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1. General Principles & Basic Science MCQs

Practice Set 133 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 2641

Topic: 1. General Principles & Basic Science

In the context of distraction osteogenesis and limb lengthening, how is the Bone Healing Index (BHI) defined?

. The total length of regenerate bone divided by the patient's age.
. The time the external fixator is applied (in months or days) per centimeter of length achieved.
. The radiographic density of the regenerate compared to the native diaphysis.
. The number of days required to achieve the first 1 cm of distraction.
. The distraction rate multiplied by the cross-sectional area of the bone.

Correct Answer & Explanation

. The time the external fixator is applied (in months or days) per centimeter of length achieved.

Explanation

The Bone Healing Index (BHI) is a standard metric used to evaluate the efficiency of bone consolidation. It is defined as the total time the frame is on the patient divided by the amount of length achieved in centimeters (e.g., months/cm or days/cm).

Question 2642

Topic: 1. General Principles & Basic Science

A patient with a severe procurvatum deformity of the tibia is treated with a closing wedge osteotomy. To achieve angular correction without introducing secondary translation, where must the geometric hinge axis be placed?

. On the anterior (convex) cortex at the CORA.
. On the posterior (concave) cortex at the CORA.
. In the exact center of the medullary canal.
. At the level of the tibial tubercle.
. On the medial cortex to prevent varus collapse.

Correct Answer & Explanation

. On the posterior (concave) cortex at the CORA.

Explanation

For a closing wedge osteotomy, the hinge must be placed on the concave cortex of the deformity. In a procurvatum (apex anterior) deformity, the concavity is posterior, so the hinge must be on the posterior cortex at the CORA.

Question 2643

Topic: 1. General Principles & Basic Science

You plan to lengthen the femur of a 30-year-old using a motorized intramedullary lengthening nail. The patient has a 4 cm length discrepancy but a perfectly normal mechanical axis. To minimize the risk of inducing a new angular deformity during lengthening, where is the optimal location for the osteotomy?

. At the level of the lesser trochanter.
. At the exact center of the diaphysis, regardless of bowing.
. At the apex of the physiological diaphyseal bow.
. In the distal metaphysis just proximal to the joint capsule.
. At the level of the most dense cortical bone.

Correct Answer & Explanation

. At the apex of the physiological diaphyseal bow.

Explanation

When lengthening an anatomically normal bone with an IM nail, the osteotomy should be placed at the apex of the physiological bow. Lengthening away from the apex with a straight nail can induce secondary deformities (e.g., unintended translation or angulation).

Question 2644

Topic: Biology, Genetics & Bone Healing

A patient undergoing tibial lengthening is evaluated at the 3-week post-operative mark. Radiographs show early premature consolidation of the regenerate bone. The patient admits they have only been distracting 0.25 mm per day. What is the most appropriate next step in management?

. Immediately increase the distraction rate to 2.0 mm per day.
. Reverse the distraction to compress the regenerate, then pull again.
. Perform a repeat corticotomy and resume distraction at the standard 1.0 mm/day rate.
. Remove the frame and convert to plate osteosynthesis.
. Inject bone morphogenetic protein (BMP) into the osteotomy site.

Correct Answer & Explanation

. Perform a repeat corticotomy and resume distraction at the standard 1.0 mm/day rate.

Explanation

Premature consolidation occurs when the distraction rate is too slow. Once the bone has consolidated, adjusting the rate is ineffective. The required treatment is to surgically repeat the corticotomy and then resume distraction at the proper rate (1.0 mm/day).

Question 2645

Topic: 1. General Principles & Basic Science

A surgeon is planning to correct a diaphyseal tibial deformity. The Center of Rotation of Angulation (CORA) is identified in the mid-diaphysis. According to Paley's Osteotomy Rule 1, if both the osteotomy and the Axis of Correction of Angulation (ACA) are placed exactly at the CORA, what will be the resulting alignment of the bone segments?

. The segments will angulate and translate at the osteotomy site, but the mechanical axes will remain parallel.
. The segments will angulate without translation, and the proximal and distal mechanical axes will become collinear.
. The segments will translate without angulation, resulting in parallel mechanical axes.
. The mechanical axes will intersect at a new secondary CORA distal to the osteotomy.
. The segments will experience pure lengthening without altering the mechanical axis deviation.

Correct Answer & Explanation

. The segments will angulate without translation, and the proximal and distal mechanical axes will become collinear.

Explanation

Paley's Rule 1 states that when the osteotomy and the ACA are both located at the CORA, correction results in pure angulation without translation. The proximal and distal mechanical axes become perfectly collinear.

Question 2646

Topic: 1. General Principles & Basic Science

During preoperative planning for a distal femoral valgus deformity, the CORA is located intra-articularly. To preserve the joint capsule and hardware placement, the surgeon performs the osteotomy 4 cm proximal to the CORA but places the ACA at the CORA hinge. According to Paley's Osteotomy Rule 2, what is the expected outcome?

. Pure angulation at the osteotomy site with non-collinear mechanical axes.
. Angulation and translation at the osteotomy site with perfectly collinear mechanical axes.
. Pure translation at the osteotomy site with perfectly collinear mechanical axes.
. Angulation without translation at the osteotomy site, with parallel mechanical axes.
. Translation and angulation resulting in a secondary varus deformity.

Correct Answer & Explanation

. Angulation and translation at the osteotomy site with perfectly collinear mechanical axes.

Explanation

Paley's Rule 2 states that if the ACA is at the CORA but the osteotomy is at a different level, the correction will result in both angulation and translation at the osteotomy site. However, the proximal and distal mechanical axes will successfully become collinear.

Question 2647

Topic: 1. General Principles & Basic Science

A patient undergoes a corrective osteotomy for a tibial varus deformity. The surgeon inadvertently places both the osteotomy and the ACA 3 cm distal to the true CORA. According to Paley's Osteotomy Rule 3, what biomechanical consequence will occur?

. The mechanical axes will become collinear without translation at the osteotomy.
. The mechanical axes will become parallel but will be translated relative to one another.
. The osteotomy will gap open asymmetrically, creating a length discrepancy but collinear axes.
. The bone will undergo pure translation at the osteotomy site without any angular correction.
. The joint line orientation will be perfectly restored but the mechanical axis deviation will worsen.

Correct Answer & Explanation

. The mechanical axes will become parallel but will be translated relative to one another.

Explanation

Paley's Rule 3 states that if both the ACA and the osteotomy are placed away from the CORA, the correction will result in parallel but translated (non-collinear) proximal and distal mechanical axes. This causes an iatrogenic translation deformity.

Question 2648

Topic: 1. General Principles & Basic Science

Which of the following is the correct sequential order of steps when performing Fixator-Assisted Nailing (FAN) for deformity correction?

. Ream canal -> Apply fixator -> Correct deformity -> Insert nail -> Remove fixator
. Insert nail -> Apply fixator -> Correct deformity -> Ream canal -> Remove fixator
. Apply fixator pins -> Perform osteotomy and correct deformity -> Apply fixator rod -> Ream and insert nail -> Remove fixator
. Perform osteotomy -> Ream canal -> Insert nail -> Apply fixator to finalize correction
. Apply fixator -> Insert nail -> Perform osteotomy -> Ream canal -> Remove fixator

Correct Answer & Explanation

. Apply fixator pins -> Perform osteotomy and correct deformity -> Apply fixator rod -> Ream and insert nail -> Remove fixator

Explanation

The FAN technique relies on the fixator to act as a temporary reduction tool. The correct sequence is: insert pins, perform osteotomy, correct the deformity, lock the fixator, ream the canal, insert the nail, and finally remove the temporary fixator.

Question 2649

Topic: 1. General Principles & Basic Science

In assessing lower extremity alignment, a Joint Line Convergence Angle (JLCA) of 6 degrees (opening laterally) is measured on a standing AP radiograph. What does this abnormal JLCA most likely represent in the context of varus deformity?

. A compensatory valgus deformity of the distal tibia.
. Lateral compartment arthritis with medial collateral ligament contracture.
. Intra-articular deformity or lateral ligamentous laxity.
. A pure diaphyseal femoral deformity.
. A normal variant in patients over 65 years old.

Correct Answer & Explanation

. Intra-articular deformity or lateral ligamentous laxity.

Explanation

A normal JLCA is 0 to 2 degrees. An increased JLCA opening laterally in a varus knee typically indicates lateral collateral ligament laxity, medial compartment cartilage loss, or an intra-articular bony defect contributing to the mechanical axis deviation.

Question 2650

Topic: 1. General Principles & Basic Science

A patient presents with a diaphyseal femoral deformity measuring 15 degrees of varus on the AP radiograph and 20 degrees of apex anterior bowing (procurvatum) on the lateral radiograph. Using the principles of oblique plane deformity, what is the approximate true magnitude of this deformity?

. 15 degrees
. 20 degrees
. 25 degrees
. 35 degrees
. 5 degrees

Correct Answer & Explanation

. 25 degrees

Explanation

An oblique plane deformity magnitude is calculated using the Pythagorean theorem (a^2 + b^2 = c^2). Here, 15^2 + 20^2 = 225 + 400 = 625. The square root of 625 is 25 degrees.

Question 2651

Topic: 1. General Principles & Basic Science

A pure translation deformity of the tibial diaphysis is noted on radiographs, with zero degrees of angular deformity. Where is the Center of Rotation of Angulation (CORA) located in this specific scenario?

. Exactly at the level of the translation.
. At the proximal tibial joint line.
. At the distal tibial joint line.
. At infinity.
. At the intersection of the anatomic and mechanical axes.

Correct Answer & Explanation

. At infinity.

Explanation

In a pure translation deformity, the proximal and distal axes are parallel but not collinear. Because parallel lines never intersect, the CORA for a pure translation deformity is mathematically considered to be at infinity.

Question 2652

Topic: 1. General Principles & Basic Science

When performing a closing wedge osteotomy at the CORA for a varus deformity of the tibia, where should the Axis of Correction of Angulation (ACA) be positioned to prevent any iatrogenic translation?

. On the concave cortex of the deformity.
. On the convex cortex of the deformity.
. In the center of the medullary canal.
. Outside the bone on the concave side.
. Outside the bone on the convex side.

Correct Answer & Explanation

. On the convex cortex of the deformity.

Explanation

To execute a pure closing wedge osteotomy without translation (following Rule 1), the ACA (hinge) must be placed on the convex cortex of the deformity at the level of the CORA.

Question 2653

Topic: 1. General Principles & Basic Science

You are treating a patient with a severe distal tibial deformity using a circular external fixator. The surgeon plans a neutral wedge (dome) osteotomy. Where is the ACA located in a perfectly executed neutral wedge osteotomy?

. On the concave cortex.
. On the convex cortex.
. At the central axis of the bone.
. At the level of the adjacent joint line.
. At infinity.

Correct Answer & Explanation

. At the central axis of the bone.

Explanation

A neutral wedge osteotomy (often achieved via a dome or focal dome osteotomy) neither lengthens nor shortens the bone segment. To achieve this, the ACA must be located precisely at the central axis of the bone.

Question 2654

Topic: 1. General Principles & Basic Science

A surgeon is evaluating a patient with a significant diaphyseal femur deformity. The angle between the anatomic axis and the mechanical axis of the normal femur (Anatomic-Mechanical Angle, AMA) is typically:

. 0 degrees
. 1 to 3 degrees
. 5 to 7 degrees
. 9 to 11 degrees
. 12 to 15 degrees

Correct Answer & Explanation

. 5 to 7 degrees

Explanation

The normal Anatomic-Mechanical Angle (AMA) of the femur is approximately 5 to 7 degrees, depending on pelvic width and femoral length. The mechanical axis is a straight line from the femoral head center to the knee center, while the anatomic axis follows the medullary canal.

Question 2655

Topic: 1. General Principles & Basic Science

During a FAN procedure for a proximal tibial deformity, the surgeon plans to use a Poller screw to correct a procurvatum tendency. To properly narrow the canal and push the nail posteriorly, where should the Poller screw be placed in the proximal fragment?

. Anterior to the planned nail path.
. Posterior to the planned nail path.
. Medial to the planned nail path.
. Lateral to the planned nail path.
. Directly through the osteotomy site.

Correct Answer & Explanation

. Anterior to the planned nail path.

Explanation

Procurvatum is an apex anterior deformity. The concave side of the deformity is anterior. Placing the Poller screw anteriorly in the proximal fragment blocks the nail from migrating anteriorly, forcing it posterior and correcting the procurvatum.

Question 2656

Topic: 1. General Principles & Basic Science

A surgeon is planning to correct a diaphyseal tibial deformity. The mechanical axes of the proximal and distal segments intersect at the Center of Rotation of Angulation (CORA). The surgeon decides to perform the osteotomy 4 cm distal to the CORA but places the axis of correction (hinge) exactly at the CORA. According to Paley's osteotomy rules, what is the expected biomechanical outcome?

. The mechanical axes will remain angulated and translated.
. The mechanical axes will become parallel but not collinear, creating a secondary translation.
. The mechanical axes will become perfectly collinear, but translation will occur at the osteotomy site.
. The bone ends will perfectly appose without any translation at the osteotomy site.
. The mechanical axes will deviate further, worsening the mechanical axis deviation (MAD).

Correct Answer & Explanation

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

Explanation

This describes Paley's Osteotomy Rule 2. When the osteotomy is performed away from the CORA but the hinge is maintained at the CORA, the mechanical axes will align (collinear), but predictable translation will occur at the osteotomy site.

Question 2657

Topic: 1. General Principles & Basic Science

According to Paley's Osteotomy Rule 3, what occurs when both the osteotomy and the axis of correction (hinge) are located away from the Center of Rotation of Angulation (CORA)?

. Pure angulation with collinear mechanical axes.
. Collinear mechanical axes with translation at the osteotomy site.
. Complete correction of both angulation and translation without bone gap.
. The proximal and distal mechanical axes become parallel but not collinear, creating a translation deformity.
. The joint line convergence angle undergoes an obligatory 5-degree shift.

Correct Answer & Explanation

. The proximal and distal mechanical axes become parallel but not collinear, creating a translation deformity.

Explanation

Rule 3 states that if the osteotomy and hinge are away from the CORA, the correction will result in the proximal and distal mechanical axes being parallel but translated, thereby creating a new translation deformity.

Question 2658

Topic: 1. General Principles & Basic Science

A surgeon plans an acute valgus-producing high tibial osteotomy to correct a severe proximal tibial varus deformity. During the acute correction into valgus, which neurovascular structure is at the greatest risk of stretch injury?

. Tibial nerve
. Sural nerve
. Common peroneal nerve
. Saphenous nerve
. Popliteal artery

Correct Answer & Explanation

. Common peroneal nerve

Explanation

Correcting a severe varus deformity acutely into valgus stretches the lateral structures of the knee. The common peroneal nerve is tethered around the fibular neck and is highly susceptible to stretch palsy.

Question 2659

Topic: 1. General Principles & Basic Science

When calculating parameters for femoral deformity correction, what is the normal average Anatomic-Mechanical Angle (AMA) of the femur, and how do the axes relate?

. 0 degrees; they are perfectly parallel.
. 3 degrees; the anatomic axis diverges laterally from distal to proximal.
. 7 degrees; the anatomic axis diverges laterally from distal to proximal.
. 12 degrees; the anatomic axis diverges medially from distal to proximal.
. 15 degrees; the anatomic axis diverges laterally from distal to proximal.

Correct Answer & Explanation

. 7 degrees; the anatomic axis diverges laterally from distal to proximal.

Explanation

The Anatomic-Mechanical Angle (AMA) of the femur is typically between 5 and 7 degrees (average 7). The anatomic axis runs from the piriformis fossa to the center of the knee, diverging laterally from the mechanical axis proximally.

Question 2660

Topic: 1. General Principles & Basic Science

A patient presents with a Mechanical Axis Deviation (MAD) of only 5 mm, but radiographs reveal a distal femoral valgus deformity (mLDFA of 80 degrees) and a proximal tibial varus deformity (MPTA of 80 degrees). This scenario best illustrates which of the following concepts?

. Translation deformity
. Multi-apical single-bone deformity
. Compensatory deformity
. Fixator-induced malalignment
. Ligamentous laxity

Correct Answer & Explanation

. Compensatory deformity

Explanation

A compensatory deformity occurs when a primary deformity in one bone (e.g., femoral valgus) is offset by an opposite deformity in the adjacent bone (e.g., tibial varus), resulting in a deceptively normal overall mechanical axis.

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