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1. General Principles & Basic Science MCQs

Practice Set 123 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 2441

Topic: 1. General Principles & Basic Science

A surgeon is planning a tibial osteotomy for a diaphyseal varus deformity. The osteotomy is planned exactly at the Center of Rotation of Angulation (CORA), and the axis of correction of angulation (ACA) will pass through the CORA. What is the expected geometric outcome of this correction?

. Angulation with simultaneous translation.
. Pure angulation without translation.
. Pure translation without angulation.
. Paradoxical translation causing a zigzag deformity.
. Lengthening along the mechanical axis without angular correction.

Correct Answer & Explanation

. Pure angulation without translation.

Explanation

According to Paley's Osteotomy Rule 1, when the osteotomy and the ACA both pass through the CORA, pure angulation occurs without translation. This completely restores the mechanical axis without displacing the bone ends.

Question 2442

Topic: 1. General Principles & Basic Science

A patient requires a distal femoral osteotomy for a valgus deformity. The surgeon plans the osteotomy proximal to the Center of Rotation of Angulation (CORA) due to poor bone quality at the CORA, but places the hinge (ACA) exactly at the CORA. Which of the following best describes the resulting correction?

. The mechanical axis is restored through angulation and expected translation at the osteotomy site.
. The mechanical axis will remain deviated due to paradoxical translation.
. Pure angulation will occur at the osteotomy site without any translation.
. The joint line orientation will become pathologic.
. The limb will undergo pure shortening.

Correct Answer & Explanation

. The mechanical axis is restored through angulation and expected translation at the osteotomy site.

Explanation

Paley's Osteotomy Rule 2 states that if the ACA is at the CORA but the osteotomy is at a different level, the mechanical axis is fully restored. However, this correction requires a combination of angulation and translation at the osteotomy site.

Question 2443

Topic: 1. General Principles & Basic Science

When analyzing sagittal plane alignment of the femur and tibia on a full-length lateral radiograph, which of the following angle ranges best represents the normal Posterior Proximal Tibial Angle (PPTA)?

. 77 to 84 degrees
. 87 to 90 degrees
. 95 to 100 degrees
. 105 to 110 degrees
. 65 to 70 degrees

Correct Answer & Explanation

. 77 to 84 degrees

Explanation

The normal Posterior Proximal Tibial Angle (PPTA) typically ranges from 77 to 84 degrees. This reflects the normal posterior tibial slope of approximately 6 to 13 degrees relative to the tibial anatomic axis.

Question 2444

Topic: 1. General Principles & Basic Science

In a normal lower extremity, the mechanical axis of the femur deviates from the anatomic axis of the femur. What is the normal angle between the femoral mechanical axis and the femoral anatomic axis?

. 1 degree
. 3 degrees
. 7 degrees
. 11 degrees
. 15 degrees

Correct Answer & Explanation

. 7 degrees

Explanation

The anatomic axis of the femur is oriented in approximately 7 degrees of valgus relative to the mechanical axis. Understanding this 7-degree difference is critical when converting anatomic angular measurements to mechanical goals.

Question 2445

Topic: 1. General Principles & Basic Science

A patient presents with a tibial deformity consisting of 15 degrees of varus on the AP radiograph and 20 degrees of apex anterior (procurvatum) angulation on the lateral radiograph. Using the principles of deformity analysis, how should this deformity be fundamentally conceptualized for correction with a single hinge?

. As two distinct deformities requiring a double-level osteotomy.
. As a single oblique plane deformity with a true magnitude of 25 degrees.
. As a single oblique plane deformity with a true magnitude of 35 degrees.
. As a rotational deformity that manifests as false angulation.
. As a translational deformity in the coronal plane.

Correct Answer & Explanation

. As a single oblique plane deformity with a true magnitude of 35 degrees.

Explanation

Coronal and sagittal angular deformities at the same level represent a single oblique plane deformity. The true magnitude is calculated using the Pythagorean theorem (15^2 + 20^2 = 625), making the true magnitude 25 degrees.

Question 2446

Topic: 1. General Principles & Basic Science

A 45-year-old patient has a significant genu varum deformity. On the standing AP long-leg radiograph, the Joint Line Convergence Angle (JLCA) is measured at 6 degrees, opening laterally. What is the most likely primary contributor to this abnormal JLCA?

. Medial collateral ligament contracture.
. Lateral compartment osteoarthritis with bone loss.
. Medial compartment articular cartilage loss and lateral ligamentous laxity.
. Spurious measurement due to external rotation of the limb.
. Distal femoral diaphyseal varus bowing.

Correct Answer & Explanation

. Medial compartment articular cartilage loss and lateral ligamentous laxity.

Explanation

A JLCA greater than 2 degrees implies intra-articular deformity or soft tissue laxity. A JLCA opening laterally in a varus knee typically results from medial compartment space narrowing combined with lateral collateral ligament laxity.

Question 2447

Topic: Biology, Genetics & Bone Healing

What is the primary purpose of the latency period (typically 5-7 days) between the osteotomy and the initiation of distraction in limb lengthening?

. To allow resolution of acute post-operative pain before moving the frame.
. To allow formation of a robust fracture hematoma and early mesenchymal tissue.
. To permit early weight-bearing without hardware failure.
. To ensure the pin sites have completely epithelialized.
. To prevent deep vein thrombosis by allowing full mobilization.

Correct Answer & Explanation

. To allow formation of a robust fracture hematoma and early mesenchymal tissue.

Explanation

The latency period allows for the initial inflammatory and reparative phases of bone healing to occur. This establishes a vascularized mesenchymal tissue bridge (callus) that will subsequently be distracted to form regenerate bone.

Question 2448

Topic: 1. General Principles & Basic Science

In Paley's terminology of lower limb deformity, which of the following best defines \"malorientation\"?

. An abnormal relationship between the anatomic and mechanical axes of a single bone.
. A deviation of the mechanical axis of the entire lower extremity from its normal center over the knee joint.
. An abnormal joint orientation angle of a single bone segment.
. A torsional deformity of the diaphysis without angular change.
. A limb length discrepancy greater than 2 cm.

Correct Answer & Explanation

. An abnormal joint orientation angle of a single bone segment.

Explanation

Malorientation refers specifically to abnormal joint line angles (e.g., mLDFA, MPTA) of individual bone segments. Malalignment, by contrast, refers to the deviation of the mechanical axis of the entire limb.

Question 2449

Topic: Biomechanics & Biomaterials

The Taylor Spatial Frame (TSF) utilizes the mathematical principles of a Stewart platform to correct complex deformities simultaneously. Which of the following is NOT one of the six degrees of freedom addressed by this hexapod system?

. Coronal angulation.
. Sagittal translation.
. Axial rotation.
. Viscoelastic tissue creep.
. Axial translation (lengthening/shortening).

Correct Answer & Explanation

. Viscoelastic tissue creep.

Explanation

The six degrees of freedom in deformity correction are angulation and translation in three orthogonal planes (coronal, sagittal, axial). Viscoelastic tissue creep is a biological property, not a spatial dimension of alignment.

Question 2450

Topic: 1. General Principles & Basic Science

A 12-year-old patient undergoing 5 cm of femoral lengthening with an external fixator develops decreased active and passive knee flexion and extension over 4 weeks. What is the most critical management strategy to prevent irreversible joint damage?

. Increase the distraction rate to rapidly complete the lengthening process.
. Immediately remove the external fixator and apply a spica cast.
. Aggressive physical therapy, possible botulinum toxin injection, and slowing or stopping the rate of distraction.
. Perform an acute quadriceps tendon lengthening.
. Switch to a monolateral fixator system.

Correct Answer & Explanation

. Aggressive physical therapy, possible botulinum toxin injection, and slowing or stopping the rate of distraction.

Explanation

Joint contracture is a common and severe complication of limb lengthening. Management involves aggressive physical therapy, splinting, and decreasing or temporarily halting the rate of distraction to allow soft tissues to adapt.

Question 2451

Topic: Biology, Genetics & Bone Healing

Which of the following is the primary mechanical advantage of utilizing a dome (cylindrical) osteotomy for the correction of a metaphyseal angular deformity compared to an opening wedge osteotomy?

. It reliably produces exactly 2 cm of limb lengthening.
. It corrects angulation without creating a secondary translational deformity and maintains bone length.
. It does not require any form of internal or external fixation.
. It relies exclusively on intramembranous ossification without a latency period.
. It is the only osteotomy that can correct a pure rotational deformity.

Correct Answer & Explanation

. It corrects angulation without creating a secondary translational deformity and maintains bone length.

Explanation

A dome osteotomy allows the bone fragments to rotate around a central axis when the ACA is placed appropriately. This corrects the angular deformity without significantly altering limb length or creating a gap, maximizing bone contact.

Question 2452

Topic: 1. General Principles & Basic Science

A patient undergoes a proximal tibial osteotomy for a varus deformity. The center of rotation of angulation (CORA) is determined to be at the metaphyseal-diaphyseal junction. The surgeon plans an osteotomy distal to the CORA but places the hinge (axis of correction) exactly at the CORA. Which of the following describes the resulting correction?

. Complete correction of angulation with no translation.
. Complete correction of angulation with intentional translation of the distal segment.
. Incomplete correction of angulation with creation of a secondary deformity.
. Correction of angulation but with translation of the mechanical axis.
. Pure translation without angular correction.

Correct Answer & Explanation

. Complete correction of angulation with intentional translation of the distal segment.

Explanation

Osteotomy Rule 2 states that if the osteotomy is at a different level than the CORA but the hinge (axis of correction) is at the CORA, angulation will be corrected, but translation of the bone segments will occur.

Question 2453

Topic: 1. General Principles & Basic Science

When evaluating the sagittal plane alignment of the normal lower extremity, the posterior distal femoral angle (PDFA) and posterior proximal tibial angle (PPTA) are expected to be approximately:

. PDFA 83°, PPTA 81°
. PDFA 87°, PPTA 87°
. PDFA 90°, PPTA 90°
. PDFA 81°, PPTA 83°
. PDFA 75°, PPTA 75°

Correct Answer & Explanation

. PDFA 83°, PPTA 81°

Explanation

In the sagittal plane, the normal PDFA is 83° (indicating distal femoral flexion) and the normal PPTA is 81° (indicating the normal posterior slope of the proximal tibia).

Question 2454

Topic: 1. General Principles & Basic Science

A 40-year-old female presents with a varus knee and a medial mechanical axis deviation (MAD). Her MPTA is 87°, mLDFA is 87°, and JLCA is 8°. A stress radiograph shows correction of the JLCA to 2°. What is the primary cause of her varus malalignment?

. Proximal tibial structural varus
. Distal femoral structural varus
. Medial compartment cartilage loss and/or lateral ligamentous laxity
. Patellofemoral tracking dysfunction
. Distal tibial deformity

Correct Answer & Explanation

. Medial compartment cartilage loss and/or lateral ligamentous laxity

Explanation

The structural joint orientation angles (mLDFA and MPTA) are normal, but the JLCA is elevated and corrects with stress. This indicates that intra-articular factors, such as cartilage loss or lateral ligamentous laxity, are the primary cause.

Question 2455

Topic: 1. General Principles & Basic Science

A surgeon is planning a distal femoral osteotomy for a valgus deformity. A lateral opening wedge osteotomy is chosen over a medial closing wedge. What is an expected biomechanical and dimensional consequence of this specific choice?

. Shortening of the overall limb length.
. Increased slack in the lateral collateral ligament.
. Lengthening of the overall limb length and increased tension laterally.
. Decreased risk of delayed union due to larger bone contact.
. Decreased patellofemoral joint pressure.

Correct Answer & Explanation

. Lengthening of the overall limb length and increased tension laterally.

Explanation

Opening wedge osteotomies inherently add length to the bone, whereas closing wedges shorten it. A lateral opening wedge also tightens the lateral soft tissue structures, including the IT band.

Question 2456

Topic: 1. General Principles & Basic Science

During deformity analysis using the anatomic axis method, the surgeon notes an angle of 7 degrees between the anatomic and mechanical axes of the normal femur (AMA). If a midshaft femoral deformity is corrected based solely on properly aligning the proximal and distal anatomic axes, what will be the effect on the mechanical axis?

. The mechanical axis will have a residual varus deviation.
. The mechanical axis will have a residual valgus deviation.
. The mechanical axis is restored only if the mLDFA is overcorrected.
. Anatomic axis correction inherently corrects the mechanical axis.
. A significant translation of the mechanical axis will persist.

Correct Answer & Explanation

. Anatomic axis correction inherently corrects the mechanical axis.

Explanation

Because the mechanical and anatomic axes normally maintain a fixed geometric relationship (the AMA), perfectly restoring the normal anatomic axis of the bone inherently restores its mechanical axis.

Question 2457

Topic: 1. General Principles & Basic Science

A 16-year-old male presents with a mid-diaphyseal tibial varus deformity. During preoperative planning, the Center of Rotation of Angulation (CORA) is determined. According to Paley's osteotomy rules, if the osteotomy is performed at a level different from the CORA, but the hinge (axis of rotation) is placed exactly at the CORA, what is the expected outcome of the correction?

. Angulation correction without translation of the bone ends
. Angulation correction with intentional translation of the bone ends
. Translation without angulation correction
. Creation of a secondary deformity in the opposite direction
. Angulation correction with unintended shortening of the limb

Correct Answer & Explanation

. Angulation correction with intentional translation of the bone ends

Explanation

According to Osteotomy Rule 2, placing the hinge at the CORA but performing the osteotomy at a different level results in correction of the angulation along with intentional translation of the bone ends. This perfectly realigns the mechanical axis.

Question 2458

Topic: 1. General Principles & Basic Science

A surgeon is planning a corrective osteotomy for a patient with a complex angular deformity of the tibia. After drawing the proximal and distal mechanical axes of the deformed bone segment, they intersect at a specific point, as depicted in the diagram below. What does this intersection point represent, and what is its primary significance in Paley's principles?

. The anatomical axis, indicating the bone's true longitudinal center.
. The mechanical axis deviation, quantifying the degree of malalignment.
. The Center of Rotation of Angulation (CORA), dictating the ideal osteotomy and hinge placement.
. The joint line convergence angle, assessing knee joint congruity.
. The planned osteotomy site, where the bone cut will be made.

Correct Answer & Explanation

. The Center of Rotation of Angulation (CORA), dictating the ideal osteotomy and hinge placement.

Explanation

Correct Answer: CThe diagram illustrates the method for identifying the Center of Rotation of Angulation (CORA). As per the case content, the CORA is the exact point of intersection where the extended proximal and distal mechanical (or anatomic) axis lines of a deformed bone segment meet. This point is the absolute cornerstone of Dr. Paley's principles, as it dictates two critical surgical decisions: the ideal anatomical location for the bone cut (osteotomy) and the required spatial placement of the mechanical hinge on the external fixator (or the pivot point of an internal plate). To achieve a pure angular correction, the bone segments must be rotated exactly around the CORA.Option A is incorrect; the anatomical axis is a different concept, typically drawn through the center of the medullary canal. Option B is incorrect; Mechanical Axis Deviation (MAD) quantifies malalignment but is a distance, not an intersection point. Option D is incorrect; the Joint Line Convergence Angle (JLCA) assesses knee joint congruity and is not represented by this intersection. Option E is incorrect; while the CORA influences the osteotomy site, the intersection itself is the CORA, not necessarily the osteotomy site, especially in scenarios governed by Rule 2 or 3.

Question 2459

Topic: 1. General Principles & Basic Science

A 25-year-old patient requires a corrective osteotomy for a mid-diaphyseal femoral varus deformity. The surgeon identifies the CORA precisely at the apex of the deformity, which is in a healthy bone segment with good soft tissue coverage. The surgical plan involves performing the osteotomy exactly at the CORA and placing the mechanical hinge of the external fixator also precisely at the CORA. According to Paley's osteotomy rules, what is the expected geometric outcome of this approach?

. Perfect angular correction with an obligatory, predictable translation of bone segments.
. Angular correction resulting in parallel but translated proximal and distal axes.
. Pure, perfect angular correction with the proximal and distal mechanical axes becoming perfectly collinear without any shift.
. Angular correction that creates a new iatrogenic translational deformity.
. A correction that requires counter-opposed olive wires to manage translation.

Correct Answer & Explanation

. Pure, perfect angular correction with the proximal and distal mechanical axes becoming perfectly collinear without any shift.

Explanation

Correct Answer: CThis scenario perfectly describes Paley's Osteotomy Rule 1. Rule 1 states that when the osteotomy is performed exactly AT the CORA, and the mechanical hinge is placed exactly AT the CORA, the result is pure, perfect angular correction. The geometric outcome is that the proximal and distal mechanical axes become perfectly collinear without any shift or translation at the osteotomy site. The bone ends pivot directly on each other, maintaining maximum cortical apposition. This is considered the most biomechanically stable and biologically favorable condition, maximizing bone contact and promoting rapid healing.Option A describes Rule 2, where translation is obligatory. Option B and D describe Rule 3, which creates an iatrogenic translational deformity. Option E is relevant to Rule 2 when using all-wire frames, but not Rule 1, where translation is absent.

Question 2460

Topic: 1. General Principles & Basic Science

A 40-year-old patient presents with a severe proximal tibial varus deformity. The CORA is identified just millimeters below the articular joint line, making it anatomically hostile for direct osteotomy and hinge placement. The surgeon decides to perform the osteotomy 3 cm distal to the CORA in a safer metaphyseal region, while meticulously positioning the mechanical hinge of the external fixator precisely at the CORA in space using a juxta-articular assembly. Which of Paley's osteotomy rules is being applied, and what is the expected outcome?

. Osteotomy Rule 1; pure angular correction with no translation.
. Osteotomy Rule 2; perfect angular correction accompanied by an obligatory, predictable translation.
. Osteotomy Rule 3; angular correction with a new, iatrogenic translational deformity.
. Osteotomy Rule 1; angular correction with automatic translation due to hinge offset.
. Osteotomy Rule 3; angular correction with the proximal and distal axes becoming collinear.

Correct Answer & Explanation

. Osteotomy Rule 2; perfect angular correction accompanied by an obligatory, predictable translation.

Explanation

Correct Answer: BThis clinical scenario describes the application of Paley's Osteotomy Rule 2. Rule 2 applies when the mechanical hinge is placed AT the CORA, but the osteotomy is performed at a different anatomical level (either proximal or distal to the CORA). The result is perfect angular correction accompanied by an obligatory, predictable translation. Because the bone is cut at a distance from the center of rotation, the bone ends must slide past one another during the angular correction. This translation is a strict mathematical necessity and is anticipated and managed by the surgeon, often when the CORA is in an anatomically hostile area, as described in the question.Option A describes Rule 1, which requires both the osteotomy and hinge to be at the CORA. Options C and E describe Rule 3, which results in an iatrogenic translational deformity and non-collinear axes. Option D incorrectly applies Rule 1 to a scenario involving hinge offset and translation.

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