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1. General Principles & Basic Science MCQs

Practice Set 127 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 2521

Topic: 1. General Principles & Basic Science

A 45-year-old male with medial compartment osteoarthritis and varus deformity undergoes a medial opening wedge high tibial osteotomy (HTO). Postoperatively, he exhibits an unintended increase in the posterior tibial slope. Which of the following technical errors most likely occurred?

. The anterior gap was opened more than the posterior gap.
. The posterior gap was opened more than the anterior gap.
. The osteotomy was performed strictly distal to the tibial tubercle.
. The lateral cortex hinge was dynamically compressed.
. The fibula was inadvertently osteotomized.

Correct Answer & Explanation

. The anterior gap was opened more than the posterior gap.

Explanation

Due to the triangular shape of the proximal tibia, maintaining the native sagittal slope during a medial opening wedge HTO requires the anterior gap to be roughly half the size of the posterior gap. Opening the anterior gap equally or more than the posterior gap inadvertently increases the posterior tibial slope, potentially causing cruciate ligament instability.

Question 2522

Topic: 1. General Principles & Basic Science

In the application of a circular external fixator, the surgeon utilizes tensioned "olive" wires. What is the primary biomechanical advantage of incorporating an olive wire into the construct?

. To increase the overall axial stiffness of the ring fixator.
. To generate interfragmentary compression and prevent unwanted bone translation.
. To reduce the rate of superficial pin tract infections.
. To allow for an increased distraction rate without wire breakage.
. To eliminate the need for half-pins in the metaphyseal bone.

Correct Answer & Explanation

. To generate interfragmentary compression and prevent unwanted bone translation.

Explanation

Olive wires possess a small bead that abuts the bone cortex, preventing the bone from sliding along the wire. When tensioned against the frame, they are used to "pull" the bone toward the olive, providing interfragmentary compression, aiding in fragment reduction, and resisting unwanted lateral translational forces.

Question 2523

Topic: Biology, Genetics & Bone Healing

In a bone transport procedure for a 5 cm segmental tibial defect, the surgeon enforces a 7-day latent period before initiating distraction. What is the primary histological rationale for this delay?

. To allow complete woven bone formation bridging the osteotomy.
. To allow hematoma organization and initial mesenchymal stem cell proliferation.
. To ensure complete soft tissue closure to prevent pin tract infection.
. To promote primary cortical healing via Haversian remodeling.
. To allow the acute inflammatory phase to completely resolve before stretching tissues.

Correct Answer & Explanation

. To allow hematoma organization and initial mesenchymal stem cell proliferation.

Explanation

The latent period (typically 5-7 days) allows the initial fracture hematoma to organize and provides time for pluripotential mesenchymal stem cells to populate the osteotomy gap. Initiating distraction before this early angiogenic and proliferative phase is established disrupts the local biology, significantly increasing the risk of poor regenerate formation.

Question 2524

Topic: 1. General Principles & Basic Science
A surgeon is adjusting a circular external fixator for maximum stability. Which of the following frame modifications will most significantly decrease the axial and torsional stiffness of the construct?
. Increasing the wire crossing angle from 45 to 90 degrees.
. Decreasing the diameter of the rings relative to the limb.
. Increasing the distance (stand-off) between the rings and the bone surface.
. Using 1.8 mm tensioned wires instead of 1.5 mm wires.
. Increasing the tension on the wires from 90 kg to 130 kg.

Correct Answer & Explanation

. Increasing the distance (stand-off) between the rings and the bone surface.

Explanation

Frame stability is highly dependent on the distance between the support (the ring) and the load (the bone). Increasing the "stand-off" distance significantly decreases the stiffness of the construct, making it less stable; conversely, smaller rings, thicker wires, higher tension, and orthogonal crossing angles increase stiffness.

Question 2525

Topic: 1. General Principles & Basic Science

A patient with a multi-apical tibial deformity has two distinct CORAs identified on preoperative planning. The surgeon decides to perform a single osteotomy located exactly halfway between the two CORAs to correct the overall clinical angulation. According to Paley's principles, what will be the resulting mechanical axis alignment?

. The mechanical axis will be perfectly restored to the center of the joint with no offset.
. The mechanical axes of the proximal and distal segments will be parallel but translated (non-collinear).
. Pure translation will occur without any angular correction.
. A significant rotational deformity will be inevitably induced.
. The mechanical axis will shift entirely to the lateral compartment of the knee.

Correct Answer & Explanation

. The mechanical axes of the proximal and distal segments will be parallel but translated (non-collinear).

Explanation

Attempting to correct a multi-apical (two-apex) deformity with a single osteotomy between the CORAs effectively acts like Rule 3. The overall angulation may appear corrected clinically, but the mechanical axes will remain parallel and translated (a zig-zag deformity).

Question 2526

Topic: 1. General Principles & Basic Science

To increase the overall stiffness and stability of a circular external fixator construct, which of the following modifications is most effective?

. Increasing the ring diameter to provide more soft tissue clearance.
. Decreasing the ring diameter while safely maintaining a 2 cm skin clearance.
. Increasing the distance between the two rings.
. Using smooth wires exclusively instead of olive wires.
. Decreasing the wire tension by 20 percent.

Correct Answer & Explanation

. Decreasing the ring diameter while safely maintaining a 2 cm skin clearance.

Explanation

Decreasing the ring diameter is one of the most effective ways to increase frame stiffness, as it reduces the unsupported working length of the tensioned wires. A standard minimum skin clearance of roughly 2 fingerbreadths (approx 2 cm) must be maintained to accommodate swelling.

Question 2527

Topic: 1. General Principles & Basic Science

When inserting a transverse reference wire from lateral to medial at the level of the fibular neck during tibial frame application, which of the following anatomic structures is at greatest risk of direct injury?

. Deep peroneal nerve.
. Common peroneal nerve.
. Anterior tibial artery.
. Saphenous nerve.
. Posterior tibial artery.

Correct Answer & Explanation

. Common peroneal nerve.

Explanation

The common peroneal nerve wraps around the neck of the fibula superficially. Wire insertion from lateral to medial at this precise level places the nerve at extremely high risk of penetration or tethering.

Question 2528

Topic: 1. General Principles & Basic Science

A Taylor Spatial Frame (TSF) is selected for a complex 6-axis deformity correction. Which of the following is NOT one of the four standard mounting parameters required by the software to define the position of the frame relative to the reference bone segment?

. Anteroposterior (AP) translation.
. Medial/Lateral translation.
. Axial translation.
. Rotary offset.
. Bone diameter at the osteotomy site.

Correct Answer & Explanation

. Bone diameter at the osteotomy site.

Explanation

The TSF software requires four specific mounting parameters to localize the reference ring relative to the origin: AP translation, Medial/Lateral translation, Axial translation (offset), and Rotary offset. Bone diameter is not a mounting parameter.

Question 2529

Topic: Infection, Pharmacology & VTE

A patient undergoing tibial lengthening presents to the clinic 4 weeks postoperatively with erythema, localized pain, and serous discharge at a single pin site. There is no evidence of pin loosening or systemic illness. What is the most appropriate initial management?

. Immediate surgical removal of the pin.
. Intravenous vancomycin and hospital admission.
. Oral antibiotics and optimization of local pin site care.
. Surgical debridement of the pin tract.
. Complete revision of the external fixator frame.

Correct Answer & Explanation

. Oral antibiotics and optimization of local pin site care.

Explanation

This presentation is consistent with a minor (Checketts-burns Grade 1 or 2) pin tract infection. The standard of care is local pin care optimization and a short course of oral antibiotics covering skin flora. Pin removal is reserved for loose pins or refractory deep infections.

Question 2530

Topic: 1. General Principles & Basic Science

According to Paley's Osteotomy Rule 3, what is the expected geometric outcome if both the osteotomy and the hinge are placed away from the Center of Rotation of Angulation (CORA)?

. Pure angulation resulting in perfectly collinear mechanical axes.
. Angulation and translation resulting in parallel, non-collinear mechanical axes.
. Pure translation with a complete loss of joint congruence.
. Immediate premature consolidation of the regenerate.
. Correction of the rotational profile without altering the coronal plane.

Correct Answer & Explanation

. Angulation and translation resulting in parallel, non-collinear mechanical axes.

Explanation

Rule 3 states that if neither the hinge nor the osteotomy is at the CORA, the mechanical axes will undergo angulation and translation, resulting in parallel but displaced (non-collinear) axes, mimicking a translation deformity.

Question 2531

Topic: 1. General Principles & Basic Science

In evaluating the normal alignment of the lower extremity, the normal angle between the mechanical axis and the anatomic axis of the femur is approximately:

. 0 degrees.
. 2 to 3 degrees.
. 5 to 7 degrees.
. 10 to 12 degrees.
. 14 to 16 degrees.

Correct Answer & Explanation

. 5 to 7 degrees.

Explanation

The mechanical axis of the femur runs from the center of the femoral head to the center of the knee, while the anatomic axis follows the medullary canal. The normal angle between these two axes is typically 5 to 7 degrees.

Question 2532

Topic: 1. General Principles & Basic Science

A surgeon is planning a single-level correction of a distal tibial varus deformity. Due to soft tissue constraints, both the osteotomy and the hinge of the external fixator are placed 4 cm proximal to the identified Center of Rotation of Angulation (CORA).

According to Paley's Osteotomy Rules, what is the expected geometric outcome of this correction?

. The mechanical axes will be collinear with no translation.
. The mechanical axes will be collinear with translation at the osteotomy site.
. The mechanical axes will be parallel but translated, creating a secondary translation deformity.
. The osteotomy will result in pure distraction without angular correction.
. The mechanical axes will intersect exactly at the new hinge location without translation.

Correct Answer & Explanation

. The mechanical axes will be parallel but translated, creating a secondary translation deformity.

Explanation

Paley's Rule 3 states that if the hardware hinge is placed outside the CORA, the resulting proximal and distal mechanical axes will be parallel but non-collinear. This inadvertently introduces a translation deformity.

Question 2533

Topic: Biomechanics & Biomaterials

A 62-year-old male presents with progressive right knee pain, worse with activity. Full-length standing AP radiographs reveal a Mechanical Axis Deviation (MAD) of 15mm medial to the center of the knee joint. The surgeon suspects a varus deformity originating from the proximal tibia. Based on Paley's principles, which of the following angles, if found to be abnormal, would most directly confirm a proximal tibial varus deformity and guide a high tibial osteotomy (HTO)?

. A. Mechanical Lateral Distal Femoral Angle (mLDFA)
. B. Lateral Distal Tibial Angle (LDTA)
. C. Medial Proximal Tibial Angle (MPTA)
. D. Posterior Proximal Tibial Angle (PPTA)
. E. Neck-Shaft Angle (NSA)

Correct Answer & Explanation

. C. Medial Proximal Tibial Angle (MPTA)

Explanation

Correct Answer: CThe correct answer is C, the Medial Proximal Tibial Angle (MPTA). The case describes a patient with medial Mechanical Axis Deviation (MAD) and a suspicion of proximal tibial varus. According to Paley's principles, the MPTA is the cornerstone of tibial alignment in the frontal plane. A normal MPTA ranges from 85° to 90° (average ~87°). An MPTA of less than 85° specifically indicates tibia vara, which is a proximal tibial varus deformity. High Tibial Osteotomies (HTOs) are designed to correct this angle, typically restoring it to a normal or slightly valgus alignment (e.g., 89-90°) to offload the medial compartment.Option A (mLDFA)is the mechanical Lateral Distal Femoral Angle. While critical for overall limb alignment, it assesses distal femoral alignment (normal 85-90°). An abnormality here would indicate a femoral deformity, not a proximal tibial one.Option B (LDTA)is the Lateral Distal Tibial Angle. This angle assesses distal tibial alignment in the frontal plane (normal 86-92°). An abnormality here would indicate a deformity at the ankle level, not the proximal tibia.Option D (PPTA)is the Posterior Proximal Tibial Angle. This angle assesses the sagittal plane alignment (posterior tibial slope) of the proximal tibia (normal 77-84°). While important for knee kinematics, it does not directly quantify frontal plane varus/valgus deformity.Option E (NSA)is the Neck-Shaft Angle. This angle assesses the frontal plane alignment of the proximal femur (normal 124-136°). It is unrelated to knee or tibial deformities.

Question 2534

Topic: 1. General Principles & Basic Science

A 62-year-old male presents with progressive right knee pain, worse with ambulation. A long-standing, weight-bearing anteroposterior radiograph of the entire lower extremity is obtained, as shown in the diagram below, demonstrating the mechanical axis of the lower limb. The orthopedic surgeon measures the perpendicular distance from the mechanical axis to the center of the knee joint.

Based on Paley's principles, what is the normal range for this measurement, and what does an excessive medial deviation indicate?

. A. 0 mm (± 5 mm) lateral; indicates valgus alignment.
. B. 8 mm (± 7 mm) lateral; indicates varus alignment.
. C. 8 mm (± 7 mm) medial; indicates varus alignment.
. D. 0 mm (± 5 mm) medial; indicates valgus alignment.
. E. 15 mm (± 10 mm) medial; indicates valgus alignment.

Correct Answer & Explanation

. C. 8 mm (± 7 mm) medial; indicates varus alignment.

Explanation

Correct Answer: CThe question describes the Mechanical Axis Deviation (MAD), which is the perpendicular distance from the mechanical axis of the entire lower limb to the center of the knee joint. According to the case, the normal MAD is approximately 8 mm (± 7 mm) medial to the center of the knee. An excessive medial deviation (i.e., the mechanical axis passing significantly medial to the knee center) indicates a varus alignment, which predisposes to medial compartment osteoarthritis. Conversely, a mechanical axis passing lateral to the knee center indicates a valgus alignment.Option A is incorrect because the normal MAD is medial, not lateral, and 0 mm is not the typical normal value.Option B is incorrect because the normal MAD is medial, not lateral.Option D is incorrect because the normal MAD is approximately 8 mm medial, not 0 mm, and an excessive medial deviation indicates varus, not valgus.Option E is incorrect because 15 mm is outside the normal range, and an excessive medial deviation indicates varus, not valgus.

Question 2535

Topic: 1. General Principles & Basic Science

A 35-year-old female presents with a progressive varus deformity of her left knee. A full-length standing radiograph is obtained, and the orthopedic surgeon performs a detailed deformity analysis using Paley's principles. The diagram below illustrates the key frontal plane angles.

The surgeon measures the mLDFA as 95° and the MPTA as 80°. Based on these findings, what is the primary contributor to the patient's varus deformity?

. A. Femoral valgus and tibial valgus.
. B. Femoral varus and tibial varus.
. C. Isolated femoral varus.
. D. Isolated tibial varus.
. E. Normal femoral alignment with tibial valgus.

Correct Answer & Explanation

. B. Femoral varus and tibial varus.

Explanation

Correct Answer: BAccording to the case, the normal mLDFA (mechanical Lateral Distal Femoral Angle) is 88° (range: 85–90°). An mLDFA > 90° indicates femoral varus. The patient's mLDFA of 95° clearly indicates femoral varus.The normal MPTA (Medial Proximal Tibial Angle) is 87° (range: 85–90°). An MPTA < 85° indicates tibial varus. The patient's MPTA of 80° clearly indicates tibial varus.Therefore, both the femur and the tibia are contributing to the patient's overall varus deformity.Option A is incorrect as both measurements indicate varus, not valgus.Options C and D are incorrect because both bones are contributing to the varus deformity, not just one in isolation.Option E is incorrect as both femoral and tibial alignments are abnormal and indicate varus, not valgus.

Question 2536

Topic: 1. General Principles & Basic Science

A 40-year-old female presents with a severe valgus deformity of her right knee. A long-standing radiograph reveals an overall mechanical axis deviation lateral to the knee center. The surgeon measures the mLDFA and MPTA, finding both to be within normal limits. However, the medial aspect of the knee joint appears significantly widened on the radiograph, as shown conceptually in the alignment diagram below.

Based on these findings and Paley's principles, what is the most likely primary cause of this patient's valgus malalignment, and what is its normal value?

. A. Femoral valgus (mLDFA < 85°); normal value 88°.
. B. Tibial valgus (MPTA > 90°); normal value 87°.
. C. Intra-articular deformity due to a widened Joint Line Convergence Angle (JLCA); normal value 0–2°.
. D. Femoral varus (mLDFA > 90°); normal value 88°.
. E. Tibial varus (MPTA < 85°); normal value 87°.

Correct Answer & Explanation

. C. Intra-articular deformity due to a widened Joint Line Convergence Angle (JLCA); normal value 0–2°.

Explanation

Correct Answer: CThe case states that if a patient has a severe varus or valgus deformity, but the mLDFA and MPTA are normal, the deformity is intra-articular. A widened JLCA (Joint Line Convergence Angle) on the lateral side indicates lateral collateral ligament laxity or severe medial cartilage loss in a varus knee, and conversely, a widened medial JLCA indicates medial collateral ligament laxity or severe lateral cartilage loss in a valgus knee. The normal JLCA is 0–2°, meaning the distal femoral and proximal tibial joint lines should be nearly parallel. In this patient, normal mLDFA and MPTA with a severe valgus deformity and a significantly widened medial aspect of the knee joint strongly suggest an intra-articular deformity, specifically medial collateral ligament laxity, leading to an increased JLCA.Options A and B are incorrect because the mLDFA and MPTA are stated to be within normal limits, ruling out primary femoral or tibial bony deformities.Options D and E describe varus deformities, which contradict the patient's presentation of a valgus deformity.

Question 2537

Topic: 1. General Principles & Basic Science

During the preoperative radiographic assessment for a complex varus knee deformity using Paley's malalignment test, the Joint Line Convergence Angle (JLCA) is measured at 6 degrees (open laterally). What does this most likely indicate?

. Normal joint line obliquity
. Lateral collateral ligament contracture
. Medial collateral ligament contracture and lateral compartment wear
. Severe intra-osseous tibial deformity
. Medial compartment cartilage loss with lateral ligamentous laxity

Correct Answer & Explanation

. Medial compartment cartilage loss with lateral ligamentous laxity

Explanation

An increased JLCA indicates intra-articular deformity or ligamentous imbalance. In a varus knee, a JLCA > 2 degrees (converging medially/open laterally) typically reflects asymmetric cartilage wear medially and stretching/laxity of the lateral soft tissues.

Question 2538

Topic: Biology, Genetics & Bone Healing

You are performing a corticotomy for tibial lengthening using a circular frame. What is the primary biological rationale for observing a 5 to 7-day latent period prior to initiating distraction?

. To allow the inflammatory phase of fracture healing to subside completely
. To facilitate initial angiogenesis and mesenchymal stem cell aggregation
. To prevent premature consolidation of the regenerate
. To allow the patient to adjust to the external fixator
. To allow soft tissue swelling to resolve and pin tracks to epithelialize

Correct Answer & Explanation

. To facilitate initial angiogenesis and mesenchymal stem cell aggregation

Explanation

The latent period of 5-7 days allows for early callus formation, primary angiogenesis, and cellular proliferation at the corticotomy site. This ensures robust regenerate bone formation during the subsequent distraction phase.

Question 2539

Topic: 1. General Principles & Basic Science

A patient requires correction of a distal femoral valgus deformity. The surgeon plans an osteotomy distal to the CORA and places the hinge axis at the osteotomy site rather than the CORA. What is the expected mechanical outcome according to Paley's principles?

. Collinear translation with perfect mechanical axis alignment
. Pure angulation without translation
. Angulation with a residual translation deformity
. Lengthening without angulation
. Perfect anatomic axis restoration without translation

Correct Answer & Explanation

. Angulation with a residual translation deformity

Explanation

Paley's Rule 3 states that if the osteotomy and the hinge are both placed away from the CORA, the mechanical axis of the newly aligned segment will be parallel to the target axis, resulting in a residual translation deformity.

Question 2540

Topic: 1. General Principles & Basic Science

A 22-year-old female undergoes cosmetic bilateral femoral lengthening using an intramedullary lengthening nail. The lengthening is performed exactly along the anatomical axis of the femur. Without additional surgical modifications, what is the expected effect on the mechanical axis of the lower limb?

. Lateral deviation of the mechanical axis (valgus shift)
. Medial deviation of the mechanical axis (varus shift)
. No change in the mechanical axis
. Creation of an intra-articular recurvatum deformity
. Significant internal rotation of the distal fragment

Correct Answer & Explanation

. Lateral deviation of the mechanical axis (valgus shift)

Explanation

Because the normal anatomical axis of the femur is oriented in roughly 6-9 degrees of valgus relative to the mechanical axis, lengthening strictly along the anatomical axis without compensation shifts the mechanical axis laterally, creating a valgus alignment.

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