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1. General Principles & Basic Science MCQs

Practice Set 146 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 2901

Topic: 1. General Principles & Basic Science

A patient presents with an obvious clinical deformity of the leg. Radiographic analysis reveals that the proximal and distal anatomical axes of the tibia are perfectly parallel but not collinear. According to Paley's principles, where is the Center of Rotation of Angulation (CORA) located in a pure translational deformity?

. At the level of the joint line
. At the geometric center of the diaphyseal bone segment
. At infinity
. Exactly at the site of the translation
. Midway between the proximal and distal metaphyses

Correct Answer & Explanation

. At infinity

Explanation

In a pure translational deformity, the proximal and distal axes never intersect. Mathematically and geometrically, parallel lines intersect at infinity, meaning the CORA is located at infinity.

Question 2902

Topic: 1. General Principles & Basic Science

A full-length weight-bearing radiograph demonstrates a complex tibial deformity with two distinct apices of angulation (multi-apical). If the surgeon plans a single osteotomy to correct the entire mechanical axis deviation, what is the most likely consequence?

. Perfect restoration of the anatomical axis and collinear mechanical axes
. Creation of an unacceptable residual translational deformity to achieve a collinear mechanical axis
. Correction of the angular deformity with an improved JLCA
. Elimination of the need for a latency period during distraction osteogenesis
. An increase in the overall length of the tibia without angular correction

Correct Answer & Explanation

. Creation of an unacceptable residual translational deformity to achieve a collinear mechanical axis

Explanation

Correcting a multi-apical deformity with a single osteotomy usually requires placing the hinge at an 'average' CORA, which acts via Paley's Rule 3, resulting in massive, often cosmetically and functionally unacceptable, translational deformity to restore the mechanical axis.

Question 2903

Topic: Biology, Genetics & Bone Healing

When performing distraction osteogenesis using an Ilizarov circular fixator to treat a limb length discrepancy, what is the primary biological purpose of the 7-to-10 day 'latency period' before initiating distraction?

. To allow the patient to acclimatize to the external fixator
. To permit primary bone healing and endochondral ossification across the gap
. To allow the acute inflammatory phase to subside and mesenchymal stem cells to populate the hematoma
. To prevent pin tract infections from migrating into the osteotomy site
. To allow for the complete resorption of necrotic bone edges

Correct Answer & Explanation

. To allow the acute inflammatory phase to subside and mesenchymal stem cells to populate the hematoma

Explanation

The latency period allows the initial fracture hematoma to form, acute inflammation to resolve, and mesenchymal stem cells to migrate and begin early callus formation (intramembranous ossification) before distraction begins.

Question 2904

Topic: 1. General Principles & Basic Science

A surgeon is using a Taylor Spatial Frame (TSF) to correct a complex 6-axis tibial deformity.

To generate an accurate computer prescription, the software requires specific mounting parameters. What do these mounting parameters represent?

. The mechanical axis deviation and joint line convergence angle
. The exact geographic location of the CORA relative to the knee joint
. The position of the reference ring relative to the origin of the deformity (the reference bone segment)
. The daily rate and rhythm of the strut adjustments
. The total length of the regenerate bone required

Correct Answer & Explanation

. The position of the reference ring relative to the origin of the deformity (the reference bone segment)

Explanation

Mounting parameters in the TSF software define the exact position (AP, lateral, axial, and rotary offset) of the reference ring relative to the reference bone segment. Accurate input is critical for the software to map the deformity correction.

Question 2905

Topic: 1. General Principles & Basic Science

A surgeon is performing a medial opening-wedge high tibial osteotomy for a varus deformity. The preoperative plan indicates a significant correction angle requiring a concomitant fibular osteotomy to prevent tethering. If the surgeon performs the fibular osteotomy at the junction of the middle and distal thirds, which nerve is at the greatest risk of injury?

. Deep peroneal nerve
. Common peroneal nerve
. Superficial peroneal nerve
. Sural nerve
. Tibial nerve

Correct Answer & Explanation

. Superficial peroneal nerve

Explanation

A fibular osteotomy at the middle/distal third junction puts the superficial peroneal nerve at risk as it exits the deep fascia. Proximal fibular osteotomies risk the common peroneal nerve.

Question 2906

Topic: 1. General Principles & Basic Science

A patient has a tibial diaphyseal deformity. Preoperative planning places the osteotomy exactly at the CORA, and the hinge of the external fixator is also placed at the CORA. What is the expected geometric outcome based on Paley's Osteotomy Rule 1?

. Complete alignment without translation
. Complete alignment with translation at the osteotomy site
. Parallel mechanical axes with translation
. Correction of angulation but creation of a secondary length discrepancy
. Incomplete correction of angulation due to hinge placement

Correct Answer & Explanation

. Complete alignment without translation

Explanation

According to Paley's Rule 1, if the osteotomy and the hinge are both placed at the CORA, angular deformity is fully corrected without introducing any translation at the osteotomy site.

Question 2907

Topic: 1. General Principles & Basic Science

A surgeon is planning to correct a distal femoral varus deformity. The CORA is located near the joint line, making an osteotomy at the CORA impossible due to inadequate distal fixation. The surgeon performs the osteotomy proximal to the CORA but places the hinge axis at the CORA. Which of Paley's rules does this describe, and what is the expected outcome?

. Rule 1; alignment without translation
. Rule 2; alignment with expected translation at the osteotomy site
. Rule 3; parallel axes with persistent translation
. Rule 1; parallel axes with persistent translation
. Rule 2; alignment without translation

Correct Answer & Explanation

. Rule 2; alignment with expected translation at the osteotomy site

Explanation

Paley's Rule 2 states that if the osteotomy is at a different level than the CORA, but the hinge is placed at the CORA, the mechanical axes will align but translation will intentionally occur at the osteotomy site.

Question 2908

Topic: Biology, Genetics & Bone Healing

A 30-year-old male with a history of rickets presents with a "windswept" deformity. On the right lower extremity, the joint line convergence angle (JLCA) is measured at 6 degrees. What does an abnormally high JLCA typically indicate in the context of deformity planning?

. Diaphyseal procurvatum deformity
. Extra-articular femoral valgus
. Intra-articular deformity or collateral ligamentous laxity
. Normal physiological variation
. Fixed equinus contracture

Correct Answer & Explanation

. Intra-articular deformity or collateral ligamentous laxity

Explanation

The normal JLCA is 0-2 degrees. An increased JLCA suggests either intra-articular deformity (e.g., cartilage loss) or collateral ligament laxity causing joint subluxation.

Question 2909

Topic: 1. General Principles & Basic Science

A patient undergoes a closing wedge high tibial osteotomy (HTO) for a varus deformity. If the hinge of the osteotomy (the intact lateral cortex) does not perfectly align with the CORA, what compensatory change occurs according to the principles of deformity correction?

. Worsening of the varus angle
. Inadvertent lengthening of the tibia
. Translation of the mechanical axis
. Widening of the JLCA
. Complete loss of regenerate bone

Correct Answer & Explanation

. Translation of the mechanical axis

Explanation

If an osteotomy hinge is placed at a site other than the CORA (Paley's Rule 3), correction of the angulation will inevitably result in translation of the mechanical axis.

Question 2910

Topic: 1. General Principles & Basic Science

A 16-year-old presents with a distal femoral valgus deformity. Radiographs show an mLDFA of 75 degrees. The surgeon decides to perform a medial closing wedge osteotomy. What happens to the overall limb length following a closing wedge osteotomy compared to an opening wedge?

. Limb length is strictly maintained
. Limb length is shortened
. Limb length strictly increases
. Limb length is maintained but mechanical axis is laterally deviated
. Limb length increases proportionally to the wedge base

Correct Answer & Explanation

. Limb length is shortened

Explanation

A closing wedge osteotomy inherently removes a segment of bone, leading to a net shortening of the limb, whereas an opening wedge osteotomy tends to lengthen the limb.

Question 2911

Topic: 1. General Principles & Basic Science

When calculating the true magnitude of an angular deformity that is present in both the coronal and sagittal planes, which of the following mathematical principles is commonly utilized?

. Rule of nines
. Law of Cosines or tangent formulas
. Inverse square law
. Fibonacci sequence
. Pythagorean theorem applied to joint angles

Correct Answer & Explanation

. Law of Cosines or tangent formulas

Explanation

The magnitude and orientation of a multiplanar deformity can be calculated using tangent formulas and trigonometric rules, or by utilizing graphical methods derived from the Law of Cosines.

Question 2912

Topic: 1. General Principles & Basic Science

A patient with a significant varus deformity of the proximal tibia is planned for a high tibial osteotomy (HTO). Based on the mechanical axis deviation, the CORA is identified exactly at the knee joint line. If an osteotomy is performed at the proximal metaphysis and the hinge is placed laterally at the osteotomy site, what will be the result?

. The mechanical axis will perfectly align without translation
. A new translation deformity will be created to parallel the axes
. The patient will experience a complete loss of knee flexion
. The anatomical axes will perfectly align while the mechanical axes diverge
. Ligamentous laxity will resolve spontaneously

Correct Answer & Explanation

. A new translation deformity will be created to parallel the axes

Explanation

This scenario follows Paley's Rule 3 (osteotomy and hinge both away from the CORA). The angulation is corrected, but the mechanical axes remain translated, creating a new translational deformity.

Question 2913

Topic: 1. General Principles & Basic Science

During preoperative planning for a distal femoral deformity, the surgeon evaluates the sagittal plane using the mechanical Posterior Distal Femoral Angle (mPDFA). What is the standard normal value for the mPDFA?

. 75 degrees
. 83 degrees
. 87 degrees
. 90 degrees
. 95 degrees

Correct Answer & Explanation

. 83 degrees

Explanation

The normal mechanical Posterior Distal Femoral Angle (mPDFA) is 83 degrees (range 79-87 degrees), which dictates the normal sagittal bow and distal articular orientation of the femur.

Question 2914

Topic: 1. General Principles & Basic Science

In the application of Paley's rules of deformity correction,

if the mechanical axes of the proximal and distal bone segments are found to be parallel but not collinear, which type of deformity is present?

. Pure angular deformity
. Pure translational deformity
. Multi-apical angular deformity
. Rotational malalignment
. Length discrepancy only

Correct Answer & Explanation

. Pure translational deformity

Explanation

When the proximal and distal mechanical axes are perfectly parallel but do not overlap (are not collinear), the deformity is defined as a pure translational deformity.

Question 2915

Topic: 1. General Principles & Basic Science

A 55-year-old patient presents with a long-standing tibial deformity. Radiographic analysis is performed, and the image below illustrates different types of CORA locations. Which panel correctly depicts a pure translation deformity, and what is the theoretical location of its CORA?

. Panel (c); The CORA is located at the anatomical apex of the deformity.
. Panel (d); The CORA is theoretically located at infinity.
. Panel (e); The CORA is located proximal to the deformity apex.
. Panel (f); The CORA is located distal to the deformity apex.
. Panel (c) and (f); The CORA is located at the anatomical apex of the deformity.

Correct Answer & Explanation

. Panel (d); The CORA is theoretically located at infinity.

Explanation

Correct Answer: BPanel (d) in the provided image clearly demonstrates a pure translation deformity. In this scenario, the proximal and distal axes of the bone are perfectly parallel, meaning they never intersect. Geometrically, the Center of Rotation of Angulation (CORA) for a pure translation deformity is theoretically located at infinity because there is no angulation, only a shift. Panels (c) and (f) depict pure angulation deformities where the CORA is located precisely at the anatomical apex of the deformity, where the proximal and distal axes intersect. Panel (e) is not explicitly described in the text but shows a CORA that is not at the apex, implying a combined angulation-translation deformity where the CORA is displaced from the anatomical apex.

Question 2916

Topic: 1. General Principles & Basic Science

According to Paley's principles of deformity correction, if an osteotomy is performed at a level distinct from the center of rotation of angulation (CORA), but the hinge axis is placed exactly at the CORA, what is the geometric result?

. Pure angular correction without translation
. Angulation correction with a resulting translation of the axis
. Pure translation without angular correction
. Creation of a secondary angular deformity in the orthogonal plane
. Complete realignment without collinear mechanical axes

Correct Answer & Explanation

. Angulation correction with a resulting translation of the axis

Explanation

This describes Paley's Osteotomy Rule 2. When the osteotomy is outside the CORA but the hinge axis is at the CORA, the mechanical axes will realign, but the bone ends at the osteotomy site will translate.

Question 2917

Topic: 1. General Principles & Basic Science

A 45-year-old patient is undergoing a medial opening wedge high tibial osteotomy (HTO) for medial compartment osteoarthritis with a varus deformity. To maintain the patient's normal sagittal plane tibial slope, where should the osteotomy gap be slightly larger?

. Anterior cortex
. Posterior cortex
. Directly medial
. Anterolateral cortex
. Posteromedial cortex

Correct Answer & Explanation

. Posterior cortex

Explanation

The normal proximal tibia has a posterior slope and a triangular cross-section. Due to this shape, a medial opening wedge must be slightly larger posteriorly to avoid inadvertently increasing the posterior slope.

Question 2918

Topic: 1. General Principles & Basic Science

A deformity characterized solely by translation without any angular deviation implies that the Center of Rotation of Angulation (CORA) is located where geometrically?

. At the exact mid-diaphysis
. At the adjacent joint line
. At infinity
. At the metadiaphyseal junction
. Within the anatomical axis but outside the mechanical axis

Correct Answer & Explanation

. At infinity

Explanation

A pure translational deformity has parallel proximal and distal axes that never intersect. Therefore, the CORA for a pure translation is theoretically located at infinity.

Question 2919

Topic: 1. General Principles & Basic Science

When performing an acute correction of a severe proximal tibial valgus deformity, which of the following structures is placed at the highest risk of iatrogenic injury?

. Tibial nerve
. Common peroneal nerve
. Popliteal artery
. Saphenous nerve
. Deep peroneal nerve

Correct Answer & Explanation

. Common peroneal nerve

Explanation

Acute correction of a severe proximal tibial valgus deformity elongates the lateral structures. This places the common peroneal nerve at high risk for a stretch-induced neuropraxia or palsy.

Question 2920

Topic: 1. General Principles & Basic Science

A patient presents with a complex multi-apical varus deformity of the tibia.

To correct this using a single Taylor Spatial Frame, which of the following inputs is essential for the software planning?

. Mounting parameters, deformity parameters (including CORA), and frame parameters
. Calculation of the joint line convergence angle strictly in the coronal plane
. Creation of two separate distinct rings at each individual apex
. Using a monoplanar external fixator setup instead
. Ignoring the proximal deformity if its magnitude is less than 5 degrees

Correct Answer & Explanation

. Mounting parameters, deformity parameters (including CORA), and frame parameters

Explanation

The Taylor Spatial Frame (TSF) requires accurate input of mounting parameters, deformity parameters (including CORA), and frame parameters. This enables the software to correct multi-planar and multi-apical deformities simultaneously via a virtual hinge.

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