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1. General Principles & Basic Science MCQs

Practice Set 157 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 3121

Topic: 1. General Principles & Basic Science

A 45-year-old male requires correction of a tibial diaphyseal deformity. The surgeon plans an osteotomy. According to Paley's osteotomy rules, if the osteotomy and the hinge are both placed exactly at the Center of Rotation of Angulation (CORA), what is the resultant geometric effect on the bone fragments?

. Pure angulation without translation
. Angulation with purposeful translation
. Pure translation without angulation
. Angulation with secondary deformity
. Length discrepancy only

Correct Answer & Explanation

. Pure angulation without translation

Explanation

Paley's Rule 1 states that when both the osteotomy and the hinge are placed at the CORA, the deformity corrects purely by angulation without any translation of the bone fragments. This aligns the anatomic and mechanical axes accurately.

Question 3122

Topic: 1. General Principles & Basic Science

A surgeon is correcting a distal femoral varus deformity but is unable to make the osteotomy cut exactly at the CORA due to poor soft tissue envelope. The osteotomy is made proximal to the CORA, but the hinge of the fixator is placed exactly at the CORA. What is the expected outcome of the deformity correction based on Paley's osteotomy rules?

. Pure angulation without translation
. Angular correction with translation of the bone ends resulting in a collinear mechanical axis
. Angular correction with a residual mechanical axis deviation
. Pure translation of the diaphysis
. Incomplete angular correction due to hinge mismatch

Correct Answer & Explanation

. Angular correction with translation of the bone ends resulting in a collinear mechanical axis

Explanation

Paley's Rule 2 dictates that if the hinge is at the CORA but the osteotomy is at a different level, angular correction will occur alongside translation of the bone ends. This translation correctly re-establishes a collinear mechanical axis.

Question 3123

Topic: 1. General Principles & Basic Science

When evaluating a full-length lower extremity radiograph for deformity correction, the surgeon maps out the mechanical and anatomic axes of the femur. Which of the following statements accurately describes the relationship between these two axes in a normal femur?

. They are parallel and separated by 2-3 cm
. The anatomic axis diverges laterally from the mechanical axis by 7 degrees on average
. The anatomic axis diverges medially from the mechanical axis by 7 degrees on average
. They are completely collinear from the hip center to the knee center
. The mechanical axis passes directly through the greater trochanter

Correct Answer & Explanation

. The anatomic axis diverges laterally from the mechanical axis by 7 degrees on average

Explanation

In a normal femur, the anatomic axis diverges laterally from the mechanical axis by approximately 7 degrees (normal range 5 to 7 degrees). The mechanical axis connects the center of the femoral head to the center of the knee.

Question 3124

Topic: 1. General Principles & Basic Science

A surgeon plans a medial opening wedge high tibial osteotomy (HTO) for a patient with varus gonarthrosis. The CORA is at the level of the joint line, but the osteotomy is performed in the proximal metaphysis. If the hinge is maintained at the CORA, which of the following is true regarding the bone cut?

. It follows Paley's Rule 1 and produces pure angulation
. It follows Paley's Rule 2 and creates an intentional translation to correct the mechanical axis
. It follows Paley's Rule 3 and causes an iatrogenic zig-zag deformity
. It requires an osteotomy distal to the tibial tubercle to be effective
. It will fail to alter the mechanical axis deviation

Correct Answer & Explanation

. It follows Paley's Rule 2 and creates an intentional translation to correct the mechanical axis

Explanation

This scenario applies Paley's Rule 2. The osteotomy is separate from the CORA (which is at the joint line), but by keeping the hinge axis at the CORA, angular correction is coupled with translation, correctly realigning the mechanical axis.

Question 3125

Topic: 1. General Principles & Basic Science

A 55-year-old male presents with medial compartment knee pain and a varus deformity. A standing full-length radiograph is obtained, as depicted in the initial state of the image below. The mechanical axis deviation (MAD) is measured to pass significantly medial to the center of the knee joint. The mechanical lateral distal femoral angle (mLDFA) is 88 degrees, and the medial proximal tibial angle (MPTA) is 80 degrees. The patient is a good candidate for a high tibial osteotomy (HTO). What is the primary goal of this realignment osteotomy?

. To increase the mLDFA to 90 degrees.
. To decrease the MPTA to 75 degrees.
. To shift the mechanical axis laterally, through the central or slightly lateral compartment of the knee.
. To correct the anatomical axis deviation.
. To achieve a neutral joint line obliquity.

Correct Answer & Explanation

. To shift the mechanical axis laterally, through the central or slightly lateral compartment of the knee.

Explanation

Correct Answer: CThe primary goal of a realignment osteotomy for a varus knee, such as a high tibial osteotomy (HTO), is to shift the mechanical axis laterally. In a varus knee, the mechanical axis passes medial to the center of the knee, overloading the medial compartment. By performing an HTO, the tibia is realigned to shift the weight-bearing axis laterally, typically aiming for the mechanical axis to pass through the central or slightly lateral compartment of the knee. This offloads the diseased medial compartment and transfers load to the healthier lateral compartment, thereby reducing pain and potentially slowing the progression of osteoarthritis.Option A is incorrect because increasing the mLDFA (normal 85-90 degrees) would correct a valgus deformity originating from the femur, not a varus deformity primarily addressed by HTO. Option B is incorrect because decreasing the MPTA (normal 85-90 degrees) would worsen a varus deformity or create a varus deformity if the MPTA is already normal. An HTO typically increases the MPTA to correct varus. Option D is incorrect because while the anatomical axis is affected, the primary goal of realignment osteotomy is to correct the mechanical axis deviation, which directly relates to load distribution across the joint. Option E is incorrect because while joint line obliquity can be affected, it is a secondary consideration; the primary goal is mechanical axis realignment. Maintaining a relatively neutral joint line is often desired, but it's not the overarching primary goal of the procedure itself.

Question 3126

Topic: 1. General Principles & Basic Science

A 48-year-old active patient presents with a symptomatic genu valgum deformity. Preoperative planning, as illustrated in the diagram below, involves identifying the Center of Rotation of Angulation (CORA) to precisely plan a distal femoral osteotomy (DFO). Which of the following statements accurately describes the significance of the CORA in this planning process?

. The CORA represents the point where the anatomical axis intersects the joint line.
. Placing the osteotomy at the CORA ensures correction of the angular deformity without creating translation.
. The CORA is always located at the apex of the deformity in the sagittal plane.
. The CORA dictates the amount of bone to be resected for a closing wedge osteotomy.
. The CORA is primarily used to determine the final mechanical axis deviation.

Correct Answer & Explanation

. Placing the osteotomy at the CORA ensures correction of the angular deformity without creating translation.

Explanation

Correct Answer: BThe Center of Rotation of Angulation (CORA) is a fundamental concept in deformity correction. It is defined as the intersection point of the proximal and distal anatomical axes of the deformed bone. When an osteotomy is performed precisely at the CORA, and the bone segments are rotated around this point, the angular deformity is corrected without introducing any translational deformity (i.e., shift of the bone segments relative to each other). This results in a 'pure' angular correction, which is often desirable for maintaining limb alignment and joint congruity.Option A is incorrect; the CORA is the intersection of the proximal and distal anatomical axes, not necessarily the joint line. Option C is incorrect; the CORA is identified in the plane of the deformity (e.g., frontal plane for varus/valgus), not necessarily the sagittal plane, and it is the apex of the angular deformity, not just 'at the apex'. Option D is incorrect; while the CORA helps determine the location of the osteotomy, the amount of bone to be resected (wedge size) is determined by the desired angular correction, not directly by the CORA itself. Option E is incorrect; the CORA is used to plan the osteotomy location for angular correction, which in turn affects the mechanical axis, but it does not directly determine the final mechanical axis deviation; rather, the desired final mechanical axis guides the amount of correction needed at the CORA.

Question 3127

Topic: 1. General Principles & Basic Science

A surgeon is planning a high tibial osteotomy for a patient with a varus knee deformity. The goal is to correct the varus and achieve a slight valgus overcorrection. The surgeon is considering either a medial opening wedge osteotomy or a lateral closing wedge osteotomy. Based on the principles of deformity correction and the images provided, which statement accurately describes a potential difference in outcome between these two techniques regarding joint line obliquity?

. A medial opening wedge osteotomy always decreases the joint line obliquity.
. A lateral closing wedge osteotomy always increases the joint line obliquity.
. A medial opening wedge osteotomy can elevate the medial joint line, potentially increasing joint line obliquity if not carefully planned.
. A lateral closing wedge osteotomy typically lowers the lateral joint line, always resulting in a more horizontal joint line.
. Both techniques have no significant impact on the joint line obliquity if the CORA is correctly identified.

Correct Answer & Explanation

. A medial opening wedge osteotomy can elevate the medial joint line, potentially increasing joint line obliquity if not carefully planned.

Explanation

Correct Answer: CThe imagech_53_fig_13ca8f.webpillustrates a varus deformity, which often presents with some degree of joint line obliquity. When performing a medial opening wedge high tibial osteotomy, the medial side of the tibia is opened, and a wedge is inserted. This effectively lengthens the medial side of the tibia relative to the lateral side. If the osteotomy is not perfectly parallel to the joint line or if the correction is significant, this can lead to an elevation of the medial joint line, potentially increasing the overall joint line obliquity (making the joint line more sloped). This is a known consideration with opening wedge HTOs, especially if the hinge is not precisely controlled or if the correction is large.Option A is incorrect; an opening wedge can increase or decrease obliquity depending on the hinge and amount of correction, but it does not always decrease it. Option B is incorrect; a lateral closing wedge osteotomy removes bone from the lateral side, which can lower the lateral joint line. This can also affect joint line obliquity, but it doesn't always increase it; it often aims to make it more horizontal. Option D is incorrect; while a lateral closing wedge lowers the lateral joint line, it doesn't always result in a more horizontal joint line; the final obliquity depends on the initial deformity and the precise execution of the osteotomy. Option E is incorrect; while identifying the CORA helps with angular correction without translation, both opening and closing wedge osteotomies, especially if performed away from the joint line or with specific hinge points, can influence joint line obliquity. The effect on joint line obliquity is a critical consideration in osteotomy planning.

Question 3128

Topic: 1. General Principles & Basic Science

A 62-year-old male presents with progressive right knee pain, worse with activity. Full-length weight-bearing radiographs reveal a mechanical axis that passes 15 mm medial to the center of the knee joint. The patient has a palpable medial compartment tenderness and early signs of medial compartment osteoarthritis. Which of the following best describes this patient's primary biomechanical malalignment and its immediate implication?

. A. Valgus deformity with a negative Mechanical Axis Deviation (MAD), leading to lateral compartment overload.
. B. Varus deformity with a positive Mechanical Axis Deviation (MAD), leading to medial compartment overload.
. C. Valgus deformity with a positive Mechanical Axis Deviation (MAD), leading to medial compartment overload.
. D. Varus deformity with a negative Mechanical Axis Deviation (MAD), leading to lateral compartment overload.
. E. Neutral alignment with a zero Mechanical Axis Deviation (MAD), indicating ligamentous laxity.

Correct Answer & Explanation

. B. Varus deformity with a positive Mechanical Axis Deviation (MAD), leading to medial compartment overload.

Explanation

Correct Answer: BThe case describes a mechanical axis passing 15 mm medial to the center of the knee joint. According to the teaching case, a varus deformity is characterized by the mechanical axis passing significantly medial to the knee center, resulting in a positive MAD. This pathologically overloads the medial compartment of the knee, which aligns with the patient's symptoms of medial compartment tenderness and osteoarthritis. The fundamental goal of a frontal plane osteotomy is to shift the mechanical axis back to its neutral position, reducing the MAD to zero.Option A is incorrect because a valgus deformity would have the mechanical axis passing lateral to the knee center, resulting in a negative MAD and lateral compartment overload. Option C incorrectly associates a valgus deformity with a positive MAD. Option D incorrectly associates a varus deformity with a negative MAD and lateral compartment overload. Option E is incorrect as a 15 mm deviation indicates significant malalignment, not neutral alignment, and MAD is a measure of alignment, not primarily ligamentous laxity (though laxity can influence joint line convergence).

Question 3129

Topic: Surgical Anatomy & Approaches
A 40-year-old patient requires a distal femoral osteotomy for a valgus deformity. The center of rotation of angulation (CORA) is identified within the epiphysis, making a direct osteotomy at this level technically challenging due to joint proximity and fixation concerns. The surgeon decides to perform the osteotomy more proximally in the metaphysis but ensures the angulation correction axis (ACA) is mathematically placed at the CORA. Referring to the provided image, which diagram set (i, ii, iii, or iv) best illustrates the expected outcome of this surgical approach, consistent with Paley's Rule Two?
. A. Diagram set (b), Roman numeral (i)
. B. Diagram set (b), Roman numeral (ii)
. C. Diagram set (b), Roman numeral (iii)
. D. Diagram set (b), Roman numeral (iv)
. E. Diagram set (c), Roman numeral (i)

Correct Answer & Explanation

. D. Diagram set (b), Roman numeral (iv)

Explanation

Paley's Rule Two states: 'When the ACA passes through the CORA, but the osteotomy is performed at a different level (either proximal or distal to the CORA), the mechanical axes will align perfectly, but the bone segments will translate.' The teaching case describes this as a common pragmatic approach when the CORA is in a difficult location. The image's 'Deformity Planning and Osteotomy Considerations' section for 'Opening Wedge Sequence' describes Rule 2 Variation (iv) as: 'Osteotomy line is distal to CORA, ACA is through the CORA. Result: 37° angular correction, no MAD, normal anatomic axis alignment of the distal tibia (though a cortical bump is present because of the level of osteotomy and obligatory translation), and normal ankle and knee joint orientation.' This perfectly matches the scenario described in the question, where the osteotomy is performed away from the CORA but the ACA is at the CORA, leading to correction with translation.

Question 3130

Topic: 1. General Principles & Basic Science

A surgeon performs a high tibial osteotomy for a varus deformity. During the procedure, the surgeon makes the osteotomy cut in the mid-diaphysis of the tibia, far from the identified CORA in the proximal metaphysis. The Angulation Correction Axis (ACA) is also established at the level of this mid-diaphyseal cut. Postoperatively, despite achieving what appears to be visual angular correction, the patient's Mechanical Axis Deviation (MAD) persists, and the mechanical axes of the proximal and distal segments are parallel but not collinear. Which of Paley's Osteotomy Rules was violated, leading to this outcome?

. A. Rule One: The Anatomic Ideal
. B. Rule Two: Pragmatic Correction with Obligatory Translation
. C. Rule Three: The Rule of Unintended Consequences
. D. The Rule of Joint Line Convergence
. E. The Rule of Mechanical Lateral Distal Femoral Angle

Correct Answer & Explanation

. C. Rule Three: The Rule of Unintended Consequences

Explanation

Correct Answer: CThe scenario describes a situation where both the osteotomy cut and the Angulation Correction Axis (ACA) are located at the same level, but this level is away from the true CORA. The teaching case explicitly states that this is Paley's Rule Three: 'When both the osteotomy cut and the ACA are located at the same level, but this level is away from the CORA, a new deformity is created.' The consequence is that 'the angular deformity (the "bend" in the bone) may visually appear corrected, but the mechanical axes of the proximal and distal segments will become parallel but not collinear. This introduces a massive, iatrogenic translation, and the Mechanical Axis Deviation (MAD) will persist, meaning the knee joint remains pathologically overloaded.' This perfectly matches the clinical outcome described in the question.Rule One describes perfect correction at the CORA with no translation. Rule Two describes correction with translation when the osteotomy is away from the CORA but the ACA is at the CORA. Options D and E are not among Paley's three fundamental osteotomy rules.

Question 3131

Topic: 1. General Principles & Basic Science
A 50-year-old patient with a severe 15° varus deformity of the proximal tibia has a CORA located 2 cm distal to the joint line. The surgeon plans an opening wedge high tibial osteotomy. Due to concerns about hardware placement and bone stock, the osteotomy cut is made 5 cm distal to the joint line, and the angulation correction axis (ACA) is established at the level of this cut. To achieve a neutral mechanical axis deviation (MAD) postoperatively, the surgeon must account for the geometry. Based on Paley's Rule Three, what is the most likely consequence and necessary adjustment?
. A. Pure angular correction with no translation, requiring exactly 15° of opening.
. B. Obligatory translation of the distal fragment, requiring exactly 15° of opening.
. C. Creation of a new deformity with persistent MAD, requiring an intentional overcorrection of the angular deformity.
. D. Spontaneous normalization of the MAD, regardless of the amount of opening.
. E. Limb shortening, requiring a bone graft to compensate.

Correct Answer & Explanation

. C. Creation of a new deformity with persistent MAD, requiring an intentional overcorrection of the angular deformity.

Explanation

This scenario describes a situation where both the osteotomy cut and the ACA are located at the same level, but this level is away from the true CORA (osteotomy at 5 cm distal to joint line, CORA at 2 cm distal to joint line). This is a direct application of Paley's Rule Three: 'When both the osteotomy cut and the ACA are located at the same level, but this level is away from the CORA, a new deformity is created.' The teaching case further explains that the angular deformity may visually appear corrected, but the mechanical axes of the proximal and distal segments will become parallel but not collinear. This introduces a massive, iatrogenic translation, and the MAD will persist. However, a master surgeon can use Rule Three intentionally by calculating the exact amount of angular overcorrection needed to force the translated mechanical axis back through the center of the knee.

Question 3132

Topic: 1. General Principles & Basic Science

According to Paley's rules of deformity correction, what is the expected result when the osteotomy and the hinge (axis of correction) are both placed precisely at the Center of Rotation of Angulation (CORA)?

. Pure translation without angulation
. Angulation combined with secondary translation
. Pure angulation without translation
. Axial lengthening without angular correction
. Pure multi-planar rotation

Correct Answer & Explanation

. Pure translation without angulation

Explanation

Paley's Rule 1 states that if the osteotomy and the axis of correction (hinge) are both placed at the CORA, the deformity corrects with pure angulation and the mechanical axes become perfectly collinear without translation.

Question 3133

Topic: 1. General Principles & Basic Science

A 45-year-old male undergoes a medial opening-wedge high tibial osteotomy (HTO) proximal to the tibial tubercle for medial compartment osteoarthritis. Which of the following is an expected consequence regarding patellar height and tibial slope if standard techniques are used?

. Patella alta and decreased posterior slope
. Patella baja and decreased posterior slope
. Patella alta and increased posterior slope
. Relative patella baja and increased posterior tibial slope
. No change in patellar height or posterior slope

Correct Answer & Explanation

. Relative patella baja and increased posterior tibial slope

Explanation

Because the osteotomy is proximal to the tubercle, the joint line is elevated relative to the tubercle, causing a relative patella baja. Additionally, standard medial opening-wedge HTO tends to increase the posterior tibial slope because the anterior aspect of the proximal tibia opens more easily than the wider posterior aspect.

Question 3134

Topic: 1. General Principles & Basic Science

Based on the principles of deformity correction (Paley's Rule 2), if the axis of correction (hinge) is placed at the CORA, but the osteotomy is performed at a different level outside the CORA, what is the resulting geometric correction?

. Pure angulation with no translation
. Pure translation with no angulation
. A secondary deformity that cannot be corrected
. Angulation resulting in fully collinear axes, achieved by secondary translation at the osteotomy site
. Pure axial shortening

Correct Answer & Explanation

. Angulation resulting in fully collinear axes, achieved by secondary translation at the osteotomy site

Explanation

Paley's Rule 2 states that if the hinge is at the CORA but the osteotomy is away from the CORA, the mechanical axes will fully realign (collinear), but there will be an obligatory translation of the bone fragments at the osteotomy site.

Question 3135

Topic: 1. General Principles & Basic Science

A 50-year-old female presents with symptomatic genu valgum and lateral compartment knee arthritis. Her Mechanical Lateral Distal Femoral Angle (mLDFA) is 80 degrees, and her Medial Proximal Tibial Angle (MPTA) is 88 degrees. She is planned for a medial closing-wedge distal femoral osteotomy. What is the primary anatomical advantage of this approach compared to a lateral opening-wedge osteotomy?

. Increased limb lengthening
. Faster union due to broader cancellous bone contact and compression
. Complete avoidance of the femoral artery in the adductor canal
. Decreased risk of peroneal nerve injury
. It requires a much smaller surgical incision

Correct Answer & Explanation

. Faster union due to broader cancellous bone contact and compression

Explanation

A medial closing-wedge osteotomy provides bone-on-bone compression over a broad surface area, allowing for faster healing and greater inherent stability. It does, however, result in slight limb shortening compared to an opening-wedge technique.

Question 3136

Topic: Biomechanics & Biomaterials

Utilizing the principles illustrated in multi-planar deformity correction

, the Taylor Spatial Frame (TSF) utilizes a specific kinematic concept to correct complex deformities simultaneously. Which of the following correctly describes this mechanism?

. Single-axis rotational hinges
. Orthogonal planar adjustments requiring sequential manual correction
. Stewart-Gough platform kinematics (six degrees of freedom)
. Direct skeletal traction without a virtual hinge
. Dynamic compression using pure axial loading

Correct Answer & Explanation

. Stewart-Gough platform kinematics (six degrees of freedom)

Explanation

Hexapod external fixators, such as the Taylor Spatial Frame, are based on the Stewart-Gough platform mechanism. This allows for simultaneous multi-planar correction in all six degrees of freedom using a virtual hinge.

Question 3137

Topic: 1. General Principles & Basic Science

A surgeon plans an osteotomy for a diaphyseal tibial deformity. The osteotomy and the hinge (axis of correction) are both placed completely away from the true Center of Rotation of Angulation (CORA). According to Paley's Rule 3, what will be the final alignment of the mechanical axes?

. The axes will be fully collinear
. The axes will be parallel but translated, creating a secondary translation deformity
. Pure angulation will occur at the true CORA without translation
. The limb will significantly lengthen without angular correction
. The axes will remain angulated and uncorrected

Correct Answer & Explanation

. The axes will be parallel but translated, creating a secondary translation deformity

Explanation

Paley's Rule 3 states that if the hinge and the osteotomy are both located away from the true CORA, angular correction is possible, but it will result in mechanical axes that are parallel rather than collinear, effectively inducing a translation deformity.

Question 3138

Topic: 1. General Principles & Basic Science

When planning a deformity correction, the surgeon must mathematically account for the difference between the anatomic and mechanical axes. In a normal femur, the anatomic axis diverges from the mechanical axis by approximately how many degrees?

. 1 to 2 degrees
. 5 to 7 degrees
. 9 to 11 degrees
. 13 to 15 degrees
. They are entirely collinear

Correct Answer & Explanation

. 5 to 7 degrees

Explanation

The normal femoral mechanical axis is a line from the center of the femoral head to the intercondylar notch. The anatomic axis bisects the diaphysis. The angle between these two axes is typically 5 to 7 degrees of valgus.

Question 3139

Topic: 1. General Principles & Basic Science

According to Paley's osteotomy rules, if the osteotomy and the hinge are both located at the CORA (Center of Rotation of Angulation), what is the resulting geometric effect?

. Pure angulation without translation
. Angulation with translation
. Pure translation
. Shortening
. Lengthening

Correct Answer & Explanation

. Pure angulation without translation

Explanation

Paley's Osteotomy Rule 1 states that when the osteotomy and the hinge (axis of correction) are both located at the CORA, the deformity corrects with pure angulation and no translation.

Question 3140

Topic: 1. General Principles & Basic Science

A surgeon plans a corrective osteotomy for a diaphyseal deformity. The osteotomy is performed at a level different from the CORA, but the hinge is placed exactly on the bisector line of the CORA. What is the expected outcome of this correction?

. Pure angulation
. Angulation with translation
. Pure translation without angulation
. Angulation with a secondary deformity
. Complete failure of correction

Correct Answer & Explanation

. Angulation with translation

Explanation

Paley's Osteotomy Rule 2 dictates that if the hinge is on the CORA bisector line but the osteotomy is at a different level, the correction will result in angulation combined with translation. This allows the mechanical axis to realign correctly.

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