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1. General Principles & Basic Science MCQs

Practice Set 129 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 2561

Topic: Biomechanics & Biomaterials

A 45-year-old male with medial compartment knee osteoarthritis undergoes a medial opening wedge high tibial osteotomy (HTO). Postoperatively, the patient experiences anterior knee pain. Radiographs reveal an unintended increase in the posterior tibial slope. Which surgical error most likely caused this outcome?

. Over-distraction of the anterior cortex relative to the posterior cortex
. Over-distraction of the posterior cortex relative to the anterior cortex
. Placement of the hinge too anteriorly
. Placing the osteotomy distal to the tibial tubercle
. Failure to release the superficial medial collateral ligament

Correct Answer & Explanation

. Over-distraction of the anterior cortex relative to the posterior cortex

Explanation

In an opening wedge HTO, the posterior tibial cortex is naturally wider than the anterior cortex. If the anterior aspect is opened symmetrically or more than the posterior aspect, the posterior tibial slope unintentionally increases, which alters knee kinematics and strains the ACL.

Question 2562

Topic: 1. General Principles & Basic Science

A surgeon corrects a tibial deformity by placing the osteotomy distal to the center of rotation of angulation (CORA) and the hinge of the external fixator distal to the CORA. What is the expected biomechanical result of this configuration?

. Pure angulation without translation of the bone ends
. Angulation with translation that perfectly realigns the mechanical axis
. Angulation creating a translation of the mechanical axis (zig-zag deformity)
. Pure translation without angulation
. Failure of the regenerate bone to form

Correct Answer & Explanation

. Angulation creating a translation of the mechanical axis (zig-zag deformity)

Explanation

According to Paley's Rule 3, if both the osteotomy and the hinge are placed outside the CORA, correction results in a 'zig-zag' deformity. This happens because a new, unintended translation of the mechanical axis is created.

Question 2563

Topic: 1. General Principles & Basic Science

A 14-year-old male with severe Blount disease presents with a proximal tibial varus deformity of 25 degrees. The surgeon plans an acute correction with a closing wedge osteotomy. What nerve is at greatest risk of stretch injury during acute correction of this severe varus deformity?

. Tibial nerve
. Deep peroneal nerve
. Superficial peroneal nerve
. Common peroneal nerve
. Saphenous nerve

Correct Answer & Explanation

. Common peroneal nerve

Explanation

Acute correction of a severe varus deformity into valgus (normal alignment) dramatically stretches the structures on the lateral side of the knee. The common peroneal nerve is tethered at the fibular neck and is at highest risk for traction neurapraxia or palsy.

Question 2564

Topic: 1. General Principles & Basic Science

The Taylor Spatial Frame (TSF) utilizes a Stewart-Gough platform concept for deformity correction. How many degrees of freedom does this system address simultaneously during a multiplanar deformity correction?

. Three
. Four
. Five
. Six
. Eight

Correct Answer & Explanation

. Six

Explanation

The TSF allows simultaneous correction in all six degrees of freedom. This includes three planes of angulation (coronal, sagittal, axial) and three planes of translation (coronal, sagittal, axial).

Question 2565

Topic: 1. General Principles & Basic Science

When evaluating a multi-apical tibial diaphyseal deformity for a double-level osteotomy, the surgeon defines the mechanical axis lines of the proximal, middle, and distal segments. How is the center of rotation of angulation (CORA) for each osteotomy level geometrically identified?

. The midpoint of the anatomic axis of each segment
. The intersection of the mechanical axes of the adjacent segments
. The intersection of the anatomic axis of the proximal segment and mechanical axis of the distal segment
. The region of maximal diaphyseal bowing
. The exact center of the planned distraction regenerate

Correct Answer & Explanation

. The intersection of the mechanical axes of the adjacent segments

Explanation

In a multi-apical deformity, each distinct CORA is identified by the intersection of the mechanical axes (or anatomic axes, if parallel to mechanical) of the two adjacent, non-deformed bone segments. This intersection dictates the hinge placement for pure angular correction.

Question 2566

Topic: 1. General Principles & Basic Science

A surgeon is planning a corrective osteotomy for a diaphyseal tibial deformity. The Center of Rotation of Angulation (CORA) is located in the middle third of the diaphysis. To optimize soft tissue coverage, the surgeon decides to perform the osteotomy at a different level than the CORA, but places the corrective hinge exactly at the CORA. According to the principles of deformity correction (Osteotomy Rule 2), what will be the geometric result of this correction?

. Pure angulation with no translation.
. Complete correction of the mechanical axis but with translation at the osteotomy site.
. Parallel displacement of the mechanical axis resulting in residual malalignment.
. Creation of a secondary multi-apical deformity.
. Correction of length without angular correction.

Correct Answer & Explanation

. Complete correction of the mechanical axis but with translation at the osteotomy site.

Explanation

Osteotomy Rule 2 states that if the osteotomy is outside the CORA but the hinge is placed at the CORA, the mechanical axes will realign perfectly, but translation will occur at the osteotomy site. This translation is expected and functionally acceptable.

Question 2567

Topic: Biomechanics & Biomaterials

A 45-year-old active male is undergoing a high tibial osteotomy (HTO) for medial compartment osteoarthritis and varus deformity. The surgeon chooses a medial opening wedge HTO. To prevent unintended alterations in the sagittal plane knee kinematics, how should the anterior and posterior gaps of the osteotomy compare?

. The anterior gap should be roughly equal to the posterior gap.
. The anterior gap should be approximately half the size of the posterior gap.
. The anterior gap should be twice the size of the posterior gap.
. The anterior gap should be maximally opened while the posterior gap remains closed.
. The posterior gap should be grafted while the anterior gap is stabilized with a plate.

Correct Answer & Explanation

. The anterior gap should be approximately half the size of the posterior gap.

Explanation

Because the proximal tibia is naturally triangular and narrower anteriorly, opening the anterior and posterior gaps equally will inadvertently increase the posterior tibial slope. To maintain the native slope, the anterior opening gap should be approximately 50% of the posterior gap.

Question 2568

Topic: Biology, Genetics & Bone Healing

During distraction osteogenesis of the tibia using an Ilizarov frame, which of the following best describes the predominant type of bone formation that occurs in the distraction gap?

. Endochondral ossification
. Intramembranous ossification
. Creeping substitution
. Appositional chondrogenesis
. Woven bone remodeling exclusively via osteoclasts

Correct Answer & Explanation

. Intramembranous ossification

Explanation

Distraction osteogenesis relies primarily on intramembranous ossification, where bone forms directly from mesenchymal tissue under mechanical tension without a cartilaginous intermediate. This requires stable fixation and an appropriate distraction rate.

Question 2569

Topic: 1. General Principles & Basic Science

Which of the following modifications to a circular external fixator will most significantly increase its overall mechanical stiffness?

. Increasing the internal diameter of the rings
. Decreasing the tension of the wires from 130 kg to 90 kg
. Using half-pins instead of tensioned wires exclusively
. Decreasing the distance between the ring and the bone
. Using smooth wires instead of olive wires

Correct Answer & Explanation

. Decreasing the distance between the ring and the bone

Explanation

Decreasing the distance between the bone and the ring (using a smaller ring diameter) exponentially increases the stiffness of the frame. Increasing wire tension, using thicker wires, and proper wire crossing angles also improve stability.

Question 2570

Topic: 1. General Principles & Basic Science

In deformity correction principles, if an osteotomy is performed outside the CORA and the hinge is also placed outside the CORA (Osteotomy Rule 3), what is the resulting geometric relationship of the proximal and distal mechanical axes?

. They become collinear.
. They intersect at an angle equal to the magnitude of correction.
. They become parallel but translated, exacerbating or creating mechanical axis deviation.
. They perfectly align without any length changes.
. They result in a pure rotational deformity.

Correct Answer & Explanation

. They become parallel but translated, exacerbating or creating mechanical axis deviation.

Explanation

According to Osteotomy Rule 3, if both the osteotomy and the hinge are placed away from the CORA, the mechanical axes of the segments will end up parallel to each other, introducing a translation deformity and failing to fully restore collinearity.

Question 2571

Topic: 1. General Principles & Basic Science



A surgeon is using a Taylor Spatial Frame (TSF) to correct a complex multiplanar deformity of the tibia. The TSF relies on a six-axis Stewart-Gough platform mechanism. Which of the following parameters is NOT directly corrected via the standard six degrees of freedom mathematical model utilized by this frame?

. Anteroposterior translation
. Mediolateral translation
. Axial rotation
. Joint line convergence angle elasticity
. Axial length (distraction/compression)

Correct Answer & Explanation

. Anteroposterior translation

Explanation

The Taylor Spatial Frame corrects deformities in 6 degrees of freedom: AP translation, mediolateral translation, axial translation (length), pitch (flexion/extension), roll (varus/valgus), and yaw (internal/external rotation). It does not inherently alter intrinsic ligamentous elasticity or directly target dynamic intra-articular JLCA unless addressing bone alignment.

Question 2572

Topic: Biomechanics & Biomaterials

In the context of external fixation biomechanics, when utilizing half-pins to augment a circular frame, the bending stiffness of the pin is highly dependent on its core diameter. According to biomechanical principles, the bending stiffness is proportional to the radius raised to which power?

. Second power (r^2)
. Third power (r^3)
. Fourth power (r^4)
. Fifth power (r^5)
. It is inversely proportional to the radius.

Correct Answer & Explanation

. Fourth power (r^4)

Explanation

The bending stiffness of a pin or screw is proportional to the area moment of inertia, which for a solid cylinder is a function of the radius to the fourth power (r^4). Therefore, small increases in core diameter exponentially increase the pin's stiffness.

Question 2573

Topic: Biomechanics & Biomaterials

A 22-year-old patient is undergoing correction of a severe proximal tibial procurvatum deformity (apex anterior). If left uncorrected, how does a diaphyseal procurvatum deformity of the tibia mechanically affect knee kinematics?

. It functionally increases the posterior tibial slope, potentially increasing ACL strain and causing a knee flexion contracture.
. It functionally decreases the posterior tibial slope, predisposing to PCL insufficiency.
. It forces the knee into recurvatum during weight-bearing.
. It restricts internal rotation of the tibia during the screw-home mechanism.
. It uniformly decreases patellofemoral contact pressures.

Correct Answer & Explanation

. It functionally increases the posterior tibial slope, potentially increasing ACL strain and causing a knee flexion contracture.

Explanation

An apex anterior deformity (procurvatum) of the tibia tilts the knee joint line such that the effective posterior tibial slope is increased. This alters knee kinematics by increasing anterior tibial translation forces, putting stress on the ACL and potentially leading to a functional flexion contracture.

Question 2574

Topic: 1. General Principles & Basic Science

A 16-year-old girl is evaluated for a varus deformity of the right leg. The mechanical axis falls in zone 3 of the medial plateau. Radiographs reveal an MPTA of 75° and mLDFA of 88°. The surgeon plans a dome osteotomy of the proximal tibia. What is a key biomechanical advantage of a dome osteotomy over a standard closing-wedge osteotomy?

. It strictly requires internal fixation and cannot be done with external fixators.
. It corrects angulation without significant limb shortening or creating a secondary translation offset.
. It intrinsically decompresses the common peroneal nerve.
. It heals via endochondral ossification exclusively.
. It relies solely on the medial collateral ligament for stability.

Correct Answer & Explanation

. It corrects angulation without significant limb shortening or creating a secondary translation offset.

Explanation

A dome (cylindrical) osteotomy allows for angular correction without significantly altering limb length. Because the cut is an arc that allows the bone ends to slide, if the center of the dome (hinge) is placed near the CORA, it corrects deformity without creating large translational offsets or major limb shortening.

Question 2575

Topic: Biology, Genetics & Bone Healing

During the latency phase of distraction osteogenesis, what primary biological event is taking place at the corticotomy site?

. Rapid osteoclast-mediated bone resorption of the necrotic bone ends.
. Formation of a fracture hematoma and early recruitment of mesenchymal stem cells.
. Complete endochondral ossification of the gap.
. Maturation of lamellar bone from woven bone.
. Cortical remodeling and haversian canal formation.

Correct Answer & Explanation

. Formation of a fracture hematoma and early recruitment of mesenchymal stem cells.

Explanation

The latency phase (typically 5-7 days) allows for fracture hematoma organization, inflammation, and the recruitment of mesenchymal stem cells before mechanical tension is applied. This initiates the reparative phase essential for successful intramembranous ossification.

Question 2576

Topic: Biology, Genetics & Bone Healing

Which of the following is the predominant mechanism of new bone formation during standard distraction osteogenesis (callotasis)?

. Endochondral ossification
. Intramembranous ossification
. Creeping substitution
. Appositional bone growth on uncalcified cartilage
. Osteoclastic resorption followed by lamellar deposition

Correct Answer & Explanation

. Intramembranous ossification

Explanation

Distraction osteogenesis occurs primarily via intramembranous ossification. The gradual tension placed on the osteotomy callus stimulates osteoblasts to lay down new bone directly along the lines of tension without a cartilaginous intermediate.

Question 2577

Topic: 1. General Principles & Basic Science

Which of the following patients presents with 'Miserable Malalignment Syndrome', a complex torsional deformity of the lower extremities?

. Decreased femoral anteversion and excessive internal tibial torsion
. Excessive femoral anteversion and excessive external tibial torsion
. Excessive femoral retroversion and excessive external tibial torsion
. Decreased femoral anteversion and varus knee deformity
. Excessive femoral anteversion and excessive internal tibial torsion

Correct Answer & Explanation

. Excessive femoral anteversion and excessive external tibial torsion

Explanation

Miserable malalignment syndrome consists of increased femoral anteversion combined with compensatory increased external tibial torsion. This complex torsional profile often leads to significant patellofemoral tracking issues and anterior knee pain.

Question 2578

Topic: Biology, Genetics & Bone Healing

During limb lengthening via a corticotomy and circular external fixator, the ideal 'latency period' before initiating distraction is generally considered to be:

. 0 to 1 day
. 3 to 4 days
. 7 to 10 days
. 14 to 21 days
. 28 to 35 days

Correct Answer & Explanation

. 7 to 10 days

Explanation

A latency period of 7 to 10 days is typically standard in distraction osteogenesis to allow the initial inflammatory phase and early soft callus formation to begin. Shorter latency can lead to nonunion, while excessively long latency increases the risk of premature consolidation.

Question 2579

Topic: 1. General Principles & Basic Science
According to Paley's Rule 3 of deformity correction, what is the geometric outcome when both the osteotomy and the axis of correction of angulation (ACA) are placed outside the center of rotation of angulation (CORA)?
. The mechanical axis aligns perfectly without any translation.
. Translation will occur at the osteotomy site, but the mechanical axes will be collinear.
. The mechanical axes will be parallel but not collinear, resulting in a persistent translational deformity.
. An exact multi-planar correction is achieved regardless of the hinge position.
. The osteotomy will be locked in distraction, preventing further angular correction.

Correct Answer & Explanation

. The mechanical axes will be parallel but not collinear, resulting in a persistent translational deformity.

Explanation

Under Paley's Rule 3, if the ACA and osteotomy are not at the CORA, the proximal and distal mechanical axes will become parallel but will remain translated relative to one another, leaving a persistent translational deformity.

Question 2580

Topic: 1. General Principles & Basic Science

When calculating lower extremity joint orientation angles, what is the normal relationship between the anatomic and mechanical axes of the femur in a healthy adult?

. They are collinear and identical.
. The mechanical axis is in approximately 5 to 7 degrees of valgus relative to the anatomic axis.
. The anatomic axis is in approximately 5 to 7 degrees of valgus relative to the mechanical axis.
. The mechanical axis originates from the greater trochanter, while the anatomic axis originates from the center of the femoral head.
. They intersect at the distal femoral metaphysis rather than the joint line.

Correct Answer & Explanation

. The mechanical axis is in approximately 5 to 7 degrees of valgus relative to the anatomic axis.

Explanation

The anatomic axis of the femur lies in approximately 5 to 7 degrees of valgus compared to the mechanical axis, which is defined as a line from the center of the femoral head to the center of the knee.

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