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1. General Principles & Basic Science MCQs

Practice Set 131 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 2601

Topic: 1. General Principles & Basic Science

In the context of valgus knee realignment for LCOA, the primary biomechanical goal is to shift the mechanical axis. What is the generally accepted target post-operative mechanical axis deviation (MAD) to optimally offload the lateral compartment and promote longevity of the native knee joint, according to modern principles?

. 0 degrees (neutral mechanical axis).
. 5 degrees of mechanical valgus.
. 2-4 degrees of mechanical varus.
. 10 degrees of mechanical varus.
. A mechanical axis passing through the lateral third of the medial compartment.

Correct Answer & Explanation

. 2-4 degrees of mechanical varus.

Explanation

Correct Answer: CFor valgus knee realignment in the setting of LCOA, the goal is to offload the diseased lateral compartment and transfer the weight-bearing axis to the healthier medial compartment. While a 'neutral' mechanical axis (0 degrees) might seem intuitive, clinical experience and studies have shown that a slight overcorrection into 2-4 degrees of mechanical varus is often more effective for long-term pain relief and delaying the progression of OA. This slight varus ensures consistent offloading of the lateral compartment and places the load more centrally within the medial compartment.Option A is incorrectbecause while a neutral axis is a good starting point, a slight varus overcorrection is often preferred for LCOA to ensure adequate offloading.Option B is incorrectbecause 5 degrees of mechanical valgus would mean the mechanical axis is still passing through the lateral compartment, which would worsen or fail to correct the LCOA.Option D is incorrectbecause 10 degrees of mechanical varus would be an excessive overcorrection, potentially leading to significant overloading of the medial compartment and accelerating medial compartment OA.Option E is incorrectbecause while the goal is to shift the axis medially, 'the lateral third of the medial compartment' is a less precise and less commonly used target than a specific angular mechanical axis deviation (e.g., 2-4 degrees mechanical varus).

Question 2602

Topic: Biomechanics & Biomaterials

Following a successful valgus knee realignment with a distal femoral osteotomy, a patient reports persistent lateral knee pain despite good radiographic correction of the mechanical axis. On examination, the patient has tenderness over the lateral epicondyle and pain with varus stress. What is the most likely cause of this persistent pain?

. Nonunion of the osteotomy site.
. Overcorrection leading to medial compartment overload.
. Development of patellofemoral instability.
. Iliotibial band (ITB) friction syndrome due to altered biomechanics.
. Recurrence of the valgus deformity.

Correct Answer & Explanation

. Iliotibial band (ITB) friction syndrome due to altered biomechanics.

Explanation

Correct Answer: DIliotibial band (ITB) friction syndrome is a known complication or cause of persistent pain after valgus knee realignment. The osteotomy changes the biomechanics of the knee, potentially altering the tension and tracking of the ITB over the lateral femoral epicondyle. This can lead to inflammation and pain, especially with activities involving repetitive knee flexion and extension. Tenderness over the lateral epicondyle and pain with varus stress (which can tension the ITB) are classic signs.Option A is incorrectbecause nonunion would typically present with more diffuse pain, instability, and often radiographic signs of failed healing, not localized lateral epicondyle tenderness.Option B is incorrectbecause overcorrection leading to medial compartment overload would cause medial knee pain, not lateral knee pain.Option C is incorrectbecause patellofemoral instability would typically present with anterior knee pain, catching, or giving way, not primarily lateral epicondyle tenderness.Option E is incorrectbecause recurrence of the valgus deformity would lead to a return of lateral compartment pain due to loading, but the question states 'good radiographic correction of the mechanical axis' and points to specific lateral epicondyle tenderness.

Question 2603

Topic: 1. General Principles & Basic Science

A patient undergoes a distal femoral osteotomy for a severe valgus deformity. The surgeon plans the osteotomy and places the hinge exactly at the Center of Rotation of Angulation (CORA). According to Paley's First Osteotomy Rule, which of the following best describes the resulting biomechanical realignment?

. Pure angulation without translation
. Pure translation without angulation
. Angulation combined with translational step-off
. Correction of mechanical axis with secondary joint line obliquity
. Induction of a secondary rotational deformity

Correct Answer & Explanation

. Pure angulation without translation

Explanation

Paley's Rule 1 states that if the osteotomy and the hinge are both located at the CORA, the deformity corrects by pure angulation without any translation. This perfectly restores the mechanical axis while maintaining optimal bony contact.

Question 2604

Topic: 1. General Principles & Basic Science

During the correction of a proximal tibial recurvatum deformity, anatomical constraints dictate that the osteotomy be performed proximal to the CORA, but the surgeon maintains the corrective hinge exactly at the CORA. What is the expected geometrical consequence at the osteotomy site (Paley's Osteotomy Rule 2)?

. Pure angulation
. Angulation combined with translation
. Translation without angulation
. Rotational malalignment
. Complete loss of bony contact

Correct Answer & Explanation

. Angulation combined with translation

Explanation

Paley's Rule 2 dictates that if the hinge is at the CORA but the osteotomy is at a different level, the correction will result in angulation along with a translational step-off. The mechanical axis is fully restored, but local translation occurs at the osteotomy site.

Question 2605

Topic: 1. General Principles & Basic Science

According to the principles of sagittal alignment and biomechanics of the knee joint, where does the normal mechanical axis of the lower extremity pass in relation to the center of the knee joint during the stance phase of gait?

. 5-15 mm posterior to the joint center
. Directly through the exact center of the joint
. 5-15 mm anterior to the joint center
. 25-30 mm anterior to the joint center
. 25-30 mm posterior to the joint center

Correct Answer & Explanation

. 5-15 mm posterior to the joint center

Explanation

The normal sagittal mechanical axis passes slightly anterior (5-15 mm) to the center of the knee joint. This alignment provides an extension moment during the stance phase, locking the knee and reducing the workload on the quadriceps.

Question 2606

Topic: 1. General Principles & Basic Science

When analyzing a full-length standing AP radiograph of the lower extremities for a coronal plane deformity around the knee, what are the normal accepted values for the mechanical lateral distal femoral angle (mLDFA) and medial proximal tibial angle (MPTA)?

. mLDFA 80-84 deg and MPTA 90-95 deg
. mLDFA 85-90 deg and MPTA 85-90 deg
. mLDFA 90-95 deg and MPTA 80-84 deg
. mLDFA 95-100 deg and MPTA 85-90 deg
. mLDFA 80-85 deg and MPTA 80-85 deg

Correct Answer & Explanation

. mLDFA 85-90 deg and MPTA 85-90 deg

Explanation

The normal mLDFA is approximately 87 degrees (range 85-90), and the normal MPTA is also approximately 87 degrees (range 85-90). Deviations from these ranges indicate extra-articular femoral or tibial coronal deformities.

Question 2607

Topic: 1. General Principles & Basic Science

When utilizing Paley's methods to plan a corrective osteotomy for a lower extremity deformity, the surgeon draws the proximal and distal anatomical axes on the radiograph. The specific point where these two anatomical axes intersect is termed the:

. Mechanical axis deviation (MAD)
. Center of rotation of angulation (CORA)
. Joint line convergence point
. Osteotomy node
. Anatomical-mechanical divergence angle

Correct Answer & Explanation

. Center of rotation of angulation (CORA)

Explanation

The Center of Rotation of Angulation (CORA) is determined by the intersection of the proximal and distal mechanical or anatomical axes of a deformed bone segment. It is the geometric apex of the deformity.

Question 2608

Topic: 1. General Principles & Basic Science

A surgeon performs a deformity correction utilizing Paley's Osteotomy Rule 3. In this scenario, both the osteotomy and the corrective hinge are placed at a site separate from the CORA. What is the mandatory geometric action required at the osteotomy site to achieve full mechanical axis realignment without inducing a secondary deformity?

. Pure angulation with no translation
. Complete diaphyseal overlap (shortening)
. Angulation combined with a translational shift
. Induction of a compensatory rotational deformity
. Lengthening through the osteotomy site alone

Correct Answer & Explanation

. Angulation combined with a translational shift

Explanation

Paley's Rule 3 states that if the hinge and osteotomy are completely separated from the CORA, the mechanical axis can only be restored if both angulation and translation are performed simultaneously at the osteotomy site.

Question 2609

Topic: 1. General Principles & Basic Science

When correcting a distal femoral valgus deformity via a medial closing wedge osteotomy, if the intact lateral cortex is utilized as the primary hinge, what is the predictable shift of the mechanical axis relative to the center of the knee joint?

. Shifts medially
. Shifts laterally
. Remains perfectly central
. Shifts anteriorly
. Shifts posteriorly

Correct Answer & Explanation

. Shifts medially

Explanation

Closing a medial wedge with a lateral hinge for a valgus deformity will angle the distal segment into varus, effectively shifting the mechanical axis medially. Careful planning is required to avoid overcorrection.

Question 2610

Topic: 1. General Principles & Basic Science

During pre-operative deformity planning, an exact understanding of the relationship between the anatomical and mechanical axes is crucial. In a structurally normal adult femur, what is the typical anatomical-mechanical angle (AMA)?

. 0 degrees
. 2 degrees
. 7 degrees
. 12 degrees
. 15 degrees

Correct Answer & Explanation

. 7 degrees

Explanation

In the femur, the anatomical axis runs down the center of the diaphysis, while the mechanical axis runs from the center of the femoral head to the center of the knee. The typical divergence (AMA) is approximately 7 degrees (range 5-9 degrees).

Question 2611

Topic: Biology, Genetics & Bone Healing

A surgeon plans to acutely correct a 15-degree tibial varus deformity using the Fixator-Assisted Plating (FAP) technique. Which of the following best describes the primary biomechanical advantage of utilizing this specific technique?

. It relies exclusively on secondary bone healing via callus formation
. It allows for continuous post-operative gradual adjustment of alignment over weeks
. It provides precise intraoperative alignment control while avoiding the morbidity of prolonged external fixation
. It eliminates the need for an osteotomy by stretching the physis
. It requires a smaller incision than entirely percutaneous pinning techniques

Correct Answer & Explanation

. It provides precise intraoperative alignment control while avoiding the morbidity of prolonged external fixation

Explanation

Fixator-Assisted Plating uses a temporary external fixator or distraction tool to acutely achieve perfectly planned alignment intraoperatively. A plate is then applied to hold the correction, allowing immediate removal of the frame.

Question 2612

Topic: 1. General Principles & Basic Science

A 24-year-old male presents with a mid-diaphyseal tibial deformity. Preoperative planning identifies the Center of Rotation of Angulation (CORA). According to Paley's Rule 2, if the osteotomy is performed at a level distant from the CORA, but the hinge is placed exactly at the CORA, what is the expected geometric outcome of the correction?

. Realignment of the mechanical axis with pure angular correction and no translation.
. Realignment of the mechanical axis with expected translation of the bone ends at the osteotomy site.
. Parallel displacement of the mechanical axis resulting in a new iatrogenic translational deformity.
. Failure to correct the mechanical axis deviation with persistent angular deformity.
. Lengthening of the mechanical axis without angular correction.

Correct Answer & Explanation

. Realignment of the mechanical axis with expected translation of the bone ends at the osteotomy site.

Explanation

Paley's Rule 2 states that if the hinge is at the CORA but the osteotomy is at a different level, the mechanical axes will realign, but translation will occur at the osteotomy site. This is often used when bone quality at the CORA is poor.

Question 2613

Topic: Physiology & Rehabilitation

During gait, the normal sagittal mechanical axis plumb line (from the center of the femoral head to the center of the ankle joint) passes in which relation to the knee joint, and what biomechanical advantage does this provide?

. Posterior to the knee center of rotation, preventing excessive hyperextension.
. Through the exact center of rotation, minimizing collateral ligament strain.
. Anterior to the knee center of rotation, locking the knee in extension with minimal quadriceps effort.
. Anterior to the knee center of rotation, requiring constant hamstring contraction to prevent buckling.
. Posterior to the knee center of rotation, utilizing the quadriceps to maintain stance phase stability.

Correct Answer & Explanation

. Anterior to the knee center of rotation, locking the knee in extension with minimal quadriceps effort.

Explanation

The normal sagittal mechanical axis passes anterior to the center of rotation of the knee. This creates an extension moment, allowing the knee to 'lock' efficiently during stance phase without requiring excessive active quadriceps contraction.

Question 2614

Topic: 1. General Principles & Basic Science

A patient presents with a severe valgus deformity of the lower extremity. Full-length radiographs reveal a mechanical lateral distal femoral angle (mLDFA) of 75 degrees and a medial proximal tibial angle (MPTA) of 98 degrees. Why is a double-level osteotomy indicated rather than correcting the entire deformity in the femur?

. Correcting purely in the femur risks excessive limb shortening.
. A single-level correction will result in unacceptable joint line obliquity, predisposing to shear forces.
. The fibular collateral ligament will be over-tensioned if only the femur is corrected.
. A single-level correction inherently causes a secondary sagittal plane deformity.
. Double-level osteotomies heal faster due to preserved periosteal blood supply.

Correct Answer & Explanation

. A single-level correction will result in unacceptable joint line obliquity, predisposing to shear forces.

Explanation

When a severe multi-apical or multi-bone deformity exists, correcting the entire mechanical axis deviation (MAD) at a single bone leads to an abnormal joint line obliquity. Parallelism of the knee joint line to the ground is critical to prevent abnormal shear stresses.

Question 2615

Topic: 1. General Principles & Basic Science

According to Paley's principles of deformity analysis, which of the following represents the normal ranges for the mechanical lateral distal femoral angle (mLDFA) and the medial proximal tibial angle (MPTA) in the coronal plane?

. mLDFA 80-84 degrees, MPTA 80-84 degrees.
. mLDFA 85-90 degrees, MPTA 85-90 degrees.
. mLDFA 90-95 degrees, MPTA 90-95 degrees.
. mLDFA 95-100 degrees, MPTA 85-90 degrees.
. mLDFA 85-90 degrees, MPTA 95-100 degrees.

Correct Answer & Explanation

. mLDFA 85-90 degrees, MPTA 85-90 degrees.

Explanation

Normal mLDFA is 87 degrees (range 85-90 degrees) and normal MPTA is 87 degrees (range 85-90 degrees). These angles are fundamental to assessing joint orientation in the coronal plane.

Question 2616

Topic: Biology, Genetics & Bone Healing

During Ilizarov distraction osteogenesis for lengthening after deformity correction, what is the standard recommended rate and rhythm of distraction to optimize bone regenerate healing?

. 0.25 mm per day, performed in a single adjustment.
. 1.0 mm per day, divided into four 0.25 mm increments.
. 2.0 mm per day, divided into two 1.0 mm increments.
. 1.5 mm per day, performed continuously.
. 0.5 mm per day, divided into two 0.25 mm increments.

Correct Answer & Explanation

. 1.0 mm per day, divided into four 0.25 mm increments.

Explanation

The optimal rate of distraction for callus formation is 1.0 mm per day. The optimal rhythm is dividing this rate into smaller, frequent increments (e.g., 0.25 mm every 6 hours) to minimize soft tissue trauma and optimize bone regeneration.

Question 2617

Topic: 1. General Principles & Basic Science

A 50-year-old male undergoes a medial opening wedge high tibial osteotomy (HTO). Postoperatively, he complains of anterior knee pain. Radiographs reveal a decreased Insall-Salvati ratio compared to preoperative films. What aspect of the surgical procedure most directly contributes to this anatomic change?

. Proximal translation of the tibial tubercle relative to the joint line.
. Distalization of the joint line relative to the tibial tubercle, creating patella baja.
. Over-tensioning of the quadriceps tendon during closure.
. Inadvertent lateral translation of the distal tibial segment.
. Failure to release the superficial medial collateral ligament.

Correct Answer & Explanation

. Distalization of the joint line relative to the tibial tubercle, creating patella baja.

Explanation

An opening wedge HTO done proximal to the tibial tubercle elevates the joint line relative to the tubercle, effectively shortening the patellar tendon distance to the joint and causing patella baja (infera).

Question 2618

Topic: 1. General Principles & Basic Science

When performing deformity analysis of the lower extremity, the relationship between the anatomic and mechanical axes is crucial. Which of the following statements accurately describes this relationship in a normal lower extremity?

. The femoral anatomic and mechanical axes are collinear.
. The tibial anatomic and mechanical axes are collinear.
. The femoral anatomic axis diverges from the mechanical axis by exactly 15 degrees.
. The tibial anatomic axis diverges from the mechanical axis by 7 degrees.
. Both the femoral and tibial anatomic axes diverge from their mechanical axes by 5-7 degrees.

Correct Answer & Explanation

. The tibial anatomic and mechanical axes are collinear.

Explanation

In the normal tibia, the anatomic and mechanical axes are parallel and essentially collinear. In the normal femur, the anatomic axis is in roughly 5-9 degrees (average 7) of valgus relative to the mechanical axis.

Question 2619

Topic: 1. General Principles & Basic Science

According to Paley's Rule 3, what is the expected result if an osteotomy is created at a level distant from the CORA, and the mechanical hinge is also placed at that same distant level (away from the CORA)?

. Pure angular correction with full restoration of the mechanical axis.
. Angular correction but with a resultant translational deformity (parallel shift of the axis).
. Correction of translation but failure to correct angulation.
. Complete rigid fixation without any possibility of movement.
. A pure lengthening effect with no change in alignment.

Correct Answer & Explanation

. Angular correction but with a resultant translational deformity (parallel shift of the axis).

Explanation

Paley's Rule 3 states that if both the osteotomy and the hinge are placed away from the CORA, the mechanical axes will undergo a parallel shift (translation) relative to each other, creating an iatrogenic translational deformity.

Question 2620

Topic: 1. General Principles & Basic Science



Based on Paley's principles, which technique correctly defines the true Center of Rotation of Angulation (CORA) for a uniapical long bone deformity on a standard radiograph?

. The bisection of the angle formed by the joint lines.
. The intersection point of the proximal and distal mechanical or anatomic axis lines.
. The geometric center of the diaphyseal bowing.
. The exact level of the largest visible osseous defect.
. The point located exactly 5 cm proximal to the joint line.

Correct Answer & Explanation

. The intersection point of the proximal and distal mechanical or anatomic axis lines.

Explanation

The CORA is defined geometrically as the point of intersection between the proximal mid-diaphyseal axis (mechanical or anatomic) and the distal mid-diaphyseal axis.

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