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Lower Extremity Trauma MCQs

Practice Set 7 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 121

Topic: Lower Extremity Trauma



In applying Paley's Rule 1 to correct a sagittal deformity of the distal femur, which of the following statements strictly characterizes the surgical technique?

. The osteotomy and the hinge are both located exactly at the CORA
. The osteotomy is at the CORA, but the hinge is placed distally
. The hinge is at the CORA, but the osteotomy is made proximally
. The osteotomy creates translation to maintain limb length
. The correction relies primarily on distraction osteogenesis

Correct Answer & Explanation

. The osteotomy and the hinge are both located exactly at the CORA

Explanation

Paley's Rule 1 dictates that both the osteotomy cut and the mechanical axis of rotation (hinge) are located at the Center of Rotation of Angulation (CORA), resulting in pure angular correction without translation.

Question 122

Topic: Lower Extremity Trauma

A 45-year-old patient presents with a clinically apparent knee procurvatum (flexion deformity). Full-length sagittal radiographs reveal a normal mPPTA of 82° and an abnormal femoral parameter. Which of the following mPDFA values confirms an apex anterior (procurvatum) deformity of the distal femur?

. 98°
. 90°
. 83°
. 72°
. 88°

Correct Answer & Explanation

. 72°

Explanation

An mPDFA significantly less than 80° indicates an apex anterior bow (procurvatum) of the distal femur, leading to a fixed flexion deformity. An mPDFA greater than 85° indicates recurvatum.

Question 123

Topic: Lower Extremity Trauma

A patient presents with a severe knee recurvatum deformity. Radiographs reveal a mechanical posterior distal femoral angle (mPDFA) of 96 degrees and a mechanical posterior proximal tibial angle (mPPTA) of 81 degrees. According to Paley's principles, where is the primary site of the bony deformity?

. Distal femur with an apex anterior deformity
. Distal femur with an apex posterior deformity
. Proximal tibia with an apex anterior deformity
. Proximal tibia with an apex posterior deformity
. Intra-articular sagittal plane subluxation

Correct Answer & Explanation

. Distal femur with an apex posterior deformity

Explanation

The normal mPDFA is 83 degrees. An increased mPDFA (96 degrees) indicates the distal articular surface is extended relative to the shaft, representing a distal femoral apex posterior deformity (recurvatum).

Question 124

Topic: Lower Extremity Trauma

When analyzing the sagittal plane alignment of the lower extremity using Paley's principles, where should the normal mechanical axis (plumb line from the center of the femoral head) pass relative to the knee joint?

. Exactly through the center of the knee joint
. Posterior to the posterior cortex of the distal femur
. Through the fibular head
. Anterior to the center of the knee joint
. Through the posterior cruciate ligament attachment

Correct Answer & Explanation

. Anterior to the center of the knee joint

Explanation

In the sagittal plane, the normal mechanical axis (plumb line) drops from the center of the femoral head and passes slightly anterior to the center of the knee joint, terminating at the center of the ankle.

Question 125

Topic: Lower Extremity Trauma

While performing a medial opening wedge high tibial osteotomy (HTO) for a coronal varus deformity, the surgeon inadvertently opens the anterior gap more than the posterior gap. What is the expected iatrogenic effect in the sagittal plane?

. Decreased posterior tibial slope causing a recurvatum effect
. Increased posterior tibial slope causing a procurvatum effect
. Decreased mPDFA
. Increased mPDFA
. Pure axial translation of the tibia

Correct Answer & Explanation

. Increased posterior tibial slope causing a procurvatum effect

Explanation

Opening the anterior cortex more than the posterior cortex in an HTO tilts the tibial plateau posteriorly. This increases the posterior tibial slope, which is an apex anterior (procurvatum) morphologic change, increasing strain on the ACL.

Question 126

Topic: Lower Extremity Trauma

Historically, single-level pelvic support osteotomies were largely abandoned due to significant complications. Dr. Paley's modern double-level PSO technique overcame these limitations. What was the primary biomechanical failure of the historical single-level PSO that the double-level technique specifically addressed?

. Inability to tension the abductor muscles effectively.
. Failure to create a stable bony abutment against the pelvis.
. Creation of severe knee valgus and unacceptable Mechanical Axis Deviation (MAD).
. High rates of non-union at the osteotomy site.
. Inability to correct limb length discrepancy.

Correct Answer & Explanation

. Creation of severe knee valgus and unacceptable Mechanical Axis Deviation (MAD).

Explanation

Correct Answer: CThe case clearly states: 'The historical failure—creating a stable hip at the expense of a catastrophically malaligned knee—has been definitively solved.' It further elaborates that a proximal valgus osteotomy stabilizes the hip but forces the distal femur into severe valgus, shifting the mechanical axis far lateral to the knee center. This 'guarantees the rapid onset of lateral compartment knee arthritis and severe limb shortening.' The modern double-level PSO, by adding a distal osteotomy, specifically addresses and corrects this unacceptable Mechanical Axis Deviation (MAD) and knee valgus, while also allowing for limb length correction. Options A and B are incorrect as single-level PSO did stabilize the hip and tension abductors. Options D and E were complications but not the primary biomechanical failure that led to its abandonment and the development of the double-level technique.

Question 127

Topic: Lower Extremity Trauma

During the consolidation phase of distraction osteogenesis, plain radiographs reveal a wide, radiolucent gap in the center of the regenerate bone that is failing to mineralize. What is the most appropriate initial management strategy?

. Immediate autologous bone grafting
. Compression of the regenerate using the "accordion technique"
. Empiric intravenous antibiotics
. Exchange of the external fixator to an intramedullary nail
. Increasing the daily rate of distraction

Correct Answer & Explanation

. Compression of the regenerate using the "accordion technique"

Explanation

Poor or delayed regenerate mineralization is highly responsive to the "accordion technique." This process involves alternating cycles of compression and distraction to intensely stimulate local osteogenesis and accelerate mineralization.

Question 128

Topic: Lower Extremity Trauma

An 11-year-old girl with a skeletal bone age of 11 years has a 3.0 cm leg length discrepancy due to a left femoral overgrowth. Utilizing the Menelaus method, what is the most appropriate timing to perform a right distal femoral epiphysiodesis to equalize her leg lengths at maturity?

. Immediately at bone age 11
. Wait until bone age 12
. Wait until bone age 12.5
. Wait until bone age 13
. Perform a proximal tibial epiphysiodesis instead

Correct Answer & Explanation

. Immediately at bone age 11

Explanation

Using the Menelaus method, girls mature at 14 years. At bone age 11, she has 3 years of growth remaining. The distal femur grows at 1 cm/year (3 years x 1 cm/year = 3 cm). Immediate epiphysiodesis of the distal femur is indicated.

Question 129

Topic: Lower Extremity Trauma



A 14-year-old boy is evaluated for a lower extremity deformity. Radiographs show a mechanical axis deviation (MAD) of 40 mm medial to the knee center. The mechanical Lateral Distal Femoral Angle (mLDFA) is 88 degrees (normal 85-90) and the Medial Proximal Tibial Angle (MPTA) is 75 degrees (normal 85-90). Where is the primary source of the deformity?

. Proximal femur
. Distal femur
. Intra-articular knee ligaments
. Proximal tibia
. Distal tibia

Correct Answer & Explanation

. Proximal tibia

Explanation

The normal mLDFA indicates the distal femur is properly aligned. The abnormally low MPTA identifies a varus deformity originating in the proximal tibia, which drives the medial mechanical axis deviation.

Question 130

Topic: Lower Extremity Trauma

A 12-year-old girl with a projected LLD of 3.5 cm at skeletal maturity is scheduled for a percutaneous epiphysiodesis. Based on the Green-Anderson growth data, what is the accepted average rate of growth per year from the distal femur and proximal tibia?

. Distal femur 6 mm/yr; Proximal tibia 10 mm/yr
. Distal femur 10 mm/yr; Proximal tibia 6 mm/yr
. Distal femur 12 mm/yr; Proximal tibia 8 mm/yr
. Distal femur 8 mm/yr; Proximal tibia 12 mm/yr
. Distal femur 10 mm/yr; Proximal tibia 10 mm/yr

Correct Answer & Explanation

. Distal femur 10 mm/yr; Proximal tibia 6 mm/yr

Explanation

The distal femur grows at approximately 10 mm (3/8 inch) per year, and the proximal tibia grows at about 6 mm (1/4 inch) per year. This rule of thumb is critical for timing an epiphysiodesis.

Question 131

Topic: Lower Extremity Trauma

A resident is performing a Mechanical Axis Test (MAT) on a long-leg radiograph to assess a patient's frontal plane alignment. After drawing the necessary lines, they are measuring the orientation of the distal femur.

Which of the following represents the *normal* range for the Mechanical Lateral Distal Femoral Angle (mLDFA)?

. 80°–85°
. 85°–90°
. 90°–95°
. 75°–80°
. 95°–100°

Correct Answer & Explanation

. 85°–90°

Explanation

Correct Answer: BThe Mechanical Lateral Distal Femoral Angle (mLDFA) is a crucial measurement in assessing frontal plane alignment of the femur. It is formed by the distal femoral joint orientation line and the femoral mechanical axis. According to the provided text, the normal range for the mLDFA is 85°-90°. An mLDFA less than 85° indicates a femoral valgus deformity, while an mLDFA greater than 90° indicates a femoral varus deformity. Options A, C, D, and E represent ranges outside the established normal values.

Question 132

Topic: Lower Extremity Trauma

A 70-year-old patient with a significant knee flexion contracture (e.g., 30° procurvatum of the distal femur) requires an AP long-leg radiograph to assess frontal plane alignment. Standard AP views obtained with the beam perpendicular to the film show overlapped joint surfaces, making accurate measurements impossible.

To obtain a clear AP view of the knee joint surfaces for accurate measurement in this scenario, what modification to the radiographic technique is necessary?

. Increase the X-ray beam intensity to penetrate the overlapped bone
. Position the patient supine with the knee fully extended by force
. Angle the X-ray beam upward, tangential to the joint surfaces, by the amount of sagittal angulation
. Rotate the limb externally by 15 degrees to separate the condyles
. Obtain a lateral view radiograph instead, as AP views are unreliable in this situation

Correct Answer & Explanation

. Angle the X-ray beam upward, tangential to the joint surfaces, by the amount of sagittal angulation

Explanation

Correct Answer: CThe text addresses the challenge of obtaining clear radiographs when a deformity component exists in an orthogonal plane. Specifically, for a sagittal plane deformity affecting an AP view, it states: 'When there is a sagittal plane component of deformity, the AP view radiograph obtained in the usual fashion appears distorted (~Fig. 3-25a). To assess the joint orientation, the radiograph should be obtained inclined by the amount of sagittal plane angulation (~Fig. 3-25b and c).' This means angling the beam to be tangential to the joint surfaces, which in the case of procurvatum (flexion deformity) would involve aiming the beam upward from an anterior-proximal to a posterior-distal position. Options A, B, D, and E either do not address the issue of joint surface overlap, are impractical, or would not yield the desired frontal plane alignment information.

Question 133

Topic: Lower Extremity Trauma

A 35-year-old male presents with a complex post-traumatic deformity of the right femur. During preoperative planning, the surgeon draws the anatomic and mechanical axes of the femur. Which of the following statements accurately describes the relationship between the femoral anatomic and mechanical axes in the frontal plane?

. The femoral anatomic axis and mechanical axis are collinear, similar to the tibia.
. The femoral anatomic axis passes through the center of the hip joint, while the mechanical axis exits at the greater trochanter.
. The femoral anatomic axis and mechanical axis diverge by approximately 7 degrees (± 2°) in the frontal plane.
. The femoral anatomic axis is used for intramedullary nailing, but it is always parallel to the mechanical axis.
. The femoral mechanical axis is defined by the mid-diaphyseal line, whereas the anatomic axis connects joint centers.

Correct Answer & Explanation

. The femoral anatomic axis and mechanical axis diverge by approximately 7 degrees (± 2°) in the frontal plane.

Explanation

Correct Answer: CThe case explicitly states, "in the frontal plane of the femur, the mechanical and anatomic axes diverge by approximately 7 degrees (± 2°). Therefore, the femoral PMA and PAA are distinctly different lines, as are the DMA and DAA. Recognizing this 7-degree divergence is critical when planning distal femoral osteotomies." This divergence is a fundamental concept in lower limb deformity correction.Option A is incorrectbecause, while the tibial anatomic and mechanical axes are nearly collinear, the femoral axes are not. Conflating the two is a common pitfall.Option B is incorrect. The anatomic axis of the femur exits proximally at the tip of the greater trochanter (or piriformis fossa), not through the center of the hip joint. The mechanical axis connects the center of the femoral head to the center of the knee joint.Option D is incorrect. While the anatomic axis is indeed used for intramedullary nailing, it is not always parallel to the mechanical axis in the femur; they diverge by approximately 7 degrees.Option E is incorrect. This statement reverses the definitions. The anatomic axis is defined by the mid-diaphyseal line, and the mechanical axis connects the center points of the joints.

Question 134

Topic: Lower Extremity Trauma

During correction of a tibial shaft deformity, the osteotomy and the hinge (axis of correction of angulation, ACA) are both placed distal to the true Center of Rotation of Angulation (CORA). What is the primary mechanical consequence of this technical error?

. Perfect realignment of the mechanical axis.
. Correction of the angular deformity with a new translational deformity (zigzag effect).
. Pure translation without any angular change.
. Spontaneous correction of rotational malalignment.
. Preservation of the anatomical axis with deviation of the joint lines.

Correct Answer & Explanation

. Correction of the angular deformity with a new translational deformity (zigzag effect).

Explanation

Osteotomy Rule 3 dictates that if both the osteotomy and the ACA are placed away from the CORA, the angular deformity may be corrected but a new unintended translational deformity will be created. This leads to a zigzag mechanical axis.

Question 135

Topic: Lower Extremity Trauma

In evaluating a lower extremity deformity, a standing full-length radiograph

reveals a mechanical axis deviation (MAD) of 30 mm medial to the knee center. The mechanical lateral distal femoral angle (mLDFA) is 87° and the medial proximal tibial angle (MPTA) is 78°. The joint line convergence angle (JLCA) is 2°. Which of the following is the primary location of the deformity?

. Proximal femur
. Distal femur
. Proximal tibia
. Distal tibia
. Intra-articular knee ligamentous laxity

Correct Answer & Explanation

. Proximal tibia

Explanation

The MPTA is abnormally low (normal is 87°), indicating a structural proximal tibial varus deformity. The mLDFA and JLCA are within normal limits, ruling out femoral and intra-articular causes.

Question 136

Topic: Lower Extremity Trauma

An 18-year-old male with a shortened limb and a valgus deformity requires correction. A dome osteotomy is planned at the distal femur. What is the primary geometric advantage of a dome osteotomy in this scenario?

. It inherently lengthens the limb by 2 cm without distraction.
. It allows correction of angulation without altering length or causing translation when the hinge is at the center.
. It avoids the need for internal fixation.
. It permits correction of rotational deformities more easily than a transverse cut.
. It drastically alters the mechanical lateral proximal femoral angle.

Correct Answer & Explanation

. It allows correction of angulation without altering length or causing translation when the hinge is at the center.

Explanation

A dome osteotomy permits pure angular correction by rotating the bone segments along the arc of the cut. When the CORA is at the center of the dome, no gap is created, length is preserved, and translation is avoided.

Question 137

Topic: Lower Extremity Trauma

A 38-year-old male presents with progressive right knee pain and a noticeable bowing deformity of his lower extremity. A full-length, weight-bearing anteroposterior radiograph reveals a mechanical axis that passes 15 mm medial to the center of the knee joint. Further analysis shows a Mechanical Lateral Distal Femoral Angle (mLDFA) of 88° and a Medial Proximal Tibial Angle (MPTA) of 78°. Based on these findings, which of the following statements is most accurate regarding the patient's deformity?

. The patient has a valgus deformity primarily originating from the distal femur.
. The patient has a varus deformity primarily originating from the proximal tibia.
. The patient has a varus deformity primarily originating from the distal femur.
. The patient has a valgus deformity primarily originating from the proximal tibia.
. The patient's deformity is likely multi-apical, involving both the femur and tibia equally.

Correct Answer & Explanation

. The patient has a varus deformity primarily originating from the proximal tibia.

Explanation

Correct Answer: BThe patient's mechanical axis passes 15 mm medial to the center of the knee, which quantitatively defines a varus (bow-legged) deformity. The normal range for the Mechanical Lateral Distal Femoral Angle (mLDFA) is 85° to 90° (average 87°). An mLDFA of 88° is within the normal range, indicating that the distal femur is well-aligned and not contributing to the angular deformity. The normal range for the Medial Proximal Tibial Angle (MPTA) is 85° to 90° (average 87°). An MPTA of 78° is significantly less than 85°, which indicates a varus deformity originating from the proximal tibia. Therefore, the patient has a varus deformity primarily originating from the proximal tibia.Option A is incorrect because the MAD indicates varus, not valgus, and the mLDFA is normal. Option C is incorrect because the mLDFA is normal, indicating no significant distal femoral deformity. Option D is incorrect because the MAD indicates varus, not valgus. Option E is incorrect because the mLDFA is normal, suggesting the deformity is not equally multi-apical but rather predominantly tibial.

Question 138

Topic: Lower Extremity Trauma

A 32-year-old male presents with progressive knee pain and a noticeable bowing of his left lower extremity. A standing, full-length AP radiograph is obtained, revealing a mechanical axis that passes 25 mm medial to the center of the knee joint. Further analysis of joint orientation angles shows a Mechanical Lateral Distal Femoral Angle (mLDFA) of 87° and a Medial Proximal Tibial Angle (MPTA) of 78°. The Joint Line Convergence Angle (JLCA) is 1°. Based on Paley's principles, which of the following statements best describes the primary anatomical location of this patient's deformity?

. The primary deformity is located in the distal femur, causing a valgus malalignment.
. The primary deformity is located in the proximal tibia, causing a varus malalignment.
. The primary deformity is located in the distal femur, causing a varus malalignment.
. The primary deformity is intra-articular, indicating significant cartilage loss or ligamentous laxity.
. The deformity is equally distributed between the distal femur and proximal tibia.

Correct Answer & Explanation

. The primary deformity is located in the proximal tibia, causing a varus malalignment.

Explanation

Correct Answer: BThe patient presents with a mechanical axis deviation (MAD) of 25 mm medial to the knee center, which indicates a significant varus deformity of the limb. To pinpoint the anatomical source, we evaluate the joint orientation angles against normal ranges. The normal mLDFA is 85° to 90° (average 87°), and the patient's mLDFA is 87°, indicating a normal distal femoral alignment. The normal MPTA is 85° to 90° (average 87°), but the patient's MPTA is 78°. An MPTA less than 85° indicates a proximal tibial varus deformity. Therefore, the primary anatomical location of the deformity is the proximal tibia, contributing to the overall limb varus. The JLCA of 1° is within the normal range (0° to 2°), ruling out significant intra-articular pathology as the primary source of the angular deformity. While the overall limb is in varus, the specific angle (MPTA) points to the proximal tibia as the source, not the distal femur. If the distal femur were in varus, the mLDFA would be greater than 90°.

Question 139

Topic: Lower Extremity Trauma

A 24-year-old patient undergoes a malalignment test for a suspected genu valgum deformity. The mechanical axis falls lateral to the center of the knee. What is the normal physiological range for the mechanical Lateral Distal Femoral Angle (mLDFA)?

. 80 to 84 degrees
. 85 to 90 degrees
. 91 to 95 degrees
. 96 to 100 degrees
. 101 to 105 degrees

Correct Answer & Explanation

. 85 to 90 degrees

Explanation

The normal mechanical Lateral Distal Femoral Angle (mLDFA) ranges from 85 to 90 degrees, with an average of 87 to 88 degrees. An mLDFA less than 85 degrees indicates a valgus deformity originating in the distal femur.

Question 140

Topic: Lower Extremity Trauma

During tibial lengthening using distraction osteogenesis, a patient returns for a 4-week follow-up. Radiographs reveal a sparse, patchy regenerate with a central radiolucent gap wider than 5 mm. The patient has been distracting at a rate of 1.5 mm per day. What is the most appropriate next step in management?

. Continue distraction at 1.5 mm/day
. Increase distraction rate to 2 mm/day
. Decrease the distraction rate or temporarily compress the frame
. Perform immediate autologous bone grafting
. Remove the frame and place an intramedullary nail

Correct Answer & Explanation

. Decrease the distraction rate or temporarily compress the frame

Explanation

A sparse regenerate with a wide gap suggests the distraction rate is too fast, outpacing bone formation. The appropriate management is to slow the distraction rate, pause, or temporarily apply compression to stimulate osteogenesis.

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