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1. General Principles & Basic Science MCQs

Practice Set 151 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 3001

Topic: Biology, Genetics & Bone Healing

A 22-year-old female is undergoing distraction osteogenesis for a post-traumatic femoral deformity. At 4 weeks into distraction, radiographs show an "hourglass" appearance of the regenerate bone with an extremely thin, radiolucent central zone. What is the most appropriate initial management?

. Increase the distraction rate to 2 mm per day.
. Perform an acute bone grafting of the distraction gap.
. Decrease the distraction rate or perform temporary compression.
. Remove the external fixator and convert to an intramedullary nail immediately.
. Administer intravenous bisphosphonates to stimulate ossification.

Correct Answer & Explanation

. Decrease the distraction rate or perform temporary compression.

Explanation

An "hourglass" regenerate with a very thin central radiolucent zone indicates that the distraction rate is too fast, leading to poor bone formation. The appropriate management is to slow the rate of distraction or temporarily compress to stimulate robust regenerate.

Question 3002

Topic: 1. General Principles & Basic Science

A 35-year-old male undergoes a 5 cm femoral lengthening using a fully implantable motorized intramedullary lengthening nail. Postoperatively, he experiences a severe reduction in knee flexion. Tightness of which specific structure is the most likely anatomical restraint causing this complication?

. Biceps femoris
. Semitendinosus
. Rectus femoris and vastus intermedius
. Iliotibial band
. Sartorius

Correct Answer & Explanation

. Rectus femoris and vastus intermedius

Explanation

During femoral lengthening, knee flexion is predominantly restricted by the quadriceps mechanism, specifically the rectus femoris and vastus intermedius, which span the anterior thigh and tether over the elongating bone.

Question 3003

Topic: 1. General Principles & Basic Science

A surgeon is evaluating a bi-apical (double-level) deformity of the tibia. To accurately find the two Centers of Rotation of Angulation (CORAs), which of the following radiographic steps is necessary?

. Drawing only the proximal and distal mechanical axes and finding their single intersection.
. Drawing a third 'middle' axis line along the intercalary segment to intersect with the proximal and distal axes.
. Measuring the Joint Line Convergence Angle and subtracting it from the mMPTA.
. Using the Paley multiplier to calculate the exact mid-diaphyseal point.
. Applying a virtual hinge at the level of the tibial tubercle.

Correct Answer & Explanation

. Drawing a third 'middle' axis line along the intercalary segment to intersect with the proximal and distal axes.

Explanation

In multi-apical deformities, a single intersection is insufficient. A 'middle' axis line must be drawn through the intercalary segment between the deformities. The intersections of this middle line with the proximal and distal axes identify the two distinct CORAs.

Question 3004

Topic: Biology, Genetics & Bone Healing

In distraction osteogenesis using the Ilizarov method, the standard protocol includes a latency period before beginning distraction. What is the primary biological purpose of this latency phase?

. To allow the pin tracts to fully epithelialize, preventing infection.
. To allow for the resolution of postoperative edema before stretching the skin.
. To permit initial hematoma organization and early mesenchymal stem cell aggregation for soft callus formation.
. To ensure the corticotomy site undergoes complete rigid endochondral ossification.
. To acclimate the patient to the weight of the external fixator.

Correct Answer & Explanation

. To permit initial hematoma organization and early mesenchymal stem cell aggregation for soft callus formation.

Explanation

The latency phase (typically 7-10 days) is critical to allow the early stages of fracture healing to commence, specifically the formation of a vascularized soft callus, before mechanical distraction forces are applied.

Question 3005

Topic: 1. General Principles & Basic Science

A resident is using a Taylor Spatial Frame to correct a complex deformity. If both the osteotomy and the ACA (hinge) are placed at a level different from the CORA (Paley's Rule 3), what is the definitive consequence on the limb's alignment?

. The mechanical axes will be collinear
. A purely rotational deformity will be induced
. The mechanical axes will become parallel but not collinear, creating a new translation deformity
. The osteotomy site will distract symmetrically without angular change
. The joint line convergence angle will increase dramatically

Correct Answer & Explanation

. The mechanical axes will become parallel but not collinear, creating a new translation deformity

Explanation

Under Paley's Rule 3, placing both the osteotomy and the ACA away from the CORA results in the proximal and distal mechanical axes becoming parallel but not collinear. This intentionally or unintentionally induces a translation deformity.

Question 3006

Topic: 1. General Principles & Basic Science

When assessing a patient with a suspected intra-articular deformity or severe collateral ligament laxity contributing to malalignment, which radiographic parameter is most critical to evaluate?

. Mechanical lateral distal femoral angle (mLDFA)
. Mechanical medial proximal tibial angle (mMPTA)
. Joint line convergence angle (JLCA)
. Anatomic mechanical angle (AMA)
. Proximal posterior tibial angle (PPTA)

Correct Answer & Explanation

. Joint line convergence angle (JLCA)

Explanation

The Joint Line Convergence Angle (JLCA) measures the convergence of the distal femoral and proximal tibial articular surfaces. A normal JLCA is 0 to 2 degrees; values above this indicate intra-articular deformity or ligamentous laxity.

Question 3007

Topic: 1. General Principles & Basic Science

A surgeon is planning to correct a sagittal plane deformity of the proximal tibia (genu recurvatum). To restore normal anatomy, what is the target proximal posterior tibial angle (PPTA) that should be achieved?

. 90 degrees
. 87 degrees
. 81 degrees
. 75 degrees
. 65 degrees

Correct Answer & Explanation

. 81 degrees

Explanation

The normal proximal posterior tibial angle (PPTA), which defines the anatomic sagittal slope of the proximal tibia, is approximately 81 degrees (range 77 to 84 degrees).

Question 3008

Topic: Biology, Genetics & Bone Healing

A patient is undergoing Ilizarov distraction osteogenesis for a tibial length discrepancy. What is the biological rationale for waiting 5 to 7 days (the latency period) before initiating distraction?

. To allow the hematoma to dissipate entirely to prevent infection
. To permit initial mesenchymal stem cell aggregation and vascular ingrowth (pro-callus formation)
. To allow the periosteum to completely fuse over the osteotomy gap
. To decrease the risk of pin tract infections during the distraction phase
. To allow the bone to undergo endochondral ossification first

Correct Answer & Explanation

. To permit initial mesenchymal stem cell aggregation and vascular ingrowth (pro-callus formation)

Explanation

The latency period of 5-7 days allows the fracture hematoma to organize and mesenchymal stem cells to begin forming a vascularized pro-callus. Premature distraction disrupts this crucial initial vascular network, leading to poor regenerate.

Question 3009

Topic: 1. General Principles & Basic Science

A surgeon is planning an opening wedge high tibial osteotomy. According to the principles of deformity correction, where should the axis of correction of angulation (ACA) be positioned to create a pure opening wedge without translational shift?

. On the convex cortex of the deformity
. On the concave cortex of the deformity
. Directly in the center of the medullary canal
. 10 mm anterior to the CORA on the bisector line
. Away from the convex cortex on the transverse bisector line

Correct Answer & Explanation

. On the concave cortex of the deformity

Explanation

Placing the ACA on the concave cortex of the deformity results in an opening wedge correction. Placing it on the convex cortex results in a closing wedge correction.

Question 3010

Topic: 1. General Principles & Basic Science

A 30-year-old male is undergoing simultaneous deformity correction and limb lengthening. If the surgeon places the hinge (ACA) along the bisector line but displaced far away from the convex cortex in space, what will be the effect on the osteotomy site?

. Pure closing wedge correction
. Opening wedge correction with symmetrical distraction (lengthening) of both cortices
. Translation of the mechanical axis without any angular correction
. Rotational malalignment proportional to the distance from the cortex
. Complete collapse of the osteotomy gap

Correct Answer & Explanation

. Opening wedge correction with symmetrical distraction (lengthening) of both cortices

Explanation

Moving the ACA away from the convex cortex along the bisector line causes both the concave and convex cortices to distract during angular correction, resulting in simultaneous angulation and lengthening.

Question 3011

Topic: 1. General Principles & Basic Science

A patient with an external fixator for tibial lengthening presents to the clinic 4 weeks into the distraction phase. Radiographs show premature consolidation of the regenerate. Which of the following is the most likely cause?

. A latency period of 3 days
. A distraction rate of 1.5 mm per day
. A distraction rate of 0.5 mm per day
. Use of a Gigli saw for the osteotomy
. Aggressive physical therapy protocols

Correct Answer & Explanation

. A distraction rate of 0.5 mm per day

Explanation

Premature consolidation occurs when the bone heals faster than it is being distracted, typically due to a too-slow distraction rate (< 1 mm/day) or an excessively long latency period.

Question 3012

Topic: 1. General Principles & Basic Science

When planning a distal femoral osteotomy using anatomic axes rather than mechanical axes, the surgeon must account for the normal anatomic-mechanical angle (AMA) of the femur. What is the typical normal AMA of the femur?

. 0 to 2 degrees
. 3 to 4 degrees
. 5 to 7 degrees
. 9 to 11 degrees
. 12 to 14 degrees

Correct Answer & Explanation

. 5 to 7 degrees

Explanation

The anatomic axis of the femur is normally in 5 to 7 degrees of valgus relative to the mechanical axis. This AMA must be factored in when using intramedullary devices that follow the anatomic axis.

Question 3013

Topic: 1. General Principles & Basic Science

A 19-year-old patient requires acute correction of a severe valgus deformity of the proximal tibia (20 degrees). Which of the following soft tissue structures is at the highest risk of injury during acute correction and may dictate the need for a gradual correction instead?

. Tibial nerve
. Popliteal artery
. Common peroneal nerve
. Saphenous nerve
. Medial collateral ligament

Correct Answer & Explanation

. Common peroneal nerve

Explanation

Acute correction of severe valgus places the lateral structures on significant stretch. The common peroneal nerve is particularly susceptible to stretch neuropraxia, making gradual correction safer for severe valgus.

Question 3014

Topic: 1. General Principles & Basic Science

In deformity planning, apparent angulation on an AP radiograph may actually represent a multiplanar deformity projected onto a 2D plane. Which of the following best confirms the 'true plane' of a uniapical deformity?

. A CT scan with 3D reconstruction showing pure rotation
. The radiographic view where the deformity shows maximum angulation and the orthogonal view shows zero angulation
. A standing long-leg film demonstrating a normal JLCA
. The view where the mechanical axis directly crosses the anatomic axis
. An axial MRI through the apex of the deformity

Correct Answer & Explanation

. The radiographic view where the deformity shows maximum angulation and the orthogonal view shows zero angulation

Explanation

The true plane of a deformity is found on the projection where the magnitude of angulation is maximized. In the orthogonal view (90 degrees to the true plane), the angulation will appear to be zero.

Question 3015

Topic: Infection, Pharmacology & VTE

A patient undergoing tibial lengthening with a circular external fixator presents with erythema, pain, and serous drainage at a proximal half-pin site. The pin remains rigidly fixed in the bone. According to standard protocols (e.g., Checketts-Burns), what is the most appropriate initial management?

. Immediate removal of the pin and re-insertion at a different site
. Intravenous vancomycin and surgical debridement
. Oral antibiotics and aggressive local pin site care
. Cessation of distraction until the erythema resolves
. Observation only, as this is a normal reaction to tension

Correct Answer & Explanation

. Oral antibiotics and aggressive local pin site care

Explanation

Superficial pin tract infections with a stable pin (Checketts-Burns grades 1-3) are best managed with oral antibiotics and improved local pin care. Pin removal is reserved for loose pins or deep osteomyelitis.

Question 3016

Topic: 1. General Principles & Basic Science

A surgeon is utilizing a Taylor Spatial Frame (TSF) for a complex hexapod correction. The 'Mounting Parameters' are critical for the software to calculate the strut adjustments. Which of the following accurately describes the essential mounting parameters required?

. The distance from the reference ring to the joint line in AP, Lateral, and Axial planes
. The offset of the reference ring from the origin of the reference bone fragment in the AP, Lateral, and Axial planes
. The precise angles of the six struts prior to making the osteotomy
. The distance of the CORA from the skin surface in millimeters
. The mechanical axis deviation measured preoperatively

Correct Answer & Explanation

. The offset of the reference ring from the origin of the reference bone fragment in the AP, Lateral, and Axial planes

Explanation

Mounting parameters tell the TSF software exactly where the reference ring is located relative to the reference bone fragment (origin) in orthogonal space: AP offset, Lateral offset, and Axial (length) offset.

Question 3017

Topic: 1. General Principles & Basic Science

A 45-year-old patient presents with a distal femoral valgus deformity. The CORA is identified 1.5 cm proximal to the joint line. Due to the need for adequate distal bone stock for fixation, the surgeon performs the osteotomy 6 cm proximal to the joint line but maintains the axis of correction of angulation (ACA) exactly at the CORA. What is the expected outcome of this correction based on Paley's principles?

. The mechanical axes will remain deviated resulting in a zigzag deformity.
. The deformity will undergo pure angulation with no translation.
. The mechanical axes will become collinear, but there will be translation at the osteotomy site.
. The deformity will fail to correct in the coronal plane, necessitating a second osteotomy.
. Pure translation will occur without any change in the mechanical axis deviation.

Correct Answer & Explanation

. The mechanical axes will become collinear, but there will be translation at the osteotomy site.

Explanation

According to Paley's Rule 2, if the ACA is placed at the CORA but the osteotomy is performed at a different level, the mechanical axes will successfully become collinear. However, this obligates translation of the bone segments at the osteotomy site.

Question 3018

Topic: 1. General Principles & Basic Science

A surgeon evaluates a patient for a high tibial osteotomy. The varus deformity's CORA is located in the mid-diaphysis, but the surgeon decides to place both the osteotomy and the hinge (ACA) in the proximal metaphysis. Which of the following accurately describes the resulting alignment after angular correction?

. The mechanical axes will be collinear with pure rotational correction.
. The mechanical axes will be parallel but translated, causing a zigzag deformity.
. The osteotomy will result in pure translation without any angular correction.
. The joint line will become perfectly horizontal with collinear mechanical axes.
. The mechanical axes will perfectly intersect at the level of the knee joint.

Correct Answer & Explanation

. The mechanical axes will be parallel but translated, causing a zigzag deformity.

Explanation

Paley's Rule 3 dictates that if both the ACA and the osteotomy are placed at a level other than the CORA, the proximal and distal mechanical axes will end up parallel but translated. This results in iatrogenic mechanical axis deviation, often called a zigzag deformity.

Question 3019

Topic: 1. General Principles & Basic Science

When analyzing full-length standing lower extremity radiographs for a complex post-traumatic genu valgum deformity, the surgeon measures the mechanical lateral distal femoral angle (mLDFA) and the anatomic lateral distal femoral angle (aLDFA). In a normal population, what is the accepted standard reference value for the mLDFA utilized in deformity planning?

. 81 degrees
. 87 degrees
. 90 degrees
. 93 degrees
. 95 degrees

Correct Answer & Explanation

. 87 degrees

Explanation

The normal mechanical lateral distal femoral angle (mLDFA) is approximately 87 degrees (range 85-90 degrees). The normal anatomic lateral distal femoral angle (aLDFA) is typically around 81 degrees.

Question 3020

Topic: 1. General Principles & Basic Science

A 38-year-old male is undergoing a proximal tibial osteotomy for genu varum. The surgeon plans an opening-wedge correction using Paley's principles to avoid unwanted translation. Where must the axis of correction of angulation (ACA) be positioned relative to the bone to achieve a pure opening-wedge osteotomy?

. Exactly at the central intramedullary axis
. On the concave cortex of the deformity
. On the convex cortex of the deformity
. 1 cm distal to the CORA on the medial side
. At the level of the joint line laterally

Correct Answer & Explanation

. On the convex cortex of the deformity

Explanation

To perform a pure opening-wedge osteotomy, the ACA (the hinge) must be placed on the convex cortex of the deformity. Placing the ACA on the concave cortex would result in a closing-wedge osteotomy.

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