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1. General Principles & Basic Science MCQs

Practice Set 771 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 15401

Topic: 1. General Principles & Basic Science

According to the principles of deformity correction, if an osteotomy is performed exactly at the center of rotation of angulation (CORA) and the mechanical hinge is also placed at the CORA, what is the expected outcome regarding the bone ends?

. Angulation accompanied by unintended translation
. Pure angulation of the bone ends without translation
. Pure translation without angular correction
. Opening wedge angulation with severe secondary length loss

Correct Answer & Explanation

. Pure angulation of the bone ends without translation

Explanation

Placing both the osteotomy cut and the mechanical hinge axis directly at the CORA (Rule 1 of deformity correction) results in pure angular correction without translation.

Question 15402

Topic: 1. General Principles & Basic Science

In a diaphyseal deformity, if the osteotomy is performed at a level distinct from the center of rotation of angulation (CORA), but the mechanical hinge is placed exactly at the CORA, what is the geometric consequence?

. Pure angulation with complete anatomic alignment
. Angulation accompanied by obligate translation of the bone ends
. Pure translation without angular correction
. Complete failure to restore the mechanical axis

Correct Answer & Explanation

. Angulation accompanied by obligate translation of the bone ends

Explanation

This illustrates Deformity Rule 2: placing the hinge at the CORA will fully correct the mechanical axis. However, if the osteotomy is made away from the CORA, obligate translation of the bone ends occurs.

Question 15403

Topic: Physiology & Rehabilitation

A patient exhibits a compensated Trendelenburg gait characterized by leaning the trunk laterally over the affected hip during the stance phase. What is the precise biomechanical consequence of this maneuver?

. It moves the center of gravity closer to the hip center, decreasing the body weight lever arm
. It increases the required force of the hip abductors to maintain a level pelvis
. It shifts the mechanical axis laterally to offload the medial compartment of the knee
. It decreases the femoral offset, reducing joint reaction forces

Correct Answer & Explanation

. It moves the center of gravity closer to the hip center, decreasing the body weight lever arm

Explanation

Leaning the trunk over the affected, weak hip shifts the body's center of gravity closer to the hip's center of rotation. This dramatically decreases the body weight lever arm, thereby reducing the necessary counter-force required from the weakened abductors.

Question 15404

Topic: 1. General Principles & Basic Science

A patient presents with a mid-diaphyseal tibial deformity. If a single-cut opening wedge osteotomy is placed precisely at the CORA, what secondary physical effect on the limb is expected?

. Limb shortening
. Obligate mechanical translation
. Limb lengthening
. Creation of a secondary multiplanar CORA

Correct Answer & Explanation

. Limb lengthening

Explanation

An opening wedge osteotomy corrects the angular deformity by creating a wedge-shaped gap on the convex side while hinging on the concave cortex. This invariably results in an increase in the overall absolute length of the bone segment.

Question 15405

Topic: 1. General Principles & Basic Science

According to Paley's principles of deformity correction, which of the following accurately describes Osteotomy Rule 1?

. When the osteotomy and the mechanical hinge are both placed at the Center of Rotation of Angulation (CORA), angular correction is achieved without any translation.
. When the osteotomy is at the CORA but the hinge is away from the CORA, pure translation occurs.
. When the hinge is at the CORA and the osteotomy is away from the CORA, pure angulation occurs without translation.
. When both the osteotomy and hinge are away from the CORA, angular correction is achieved without translation.
. When the osteotomy and hinge are at the CORA, correction results in both angulation and translation.

Correct Answer & Explanation

. When the osteotomy and the mechanical hinge are both placed at the Center of Rotation of Angulation (CORA), angular correction is achieved without any translation.

Explanation

Osteotomy Rule 1 states that placing both the osteotomy and the mechanical hinge at the Center of Rotation of Angulation (CORA) results in pure angular correction without translation of the bone ends.

Question 15406

Topic: 1. General Principles & Basic Science

When analyzing full-length standing lower extremity radiographs for a coronal plane deformity, what is the normal accepted range for the mechanical Lateral Distal Femoral Angle (mLDFA)?

. 80 to 84 degrees
. 85 to 90 degrees
. 91 to 95 degrees
. 96 to 100 degrees
. 101 to 105 degrees

Correct Answer & Explanation

. 85 to 90 degrees

Explanation

The normal mechanical lateral distal femoral angle (mLDFA) ranges from 85 to 90 degrees, with an average of 87 to 88 degrees. Angles less than 85 degrees indicate a valgus deformity, while those greater than 90 degrees indicate varus.

Question 15407

Topic: 1. General Principles & Basic Science

A surgeon is planning a deformity correction using an external fixator. Due to poor skin quality at the apex, the osteotomy must be placed 3 cm proximal to the Center of Rotation of Angulation (CORA), while the mechanical hinge remains exactly at the CORA. What is the expected geometric outcome according to Osteotomy Rule 2?

. Pure angular correction with no translation.
. Angular correction accompanied by translation of the bone ends.
. Pure translation without any change in angulation.
. Failure of the mechanical axis to realign due to hinge mismatch.
. Creation of a secondary rotational deformity.

Correct Answer & Explanation

. Angular correction accompanied by translation of the bone ends.

Explanation

Osteotomy Rule 2 states that if the osteotomy is made away from the CORA but the mechanical hinge is maintained at the CORA, the mechanical axis will realign through angular correction accompanied by translation of the bone fragments.

Question 15408

Topic: Physiology & Rehabilitation

A patient with severe unilateral hip abductor weakness demonstrates a classic Trendelenburg gait. Biomechanically, how does shifting the torso laterally over the affected hip compensate for this weakness?

. It moves the center of gravity closer to the hip joint, decreasing the body weight moment arm.
. It moves the center of gravity further from the hip joint, increasing the abductor moment arm.
. It increases the lever arm of the iliotibial band to substitute for the gluteus medius.
. It artificially increases the joint reaction force to lock the hip in extension.
. It shifts the mechanical axis medially to reduce valgus stress on the knee.

Correct Answer & Explanation

. It moves the center of gravity closer to the hip joint, decreasing the body weight moment arm.

Explanation

In a Trendelenburg gait, the patient shifts their torso over the affected hip to move their center of gravity closer to the joint's center of rotation. This drastically reduces the body weight moment arm, decreasing the required abductor force.

Question 15409

Topic: 1. General Principles & Basic Science

When evaluating a lower extremity deformity, the mechanical axis of the proximal segment and the mechanical axis of the distal segment intersect at a specific point. What is this point defined as?

. Osteotomy rule 1.
. Hinge point.
. Center of Rotation of Angulation (CORA).
. Mechanical axis deviation (MAD).
. Apex of bowing.

Correct Answer & Explanation

. Center of Rotation of Angulation (CORA).

Explanation

The Center of Rotation of Angulation (CORA) is defined as the intersection of the proximal and distal anatomical or mechanical axes of a deformed bone segment in a given plane.

Question 15410

Topic: 1. General Principles & Basic Science

According to Paley's osteotomy rules, if the osteotomy line and the hinge axis are both placed directly at the Center of Rotation of Angulation (CORA), what is the resulting correction?

. Pure angulation with no translation.
. Angulation with unintended translation.
. Pure translation with no angulation.
. Lengthening without angulation.
. Angulation with planned shortening.

Correct Answer & Explanation

. Pure angulation with no translation.

Explanation

Paley's Osteotomy Rule 1 states that if the osteotomy line and the hinge axis both pass through the CORA, a pure angular correction is achieved without any translation of the bone segments.

Question 15411

Topic: 1. General Principles & Basic Science

If a deformity correction osteotomy is performed at a site different from the CORA, but the hinge is appropriately placed at the CORA, what occurs during the correction process?

. Pure angulation without translation.
. Angulation and translation maintaining collinear mechanical axes.
. Translation without any angulation.
. Angulation resulting in parallel non-collinear axes.
. Complete loss of axial alignment.

Correct Answer & Explanation

. Angulation and translation maintaining collinear mechanical axes.

Explanation

Paley's Osteotomy Rule 2 dictates that if the hinge is at the CORA but the osteotomy is at a different level, the correction will result in angulation along with translation, keeping the mechanical axes collinear.

Question 15412

Topic: 1. General Principles & Basic Science

When analyzing coronal plane alignment of the lower extremity, what is the normal mechanical lateral distal femoral angle (mLDFA)?

. 81 degrees
. 87 degrees
. 93 degrees
. 99 degrees
. 105 degrees

Correct Answer & Explanation

. 87 degrees

Explanation

The normal mechanical lateral distal femoral angle (mLDFA) is 87 degrees, with a typical normal range between 85 and 90 degrees.

Question 15413

Topic: 1. General Principles & Basic Science

An oblique plane deformity of the tibia consists of 15 degrees varus in the coronal plane and 20 degrees procurvatum in the sagittal plane. How is the true magnitude of this oblique deformity calculated?

. By adding the coronal and sagittal values directly.
. By using the Pythagorean theorem with the coronal and sagittal angles.
. By subtracting the smaller angle from the larger angle.
. By relying solely on the maximum coronal deformity measured.
. By averaging the varus and procurvatum angles.

Correct Answer & Explanation

. By using the Pythagorean theorem with the coronal and sagittal angles.

Explanation

An oblique plane deformity is the vector sum of the coronal and sagittal deformities. Its true magnitude is calculated using the Pythagorean theorem (the square root of the sum of the squares of the two orthogonal angles).

Question 15414

Topic: Physiology & Rehabilitation

An uncompensated Trendelenburg gait in a patient with a right hip abductor deficiency is characterized by which of the following kinematic patterns during the stance phase on the right leg?

. The pelvis drops on the right side and the trunk leans right.
. The pelvis drops on the left side and the trunk remains relatively vertical.
. The pelvis drops on the left side and the trunk aggressively leans to the right.
. The pelvis drops on the right side and the trunk leans left.
. The pelvis elevates on the left side.

Correct Answer & Explanation

. The pelvis drops on the left side and the trunk remains relatively vertical.

Explanation

In an uncompensated Trendelenburg gait, weak right hip abductors fail to maintain a level pelvis during right single-leg stance, causing the contralateral (left) pelvis to drop while the trunk remains vertically oriented.

Question 15415

Topic: 1. General Principles & Basic Science

According to Paley's Osteotomy Rule 3, if the osteotomy and the hinge are both placed away from the Center of Rotation of Angulation (CORA), what is the expected outcome of the deformity correction?

. Pure angulation maintaining original axes.
. Angulation with collinear alignment.
. Angulation with translation resulting in parallel but non-collinear mechanical axes.
. Complete correction of both length and angular alignment.
. Pure translation with no change in angulation.

Correct Answer & Explanation

. Angulation with translation resulting in parallel but non-collinear mechanical axes.

Explanation

Osteotomy Rule 3 states that if the osteotomy and hinge axis are placed outside the CORA, angular correction will result in translation, leaving the mechanical axes parallel but non-collinear (producing a secondary translation deformity).

Question 15416

Topic: 1. General Principles & Basic Science

During a normal single-leg stance, the joint reaction force acting across the hip joint is approximately how many times the individual's total body weight?

. 1.0 to 1.5 times.
. 2.5 to 3.0 times.
. 4.0 to 5.0 times.
. 6.0 to 7.0 times.
. 8.0 to 9.0 times.

Correct Answer & Explanation

. 2.5 to 3.0 times.

Explanation

During single-leg stance, the hip joint reaction force is approximately 2.5 to 3.0 times body weight. This is the sum of the force of body weight and the substantial abductor muscle force required to maintain pelvic equilibrium.

Question 15417

Topic: 1. General Principles & Basic Science

The Taylor Spatial Frame utilizes a hexapod construct based on the Stewart-Gough platform. How many degrees of freedom does this system provide for simultaneously correcting complex deformities?

. Three
. Four
. Five
. Six
. Eight

Correct Answer & Explanation

. Six

Explanation

The Taylor Spatial Frame (a hexapod fixator) allows for simultaneous deformity correction in six degrees of freedom: angulation and translation in both the coronal and sagittal planes, axial rotation, and axial length.

Question 15418

Topic: 1. General Principles & Basic Science

In a mechanically neutral lower extremity, where does the mechanical axis (Mikulicz line) pass in relation to the knee joint center?

. 15 mm lateral to the center.
. 10 mm medial to the center.
. Through or just 1-3 mm medial to the center.
. 10 mm lateral to the center.
. 20 mm medial to the center.

Correct Answer & Explanation

. Through or just 1-3 mm medial to the center.

Explanation

The normal mechanical axis of the lower extremity passes directly through or just slightly medial (typically 1-3 mm) to the center of the knee joint. Deviation from this defines a varus or valgus mechanical axis deviation (MAD).

Question 15419

Topic: 1. General Principles & Basic Science

A patient with severe unilateral hip osteoarthritis uses a cane in the contralateral hand. How does this mechanical intervention primarily alter the biomechanics of the affected hip during the stance phase?

. It increases the abductor moment arm length.
. It decreases the body weight lever arm length.
. It provides an upward counter-moment that reduces the required abductor muscle force.
. It shifts the center of gravity laterally away from the stance hip.
. It directly increases the joint reaction force to physically stabilize the pelvis.

Correct Answer & Explanation

. It provides an upward counter-moment that reduces the required abductor muscle force.

Explanation

Using a cane in the contralateral hand provides an upward counter-moment to gravity. This significantly decreases the force required by the hip abductors to maintain a level pelvis, thereby greatly reducing the overall joint reaction force on the affected hip.

Question 15420

Topic: 1. General Principles & Basic Science

According to the principles of deformity correction (Osteotomy Rule 2), if an osteotomy is performed at a level separate from the Center of Rotation of Angulation (CORA), but the Axis of Correction of Angulation (ACA) still passes through the CORA, what is the expected geometric outcome?

. Pure angulation without translation.
. Angulation with translation.
. Pure translation without angulation.
. Angulation with compression.
. Pure rotation.

Correct Answer & Explanation

. Angulation with translation.

Explanation

Osteotomy Rule 2 states that when the ACA passes through the CORA but the osteotomy is made at a different level, the correction will result in both angulation and translation at the osteotomy site. This translation is mathematically necessary to realign the mechanical axis.

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