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1. General Principles & Basic Science MCQs

Practice Set 137 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 2721

Topic: 1. General Principles & Basic Science

An osteotomy and the hinge axis are both placed at a level proximal to the Center of Rotation of Angulation (CORA). Which of the following best describes the resulting alignment after angular correction is completed?

. Realignment without translation
. Realignment with translation at the osteotomy
. A secondary translational deformity resulting in parallel but non-collinear axes
. Perfect restoration of both anatomic and mechanical axes
. Pure rotational deformity without axis shift

Correct Answer & Explanation

. A secondary translational deformity resulting in parallel but non-collinear axes

Explanation

Paley's Rule 3 states that if the hinge and osteotomy are placed at a level different from the CORA, the angular correction will result in parallel but non-collinear mechanical axes. This creates a secondary translational deformity and a new mechanical axis deviation.

Question 2722

Topic: Biomechanics & Biomaterials

When measuring a patient's lower extremity alignment parameters, the Joint Line Congruency Angle (JLCA) is found to be 6 degrees, opening laterally. What is the most likely clinical correlate to this radiographic finding?

. Normal knee joint kinematics
. Medial compartment cartilage loss or lateral ligament laxity
. Lateral compartment cartilage loss or medial ligament laxity
. Fixed valgus deformity of the distal femur
. Normal physiologic bowing of the tibia

Correct Answer & Explanation

. Medial compartment cartilage loss or lateral ligament laxity

Explanation

A normal JLCA is 0 to 2 degrees. A JLCA that opens laterally implies that the medial joint space is abnormally narrowed or the lateral side is widened, typically indicating medial compartment cartilage wear or lateral ligamentous laxity.

Question 2723

Topic: 1. General Principles & Basic Science

In evaluating a diaphyseal deformity of the tibia, the mechanical axis line of the proximal segment and the mechanical axis line of the distal segment are drawn. They do not intersect but are perfectly parallel. This pattern is characteristic of what type of deformity?

. Single-apical angular deformity
. Pure translational deformity
. Multi-apical angular deformity
. Pure rotational deformity
. Pure limb length discrepancy

Correct Answer & Explanation

. Pure translational deformity

Explanation

When the proximal and distal anatomic or mechanical axes are parallel but not collinear, it defines a pure translational deformity. Mathematically, this condition lacks a localized Center of Rotation of Angulation (CORA) and is described as having an infinite CORA.

Question 2724

Topic: 1. General Principles & Basic Science

A patient has a multi-apical deformity of the femur. The surgeon decides to correct the overall mechanical axis deviation with a single osteotomy located at a "compromise" CORA. What is the expected anatomic result at the osteotomy site?

. Anatomic collinearity without translation
. Anatomic collinearity with an induced angular deformity
. Overall mechanical axis correction with local translation at the osteotomy
. Overall mechanical axis correction with an induced rotational mismatch
. Failure to correct the mechanical axis deviation

Correct Answer & Explanation

. Overall mechanical axis correction with local translation at the osteotomy

Explanation

When correcting a multi-apical deformity using a single osteotomy at a calculated compromise CORA, the overall mechanical axis of the limb is restored. However, because the cut is not at the true local apices, an obligatory translational deformity will occur at the osteotomy site.

Question 2725

Topic: Biology, Genetics & Bone Healing

A 14-year-old undergoes tibial lengthening. At the two-week follow-up, radiographs show premature consolidation of the regenerate bone. Which of the following is the most appropriate initial management?

. Abandon the lengthening and remove the frame immediately
. Acutely increase the distraction rate or perform acute distraction under anesthesia
. Perform an immediate open osteoclasis with a saw
. Administer bisphosphonates to inhibit osteoblast activity
. Decrease the distraction rate to 0.5 mm/day

Correct Answer & Explanation

. Acutely increase the distraction rate or perform acute distraction under anesthesia

Explanation

Premature consolidation occurs when bone heals faster than the distraction rate. The initial management is to acutely increase the distraction rhythm (e.g., up to 2 mm/day) or perform an acute frame distraction under anesthesia to break the early consolidation.

Question 2726

Topic: 1. General Principles & Basic Science

The Taylor Spatial Frame utilizes a specialized 6-axis deformity correction software. Which of the following parameters is absolutely required by the software to accurately correct the structural deformity?

. Joint Line Congruency Angle (JLCA)
. The diameter of the intramedullary canal
. Mounting parameters (AP and Lateral view frame offsets)
. The patient's absolute body weight and height
. Mechanical axis deviation measured exclusively in millimeters

Correct Answer & Explanation

. Mounting parameters (AP and Lateral view frame offsets)

Explanation

The Taylor Spatial Frame software requires exact inputs of deformity parameters, frame parameters, and mounting parameters. Mounting parameters define the spatial relationship of the reference ring relative to the bone origin and are critical for generating a correct strut prescription.

Question 2727

Topic: 1. General Principles & Basic Science

When digitally planning a deformity correction using standard radiographs without a magnification marker, what error is most likely to occur in preoperative templating?

. Incorrect calculation of the angular deformity magnitude
. Incorrect calculation of the CORA location
. Incorrect calculation of required translation in millimeters
. Incorrect calculation of the Joint Line Congruency Angle (JLCA)
. Incorrect assessment of the Mechanical Axis Deviation direction

Correct Answer & Explanation

. Incorrect calculation of required translation in millimeters

Explanation

Angular measurements (e.g., CORA angles, mLDFA, mMPTA) are independent of radiographic magnification. However, linear measurements such as translation distances, leg length discrepancies, and absolute MAD in millimeters will be highly inaccurate without a known magnification marker.

Question 2728

Topic: 1. General Principles & Basic Science

According to Paley's principles, if a single-cut osteotomy is planned for angular correction, but the surgeon intentionally translates the distal segment laterally, what effect does this have on the overall mechanical axis?

. It creates an unintended procurvatum deformity
. It modifies the required rate of bone distraction
. It shifts the mechanical axis laterally without changing the anatomic axis angle
. It shifts both the mechanical and anatomic axes medially
. It has absolutely no effect on the final mechanical axis

Correct Answer & Explanation

. It shifts the mechanical axis laterally without changing the anatomic axis angle

Explanation

Pure translation of a bone segment shifts the mechanical axis parallel to its original path in the direction of the translation. Intentionally translating the distal segment laterally shifts the limb's mechanical axis laterally, a technique sometimes used to further unload a medial compartment.

Question 2729

Topic: 1. General Principles & Basic Science

A 24-year-old patient presents with a uniapical varus tibial deformity. Radiographic analysis identifies a single Center of Rotation of Angulation (CORA). If the surgeon places the osteotomy at a different level than the CORA, but places the hinge axis exactly on the CORA, what will be the resulting correction pattern according to Paley's principles?

. Pure angular correction without translation
. Angular correction with collinear axis but translation of bone ends at osteotomy site
. Translation of mechanical axis without angular correction
. Angular correction resulting in translation of the mechanical axis
. Pure translation with no angular correction

Correct Answer & Explanation

. Angular correction with collinear axis but translation of bone ends at osteotomy site

Explanation

Paley's Osteotomy Rule 2 states that if the hinge is placed at the CORA and the osteotomy is at a different level, the mechanical axes will realign collinear. However, the bone ends will translate at the osteotomy site as a consequence.

Question 2730

Topic: 1. General Principles & Basic Science

When evaluating a patient with a lower extremity deformity, the mechanical Lateral Distal Femoral Angle (mLDFA) and mechanical Medial Proximal Tibial Angle (mMPTA) are calculated. What are the accepted normal values for mLDFA and mMPTA, respectively?

. 85 degrees and 90 degrees
. 88 degrees and 87 degrees
. 93 degrees and 81 degrees
. 90 degrees and 90 degrees
. 81 degrees and 87 degrees

Correct Answer & Explanation

. 88 degrees and 87 degrees

Explanation

The normal mean mLDFA is approximately 88 degrees (range 85-90), and the normal mMPTA is 87 degrees (range 85-90). These angles are crucial for determining whether a mechanical axis deviation is femoral or tibial in origin.

Question 2731

Topic: 1. General Principles & Basic Science

A surgeon is correcting a distal femoral valgus deformity. The osteotomy and the hinge are both placed proximal to the CORA. According to Paley's Rule 3, what is the biomechanical consequence of this setup upon completing the angular correction?

. The mechanical axis of the proximal and distal segments will be collinear
. The mechanical axis of the proximal and distal segments will be parallel but translated
. Pure translation without angular change will occur
. The bone ends will translate but the mechanical axis will remain uncorrected
. The joint line will become oblique but the axis collinear

Correct Answer & Explanation

. The mechanical axis of the proximal and distal segments will be parallel but translated

Explanation

Paley's Rule 3 states that if both the osteotomy and the hinge are placed away from the CORA, angular correction will result in the proximal and distal mechanical axes becoming parallel but translated, rather than collinear.

Question 2732

Topic: 1. General Principles & Basic Science

What is the defining characteristic of a true multiapical deformity when performing the Malalignment Test for the lower extremity?

. The mechanical axis passes perfectly through the center of the knee
. The anatomical axis lines intersect at a single point
. The proximal and distal mechanical axes do not intersect at the clinical apex of deformity
. A single CORA is found exactly on the joint line
. The mLDFA and mMPTA are both within normal limits

Correct Answer & Explanation

. The proximal and distal mechanical axes do not intersect at the clinical apex of deformity

Explanation

In a multiapical deformity, drawing the proximal and distal mechanical axis lines will result in an intersection (apparent CORA) that does not match the actual clinical levels of deformity, necessitating mid-diaphyseal lines to find multiple true CORAs.

Question 2733

Topic: 1. General Principles & Basic Science

In calculating the anatomical axis of the femur in the sagittal plane for deformity correction, which of the following is the standard reference line?

. A line connecting the center of the femoral head and center of the knee
. A mid-diaphyseal line drawn on the true lateral radiograph
. A line parallel to the anterior femoral cortex
. A line drawn parallel to the posterior femoral condyles
. A line connecting the greater trochanter to the lateral epicondyle

Correct Answer & Explanation

. A mid-diaphyseal line drawn on the true lateral radiograph

Explanation

The anatomical axis of the femur in the sagittal plane is typically defined by a mid-diaphyseal line connecting the midpoints of the medullary canal at different levels on a true lateral radiograph.

Question 2734

Topic: 1. General Principles & Basic Science

A patient is undergoing femoral lengthening with a monolateral external fixator. Radiographs at 4 weeks show very sparse, wispy regenerate bone. What is the most appropriate modification to the distraction protocol?

. Increase the distraction rate to 1.5 mm/day
. Decrease the distraction rate to 0.5 mm/day or perform an accordion maneuver
. Perform bone grafting of the regenerate gap immediately
. Switch to a circular frame construct
. Begin weight-bearing as tolerated without frame modification

Correct Answer & Explanation

. Decrease the distraction rate to 0.5 mm/day or perform an accordion maneuver

Explanation

Poor or sparse regenerate (hypotrophic regenerate) suggests the bone healing response is lagging behind the mechanical distraction. The most appropriate initial step is to decrease the distraction rate or compress the site (accordion technique) to stimulate osteogenesis.

Question 2735

Topic: 1. General Principles & Basic Science

A 16-year-old female presents with a limb length discrepancy (LLD). The Paley Multiplier method is chosen to predict her discrepancy at skeletal maturity. This method primarily relies on which of the following parameters?

. The patient's current chronologic age and LLD
. The patient's bone age, current LLD, and a gender-specific multiplier
. Serial radiographs taken over 3 consecutive years
. A standard nomogram using the patient's height and weight
. The difference between the anatomical and mechanical axes

Correct Answer & Explanation

. The patient's bone age, current LLD, and a gender-specific multiplier

Explanation

The Paley Multiplier method predicts limb length discrepancy at maturity using a formula that multiplies the current discrepancy by a specific, gender- and bone-age-dependent coefficient.

Question 2736

Topic: 1. General Principles & Basic Science

During preoperative planning for a proximal tibial varus deformity, the magnitude of the deformity is 15 degrees. If the hinge is placed 1 cm lateral to the CORA on the bisector line, what will occur during angular correction?

. 15 degrees of angular correction and lateral translation of the distal segment
. 15 degrees of angular correction and medial translation of the distal segment
. 15 degrees of angular correction with no translation
. Pure medial translation without angular correction
. Pure lateral translation without angular correction

Correct Answer & Explanation

. 15 degrees of angular correction and medial translation of the distal segment

Explanation

Placing the hinge away from the CORA on the bisector line (Paley Rule 3) results in angular correction accompanied by translation. A hinge placed lateral to the CORA during varus correction will force the distal segment to translate medially.

Question 2737

Topic: 1. General Principles & Basic Science

A 30-year-old male has an oblique plane deformity of the tibia. Radiographs show 10 degrees of varus on the AP view and 10 degrees of apex anterior (procurvatum) on the lateral view. What is the true magnitude of the deformity in the oblique plane?

. 10 degrees
. 14.1 degrees
. 20 degrees
. 100 degrees
. 7.1 degrees

Correct Answer & Explanation

. 14.1 degrees

Explanation

For an oblique plane deformity, the true magnitude can be calculated using the Pythagorean theorem: the square root of (10^2 + 10^2) equals the square root of 200, which is approximately 14.1 degrees.

Question 2738

Topic: Biology, Genetics & Bone Healing

The latency period in distraction osteogenesis refers to the time between the osteotomy and the initiation of distraction. What is the primary biological purpose of this period?

. To allow soft tissues to heal and reduce infection risk
. To permit the hematoma to organize and early callus to form
. To ensure the external fixator pins are osteointegrated
. To allow the patient to adjust to the weight of the frame
. To prevent premature consolidation of the osteotomy

Correct Answer & Explanation

. To permit the hematoma to organize and early callus to form

Explanation

The latency period (typically 5-7 days) allows the initial fracture hematoma to organize, mesenchymal stem cells to migrate, and the early stages of woven bone callus to form before mechanical stretching begins.

Question 2739

Topic: 1. General Principles & Basic Science

When addressing a rotational deformity of the femur along with an angular deformity, a transverse osteotomy is planned. Which of the following statements regarding the axis of correction is true?

. The hinge must be placed perpendicular to the mechanical axis
. The angular and rotational corrections must be done at separate levels
. Rotational correction does not affect the mechanical axis deviation (MAD)
. If rotation is corrected at a level other than the CORA, it will induce a secondary angular deformity
. Rotational correction at the CORA requires an oblique osteotomy

Correct Answer & Explanation

. If rotation is corrected at a level other than the CORA, it will induce a secondary angular deformity

Explanation

In a bone with an existing bow or angular deformity, rotating the bone at a level other than the apex of the bow (CORA) will alter the plane of the deformity and predictably induce secondary translation or angular changes.

Question 2740

Topic: 1. General Principles & Basic Science

A patient requires correction of a uniapical diaphyseal tibial deformity. The surgeon plans the osteotomy and places the hinge exactly at the Center of Rotation of Angulation (CORA). According to Paley's rules, what is the expected outcome?

. Pure angular correction without translation
. Angular correction accompanied by translation
. Pure translation without angular correction
. Creation of a secondary translation deformity
. Correction of the mechanical axis with obligate limb shortening

Correct Answer & Explanation

. Pure angular correction without translation

Explanation

According to Paley's Rule 1, when the osteotomy and the hinge are both located exactly at the Center of Rotation of Angulation (CORA), pure angular correction is achieved collinearly without any translation.

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