Menu

1. General Principles & Basic Science MCQs

Practice Set 152 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 3021

Topic: 1. General Principles & Basic Science

When planning a sagittal plane deformity correction for a patient with a tibial procurvatum deformity, establishing the correct anatomical axis is critical. What are the normal reference values for the posterior proximal tibial angle (PPTA) and the anterior distal tibial angle (ADTA) in the sagittal plane?

. PPTA 90 degrees, ADTA 90 degrees
. PPTA 81 degrees, ADTA 80 degrees
. PPTA 87 degrees, ADTA 87 degrees
. PPTA 95 degrees, ADTA 81 degrees
. PPTA 80 degrees, ADTA 90 degrees

Correct Answer & Explanation

. PPTA 81 degrees, ADTA 80 degrees

Explanation

In the sagittal plane, the normal posterior proximal tibial angle (PPTA) is approximately 81 degrees (reflecting normal posterior slope), and the anterior distal tibial angle (ADTA) is approximately 80 degrees. These are essential for identifying the sagittal CORA.

Question 3022

Topic: Biology, Genetics & Bone Healing

A patient with hypophosphatemic rickets presents with a severe bow-leg deformity consisting of both a diaphyseal bow and a metaphyseal varus deformity in the same femur. Which of the following principles must be applied to accurately identify the true CORAs in this multi-apical deformity?

. Draw a single mechanical axis from the femoral head to the condyles and bisect it.
. Divide the bone into individual segments, drawing separate anatomical axes for each segment to find their intersections.
. Use the contralateral unaffected leg as an exact template to map a single osteotomy site.
. Place the ACA exactly halfway between the metaphyseal and diaphyseal deformities.
. Perform a single closing wedge osteotomy at the site of maximum bowing.

Correct Answer & Explanation

. Divide the bone into individual segments, drawing separate anatomical axes for each segment to find their intersections.

Explanation

In multi-apical deformities, the bone must be divided into three or more segments. Anatomical or mechanical axis lines are drawn for each individual segment, and their intersection points dictate the multiple separate CORAs required for correction.

Question 3023

Topic: 1. General Principles & Basic Science
A 40-year-old patient undergoes preoperative planning for a complex tibial deformity. The planning process, as depicted in the image below, has identified two distinct CORAs (CORA1 and CORA2) with magnitudes of 34° and 32° respectively. What is the most accurate interpretation of this specific finding in the context of Paley's principles?
. The deformity is simple and uniapical, requiring a single osteotomy at the larger CORA.
. The deformity is multiapical, and each CORA represents a true anatomic apex requiring a separate osteotomy or a controlled correction strategy.
. The presence of two CORAs indicates an error in drawing the mechanical axis lines, and the planning should be restarted.
. The two CORAs represent the resolved apex, and a single osteotomy should be performed at the midpoint between them.
. This is a normal variant of tibial alignment, and no surgical correction is indicated.

Correct Answer & Explanation

. The deformity is multiapical, and each CORA represents a true anatomic apex requiring a separate osteotomy or a controlled correction strategy.

Explanation

Correct Answer: B. The image clearly illustrates a complex tibial deformity where the initial proximal and distal mechanical axis lines, along with an intermediate axis (implied by the two distinct CORAs), have been used to identify two separate Centers of Rotation of Angulation (CORA1 and CORA2). As described in the text, the presence of multiple distinct CORAs within a single bone signifies a multiapical deformity. Each CORA represents a true anatomic apex, meaning the bone is bent in more than one place. For a precise correction, each of these apices needs to be addressed, either through separate osteotomies or a controlled correction strategy (e.g., using an external fixator with hinges at each CORA) to avoid inducing translational deformities. Option A is incorrect because the presence of two distinct CORAs explicitly indicates a multiapical, not a simple uniapical, deformity. Option C is incorrect because the diagram is presented as a 'comprehensive series of diagrams illustrates the complete mechanical axis planning process for a complex tibial deformity,' implying this is a correct and valid finding, not an error. Option D is incorrect because the 'resolved apex CORA' is a single, often illogical, intersection point that represents the sum of multiple deformities. Here, two distinct CORAs have been identified, indicating individual apices, not a single resolved apex. Performing a single osteotomy at a midpoint would lead to an imprecise correction and translation. Option E is incorrect because the text explicitly states this is a 'complex tibial deformity' requiring correction, and the magnitudes of 34° and 32° are significant, not a normal variant.

Question 3024

Topic: 1. General Principles & Basic Science

A 48-year-old patient underwent a high tibial osteotomy for a varus deformity. Six months postoperatively, a standing full-length AP radiograph is obtained to assess the correction. According to Paley's principles, what is the ultimate postoperative benchmark for a successful correction?

. The Medial Proximal Tibial Angle (MPTA) should be exactly 87°.
. The Mechanical Lateral Distal Femoral Angle (mLDFA) should be exactly 87°.
. The Joint Line Convergence Angle (JLCA) should be 0°.
. The Mechanical Axis Deviation (MAD) should be restored to the normal physiologic range (8-10mm medial to the center of the knee).
. The Center of Rotation of Angulation (CORA) should be located at the osteotomy site.

Correct Answer & Explanation

. The Mechanical Axis Deviation (MAD) should be restored to the normal physiologic range (8-10mm medial to the center of the knee).

Explanation

Correct Answer: DThe case explicitly states: 'Quantifying the MAD is far more than an academic exercise. It dictates the clinical significance of the deformity, guides the threshold for surgical intervention, and serves as the ultimate postoperative benchmark for a successful correction. If your postoperative MAD is not restored to the normal physiologic range, the surgery has not fully succeeded.' The normal physiologic range for the mechanical axis is typically 8 to 10 millimeters medial to the exact center of the knee joint.Option A is incorrectbecause while an MPTA of 87° is the normal average, the ultimate success of theoverall limb alignmentis judged by the MAD, not a single joint orientation angle. The MPTA is a target for the tibial correction, but the MAD reflects the entire limb's weight-bearing axis.Option B is incorrectbecause the mLDFA relates to the femur, and while it should be normal if the femur was not involved, it is not the ultimate benchmark for a tibial osteotomy's success in restoring overall limb alignment.Option C is incorrectbecause a JLCA of 0° is ideal but a range of 0-2° is normal, and it primarily assesses intra-articular pathology, not the overall mechanical axis restoration.Option E is incorrectbecause while the CORA dictateswhereto perform the osteotomy for a precise correction, its location relative to the osteotomy site is a planning step, not the ultimate postoperative benchmark for thefunctional outcomeof the limb's alignment.

Question 3025

Topic: 1. General Principles & Basic Science

A 62-year-old male presents with chronic right knee pain and a progressive bowing deformity. A standing full-length anteroposterior radiograph of the lower extremity is obtained, as shown below. Based on the principles of deformity correction, what is the most accurate interpretation of this image?

. The limb demonstrates a valgus deformity with a lateral Mechanical Axis Deviation (MAD).
. The limb demonstrates a varus deformity with the mechanical axis passing lateral to the center of the knee.
. The limb demonstrates a varus deformity with the mechanical axis passing medial to the center of the knee.
. The limb demonstrates a valgus deformity with the mechanical axis passing medial to the center of the knee.
. The limb demonstrates a neutral mechanical axis, indicating no significant frontal plane deformity.

Correct Answer & Explanation

. The limb demonstrates a varus deformity with the mechanical axis passing medial to the center of the knee.

Explanation

Correct Answer: CThe image clearly shows the mechanical axis (the line connecting the center of the femoral head to the center of the talar dome) passing significantly medial to the center of the knee joint. This configuration is characteristic of a varus deformity. A medial Mechanical Axis Deviation (MAD) quantifies this medial displacement. In contrast, a valgus deformity would show the mechanical axis passing lateral to the center of the knee, resulting in a lateral MAD. A neutral mechanical axis would pass through or very close to the center of the knee.

Question 3026

Topic: 1. General Principles & Basic Science

A 55-year-old female presents with left knee pain and a 'knock-knee' appearance. A standing full-length anteroposterior radiograph of the lower extremity is obtained, as depicted below. According to Paley's principles, which of the following statements best describes the observed deformity?

. The limb exhibits a varus deformity with the mechanical axis passing medial to the center of the knee.
. The limb exhibits a valgus deformity with the mechanical axis passing lateral to the center of the knee.
. The limb exhibits a neutral mechanical axis, indicating no need for correction.
. The limb exhibits a varus deformity with a lateral Mechanical Axis Deviation (MAD).
. The limb exhibits a valgus deformity with the mechanical axis passing through the center of the knee.

Correct Answer & Explanation

. The limb exhibits a valgus deformity with the mechanical axis passing lateral to the center of the knee.

Explanation

Correct Answer: BThe provided image illustrates a mechanical axis that passes lateral to the center of the knee joint. This is the defining characteristic of a valgus deformity. The distance from the center of the knee to where the mechanical axis crosses is the Mechanical Axis Deviation (MAD), and in this case, it would be a lateral MAD. A varus deformity would show the mechanical axis passing medial to the knee center. A neutral mechanical axis would pass through the center of the knee.

Question 3027

Topic: 1. General Principles & Basic Science

According to Paley's principles, what is the primary and overarching goal of lower extremity deformity correction in the frontal plane?

. To achieve a Joint Line Convergence Angle (JLCA) of exactly 0°.
. To restore the limb's normal mechanical axis to pass through the center of the knee and ensure joint surfaces are parallel to the ground.
. To maximize the Medial Proximal Tibial Angle (MPTA) and Mechanical Lateral Distal Femoral Angle (mLDFA).
. To eliminate all Mechanical Axis Deviation (MAD) regardless of joint orientation.
. To ensure the anatomic axis passes through the center of the knee.

Correct Answer & Explanation

. To restore the limb's normal mechanical axis to pass through the center of the knee and ensure joint surfaces are parallel to the ground.

Explanation

Correct Answer: BThe case explicitly states that the ultimate goal of deformity correction is twofold: 1) To realign the mechanical axis so it passes through the center of the knee, and 2) To ensure the joint surfaces of the knee and ankle are oriented parallel to the ground during the stance phase of gait. This restoration of normal biomechanics is crucial for preserving long-term joint health and function. While eliminating MAD is part of this, it must be done while maintaining appropriate joint orientation. The anatomic axis is distinct from the mechanical axis and is not the primary target for overall limb alignment in Paley's method.

Question 3028

Topic: 1. General Principles & Basic Science

A 40-year-old patient undergoes preoperative planning for a proximal tibial osteotomy. The surgeon measures a Joint Line Convergence Angle (JLCA) of 5° on the affected limb. The contralateral limb has a JLCA of 1°. What is the most critical implication of the abnormal JLCA in the affected limb for surgical planning?

. It indicates a primary femoral deformity that must be corrected first.
. It suggests significant intra-articular pathology, cartilage loss, or ligamentous laxity that could lead to over- or under-correction if only bony deformity is addressed.
. It confirms that the deformity is purely extra-articular and can be corrected with a simple osteotomy.
. It implies that the Mechanical Lateral Distal Femoral Angle (mLDFA) is also abnormal.
. It necessitates a distal femoral osteotomy in addition to the proximal tibial osteotomy.

Correct Answer & Explanation

. It suggests significant intra-articular pathology, cartilage loss, or ligamentous laxity that could lead to over- or under-correction if only bony deformity is addressed.

Explanation

Correct Answer: BThe case highlights the importance of the JLCA, stating, 'A value > 2° suggests intra-articular pathology, cartilage loss, or ligamentous laxity.' It further warns, 'If the JLCA is abnormal due to collateral ligament laxity, planning a purely bony correction will result in an over- or under-correction once the limb is loaded.' Therefore, a JLCA of 5° (significantly greater than the normal 0-2°) is a critical finding that indicates intra-articular issues that could confound purely bony deformity correction and must be accounted for in the surgical plan.

Question 3029

Topic: 1. General Principles & Basic Science

A surgeon is performing Step 1 of the CORA planning method for a tibial deformity. The ipsilateral femur has an mLDFA of 92°, and the knee joint exhibits a JLCA of 3°. Based on the case's guidelines, how should the Proximal Mechanical Axis (PMA) for the tibia be defined in this scenario?

. By extending the mechanical axis of the ipsilateral femur distally across the knee joint.
. By drawing a line from the center of the knee distally, creating an angle with the proximal tibial joint line equal to a normal MPTA (e.g., 87°).
. By drawing a line from the center of the femoral head to the center of the talar dome.
. By using the anatomic axis of the femur and extending it distally.
. By simply connecting the center of the knee to the identified CORA.

Correct Answer & Explanation

. By drawing a line from the center of the knee distally, creating an angle with the proximal tibial joint line equal to a normal MPTA (e.g., 87°).

Explanation

Correct Answer: BThe case outlines two scenarios for defining the Proximal Mechanical Axis (PMA) in Step 1. Scenario B applies when the ipsilateral femur is deformed (abnormal mLDFA, here 92° > 90° indicating femoral valgus) or there is significant joint laxity (abnormal JLCA, here 3° > 2°). In this situation, the text explicitly states, 'youcannotextend the femoral line. Doing so would incorporate the femoral or intra-articular pathology into your tibial plan, guaranteeing a malcorrection. In this case, the PMA must be drawn independently. The surgeon identifies the center of the knee and draws a line distally, creating an angle with the proximal tibial joint line that is equal to a normal MPTA (e.g., 87° or the specific value matched from the normal contralateral side).'

Question 3030

Topic: 1. General Principles & Basic Science

A 45-year-old male undergoes a tibial osteotomy for a varus deformity. The surgeon plans the osteotomy and the hinge exactly at the Center of Rotation of Angulation (CORA). Which of the following accurately describes the expected mechanical result of this correction?

. Pure angulation occurs with complete realignment of the mechanical axis without translation.
. Angulation occurs with translation at the osteotomy site, restoring the mechanical axis.
. Angulation occurs with translation at the osteotomy site, creating a secondary deformity.
. Translation occurs without angulation, restoring the mechanical axis.
. The mechanical axis remains deviated due to failure to translate.

Correct Answer & Explanation

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

Explanation

According to Paley's Osteotomy Rule 1, when the osteotomy and the hinge are both placed at the CORA, pure angulation occurs without translation, successfully restoring the mechanical axis.

Question 3031

Topic: 1. General Principles & Basic Science

A resident is planning a deformity correction for a valgus tibia. They inadvertently place the correction hinge away from the true CORA, and the osteotomy is also performed away from the CORA. What is the mechanical consequence of this error?

. The mechanical axis will be restored but with significant limb shortening.
. The osteotomy will angulate and translate, but the mechanical axis will not be restored.
. The osteotomy will heal with a pure rotational deformity.
. The mechanical axis will be restored through compensatory joint subluxation.
. Pure angulation will occur, realigning the mechanical axis.

Correct Answer & Explanation

. The osteotomy will angulate and translate, but the mechanical axis will not be restored.

Explanation

According to Paley's Osteotomy Rule 3, placing both the hinge and the osteotomy away from the CORA results in angulation and translation that fails to restore the mechanical axis, effectively creating a new deformity (a secondary translation).

Question 3032

Topic: 1. General Principles & Basic Science

To perform a pure opening wedge osteotomy without introducing translation, a surgeon must place the hinge exactly on the CORA. Specifically, to prevent longitudinal translation (lengthening or shortening of the mechanical axis), where must the hinge be positioned relative to the intersecting axes?

. On the transverse bisector line
. On the convex side of the anatomic axis
. On the concave side of the mechanical axis
. Directly on the joint line
. Perpendicular to the diaphyseal axis

Correct Answer & Explanation

. On the transverse bisector line

Explanation

To achieve pure angulation without inadvertently altering the length along the mechanical axis, the hinge must be placed on the transverse bisector line of the angle formed by the intersecting proximal and distal axes at the CORA.

Question 3033

Topic: Biology, Genetics & Bone Healing

Following a corticotomy for tibial lengthening, the surgeon prescribes a latency period before initiating distraction. What is the optimal latency period for a healthy young adult to optimize regenerate bone formation?

. 0-1 days
. 5-7 days
. 14-21 days
. 28-35 days
. 60 days

Correct Answer & Explanation

. 5-7 days

Explanation

A latency period of 5 to 7 days is generally recommended before beginning distraction. This allows for the initial inflammatory and soft callus phases of fracture healing to commence, optimizing the local biological environment for distraction osteogenesis.

Question 3034

Topic: 1. General Principles & Basic Science

When planning a deformity correction of the femur, the surgeon notes a discrepancy between the anatomic and mechanical axes. In a normal lower extremity, which of the following best describes the relationship between the mechanical and anatomic axes of the femur?

. They are completely parallel.
. The anatomic axis diverges from the mechanical axis by approximately 7°.
. The mechanical axis lies completely outside the soft tissues of the thigh.
. They intersect exactly at the lesser trochanter.
. They are identical and superimpose perfectly.

Correct Answer & Explanation

. The anatomic axis diverges from the mechanical axis by approximately 7°.

Explanation

In a normal femur, the anatomic axis diverges from the mechanical axis by an angle of approximately 5° to 7° (the anatomic-mechanical angle), due to the femoral neck offset and the position of the femoral head relative to the knee center.

Question 3035

Topic: 1. General Principles & Basic Science

A 14-year-old boy has a distal femoral valgus deformity. Preoperative planning places the center of rotation of angulation (CORA) at the metadiaphyseal junction. If the osteotomy is performed at the diaphyseal level and the correction hinge is placed exactly at the CORA, what is the expected radiographic outcome according to Paley's osteotomy rules?

. Collinear mechanical axes with no translation at the osteotomy site.
. Collinear mechanical axes with translation of the bone ends at the osteotomy site.
. Parallel mechanical axes with no translation at the osteotomy site.
. Parallel mechanical axes with translation of the bone ends at the osteotomy site.
. Angulation is not corrected, but pure translation occurs.

Correct Answer & Explanation

. Collinear mechanical axes with translation of the bone ends at the osteotomy site.

Explanation

Paley's Osteotomy Rule 2 states that if the hinge is placed at the CORA but the osteotomy is performed at a different level, the mechanical axes will realign (collinear), but the bone ends will translate at the osteotomy site.

Question 3036

Topic: 1. General Principles & Basic Science

According to Paley's principles of deformity correction, which of the following is the expected outcome if the osteotomy and the hinge (axis of rotation) are both placed exactly at the Center of Rotation of Angulation (CORA)?

. Angulation correction is achieved, but an unintended translation of the bone ends occurs.
. The mechanical axes become parallel but not collinear, resulting in a zigzag deformity.
. The deformity is corrected by pure angulation without translation at the osteotomy site.
. A pure translational correction occurs without any angular change.
. Premature consolidation of the regenerate bone occurs.

Correct Answer & Explanation

. The deformity is corrected by pure angulation without translation at the osteotomy site.

Explanation

Osteotomy Rule 1 states that when the osteotomy and the hinge are both placed at the CORA, the deformity corrects through pure angulation. The bone ends remain opposed without translation.

Question 3037

Topic: 1. General Principles & Basic Science

A surgeon is planning a deformity correction using an external fixator. The Center of Rotation of Angulation (CORA) is identified in the diaphysis, but due to poor soft tissue coverage, the osteotomy is performed metaphyseally. If the fixator hinge is correctly placed at the CORA, what is the geometric result at the osteotomy site?

. Pure angulation with no translation.
. Angulation combined with translation, resulting in collinear mechanical axes.
. Angulation combined with translation, resulting in parallel but non-collinear mechanical axes.
. Pure translation with no angular change.
. Complete loss of mechanical axis alignment.

Correct Answer & Explanation

. Angulation combined with translation, resulting in collinear mechanical axes.

Explanation

Osteotomy Rule 2 states that if the hinge is at the CORA but the osteotomy is at a different level, the correction will involve both angulation and translation at the osteotomy site. However, the proximal and distal mechanical axes will be successfully restored to a collinear alignment.

Question 3038

Topic: 1. General Principles & Basic Science

A patient undergoes a tibial osteotomy for a varus deformity. The surgeon inadvertently places the external fixator hinge proximal to the CORA and performs the osteotomy at the hinge level. Which of the following best describes the resulting alignment based on Paley's Osteotomy Rule 3?

. The mechanical axes become collinear with pure angulation at the osteotomy.
. The mechanical axes become parallel but remain non-collinear, creating a zigzag deformity.
. A pure translation deformity is created without angular correction.
. The mechanical axes remain in their preoperative varus alignment without change.
. The resulting correction leads to an iatrogenic valgus overcorrection.

Correct Answer & Explanation

. The mechanical axes become parallel but remain non-collinear, creating a zigzag deformity.

Explanation

Osteotomy Rule 3 states that if the osteotomy and hinge are both placed away from the CORA, the correction will result in angulation and translation. The proximal and distal axes will become parallel but not collinear, resulting in a zigzag deformity.

Question 3039

Topic: Biology, Genetics & Bone Healing

In distraction osteogenesis (Ilizarov method) for limb lengthening, what is the primary biological purpose of the 'latent period' prior to initiating distraction?

. To allow the patient to adjust to the external fixator psychologically.
. To permit the initial organization of the fracture hematoma and formation of a mesenchymal bridge.
. To wait for complete resorption of necrotic bone ends at the osteotomy site.
. To ensure cortical bridging is fully established prior to stress.
. To stretch the adjacent neurovascular structures gradually.

Correct Answer & Explanation

. To permit the initial organization of the fracture hematoma and formation of a mesenchymal bridge.

Explanation

The latent period (typically 5-7 days) allows for the inflammatory phase and early soft callus formation. This ensures a vascularized mesenchymal tissue bridge is present to form quality regenerate bone upon distraction.

Question 3040

Topic: 1. General Principles & Basic Science

A fundamental concept in evaluating lower extremity alignment is the relationship between the mechanical and anatomic axes. Which of the following statements is true regarding the normal alignment of the femur?

. The mechanical axis is parallel and identical to the anatomic axis.
. The anatomic axis diverges approximately 5 to 7 degrees in varus relative to the mechanical axis.
. The anatomic axis diverges approximately 5 to 7 degrees in valgus relative to the mechanical axis.
. The mechanical axis passes through the center of the intramedullary canal.
. The mechanical axis is determined by a line drawn from the greater trochanter to the lateral femoral condyle.

Correct Answer & Explanation

. The anatomic axis diverges approximately 5 to 7 degrees in varus relative to the mechanical axis.

Explanation

In the femur, the mechanical axis is a line from the center of the femoral head to the center of the knee. The anatomic axis (down the intramedullary canal) lies roughly 5-7 degrees in valgus relative to the mechanical axis.

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page