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8. Foot and Ankle MCQs

Practice Set 71 of 353

This practice set contains high-yield board review questions covering key concepts in 8. Foot and Ankle. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 1401

Topic: Ankle Trauma & Sports

When performing a tibial deformity correction that requires a fibular osteotomy, at what anatomical level should the fibular osteotomy ideally be performed to minimize complications?

. The proximal metaphyseal-diaphyseal junction
. The mid-diaphysis
. The junction of the middle and distal thirds
. Distal to the syndesmosis
. Directly through the fibular head

Correct Answer & Explanation

. The junction of the middle and distal thirds

Explanation

Fibular osteotomies are generally performed at the junction of the middle and distal thirds of the diaphysis. This level is safely distal to the common peroneal nerve and proximal enough to preserve the distal tibiofibular syndesmosis.

Question 1402

Topic: 8. Foot and Ankle

In defining the joint orientation lines for the distal tibia on an AP radiograph, the normal Lateral Distal Tibial Angle (LDTA) is roughly 89 degrees. Which anatomic landmarks are used to draw the joint line of the ankle mortise?

. The tips of the medial and lateral malleoli
. The subchondral line of the tibial plafond
. A line connecting the syndesmosis to the deltoid ligament origin
. The superior articular surface of the talar dome
. The geometric center of the calcaneal tuberosity to the medial malleolus

Correct Answer & Explanation

. The subchondral line of the tibial plafond

Explanation

The distal tibial joint orientation line in the coronal plane is defined by drawing a line across the subchondral bone of the distal tibial articular surface (the tibial plafond).

Question 1403

Topic: 8. Foot and Ankle

A 32-year-old male presents with progressive right knee pain and a clinical varus deformity. To accurately assess his frontal plane alignment for potential corrective osteotomy, which of the following radiographic techniques is most critical according to Paley's principles?

. Bilateral knee AP and lateral views with the patient supine.
. Standing, weight-bearing AP radiograph of the affected knee only, ensuring full extension.
. Standing, weight-bearing long-leg AP radiograph with the patella facing strictly forward.
. Non-weight-bearing long-leg AP radiograph with the feet in a comfortable position.
. Standing lateral radiograph of the entire limb to assess sagittal plane alignment.

Correct Answer & Explanation

. Standing, weight-bearing long-leg AP radiograph with the patella facing strictly forward.

Explanation

Correct Answer: CPaley's principles of deformity correction rely entirely on accurate, standardized radiographs. The text explicitly states that astanding, weight-bearing, long-leg anteroposterior (AP) radiographis essential. Crucially, the patellae must be facing strictly forward (the 'patella forward' position) to prevent sagittal plane geometry from skewing frontal plane assessment. The radiograph must also capture the entire limb from the top of the pelvis to the bottom of the ankle mortise. Options A, B, D, and E describe radiographs that either lack weight-bearing, full limb capture, or the critical 'patella forward' positioning, all of which would lead to inaccurate measurements and flawed surgical planning.

Question 1404

Topic: 8. Foot and Ankle

A 38-year-old male presents with progressive knee pain and a clinical presentation suggestive of a varus deformity. Preoperative planning for a femoral osteotomy is initiated using the Paley method. According to the foundational principles outlined in the case, what is the ultimate objective of this femoral deformity correction?

. To achieve an Anatomic-Mechanical Angle (AMA) of 0 degrees.
. To ensure the femoral anatomic axis is perfectly parallel to the tibial anatomic axis.
. To restore the mechanical axis of the lower extremity to pass directly through the center of the knee joint.
. To normalize the Joint Line Convergence Angle (JLCA) to greater than 5 degrees.
. To align the femoral anatomic axis with the center of the femoral head and ankle mortise.

Correct Answer & Explanation

. To restore the mechanical axis of the lower extremity to pass directly through the center of the knee joint.

Explanation

Correct Answer: CThe case explicitly states, 'The core objective infemoral deformity correctionis always the same: to restore the mechanical axis of the lower extremity so that the line of force transmission passes directly through the center of the knee joint.' This is the fundamental biomechanical goal to ensure even load distribution and prevent accelerated osteoarthritis or implant failure.Option A is incorrectbecause the AMA is an intrinsic angle (normally 7 degrees) between the femoral anatomic and mechanical axes; attempting to make it 0 degrees would create a severe iatrogenic deformity.Option B is incorrectbecause while the tibial mechanical and anatomic axes are nearly parallel, the femoral axes are not. The goal is mechanical axis alignment, not necessarily parallel anatomic axes between femur and tibia.Option D is incorrectbecause the JLCA measures ligamentous laxity or cartilage wear and is normally 0-2 degrees. Increasing it to greater than 5 degrees would indicate significant joint space opening, which is pathological.Option E is incorrectbecause the line connecting the center of the femoral head to the ankle mortise defines the mechanical axis, not the femoral anatomic axis. The anatomic axis follows the intramedullary canal.

Question 1405

Topic: 8. Foot and Ankle

A 55-year-old patient presents with a complex femoral deformity. During the Paley planning process, the surgeon has established the Proximal Mechanical Axis (PMA) and the Distal Mechanical Axis (DMA). The next crucial step is to locate the Center of Rotation of Angulation (CORA). Which of the following accurately describes how the CORA is identified?

. By measuring the perpendicular distance from the knee center to the mechanical axis.
. By drawing a line from the center of the femoral head to the center of the ankle mortise.
. By extending the PMA distally and the DMA proximally until they intersect.
. By calculating the difference between the mLDFA and the aLDFA.
. By identifying the midpoint of the femoral diaphysis.

Correct Answer & Explanation

. By extending the PMA distally and the DMA proximally until they intersect.

Explanation

Correct Answer: CThe case clearly outlines the process for locating the CORA: 'To find the CORA, simply extend the PMA line distally and the DMA line proximally until they intersect. This point of intersectionisthe CORA.' The provided image also visually demonstrates this intersection point as the CORA.Option A is incorrectbecause this describes how Mechanical Axis Deviation (MAD) is measured, not the CORA.Option B is incorrectbecause this describes how the overall mechanical axis of the limb is drawn, not the CORA.Option D is incorrectbecause the difference between mLDFA and aLDFA is approximately 7 degrees, which is the Anatomic-Mechanical Angle (AMA), not the CORA.Option E is incorrectbecause the midpoint of the femoral diaphysis is not a specific anatomical or geometric landmark for identifying the CORA in deformity correction.

Question 1406

Topic: 8. Foot and Ankle

A patient has a multi-apical tibial deformity. How is the mechanical axis of the intermediate segment determined in a diaphysis with two distinct Centers of Rotation of Angulation (CORAs)?

. By connecting the two CORAs
. By extending a line perpendicular to the joint orientation line
. By drawing a line parallel to the anatomic axis of the femur
. By bisecting the overall mechanical axis deviation
. By drawing a line from the tibial tubercle to the center of the ankle

Correct Answer & Explanation

. By connecting the two CORAs

Explanation

In a multi-apical deformity, the mechanical axis of the intermediate segment is established by drawing a line that connects the proximal CORA directly to the distal CORA. This delineates the orientation of the middle segment for precise corrective planning.

Question 1407

Topic: 8. Foot and Ankle

A 55-year-old patient with a history of osteoarthritis presents for evaluation of knee pain and limb deformity. A full-length standing radiograph is obtained, as shown. The mechanical axis of the lower extremity passes 25 mm medial to the center of the knee joint.

. A normal mechanical axis alignment, as it is within the acceptable range of 0-8mm medial.
. A valgus deformity of the lower extremity, requiring a distal femoral osteotomy.
. A varus deformity of the lower extremity, with a Mechanical Axis Deviation (MAD) of +25 mm.
. An intra-articular deformity, as indicated by the significant deviation.
. A lateral MAD of -25 mm, suggesting a proximal tibial valgus.

Correct Answer & Explanation

. A varus deformity of the lower extremity, with a Mechanical Axis Deviation (MAD) of +25 mm.

Explanation

Correct Answer: CThe correct answer is C. According to the Malalignment Test (MAT), the mechanical axis is drawn from the center of the femoral head to the center of the ankle joint. Normal alignment dictates this line passes through the center of the knee or slightly medial to it (up to 8mm). When the line passes significantly medial to the center of the knee, it indicates a varus deformity, and the Mechanical Axis Deviation (MAD) is recorded as a positive value. A deviation of 25 mm medial is a significant varus deformity, quantified as +25 mm MAD.Option A is incorrectbecause 25 mm medial is well outside the normal range of 0-8 mm medial.Option B is incorrectbecause a medial deviation indicates a varus deformity, not a valgus deformity. The MAT identifies the presence and direction of MAD but does not specify the source (femur, tibia, or joint) or the required osteotomy.Option D is incorrectbecause while a significant MAD can be associated with intra-articular issues, the MAT itself only quantifies the overall malalignment, not its specific source. The Malorientation Test (MOT) with JLCA measurement would be needed to confirm an intra-articular deformity.Option E is incorrectbecause a medial deviation is a positive MAD (varus), not a negative (lateral) MAD (valgus).

Question 1408

Topic: 8. Foot and Ankle

During the Malorientation Test (MOT) for a patient with genu varum, the surgeon measures the Joint Line Convergence Angle (JLCA) and finds it to be 7 degrees, with medial gapping. What is the most appropriate interpretation of this finding in the context of Paley's principles?

. This indicates a primary distal femoral valgus deformity.
. This suggests a significant intra-articular problem, such as cartilage loss or ligamentous laxity.
. This confirms a proximal tibial varus deformity as the sole source of malalignment.
. This is a normal variant and does not require specific attention in deformity correction.
. This implies a distal tibial varus deformity requiring an ankle osteotomy.

Correct Answer & Explanation

. This suggests a significant intra-articular problem, such as cartilage loss or ligamentous laxity.

Explanation

Correct Answer: BThe correct answer is B. The case highlights the Joint Line Convergence Angle (JLCA) as a critical caveat during the MOT. Normally, the distal femoral joint line and the proximal tibial joint line are nearly parallel, resulting in a JLCA of 0°-2°. An abnormally widened JLCA, especially with medial or lateral gapping (as indicated by 7 degrees with medial gapping), is a definitive sign of a significant intra-articular problem, such as cartilage loss, meniscal pathology, or ligamentous laxity, rather than a purely bony deformity.Option A is incorrectbecause a high JLCA points to an intra-articular issue, not specifically a distal femoral valgus deformity, which would be indicated by an abnormal mLDFA.Option C is incorrectbecause while a patient may have a proximal tibial varus, an abnormal JLCA indicates that the joint itself is also a significant contributor to the malalignment, and it is not the sole source.Option D is incorrectbecause a JLCA of 7 degrees is significantly outside the normal range of 0°-2° and is therefore not a normal variant.Option E is incorrectbecause the JLCA relates to the knee joint, not the ankle, and indicates an intra-articular issue, not a distal tibial bony deformity.

Question 1409

Topic: 8. Foot and Ankle

Which of the following statements accurately defines the overall lower extremity mechanical axis according to Paley's principles?

. A line connecting the center of the femoral head to the center of the knee joint.
. A line connecting the center of the femoral head to the center of the ankle joint (tibial plafond).
. A line following the mid-diaphyseal course of the femur and tibia.
. A line connecting the center of the proximal tibial joint line to the center of the distal tibial joint line.
. A line connecting the greater trochanter to the lateral malleolus.

Correct Answer & Explanation

. A line connecting the center of the femoral head to the center of the ankle joint (tibial plafond).

Explanation

Correct Answer: BThe correct answer is B. The case explicitly defines the overall lower extremity mechanical axis as the most important line in limb alignment, described as 'a single, straight line drawn from the center of the femoral head to the center of the ankle joint (tibial plafond).' This line represents the true line of force transmission through the entire limb.Option A is incorrectbecause this describes the femoral mechanical axis, not the overall lower extremity mechanical axis.Option C is incorrectbecause this describes the anatomic axis, which follows the bone's intrinsic centerline, not the mechanical axis, which is dictated by load-bearing.Option D is incorrectbecause this describes the tibial mechanical axis, not the overall lower extremity mechanical axis.Option E is incorrectbecause the mechanical axis connects joint centers, not bony prominences like the greater trochanter or lateral malleolus.

Question 1410

Topic: 8. Foot and Ankle

A 60-year-old patient with a long-standing genu varum deformity is undergoing preoperative planning for a high tibial osteotomy. The image shows a similar deformity. According to the principles outlined in the case, what is the ultimate goal of most deformity corrections, particularly concerning the lower extremity?

. To achieve perfect cosmetic symmetry with the contralateral limb.
. To restore the anatomic axis of the affected bone.
. To restore the mechanical axis of the entire lower extremity.
. To eliminate all rotational components of the deformity.
. To simply achieve union of the osteotomy site.

Correct Answer & Explanation

. To restore the mechanical axis of the entire lower extremity.

Explanation

Correct Answer: CThe text explicitly states, 'Restoring this line [the mechanical axis] is the ultimate goal of most deformity corrections, as it ensures that ground reaction forces are transmitted neutrally across the knee and ankle, protecting the articular cartilage from asymmetric wear and arthritic degeneration.' While other factors like cosmetic appearance, anatomic axis restoration, and osteotomy union are important, the primary biomechanical goal for long-term joint health is the restoration of the mechanical axis of the entire limb. Rotational components are part of a 3D deformity but not the singular ultimate goal ofmostcorrections, especially in the context of frontal plane deformity.

Question 1411

Topic: 8. Foot and Ankle

A surgeon is reviewing a full-length standing radiograph of a patient with a lower extremity deformity, similar to the one shown. To accurately assess the load-bearing alignment, the surgeon needs to draw the mechanical axis of the entire lower extremity. How is this axis precisely defined according to the case?

. A line connecting the mid-diaphysis of the femur to the mid-diaphysis of the tibia.
. A straight line connecting the center of the femoral head to the center of the ankle mortise (tibial plafond).
. A line parallel to the floor, passing through the knee joint.
. The line representing the mid-diaphyseal axis of the femur only.
. The line representing the mid-diaphyseal axis of the tibia only.

Correct Answer & Explanation

. A straight line connecting the center of the femoral head to the center of the ankle mortise (tibial plafond).

Explanation

Correct Answer: BThe case provides a precise definition: 'For the entire lower extremity, the mechanical axis runs from the center of the femoral head to the center of the ankle mortise (tibial plafond).' This definition is crucial for understanding the true load-bearing alignment. Options A, C, D, and E describe other lines or incorrect definitions of the mechanical axis of the entire lower extremity.

Question 1412

Topic: 8. Foot and Ankle

A resident is reviewing a long-leg radiograph for a patient with suspected genu varum. The image appears distorted, and the resident suspects an error in acquisition. Referring to the provided diagram, which of the following statements accurately describes the optimal technical parameters for acquiring a standing long-leg anteroposterior radiograph to minimize parallax and magnification errors, as depicted in figure (a)?

. X-ray tube at 6 feet, centered at the hip.
. X-ray tube at 10 feet, centered at the ankle.
. X-ray tube at 10 feet (305 cm), centered at the knee (28 inches/71 cm from floor).
. X-ray tube at 8 feet, centered at the mid-thigh.
. X-ray tube at 6 feet, centered at the knee.

Correct Answer & Explanation

. X-ray tube at 10 feet (305 cm), centered at the knee (28 inches/71 cm from floor).

Explanation

Correct Answer: CThe case explicitly states the strict protocol for acquiring a standing long-leg radiograph to minimize parallax and magnification errors. The x-ray tube must be positioned exactly 10 feet (305 cm) from the radiographic cassette, and the x-ray beam should be centered precisely at the level of the knee joint, which corresponds to approximately 28 inches (71 cm) from the floor in an average adult. This setup, as depicted in figure (a) of the diagram, ensures the least possible geometric distortion, especially in the critical knee region.Option A is incorrect because a 6-foot tube distance would cause significant beam divergence and magnification, and centering at the hip would distort the knee and ankle. Option B is incorrect because centering at the ankle would distort the knee and hip, and while the 10-foot distance is correct, the centering is not. Option D uses an incorrect tube distance and centering. Option E uses an incorrect tube distance, which would lead to substantial magnification artifact.

Question 1413

Topic: 8. Foot and Ankle

A 35-year-old male presents with chronic knee pain and a suspected varus deformity. A long-leg radiograph is obtained, but the technician notes the patient has significant internal tibial torsion, and the foot was forced to point forward during the scan. What is the most likely consequence of forcing the foot to point forward in a patient with significant internal tibial torsion during a standing long-leg radiograph?

. An accurate representation of the true frontal plane deformity will be obtained.
. The mechanical axis deviation (MAD) will be underestimated.
. A sagittal plane deformity will be projected onto the frontal plane, leading to a false varus or valgus measurement.
. Magnification artifact will be significantly reduced.
. The joint line convergence angle (JLCA) will appear falsely decreased.

Correct Answer & Explanation

. A sagittal plane deformity will be projected onto the frontal plane, leading to a false varus or valgus measurement.

Explanation

Correct Answer: CThe case emphasizes the critical role of patient positioning, specifically the 'patella-forward view.' If a patient has a significant torsional deformity (like internal tibial torsion) and their foot is forced to point forward, the knee will internally rotate. This rotation projects a sagittal plane deformity (e.g., a flexion contracture or recurvatum) onto the frontal plane view. This creates a false varus or valgus measurement, rendering the film useless for accurate angular planning.Option A is incorrect because improper rotation directly leads to an inaccurate representation. Option B is incorrect; the MAD would likely be falsely measured, not necessarily underestimated, and the primary issue is the projection of a sagittal deformity. Option D is incorrect; tube distance, not patient rotation, primarily affects magnification. Option E is incorrect; while joint angles might be affected, the primary and most significant consequence described is the projection of a sagittal deformity onto the frontal plane, leading to false varus/valgus measurements.

Question 1414

Topic: 8. Foot and Ankle

A 25-year-old female presents with genu valgum and lateral knee pain. Radiographic analysis reveals a Mechanical Lateral Distal Femoral Angle (mLDFA) of 83 degrees. Her MPTA and other angles are within normal limits. What does an mLDFA of 83 degrees indicate in this patient?

. Normal distal femoral alignment.
. Distal femoral varus deformity.
. Distal femoral valgus deformity.
. Proximal tibial varus deformity.
. A significant ankle deformity.

Correct Answer & Explanation

. Distal femoral valgus deformity.

Explanation

Correct Answer: CThe case defines the Mechanical Lateral Distal Femoral Angle (mLDFA) as the lateral angle formed between the femoral mechanical axis and the distal femoral joint line, with a normal value of 88° (range 85-90°). An mLDFA less than 85° indicates a distal femoral valgus deformity. An mLDFA of 83 degrees falls below this normal range, confirming a distal femoral valgus deformity, which is consistent with the patient's presentation of genu valgum.Option A is incorrect because 83 degrees is outside the normal range. Option B is incorrect; distal femoral varus would be indicated by an mLDFA greater than 90°. Option D is incorrect; proximal tibial varus would be indicated by an MPTA less than 85°. Option E is incorrect; an ankle deformity would be indicated by an abnormal Lateral Distal Tibial Angle (LDTA).

Question 1415

Topic: 8. Foot and Ankle

A 62-year-old male presents with progressive medial knee pain and a noticeable bowing of his right leg. A full-length standing anteroposterior radiograph is obtained, as shown below. Based on Paley's principles of deformity analysis, what is the most appropriate interpretation of the mechanical axis deviation (MAD) and its clinical implication?

. The mechanical axis passes lateral to the center of the knee, indicating a valgus deformity and increased stress on the lateral compartment.
. The mechanical axis passes medial to the center of the knee, indicating a varus deformity and increased stress on the medial compartment.
. The mechanical axis passes directly through the center of the knee, indicating normal alignment and ruling out a significant deformity.
. The mechanical axis passes medial to the center of the knee, indicating a valgus deformity and increased stress on the medial compartment.
. The mechanical axis passes lateral to the center of the knee, indicating a varus deformity and increased stress on the lateral compartment.

Correct Answer & Explanation

. The mechanical axis passes medial to the center of the knee, indicating a varus deformity and increased stress on the medial compartment.

Explanation

Correct Answer: BThe image clearly shows the mechanical axis (the line from the center of the femoral head to the center of the ankle) passing medial to the center of the knee joint. According to Paley's principles, this indicates a medial mechanical axis deviation (MAD), which is characteristic of a varus deformity. A varus deformity pathologically increases contact stresses on the medial compartment of the knee, often leading to or exacerbating medial compartment osteoarthritis, consistent with the patient's presenting symptom of medial knee pain.Option A is incorrect because the axis is medial, not lateral, and it describes a valgus deformity, which is the opposite of what is seen. Option C is incorrect as the axis clearly deviates from the center of the knee. Option D incorrectly associates a medial MAD with a valgus deformity. Option E incorrectly states the axis is lateral and incorrectly associates a varus deformity with increased stress on the lateral compartment.

Question 1416

Topic: 8. Foot and Ankle

During a preoperative planning session for a lower limb deformity, a resident presents a full-length standing AP radiograph. The attending surgeon immediately notes that the patella is significantly rotated laterally on the image. What is the most critical implication of this improper radiographic technique according to Paley's principles?

. It will lead to an underestimation of the Mechanical Axis Deviation (MAD).
. It will primarily affect the accuracy of sagittal plane angle measurements, such as the PDFA.
. It will create 'phantom' varus or valgus measurements in the frontal plane, leading to incorrect deformity localization.
. It will only affect the assessment of tibial torsion and has no impact on frontal plane alignment.
. It will cause magnification distortion, making all linear measurements unreliable.

Correct Answer & Explanation

. It will create 'phantom' varus or valgus measurements in the frontal plane, leading to incorrect deformity localization.

Explanation

Correct Answer: CThe text explicitly states: "The patient must stand with the patellae pointing directly forward, regardless of their foot position. This 'patella forward' view ensures a true AP projection of the knee joint, neutralizing any rotational malalignment originating from the hip (femoral anteversion) or the tibia (tibial torsion). If the patella is not perfectly centered between the femoral condyles, the resulting image will create 'phantom' varus or valgus measurements, leading the surgeon to correct a deformity that does not actually exist." Therefore, improper patellar positioning, such as lateral rotation, will lead to erroneous frontal plane angle measurements and misdiagnosis of the deformity.Option A is incorrect; it can lead to overestimation or underestimation, but the primary issue is the creation of phantom deformities. Option B is incorrect; sagittal plane angles are measured on lateral radiographs. Option D is incorrect; while it relates to rotation, its impact on frontal plane alignment is significant and misleading. Option E is incorrect; magnification distortion is primarily addressed by the 10-foot rule, not patellar positioning.

Question 1417

Topic: 8. Foot and Ankle

A 40-year-old patient with a complex multi-planar deformity of the femur is scheduled for corrective osteotomy. The surgeon emphasizes the importance of obtaining a precise, full-length standing anteroposterior radiograph. Which of the following technical parameters is absolutely critical for minimizing magnification and parallax distortion, and why?

. Positioning the patient with the patellae pointing directly forward to neutralize rotational malalignment.
. Using a high-resolution digital templating software to draw lines and measure angles.
. Ensuring the X-ray tube is positioned exactly 10 feet (305 cm) from the radiographic cassette to ensure parallel X-ray beams.
. Centering the X-ray beam precisely on the knee joint for optimal visualization.
. Moving the contralateral limb out of the way to prevent bony overlap.

Correct Answer & Explanation

. Ensuring the X-ray tube is positioned exactly 10 feet (305 cm) from the radiographic cassette to ensure parallel X-ray beams.

Explanation

Correct Answer: CThe text explicitly states under 'The Standing Anteroposterior (AP) Radiograph': "The 10-Foot Rule (Tube Distance): The X-ray tube must be positioned exactly 10 feet (305 cm) from the radiographic cassette. This long distance is non-negotiable. It minimizes the magnification and parallax distortion inherent in closer-range, standard X-rays. At 10 feet, the X-ray beams are nearly parallel as they pass through the patient, providing a true-to-size representation of the limb." This rule is fundamental for accurate linear and angular measurements.Option A is crucial for preventing 'phantom' deformities but addresses rotational distortion, not magnification/parallax. Option B is a tool for measurement, not a radiographic technique parameter. Option D is important for lateral views but not the primary factor for minimizing magnification/parallax on a full-length AP. Option E is for lateral views to prevent overlap, not for magnification/parallax on AP.

Question 1418

Topic: 8. Foot and Ankle

A 16-year-old male presents with a congenital lower limb deformity. The reconstructive surgeon is performing a comprehensive radiographic analysis. The first step, according to Paley's principles, is to assess the global alignment of the entire lower extremity. Which of the following accurately defines the mechanical axis of the lower limb?

. A line drawn from the center of the greater trochanter to the center of the ankle joint.
. A line drawn from the center of the femoral head to the center of the knee joint.
. A line drawn from the center of the femoral head to the center of the ankle joint (tibial plafond).
. A line drawn from the anterior superior iliac spine to the medial malleolus.
. A line drawn along the mid-diaphyseal axis of the femur and tibia.

Correct Answer & Explanation

. A line drawn from the center of the femoral head to the center of the ankle joint (tibial plafond).

Explanation

Correct Answer: CThe text clearly defines the mechanical axis: "The mechanical axis of the lower limb is defined as a straight line drawn from the center of the femoral head to the center of the ankle joint (specifically, the center of the tibial plafond). This line represents the primary weight-bearing axis of the leg." This is the foundational definition for assessing global alignment and Mechanical Axis Deviation (MAD).Option A is incorrect as it starts from the greater trochanter, not the femoral head. Option B is incorrect as it terminates at the knee, not the ankle, and represents only a segment of the mechanical axis. Option D describes a different anatomical landmark and is not the mechanical axis. Option E describes the anatomic axes of the individual bones, not the global mechanical axis of the limb.

Question 1419

Topic: 8. Foot and Ankle

A 55-year-old patient is undergoing evaluation for a distal tibial deformity. The surgeon measures the Mechanical Lateral Distal Tibial Angle (mLDTA) on a full-length standing AP radiograph. The measured mLDTA is 84°. Based on Paley's normative data, what does this measurement indicate?

. Normal ankle joint orientation.
. Ankle varus deformity.
. Ankle valgus deformity.
. Proximal tibial varus deformity.
. Distal femoral valgus deformity.

Correct Answer & Explanation

. Ankle valgus deformity.

Explanation

Correct Answer: CAccording to Paley's principles, the normal range for the Mechanical Lateral Distal Tibial Angle (mLDTA) is 86° to 92° (average 89°). The text states: "An angle <86° indicates ankle valgus; >92° indicates ankle varus."The patient's measured mLDTA of 84° is less than 86°, which falls outside the normal range and specifically indicates an ankle valgus deformity.Option A is incorrect as 84° is outside the normal range. Option B is incorrect as ankle varus would be indicated by an angle greater than 92°. Options D and E refer to deformities at different anatomical locations (proximal tibia and distal femur, respectively) and are assessed by different angles (MPTA and mLDFA).

Question 1420

Topic: 8. Foot and Ankle

A surgeon evaluating a multi-apical tibial deformity notes two distinct Centers of Rotation of Angulation (CORAs). If only the proximal CORA is corrected perfectly with an osteotomy and hinge at that exact level, what will be the resulting mechanical axis alignment?

. The mechanical axis will perfectly bisect the knee and ankle joints.
. The mechanical axis will be completely parallel to the anatomic axis.
. The mechanical axis will still deviate from the center of the distal joint.
. The mechanical axis will pass through the center of the knee and ankle but with a translation deformity.
. The joint line convergence angle will automatically increase to compensate.

Correct Answer & Explanation

. The mechanical axis will still deviate from the center of the distal joint.

Explanation

In a multi-apical deformity, correcting only one CORA will align that specific segment, but the overall mechanical axis will still fail to pass through the center of the distal joint due to the uncorrected second CORA.

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