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1. General Principles & Basic Science MCQs

Practice Set 160 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 3181

Topic: Biomechanics & Biomaterials

A 40-year-old male with a history of trauma presents with a complex tibial deformity. The surgeon is meticulously planning a corrective osteotomy using Paley's principles. Which of the following statements best encapsulates the core philosophy underlying this methodology?

. Surgical correction should prioritize cosmetic appearance over biomechanical accuracy.
. Subjective visual estimation is a reliable method for initial deformity assessment.
. Accurate measurement is a prerequisite for effective correction.
. Advanced surgical techniques can compensate for imprecise preoperative planning.
. Localized radiographs are sufficient for diagnosing and planning all lower limb deformities.

Correct Answer & Explanation

. Accurate measurement is a prerequisite for effective correction.

Explanation

Correct Answer: CThe text explicitly states the core philosophy: 'The core philosophy underlying this methodology is simple yet profoundly impactful: you cannot correct what you cannot accurately measure.' It emphasizes that 'Successful deformity correction depends entirely on meticulous preoperative planning derived from strictly standardized radiographs.'Option A is incorrectbecause Paley's principles prioritize rigorous science and mathematical precision for predictable, reproducible, and successful patient outcomes, which inherently includes biomechanical accuracy, not just cosmetic appearance.Option B is incorrectbecause the text directly refutes this, stating that 'Subjective visual estimation—often referred to as "eyeballing" the deformity—is a dangerous relic of the past, replaced by objective, reproducible geometric analysis.'Option D is incorrectbecause the text warns: 'Operating on flawed measurements leads inevitably to imprecise osteotomies, residual deformity, altered joint biomechanics, and ultimately, compromised joint health and early-onset osteoarthritis,' indicating that advanced techniques cannot compensate for flawed planning.Option E is incorrectbecause the text clearly states that 'Standard, short-cassette radiographs of the hip, knee, or ankle... are entirely insufficient for deformity analysis. They provide a myopic, localized view that completely obscures the global mechanical relationship.'

Question 3182

Topic: Biomechanics & Biomaterials

A resident is reviewing a full-length standing AP radiograph of a patient with a suspected knee deformity. The radiograph was taken with the patient's feet pointing forward, but the patellae are clearly internally rotated. The resident proceeds to measure the Mechanical Lateral Distal Femoral Angle (mLDFA) and the Medial Proximal Tibial Angle (MPTA) from this film. Based on Paley's principles, what is the most critical implication of using this radiograph for these measurements?

. The measurements of mLDFA and MPTA will be accurate, but the overall leg length will be distorted.
. The rotational distortion will lead to an erroneous calculation of the Mechanical Axis Deviation (MAD).
. The measurements will accurately reflect the patient's true frontal plane deformity, as long as the feet are forward.
. The distortion will primarily affect the assessment of sagittal plane alignment, not frontal plane angles.
. The radiograph is acceptable for initial screening but not for definitive surgical planning.

Correct Answer & Explanation

. The rotational distortion will lead to an erroneous calculation of the Mechanical Axis Deviation (MAD).

Explanation

Correct Answer: BThe text emphasizes that the 'Patella-Forward Rule' is critical because 'aligning the feet forward can induce significant rotation at the knee. This rotation distorts the frontal plane projection, rendering all subsequent joint orientation angle measurements completely inaccurate.' If the mLDFA and MPTA are inaccurate, then the subsequent calculation of the Mechanical Axis Deviation (MAD) will be inherently flawed. The text states: 'Operating on flawed measurements leads inevitably to imprecise osteotomies, residual deformity, altered joint biomechanics...'Option A is incorrectbecause the text explicitly states that rotational distortion renders 'all subsequent joint orientation angle measurements completely inaccurate,' meaning mLDFA and MPTA would not be accurate. Leg length is less affected by knee rotation than angular measurements.Option C is incorrectbecause the text directly refutes this, stating that 'aligning the feet forward can induce significant rotation at the knee. This rotation distorts the frontal plane projection, rendering all subsequent joint orientation angle measurements completely inaccurate.'Option D is incorrectbecause rotational errors primarily affect the frontal plane projection and measurements of joint orientation angles, not sagittal plane alignment, which is assessed on lateral views.Option E is incorrectbecause the text states that a poorly positioned image is 'not just unhelpful; it is dangerously misleading and can lead to catastrophic surgical errors,' making it unacceptable even for initial screening if accurate measurements are the goal.

Question 3183

Topic: Biomechanics & Biomaterials

A 70-year-old patient presents with severe bilateral genu varum and is being considered for a high tibial osteotomy. The surgeon is reviewing the full-length standing AP radiographs. Which of the following statements accurately reflects a key principle of Paley's methodology regarding the consequences of using flawed measurements?

. Minor inaccuracies in radiographic measurements are typically compensated for by the body's natural healing processes.
. Flawed measurements primarily affect cosmetic outcomes, with minimal impact on joint biomechanics.
. Inaccurate measurements lead to imprecise osteotomies, residual deformity, altered joint biomechanics, and early-onset osteoarthritis.
. The Center of Rotation of Angulation (CORA) is unaffected by errors in joint orientation angles.
. Subjective visual estimation can often correct for small errors in objective measurements.

Correct Answer & Explanation

. Inaccurate measurements lead to imprecise osteotomies, residual deformity, altered joint biomechanics, and early-onset osteoarthritis.

Explanation

Correct Answer: CThe text directly addresses the consequences of flawed measurements: 'Operating on flawed measurements leads inevitably to imprecise osteotomies, residual deformity, altered joint biomechanics, and ultimately, compromised joint health and early-onset osteoarthritis.' This highlights the severe and long-term negative impacts of inaccurate preoperative planning.Option A is incorrectbecause the text emphasizes the critical need for precision and warns against the severe consequences of flawed measurements, implying that minor inaccuracies are not simply compensated for.Option B is incorrectbecause the text explicitly mentions 'altered joint biomechanics' and 'compromised joint health and early-onset osteoarthritis' as consequences, indicating a significant impact beyond just cosmetic outcomes.Option D is incorrectbecause the text states that 'Without this rigorous foundation, the subsequent calculation of the Mechanical Axis Deviation (MAD), Joint Orientation Angles (such as the mLDFA and MPTA), and the Center of Rotation of Angulation (CORA) will be inherently flawed.' This means CORA calculation is directly dependent on accurate joint orientation angles.Option E is incorrectbecause the text explicitly states that 'Subjective visual estimation—often referred to as "eyeballing" the deformity—is a dangerous relic of the past,' and cannot correct for errors in objective measurements.

Question 3184

Topic: Surgical Anatomy & Approaches

A 35-year-old patient presents with a pure angular varus deformity of the distal tibia. Pre-operative planning identifies the Center of Rotation of Angulation (CORA) 5 cm proximal to the ankle joint. The surgeon plans a corrective osteotomy to achieve perfect alignment without any translation of the bone segments. According to Paley's Three Rules of Osteotomy, which of the following surgical approaches is most appropriate?

. Perform the osteotomy 3 cm proximal to the CORA, with the hinge placed at the CORA.
. Perform the osteotomy 5 cm distal to the CORA, with the hinge placed at the CORA.
. Perform the osteotomy and place the hinge exactly at the CORA.
. Perform the osteotomy and place the hinge 2 cm proximal to the CORA.
. Perform a double-level osteotomy, one proximal and one distal to the CORA.

Correct Answer & Explanation

. Perform the osteotomy and place the hinge exactly at the CORA.

Explanation

Correct Answer: CThe text describes Paley's Osteotomy Rule 1: 'If the osteotomy (the bone cut) and the ACA (the hinge) pass through the CORA, the deformity will correct with pure angulation. The mechanical axes of the proximal and distal segments will perfectly align without any translation (displacement) of the bone ends. This is the ideal scenario for most simple deformities.' To achieve perfect alignment without translation, both the osteotomy cut and the hinge must be placed precisely at the CORA.Option A is incorrectbecause placing the osteotomy away from the CORA, even with the hinge at the CORA, would result in translation (Paley's Rule 2).Option B is incorrectfor the same reason as Option A; placing the osteotomy away from the CORA results in translation.Option D is incorrectbecause placing both the cut and the hinge away from the CORA would result in a new translation deformity and a zigzag appearance (Paley's Rule 3).Option E is incorrectbecause a double-level osteotomy is typically used for double-level deformities or to distribute correction, not for a pure angular deformity where the CORA is clearly identified at a single level, especially when the goal is pure angulation without translation.

Question 3185

Topic: 1. General Principles & Basic Science

A 65-year-old patient with a severe varus knee deformity undergoes pre-operative planning. The surgeon identifies a double-level deformity with an mLDFA of 94° and an MPTA of 82°. The patient also has a significant procurvatum deformity of the proximal tibia. According to Paley's principles, which of the following statements represents the most appropriate approach to surgical planning for this patient?

. Perform a single-level osteotomy at the CORA of the most severe deformity, ignoring the other deformities.
. Address the coronal plane deformities first with a double-level osteotomy, then assess the sagittal plane post-correction.
. Manage the sagittal plane deformity first or concurrently, as severe procurvatum can obscure coronal plane measurements and affect predictability.
. Prioritize correction of the MPTA, as tibial deformities are generally more critical than femoral deformities.
. A double-level osteotomy is contraindicated in the presence of a sagittal plane deformity.

Correct Answer & Explanation

. Manage the sagittal plane deformity first or concurrently, as severe procurvatum can obscure coronal plane measurements and affect predictability.

Explanation

Correct Answer: CThe text provides a crucial surgical pearl: 'Manage the Sagittal Plane First: When dealing with multiplanar deformities, severe procurvatum or recurvatum can obscure coronal plane measurements. Correcting or temporarily stabilizing the sagittal profile often makes the coronal correction more predictable.' This patient has both coronal (double-level varus) and sagittal (proximal tibial procurvatum) deformities, making it essential to consider the sagittal plane early in the planning or execution.Option A is incorrectbecause ignoring other deformities, especially in a double-level and multiplanar case, would lead to an incomplete and potentially unstable correction.Option B is incorrectbecause the text specifically advises managing the sagittal plane first, as it can impact coronal measurements and predictability, rather than addressing it only after coronal correction.Option D is incorrectbecause while both femoral and tibial deformities are important, the text does not prioritize one over the other in terms of criticality but rather emphasizes addressing multiplanar deformities systematically, with a focus on the sagittal plane first if severe.Option E is incorrectbecause a double-level osteotomy is often necessary for double-level coronal deformities, and the presence of a sagittal deformity does not contraindicate it but rather necessitates its consideration in the overall plan.

Question 3186

Topic: 1. General Principles & Basic Science

A 60-year-old male is being evaluated for femoral deformity. . This image illustrates the relationship between the femoral mechanical and anatomic axes. According to Paley's principles, what is the typical angular relationship between these two axes in a normally aligned femur?

. They are collinear, running parallel to each other.
. The anatomic axis lies in approximately 7 degrees of varus relative to the mechanical axis.
. The mechanical axis lies in approximately 7 degrees of varus relative to the anatomic axis.
. The anatomic axis lies in approximately 7 degrees of valgus relative to the mechanical axis.
. The mechanical axis lies in approximately 7 degrees of valgus relative to the anatomic axis.

Correct Answer & Explanation

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

Explanation

Correct Answer: DThe text states: 'In the femur, a critical and highly variable divergence exists. Due to the anatomical offset of the femoral head and neck, the anatomic axis of the femur lies in approximately 7 degrees of valgus relative to the femoral mechanical axis (normal range is typically 5 to 9 degrees).' The image visually supports this concept, showing the anatomic axis diverging laterally (valgus) from the mechanical axis.Option A (Collinear):This is incorrect for the femur. While nearly collinear in the tibia, the femur shows significant divergence.Option B (Anatomic axis in varus relative to mechanical):This is incorrect. The anatomic axis is in valgus relative to the mechanical axis.Option C (Mechanical axis in varus relative to anatomic):This is an inverted description of the relationship and is incorrect.Option D (Anatomic axis in valgus relative to mechanical):This is the correct statement, as described in the text.Option E (Mechanical axis in valgus relative to anatomic):This is an inverted description and is incorrect.

Question 3187

Topic: 1. General Principles & Basic Science

A surgeon is planning a corrective osteotomy for a uniapical tibial deformity identified on a 51-inch standing radiograph. . This image demonstrates the identification of the Center of Rotation of Angulation (CORA). Which of the following statements accurately describes how the CORA is identified?

. It is the midpoint of the deformed bone segment.
. It is the point where the overall limb mechanical axis crosses the deformed bone.
. It is the geometric intersection point of the proximal and distal axes of the deformed bone segment.
. It is the point of maximum curvature along the bone's anatomic axis.
. It is the center of the joint closest to the deformity.

Correct Answer & Explanation

. It is the geometric intersection point of the proximal and distal axes of the deformed bone segment.

Explanation

Correct Answer: CThe text clearly defines the CORA: 'The CORA is defined as the geometric intersection point of the proximal and distal axes of a deformed bone segment.' The steps provided are: 1. Draw the Proximal Axis. 2. Draw the Distal Axis. 3. Find the Intersection. The image visually represents this process.Option A (Midpoint of the deformed bone):Incorrect. The CORA is a geometric intersection, not necessarily the midpoint.Option B (Intersection with overall limb mechanical axis):Incorrect. The CORA is derived from the axes of thedeformed bone segmentitself, not the overall limb axis.Option C (Geometric intersection of proximal and distal axes):Correct. This is the precise definition provided in the text.Option D (Point of maximum curvature):Incorrect. While often near the point of maximum curvature, the CORA is a precise geometric intersection of the axes, not an estimation of curvature.Option E (Center of the closest joint):Incorrect. The CORA is within the bone segment, not necessarily a joint center.

Question 3188

Topic: 1. General Principles & Basic Science

Following the identification of a uniapical deformity and its Center of Rotation of Angulation (CORA), a surgeon plans a corrective osteotomy. According to Paley's 'Three Immutable Rules of Osteotomy Planning,' if the osteotomy is performed precisely at the level of the CORA and the correction hinge (Axis of Correction of Angulation, ACA) is centered at this same point, what is the expected outcome?

. Pure translation without any angulation.
. Pure angulation without any translation.
. Combined angulation and translation, requiring a second osteotomy.
. Creation of a new, iatrogenic secondary deformity.
. Correction of the deformity but with significant limb lengthening.

Correct Answer & Explanation

. Pure angulation without any translation.

Explanation

Correct Answer: BThe text introduces 'Osteotomy Rule 1: The Ideal Correction' stating: 'Condition: The osteotomy is performed exactly AT the level of the CORA, and the correction hinge (ACA) is centered AT the CORA. Result: Pure angulation without any translation. The proximal and...' (text cuts off, but the core result is clear).Option A (Pure translation):Incorrect. This would occur if the osteotomy was performed away from the CORA without appropriate translation.Option B (Pure angulation without any translation):Correct. This is the ideal outcome when the osteotomy and ACA are precisely at the CORA.Option C (Combined angulation and translation):Incorrect. This is what Rule 1 aims to avoid by placing the osteotomy at the CORA.Option D (Creation of a new, iatrogenic secondary deformity):Incorrect. This is the goal of Rule 1 to prevent such deformities.Option E (Significant limb lengthening):Incorrect. While some lengthening can occur with distraction osteogenesis, pure angulation at the CORA primarily corrects alignment, not length, unless specifically planned for.

Question 3189

Topic: 1. General Principles & Basic Science

A 25-year-old male has a post-traumatic tibial deformity. Radiographs show a midshaft varus angulation. The surgeon plans an opening wedge osteotomy. According to Paley's Osteotomy Rule 1, if both the osteotomy and the axis of rotation (hinge) are placed exactly at the Center of Rotation of Angulation (CORA), what is the geometric result?

. Pure angulation with complete realignment of the mechanical axis without translation
. Angulation with translation at the osteotomy site
. Translation without angulation
. Parallel displacement of the mechanical axes
. Intentional shortening of the limb

Correct Answer & Explanation

. Pure angulation with complete realignment of the mechanical axis without translation

Explanation

Paley's Rule 1 states that if the osteotomy and the hinge (axis of rotation) are both located at the CORA, the mechanical axes will realign perfectly through pure angulation. No translation occurs at the osteotomy site.

Question 3190

Topic: 1. General Principles & Basic Science

A 40-year-old female presents with a distal femoral valgus deformity. The CORA is identified at the level of the knee joint line. To avoid an intra-articular osteotomy, the surgeon performs the osteotomy in the distal femoral metaphysis but places the hinge (axis of rotation) exactly at the intra-articular CORA. According to Paley's Osteotomy Rule 2, what is the expected outcome?

. Pure angulation without translation at the osteotomy site
. Angulation with translation at the osteotomy site, resulting in collinear mechanical axes
. Pure translation resulting in parallel but non-collinear axes
. A new secondary CORA is created in the diaphysis
. The mechanical axis deviation will worsen

Correct Answer & Explanation

. Angulation with translation at the osteotomy site, resulting in collinear mechanical axes

Explanation

Paley's Rule 2 states that if the hinge is at the CORA but the osteotomy is at a different level, the axes will realign perfectly but translation will occur at the osteotomy site. This is frequently used when the CORA is juxta-articular or intra-articular.

Question 3191

Topic: 1. General Principles & Basic Science

A surgeon is planning a deformity correction using Paley's Osteotomy Rule 1. Both the osteotomy and the axis of rotation (hinge) are placed exactly at the Center of Rotation of Angulation (CORA). What is the expected geometric outcome of this correction?

. Pure angulation with collinear realignment of the mechanical axes
. Angulation with significant translation of the mechanical axes
. Parallel translation without angular correction
. Shortening and rotation with divergent mechanical axes
. Pure translation with collinear mechanical axes

Correct Answer & Explanation

. Pure angulation with collinear realignment of the mechanical axes

Explanation

According to Paley's Osteotomy Rule 1, placing both the osteotomy and the hinge at the CORA results in pure angulation. The bone ends remain apposed without translation, and the proximal and distal mechanical axes become perfectly collinear.

Question 3192

Topic: 1. General Principles & Basic Science

An orthopedic surgeon performs a corrective osteotomy proximal to the identified Center of Rotation of Angulation (CORA), but correctly places the hinge on the transverse bisector line exactly at the CORA. Based on Paley's Osteotomy Rule 2, what is the resultant alignment?

. The mechanical axes remain parallel but permanently translated
. The mechanical axes become collinear, but the bone ends translate at the osteotomy site
. The mechanical axes remain divergent with pure angulation
. The mechanical axes become collinear without any bone end translation
. The bone ends hinge without correcting the overall mechanical axis deviation

Correct Answer & Explanation

. The mechanical axes become collinear, but the bone ends translate at the osteotomy site

Explanation

Paley's Rule 2 states that if the hinge is at the CORA but the osteotomy is outside the CORA, the mechanical axes will successfully realign to become collinear. However, this correction requires the bone ends to translate relative to each other at the osteotomy site.

Question 3193

Topic: 1. General Principles & Basic Science

During preoperative planning for a distal femoral deformity, the surgeon notes that both the planned osteotomy site and the axis of rotation (hinge) will be located outside the CORA. According to Paley's Osteotomy Rule 3, what is the consequence of this configuration?

. The mechanical axes become perfectly collinear with bone shortening
. The mechanical axes become parallel but remain displaced (translated)
. Pure angulation occurs without translation at the osteotomy site
. The bone length increases proportionally to the angulation without shifting
. The joint orientation angles remain unchanged while the mechanical axis perfectly aligns

Correct Answer & Explanation

. The mechanical axes become parallel but remain displaced (translated)

Explanation

Paley's Rule 3 dictates that if the hinge and the osteotomy are placed at a location other than the CORA, the correction will result in parallel but displaced (translated) mechanical axes. The magnitude of displacement depends on the distance of the hinge from the CORA.

Question 3194

Topic: 1. General Principles & Basic Science

When evaluating a suspected sagittal plane deformity of the proximal tibia (e.g., procurvatum or recurvatum), a true lateral radiograph is obtained. Which of the following is the normal reference value for the posterior proximal tibial angle (PPTA)?

. 70 degrees
. 81 degrees
. 90 degrees
. 95 degrees
. 105 degrees

Correct Answer & Explanation

. 81 degrees

Explanation

The normal posterior proximal tibial angle (PPTA) in the sagittal plane is 81 degrees (range 77-84 degrees). An angle greater than this indicates recurvatum, while a lesser angle indicates procurvatum.

Question 3195

Topic: 1. General Principles & Basic Science

Accurate preoperative planning for femoral osteotomies requires distinguishing between the anatomical and mechanical axes. In a normal lower extremity, what is the approximate angle formed between the anatomical axis and the mechanical axis of the femur (AMA)?

. 0 degrees
. 3 degrees
. 7 degrees
. 11 degrees
. 15 degrees

Correct Answer & Explanation

. 7 degrees

Explanation

The normal anatomic-mechanical angle (AMA) of the femur is approximately 7 degrees (range 5 to 9 degrees). This divergence is crucial for planning when referencing the anatomical axis to correct the mechanical axis.

Question 3196

Topic: 1. General Principles & Basic Science

When analyzing coronal plane alignment, the joint line congruency angle (JLCA) is evaluated to assess intra-articular deformity or ligamentous laxity. What is the normal physiological range for the JLCA?

. 0 to 2 degrees
. 3 to 5 degrees
. 6 to 8 degrees
. 9 to 11 degrees
. 12 to 14 degrees

Correct Answer & Explanation

. 0 to 2 degrees

Explanation

The Joint Line Congruency Angle (JLCA) is normally 0 to 2 degrees, representing a near-parallel relationship between the distal femoral and proximal tibial joint lines. Values outside this range suggest intra-articular deformity, cartilage loss, or collateral ligament laxity.

Question 3197

Topic: 1. General Principles & Basic Science

To prevent rotational errors from distorting coronal plane angular measurements during a full-length standing lower limb radiograph, Dror Paley emphasizes a specific patient positioning technique. What is the correct alignment standard?

. Feet positioned parallel and pointing strictly forward
. Patellae pointing strictly forward
. 15 degrees of internal rotation of the feet
. 15 degrees of external rotation of the feet
. Weight equally distributed with 30 degrees of knee flexion

Correct Answer & Explanation

. Patellae pointing strictly forward

Explanation

Accurate AP radiographs require positioning the patient with the patellae pointing strictly forward, rather than the feet. This nullifies the effect of femoral or tibial torsion, which would otherwise alter the apparent mechanical axis and joint orientation angles.

Question 3198

Topic: 1. General Principles & Basic Science

A severe multiapical diaphyseal deformity involves two distinct centers of rotation of angulation (CORAs). If the surgeon attempts to correct the entire deformity using only a single osteotomy, what is the most likely biomechanical consequence?

. Perfect anatomical alignment with no translation
. Secondary translation and/or residual joint line obliquity
. Spontaneous correction of the adjacent joint orientation
. Complete restoration of the mechanical axis without side effects
. Elimination of all limb length discrepancy

Correct Answer & Explanation

. Secondary translation and/or residual joint line obliquity

Explanation

Treating a multiapical deformity (multiple CORAs) with a single osteotomy forces the correction to act around an average axis. This inevitably results in secondary translation of the bone ends or residual obliquity of the adjacent joint lines.

Question 3199

Topic: 1. General Principles & Basic Science

The Taylor Spatial Frame (TSF) relies on a Stewart-Gough platform utilizing a hexapod system to simultaneously correct multiplanar deformities. How many adjustable struts are manipulated in this specific external fixator system?

. 3
. 4
. 5
. 6
. 8

Correct Answer & Explanation

. 6

Explanation

The Taylor Spatial Frame is a hexapod device, meaning it utilizes 6 adjustable telescopic struts connecting two rings. Modifying the lengths of these 6 struts allows for simultaneous correction of angulation, translation, and rotation in all six degrees of freedom.

Question 3200

Topic: 1. General Principles & Basic Science

According to Paley's principles of deformity correction, if an osteotomy is performed exactly at the center of rotation of angulation (CORA) and the axis of rotation is also placed at the CORA, what is the expected geometric outcome?

. Pure angulation with no translation, resulting in realignment of the mechanical axis
. Angulation and translation, resulting in realignment of the mechanical axis
. Pure angulation resulting in translation of the mechanical axis
. Translation only with no angulation
. Angulation with a residual mechanical axis deviation

Correct Answer & Explanation

. Pure angulation with no translation, resulting in realignment of the mechanical axis

Explanation

Paley's Osteotomy Rule 1 states that if the osteotomy and the hinge (axis of rotation) are both placed at the CORA, the deformity will correct with pure angulation and no translation.

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