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1. General Principles & Basic Science MCQs

Practice Set 138 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 2741

Topic: 1. General Principles & Basic Science

A surgeon performs a proximal tibial deformity correction. The hinge is placed correctly at the CORA, but the osteotomy cut is performed 3 cm proximal to the CORA. Which of the following describes the biomechanical result according to Paley's Rule 2?

. Pure angular correction without translation.
. Angular correction accompanied by translation of the axis.
. Creation of a secondary zig-zag deformity.
. Inability to correct the Mechanical Axis Deviation (MAD).
. Pure translational correction without angular change.

Correct Answer & Explanation

. Angular correction accompanied by translation of the axis.

Explanation

Paley's Rule 2 states that if the hinge is placed at the CORA but the osteotomy is performed at a different level, the result is angular correction accompanied by translation of the bone ends. This still successfully aligns the mechanical axis.

Question 2742

Topic: 1. General Principles & Basic Science

When analyzing a standing AP radiograph of a normal lower extremity, what is the expected relationship between the anatomic axis and the mechanical axis of the femur?

. They are perfectly parallel and collinear.
. The anatomic axis diverges approximately 2 degrees from the mechanical axis.
. The anatomic axis diverges approximately 7 degrees from the mechanical axis.
. The mechanical axis diverges 15 degrees from the anatomic axis.
. They intersect exactly at the center of the lesser trochanter.

Correct Answer & Explanation

. The anatomic axis diverges approximately 7 degrees from the mechanical axis.

Explanation

The mechanical axis of the femur connects the center of the femoral head to the center of the knee. The anatomic axis runs down the intramedullary canal, normally diverging from the mechanical axis by about 7 degrees (range 5-9 degrees).

Question 2743

Topic: Biology, Genetics & Bone Healing

A 16-year-old male is undergoing tibial lengthening via distraction osteogenesis. At week 4, radiographs reveal an 'hourglass' appearance to the regenerate bone with a lucent central gap. What is the most appropriate next step in management?

. Proceed with immediate autologous bone grafting.
. Increase the distraction rate to 1.5 mm/day.
. Decrease the distraction rate or perform the accordion maneuver.
. Stop distraction completely and immediately remove the frame.
. Administer intravenous bisphosphonates to enhance mineralization.

Correct Answer & Explanation

. Decrease the distraction rate or perform the accordion maneuver.

Explanation

An hourglass appearance with a widening central lucent gap indicates poor regenerate formation, usually due to a distraction rate that is too fast. Management involves decreasing the rate or using the accordion maneuver (compressing then distracting) to stimulate osteogenesis.

Question 2744

Topic: 1. General Principles & Basic Science

During a femoral lengthening procedure using an external fixator, a patient develops a progressive knee flexion contracture. Which of the following muscle groups is primarily responsible for this specific complication?

. Gastrocnemius and soleus
. Vastus intermedius and medialis
. Hamstrings and Iliotibial band
. Adductor longus and brevis
. Gluteus maximus and medius

Correct Answer & Explanation

. Hamstrings and Iliotibial band

Explanation

During femoral lengthening, tension increases across two-joint muscles spanning the femur, particularly the hamstrings, rectus femoris, and iliotibial band. This increased tension commonly leads to progressive knee flexion contractures if not aggressively managed with therapy.

Question 2745

Topic: 1. General Principles & Basic Science

In Paley's multiplier method for predicting limb length discrepancy (LLD) at skeletal maturity, the multiplier is derived primarily based on which two patient variables?

. Current LLD and chronological age
. Current height and weight
. Gender and chronological age
. Gender and skeletal age
. Current LLD and skeletal age

Correct Answer & Explanation

. Gender and chronological age

Explanation

The Paley multiplier method relies on gender and chronological age to determine a specific multiplier constant. This multiplier is then applied to current limb length measurements to accurately predict length at skeletal maturity.

Question 2746

Topic: 1. General Principles & Basic Science

A patient requires 6-axis deformity correction using a Taylor Spatial Frame (TSF). The surgeon must input accurate 'mounting parameters' into the software. What do these parameters precisely describe?

. The relationship between the origin of the frame and the origin of the deformity.
. The exact length of the six struts prior to deformity correction.
. The relationship between the reference ring and the reference bone fragment.
. The total amount of daily distraction required to heal the bone.
. The chronologic age and gender of the patient for multiplier calculation.

Correct Answer & Explanation

. The relationship between the reference ring and the reference bone fragment.

Explanation

In TSF software, mounting parameters specifically define the exact position and orientation of the reference ring in relation to its corresponding reference bone fragment. Accurate mounting parameters are critical for generating the correct strut adjustment schedule.

Question 2747

Topic: 1. General Principles & Basic Science

A 50-year-old male undergoes a medial opening wedge high tibial osteotomy (HTO) for a varus knee deformity. Postoperatively, he has a significant unintended decrease in his posterior tibial slope. Which surgical technique error most likely caused this?

. Opening the osteotomy more anteriorly than posteriorly.
. Placing the lateral hinge too proximal.
. Opening the osteotomy more posteriorly than anteriorly.
. Resecting too much of the fibular head.
. Over-correcting the mechanical axis into valgus.

Correct Answer & Explanation

. Opening the osteotomy more posteriorly than anteriorly.

Explanation

The proximal tibia has a triangular cross-section. Opening a medial wedge osteotomy evenly often results in an unintended increase in anterior opening relative to posterior opening, which decreases the posterior tibial slope (creating relative recurvatum).

Question 2748

Topic: 1. General Principles & Basic Science

A 14-year-old male is undergoing deformity correction for a mid-diaphyseal tibial varus deformity. The surgeon plans the osteotomy according to Paley's Rule 1. Which of the following accurately describes the relationship between the Center of Rotation of Angulation (CORA), the osteotomy site, and the resultant correction?

. Osteotomy is distant to the CORA, hinge is at the CORA, resulting in angulation and translation.
. Osteotomy is at the CORA, hinge is at the CORA, resulting in pure angulation without translation.
. Osteotomy is distant to the CORA, hinge is distant to the CORA, resulting in pure translation.
. Osteotomy is at the CORA, hinge is distant to the CORA, resulting in translation and angulation.
. Osteotomy and hinge are at the CORA, resulting in pure translation.

Correct Answer & Explanation

. Osteotomy is at the CORA, hinge is at the CORA, resulting in pure angulation without translation.

Explanation

Paley's Rule 1 states that if the osteotomy and the hinge (axis of correction) are both placed at the CORA, the bone will realign with pure angular correction and no translation. This restores a collinear mechanical axis.

Question 2749

Topic: 1. General Principles & Basic Science

A 30-year-old male presents with a complex post-traumatic tibial deformity. Radiographic planning reveals that the proximal mechanical axis line and the distal mechanical axis line do not intersect within the confines of the diaphyseal bone. Based on Paley's principles, what is the most appropriate interpretation of this geometric finding?

. The deformity is entirely translational without any angular component.
. There is a single Center of Rotation of Angulation (CORA) located in the adjacent joint space.
. The patient has a concurrent rotational deformity that obscures the coronal plane axes.
. A multi-apical deformity is present, requiring the drawing of a mid-diaphyseal line to define two distinct CORAs.
. Osteotomy should be performed parallel to the joint line regardless of the axis intersection.

Correct Answer & Explanation

. A multi-apical deformity is present, requiring the drawing of a mid-diaphyseal line to define two distinct CORAs.

Explanation

When the proximal and distal mechanical axis lines do not intersect within the deformed bone segment, it signifies a multi-apical deformity (or a combination of marked translation and angulation). Planning requires drawing an additional mid-diaphyseal axis line to identify multiple CORAs for sequential or multi-level correction.

Question 2750

Topic: Biomechanics & Biomaterials



A 19-year-old male requires correction of a complex distal tibial deformity characterized by varus, procurvatum, internal rotation, and 2 cm of shortening. The surgeon elects to use a hexapod circular fixator (e.g., Taylor Spatial Frame). What is the primary biomechanical advantage of this device over a traditional Ilizarov frame for this multidimensional deformity?

. It relies strictly on manual hinge placement at the exact CORA for successful angular correction.
. It allows simultaneous correction of all six degrees of freedom utilizing a virtual hinge and software program.
. It eliminates the risk of pin-tract infections due to the use of hydroxyapatite-coated wires exclusively.
. It requires a faster distraction rate (2.0 mm/day) because the frame struts are inherently dynamic.
. It negates the need for an osteotomy if the deformity is within 5 centimeters of the joint line.

Correct Answer & Explanation

. It allows simultaneous correction of all six degrees of freedom utilizing a virtual hinge and software program.

Explanation

The Taylor Spatial Frame (hexapod system) utilizes computer software to create a 'virtual hinge' in space. This allows for the simultaneous, gradual correction of complex deformities in all six degrees of freedom (angulation, translation, and rotation across all planes) without requiring complex, physical hinge adjustments.

Question 2751

Topic: Surgical Anatomy & Approaches

A patient presents with a distal tibial valgus deformity. The CORA is located 8 cm proximal to the ankle joint. Due to concerns about soft tissue envelope and neurovascular structures, the surgeon decides to perform the osteotomy 3 cm proximal to the CORA, but meticulously places the hinge of the external fixator precisely at the CORA.

Based on Paley's osteotomy rules, what is the expected outcome of this surgical approach?

. The correction will be purely angular, with no translation required.
. An undesirable secondary translation deformity will be induced.
. The correction will require both angulation and a planned translation to achieve proper alignment.
. The deformity will be overcorrected, leading to an iatrogenic varus.
. The osteotomy will heal with delayed union due to the distance from the CORA.

Correct Answer & Explanation

. The correction will require both angulation and a planned translation to achieve proper alignment.

Explanation

Correct Answer: CThis scenario applies Paley's Osteotomy Rule 2: 'When the osteotomy is performedaway from the CORA, but the hinge is placedat the CORA, the correction requires both angulation and translation to realign the mechanical axis perfectly.' In this case, the osteotomy is 3 cm proximal to the CORA, but the hinge is at the CORA, necessitating a planned translation in addition to angulation for a successful correction.Option A describes Paley's Rule 1. Option B describes Paley's Rule 3. Options D and E are not direct consequences of this specific application of Paley's Rule 2.

Question 2752

Topic: Surgical Anatomy & Approaches

A surgeon is planning a supramalleolar osteotomy (SMO) for a patient with a significant valgus deformity of the distal tibia. Radiographic templating reveals that the Center of Rotation of Angulation (CORA) is located intra-articularly, making a direct osteotomy at the CORA impossible. To achieve angular correction and simultaneously translate the distal fragment medially, which of Paley's Osteotomy Rules should the surgeon apply?

. Osteotomy Rule 1: Cut at CORA, hinge at CORA.
. Osteotomy Rule 2: Cut at a level different from CORA, hinge at CORA.
. Osteotomy Rule 3: Cut at a level different from CORA, hinge at a level different from CORA.
. Osteotomy Rule 1 and 3 combined.
. None of the above; a different surgical approach is required.

Correct Answer & Explanation

. Osteotomy Rule 2: Cut at a level different from CORA, hinge at CORA.

Explanation

Correct Answer: BThe teaching case clearly describes Paley's Osteotomy Rule 2 as the 'absolute workhorse rule for supramalleolar correction.' It states: 'If the osteotomy cut is performed at a leveldifferentfrom the CORA (e.g., higher up in the metaphysis), but the hinge of correction is still placedatthe CORA, the angulation will be perfectly corrected, but apredictable and intentional translationwill occur at the osteotomy site.' This rule allows the surgeon to perform the osteotomy in safe metaphyseal bone while achieving both angular correction and the necessary medial translation of the distal fragment, which is biomechanically essential for valgus correction.Option A is incorrectbecause Osteotomy Rule 1, while ideal for pure angular correction with zero translation, is often anatomically impossible in distal tibial deformities where the CORA is intra-articular, as cutting through the joint would destroy it.Option C is incorrectbecause Osteotomy Rule 3 is generally avoided. It results in an angular correction but also creates a new, iatrogenic translation deformity, which is usually undesirable unless specifically planned to correct a pre-existing translation.Option D is incorrectbecause combining rules 1 and 3 is not a recognized or logical application of Paley's principles for this scenario.Option E is incorrectbecause Paley's principles, specifically Rule 2, provide the precise geometric solution for this common clinical challenge.

Question 2753

Topic: 1. General Principles & Basic Science

A 40-year-old patient is being evaluated for a distal tibial deformity. The surgeon notes that the Anterior Distal Tibial Angle (ADTA) is measured at 85 degrees. Based on Paley's principles of joint orientation angles, what does this measurement indicate?

. Option A: A normal sagittal plane alignment of the distal tibia.
. Option B: A recurvatum (extension/posterior bowing) deformity of the distal tibia.
. Option C: A procurvatum (flexion/anterior bowing) deformity of the distal tibia.
. Option D: A valgus deformity of the distal tibia in the coronal plane.
. Option E: A varus deformity of the distal tibia in the coronal plane.

Correct Answer & Explanation

. Option C: A procurvatum (flexion/anterior bowing) deformity of the distal tibia.

Explanation

Correct Answer: CThe case defines the Anterior Distal Tibial Angle (ADTA) as the key angle in the sagittal plane, with a normal range of 78° to 82°. It explicitly states: 'Increased ADTA (>82°): Indicates a procurvatum (flexion/anterior bowing) deformity.' An ADTA of 85° is greater than 82°, thus indicating a procurvatum deformity.Option A is incorrectbecause the normal range for ADTA is 78-82 degrees, and 85 degrees falls outside this range.Option B is incorrectbecause a recurvatum deformity is indicated by adecreasedADTA (<78°), not an increased ADTA.Option D is incorrectbecause valgus deformity is assessed by the Lateral Distal Tibial Angle (LDTA) in the coronal plane, not the ADTA in the sagittal plane.Option E is incorrectbecause varus deformity is also assessed by the LDTA in the coronal plane, not the ADTA.

Question 2754

Topic: 1. General Principles & Basic Science

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

. Angulation corrects with intentional translation.
. Angulation corrects without any translation.
. Translation corrects without any angulation.
. A secondary compensatory deformity is created.
. The mechanical axis will remain deviated.

Correct Answer & Explanation

. Angulation corrects without any translation.

Explanation

Paley's Rule 1 states that when the osteotomy and the hinge are both located at the CORA, the angular deformity corrects completely without causing any secondary translation.

Question 2755

Topic: 1. General Principles & Basic Science

A surgeon plans to correct a distal tibial angular deformity. Due to poor soft tissue envelope at the CORA, the osteotomy is made proximal to the CORA, but the hinge (axis of rotation) remains at the CORA. What is the expected geometric result of this correction?

. Pure angular correction without translation
. Angular correction accompanied by translation of the osteotomy ends
. Pure translation without angular correction
. Creation of a secondary angular deformity in the opposite direction
. Failure to correct the mechanical axis deviation

Correct Answer & Explanation

. Angular correction accompanied by translation of the osteotomy ends

Explanation

Paley's Rule 2 states that if the hinge is placed at the CORA but the osteotomy is made at a different level, angular correction will occur alongside expected translation of the bone ends at the osteotomy site.

Question 2756

Topic: 1. General Principles & Basic Science

According to Paley's principles, what happens if both the osteotomy and the axis of rotation (hinge) are placed at a level different from the Center of Rotation of Angulation (CORA)?

. The mechanical axis will be completely restored without translation.
. A translation deformity is corrected without angular change.
. A new secondary angular deformity (translation effect) is created, worsening mechanical axis deviation.
. The angulation is corrected, but a new translation deformity is introduced.
. It results in a perfect focal dome correction.

Correct Answer & Explanation

. A new secondary angular deformity (translation effect) is created, worsening mechanical axis deviation.

Explanation

Paley's Rule 3 states that if the osteotomy and hinge are placed away from the CORA, the angular correction will inadvertently induce a secondary translation deformity, altering the mechanical axis.

Question 2757

Topic: 1. General Principles & Basic Science

A patient presents with a symptomatic varus deformity of the distal tibia (mLDTA = 100 degrees). A medial opening wedge supramalleolar osteotomy is planned. If the hinge is placed laterally at the apex of the deformity (CORA), what is the effect on the length of the limb?

. Lengthens the limb
. Shortens the limb
. No change in limb length
. Causes simultaneous translation
. Lengthens the fibula only

Correct Answer & Explanation

. Lengthens the limb

Explanation

An opening wedge osteotomy at the CORA essentially acts as an incomplete distraction osteogenesis, resulting in angular correction and a net lengthening of the affected bone segment.

Question 2758

Topic: 1. General Principles & Basic Science

A 30-year-old male has a post-traumatic distal tibia valgus deformity with a mechanical Lateral Distal Tibial Angle (mLDTA) of 75 degrees. Which of the following procedures is most appropriate to correct the deformity if limb shortening is to be avoided?

. Medial closing wedge osteotomy
. Lateral opening wedge osteotomy
. Medial opening wedge osteotomy
. Fibular lengthening alone
. Distraction osteogenesis of the proximal tibia

Correct Answer & Explanation

. Medial opening wedge osteotomy

Explanation

A medial opening wedge supramalleolar osteotomy will correct a valgus deformity (where mLDTA is abnormally low, usually <86 degrees) while avoiding the limb shortening associated with a lateral closing wedge osteotomy.

Question 2759

Topic: 1. General Principles & Basic Science

In a patient with a multi-apical (complex) bowing deformity of the tibia, how is the deformity best analyzed according to Paley's principles?

. By drawing a single line connecting the proximal and distal joint centers
. By drawing a line connecting the maximum points of bowing
. By determining multiple CORAs using the intersection of axes for each distinct bone segment
. By calculating only the total mechanical axis deviation
. By using the normal side as a mirror template without drawing axis lines

Correct Answer & Explanation

. By determining multiple CORAs using the intersection of axes for each distinct bone segment

Explanation

Multi-apical deformities require segmenting the bone into multiple straight pieces. The mechanical or anatomical axes of each adjacent segment are drawn to find multiple, distinct CORAs.

Question 2760

Topic: 1. General Principles & Basic Science

When planning a corrective osteotomy using the center of rotation of angulation (CORA) method, the magnitude of the deformity is determined by measuring what angle?

. The angle between the anatomical axis of the femur and tibia
. The angle between the proximal and distal mechanical (or anatomical) axes of the deformed bone
. The angle between the joint line and the horizontal plane
. The angle between the tibial plafond and the floor
. The alpha angle of the proximal femur

Correct Answer & Explanation

. The angle between the proximal and distal mechanical (or anatomical) axes of the deformed bone

Explanation

The magnitude of the deformity is precisely measured as the angle subtended by the intersection of the proximal and distal mechanical or anatomical axes of the affected bone.

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