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1. General Principles & Basic Science MCQs

Practice Set 132 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 2621

Topic: 1. General Principles & Basic Science

A patient with polio residuals presents with a severe knee recurvatum deformity. You are planning a corrective proximal tibial osteotomy. To adequately address the sagittal plane deformity and prevent recurrence, how should the osteotomy wedge be oriented?

. Anterior closing wedge to increase posterior tibial slope.
. Anterior opening wedge to flex the proximal articular fragment.
. Posterior opening wedge to extend the proximal articular fragment.
. Lateral closing wedge to induce valgus.
. Medial opening wedge to induce varus.

Correct Answer & Explanation

. Anterior opening wedge to flex the proximal articular fragment.

Explanation

Recurvatum of the proximal tibia is an apex posterior deformity (loss of posterior tibial slope). It is corrected by an anterior opening wedge (or posterior closing wedge) osteotomy to pitch the articular surface into flexion and restore the normal slope.

Question 2622

Topic: Physiology & Rehabilitation

In normal sagittal plane lower extremity alignment, where does the mechanical axis line (drawn from the center of the femoral head to the center of the ankle) pass in relation to the knee joint?

. Directly through the center of the knee joint
. Posterior to the center of the knee joint
. Anterior to the center of the knee joint
. Through the posterior cortex of the tibia
. Through the patellofemoral joint

Correct Answer & Explanation

. Anterior to the center of the knee joint

Explanation

In the normal sagittal plane, the mechanical axis line passes slightly anterior to the center of the knee joint. This anterior position creates an extension moment during the stance phase, contributing to the knee's locking mechanism and efficient gait.

Question 2623

Topic: 1. General Principles & Basic Science

A surgeon plans to correct a midshaft tibial recurvatum deformity. Due to poor skin quality at the Center of Rotation of Angulation (CORA), the osteotomy is made 5 cm proximal to the CORA, but the hinge of the external fixator is placed exactly at the CORA. What is the expected outcome according to Paley's principles?

. Correction of angulation without translation
. Correction of angulation with translation of the bone ends
. Pure translation without angular correction
. Failure to correct the mechanical axis
. Creation of a secondary mechanical axis deviation

Correct Answer & Explanation

. Correction of angulation with translation of the bone ends

Explanation

According to Paley's Osteotomy Rule 2, if the hinge is at the CORA but the osteotomy is at a different level, the angulation is corrected but translation occurs at the osteotomy site. The overall mechanical axes of the proximal and distal segments will remain collinear.

Question 2624

Topic: 1. General Principles & Basic Science

A patient presents with a combined 20-degree varus and 15-degree procurvatum deformity of the tibia. According to Paley's principles, how should this deformity be conceptualized for correction with a hexapod external fixator?

. As two independent deformities with two separate CORAs
. As a single oblique plane deformity with one CORA
. As a purely rotational deformity
. As a primary coronal deformity with secondary sagittal compensation
. As a primary sagittal deformity requiring staged correction

Correct Answer & Explanation

. As a single oblique plane deformity with one CORA

Explanation

Combined coronal and sagittal plane deformities represent a single true angular deformity in an oblique plane. It has a single CORA and can be corrected simultaneously using a single hinge axis or a multiplanar external fixator.

Question 2625

Topic: Physiology & Rehabilitation

A 25-year-old male with a history of premature anterior physeal closure of the proximal tibia presents with knee pain. Radiographs demonstrate an apex posterior bony deformity. Which of the following gait abnormalities is most likely associated with this specific osseous deformity?

. Crouch gait
. Steppage gait
. Genu recurvatum thrust during stance
. Trendelenburg gait
. Stiff-knee gait

Correct Answer & Explanation

. Genu recurvatum thrust during stance

Explanation

Premature anterior physeal closure of the proximal tibia causes an osseous recurvatum deformity (apex posterior) and an increased posterior tibial slope. This leads to a genu recurvatum thrust (hyperextension) during the stance phase of gait.

Question 2626

Topic: Biomechanics & Biomaterials

A 32-year-old female with chronic ACL insufficiency and a varus-procurvatum deformity of the proximal tibia is undergoing an anterior opening-wedge high tibial osteotomy. How will correcting the procurvatum (increasing the posterior tibial slope) affect her knee biomechanics?

. It will increase anterior tibial translation, worsening ACL instability
. It will decrease anterior tibial translation, stabilizing the ACL-deficient knee
. It will have no effect on sagittal plane translation
. It will isolate stress to the lateral collateral ligament
. It will decrease patellofemoral joint reaction forces

Correct Answer & Explanation

. It will increase anterior tibial translation, worsening ACL instability

Explanation

Increasing the posterior tibial slope increases the anterior translation force on the tibia during weight-bearing. In an ACL-deficient knee, this exacerbates anterior instability, making an anterior closing-wedge (slope-decreasing) osteotomy more appropriate.

Question 2627

Topic: 1. General Principles & Basic Science

An orthopedic surgeon corrects a femoral deformity by placing both the osteotomy cut and the hinge axis at a level distinct from the true CORA. What is the geometric consequence of this configuration?

. Perfect alignment of the mechanical axes
. Angulation combined with complete translation
. A new secondary deformity with mechanical axis deviation
. Correction of rotational malalignment
. Spontaneous resolution of limb length discrepancy

Correct Answer & Explanation

. A new secondary deformity with mechanical axis deviation

Explanation

According to Paley's Osteotomy Rule 3, placing both the osteotomy and the hinge away from the CORA results in angulation with a translation effect that leaves the proximal and distal mechanical axes non-collinear. This creates a secondary deformity (iatrogenic mechanical axis deviation).

Question 2628

Topic: 1. General Principles & Basic Science

A 42-year-old patient undergoes deformity correction for a post-traumatic distal femoral procurvatum deformity. The center of rotation of angulation (CORA) is located in the diaphyseal-metaphyseal junction. To achieve pure angular correction without creating iatrogenic translation at the osteotomy site, Paley's Rule 1 dictates that the osteotomy and the hinge must be placed in which of the following configurations?

. Osteotomy at the CORA, hinge at the CORA
. Osteotomy outside the CORA, hinge at the CORA
. Osteotomy at the CORA, hinge outside the CORA
. Osteotomy outside the CORA, hinge outside the CORA
. Osteotomy at the joint line, hinge at the CORA

Correct Answer & Explanation

. Osteotomy at the CORA, hinge at the CORA

Explanation

Paley's Rule 1 states that if the osteotomy and the hinge are both placed at the CORA, angulation is corrected without introducing translation. Placing the osteotomy away from the CORA while keeping the hinge at the CORA (Rule 2) results in collinear realignment but creates translation at the osteotomy site.

Question 2629

Topic: Physiology & Rehabilitation

When assessing a patient for a sagittal plane deformity of the lower extremity, understanding normal alignment is critical for surgical planning. In a normally aligned lower extremity, where does the sagittal mechanical axis (a line drawn from the center of the femoral head to the center of the ankle joint) pass relative to the knee joint, and what is its primary biomechanical effect during the stance phase of gait?

. Posterior to the knee center, creating a flexion moment
. Posterior to the knee center, creating an extension moment
. Anterior to the knee center, creating a flexion moment
. Anterior to the knee center, creating an extension moment
. Directly through the knee center, creating no moment

Correct Answer & Explanation

. Anterior to the knee center, creating an extension moment

Explanation

The normal sagittal mechanical axis passes slightly anterior to the center of rotation of the knee joint. This physiologic alignment creates a natural extension moment during the stance phase of gait, which reduces the muscular workload required by the quadriceps to maintain knee extension.

Question 2630

Topic: 1. General Principles & Basic Science

A 28-year-old male is evaluated for a post-traumatic tibial deformity characterized by exactly 15 degrees of varus and 15 degrees of recurvatum. According to Paley's principles of deformity correction, this combined malalignment is best conceptualized as a single uniapical deformity in an oblique plane. Where is the axis of the true maximum deformity located relative to standard anatomic planes?

. Exactly midway between the coronal and sagittal planes (45 degrees)
. In a plane rotated 15 degrees from the standard coronal plane
. It depends strictly on the axial rotation of the tibia
. Only determinable using a three-dimensional computed tomography (CT) scan
. As a strict vector sum resulting in a 30-degree plane of deformity

Correct Answer & Explanation

. Exactly midway between the coronal and sagittal planes (45 degrees)

Explanation

A combined coronal and sagittal plane deformity produces a single maximum true deformity in an oblique plane. Because the magnitudes of varus (15 degrees) and recurvatum (15 degrees) are equal, the tangent of the angle is 1, placing the maximum deformity plane exactly at a 45-degree angle to the standard coronal and sagittal planes.

Question 2631

Topic: 1. General Principles & Basic Science

A 16-year-old female presents with progressive symptomatic knee recurvatum. To properly plan a corrective osteotomy based on Paley's principles, accurate measurement of the joint orientation angles is required on a true lateral radiograph. What is the accepted normal reference range for the anatomic posterior proximal tibial angle (aPPTA) in the sagittal plane?

. 71-74 degrees
. 78-84 degrees
. 85-90 degrees
. 91-95 degrees
. 96-100 degrees

Correct Answer & Explanation

. 78-84 degrees

Explanation

The normal anatomic posterior proximal tibial angle (aPPTA) ranges from 78 to 84 degrees. This corresponds to the normal anatomic posterior tibial slope of approximately 6 to 12 degrees (90 degrees minus the aPPTA).

Question 2632

Topic: 1. General Principles & Basic Science

A patient has a significant osseous genu recurvatum deformity (apex posterior) located in the proximal tibial diaphysis. The surgeon plans a corrective osteotomy. If the surgeon intentionally places the osteotomy proximal to the center of rotation of angulation (CORA) but maintains the hinge exactly at the CORA to correct the angular deformity, what secondary effect will predictably occur according to Paley's Rule 2?

. No translation will occur
. Anterior translation of the distal segment
. Posterior translation of the distal segment
. Medial translation of the distal segment
. Joint line obliquity will be significantly worsened

Correct Answer & Explanation

. Posterior translation of the distal segment

Explanation

Paley's Rule 2 dictates that placing the hinge at the CORA and the osteotomy at a different level corrects the angulation but causes predictable translation at the osteotomy site. Correcting an apex posterior (recurvatum) deformity with an osteotomy proximal to the CORA will result in posterior translation of the distal tibial segment.

Question 2633

Topic: 1. General Principles & Basic Science

A 40-year-old patient requires correction of a distal femoral valgus deformity. Preoperative planning reveals the CORA is located precisely at the articular surface of the lateral femoral condyle. To achieve perfect mechanical axis restoration while minimizing surgical morbidity and preserving the joint, the surgeon plans an osteotomy 5 cm proximal to the CORA, with the hinge of correction maintained at the CORA. According to Paley's osteotomy rules, what is the expected biomechanical result of this approach?

. Pure angulation correction with no translation at the osteotomy site.
. Correction of the angular deformity but creation of a new, secondary translational deformity.
. Restoration of the mechanical axis with an obligatory translation at the osteotomy site.
. Incomplete correction of the angular deformity, requiring further intervention.
. Limb lengthening without any angular correction.

Correct Answer & Explanation

. Restoration of the mechanical axis with an obligatory translation at the osteotomy site.

Explanation

Correct Answer: CThis scenario describes Paley's Rule Two: Correction with Obligatory Translation. The geometric rule states that the hinge of correction (ACA) is placedatthe CORA, but the actual bone cut (osteotomy) is performed at a different level (in this case, 5 cm proximal to the CORA). This is often necessary when the CORA is in an inaccessible or undesirable location, such as within the joint line. The biomechanical result is that the overall mechanical axis of the limb is perfectly restored, but a translation (sliding) of the bone fragments at the osteotomy site is an unavoidable geometric consequence. This translation must be anticipated and accommodated by the chosen hardware.Option A is incorrect. Pure angulation with no translation occurs only when both the osteotomy and the hinge are exactly at the CORA (Rule One).Option B is incorrect. Creation of a new, secondary translational deformity (a 'dog-leg') occurs when both the osteotomy and the hinge are at a leveldifferentfrom the CORA (Rule Three), which is generally to be avoided.Option D is incorrect. If planned correctly according to Rule Two, the angular deformity is fully corrected, and the mechanical axis is restored.Option E is incorrect. While an opening wedge osteotomy can lengthen the limb, the primary outcome described here is angular correction with translation, not necessarily lengthening, and certainly not without angular correction.

Question 2634

Topic: 1. General Principles & Basic Science

A 42-year-old male is undergoing a high tibial osteotomy for a varus deformity. Preoperative planning indicates a target Medial Proximal Tibial Angle (MPTA) of 87°. During the intraoperative fluoroscopic validation, the surgeon measures the MPTA as 82°. Which of the following statements best describes the significance of the MPTA and the necessary intraoperative adjustment?

. An MPTA of 82° indicates an overcorrection into valgus, and the osteotomy needs to be closed medially.
. An MPTA of 82° indicates a residual varus deformity, and the osteotomy needs to be opened further medially.
. The MPTA is primarily used for distal femoral osteotomies, and the mLDFA is the critical angle for proximal tibial corrections.
. The MPTA of 82° is within the normal range of 85° to 90°, so no further adjustment is needed.
. The MPTA defines the relationship of the knee joint line to the mechanical axis of the femur, and 82° suggests a normal alignment.

Correct Answer & Explanation

. An MPTA of 82° indicates a residual varus deformity, and the osteotomy needs to be opened further medially.

Explanation

Correct Answer: BAn MPTA of 82° indicates a residual varus deformity, and the osteotomy needs to be opened further medially. The text states the normal range for MPTA is 85° to 90°, with an average target value of 87°. An MPTA of 82° is less than the normal range, meaning the medial side of the proximal tibia is angled too acutely downwards, indicating persistent varus. To correct this, the osteotomy needs to be opened further medially to increase the MPTA towards the target of 87°.Incorrect Options:A:An MPTA of 82° is less than the target 87°, indicating varus, not overcorrection into valgus. Overcorrection into valgus would result in an MPTA greater than 90°.C:The MPTA is explicitly stated as 'The primary target in high tibial osteotomies,' while the mLDFA is crucial for distal femoral osteotomies.D:An MPTA of 82° is outside the normal range of 85° to 90°, requiring adjustment.E:The MPTA defines the relationship of the knee joint line to the mechanical axis of thetibia, not the femur. The mLDFA defines this relationship for the femur.

Question 2635

Topic: 1. General Principles & Basic Science

A 60-year-old patient with severe genu varum is scheduled for a high tibial osteotomy. Preoperative planning using a full-length weight-bearing radiograph identifies the CORA 1 cm distal to the joint line. Due to concerns about bone quality and the need for stable internal fixation, the surgeon plans the osteotomy 4 cm distal to the joint line. To ensure a perfect correction, the surgeon utilizes the goniometer method to calculate the required translation. Which of the following steps is crucial for accurately determining the amount of translation needed?

. Aligning the goniometer's pivot point with the planned osteotomy level and measuring the angle of deformity.
. Measuring the perpendicular distance from the center of the bone at the CORA to the corrected distal mechanical axis.
. Placing the goniometer's pivot point directly over the CORA, simulating the correction, and then measuring the perpendicular distance from the center of the bone at the planned osteotomy site to the new, corrected distal axis line.
. Calculating the difference between the proximal and distal mechanical axis angles and dividing by the distance between the CORA and the osteotomy site.
. Using the goniometer to confirm the normal range of the Mechanical Lateral Distal Femoral Angle (mLDFA) after the osteotomy.

Correct Answer & Explanation

. Placing the goniometer's pivot point directly over the CORA, simulating the correction, and then measuring the perpendicular distance from the center of the bone at the planned osteotomy site to the new, corrected distal axis line.

Explanation

Correct Answer: CThe crucial step for accurately determining the amount of translation needed is placing the goniometer's pivot point directly over the CORA, simulating the correction, and then measuring the perpendicular distance from the center of the bone at the planned osteotomy site to the new, corrected distal axis line. The text describes the goniometer method: '1. Identify the CORA... 2. Plan the Osteotomy Level... 3. Position the Goniometer: Place the center pivot of the goniometer directly over the CORA. ... 5. Simulate the Correction: Rotate the goniometer arm representing the distal axis until the desired correction is achieved... 6. Measure the Translation: Observe exactly where this new, corrected axis line crosses your planned osteotomy level. Measure the perpendicular distance from the center of the bone at the osteotomy site to this new line. This distance, in millimeters, is the exact amount of translation required intraoperatively.'Incorrect Options:A:The goniometer's pivot point must be over the CORA, not the osteotomy level, to accurately simulate the correction around the true apex of the deformity.B:Translation is measured at the osteotomy site, not at the CORA. The CORA is the pivot, the osteotomy site is where the translation occurs.D:While calculations are involved, this specific formula is not described as the goniometer method for determining translation. The goniometer method is a visual and direct measurement technique.E:The goniometer method is for calculating translation for the current deformity, not for confirming mLDFA after the osteotomy, which is an intraoperative fluoroscopic step.

Question 2636

Topic: Biology, Genetics & Bone Healing

During a complex tibial osteotomy, the surgeon is utilizing the multiple drill hole and osteotome twist technique. After creating a series of bicortical drill holes, the surgeon inserts a wide, flat osteotome into the center of the drill hole pattern. Which of the following actions is the most appropriate next step to complete the osteotomy and achieve the planned translation, and what is its primary biomechanical advantage?

. Aggressively hammer the osteotome to quickly connect the drill holes and separate the bone fragments, minimizing operative time.
. Use a high-speed oscillating saw to connect the remaining bone bridges, ensuring a clean, straight cut.
. Twist the osteotome with slow, controlled rotational force to connect the cancellous bone bridges and lever the distal fragment into the exact translated position, preserving osteocytes.
. Insert multiple narrow osteotomes into each drill hole and hammer them simultaneously to achieve a rapid, multi-point fracture.
. Apply direct, linear pressure to the osteotome to push the distal fragment into translation before the osteotomy is fully complete.

Correct Answer & Explanation

. Twist the osteotome with slow, controlled rotational force to connect the cancellous bone bridges and lever the distal fragment into the exact translated position, preserving osteocytes.

Explanation

Correct Answer: CTwist the osteotome with slow, controlled rotational force to connect the cancellous bone bridges and lever the distal fragment into the exact translated position, preserving osteocytes. The text explicitly describes this: 'Insert a wider, flat osteotome into the center of the drill hole pattern. Now, instead of hammering aggressively,twistthe osteotome. This rotational force will connect the remaining cancellous bone bridges and complete the osteotomy with a gentle, controlled crack.' It further states: 'The twisting motion is not just for breaking the bone; it is the mechanical engine for translation. By twisting the osteotome handle (e.g., counterclockwise), the broad blade acts as a cam, levering and pushing the distal fragment into the exact translated position calculated preoperatively.' The technique also 'drastically minimizes heat generation compared to a high-speed oscillating power saw, thereby preserving the vital osteocytes at the bone ends that are critical for rapid callus formation and healing.'Incorrect Options:A:Aggressive hammering is discouraged; the text advises 'instead of hammering aggressively,twistthe osteotome.' This can lead to uncontrolled fracture and comminution.B:The multiple drill hole and osteotome twist technique is specifically chosen tominimizeheat generation compared to a high-speed oscillating saw, which can cause thermal necrosis.D:The technique involves a single wider osteotome for the central twist, not multiple narrow osteotomes hammered simultaneously.E:Translation is achievedafterthe osteotomy is complete or during the final separation via the twist, not by applying linear pressure before the cut is fully made.

Question 2637

Topic: 1. General Principles & Basic Science

A 30-year-old patient is undergoing a complex proximal tibial osteotomy for a severe varus deformity. The surgeon is meticulously performing the osteotomy using the multiple drill hole technique. Which of the following surgical pearls is most critical to prevent a devastating complication during this specific procedure?

. Ensuring the drill bit has passed completely through the far cortex to prevent an intact far cortex from acting as a rigid hinge.
. Applying constant cold saline irrigation while drilling to prevent thermal necrosis and preserve osteocytes.
. Using a sharp, narrow osteotome to connect the drill holes at the dense medial and lateral cortices first.
. Protecting the common peroneal nerve and the posterior neurovascular bundle with blunt retractors.
. Applying slow, controlled rotational pressure to the osteotome to avoid iatrogenic comminution.

Correct Answer & Explanation

. Protecting the common peroneal nerve and the posterior neurovascular bundle with blunt retractors.

Explanation

Correct Answer: DProtecting the common peroneal nerve and the posterior neurovascular bundle with blunt retractors is most critical to prevent a devastating complication during aproximal tibial osteotomy. The text specifically highlights this under 'Surgical Pearls for Flawless Osteotomy Execution': 'Protect Neurovascular Structures: Be acutely aware of nearby structures, particularly the common peroneal nerve during proximal tibial osteotomies. Use blunt retractors to protect the posterior neurovascular bundle.' Damage to these structures can lead to permanent neurological deficits or vascular compromise, which are devastating complications.Incorrect Options:A, B, C, E:While all these are crucial surgical pearls mentioned in the text for a successful osteotomy and good bone healing, they primarily relate to the biomechanics of the cut and bone viability. Neurovascular injury, however, represents a more immediate and potentially devastating complication in terms of patient function and limb viability, especially in the context of a proximal tibial osteotomy where the common peroneal nerve is highly vulnerable.

Question 2638

Topic: 1. General Principles & Basic Science

A surgeon is planning a distal femoral osteotomy for a severe valgus deformity. The CORA is located at the joint line. To preserve the joint capsule, the surgeon places the osteotomy 4 cm proximal to the CORA, but carefully sets the hinge axis of the external fixator exactly on the CORA. What will be the result of this correction?

. Collinear realignment of the mechanical axes without translation.
. Collinear realignment of the mechanical axes with translation at the osteotomy site.
. Parallel mechanical axes with a resulting zig-zag deformity.
. Rotational malalignment without angular correction.
. Iatrogenic joint subluxation.

Correct Answer & Explanation

. Collinear realignment of the mechanical axes with translation at the osteotomy site.

Explanation

This describes Paley's Osteotomy Rule 2. When the hinge is at the CORA but the osteotomy is at a different level, the mechanical axes will become collinear, but it requires translation of the bone ends at the osteotomy site.

Question 2639

Topic: 1. General Principles & Basic Science

A 55-year-old female with knee pain has a medial Mechanical Axis Deviation (MAD). Her mLDFA is 88 degrees and MPTA is 87 degrees. However, her Joint Line Convergence Angle (JLCA) is 6 degrees, opening laterally. What is the most likely etiology of her medial MAD?

. Proximal tibial osseous varus.
. Distal femoral osseous varus.
. Lateral collateral ligament laxity or medial compartment cartilage loss.
. Excessive femoral anteversion.
. Tibial torsion.

Correct Answer & Explanation

. Lateral collateral ligament laxity or medial compartment cartilage loss.

Explanation

Normal mLDFA and MPTA indicate no significant osseous deformity in the frontal plane. An abnormally large JLCA opening laterally points to an intra-articular source of varus, such as lateral ligamentous laxity or medial joint space collapse.

Question 2640

Topic: 1. General Principles & Basic Science

When planning an opening wedge osteotomy to correct a valgus deformity of the proximal tibia using Paley principles, where must the physical hinge or axis of rotation be placed to avoid unintentional translation?

. On the concave cortex exactly at the CORA.
. On the convex cortex exactly at the CORA.
. In the center of the medullary canal.
. At the level of the joint line.
. 5 mm distal to the true CORA.

Correct Answer & Explanation

. On the convex cortex exactly at the CORA.

Explanation

For an opening wedge osteotomy, the hinge must be located on the convex cortex of the deformity at the level of the CORA. Placing it on the concave side would create a closing wedge osteotomy.

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