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1. General Principles & Basic Science MCQs

Practice Set 153 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 3041

Topic: 1. General Principles & Basic Science

A 60-year-old female presents with severe medial compartment osteoarthritis of the left knee. A standing, weight-bearing long-leg AP radiograph reveals a mechanical axis that passes 15 mm medial to the exact center of the knee joint. Based on Paley's principles, what does this finding indicate?

. A physiological valgus alignment, requiring no intervention.
. A normal mechanical axis deviation, consistent with a healthy knee.
. A pathological varus deformity, overloading the medial compartment.
. A pathological valgus deformity, overloading the lateral compartment.
. An intra-articular deformity, primarily due to ligamentous laxity.

Correct Answer & Explanation

. A pathological varus deformity, overloading the medial compartment.

Explanation

Correct Answer: CThe Mechanical Axis Deviation (MAD) is the perpendicular distance from the center of the knee joint to the mechanical axis line. A normal MAD is defined as the mechanical axis passing 1 to 8 mm medial to the exact center of the knee. If the mechanical axis passesmedialto this normal physiological zone (greater than 8 mm medial), it indicates avarus deformity (Genu Varum). A MAD of 15 mm medial is significantly outside the normal range and signifies a pathological varus deformity, which pathologically overloads the medial compartment of the knee, leading to accelerated cartilage wear and osteoarthritis. Options A and B are incorrect as 15 mm medial is outside the normal range. Option D is incorrect because a valgus deformity would have the mechanical axis passing lateral to the knee center. Option E is a possibility for contributing factors but the MAD itself describes the overall limb alignment, not specifically the intra-articular component.

Question 3042

Topic: 1. General Principles & Basic Science

A surgeon is planning a corrective osteotomy for a femoral deformity. The image below illustrates the relationship between the anatomic and mechanical axes of the femur.

Based on this diagram and Paley's principles, which statement accurately describes the implications of using either anatomic or mechanical axis planning for femoral deformities?

. The CORA for a distal femoral deformity will be significantly different between the two planning methods.
. The anatomic axis is always parallel to the mechanical axis throughout the femur.
. For a proximal femoral deformity (e.g., subtrochanteric), the mechanical and anatomic CORAs will be far apart.
. Anatomic axis planning is exclusively used for periarticular deformities, while mechanical axis planning is for diaphyseal.
. The bisector line of the deformity will be vastly different depending on the planning method chosen.

Correct Answer & Explanation

. For a proximal femoral deformity (e.g., subtrochanteric), the mechanical and anatomic CORAs will be far apart.

Explanation

Correct Answer: CThe provided image and the text explain that the anatomic and mechanical axes of the femur are not parallel; they converge distally and diverge significantly proximally. This divergence has a direct impact on the Center of Rotation of Angulation (CORA) location. The text states: 'When the deformity is in the subtrochanteric region, the mechanical CORA (based on a line to the femoral head) and the anatomic CORA (based on the shaft) are far apart.' This is visually supported by the diagram where the lines are most divergent proximally. Option A is incorrect because the text states that for distal femoral deformities, the mechanical and anatomic CORAs are very close. Option B is incorrect as the image clearly shows the axes are not parallel. Option D is incorrect; anatomic axis planning is practical for diaphyseal deformities (especially with IM nailing), and mechanical axis planning is gold standard for periarticular deformities. Option E is incorrect; the text explicitly states that 'the bisector line of the deformity (the transverse line that splits the angle of deformity perfectly in half) is nearly identical for both methods,' defining the true level of the deformity regardless of the planning method.

Question 3043

Topic: Biology, Genetics & Bone Healing

A 12-year-old patient with a history of rickets presents with a complex femoral deformity. A long-leg radiograph is obtained and the surgeon performs anatomic axis planning, identifying the axis lines as shown in Diagram 'd' of the image below.

Based on this finding, what is the most appropriate surgical strategy for correcting this deformity?

. A single osteotomy placed at CORA1, correcting the largest angle.
. A single osteotomy placed at the bisector line of the combined deformity.
. Multiple osteotomies, with one at each identified CORA (CORA1 and CORA2).
. A focal dome osteotomy to achieve a parallel shift of the mechanical axis.
. Correction using Paley's Rule One, placing the osteotomy and hinge at CORA1.

Correct Answer & Explanation

. Multiple osteotomies, with one at each identified CORA (CORA1 and CORA2).

Explanation

Correct Answer: CDiagram 'd' in the image clearly illustrates amultiapical deformity, characterized by more than one bend in the bone, resulting in multiple axis lines that do not intersect at a single point, thus creating two or more Centers of Rotation of Angulation (CORA1, CORA2). The text explicitly states: 'Attempting to correct a multiapical deformity with a single osteotomy is a catastrophic biomechanical error. It will correct the angulation at one localized level but will inevitably induce a secondary translation and malalignment, failing to restore the overall mechanical axis of the limb. Multiapical deformities strictly require multiple osteotomies, strategically planned for each individual CORA.' Therefore, options A, B, D, and E, which suggest a single osteotomy or a method not suitable for multiapical deformities, are incorrect.

Question 3044

Topic: 1. General Principles & Basic Science

A 48-year-old patient has a proximal tibial varus deformity with a CORA located in the highly vascularized proximal tibial metaphysis, an ideal location for an osteotomy. The surgeon plans to perform a high tibial osteotomy. To achieve the most biomechanically stable correction with maximal bone-to-bone contact and no translation, which of Paley's osteotomy rules should be applied?

. Osteotomy Rule One: Osteotomy and hinge placed exactly at the CORA.
. Osteotomy Rule Two: Osteotomy placed away from the CORA, hinge on the bisector line.
. Osteotomy Rule Three: Osteotomy and hinge placed off the CORA and bisector line.
. A focal dome osteotomy, which inherently causes translation.
. A single osteotomy for a multiapical deformity.

Correct Answer & Explanation

. Osteotomy Rule One: Osteotomy and hinge placed exactly at the CORA.

Explanation

Correct Answer: APaley's Osteotomy Rule One is described as the 'ideal correction.' It states: 'The osteotomy line and the hinge of rotation are both placed exactly at the CORA.' The result of this rule is that 'The deformity is corrected by pure angulation. There is absolutely no translation (shifting) of the bone fragments.' This rule maximizes bone-to-bone contact and biomechanical stability, making it the primary goal when the CORA is in a surgically accessible area with good healing potential, such as the proximal tibial metaphysis. Options B and C describe rules that involve translation or parallel shifts. Option D is a specific type of osteotomy that causes translation. Option E is incorrect as the scenario describes a uni-apical deformity (implied by a single CORA).

Question 3045

Topic: 1. General Principles & Basic Science

A 35-year-old patient requires correction of a distal femoral valgus deformity. The CORA is located in the distal femoral diaphysis, an area with poor healing potential and dense bone. To optimize healing and surgical access, the surgeon decides to perform the osteotomy in the distal femoral metaphysis, away from the CORA. However, the hinge of rotation is meticulously placed on the bisector line. Which of Paley's osteotomy rules is being applied, and what is the expected outcome?

. Rule One; pure angulation with no translation.
. Rule Two; angulation combined with necessary translation.
. Rule Three; a parallel shift of the mechanical axis.
. Rule One; a parallel shift of the mechanical axis.
. Rule Three; pure angulation with no translation.

Correct Answer & Explanation

. Rule Two; angulation combined with necessary translation.

Explanation

Correct Answer: BThis scenario perfectly describes Paley's Osteotomy Rule Two, known as the 'workhorse correction.' This rule states: 'The osteotomy line is placed at a different level from the CORA, but the hinge of rotation is placed on the bisector line.' The result is that 'The deformity is corrected by a necessary combination of angulation and translation.' This rule is commonly used to move the actual bone cut to a more favorable location (e.g., metaphysis) while still achieving perfect mechanical axis realignment, accepting the resulting fragment translation. Option A describes Rule One. Option C describes Rule Three. Options D and E incorrectly combine rules or outcomes.

Question 3046

Topic: Biomechanics & Biomaterials

Based on the case, a surgeon is planning a complex femoral deformity correction using the principles pioneered by Dr. Dror Paley. This method emphasizes a meticulous, geometric approach to restore normal lower extremity alignment and biomechanics.

. Primarily focusing on cosmetic limb length equality.
. Straightening the bone regardless of joint orientation.
. Restoring the mechanical axis of the limb while preserving joint parallelism.
. Achieving maximum bone union rates through aggressive fixation.
. Correcting only the most obvious angular deformity.

Correct Answer & Explanation

. Restoring the mechanical axis of the limb while preserving joint parallelism.

Explanation

Correct Answer: CThe fundamental principle guiding Dr. Paley's geometric approach to limb deformity correction is the restoration of the mechanical axis of the limb, ensuring that it passes through the center of the major joints (hip, knee, ankle) while simultaneously preserving the parallelism of the joint lines. This approach aims to optimize load bearing and prevent secondary osteoarthritis. Option A is incorrect as cosmetic limb length equality is a secondary goal to functional alignment. Option B is incorrect because simply straightening the bone without considering joint orientation can lead to malalignment and joint dysfunction. Option D is a general surgical goal but not the defining principle of deformity correction. Option E is incorrect as a comprehensive approach addresses all components of the deformity, not just the most obvious.

Question 3047

Topic: 1. General Principles & Basic Science

A 30-year-old patient requires frontal plane femoral deformity correction. The surgeon is reviewing the full-length standing radiograph to identify the relationship between the femoral anatomic and mechanical axes, a key concept highlighted in the case.

. 0-1 degrees
. 2-3 degrees
. 5-7 degrees
. 10-12 degrees
. 15-18 degrees

Correct Answer & Explanation

. 5-7 degrees

Explanation

Correct Answer: CThe case mentions that, unlike the tibia, the femur possesses a natural valgus bow, and its anatomic axis diverges from the mechanical axis. This divergence is approximately 5-7 degrees in the frontal plane. The mechanical axis of the femur runs from the center of the femoral head to the center of the knee, while the anatomic axis follows the center of the medullary canal. This natural valgus angulation is crucial for understanding and correcting femoral deformities. Options A, B, D, and E represent incorrect ranges for this normal anatomical divergence.

Question 3048

Topic: 1. General Principles & Basic Science

A 40-year-old patient has a distal femoral valgus deformity (genu valgum) with a CORA identified just proximal to the knee joint. An opening wedge osteotomy is planned at the CORA to correct the deformity.

. Medial opening wedge, to increase the valgus angle.
. Lateral opening wedge, to increase the varus angle.
. Medial opening wedge, to decrease the valgus angle.
. Lateral opening wedge, to decrease the valgus angle.
. Anterior opening wedge, to correct sagittal plane deformity.

Correct Answer & Explanation

. Lateral opening wedge, to decrease the valgus angle.

Explanation

Correct Answer: DA distal femoral valgus deformity means the distal segment of the femur is angled excessively laterally, resulting in genu valgum. To correct this, the distal segment needs to be shifted medially (i.e., brought into more varus alignment). An opening wedge osteotomy on the lateral side of the femur will achieve this. By opening a wedge laterally, the distal fragment is pushed medially, thereby decreasing the overall valgus angle and restoring the mechanical axis. Options A and B would worsen the valgus or create an excessive varus. Option C is incorrect as a medial opening wedge would increase valgus. Option E addresses a different plane of deformity.

Question 3049

Topic: 1. General Principles & Basic Science

Following a complex total femoral deformity correction using the Paley method, the surgeon reviews the post-operative full-length radiograph to confirm the restoration of the mechanical axis of the limb.

. Through the medial compartment.
. Through the lateral compartment.
. Through the center of the knee joint.
. Anterior to the knee joint.
. Posterior to the knee joint.

Correct Answer & Explanation

. Through the center of the knee joint.

Explanation

Correct Answer: CThe ultimate goal of frontal plane lower extremity deformity correction, as emphasized by the Paley method, is to restore the mechanical axis of the limb so that it passes through the center of the knee joint. This ensures optimal load distribution across the articular cartilage of both the medial and lateral compartments, minimizing stress and preventing the progression of osteoarthritis. Deviations from the center (e.g., through the medial or lateral compartment) indicate residual varus or valgus malalignment, respectively, which can lead to uneven loading and accelerated joint degeneration. Options D and E refer to sagittal plane alignment, not frontal plane.

Question 3050

Topic: 1. General Principles & Basic Science

While the case primarily focuses on frontal plane correction, a patient presents with a complex femoral deformity involving both frontal and sagittal plane angulation, as well as rotational malalignment. The surgeon needs to comprehensively analyze this multi-planar deformity.

. Only standard AP and lateral knee views.
. Bilateral hip MRI for soft tissue assessment.
. Full-length lateral radiograph and CT scan with rotational profiles.
. Bone scan to assess metabolic activity.
. Ultrasound of the quadriceps tendon.

Correct Answer & Explanation

. Full-length lateral radiograph and CT scan with rotational profiles.

Explanation

Correct Answer: CFor a comprehensive analysis of a multi-planar femoral deformity, additional imaging modalities beyond the full-length AP radiograph are essential. A full-length lateral radiograph is crucial for assessing sagittal plane alignment (e.g., procurvatum or recurvatum deformities) and identifying sagittal CORAs. A CT scan with rotational profiles (e.g., measuring femoral anteversion/retroversion relative to the posterior condylar axis) is indispensable for accurately quantifying rotational deformities. Options A, B, D, and E are insufficient for a complete multi-planar assessment. Standard knee views are too limited, MRI is primarily for soft tissue, bone scans for metabolic activity, and ultrasound for specific tendon issues, none of which provide the necessary bony alignment and rotational data.

Question 3051

Topic: 1. General Principles & Basic Science

A 25-year-old patient undergoes a full-length standing AP radiograph of the lower extremity for evaluation of genu valgum. During the planning phase, the surgeon measures the angle between the femoral anatomic axis and the femoral mechanical axis. Based on the provided case material, what is the normal average value for this specific angle, and what is its designation?

. 88 degrees, Mechanical Lateral Distal Femoral Angle (mLDFA)
. 87 degrees, Medial Proximal Tibial Angle (MPTA)
. 7 degrees, Anatomic-Mechanical Angle (AMA)
. 90 degrees, Lateral Proximal Femoral Angle (LPFA)
. 81 degrees, Anatomic Lateral Distal Femoral Angle (aLDFA)

Correct Answer & Explanation

. 7 degrees, Anatomic-Mechanical Angle (AMA)

Explanation

Correct Answer: CThe case defines the Anatomic-Mechanical Angle (AMA) as 'the intrinsic angle between the femur's anatomic and mechanical axes' and states its normal average value is '7° (Range: 5-9°)'. This angle accounts for the offset of the femoral head and neck, causing the femoral anatomic axis to be angled approximately 7 degrees valgus relative to its mechanical axis.Option A is incorrectbecause 88 degrees is the normal mLDFA, which defines the relationship of the knee joint to the femoral mechanical axis, not the angle between the two femoral axes themselves.Option B is incorrectbecause 87 degrees is the normal MPTA, which relates to the tibia, not the femur.Option D is incorrectbecause 90 degrees is the normal LPFA, which defines the relationship of the hip joint to the femoral mechanical axis.Option E is incorrectbecause 81 degrees is the normal aLDFA, which defines the relationship of the knee joint to the femoral anatomic axis.

Question 3052

Topic: 1. General Principles & Basic Science

A 60-year-old female presents with severe medial compartment osteoarthritis of the right knee. A full-length standing AP radiograph reveals that the mechanical axis of the lower extremity passes 15mm medial to the center of the knee joint. Based on the Paley method's interpretation of Mechanical Axis Deviation (MAD), what does this finding indicate?

. A valgus deformity with overloading of the lateral compartment.
. A varus deformity with overloading of the medial compartment.
. A normal physiological alignment, requiring no intervention.
. A translational deformity requiring a biapical osteotomy.
. An isolated tibial deformity, as the MAD is measured at the knee.

Correct Answer & Explanation

. A varus deformity with overloading of the medial compartment.

Explanation

Correct Answer: BThe case states, 'Medial MAD: The axis passes medial to the knee center. This indicates avarusdeformity, overloading the medial compartment.' A MAD of 15mm medial to the knee center clearly falls into this category, indicating a significant varus deformity and explaining the medial compartment osteoarthritis.Option A is incorrectbecause a valgus deformity would present with the mechanical axis passing lateral to the knee center (Lateral MAD).Option C is incorrectbecause while a slight medial MAD (0 to 8mm) can be physiological, 15mm medial is clearly outside the normal range and indicates a significant deformity.Option D is incorrectbecause while a translational deformity might exist, MAD itself only quantifies the overall effect of the deformity, not its specific type (uniapical vs. multiapical/translational). Further angle analysis is needed for that.Option E is incorrectbecause MAD quantifies the overall limb malalignment, which can originate from the femur, tibia, or both. It does not isolate the deformity to the tibia.

Question 3053

Topic: Biology, Genetics & Bone Healing

A 70-year-old patient with a history of childhood rickets presents with severe genu varum. A full-length standing AP radiograph is obtained, as shown below. The surgeon notes a significant medial mechanical axis deviation. Based on the principles of the Paley method, what is the most appropriate initial step to determine the *source* of this deformity?

. Immediately plan a distal femoral osteotomy at the level of the knee joint.
. Measure the Mechanical Axis Deviation (MAD) and proceed directly to surgical correction.
. Analyze the joint orientation angles (e.g., mLDFA, MPTA) and compare them to normative values.
. Perform a CT scan to assess for rotational deformity.
. Prescribe physical therapy to improve knee alignment.

Correct Answer & Explanation

. Analyze the joint orientation angles (e.g., mLDFA, MPTA) and compare them to normative values.

Explanation

Correct Answer: CThe case states, 'The MAD tells the surgeonthata deformity exists and quantifies its overall effect on the limb's weight-bearing status, but it does not tell youwherethe deformity originates. To pinpoint the anatomic source (femur vs. tibia vs. joint line), you must analyze the joint orientation angles.' Therefore, measuring angles like mLDFA and MPTA is the crucial next step after identifying the MAD, to localize the deformity to the femur, tibia, or both.Option A is incorrectbecause planning an osteotomy without localizing the deformity (femoral vs. tibial) could lead to iatrogenic malalignment or an incomplete correction.Option B is incorrectbecause MAD only quantifies the overall deformity; it doesn't provide the necessary information for precise surgical planning regarding the location of the osteotomy.Option D is incorrectbecause while rotational deformity is important, the initial focus for frontal plane malalignment (as indicated by genu varum and MAD) is on frontal plane angles. A CT scan for rotation would typically follow initial frontal and sagittal plane analysis.Option E is incorrectbecause physical therapy alone cannot correct a structural bony deformity causing severe genu varum and medial compartment osteoarthritis.

Question 3054

Topic: 1. General Principles & Basic Science

A 40-year-old patient presents with a complex femoral deformity, as seen in the full-length standing AP radiograph. During the Paley planning, the surgeon draws the Proximal Mechanical Axis (PMA) and the Distal Mechanical Axis (DMA). Instead of a single intersection, the PMA and DMA are found to be parallel, but offset from each other. What does this specific finding indicate, and how does it influence surgical planning?

. A uniapical angular deformity, requiring a simple closing wedge osteotomy at the CORA.
. A translational deformity without significant angular malalignment, requiring a translation-correcting osteotomy.
. A multiapical angular deformity, necessitating multiple osteotomies at different CORAs.
. A rotational deformity, best addressed with a derotational osteotomy at the mid-diaphysis.
. A normal alignment, indicating no surgical intervention is required.

Correct Answer & Explanation

. A translational deformity without significant angular malalignment, requiring a translation-correcting osteotomy.

Explanation

Correct Answer: BWhen the Proximal Mechanical Axis (PMA) and Distal Mechanical Axis (DMA) are parallel but offset, it indicates a pure translational deformity without an angular component. In such a scenario, there is no single CORA (as parallel lines do not intersect). The surgical correction would involve an osteotomy designed to translate the bone segments to bring the axes back into alignment, often requiring a specific translation-correcting osteotomy technique.Option A is incorrectbecause a uniapical angular deformity would present with a single, distinct CORA (intersection point), not parallel offset axes.Option C is incorrectbecause a multiapical angular deformity would involve multiple CORAs, meaning multiple intersection points, not parallel axes.Option D is incorrectbecause the Paley method with PMA and DMA primarily addresses frontal plane angular and translational deformities. Rotational deformities are assessed and corrected using different radiographic views and techniques (e.g., CT scan for torsion).Option E is incorrectbecause parallel but offset mechanical axes clearly indicate a deformity (translational MAD), requiring intervention if symptomatic.

Question 3055

Topic: 1. General Principles & Basic Science

A 28-year-old patient is undergoing preoperative planning for a distal femoral osteotomy to correct a varus deformity. The surgeon has measured the Mechanical Lateral Distal Femoral Angle (mLDFA) as 75 degrees. The goal is to restore the mLDFA to its normal average value of 88 degrees. If the surgeon plans a closing wedge osteotomy, what is the required magnitude of correction, and what would be the expected Anatomic Lateral Distal Femoral Angle (aLDFA) post-correction?

. 13 degrees of valgus correction; aLDFA would be 81 degrees.
. 13 degrees of varus correction; aLDFA would be 95 degrees.
. 7 degrees of valgus correction; aLDFA would be 75 degrees.
. 10 degrees of varus correction; aLDFA would be 88 degrees.
. 13 degrees of valgus correction; aLDFA would be 75 degrees.

Correct Answer & Explanation

. 13 degrees of valgus correction; aLDFA would be 81 degrees.

Explanation

Correct Answer: AThe current mLDFA is 75 degrees, and the target normal mLDFA is 88 degrees. To correct from 75 degrees (varus) to 88 degrees (normal), a valgus correction is needed. The magnitude of correction is 88 - 75 = 13 degrees of valgus correction.The case states that the normal aLDFA is 81 degrees and that 'aLDFA = mLDFA - 7°'. Therefore, after correcting the mLDFA to 88 degrees, the new aLDFA would be 88 - 7 = 81 degrees. This aligns with the normal average aLDFA.Option B is incorrectbecause 13 degrees of varus correction would worsen the varus deformity, and the calculated aLDFA is incorrect.Option C is incorrectbecause 7 degrees of valgus correction is insufficient (75 + 7 = 82 degrees mLDFA, still varus), and the aLDFA calculation is incorrect.Option D is incorrectbecause 10 degrees of varus correction is incorrect, and the aLDFA calculation is incorrect.Option E is incorrectbecause while 13 degrees of valgus correction is correct, the expected aLDFA post-correction would be 81 degrees, not 75 degrees.

Question 3056

Topic: 1. General Principles & Basic Science

A surgeon plans an osteotomy to correct a diaphyseal angular deformity. According to Paley's Osteotomy Rule 1, if the osteotomy and the hinge are both placed exactly at the Center of Rotation of Angulation (CORA), what is the anatomic result?

. Pure angulation with no translation
. Angulation with intended translation
. Pure translation with no angulation
. Angulation with paradoxical translation
. Shortening and translation

Correct Answer & Explanation

. Pure angulation with no translation

Explanation

Paley's Osteotomy Rule 1 states that when both the osteotomy and the hinge are placed at the CORA, the deformity corrects with pure angulation and no translation. The bone ends remain fully apposed.

Question 3057

Topic: 1. General Principles & Basic Science

According to Paley's Osteotomy Rule 2, if the osteotomy is made at a level different from the CORA, but the hinge is placed on the transverse bisector line of the CORA, what will be the resulting bone alignment?

. Correction of angulation without translation
. Correction of angulation with expected translation at the osteotomy site
. Creation of a secondary translation deformity preventing axis realignment
. Pure translation without angular correction
. Paradoxical joint line tilt

Correct Answer & Explanation

. Correction of angulation with expected translation at the osteotomy site

Explanation

Under Paley's Rule 2, placing the osteotomy away from the CORA but keeping the hinge on the bisector line results in angulation and translation at the osteotomy site. However, the overall mechanical axis is completely restored.

Question 3058

Topic: 1. General Principles & Basic Science

A patient undergoes a distal femoral osteotomy for a valgus deformity. Postoperatively, the mechanical axis remains deviated despite full angular correction. According to Paley's principles, this outcome most likely represents a violation of which rule?

. Rule 1 (Hinge and osteotomy at CORA)
. Rule 2 (Hinge on bisector, osteotomy separate)
. Rule 3 (Hinge placed off the bisector line)
. The Tension-Stress principle
. Joint Line Convergence Angle principle

Correct Answer & Explanation

. Rule 3 (Hinge placed off the bisector line)

Explanation

Paley's Rule 3 occurs when the hinge is placed off the bisector line of the CORA, regardless of the osteotomy level. This corrects angulation but induces a new translation deformity, failing to restore the overall mechanical axis.

Question 3059

Topic: 1. General Principles & Basic Science

During deformity planning, a surgeon notes an abnormally large Joint Line Convergence Angle (JLCA) of 7 degrees on a standing AP radiograph. Which of the following is the most likely cause of this abnormal JLCA?

. Extra-articular femoral diaphyseal deformity
. Extra-articular tibial diaphyseal deformity
. Collateral ligament laxity or intra-articular cartilage loss
. Normal variant in an athletic patient
. Measurement error due to internal rotation

Correct Answer & Explanation

. Collateral ligament laxity or intra-articular cartilage loss

Explanation

The JLCA normally ranges from 0 to 2 degrees. Values greater than 2 degrees typically indicate intra-articular pathology, such as asymmetric cartilage wear or collateral ligament laxity.

Question 3060

Topic: 1. General Principles & Basic Science

A surgeon chooses a focal dome osteotomy to correct a tibial deformity. To achieve pure angular correction without translation, where must the center of the dome cut and the axis of the hinge be located according to Paley's principles?

. At the medial cortex of the tibia
. At the anatomic axis of the tibia
. At the Center of Rotation of Angulation (CORA)
. At the mechanical axis of the tibia
. At the level of the desired leg lengthening

Correct Answer & Explanation

. At the Center of Rotation of Angulation (CORA)

Explanation

For a dome osteotomy to correct angulation without inducing translation, both the center of the osteotomy arc and the hinge axis must coincide with the CORA. This represents a clinical application of Paley's Rule 1.

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