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1. General Principles & Basic Science MCQs

Practice Set 115 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 2281

Topic: 1. General Principles & Basic Science

A patient has a pure translational deformity of the tibial diaphysis without any angulation. Where is the Center of Rotation of Angulation (CORA) located in this scenario?

. At the proximal tip of the translation
. At the exact midpoint of the translation
. At the distal tip of the translation
. At the adjacent joint line
. At infinity

Correct Answer & Explanation

. At infinity

Explanation

In a pure translational deformity, the proximal and distal anatomic axes are parallel and never intersect. Therefore, the CORA is mathematically considered to be at infinity.

Question 2282

Topic: 1. General Principles & Basic Science

During planning for a distal femoral deformity correction, the surgeon measures the mechanical lateral distal femoral angle (mLDFA). What is the normal average population value for the mLDFA, which serves as the target for realignment?

. 81 degrees
. 84 degrees
. 88 degrees
. 93 degrees
. 95 degrees

Correct Answer & Explanation

. 88 degrees

Explanation

The normal mechanical lateral distal femoral angle (mLDFA) is consistently around 88 degrees (range 85-90). This is a fundamental parameter for frontal plane deformity planning around the knee.

Question 2283

Topic: 1. General Principles & Basic Science

A high tibial osteotomy is being planned. The surgeon must evaluate the mechanical medial proximal tibial angle (MPTA). What is the accepted normal population mean for the MPTA?

. 81 degrees
. 84 degrees
. 87 degrees
. 90 degrees
. 93 degrees

Correct Answer & Explanation

. 87 degrees

Explanation

The normal mechanical medial proximal tibial angle (MPTA) is approximately 87 degrees (range 85-90 degrees).

Question 2284

Topic: 1. General Principles & Basic Science

When performing a single-cut osteotomy for an angular deformity, the surgeon places the hinge (Axis of Correction of Angulation) precisely on the concave cortex of the deformity. Which of the following best describes the resulting bone length change?

. The bone length remains completely unchanged.
. The bone will be shortened.
. The bone will be lengthened.
. The convex side will shorten while the concave side lengthens.
. Length changes cannot be predicted by hinge placement alone.

Correct Answer & Explanation

. The bone will be lengthened.

Explanation

Placing the ACA on the concave cortex necessitates an opening wedge osteotomy to correct the angle. An opening wedge inherently lengthens the bone segment.

Question 2285

Topic: 1. General Principles & Basic Science

According to Paley's First Osteotomy Rule, if the osteotomy and the Axis of Correction of Angulation (ACA) both pass directly through the Center of Rotation of Angulation (CORA), what is the resultant anatomic effect on the bone fragments?

. Pure angulation without translation at the osteotomy site
. Angulation with intentional translation to restore the mechanical axis
. Pure translation without angulation
. Shortening of the bone proportional to the degree of angulation
. Secondary translation deformity of the mechanical axis

Correct Answer & Explanation

. Pure angulation without translation at the osteotomy site

Explanation

Paley's Rule 1 states that when both the osteotomy and the ACA are located at the CORA, the mechanical axis is restored via pure angulation. No translation occurs at the osteotomy site.

Question 2286

Topic: 1. General Principles & Basic Science

A surgeon plans to correct a diaphyseal tibia deformity. The osteotomy is performed at a different level than the CORA due to soft tissue constraints, but the Axis of Correction of Angulation (ACA) is maintained exactly at the CORA. According to Paley's Second Rule, what will be the expected anatomical outcome?

. A new secondary angulation deformity will be introduced.
. The bone ends will translate at the osteotomy site, but the mechanical axis will be restored.
. The mechanical axis will fail to be restored, remaining translated.
. The overall length of the tibia will double.
. Pure angulation will occur at the osteotomy site without translation.

Correct Answer & Explanation

. The bone ends will translate at the osteotomy site, but the mechanical axis will be restored.

Explanation

Under Paley's Rule 2, placing the ACA at the CORA but making the osteotomy at a different level restores the mechanical axis. However, it necessitates translation of the bone ends at the osteotomy site to achieve this alignment.

Question 2287

Topic: 1. General Principles & Basic Science

When applying Paley's Third Osteotomy Rule to a severe femoral deformity, where the osteotomy and the ACA are both executed at a level distinct from the CORA, what is the expected mechanical outcome?

. The mechanical axis will be fully restored without bone gap.
. The bone ends will remain perfectly apposed without translation.
. A secondary translation deformity of the mechanical axis will occur.
. Pure angulation will flawlessly realign the joint orientation angles.
. The mechanical axis will shift into exactly 5 degrees of valgus.

Correct Answer & Explanation

. A secondary translation deformity of the mechanical axis will occur.

Explanation

Paley's Rule 3 dictates that if the ACA and osteotomy are outside the CORA, correcting the angulation will cause the proximal and distal mechanical axes to become parallel but translated. This introduces a secondary translation deformity.

Question 2288

Topic: 1. General Principles & Basic Science

A surgeon analyzes a clinically straight lower extremity. The mechanical axis passes directly through the center of the knee. However, radiographs reveal a mechanical lateral distal femoral angle (mLDFA) of 95 degrees and a medial proximal tibial angle (MPTA) of 94 degrees. What does this indicate?

. Normal anatomical alignment with standard joint orientation
. A pure translational deformity of the femur
. Compensatory deformities resulting in an oblique joint line
. A missed ligamentous injury of the knee
. Severe mechanical axis deviation to the medial compartment

Correct Answer & Explanation

. Compensatory deformities resulting in an oblique joint line

Explanation

An mLDFA of 95 (valgus femur) and an MPTA of 94 (varus tibia) represent compensatory deformities. While the overall mechanical axis may remain neutral, the knee joint line becomes abnormally oblique.

Question 2289

Topic: 1. General Principles & Basic Science

When planning an opening-wedge osteotomy to correct a diaphyseal deformity, where must the Axis of Correction of Angulation (ACA) be positioned to strictly achieve an opening wedge without any bone resection?

. At the center of the medullary canal
. On the concave cortex of the deformity
. On the convex cortex of the deformity
. Outside the bone, adjacent to the concave cortex
. At the exact center of the knee joint

Correct Answer & Explanation

. On the convex cortex of the deformity

Explanation

To create a pure opening wedge, the hinge (ACA) must be placed on the convex cortex of the deformity. This distracts the concave cortex and inevitably lengthens the bone.

Question 2290

Topic: 1. General Principles & Basic Science

In the analysis of lower extremity deformity, which of the following is considered the normal population average for the mechanical lateral distal femoral angle (mLDFA)?

. 81 degrees
. 84 degrees
. 88 degrees
. 93 degrees
. 98 degrees

Correct Answer & Explanation

. 88 degrees

Explanation

The normal average mechanical lateral distal femoral angle (mLDFA) is 88 degrees, with a typical physiological range of 85 to 90 degrees.

Question 2291

Topic: 1. General Principles & Basic Science

A 55-year-old patient presents with a true oblique plane deformity of the tibia. Orthogonal radiographs show a 15-degree varus deformity on the AP view and a 20-degree procurvatum deformity on the lateral view. What is the approximate magnitude of the maximal deformity in the true oblique plane?

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

Correct Answer & Explanation

. 25 degrees

Explanation

Using the trigonometric method (Pythagorean theorem for small angles), the true magnitude is the square root of the sum of the squares: sqrt(15^2 + 20^2) = sqrt(225 + 400) = sqrt(625) = 25 degrees.

Question 2292

Topic: 1. General Principles & Basic Science

A surgeon analyzes a long bone where the proximal and distal anatomical axes are perfectly parallel but not collinear. What type of deformity does this isolated geometric relationship describe?

. A pure rotational deformity
. A pure translation deformity
. An apex-anterior angulation deformity
. A complex multi-apical deformity
. A normal physiological bowing

Correct Answer & Explanation

. A pure translation deformity

Explanation

When the proximal and distal axes are parallel but separated by a distance and do not intersect, the bone exhibits a pure translation deformity without any angulation.

Question 2293

Topic: 1. General Principles & Basic Science

If a surgeon places the Axis of Correction of Angulation (ACA) exactly on the concave cortex of a deformed bone and performs an osteotomy at the CORA, what is the resultant effect on the bone's length?

. It results in overall lengthening of the segment.
. It results in pure translation.
. It results in shortening, effectively creating a closing wedge.
. The length remains completely unchanged.
. It produces a multiplanar oblique length increase.

Correct Answer & Explanation

. It results in shortening, effectively creating a closing wedge.

Explanation

Placing the ACA on the concave cortex forces the convex cortex to collapse together during correction. This mechanically acts as a pure closing wedge osteotomy, resulting in shortening of the bone.

Question 2294

Topic: 1. General Principles & Basic Science

A surgeon plans a tibial osteotomy for a diaphyseal varus deformity. The center of rotation of angulation (CORA) is accurately determined. The surgeon places the hinge (axis of correction of angulation, ACA) exactly at the CORA, but makes the actual bone cut (osteotomy) 4 cm proximal to the CORA. According to Paley's rules of osteotomy, what is the expected geometric result of this maneuver?

. Pure angulation with collinear anatomical axes and no translation
. Correction of angulation accompanied by translation of the bone ends
. Pure translation of the bone ends with no angular change
. Creation of a secondary multi-apical deformity requiring a second osteotomy
. Loss of mechanical axis correction with spontaneous rotational shift

Correct Answer & Explanation

. Correction of angulation accompanied by translation of the bone ends

Explanation

According to Paley's Rule 2, when the ACA is placed at the CORA but the osteotomy is made at a different level, correction of the angulation is achieved, but the bone ends will translate relative to each other. This rule is often utilized intentionally when bone quality at the CORA is poor.

Question 2295

Topic: 1. General Principles & Basic Science

According to Paley's Rule 3 of deformity correction, if both the osteotomy and the axis of correction of angulation (ACA) are placed at a level distinct from the center of rotation of angulation (CORA), what is the expected geometric outcome upon correction?

. Complete correction of the deformity with collinear anatomical axes.
. Correction of the angular deformity but with a new translation deformity (axis shift).
. Pure translation of the bone ends without any angular change.
. Spontaneous correction of accompanying length discrepancies without translation.
. An uncorrectable rotational malalignment.

Correct Answer & Explanation

. Correction of the angular deformity but with a new translation deformity (axis shift).

Explanation

Paley's Rule 3 states that when both the osteotomy and the ACA are located away from the CORA, attempting to correct the angulation will unavoidably create a translation deformity. This results in an axis shift, leaving the proximal and distal anatomical axes parallel but not collinear.

Question 2296

Topic: Biology, Genetics & Bone Healing

When employing distraction osteogenesis for deformity correction using a Taylor Spatial Frame, what is the critical physiological rationale for utilizing a latency period of 7 to 10 days before beginning distraction?

. To allow the external fixator pins to achieve rigid osteointegration with the cortex.
. To permit the acute inflammatory phase to subside and mesenchymal stem cells to populate the hematoma.
. To intentionally induce premature consolidation of the osteotomy site for better stability.
. To stretch the surrounding neurovascular structures passively before active bone movement.
. To ensure the osteotomy gap is completely filled with mature lamellar bone.

Correct Answer & Explanation

. To permit the acute inflammatory phase to subside and mesenchymal stem cells to populate the hematoma.

Explanation

The latency period allows the initial fracture healing response to progress, specifically facilitating the organization of the hematoma and the infiltration of mesenchymal cells. Initiating distraction before this soft callus begins to form disrupts the cellular foundation, potentially leading to poor or non-existent regenerate bone.

Question 2297

Topic: 1. General Principles & Basic Science

A surgeon plans to correct a severe recurvatum deformity of the proximal tibia using an opening wedge anterior osteotomy. To perfectly correct the angulation without creating any translation at the osteotomy site, where must the axis of correction of angulation (ACA) and the osteotomy be placed relative to the CORA?

. Both the ACA and the osteotomy must be located precisely at the CORA.
. The ACA must be at the CORA, but the osteotomy can be located anywhere.
. The osteotomy must be at the CORA, but the ACA must be placed at the posterior cortex.
. Both the ACA and the osteotomy must be placed away from the CORA.
. The ACA is placed at the CORA, and the osteotomy is made in the distal metaphysis.

Correct Answer & Explanation

. Both the ACA and the osteotomy must be located precisely at the CORA.

Explanation

Paley's Rule 1 dictates that for pure angular correction without any translation of the bone ends, both the osteotomy cut and the hinge (Axis of Correction of Angulation, ACA) must be located exactly at the Center of Rotation of Angulation (CORA).

Question 2298

Topic: 1. General Principles & Basic Science

A 25-year-old male presents with a 4.6 cm limb length discrepancy (LLD) of the right lower extremity following a traumatic injury. Preoperative gait analysis is performed, and the vertical ground reaction force (GRF) curve for the shorter limb is obtained. Review the GRF graph below, specifically the top curve representing the preoperative state of the short limb.

Based on the case description and the provided graph, which of the following statements accurately describes the kinetic findings on the shorter limb preoperatively?

. The GRF curve demonstrates a robust double-hump pattern, indicating efficient weight acceptance and push-off.
. Stance time on the shorter limb is prolonged, reflecting a cautious and stable gait.
. The GRF curve has a severely attenuated, blunted profile, indicating poor weight acceptance and diminished push-off.
. The vertical displacement of the center of mass is minimized due to rapid offloading.
. The patient exhibits increased metabolic efficiency due to compensatory mechanisms.

Correct Answer & Explanation

. The GRF curve has a severely attenuated, blunted profile, indicating poor weight acceptance and diminished push-off.

Explanation

Correct Answer: CThe case explicitly describes the preoperative GRF findings for a patient with a 4.6 cm LLD, stating, 'Look closely at the top graph: the GRF curve has a severely attenuated, blunted profile. It lacks the distinct 'double-hump' characteristic of normal walking. This indicates poor, hesitant weight acceptance during the loading response phase, and a severely diminished, weak push-off phase during terminal stance.' Therefore, Option C is the most accurate description. Option A is incorrect as the curve lacks a robust double-hump. Option B is incorrect; the case states, 'The most consistent and telling alteration is a marked reduction in stance time on the shorter limb.' Option D is incorrect; the center of mass drops excessively into a 'biomechanical valley' on the shorter limb, and rapid offloading is an attempt topreventfurther inefficient displacement, not to minimize it initially. Option E is incorrect; the case states these compensatory strategies are 'metabolically expensive' and lead to 'increased energy expenditure.'

Question 2299

Topic: 1. General Principles & Basic Science

Following a successful limb lengthening procedure for the 4.6 cm LLD described in the previous question, the patient undergoes a repeat gait analysis. The middle GRF curve in the image below represents the post-operative state of the corrected limb.

Comparing the post-operative GRF curve (middle graph) to the preoperative curve (top graph) and the normal control (bottom graph), what is the most significant kinetic improvement observed?

. A persistent reduction in stance time on the corrected limb, indicating continued caution.
. An increase in the initial weight acceptance peak, but a continued blunting of the push-off phase.
. Restoration of a robust, healthy double-hump pattern, signifying normalized weight acceptance and powerful push-off.
. A shift of the vertical ground reaction force vector significantly lateral to the knee joint.
. An increase in the overall magnitude of the GRF, but without a distinct double-hump.

Correct Answer & Explanation

. Restoration of a robust, healthy double-hump pattern, signifying normalized weight acceptance and powerful push-off.

Explanation

Correct Answer: CThe case describes the post-operative kinetic changes: 'More importantly, the GRF curve is completely transformed. The post-operative graph shows a robust, healthy double-hump pattern, identical to the normal control graph at the bottom. It features a restored, sharp weight acceptance peak (the first hump) and a powerful, definitive push-off phase (the second hump).' This directly supports Option C. Option A is incorrect; the case states, 'stance time on the corrected limb has increased to 0.70 seconds, now perfectly matching the normal contralateral side.' Option B is incorrect as both peaks are restored. Option D is not discussed in the context of GRF curve shape, which primarily reflects vertical forces and timing. Option E is incorrect because the distinct double-hump is indeed restored, and the magnitude is normalized, not just increased without pattern.

Question 2300

Topic: 1. General Principles & Basic Science

A 55-year-old patient with a history of poliomyelitis presents with a complex lower limb deformity. A full-length lateral standing radiograph reveals a significant sagittal plane deformity of the proximal tibia. To precisely plan a corrective osteotomy according to Paley's method, the orthopedic surgeon must first identify the Sagittal Center of Rotation of Angulation (CORA). Which of the following best describes the methodology for identifying the CORA?

. The point where the mechanical axis intersects the anatomical axis of the deformed bone.
. The midpoint of the deformity on the lateral radiograph, regardless of bone segment alignment.
. The intersection of the mid-diaphyseal line of the proximal bone segment and the mid-diaphyseal line of the distal bone segment.
. The point of maximum curvature of the bone, as determined by a best-fit circle.
. The intersection of the joint line and the anatomical axis of the more deformed segment.

Correct Answer & Explanation

. The intersection of the mid-diaphyseal line of the proximal bone segment and the mid-diaphyseal line of the distal bone segment.

Explanation

Correct Answer: CThe text clearly defines the methodology for identifying the CORA: 'Draw the mid-diaphyseal line of the proximal bone segment (the anatomical axis of the proximal fragment). Draw the mid-diaphyseal line of the distal bone segment (the anatomical axis of the distal fragment). The intersection of these two lines is the CORA.' Identifying the CORA is paramount in deformity correction, as placing the osteotomy and hardware hinge precisely at the CORA ensures pure angular correction without introducing unwanted translation.Option A is incorrect because the CORA is defined by the intersection of anatomical axes, not mechanical axes, especially in the sagittal plane where the mechanical axis is a plumb line.Option B is incorrect as the CORA is a precise geometric point, not a subjective 'midpoint' of the deformity.Option D is incorrect; while curvature is involved, the CORA is defined by the intersection of axes, not a best-fit circle.Option E is incorrect as the CORA is an extra-articular concept for bony deformity, not directly related to the joint line's intersection with a single anatomical axis.

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