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Lower Extremity Trauma MCQs

Practice Set 28 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 541

Topic: Lower Extremity Trauma

When evaluating a patient for lower extremity deformity correction, how is the mechanical axis deviation (MAD) objectively measured on standing full-length anteroposterior radiographs?

. The angle between the anatomical axis of the femur and the anatomical axis of the tibia
. The perpendicular distance from the center of the knee joint to the mechanical axis line connecting the center of the femoral head to the center of the ankle
. The angle formed by the intersection of the mechanical axis of the femur and the mechanical axis of the tibia
. The distance between the center of the tibial plateau and the mechanical axis of the femur
. The angle between the joint line of the knee and the ground

Correct Answer & Explanation

. The perpendicular distance from the center of the knee joint to the mechanical axis line connecting the center of the femoral head to the center of the ankle

Explanation

Mechanical axis deviation (MAD) is measured in millimeters as the perpendicular distance from the center of the knee joint to the mechanical axis of the entire lower extremity. A medial MAD indicates varus, while a lateral MAD indicates valgus.

Question 542

Topic: Lower Extremity Trauma

A 45-year-old active patient with symptomatic isolated lateral compartment osteoarthritis and a mechanical valgus alignment of 12 degrees undergoes a medial closing-wedge distal femoral osteotomy. Which of the following is an expected biomechanical outcome of this specific osteotomy technique compared to a lateral opening-wedge technique?

. Increased ipsilateral leg length
. Decreased ipsilateral leg length
. Increased tension on the iliotibial band
. Distalization of the patella relative to the joint line
. Increased posterior tibial slope

Correct Answer & Explanation

. Decreased ipsilateral leg length

Explanation

A medial closing-wedge osteotomy of the distal femur inherently removes bone, leading to a shortening of the leg. Conversely, a lateral opening-wedge osteotomy adds length to the lateral column, generally increasing total leg length.

Question 543

Topic: Lower Extremity Trauma



When performing a primary TKA on a patient with a significant diaphyseal varus bowing of the femur, utilizing a standard intramedullary alignment rod that traverses the entire diaphysis without accounting for the bow will most likely result in which of the following errors?

. Excessive valgus cut of the distal femur
. Excessive varus cut of the distal femur
. Excessive extension of the femoral component
. Excessive flexion of the femoral component
. Anterior notching of the distal femur

Correct Answer & Explanation

. Excessive valgus cut of the distal femur

Explanation

A long intramedullary rod placed in a femur with a coronal varus bow will align laterally at its distal end. If the standard valgus angle is dialed in based on this malaligned rod, the resulting distal femoral cut will be in excessive valgus.

Question 544

Topic: Lower Extremity Trauma

The Paley multiplier method is frequently used to predict limb length discrepancy at skeletal maturity. This predictive method is primarily based on which of the following parameters?

. The patient's current height percentile plotted on CDC growth charts
. Skeletal age determined strictly by the Greulich and Pyle atlas
. Chronological age-specific coefficients
. Extrapolation of previous longitudinal radiographic measurements
. The Green-Anderson remaining growth charts for the distal femur

Correct Answer & Explanation

. Chronological age-specific coefficients

Explanation

The Paley multiplier method simplifies limb length discrepancy prediction by using chronologic age-specific coefficients (multipliers). The current bone length or discrepancy is multiplied by this coefficient to estimate the ultimate measurement at maturity.

Question 545

Topic: Lower Extremity Trauma

When treating a non-union with plate fixation, what is often a critical adjunct to the plate itself to promote healing?

. Immediate full weight-bearing to stimulate bone remodeling.
. Using a shorter, stiffer plate to maximize compression.
. Aggressive periosteal stripping around the non-union site.
. Application of autogenous bone graft or bone graft substitutes.
. Routinely adding an intramedullary nail in conjunction with the plate.

Correct Answer & Explanation

. Application of autogenous bone graft or bone graft substitutes.

Explanation

Non-unions are often indicative of a biological healing problem. Therefore, in addition to stable mechanical fixation provided by the plate, biological augmentation is frequently critical. Autogenous bone graft (e.g., from the iliac crest) provides osteoinductive, osteoconductive, and osteogenic properties, which are essential for stimulating healing in a non-union. While stability is necessary, biological stimulation is often the missing component. Short, stiff plates might increase stress shielding, and aggressive stripping is detrimental. Immediate full weight-bearing is generally not appropriate for non-unions until early signs of healing. An IM nail with a plate is for specific complex scenarios.

Question 546

Topic: Lower Extremity Trauma

Which factor is most predictive of anterior knee pain following tibial intramedullary nailing?

. The use of a quadriceps-sparing approach.
. The prominence of the proximal end of the nail above the tibial plateau.
. The duration of immobilization post-operatively.
. The length of the intramedullary nail.
. The patient's age and activity level.

Correct Answer & Explanation

. The prominence of the proximal end of the nail above the tibial plateau.

Explanation

The most predictive factor for anterior knee pain following tibial intramedullary nailing is the prominence of the proximal end of the nail above the tibial plateau. If the nail is inserted too proud, it can impinge on the patellar tendon, quadriceps tendon, or prepatellar bursa, leading to persistent anterior knee pain. While a quadriceps-sparing approach aims to minimize soft tissue disruption, nail prominence is a direct mechanical irritant. Duration of immobilization and nail length are less direct causes. Patient age and activity level can influence symptoms but are not the primary direct cause of this specific complication.

Question 547

Topic: Lower Extremity Trauma

When positioning a patient for antegrade femoral intramedullary nailing, what is the rationale for placing the hip in adduction and internal rotation?

. To facilitate distal locking screw placement.
. To relax the iliopsoas muscle and aid in proximal fragment alignment.
. To expose the greater trochanter for the entry point.
. To reduce the risk of neurovascular injury in the groin.
. To allow the C-arm to obtain true AP and lateral views of the hip.

Correct Answer & Explanation

. To expose the greater trochanter for the entry point.

Explanation

Placing the hip in adduction and internal rotation is done to bring the greater trochanter into a more accessible position and to align the piriformis fossa or trochanteric entry point with the axis of the femoral canal. This facilitates exposure of the greater trochanter and ensures a more direct path for the guidewire and nail into the medullary canal. While it can indirectly help with C-arm views, the primary direct reason is entry point access and alignment. It doesn't primarily relax the iliopsoas (traction does that). Distal locking is unrelated. Neurovascular injury is not directly mitigated by this positioning in the groin.

Question 548

Topic: Lower Extremity Trauma

In the context of internal fixation, what does 'stress shielding' refer to?

. The protection of the implant from excessive biomechanical forces by the surrounding bone.
. The phenomenon where an implant carries a disproportionate amount of load, reducing stress on the bone.
. The ability of an implant to withstand repetitive loading cycles without failure.
. The process of bone remodeling in response to inflammatory reactions around an implant.
. The shielding of neural structures from direct contact with the implant.

Correct Answer & Explanation

. The phenomenon where an implant carries a disproportionate amount of load, reducing stress on the bone.

Explanation

Stress shielding occurs when a rigid implant (like a plate or intramedullary nail) bears a significant portion of the physiological load that would normally be carried by the bone. This reduction in stress on the bone (in accordance with Wolff's Law) can lead to localized bone resorption and reduced bone density around the implant. While sometimes unavoidable, excessive stress shielding can weaken the bone, increasing the risk of refracture upon implant removal.

Question 549

Topic: Lower Extremity Trauma

The 'isthmus' of a long bone's medullary canal is biomechanically significant because:

. It is the weakest point of the bone.
. It represents the widest part of the canal, allowing easy nail insertion.
. It is the narrowest part, providing excellent cortical contact and inherent stability for IM nails.
. It is the primary site for bone marrow harvest.
. It is where interlocking screws are exclusively placed.

Correct Answer & Explanation

. It is the narrowest part, providing excellent cortical contact and inherent stability for IM nails.

Explanation

The isthmus is the narrowest part of the medullary canal in the diaphysis of a long bone. Biomechanically, this anatomical feature is highly advantageous for intramedullary nailing. When a nail is properly sized and inserted, it creates a tight 'three-point fixation' within the isthmus, providing significant inherent bending and torsional stability even before interlocking screws are placed. This tight cortical contact maximizes the load-sharing capacity of the nail with the bone. It is not necessarily the weakest part, and interlocking screws are placed proximally and distally, not just at the isthmus.

Question 550

Topic: Lower Extremity Trauma

Biomechanically, why is it generally recommended to fully seat an IM nail to avoid distal protrusion?

. To improve the cosmetic appearance of the limb.
. To prevent neurovascular injury near the distal joint.
. To increase the effective working length of the nail.
. To avoid pain, irritation, and potential joint impingement or articular damage.
. To facilitate easier removal of the nail in the future.

Correct Answer & Explanation

. To avoid pain, irritation, and potential joint impingement or articular damage.

Explanation

A distally protruding intramedullary nail can cause significant problems. Biomechanically, the nail tip can impinge on the articular cartilage or subchondral bone, leading to pain, joint irritation, reduced range of motion, and potentially long-term articular damage and post-traumatic arthritis. In some locations (e.g., knee, ankle), it can also cause soft tissue irritation. Therefore, proper seating of the nail is crucial to avoid these complications. Neurovascular injury is possible but the primary biomechanical and clinical concern of distal protrusion is joint and soft tissue irritation. It does not increase working length or necessarily facilitate removal.

Question 551

Topic: Lower Extremity Trauma

When measuring the normal proximal femoral geometry on an AP radiograph, what is the accepted normal range for the Lateral Proximal Femoral Angle (LPFA) and Mechanical Lateral Proximal Femoral Angle (mLPFA)?

. LPFA 80 degrees, mLPFA 80 degrees
. LPFA 90 degrees, mLPFA 90 degrees
. LPFA 100 degrees, mLPFA 90 degrees
. LPFA 130 degrees, mLPFA 130 degrees
. LPFA 85 degrees, mLPFA 95 degrees

Correct Answer & Explanation

. LPFA 90 degrees, mLPFA 90 degrees

Explanation

The normal LPFA (anatomical) and mLPFA (mechanical) are both approximately 90 degrees. This reflects the relationship between the tip of the greater trochanter and the center of the femoral head relative to the femoral shaft.

Question 552

Topic: Lower Extremity Trauma

During an Ilizarov pelvic support osteotomy for a chronically dislocated hip, the proximal femoral osteotomy is placed in extension and valgus. What clinical parameter dictates the optimal amount of valgus angulation required at the proximal osteotomy?

. The angle required to make the femoral shaft purely vertical.
. The degree of preoperative Trendelenburg dip.
. The maximum adduction of the femur to the pelvis plus 15 degrees for overcorrection.
. The contralateral anatomic neck-shaft angle.
. A fixed correction of exactly 45 degrees for all patients.

Correct Answer & Explanation

. The maximum adduction of the femur to the pelvis plus 15 degrees for overcorrection.

Explanation

The valgus angle is determined by maximal adduction of the hip with the pelvis level. Paley recommends overcorrecting this angle by 10 to 15 degrees to guarantee elimination of the Trendelenburg drop and provide a strong pelvic support strut.

Question 553

Topic: Lower Extremity Trauma

A patient presents with medial mechanical axis deviation (MAD) causing varus gonarthrosis. Preoperative full-length standing radiographs reveal a mechanical lateral distal femoral angle (mLDFA) of 98 degrees (normal 87) and a medial proximal tibial angle (MPTA) of 87 degrees (normal 87). Joint line convergence angle (JLCA) is 2 degrees. Based on Paley's principles of joint orientation, where is the primary source of the deformity?

. Proximal tibia
. Distal femur
. Knee joint collateral ligaments (laxity)
. Proximal femur
. Ankle joint

Correct Answer & Explanation

. Distal femur

Explanation

The source of the mechanical axis deviation is identified by abnormal joint orientation angles. An increased mLDFA (98 degrees) indicates a distal femoral varus deformity, while the normal MPTA and JLCA rule out the tibia and ligamentous laxity as primary causes.

Question 554

Topic: Lower Extremity Trauma

A 12-year-old presents for evaluation of genu valgum. Radiographs reveal massive cortical thinning and an "Erlenmeyer flask" deformity of the distal femur and proximal tibia metaphyses. The patient's stature is normal, and cranial nerves are completely intact. What is the most likely diagnosis?

. Craniometaphyseal dysplasia
. Pyle disease
. Metaphyseal chondrodysplasia, Schmid type
. Osteopetrosis
. Gaucher disease

Correct Answer & Explanation

. Pyle disease

Explanation

Pyle disease (familial metaphyseal dysplasia) is characterized by striking metaphyseal widening (Erlenmeyer flask deformity) with cortical thinning. Unlike craniometaphyseal dysplasia, Pyle disease typically spares the skull and cranial nerves.

Question 555

Topic: Lower Extremity Trauma

During a medial approach to the tibia to access the entire shaft, what is the structure at risk that runs parallel to the medial border of the tibia, particularly in the distal half of the leg?

. Deep peroneal nerve
. Sural nerve
. Great saphenous vein and saphenous nerve
. Posterior tibial artery
. Tibial nerve

Correct Answer & Explanation

. Great saphenous vein and saphenous nerve

Explanation

The saphenous nerve and great saphenous vein run superficially along the medial aspect of the leg, closely following the medial border of the tibia. They are the primary superficial structures at risk during a medial approach to the tibial shaft.

Question 556

Topic: Lower Extremity Trauma

When comparing a solid titanium intramedullary nail to a hollow titanium intramedullary nail of the exact same outer diameter, how does the bending stiffness (flexural rigidity) of the hollow nail compare to the solid nail?

. The hollow nail has significantly greater bending stiffness
. The hollow nail has exactly the same bending stiffness
. The hollow nail has slightly less bending stiffness
. The hollow nail has exactly half the bending stiffness
. The hollow nail has significantly less bending stiffness, proportional to the inner radius cubed

Correct Answer & Explanation

. The hollow nail has slightly less bending stiffness

Explanation

Bending stiffness is proportional to the area moment of inertia (I), which correlates to the radius to the fourth power (r^4) for a solid cylinder. For a hollow cylinder, I is proportional to (Outer Radius^4 - Inner Radius^4). Because the r^4 term is heavily influenced by the outermost material, removing the inner core (small inner radius) reduces the overall bending stiffness only slightly.

Question 557

Topic: Lower Extremity Trauma

During a fluoroscopically guided intramedullary nailing, the surgeon wishes to minimize radiation exposure. Which of the following modifications is most effective in reducing the scatter radiation received by the operating room personnel?

. Decreasing the distance between the X-ray tube and the patient
. Positioning the X-ray tube over the patient and the image intensifier under the table
. Using continuous rather than pulsed fluoroscopy
. Positioning the image intensifier as close to the patient as possible
. Removing the collimator

Correct Answer & Explanation

. Positioning the image intensifier as close to the patient as possible

Explanation

Placing the image intensifier as close to the patient as possible decreases radiation scatter and improves image resolution. The X-ray tube should also be positioned under the operating table to direct backscatter toward the floor rather than the surgeon's torso.

Question 558

Topic: Lower Extremity Trauma

A patient with a well-documented history of advanced breast carcinoma presents with a solitary lytic lesion in the distal femur, confirmed on MRI

. What is the most common physiological route through which this carcinoma metastasized to the appendicular skeleton?

. Lymphatic spread
. Direct extension
. Hematogenous spread via the venous system
. Hematogenous spread via the arterial system
. Perineural invasion

Correct Answer & Explanation

. Hematogenous spread via the venous system

Explanation

The overwhelming majority of bone metastases from carcinomas (such as breast, prostate, lung, kidney, and thyroid) disseminate via hematogenous spread, specifically through the venous system. Batson's venous plexus is a valveless paraspinal venous network that provides a direct pathway for tumor emboli to reach the axial skeleton, and venous sinuses facilitate spread to the appendicular long bones.

Question 559

Topic: Lower Extremity Trauma

During clinical evaluation of a patient with a suspected anterior cruciate ligament (ACL) tear, the examiner performs a pivot shift test. The palpable clunk that occurs during knee flexion from an extended position represents the reduction of the anteriorly subluxated tibia. Which structure is mechanically responsible for providing the force that reduces the tibia during this maneuver?

. Posterior cruciate ligament
. Medial collateral ligament
. Iliotibial band
. Biceps femoris
. Popliteus tendon

Correct Answer & Explanation

. Iliotibial band

Explanation

The pivot shift test relies on the iliotibial (IT) band. As the knee flexes past approximately 20-30 degrees, the IT band transitions from an extensor to a flexor, creating a posterior force vector that reduces the anteriorly subluxated lateral tibial plateau.

Question 560

Topic: Lower Extremity Trauma

In evaluating an intramedullary cartilaginous lesion of the distal femur, which MRI finding best distinguishes a bone infarct from an enchondroma?

. High signal intensity on T2-weighted images
. Lobular internal architecture
. A serpiginous margin of low signal intensity on T1 and T2 images
. Endosteal scalloping
. Presence of calcified matrix

Correct Answer & Explanation

. A serpiginous margin of low signal intensity on T1 and T2 images

Explanation

A bone infarct is classically characterized by a serpiginous rim of low signal on T1 and T2-weighted images (the double-line sign). Enchondromas typically show a lobulated, hyperintense pattern on T2-weighted images corresponding to their high water content.

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