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1. General Principles & Basic Science MCQs

Practice Set 145 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 2881

Topic: 1. General Principles & Basic Science

A 35-year-old female requires correction of a distal femoral deformity. The CORA is identified near the articular surface, making an osteotomy at the CORA structurally unfavorable. The surgeon decides to place the hinge at the CORA but performs the osteotomy 4 cm proximal to it. According to Paley's Rule 2, what is the expected outcome?

. The mechanical axes will not realign, creating a secondary rotational deformity
. The mechanical axes will realign, but there will be translation of the bone ends at the osteotomy site
. The mechanical axes will remain parallel but non-collinear
. Pure angular correction will occur without any translation
. The osteotomy will act as a lengthening site without angular correction

Correct Answer & Explanation

. The mechanical axes will realign, but there will be translation of the bone ends at the osteotomy site

Explanation

Paley's Rule 2 dictates that if the hinge is at the CORA but the osteotomy is placed at a different level, the mechanical axes will realign completely. However, this relies on a combination of angulation and translation at the osteotomy site to achieve the correction.

Question 2882

Topic: 1. General Principles & Basic Science

During the planning of a deformity correction using an external fixator, a resident incorrectly places both the osteotomy and the hinge at a level 5 cm away from the calculated CORA. Based on Paley's Rule 3, what is the geometric consequence of this technical error?

. The mechanical axes will realign completely, but severe lengthening will occur
. The mechanical axes will remain parallel but non-collinear, creating a new translation deformity
. The mechanical axes will realign completely with pure angular correction
. The bone will translate without any change in angular deformity
. The osteotomy site will perfectly align, but the adjacent joint will subluxate

Correct Answer & Explanation

. The mechanical axes will remain parallel but non-collinear, creating a new translation deformity

Explanation

According to Paley's Rule 3, if both the hinge and the osteotomy are placed away from the CORA, the proximal and distal mechanical axes will become parallel but not collinear. This creates a secondary translation deformity.

Question 2883

Topic: 1. General Principles & Basic Science

A patient presents with a severe post-traumatic diaphyseal tibial deformity. A pure translational deformity is noted on the orthogonal radiographs without any angular deviation. When planning the correction, where is the CORA located in a pure translational deformity?

. At the level of the visible translation
. At the adjacent proximal joint line
. At the adjacent distal joint line
. At infinity
. At the midpoint of the anatomic axis

Correct Answer & Explanation

. At infinity

Explanation

In a pure translational deformity, the proximal and distal mechanical axes are parallel to each other. Because parallel lines never intersect, the CORA for a pure translation deformity is mathematically located at infinity.

Question 2884

Topic: 1. General Principles & Basic Science

A 22-year-old patient undergoes an opening wedge high tibial osteotomy (HTO) for a varus deformity. The surgeon makes a geometrically parallel opening wedge gap. What unintended consequence is most likely to occur in the sagittal plane?

. Decreased posterior tibial slope
. Increased posterior tibial slope
. Anterior translation of the distal fragment
. Posterior translation of the distal fragment
. Profound patella baja

Correct Answer & Explanation

. Increased posterior tibial slope

Explanation

Due to the triangular cross-section of the proximal tibia, a uniform (parallel) opening wedge will inadvertently increase the posterior tibial slope. To maintain the normal sagittal slope, the anterior opening gap must be approximately half the size of the posterior gap.

Question 2885

Topic: 1. General Principles & Basic Science

A patient with a distal tibial recurvatum deformity presents for preoperative planning. What is the normal anatomic Posterior Distal Tibial Angle (aPDTA) range used as a standard reference in the sagittal plane?

. 70° - 75°
. 78° - 82°
. 85° - 90°
. 92° - 96°
. 98° - 105°

Correct Answer & Explanation

. 78° - 82°

Explanation

The normal anatomic Posterior Distal Tibial Angle (aPDTA) is typically 78°-82° (average 80°). This angle defines the normal anterior tilt of the tibial plafond relative to the tibial anatomic axis.

Question 2886

Topic: 1. General Principles & Basic Science

A surgeon evaluates a malunited femur with a mechanical axis deviation (MAD) shifted 40 mm lateral to the center of the knee. The mLDFA is 75° and the MPTA is 87°. An osteotomy is planned. What nerve is at the highest risk of injury if a concomitant proximal fibular osteotomy is performed for a fibular release?

. Tibial nerve
. Sural nerve
. Saphenous nerve
. Common peroneal nerve
. Deep peroneal nerve strictly

Correct Answer & Explanation

. Common peroneal nerve

Explanation

While the femoral valgus is the primary issue, if a proximal fibular osteotomy is performed (often in complex lower limb corrections or tibial varus corrections), the common peroneal nerve is at high risk due to its course around the fibular neck.

Question 2887

Topic: 1. General Principles & Basic Science

A 48-year-old male presents with a multi-apical deformity of the femur following a crush injury. When mapping the mechanical axes to determine the CORAs, the surgeon notes that the proximal and distal axes do not intersect with the middle segment axis at the same point. How should this multi-apical deformity be managed conceptually according to Paley's principles?

. By finding a single CORA that averages the two points and doing a single osteotomy
. By identifying separate CORAs at the intersection of the proximal/middle axes and middle/distal axes, often requiring two osteotomies
. By performing a single purely translational osteotomy at the diaphyseal midpoint
. By solely relying on intra-articular soft tissue releases to compensate
. By utilizing a pure derotational maneuver

Correct Answer & Explanation

. By identifying separate CORAs at the intersection of the proximal/middle axes and middle/distal axes, often requiring two osteotomies

Explanation

In a multi-apical deformity, the mechanical axis of the intermediate segment must be drawn. The intersections of this intermediate axis with the proximal and distal mechanical axes define two separate CORAs, which usually dictate the need for two separate osteotomies for perfect anatomic correction.

Question 2888

Topic: 1. General Principles & Basic Science

During the preoperative planning for a distal tibial deformity correction using a circular frame, you calculate the required angular correction.

What is the mathematical definition of the 'magnitude of deformity'?

. The distance between the anatomic axis and the mechanical axis
. The angle formed by the intersection of the proximal and distal reference lines (axes) of the deformed bone
. The degree of joint line obliquity relative to the horizontal floor
. The size of the wedge measured in millimeters at the outer cortex
. The offset of the mechanical axis deviation measured in millimeters

Correct Answer & Explanation

. The angle formed by the intersection of the proximal and distal reference lines (axes) of the deformed bone

Explanation

The magnitude of deformity is defined mathematically as the angle measured at the intersection (the CORA) of the proximal and distal mechanical or anatomic axes of the deformed bone segment.

Question 2889

Topic: 1. General Principles & Basic Science

A patient with a distal femoral valgus deformity is undergoing a corrective osteotomy.

The surgeon maps the CORA at the level of the joint line, but for soft tissue and biological reasons, chooses to make the osteotomy 4 cm proximal to the CORA. If the mechanical hinge is maintained at the CORA, what is the expected outcome?

. Failure to realign the mechanical axis.
. Realignment of the mechanical axis with pure angulation at the osteotomy site.
. Realignment of the mechanical axis with induced translation at the osteotomy site.
. Creation of an iatrogenic varus deformity.
. A resulting limb length discrepancy of exactly 4 cm.

Correct Answer & Explanation

. Realignment of the mechanical axis with induced translation at the osteotomy site.

Explanation

This scenario describes Paley's Osteotomy Rule 2. Placing the hinge at the CORA but the osteotomy at a different level realigns the mechanical axis but induces translation at the osteotomy ends. This is often done when the CORA is located too close to a joint.

Question 2890

Topic: 1. General Principles & Basic Science

During preoperative planning for a proximal tibial recurvatum deformity, the surgeon plans an osteotomy. By mistake, the surgeon places both the osteotomy cut and the hinge axis 3 cm away from the identified CORA. What is the geometric consequence of this technical error?

. Complete correction of the angulation and restoration of the mechanical axis.
. Angulation correction accompanied by a new iatrogenic translation deformity.
. Pure translation without any change in the angular deformity.
. A perfectly aligned axis but with unintended limb lengthening.
. Complete correction of the deformity but delayed bone healing.

Correct Answer & Explanation

. Angulation correction accompanied by a new iatrogenic translation deformity.

Explanation

According to Paley's Osteotomy Rule 3, placing both the osteotomy and the hinge away from the CORA fails to realign the mechanical axis properly. It corrects the initial angulation but creates an iatrogenic translation deformity.

Question 2891

Topic: 1. General Principles & Basic Science

A 40-year-old female presents with medial compartment knee osteoarthritis and a varus thrust. Full-length radiographs show a mechanical axis deviation (MAD) 20 mm medial to the knee center. The mechanical Lateral Distal Femoral Angle (mLDFA) is 87 degrees, and the Medial Proximal Tibial Angle (MPTA) is 80 degrees. What is the primary source of the varus alignment?

. Distal femoral valgus
. Distal femoral varus
. Proximal tibial valgus
. Proximal tibial varus
. Lateral collateral ligament laxity

Correct Answer & Explanation

. Proximal tibial varus

Explanation

The normal mLDFA is 87 degrees, and the normal MPTA is 87 degrees. An MPTA of 80 degrees indicates a proximal tibial varus deformity, which is the primary driver of this patient's medial mechanical axis deviation.

Question 2892

Topic: 1. General Principles & Basic Science

When analyzing lower extremity alignment, the Anatomic Axis of the femur is not collinear with its Mechanical Axis. What is the normal relationship between the anatomic and mechanical axes of the femur?

. They are exactly parallel.
. The anatomic axis is oriented 7 degrees valgus relative to the mechanical axis.
. The anatomic axis is oriented 7 degrees varus relative to the mechanical axis.
. The anatomic axis diverges laterally by 15 degrees from the mechanical axis.
. The mechanical axis is oriented 7 degrees valgus relative to the anatomic axis.

Correct Answer & Explanation

. The anatomic axis is oriented 7 degrees valgus relative to the mechanical axis.

Explanation

In the femur, the anatomic axis normally diverges from the mechanical axis by approximately 7 degrees (range 5-9 degrees) of valgus. This relationship is critical when using intramedullary rods to correct femoral deformities.

Question 2893

Topic: Biology, Genetics & Bone Healing

A 16-year-old male is undergoing distraction osteogenesis for a tibial leg length discrepancy. After the corticotomy, a latency period is planned before beginning the distraction phase. What is the primary biological purpose of the latency period?

. To allow complete hematoma resorption.
. To permit mesenchymal stem cells to populate the site and initiate early callus formation.
. To stretch the overlying soft tissues and minimize compartment syndrome risk.
. To prevent pin tract infections around the external fixator.
. To allow the formation of woven bone bridging the entire gap.

Correct Answer & Explanation

. To permit mesenchymal stem cells to populate the site and initiate early callus formation.

Explanation

The latency period (typically 7-10 days) allows the inflammatory phase to subside and mesenchymal stem cells to aggregate and begin early fibrocartilaginous callus formation. Distracting too early impairs regenerate formation, while waiting too long leads to premature consolidation.

Question 2894

Topic: 1. General Principles & Basic Science

When planning an opening wedge osteotomy for a varus deformity of the proximal tibia, the surgeon places the hinge on the lateral cortex. What is the expected biological gap behavior at the medial cortex during correction?

. Compression of the medial cortex.
. Distraction of the medial cortex.
. Translation without distraction.
. Rotation around the mechanical axis.
. Resorption of the medial cortex.

Correct Answer & Explanation

. Distraction of the medial cortex.

Explanation

Placing the mechanical hinge on the convex side (lateral cortex in a varus deformity) and performing the osteotomy results in an opening wedge correction. This causes distraction at the concave side (medial cortex).

Question 2895

Topic: Biology, Genetics & Bone Healing

A 50-year-old male is noted to have a "multi-apical" bowing deformity of his femur following childhood rickets. Preoperative templating reveals two distinct CORAs. If the surgeon decides to perform only a single osteotomy at a "compromise" CORA located between the two true CORAs, what unavoidable consequence will occur upon correcting the mechanical axis?

. The mechanical axis will remain deviated.
. Iatrogenic translation will occur at the osteotomy site.
. A rotational deformity will be unmasked.
. The patient will lose knee range of motion.
. The limb will automatically shorten.

Correct Answer & Explanation

. Iatrogenic translation will occur at the osteotomy site.

Explanation

When treating a multi-apical deformity with a single osteotomy at a compromise CORA, realigning the mechanical axis will obligatorily result in translation at the osteotomy site. To avoid translation, two separate osteotomies at the two distinct CORAs are required.

Question 2896

Topic: 1. General Principles & Basic Science

A patient undergoing distraction osteogenesis presents to the clinic with erythema and serous drainage around one of the proximal tibial half-pins. There is no pin loosening, and the patient is afebrile. According to the Paley modification of the Checkley-Macaulay classification, what is the best initial management?

. Immediate removal of the pin in the clinic.
. Intravenous antibiotics and surgical debridement.
. Local pin site care and oral antibiotics.
. Application of a silver-impregnated dressing and stopping distraction.
. Observation only, as this is a normal reaction to tension.

Correct Answer & Explanation

. Local pin site care and oral antibiotics.

Explanation

Superficial pin tract infections with erythema and drainage but without pin loosening or systemic symptoms are extremely common. The standard initial treatment consists of intensified local pin care and a short course of oral antibiotics.

Question 2897

Topic: 1. General Principles & Basic Science

Radiographic evaluation of a regenerate bone column during the consolidation phase of distraction osteogenesis reveals a "concave" or "hourglass" appearance. What is the most likely biomechanical or physiological cause of this regenerate morphology?

. Excessive frame instability or a distraction rate that is too fast.
. A distraction rate that is too slow.
. An excessively long latency period.
. Placement of the corticotomy in the dense diaphysis.
. Premature weight-bearing.

Correct Answer & Explanation

. Excessive frame instability or a distraction rate that is too fast.

Explanation

An hourglass or concave regenerate typically indicates a poor biological response, often due to a distraction rate that is too rapid for the bone to fill the gap or mechanical instability of the frame. A fusiform or cylindrical regenerate represents optimal healing.

Question 2898

Topic: 1. General Principles & Basic Science

A surgeon is planning to correct a diaphyseal tibial angular deformity using a monolateral external fixator. According to Paley's Osteotomy Rule 1, what is the expected outcome if both the osteotomy cut and the mechanical hinge are placed exactly at the Center of Rotation of Angulation (CORA)?

. Pure angular correction with expected translation at the osteotomy site
. Pure angular correction without any translation at the osteotomy site
. Creation of a secondary translational deformity
. Correction of translation but failure to correct angulation
. Parallel but non-collinear mechanical axes

Correct Answer & Explanation

. Pure angular correction without any translation at the osteotomy site

Explanation

Paley's Osteotomy Rule 1 states that if the osteotomy and the hinge are both located at the CORA, the deformity will correct with pure angulation and no translation, resulting in collinear mechanical axes.

Question 2899

Topic: 1. General Principles & Basic Science

A 30-year-old male requires correction of a severe mid-diaphyseal varus deformity of the tibia. To promote faster healing, the surgeon performs the osteotomy in the proximal metaphysis but places the hinge of the external fixator exactly at the diaphyseal CORA. According to Paley's principles, what is the biomechanical result of this configuration?

. The mechanical axes will realign perfectly, but translation will occur at the osteotomy site.
. A new secondary angular deformity will be created at the osteotomy site.
. The mechanical axes will remain parallel but translated.
. Pure angular correction will occur with no translation at the osteotomy site.
. The joint line orientation will become oblique without correcting the mechanical axis.

Correct Answer & Explanation

. The mechanical axes will realign perfectly, but translation will occur at the osteotomy site.

Explanation

Paley's Osteotomy Rule 2 dictates that if the hinge is at the CORA but the osteotomy is at a different level, the mechanical axes will fully realign (collinear), but expected translation will occur at the osteotomy site.

Question 2900

Topic: 1. General Principles & Basic Science

During a distal femoral osteotomy for a varus deformity, the surgeon places the hinge axis and the osteotomy cut proximal to the actual CORA. What is the expected radiologic outcome of this technical error according to Paley's Osteotomy Rule 3?

. Perfect collinear realignment of the mechanical axes
. Pure angular correction without translation
. The proximal and distal mechanical axes will become parallel but shifted (a new translational deformity)
. Correction of translation with residual angular deformity
. Increased joint line convergence angle

Correct Answer & Explanation

. The proximal and distal mechanical axes will become parallel but shifted (a new translational deformity)

Explanation

Paley's Osteotomy Rule 3 states that if the hinge and the osteotomy are both placed away from the CORA, the correction will result in the mechanical axes becoming parallel rather than collinear, creating a new translational deformity.

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