Menu

1. General Principles & Basic Science MCQs

Practice Set 463 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 9241

Topic: 1. General Principles & Basic Science



A patient presents with severe osteoarthritis and a significant varus deformity. The Joint Line Convergence Angle (JLCA) measures 6 degrees (medial convergence). What does this abnormal JLCA indicate about the deformity?

. It is purely a diaphyseal deformity
. It is caused by lateral collateral ligament laxity or medial compartment cartilage loss
. The mechanical axis is translated laterally
. There is a fixed flexion deformity of the knee
. The CORA is intra-articular

Correct Answer & Explanation

. It is caused by lateral collateral ligament laxity or medial compartment cartilage loss

Explanation

A normal JLCA is 0 to 2 degrees. An increased JLCA with medial convergence in varus osteoarthritis usually indicates intra-articular deformity stemming from severe medial cartilage wear and/or lateral ligamentous laxity.

Question 9242

Topic: Surgical Anatomy & Approaches

During a massive femoral lengthening procedure, a patient develops paresthesias in the anterolateral thigh and knee, alongside isolated weakness in knee extension. Which nerve is most likely experiencing a stretch injury?

. Sciatic nerve
. Common peroneal nerve
. Saphenous nerve
. Femoral nerve
. Lateral femoral cutaneous nerve

Correct Answer & Explanation

. Femoral nerve

Explanation

Weakness in knee extension (quadriceps) along with anterolateral thigh/knee sensory changes indicates a femoral nerve stretch injury. While sciatic nerve stretch is more common in limb lengthening, isolated quadriceps weakness distinctly localizes to the femoral nerve.

Question 9243

Topic: 1. General Principles & Basic Science

When evaluating sagittal alignment of the femur, the mechanical posterior distal femoral angle (mPDFA) is assessed. Which of the following values represents the normal anatomical range for the mPDFA?

. 79 to 83 degrees
. 83 to 87 degrees
. 87 to 90 degrees
. 90 to 95 degrees
. 95 to 100 degrees

Correct Answer & Explanation

. 83 to 87 degrees

Explanation

The normal mechanical posterior distal femoral angle (mPDFA) typically averages 83 degrees, with a normal range between 83 and 87 degrees. Values outside this range signify a procurvatum or recurvatum deformity.

Question 9244

Topic: 1. General Principles & Basic Science



According to Paley's rules of deformity correction, if an osteotomy is performed at a level different from the Center of Rotation of Angulation (CORA), but the hinge is placed exactly at the CORA (Rule 2), what is the expected biomechanical outcome?

. Pure angulation without translation
. Angulation with translation that realigns the mechanical axis
. Pure translation without angular correction
. Creation of a secondary translation deformity
. Lengthening without angular or translational correction

Correct Answer & Explanation

. Angulation with translation that realigns the mechanical axis

Explanation

Under Paley's Rule 2, placing the hinge at the CORA but the osteotomy at a different level results in simultaneous angulation and translation at the osteotomy site. This translation is intended and perfectly realigns the mechanical axis.

Question 9245

Topic: Biology, Genetics & Bone Healing

During distraction osteogenesis of the tibia using a circular fixator, a patient develops premature consolidation of the regenerate bone. What is the most appropriate initial management?

. Abandon the procedure and perform open bone grafting
. Increase the rate of distraction to 2 mm/day temporarily
. Perform a closed osteoclasis under anesthesia
. Remove the frame and apply a long leg cast
. Administer systemic bisphosphonates

Correct Answer & Explanation

. Perform a closed osteoclasis under anesthesia

Explanation

Premature consolidation occurs when the bone healing outpaces the distraction rate. The initial treatment of choice is closed osteoclasis (breaking the regenerate manually under anesthesia) to resume distraction.

Question 9246

Topic: 1. General Principles & Basic Science

In assessing lower limb coronal alignment using standard nomenclature, the normal mechanical lateral distal femoral angle (mLDFA) and medial proximal tibial angle (MPTA) are approximately:

. mLDFA 88 degrees, MPTA 87 degrees
. mLDFA 93 degrees, MPTA 82 degrees
. mLDFA 81 degrees, MPTA 95 degrees
. mLDFA 87 degrees, MPTA 90 degrees
. mLDFA 90 degrees, MPTA 90 degrees

Correct Answer & Explanation

. mLDFA 88 degrees, MPTA 87 degrees

Explanation

Normal population averages dictate that the mechanical lateral distal femoral angle (mLDFA) is 88 degrees and the medial proximal tibial angle (MPTA) is 87 degrees. These are critical reference angles for deformity planning.

Question 9247

Topic: 1. General Principles & Basic Science



When correcting a complex uniplanar deformity, if the osteotomy and the hinge are both placed away from the Center of Rotation of Angulation (CORA) (Paley's Rule 3), what is the inevitable biomechanical outcome?

. Perfect realignment of the mechanical axis without translation
. A collinear mechanical axis with a new translation deformity at the osteotomy site
. The creation of a secondary translation deformity that misaligns the mechanical axis
. Joint line obliquity exceeding 10 degrees
. Premature consolidation of the regenerate

Correct Answer & Explanation

. The creation of a secondary translation deformity that misaligns the mechanical axis

Explanation

Paley's Rule 3 states that if the hinge and osteotomy are outside the CORA, it results in a translation effect that creates a secondary deformity. The mechanical axis will remain misaligned unless an independent translation correction is applied.

Question 9248

Topic: 1. General Principles & Basic Science

A 14-year-old male presents with anterior knee pain and an out-toeing gait. Examination shows hip internal rotation of 10 degrees and external rotation of 80 degrees. The mechanical axis is neutral. What deformity is most likely present and what is the optimal correction?

. Femoral retroversion requiring internal rotation osteotomy
. Femoral anteversion requiring external rotation osteotomy
. Tibial external torsion requiring internal rotation osteotomy
. Tibial internal torsion requiring external rotation osteotomy
. Femoral retroversion requiring external rotation osteotomy

Correct Answer & Explanation

. Femoral retroversion requiring internal rotation osteotomy

Explanation

Increased hip external rotation with restricted internal rotation points to femoral retroversion. The definitive surgical management for symptomatic femoral retroversion is a derotational (internal rotation) femoral osteotomy.

Question 9249

Topic: 1. General Principles & Basic Science

When planning a single-stage correction of an oblique plane deformity (combined varus and recurvatum) in the proximal tibia, the true axis of the deformity is determined by:

. The sum of the coronal and sagittal angle magnitudes
. The geometric tangent of the sagittal over coronal plane deformities
. Vector addition calculating the magnitude and direction using a trigonometric or graphical method
. Performing independent osteotomies in both planes
. Utilizing the mechanical axis deviation in the coronal plane only

Correct Answer & Explanation

. Vector addition calculating the magnitude and direction using a trigonometric or graphical method

Explanation

An oblique plane deformity represents a single true deformity that projects onto the coronal and sagittal planes. Its true magnitude and direction are calculated via vector addition, allowing correction with a single osteotomy.

Question 9250

Topic: 1. General Principles & Basic Science

A patient undergoing tibial lengthening with a circular fixator develops erythema, induration, and purulent discharge around a proximal wire site. Radiographs show no lucency around the wire. According to the Checketts-Otburn classification, what is the appropriate management for this Grade 2 pin site infection?

. Immediate wire removal and IV antibiotics
. Local pin care and oral antibiotics
. Surgical debridement and frame removal
. Exchange of the wire and local debridement
. Observation and local pin care only

Correct Answer & Explanation

. Local pin care and oral antibiotics

Explanation

Checketts-Otburn Grade 2 infections involve soft tissue inflammation and purulent discharge without radiographic bone involvement. They are successfully treated with intensified local pin care and oral antibiotics.

Question 9251

Topic: Biomechanics & Biomaterials

In utilizing a hexapod circular fixator (e.g., Taylor Spatial Frame) for lower limb deformity correction, the concept of "chronic automation" relies primarily on which of the following mathematical principles?

. Paley's Rule of 2s
. The Stewart platform and 6 degrees of freedom kinematics
. The Pauwels classification of mechanical stress
. The Euler-Bernoulli beam theory
. The Hueter-Volkmann law

Correct Answer & Explanation

. The Stewart platform and 6 degrees of freedom kinematics

Explanation

Hexapod fixators are based on the Stewart-Gough platform, utilizing 6 degrees of freedom kinematics. This mathematical foundation allows simultaneous correction of multiplanar deformities through software-driven strut adjustments.

Question 9252

Topic: 1. General Principles & Basic Science

A 14-year-old boy is undergoing correction of a severe varus deformity in the tibial diaphysis. The Center of Rotation of Angulation (CORA) is correctly identified. The surgeon performs the osteotomy 4 cm distal to the CORA but places the hinge axis of the external fixator exactly on the CORA. According to Paley's Rule 2 of deformity correction, what is the expected geometric outcome once angular correction is achieved?

. The mechanical axes will remain parallel but translated, without any translation of the bone ends.
. The mechanical axes will be collinear, but the bone ends will translate relative to each other at the osteotomy site.
. The mechanical axes will be collinear, with perfect anatomical alignment of the bone ends.
. The deformity will inadvertently transition into a procurvatum deformity without coronal translation.

Correct Answer & Explanation

. The mechanical axes will be collinear, but the bone ends will translate relative to each other at the osteotomy site.

Explanation

Paley's Rule 2 states that if the osteotomy is performed at a different level than the CORA, but the hinge is placed exactly at the CORA, the mechanical axes will fully align (become collinear), but the anatomical bone ends will translate relative to each other.

Question 9253

Topic: 1. General Principles & Basic Science

A surgeon is planning to correct a tibial deformity. According to Paley's Rule 2 of deformity correction, if the hinge axis is placed exactly on the Center of Rotation of Angulation (CORA) but the osteotomy is performed at a different level (proximal or distal to the CORA), what is the expected geometric outcome at the osteotomy site?

. Pure angulation without translation
. Angulation and translation
. Pure translation without angulation
. Deformity of the mechanical axis without joint parallelity
. Alteration of the joint line convergence angle only

Correct Answer & Explanation

. Angulation and translation

Explanation

According to Paley's Rule 2, if the hinge is placed at the CORA but the osteotomy is at a different level, the correction will result in both angulation and translation at the osteotomy site. This simultaneous translation and angulation successfully realigns the mechanical axis without introducing a secondary translation deformity.

Question 9254

Topic: Physiology & Rehabilitation

A patient presents with a severe procurvatum deformity of the proximal tibia (apex anterior angulation) due to a prior unreduced fracture. Which of the following compensatory gait abnormalities is mechanically most likely to be observed?

. Increased ankle dorsiflexion during the late stance phase
. Severe genu recurvatum during the stance phase
. A functional knee flexion contracture during the stance phase
. A hip extension thrust during the swing phase
. An excessive internal foot progression angle

Correct Answer & Explanation

. A functional knee flexion contracture during the stance phase

Explanation

A procurvatum deformity of the proximal tibia tilts the tibial plateau posteriorly relative to the mechanical axis, mechanically mimicking a knee flexion contracture. This limits full extension during the stance phase of gait, causing the patient to compensate by walking with a continuously flexed knee.

Question 9255

Topic: 1. General Principles & Basic Science

When utilizing a hexapod external fixator (e.g., Taylor Spatial Frame) to correct a multiplanar deformity, accurate input of mounting parameters is critical. Which of the following best defines the 'rotary frame offset' parameter?

. The distance from the center of the reference ring to the mechanical axis in the coronal plane
. The axial distance between the reference ring and the planned osteotomy site
. The rotational difference between the anterior master tab of the reference ring and the true anterior-posterior axis of the bone
. The degree of internal or external rotation of the distal bone segment relative to the proximal segment
. The angulation of the reference ring relative to the mechanical axis in the sagittal plane

Correct Answer & Explanation

. The rotational difference between the anterior master tab of the reference ring and the true anterior-posterior axis of the bone

Explanation

The rotary frame offset specifically accounts for the rotational misalignment between the master tab on the reference ring and the true sagittal (anterior-posterior) axis of the reference bone segment. Incorrect measurement of this offset will result in unintended rotational malalignment during the automated correction process.

Question 9256

Topic: 1. General Principles & Basic Science

According to Paley's principles of deformity correction, if the osteotomy is performed at a different level than the Center of Rotation of Angulation (CORA) but the hinge is placed exactly on the CORA, what is the geometric result after correction?

. The mechanical axes will align collinearly, but translation will occur at the osteotomy site.
. The mechanical axes will remain parallel and translated, with no angulation.
. The mechanical axes will be collinear, and the bone ends will have pure rotational correction.
. The mechanical axes will translate, and angular deformity will persist.
. Pure angular correction will occur without any translation at the osteotomy site.

Correct Answer & Explanation

. The mechanical axes will align collinearly, but translation will occur at the osteotomy site.

Explanation

Paley's Rule 2 states that when the hinge is at the CORA but the osteotomy is outside the CORA, the bone axes will become collinear. However, this relies on an obligatory translation occurring at the osteotomy site to achieve this alignment.

Question 9257

Topic: 1. General Principles & Basic Science

A surgeon is planning a corrective osteotomy for a tibial diaphyseal deformity. According to Paley's principles (Rule 2), if the hinge axis is placed exactly at the Center of Rotation of Angulation (CORA) but the osteotomy is performed at a different level, what is the expected biomechanical outcome?

. Pure angular correction with no translation at the osteotomy site.
. Angulation and translation at the osteotomy site, resulting in collinear mechanical axes.
. Parallel displacement of the mechanical axes without angular correction.
. Angulation and translation at the osteotomy site, resulting in parallel but displaced mechanical axes.
. Complete anatomical realignment but persistent mechanical axis deviation.

Correct Answer & Explanation

. Angulation and translation at the osteotomy site, resulting in collinear mechanical axes.

Explanation

Paley's Rule 2 states that if the osteotomy is at a different level than the CORA but the hinge axis remains at the CORA, the result is angulation and translation at the osteotomy site. This maintains collinear mechanical axes of the proximal and distal segments.

Question 9258

Topic: 1. General Principles & Basic Science

When evaluating a sagittal plane deformity of the distal tibia using standard lateral radiographs, what is the generally accepted normal value for the mechanical posterior distal tibial angle (mPDTA)?

. 70 degrees
. 80 degrees
. 87 degrees
. 90 degrees
. 95 degrees

Correct Answer & Explanation

. 80 degrees

Explanation

The normal mechanical posterior distal tibial angle (mPDTA) is approximately 80 degrees (range 78-82 degrees). Accurately assessing this angle is critical for planning corrections of recurvatum or procurvatum deformities.

Question 9259

Topic: 1. General Principles & Basic Science

A surgeon applies Paley's Rule 3 during a deformity correction, placing both the osteotomy and the hinge axis at a location distant from the Center of Rotation of Angulation (CORA). What is the expected biomechanical consequence of this configuration?

. Collinear alignment of the proximal and distal mechanical axes.
. Parallel displacement (translation) of the mechanical axes, creating a secondary deformity.
. Pure translation without any angular correction.
. Creation of an intra-articular step-off.
. Correction of limb length without altering the mechanical axis.

Correct Answer & Explanation

. Parallel displacement (translation) of the mechanical axes, creating a secondary deformity.

Explanation

Paley's Rule 3 dictates that if the hinge and osteotomy are placed away from the CORA, angular correction occurs, but the proximal and distal mechanical axes will be parallel and translated. This introduces a secondary translation deformity.

Question 9260

Topic: Biology, Genetics & Bone Healing

A 35-year-old patient is undergoing tibial lengthening via distraction osteogenesis (Ilizarov technique) at a standard rate of 1 mm/day. Radiographs at 6 weeks reveal a central radiolucent fibrous interzone of 9 mm with poor regenerate bone formation. What is the most appropriate next step in management?

. Increase the distraction rate to 1.5 mm/day to stimulate the periosteum.
. Proceed immediately with autologous iliac crest bone grafting.
. Perform an accordion maneuver (sequential compression and distraction).
. Remove the external fixator and transition to a patellar tendon-bearing cast.
. Administrate low-dose bisphosphonates to prevent regenerate resorption.

Correct Answer & Explanation

. Perform an accordion maneuver (sequential compression and distraction).

Explanation

Delayed consolidation or poor regenerate during distraction osteogenesis is effectively managed with the accordion maneuver. This process of alternating compression and distraction stimulates local angiogenesis and enhances osteogenesis.

Test Yourself

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

On this Page