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Lower Extremity Trauma MCQs

Practice Set 10 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 181

Topic: Lower Extremity Trauma

A 42-year-old active patient presents with LCOA and a valgus deformity. A long leg standing radiograph is obtained, as shown. The mechanical lateral distal femoral angle (mLDFA) is measured at 82 degrees, and the medial proximal tibial angle (MPTA) is 87 degrees. Based on these measurements and Paley's principles, what is the primary anatomical location of the deformity requiring correction?

. Proximal tibia
. Distal femur
. Both proximal tibia and distal femur equally
. Patellofemoral joint
. Mid-diaphysis of the femur

Correct Answer & Explanation

. Distal femur

Explanation

Correct Answer: BAccording to Paley's principles, the anatomical location of a deformity is determined by comparing measured angles to normal reference values. The normal mLDFA is 87 ± 3 degrees (range 84-90 degrees), and the normal MPTA is 87 ± 3 degrees (range 84-90 degrees). In this patient, the mLDFA is 82 degrees, which is significantly less than the normal range, indicating a valgus deformity originating from the distal femur. The MPTA of 87 degrees is within the normal range, indicating no significant deformity at the proximal tibia. Therefore, the primary anatomical location of the deformity is the distal femur.Option A is incorrectbecause the MPTA of 87 degrees is normal, indicating no significant deformity in the proximal tibia.Option C is incorrectbecause the deformity is primarily femoral, with a normal MPTA.Option D is incorrectbecause while patellofemoral issues can coexist, the primary angular deformity affecting the mechanical axis is at the tibiofemoral level, specifically the distal femur in this case.Option E is incorrectbecause a deformity in the mid-diaphysis of the femur would typically manifest as a bowing deformity, which is less common for primary valgus knee OA and would be reflected in different angular measurements or a more diffuse curvature.

Question 182

Topic: Lower Extremity Trauma

A 60-year-old patient with LCOA and a valgus knee deformity is undergoing preoperative planning for a distal femoral osteotomy (DFO). The image shows a close-up of the knee joint. The surgeon aims to correct the mechanical axis while preserving the joint line obliquity. Which of the following angular measurements is most critical for determining the *amount* of correction needed at the distal femur to achieve a neutral mechanical axis?

. Medial Proximal Tibial Angle (MPTA)
. Anatomical Lateral Distal Femoral Angle (aLDFA)
. Mechanical Lateral Distal Femoral Angle (mLDFA)
. Posterior Tibial Slope (PTS)
. Joint Line Convergence Angle (JLCA)

Correct Answer & Explanation

. Mechanical Lateral Distal Femoral Angle (mLDFA)

Explanation

Correct Answer: CThe Mechanical Lateral Distal Femoral Angle (mLDFA) is the angle between the mechanical axis of the femur and the distal femoral joint line. It directly quantifies the angular deformity of the distal femur relative to the mechanical axis. A normal mLDFA is 87 ± 3 degrees. In a valgus knee with a distal femoral deformity, the mLDFA will be less than 84 degrees. The amount of correction needed for a DFO is calculated to bring the mLDFA back to the desired range (e.g., 87 degrees) to realign the mechanical axis. This is a cornerstone of Paley's principles for deformity correction, focusing on correcting the deformity at its anatomical location (CORA).Option A is incorrectbecause the MPTA measures the deformity at the proximal tibia. While important for overall assessment, it does not directly determine the amount of correction for adistal femoralosteotomy if the deformity is primarily femoral.Option B is incorrectbecause the anatomical LDFA (aLDFA) is measured relative to the anatomical axis, which is less relevant for mechanical axis correction than the mLDFA.Option D is incorrectbecause the Posterior Tibial Slope (PTS) measures the sagittal plane alignment of the tibia and is not directly used for coronal plane valgus correction.Option E is incorrectbecause the Joint Line Convergence Angle (JLCA) indicates the amount of joint space opening or closing due to cartilage loss or ligamentous laxity, but it does not directly quantify the bony angular deformity requiring osteotomy correction.

Question 183

Topic: Lower Extremity Trauma

A 50-year-old patient with symptomatic LCOA and a valgus deformity is being planned for a distal femoral osteotomy. The image illustrates a common method for planning osteotomies. If the surgeon chooses an opening wedge distal femoral osteotomy, which of the following is a potential advantage compared to a closing wedge osteotomy in this specific scenario?

. Faster bone healing due to compression at the osteotomy site.
. Less risk of neurovascular injury due to medial approach.
. Ability to simultaneously lengthen the limb, which can be beneficial in cases of limb length discrepancy.
. Greater stability of fixation, allowing earlier weight-bearing.
. Reduced risk of patella baja.

Correct Answer & Explanation

. Ability to simultaneously lengthen the limb, which can be beneficial in cases of limb length discrepancy.

Explanation

Correct Answer: CAn opening wedge distal femoral osteotomy (OWDFO) involves creating a wedge-shaped gap on the medial side of the distal femur. This technique effectively lengthens the limb on the medial side. If the patient has a pre-existing limb length discrepancy (LLD) with the affected limb being shorter, an OWDFO can be advantageous as it can simultaneously correct the valgus deformity and address the LLD by lengthening the limb. This is a key consideration in surgical planning.Option A is incorrectbecause opening wedge osteotomies typically heal by secondary intention (gap healing) and may require bone grafting, which can sometimes lead to slower healing compared to closing wedge osteotomies where bone-to-bone contact and compression are achieved.Option B is incorrectbecause an OWDFO typically involves a medial approach, which places the femoral artery and vein at risk, particularly if the osteotomy is performed too proximally or if the medial periosteum is not carefully protected. A closing wedge osteotomy is usually performed laterally.Option D is incorrectbecause opening wedge osteotomies, especially larger corrections, can be less stable initially due to the gap and may require more robust fixation and/or delayed weight-bearing compared to closing wedge osteotomies which benefit from inherent bony stability and compression.Option E is incorrectbecause an opening wedge DFO does not typically cause patella baja. Patella baja is more commonly associated with proximal tibial osteotomies, particularly closing wedge techniques, due to shortening of the patellar tendon relative to the tibial tubercle.

Question 184

Topic: Lower Extremity Trauma

A 35-year-old patient presents with symptomatic LCOA and a valgus deformity. Preoperative planning, as depicted in the image, reveals a mechanical axis deviation of 15 degrees valgus, mLDFA of 80 degrees, and MPTA of 88 degrees. The surgeon plans a distal femoral osteotomy. Which of the following statements best describes the appropriate correction strategy based on Paley's principles?

. Perform a closing wedge proximal tibial osteotomy to correct the MPTA to 90 degrees.
. Perform an opening wedge distal femoral osteotomy to increase the mLDFA to 87 degrees.
. Perform a combined distal femoral and proximal tibial osteotomy due to the severe deformity.
. Perform a closing wedge distal femoral osteotomy to decrease the mLDFA to 87 degrees.
. Perform a medial opening wedge osteotomy at the distal femur to achieve a final mLDFA of 90 degrees.

Correct Answer & Explanation

. Perform an opening wedge distal femoral osteotomy to increase the mLDFA to 87 degrees.

Explanation

Correct Answer: BThe normal mLDFA is 87 ± 3 degrees, and the normal MPTA is 87 ± 3 degrees. In this patient, the mLDFA is 80 degrees, which is significantly decreased (valgus deformity at the femur). The MPTA of 88 degrees is within the normal range. Therefore, the deformity is primarily located at the distal femur. To correct a valgus deformity at the distal femur, an opening wedge osteotomy on the medial side (or a closing wedge on the lateral side) is performed to increase the mLDFA towards the normal range, typically aiming for 87 degrees to achieve a neutral mechanical axis, or slightly more (e.g., 89-90 degrees) for slight varus overcorrection to offload the lateral compartment.Option A is incorrectbecause the MPTA is normal (88 degrees), so a proximal tibial osteotomy is not indicated. Correcting it to 90 degrees would create a varus deformity at the tibia.Option C is incorrectbecause the deformity is isolated to the distal femur (normal MPTA), so a combined osteotomy is not necessary and would violate the principle of correcting the deformity at its CORA.Option D is incorrectbecause a closing wedge distal femoral osteotomy on the lateral side wouldincreasethe mLDFA, not decrease it. Decreasing the mLDFA would worsen the valgus deformity. The goal is to increase the mLDFA from 80 degrees to 87 degrees.Option E is incorrectbecause while a medial opening wedge osteotomy is the correct approach, aiming for a final mLDFA of 90 degrees would result in a significant varus overcorrection at the femur, potentially leading to excessive medial compartment loading and an overly steep joint line. A target of 87-89 degrees is generally preferred.

Question 185

Topic: Lower Extremity Trauma

A 45-year-old female undergoes a medial opening wedge high tibial osteotomy (HTO) for medial compartment osteoarthritis. Intraoperatively, the surgeon inadvertently opens the anterior aspect of the osteotomy gap equally to the posterior aspect. What is the most likely consequence on the sagittal alignment of the tibia?

. Increase in the posterior tibial slope.
. Decrease in the posterior tibial slope.
. Maintenance of the native posterior tibial slope.
. Creation of an apex posterior translational deformity.
. Creation of an iatrogenic fixed flexion deformity.

Correct Answer & Explanation

. Increase in the posterior tibial slope.

Explanation

Because the proximal tibia is triangular, opening the anterior gap equally to the posterior gap will pitch the tibial plateau into relative extension, thereby increasing the posterior tibial slope. To maintain normal slope, the anterior gap must be smaller than the posterior gap (typically a 1:2 ratio).

Question 186

Topic: Lower Extremity Trauma

A patient presents with an isolated structural procurvatum deformity of the distal femur. What is the most characteristic clinical symptom or physical examination finding associated with this specific sagittal plane deformity?

. Severe recurvatum of the knee during the stance phase of gait.
. A clinical fixed flexion deformity (FFD) of the knee.
. Patella alta and secondary extensor mechanism lag.
. An apparent lengthening of the affected lower extremity.
. Increased baseline passive knee hyperextension on the table.

Correct Answer & Explanation

. A clinical fixed flexion deformity (FFD) of the knee.

Explanation

An apex-anterior (procurvatum) deformity of the distal femur limits the mechanical extension of the knee joint. Clinically, this presents as an inability to fully extend the leg, mimicking a fixed flexion deformity.

Question 187

Topic: Lower Extremity Trauma

When evaluating lower extremity alignment on standing full-length radiographs, a Joint Line Convergence Angle (JLCA) of 6 degrees is noted in a knee with severe varus deformity. According to Paley's principles, what does an abnormally elevated JLCA indicate?

. A purely extra-articular diaphyseal tibial deformity.
. Intra-articular deformity such as cartilage loss or ligamentous laxity.
. A compensatory deformity in the distal femur.
. A normal physiologic response to medial compartment loading.
. An apex-posterior sagittal plane deformity.

Correct Answer & Explanation

. Intra-articular deformity such as cartilage loss or ligamentous laxity.

Explanation

The JLCA evaluates the parallelism of the distal femoral and proximal tibial articular surfaces. A normal JLCA is 0-2 degrees. An elevated JLCA indicates intra-articular pathology, typically cartilage volume loss or asymmetric ligamentous laxity.

Question 188

Topic: Lower Extremity Trauma

A surgeon is planning a high tibial osteotomy (HTO) for a 45-year-old laborer with symptomatic medial compartment osteoarthritis and varus malalignment. To optimize load distribution, the postoperative mechanical axis should be targeted to pass through which specific coordinate of the tibial plateau?

. Exactly at the center (50%) of the tibial plateau.
. At the Fujisawa point, approximately 62% of the width from the medial edge.
. At the medial tibial spine, approximately 40% of the width from the medial edge.
. At the far lateral edge, approximately 85% of the width from the medial edge.
. At the center of the medial compartment to stimulate fibrocartilage growth.

Correct Answer & Explanation

. At the Fujisawa point, approximately 62% of the width from the medial edge.

Explanation

For medial compartment osteoarthritis, HTO aims to slightly overcorrect alignment into valgus. The optimal target is the Fujisawa point, located at 62-62.5% of the tibial width from the medial border, which appropriately unloads the medial compartment.

Question 189

Topic: Lower Extremity Trauma

A 16-year-old patient presents with a symptomatic apex anterior (procurvatum) deformity of the distal femur. A single-level corrective osteotomy is planned. Which of the following osteotomy configurations is biomechanically appropriate to correct this sagittal deformity?

. Anterior opening wedge or posterior closing wedge.
. Anterior closing wedge or posterior opening wedge.
. Medial closing wedge.
. Lateral opening wedge.
. Pure transverse rotational osteotomy.

Correct Answer & Explanation

. Anterior closing wedge or posterior opening wedge.

Explanation

An apex anterior (procurvatum) deformity requires extension of the distal fragment. This is achieved by taking an anterior closing wedge or creating a posterior opening wedge at the level of the deformity.

Question 190

Topic: Lower Extremity Trauma

During the preoperative planning for a distal femoral osteotomy using Paley's Malalignment Test, the surgeon draws a mechanical axis line from the center of the femoral head to the center of the ankle. The line falls 25 mm medial to the center of the knee. The MPTA is measured at 88 degrees, and the mLDFA is measured at 100 degrees. What is the primary source of the deformity?

. Tibial varus.
. Femoral varus.
. Femoral valgus.
. Combined femoral and tibial varus.
. Ligamentous laxity.

Correct Answer & Explanation

. Femoral varus.

Explanation

The mechanical axis deviation (MAD) is medial, indicating a varus lower extremity. The MPTA is normal (87 +/- 3), but the mLDFA is abnormally high (100 degrees, normal is 87), indicating the primary structural varus deformity is located in the distal femur.

Question 191

Topic: Lower Extremity Trauma

When evaluating the sagittal plane alignment of the distal femur, which of the following angles represents the normal anatomic posterior distal femoral angle (aPDFA)?

. 70 degrees
. 83 degrees
. 90 degrees
. 95 degrees
. 100 degrees

Correct Answer & Explanation

. 83 degrees

Explanation

The normal anatomic posterior distal femoral angle (aPDFA) in the sagittal plane is approximately 83 degrees. Deviations from this angle indicate an osseous procurvatum or recurvatum deformity in the distal femur.

Question 192

Topic: Lower Extremity Trauma

When using a Taylor Spatial Frame to gradually correct a severe soft-tissue knee flexion contracture, where should the virtual hinge be placed to prevent iatrogenic joint subluxation?

. At the anterior cortex of the distal femur
. At the posterior joint line of the tibia
. At the instant center of rotation of the knee joint
. At the CORA of the tibial diaphysis
. At the tibial tubercle

Correct Answer & Explanation

. At the instant center of rotation of the knee joint

Explanation

To correct a knee joint contracture without causing iatrogenic subluxation or compression, the hinge (or virtual hinge) must be placed at the anatomical axis of rotation of the joint, which is the instant center of rotation located in the posterior femoral condyles.

Question 193

Topic: Lower Extremity Trauma

A 32-year-old male presents with chronic right knee pain and a progressive varus deformity. Standing long-leg radiographs reveal a Mechanical Axis Deviation (MAD) of 25mm medial to the center of the knee. Further analysis shows a Mechanical Lateral Distal Femoral Angle (mLDFA) of 88° and a Medial Proximal Tibial Angle (MPTA) of 75°. The Joint Line Convergence Angle (JLCA) is 1°. Based on Paley's principles, which of the following statements best describes the location and nature of this patient's deformity?

. The deformity is primarily femoral, requiring a distal femoral osteotomy.
. The deformity is intra-articular, indicating significant cartilage wear or ligamentous laxity.
. The deformity is entirely tibial, localized to the proximal tibia.
. The deformity is a combined femoral and tibial malalignment, requiring a bi-level osteotomy.
. The MAD is within normal limits, suggesting no significant extra-articular deformity.

Correct Answer & Explanation

. The deformity is entirely tibial, localized to the proximal tibia.

Explanation

Correct Answer: CThe patient presents with a significant varus deformity, indicated by the MAD of 25mm medial to the center of the knee (normal is 8-10mm medial). To localize the deformity, we use the joint orientation angles. The mLDFA is 88°, which is within the normal range (85-90°, average 88°), indicating no significant deformity in the distal femur. However, the MPTA is 75°, which is significantly outside the normal range (85-90°, average 87°). An abnormal MPTA points directly to a tibial-based deformity, specifically in the proximal tibia. The JLCA of 1° is normal (0-2°), ruling out significant intra-articular pathology as the primary cause of the angular deformity.Option A is incorrectbecause the mLDFA is normal, ruling out a primary femoral deformity.Option B is incorrectbecause the JLCA is normal, suggesting the primary issue is extra-articular bony malalignment, not intra-articular pathology or laxity.Option D is incorrectbecause the mLDFA is normal, localizing the deformity solely to the tibia.Option E is incorrectbecause a MAD of 25mm medial is significantly abnormal, indicating a clear varus deformity.

Question 194

Topic: Lower Extremity Trauma

A 55-year-old patient presents with a severe tibial varus deformity, as shown in the preoperative planning radiograph below. The surgeon has meticulously drawn the mechanical axes of the proximal and distal tibial segments, identifying their intersection point. Which of the following statements accurately describes the significance of this intersection point in Paley's methodology?

. It represents the ideal location for the intramedullary nail entry point.
. It is the point where the mechanical axis of the entire limb should pass after correction.
. It is the Center of Rotation of Angulation (CORA), dictating the ideal osteotomy and hinge placement.
. It signifies the maximum point of cartilage wear in the knee joint.
. It indicates the optimal position for interference (Poller) screw placement.

Correct Answer & Explanation

. It is the Center of Rotation of Angulation (CORA), dictating the ideal osteotomy and hinge placement.

Explanation

Correct Answer: CThe image on the left (a) in the provided figure demonstrates the identification of the Center of Rotation of Angulation (CORA). The CORA is the geometric point where the proximal and distal mechanical (or anatomic) axes of a deformed bone intersect. According to Paley's principles, identifying the CORA is the single most important step in preoperative planning as it dictates the ideal location for the osteotomy and governs the mechanical behavior of the entire limb during correction. Placing the osteotomy and the hinge of correction (ACA) at the CORA (Rule One) allows for pure angulation correction without translation.Option A is incorrect. The nail entry point is typically suprapatellar or parapatellar for the tibia, not necessarily at the CORA.Option B is incorrect. The mechanical axis of the entire limb is drawn from the femoral head to the ankle mortise, and its restoration is the goal, but the intersection of thesegmentalaxes defines the CORA.Option D is incorrect. While severe deformity can lead to cartilage wear, the CORA is a geometric construct for bony deformity, not a direct indicator of cartilage pathology.Option E is incorrect. Poller screws are placed strategically around the nail in the metaphysis to prevent toggle, which is related to the corrected alignment, not the CORA itself.

Question 195

Topic: Lower Extremity Trauma

A 35-year-old patient undergoes Fixator Assisted Nailing (FAN) for a valgus deformity of the distal femur. The deformity has been acutely corrected, and the intramedullary nail is in place. To prevent the 'bell-clapper effect' and maintain the corrected alignment, the surgeon plans to insert interference (Poller) screws. According to the golden rules for Poller screw placement, where should these screws be strategically positioned?

. On the medial side of the nail, in the acute angle of the deformity.
. On the lateral side of the nail, in the acute angle of the deformity.
. Anterior to the nail, in the sagittal plane.
. Posterior to the nail, in the sagittal plane.
. Proximal and distal to the nail's locking screws.

Correct Answer & Explanation

. On the lateral side of the nail, in the acute angle of the deformity.

Explanation

Correct Answer: BThe golden rule for interference screw placement is to 'Place on the Concave Side of the Deformity' and 'Place in the Acute Angle'. For a valgus deformity, the concavity is on thelateralside of the limb. Therefore, to block the nail from drifting laterally and prevent the bone from settling back into a valgus position, the blocking screws must be placed on thelateralside of the nail. They are placed in the acute angle formed by the nail and the bone's axis to effectively narrow the canal and prevent toggle.Option A is incorrect. Medial placement would be for a varus deformity, not valgus.Option C and D are incorrect. While Poller screws can be placed in the sagittal plane, the primary rule for angular deformity correction is based on the coronal plane concavity/convexity. Anterior/posterior placement would address sagittal plane instability, but for a valgus deformity (coronal plane), lateral placement is key.Option E is incorrect. Poller screws are placedaroundthe nail, typically in the metaphyseal region where the canal is wide, not specifically proximal or distal to the locking screws, which have a different function.

Question 196

Topic: Lower Extremity Trauma

During a Fixator-Assisted Nailing (FAN) procedure for a proximal tibial varus deformity, the surgeon considers inserting interference (Poller) screws. Which of the following statements accurately describes the purpose and optimal timing for inserting these screws in this context?

. Poller screws are inserted to provide primary fixation for the osteotomy, replacing the need for an intramedullary nail.
. Poller screws are used to artificially narrow the medullary canal, forcing the nail into the optimal trajectory and preventing translation, and are typically insertedbeforeremoving the external fixator.
. Poller screws are primarily used in distal femoral FAN to prevent rotational instability of the nail.
. Poller screws are insertedafterthe external fixator is removed to augment stability if the nail feels loose.
. Poller screws are used to create a hinge point for gradual correction of the deformity post-operatively.

Correct Answer & Explanation

. Poller screws are used to artificially narrow the medullary canal, forcing the nail into the optimal trajectory and preventing translation, and are typically insertedbeforeremoving the external fixator.

Explanation

Correct Answer: BPoller screws are used to artificially narrow the medullary canal, forcing the nail into the optimal trajectory and preventing translation, and are typically insertedbeforeremoving the external fixator. The text states: 'For added mechanical stability, interference screws (often called blocking or Poller screws) may be inserted to artificially narrow the medullary canal. This forces the nail into the optimal trajectory and prevents the nail from translating within the wide metaphyseal bone.' It also notes: 'Note:These interference screws are typically insertedbeforeremoving the external fixator to ensure the alignment isn't lost during screw placement.'Incorrect Options:A:Poller screws are foraugmentingstability and guiding the nail, not for primary fixation or replacing the nail.C:The text specifically states: 'This step is vastly more important for proximal tibial FAN than for distal femoral FAN due to the funnel shape of the proximal tibia.'D:Poller screws are typically insertedbeforeremoving the external fixator to maintain alignment during their placement.E:Poller screws are for rigid internal fixation, not for creating a hinge point for gradual correction.

Question 197

Topic: Lower Extremity Trauma

A 35-year-old patient is undergoing a distal femoral osteotomy for a valgus deformity. The surgeon is aiming to restore normal joint orientation angles. Which of the following angles is the primary target for this specific correction, and what is its average target value?

. Medial Proximal Tibial Angle (MPTA); 87°
. Mechanical Lateral Distal Femoral Angle (mLDFA); 87°
. Mechanical Lateral Distal Tibial Angle (mLDTA); 89°
. Joint Line Convergence Angle (JLCA); 0°
. Lateral Proximal Femoral Angle (LPFA); 90°

Correct Answer & Explanation

. Mechanical Lateral Distal Femoral Angle (mLDFA); 87°

Explanation

Correct Answer: BThe primary target for a distal femoral osteotomy is the Mechanical Lateral Distal Femoral Angle (mLDFA), with an average target value of 87°. The table in the text lists 'mLDFA' as 'Crucial for distal femoral osteotomies' with an 'Average Target Value' of '87°'.Incorrect Options:A:MPTA is the primary target for high tibial osteotomies, not distal femoral.C:mLDTA is essential for supramalleolar corrections, not distal femoral.D:JLCA measures ligamentous laxity or cartilage loss, not a primary target for bone correction itself, though it's an important assessment.E:LPFA defines the relationship of the hip joint to the proximal femoral axis, not the distal femur.

Question 198

Topic: Lower Extremity Trauma

An 18-year-old male presents with bilateral genu varum. Standing long-leg radiographs reveal a Mechanical Axis Deviation (MAD) of 35 mm medial to the center of the knee. The mechanical Lateral Distal Femoral Angle (mLDFA) is measured at 87 degrees, and the Medial Proximal Tibial Angle (MPTA) is measured at 76 degrees. The Joint Line Convergence Angle (JLCA) is 1 degree. Where is the primary source of the deformity?

. Distal femur
. Proximal tibia
. Intra-articular (ligamentous laxity)
. Ankle joint
. Femoral neck

Correct Answer & Explanation

. Proximal tibia

Explanation

The normal mLDFA is 85-90 degrees (average 88) and normal MPTA is 85-90 degrees (average 87). The patient's MPTA is abnormally low (76 degrees), indicating proximal tibial varus is the primary driver of the medial MAD.

Question 199

Topic: Lower Extremity Trauma

During Fixator-Assisted Nailing (FAN) for a distal tibial valgus deformity, the surgeon intends to use a blocking (Poller) screw to prevent the intramedullary nail from following the path of least resistance into the deformed metaphysis. To effectively guide the nail and correct the valgus, where should the blocking screw be placed in the distal segment?

. On the convex (medial) side of the planned nail path.
. On the concave (lateral) side of the planned nail path.
. Directly in the center of the medullary canal.
. Posterior to the nail to control sagittal alignment.
. Proximal to the osteotomy site only.

Correct Answer & Explanation

. On the concave (lateral) side of the planned nail path.

Explanation

Blocking screws should be placed on the concave side of the deformity (the wider side of the planned nail path) to narrow the metaphysis and force the nail towards the center of the bone. In a valgus deformity, the concavity is lateral, so the screw goes on the lateral side of the distal segment.

Question 200

Topic: Lower Extremity Trauma

When evaluating sagittal plane deformities of the lower extremity using Paley's joint orientation angles, what is the normal expected Posterior Distal Femoral Angle (PDFA) referenced from the mechanical axis?

. 79 degrees
. 83 degrees
. 87 degrees
. 90 degrees
. 95 degrees

Correct Answer & Explanation

. 83 degrees

Explanation

The normal Posterior Distal Femoral Angle (PDFA) is 83 degrees. Deviations from this value indicate a sagittal plane deformity, such as a flexion or extension deformity of the distal femur.

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