates the bridging of the hard callus.
. It permanently inhibits osteoblast proliferation.
. It delays the remodeling phase by inhibiting osteoclast activity.
. It induces massive heterotopic ossification.

Correct Answer & Explanation

. It delays the remodeling phase by inhibiting osteoclast activity.

Explanation

Bisphosphonates work by inhibiting osteoclast function. While they generally do not prevent clinical fracture union, they significantly delay the remodeling phase of fracture healing, which relies on osteoclastic resorption of the primary callus.

Question 1997

Topic: 1. General Principles & Basic Science

A 66-year-old male presents with a posterolateral tibial plateau fracture. To optimally visualize and buttress this specific fragment, which of the following surgical approaches is most appropriate?

. Posterolateral approach with or without a fibular osteotomy.
. Anterolateral approach with a submeniscal arthrotomy.
. Standard medial approach utilizing a pes anserinus takedown.
. Posteromedial approach interval between the medial gastrocnemius and pes anserinus.
. Direct posterior approach through the popliteal fossa.

Correct Answer & Explanation

. Posterolateral approach with or without a fibular osteotomy.

Explanation

A posterolateral tibial plateau fracture is difficult to reduce and plate from an anterior approach. A dedicated posterolateral approach, often requiring a fibular head osteotomy or working between the biceps femoris and IT band, allows direct visualization and buttress plating.

Question 1998

Topic: 1. General Principles & Basic Science

An 80-year-old female with a known history of severe osteoporosis is treated for a comminuted midshaft tibia fracture with conventional (non-locked) plates and screws. Two weeks postoperatively, she presents with failure of the construct. What is the most common mode of failure for conventional plating in osteoporotic bone?

. Fatigue failure and breakage of the plate at the fracture site.
. Screw pullout from the bone due to poor thread purchase.
. Shear failure of the screw heads.
. Plastic deformation of the plate.
. Intramedullary migration of the screws.

Correct Answer & Explanation

. Screw pullout from the bone due to poor thread purchase.

Explanation

Conventional plates rely on friction generated by compressing the plate to the bone via screws. In osteoporotic bone, the poor quality of the cancellous and cortical bone leads to poor thread purchase, making screw pullout the most common mode of failure.

Question 1999

Topic: Infection, Pharmacology & VTE

A 67-year-old female sustains a posteromedial shear fracture of the tibial plateau.

What is the optimal surgical interval to address this specific fracture fragment with buttress plating?

. Between the tibialis anterior and extensor hallucis longus.
. Between the medial head of the gastrocnemius and the pes anserinus.
. Between the lateral collateral ligament and the biceps femoris.
. Through the patellar tendon.
. Between the popliteus and the soleus.

Correct Answer & Explanation

. Between the medial head of the gastrocnemius and the pes anserinus.

Explanation

Posteromedial plateau fragments require buttress plating applied from the posteromedial side to effectively counteract shear forces. The classic posteromedial approach utilizes the interval between the medial head of the gastrocnemius (retracted posteriorly) and the pes anserinus (retracted anteriorly).

Question 2000

Topic: Infection, Pharmacology & VTE

A patient is considering ankle fusion and asks about potential complications.

Which of the following is NOT listed in the case as a potential complication of ankle fusion?

. Non-union
. Malunion
. Deep vein thrombosis (DVT) / Pulmonary embolism (PE)
. Stress fracture of the ipsilateral tibia
. Exacerbating or developing arthritis in other joints

Correct Answer & Explanation

. Exacerbating or developing arthritis in other joints

Explanation

Correct Answer: DThe candidate lists the following complications for ankle fusion: 'Non-union, malunion, delayed union, infection, wound-healing problems, nerve or vessel damage, DVT/PE, risk of exacerbating or developing arthritis in other joints.' Stress fracture of the ipsilateral tibia is not mentioned in this list.Options A, B, C, and E are all explicitly listed as potential complications of ankle fusion in the case.

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