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Lower Extremity Trauma MCQs

Practice Set 6 of 34

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

Question 101

Topic: Lower Extremity Trauma

A 30-year-old active duty military personnel presents with a chronic distal femoral deformity following a combat injury. Preoperative planning reveals a significant procurvatum deformity of the distal femur, with a Posterior Distal Femoral Angle (PDFA) measured at 70°. The surgeon plans a Fixator-Assisted Nailing (FAN) procedure to correct this deformity. According to Paley's principles, what is the most appropriate interpretation of this PDFA measurement and the primary goal for its correction?

. A PDFA of 70° indicates a recurvatum deformity, and the goal is to increase the angle to 83°.
. A PDFA of 70° indicates a procurvatum deformity, and the goal is to increase the angle to 83°.
. A PDFA of 70° indicates a recurvatum deformity, and the goal is to decrease the angle to 83°.
. A PDFA of 70° indicates a procurvatum deformity, and the goal is to decrease the angle to 83°.
. A PDFA of 70° is within the normal range, and no sagittal plane correction is needed.

Correct Answer & Explanation

. A PDFA of 70° indicates a procurvatum deformity, and the goal is to increase the angle to 83°.

Explanation

Correct Answer: BThe Posterior Distal Femoral Angle (PDFA) evaluates the sagittal plane alignment of the distal femur. The normal value range is 79° to 87°, with an average of 83°. An angle less than 79° indicates a procurvatum (flexion deformity), while an angle greater than 87° indicates recurvatum (hyperextension). Therefore, a PDFA of 70° is significantly less than the normal range, confirming a procurvatum deformity. The primary goal of correction would be to increase this angle to the average normal value of 83° to restore proper sagittal alignment.Option A is incorrect:A PDFA of 70° is less than 79°, which indicates procurvatum, not recurvatum.Option C is incorrect:A PDFA of 70° indicates procurvatum, not recurvatum. The goal is to increase the angle, not decrease it.Option D is incorrect:While a PDFA of 70° indicates procurvatum, the goal is to increase the angle to 83°, not decrease it.Option E is incorrect:A PDFA of 70° is well outside the normal range of 79° to 87°, indicating a significant deformity requiring correction.

Question 102

Topic: Lower Extremity Trauma

A 60-year-old female presents with a chronic distal femoral varus deformity. Preoperative planning indicates a need for a valgus-producing osteotomy and Fixator-Assisted Nailing (FAN). To prevent recurrent varus deformity and ensure the intramedullary nail maintains the corrected alignment, where should a blocking (Poller) screw be strategically placed in the distal fragment?

. Medially, to force the nail laterally and prevent valgus recurrence.
. Laterally, to force the nail medially and prevent varus recurrence.
. Anteriorly, to prevent procurvatum.
. Posteriorly, to prevent recurvatum.
. Centrally, to stabilize the osteotomy site.

Correct Answer & Explanation

. Laterally, to force the nail medially and prevent varus recurrence.

Explanation

Correct Answer: BThe 'Golden Rule' for blocking screw placement is to 'Always place the blocking screw on the concave side of the deformity you are trying to prevent.' For a varus deformity, the concave side is lateral. Therefore, to prevent recurrent varus (i.e., to hold the bone in the corrected valgus alignment), a blocking screw should be placed laterally in the distal fragment. This narrows the lateral canal, forcing the nail medially and preventing the distal fragment from sliding back into varus.Option A is incorrect:Placing a screw medially would be done to prevent recurrent valgus, not varus.Option C is incorrect:Placing a screw anteriorly is not the primary strategy for frontal plane varus/valgus control; it would be used to prevent recurvatum.Option D is incorrect:Placing a screw posteriorly is used to prevent procurvatum, not recurrent varus.Option E is incorrect:While blocking screws contribute to stability, their primary role is to guide the nail's trajectory and prevent specific malalignments, not just general stabilization at the osteotomy site.

Question 103

Topic: Lower Extremity Trauma

A 50-year-old male presents with a long-standing distal femoral valgus deformity and associated lateral compartment knee pain. Preoperative planning indicates an mLDFA of 75° and a negative MAD of 20 mm. The surgeon plans a distal femoral osteotomy using Fixator-Assisted Nailing (FAN). To achieve optimal correction and prevent the most common iatrogenic complications, which combination of strategies is most critical?

. Performing a simple transverse osteotomy at the CORA and using a two-pin external fixator.
. Placing a blocking screw medially in the distal fragment and using a multi-planar external fixator with an anterior distal pin.
. Placing a blocking screw laterally in the distal fragment and using a single-bar external fixator.
. Performing an opening wedge osteotomy to lengthen the limb and avoiding blocking screws.
. Inserting the intramedullary nail first, then applying the external fixator for correction.

Correct Answer & Explanation

. Placing a blocking screw medially in the distal fragment and using a multi-planar external fixator with an anterior distal pin.

Explanation

Correct Answer: BThe patient has a valgus deformity (mLDFA 75°, negative MAD 20 mm). To correct this, the nail needs to be guided to create a varus-producing effect. According to the 'Golden Rule' for blocking screws, to prevent recurrent valgus (the original deformity), a blocking screw should be placed on the concave side, which is medially in the distal fragment. This forces the nail laterally, correcting the valgus. Furthermore, the case emphasizes that the most common and critical error in distal femoral FAN is iatrogenic procurvatum due to inadequate sagittal plane control. This is prevented by using a multi-planar external fixator, specifically by supplementing lateral pins with at least one anterior pin in the distal segment to counteract gastrocnemius pull and nail trajectory.Option A is incorrect:A simple transverse osteotomy is inferior to a dome osteotomy biomechanically, and a two-pin external fixator is biomechanically incompetent in the sagittal plane, leading to procurvatum.Option C is incorrect:Placing a blocking screw laterally would be for a varus deformity to prevent recurrent varus, not for a valgus deformity. A single-bar fixator is inadequate for sagittal control.Option D is incorrect:An opening wedge osteotomy is a valid technique, but avoiding blocking screws for a valgus deformity would risk recurrence. Limb lengthening is not the primary goal here, and the choice of osteotomy type (opening wedge vs. dome) is a separate consideration from the critical hardware strategies for stability.Option E is incorrect:The workflow clearly states that the external fixator is applied and correction achievedbeforereaming and nail insertion. Inserting the nail first would make acute correction impossible and risk malalignment.

Question 104

Topic: Lower Extremity Trauma

On a long-leg AP radiograph of a patient with a diaphyseal femoral deformity, the anatomic axis of the proximal segment and the anatomic axis of the distal segment intersect at the CORA. The angle measured between these two lines is 18 degrees. What does this angle represent?

. The joint line convergence angle
. The mechanical axis deviation
. The magnitude of the angulation deformity
. The required length of the intramedullary nail
. The required translation offset

Correct Answer & Explanation

. The magnitude of the angulation deformity

Explanation

The angle formed by the intersection of the proximal and distal anatomic (or mechanical) axes at the CORA represents the true magnitude of the angular deformity in that specific plane.

Question 105

Topic: Lower Extremity Trauma

During a Fixator-Assisted Nailing (FAN) procedure for a distal femoral valgus deformity, blocking (Poller) screws are utilized. To prevent loss of reduction and guide the nail correctly, where should the blocking screw be placed in the distal fragment?

. Medial to the intended path of the intramedullary nail
. Lateral to the intended path of the intramedullary nail
. Directly anterior to the intramedullary nail
. Directly posterior to the intramedullary nail
. In the exact center of the medullary canal

Correct Answer & Explanation

. Lateral to the intended path of the intramedullary nail

Explanation

In a valgus deformity, the apex is medial and the concave side is lateral. Blocking screws should be placed on the concave side of the deformity (lateral) to narrow the canal and force the nail to maintain the corrected alignment.

Question 106

Topic: Lower Extremity Trauma

A patient presents with a biapical (two-level) tibial deformity. The surgeon chooses to perform a single osteotomy located exactly halfway between the two CORAs. To successfully restore a collinear mechanical axis, what mandatory geometric maneuver must be performed at the osteotomy site?

. Pure angular rotation
. Bone grafting of the medial cortex only
. Substantial translation of the bone segments
. Shortening of the bone by 3 centimeters
. Use of a flexible intramedullary nail instead of a rigid one

Correct Answer & Explanation

. Substantial translation of the bone segments

Explanation

When a single osteotomy is placed between two CORAs, correcting the overall alignment mathematically requires significant translation of the bone segments at the osteotomy site to restore the mechanical axis.

Question 107

Topic: Lower Extremity Trauma

During deformity planning with Paley's methods, what geometric advantage does a true dome osteotomy performed at the CORA provide over a simple transverse single-cut osteotomy?

. It allows for translation without any angular change.
. It enables angular correction without creating an asymmetric gap or altering bone length.
. It guarantees a 20% increase in overall bone length.
. It strictly requires plate fixation instead of intramedullary nailing.
. It intentionally alters the mechanical axis away from the joint center.

Correct Answer & Explanation

. It enables angular correction without creating an asymmetric gap or altering bone length.

Explanation

A dome osteotomy (cylindrical cut) centered on the CORA allows the bone ends to rotate against each other without creating large bone gaps or inherently altering the length, facilitating excellent bone contact.

Question 108

Topic: Lower Extremity Trauma

A patient with a mechanical axis deviation (MAD) of 35 mm medial to the center of the knee is being evaluated. This MAD value is most strongly indicative of which primary alignment abnormality?

. Severe genu valgum
. Severe genu varum
. Procurvatum of the proximal tibia
. Recurvatum of the distal femur
. Rotational malalignment of the femur

Correct Answer & Explanation

. Severe genu varum

Explanation

A medial mechanical axis deviation (MAD) indicates that the weight-bearing axis falls medial to the center of the knee joint, which is the classic presentation of genu varum (varus deformity).

Question 109

Topic: Lower Extremity Trauma

When planning Fixator-Assisted Plating (FAP) over Fixator-Assisted Nailing (FAN) for a distal femur deformity, which specific anatomic factor makes FAP the overwhelmingly preferred option?

. A purely diaphyseal location of the deformity
. An extremely short distal metaphyseal segment (e.g., 2 cm) precluding adequate nail interlocking
. A concurrent ipsilateral tibial shaft fracture
. A history of deep vein thrombosis
. The presence of a wide intramedullary canal

Correct Answer & Explanation

. An extremely short distal metaphyseal segment (e.g., 2 cm) precluding adequate nail interlocking

Explanation

FAP is preferred for periarticular deformities where the remaining bone segment is too short to accommodate the distal locking screws of an intramedullary nail securely. A plate can utilize multiple locking screws in a very short segment.

Question 110

Topic: Lower Extremity Trauma

A patient presents with knee pain and a noticeable leg deformity. Full-length standing radiographs reveal a mechanical axis deviation (MAD) of 45 mm medial to the center of the knee joint. The mechanical lateral distal femoral angle (mLDFA) is 102 degrees (normal 85-90 degrees) and the medial proximal tibial angle (MPTA) is 88 degrees (normal 85-90 degrees). What is the primary diagnosis?

. Primary proximal tibial varus deformity
. Primary distal femoral varus deformity
. Primary distal femoral valgus deformity
. Primary proximal tibial valgus deformity
. Combined femoral and tibial varus deformity

Correct Answer & Explanation

. Primary distal femoral varus deformity

Explanation

A medial mechanical axis deviation indicates overall varus alignment. An abnormally high mLDFA (>90 degrees) specifically localizes the varus deformity to the distal femur, while the normal MPTA indicates the proximal tibia is not the source of the deformity.

Question 111

Topic: Lower Extremity Trauma

A 40-year-old patient has a multi-apical tibial deformity secondary to a prior severe crush injury. When analyzing the preoperative radiographs to find the Centers of Rotation of Angulation (CORAs), which of the following best describes the correct geometric method for locating them?

. Identifying the intersection of the mechanical axis of the femur with the anatomical axis of the tibia.
. Identifying the intersections of the mid-diaphyseal lines of the proximal, middle, and distal bone segments.
. Placing a single CORA at the joint line regardless of the diaphyseal bowing.
. Measuring the angle between the tibial anatomical axis and the tibial plateau exclusively.
. Identifying the single point of maximum soft tissue contracture on the concave side.

Correct Answer & Explanation

. Identifying the intersections of the mid-diaphyseal lines of the proximal, middle, and distal bone segments.

Explanation

In a multi-apical deformity, the bone is functionally divided into three or more segments. The multiple CORAs are identified at the intersection points of the anatomical (mid-diaphyseal) axes of each adjacent segment (e.g., proximal to middle, and middle to distal).

Question 112

Topic: Lower Extremity Trauma

A surgeon is planning a corrective osteotomy for an angular deformity of the tibia. After drawing the proximal and distal mechanical axes of the deformed tibia on a full-length radiograph, they identify the point where these two lines intersect, as conceptually illustrated in the diagram below.

According to Paley's principles, this critical intersection point is known as the:

. Mechanical Axis Deviation (MAD).
. Joint Line Convergence Angle (JLCA).
. Center of Rotation of Angulation (CORA).
. Fujisawa Point.
. Anatomic Axis Intersection (AAI).

Correct Answer & Explanation

. Center of Rotation of Angulation (CORA).

Explanation

Correct Answer: CThe case defines the CORA: 'The CORA is the absolute foundational concept of the Paley deformity correction system. It is defined as the precise point in two-dimensional space where the proximal mechanical axis line of a deformed bone intersects with the distal mechanical axis line of that same bone.' The diagram provided clearly illustrates this concept. Therefore, this critical intersection point is the Center of Rotation of Angulation (CORA) (Option C). Option A (MAD) is a distance measurement, not an intersection point. Option B (JLCA) is an angle. Option D (Fujisawa Point) is a specific point on the tibial plateau related to normal mechanical axis alignment. Option E (AAI) is not a standard term in Paley's system for this specific intersection.

Question 113

Topic: Lower Extremity Trauma

In the management of a large segmental tibial defect using Ilizarov bone transport, the advancing bone segment eventually meets the target bone at the 'docking site'. Which secondary intervention is most frequently required at this site to ensure definitive union?

. Fibular osteotomy
. Bone grafting and site preparation
. Conversion to an intramedullary nail
. Application of a bridging plate
. Free vascularized fibula transfer

Correct Answer & Explanation

. Bone grafting and site preparation

Explanation

The docking site in bone transport is often compromised by dense scar tissue and sclerotic bone ends. Consequently, it frequently requires surgical freshening of the bone ends and autologous bone grafting to achieve successful union.

Question 114

Topic: Lower Extremity Trauma

A 55-year-old male presents with significant knee recurvatum. Preoperative planning reveals a Mechanical Posterior Proximal Tibial Angle (mPPTA) of 88° and a normal Mechanical Posterior Distal Femoral Angle (mPDFA) of 82°. The surgeon, aiming for a 'straight leg,' performs a distal femoral flexion osteotomy to correct the clinical hyperextension.

. Iatrogenic anterior knee subluxation
. Iatrogenic posterior knee subluxation
. Patella baja
. Non-union of the osteotomy
. Overcorrection leading to a fixed flexion deformity

Correct Answer & Explanation

. Iatrogenic posterior knee subluxation

Explanation

Correct Answer: BThe case content emphasizes the critical axiom: 'You must correct the deformity in the bone where it actually exists.' The patient has a reversed posterior tibial slope (mPPTA > 84°), indicating that the tibia is the true source of the recurvatum. The mPDFA is normal, meaning the femur is not deformed. By performing a flexion osteotomy of the distal femur (the wrong bone), the femoral condyles are now pointing abnormally downward onto a tibial plateau that is still sloped backward. The text explicitly states: 'With every single step, weight-bearing forces will cause the femur to literally slide off the back of the tibia, creating a devastatingiatrogenic posterior knee subluxation.'Option A is incorrect; anterior subluxation would occur if femoral recurvatum were corrected in the tibia. Option C (patella baja) is typically associated with proximal tibial osteotomies performed incorrectly relative to the tibial tuberosity, not distal femoral osteotomies. Options D and E are general surgical complications but not the specific biomechanical catastrophe predicted by violating Paley's fundamental rule in this scenario.

Question 115

Topic: Lower Extremity Trauma

A patient with a severe knee deformity undergoes full-length weight-bearing lateral radiography. A plumb line dropped from the center of the femoral head passes significantly posterior to the center of the knee joint.

. Knee flexion deformity (procurvatum)
. Knee hyperextension (recurvatum)
. Normal sagittal alignment
. Coronal plane varus deformity
. Coronal plane valgus deformity

Correct Answer & Explanation

. Knee hyperextension (recurvatum)

Explanation

Correct Answer: BThe case content describes the normal sagittal mechanical axis: 'In a normal, healthy standing posture... a plumb line dropped from the center of the femoral head should pass...Anterior to the center of the knee joint... This specific anterior positioning creates a natural extension moment at the knee.' It then states: 'Conversely, excessive posterior deviation, where the mechanical axis falls behind the center of the knee, signifies a hyperextension deformity (recurvatum).' Therefore, a plumb line passing significantly posterior to the knee joint indicates recurvatum.Option A is incorrect; excessive anterior deviation of the distal femur or proximal tibia indicates a flexion deformity (procurvatum). Option C is incorrect as the axis should pass anterior to the knee. Options D and E describe coronal plane deformities, which are not assessed by the sagittal mechanical axis.

Question 116

Topic: Lower Extremity Trauma

A 28-year-old patient presents with 18 degrees of clinical knee hyperextension. Full-length lateral radiographs reveal a Mechanical Posterior Distal Femoral Angle (mPDFA) of 82° (normal 80-85°) and a Mechanical Posterior Proximal Tibial Angle (mPPTA) of 89° (normal 77-84°).

. Femoral recurvatum
. Tibial recurvatum
. Pure soft tissue laxity
. Combined femoral and tibial osseous deformity
. Neuromuscular recurvatum

Correct Answer & Explanation

. Tibial recurvatum

Explanation

Correct Answer: BThe case content provides a clear diagnostic algorithm: 'If the mPDFA is > 85°, the source of the deformity isfemoral. If the mPPTA is > 84°, the source of the deformity istibial.' In this patient, the mPDFA of 82° is within the normal range, ruling out femoral osseous deformity. However, the mPPTA of 89° is significantly greater than the normal upper limit of 84°, indicating a flattened or reversed posterior slope of the tibial plateau. This directly points to tibial recurvatum as the primary source of the deformity.Option A is incorrect because the mPDFA is normal. Option C is incorrect because the mPPTA is abnormal, indicating an osseous deformity. Option D is incorrect because only the tibia shows an osseous deformity. Option E is a potential etiology but the question asks for the primary source of the deformity based on the given radiographic measurements, which clearly point to a structural tibial issue.

Question 117

Topic: Lower Extremity Trauma

A 48-year-old male presents with a sagittal plane knee deformity. To accurately quantify the bony architecture, a true lateral radiograph is obtained. Which of the following statements correctly defines the Posterior Distal Femoral Angle (PDFA) and its normal range, according to Paley's principles?

. The angle formed between the anatomic axis of the tibia and the joint line of the tibial plateau, normally 83° ± 4°.
. The angle formed between the anatomic axis of the femur and the joint line of the distal femoral condyles, normally 81° ± 4°.
. The angle formed between the anatomic axis of the femur and the joint line of the distal femoral condyles, normally 83° ± 4°.
. The angle formed between the mechanical axis of the femur and the joint line of the distal femoral condyles, normally 83° ± 4°.
. The angle formed between the anatomic axis of the tibia and the joint line of the tibial plateau, normally 81° ± 4°.

Correct Answer & Explanation

. The angle formed between the anatomic axis of the femur and the joint line of the distal femoral condyles, normally 83° ± 4°.

Explanation

Correct Answer: CThe case defines the Posterior Distal Femoral Angle (PDFA) as 'the angle formed between the anatomic axis of the femur and the joint line of the distal femoral condyles.' It also states the normal value range for PDFA is '83° ± 4°'.Option A describes the PPTA and its normal range is incorrect for PDFA. Option B correctly defines PDFA but provides the normal range for PPTA. Option D incorrectly refers to the mechanical axis instead of the anatomic axis. Option E describes the PPTA and its normal range, not the PDFA.

Question 118

Topic: Lower Extremity Trauma

According to Paley's principles, the Center of Rotation of Angulation (CORA) is a critical concept for precise deformity correction. For a patient presenting with an isolated femoral procurvatum deformity, where would the CORA typically be located?

. In the proximal tibia, at the level of the tibial tubercle.
. In the distal femur, proximal to the joint line.
. At the knee joint line, representing a combined deformity.
. In the mid-diaphysis of the femur, away from the joint.
. In the patellofemoral joint, indicating a patellar maltracking issue.

Correct Answer & Explanation

. In the distal femur, proximal to the joint line.

Explanation

Correct Answer: BThe case states, 'A decreased PDFA signifies that the distal femoral joint surface is pathologically tilted anteriorly (into extension) relative to the femoral shaft. This creates afemoral procurvatumdeformity. The CORA for this specific deformity is located in the distal femur.' While the exact point within the distal femur can vary, it is generally proximal to the joint line, where the angulation occurs.Option A is incorrect as it describes the location for a tibial deformity. Option C is incorrect; a CORA at the joint line would imply a joint-level deformity, not a specific bony angulation within the femur. Option D is incorrect; mid-diaphyseal CORAs are typically associated with diaphyseal bowing, not juxta-articular procurvatum. Option E is unrelated to the CORA of a femoral procurvatum.

Question 119

Topic: Lower Extremity Trauma

When calculating the mPDFA for preoperative planning of a sagittal deformity, the mechanical axis of the femur in the sagittal plane must be drawn. Which two anatomic landmarks properly define this axis?

. Center of the femoral head and the anterior cortex of the distal femur
. Center of the greater trochanter and the center of the knee joint
. Center of the femoral head and the center of the distal femoral joint line in the sagittal profile
. The medullary canal bisector from proximal to distal
. Anterior superior iliac spine (ASIS) to the patella

Correct Answer & Explanation

. Center of the femoral head and the center of the distal femoral joint line in the sagittal profile

Explanation

The sagittal mechanical axis of the femur is defined by a line connecting the center of rotation of the femoral head to the center of the distal femoral joint space on a true lateral radiograph.

Question 120

Topic: Lower Extremity Trauma

When analyzing the Joint Line Convergence Angle (JLCA) in the sagittal plane of a normal knee, how do the distal femoral and proximal tibial joint lines relate to one another?

. They intersect at a 15-degree angle pointing anteriorly
. They are roughly parallel (angle close to 0 degrees)
. They intersect at a 15-degree angle pointing posteriorly
. They diverge widely in full extension
. The femoral joint line is perpendicular to the tibial joint line

Correct Answer & Explanation

. They are roughly parallel (angle close to 0 degrees)

Explanation

In the normal knee, the sagittal joint lines of the distal femur and proximal tibia are roughly parallel (JLCA near 0 degrees). Significant deviation indicates either cartilage loss, ligamentous laxity, or intra-articular deformity.

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