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6. Spine MCQs

Practice Set 97 of 379

This practice set contains high-yield board review questions covering key concepts in 6. Spine. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 1921

Topic: 6. Spine

A surgeon is preparing a patient for a posterior lumbar spine fusion. The patient is positioned prone on a specialized spinal surgical frame. What is the primary biomechanical advantage of ensuring the patient's abdomen hangs freely in this position?

. Facilitates easier access for anterior column instrumentation.
. Reduces intra-abdominal pressure, thereby decreasing epidural venous bleeding.
. Prevents pressure ulcers on the anterior abdominal wall.
. Optimizes lumbar lordosis for fusion.
. Allows for better visualization of the iliac crest for bone graft harvest.

Correct Answer & Explanation

. Reduces intra-abdominal pressure, thereby decreasing epidural venous bleeding.

Explanation

Correct Answer: BExplanation:Under 'Patient Positioning,' the case states: 'The patient is typically positioned prone on a specialized spinal surgical frame... This position offers several advantages: Minimizes Abdominal Compression: Allows the abdomen to hang freely, reducing intra-abdominal pressure. This decreases epidural venous bleeding, which significantly improves visualization in the surgical field.' Reduced epidural bleeding is crucial for clear visualization and safer dissection in the spinal canal.Option A (Facilitates easier access for anterior column instrumentation):Prone positioning is for posterior approaches. Anterior column instrumentation would typically require an anterior approach.Option C (Prevents pressure ulcers on the anterior abdominal wall):While padding is important to prevent pressure injuries, the primary biomechanical advantage of free abdominal hang is related to venous pressure, not just skin protection.Option D (Optimizes lumbar lordosis for fusion):While some frames can optimize spinal alignment, the specific advantage of free abdominal hang is about venous pressure, not primarily lordosis.Option E (Allows for better visualization of the iliac crest for bone graft harvest):While the iliac crest may be accessible in this position, the primary biomechanical advantage described is related to intra-abdominal and epidural venous pressure.

Question 1922

Topic: 6. Spine

A 16-year-old male presents with painful scoliosis. Radiographs demonstrate a levoscoliosis (convexity to the left). An osteoid osteoma is identified in the thoracic spine. Which of the following is the most likely location of the lesion?

. Right pedicle
. Left pedicle
. Right vertebral body
. Left vertebral body
. Spinous process

Correct Answer & Explanation

. Right pedicle

Explanation

In spinal osteoid osteomas, patients typically present with painful scoliosis where the concavity is on the side of the lesion due to asymmetric muscle spasm. A left-sided convexity (levoscoliosis) has its concavity on the right, pointing to a right-sided posterior element lesion like the pedicle.

Question 1923

Topic: 6. Spine

While percutaneous radiofrequency ablation (RFA) is often the treatment of choice for osteoid osteoma, it is generally contraindicated for which of the following spinal lesions?

. Lesions in the pars interarticularis
. Lesions within 1 cm of the spinal cord or major nerve root
. Lesions causing painful scoliosis
. Lesions in the cervical spine lamina
. Lesions larger than 0.5 cm

Correct Answer & Explanation

. Lesions within 1 cm of the spinal cord or major nerve root

Explanation

Radiofrequency ablation relies on thermal destruction of the nidus. It is generally contraindicated when the lesion is located within 1 cm of critical neurologic structures, such as the spinal cord or a major nerve root, to prevent thermal injury.

Question 1924

Topic: 6. Spine

A 14-year-old male presents with persistent mid-back pain that is worse at night and relieved by ibuprofen. Standing radiographs demonstrate a structural scoliosis. If this patient has an osteoid osteoma of the spine, what is the expected relationship between the lesion and the scoliotic curve?

. The lesion is located at the apex on the convex side of the curve.
. The lesion is located at the apex on the concave side of the curve.
. The lesion is situated predominantly in the anterior vertebral body.
. The lesion causes a compensatory curve strictly above the involved level.
. The location of the lesion has no reliable correlation with the curve concavity.

Correct Answer & Explanation

. The lesion is located at the apex on the concave side of the curve.

Explanation

In painful scoliosis secondary to a spinal osteoid osteoma, local muscle spasm causes the spine to curve away from the lesion. Therefore, the lesion is characteristically located at the apex on the concave side of the scoliotic curve.

Question 1925

Topic: 6. Spine

A 14-year-old boy presents with back pain that is worse at night and significantly relieved by NSAIDs. Physical exam reveals a painful scoliosis. Radiographs demonstrate a sclerotic lesion in the lumbar spine. Which of the following correctly describes the expected relationship between the lesion and the scoliotic curve?

. The lesion is located on the convexity of a structural curve
. The lesion is located on the concavity of a non-structural curve
. The lesion is located on the convexity of a non-structural curve
. The lesion is located anteriorly, causing a pure kyphosis
. The lesion is in the vertebral body, causing a structural curve

Correct Answer & Explanation

. The lesion is located on the concavity of a non-structural curve

Explanation

Spinal osteoid osteomas most commonly involve the posterior elements and cause asymmetric muscle spasm. This results in a non-structural scoliotic curve with the concavity directed toward the side of the lesion.

Question 1926

Topic: 6. Spine

A 14-year-old boy presents with a painful left thoracic scoliosis. He reports waking up at night with severe back pain that is completely relieved by ibuprofen. Radiographs and CT imaging reveal a lesion in the posterior elements of the thoracic spine. Which of the following best describes the typical relationship between this lesion and the spinal deformity?

. The lesion is located at the apex on the convex side of the curve.
. The lesion is located at the apex on the concave side of the curve.
. The lesion is located at the lower end vertebrae of the convex side.
. The lesion causes a compensatory structural contralateral curve.
. The lesion induces a rapid progression of vertebral wedging.

Correct Answer & Explanation

. The lesion is located at the apex on the concave side of the curve.

Explanation

Painful scoliosis secondary to a spinal osteoid osteoma is typically non-structural initially, with the lesion characteristically located on the concave side of the curve at the apex. Prompt removal of the lesion usually resolves the deformity if treated within 15 months.

Question 1927

Topic: 6. Spine

A 21-year-old male track athlete presents with severe bilateral calf cramping and numbness in the soles of his feet after sprinting. His resting compartment pressures are normal. Examination reveals diminished pedal pulses upon forceful active plantarflexion against resistance. What is the most appropriate next step in diagnosis?

. Measurement of post-exercise intracompartmental pressures
. MRI of the lumbar spine
. Arterial duplex ultrasound or magnetic resonance angiography (MRA)
. Electromyography (EMG) of the lower extremities
. Radiographs of the tibia and fibula

Correct Answer & Explanation

. Arterial duplex ultrasound or magnetic resonance angiography (MRA)

Explanation

The presentation of claudication, distal numbness, and diminished pulses with active plantarflexion is classic for popliteal artery entrapment syndrome. Advanced vascular imaging, such as duplex ultrasound or MRA with provocative maneuvers, is the best diagnostic step.

Question 1928

Topic: 6. Spine

A 50-year-old patient presents with a 3 cm leg length discrepancy (LLD) on the right side. On full-length standing radiographs, the horizontal line of the pelvis, established using the inferior SI joints, is found to be tilted, with the right side lower than the left. The patient also exhibits a fixed adduction contracture of the right hip. Based on Paley's principles, how should this pelvic obliquity and LLD be interpreted?

. This represents a true, structural leg length discrepancy, requiring femoral lengthening.
. The pelvic obliquity is compensatory, driven by a true LLD, and will resolve with lengthening.
. The pelvic obliquity is fixed, likely driven by the hip adduction contracture, and must be addressed before or concurrently with any femoral correction.
. The LLD is entirely apparent, caused by the pelvic tilt, and no skeletal lengthening is needed.
. The patient has a primary spinal deformity (scoliosis) causing the fixed pelvic obliquity.

Correct Answer & Explanation

. The pelvic obliquity is fixed, likely driven by the hip adduction contracture, and must be addressed before or concurrently with any femoral correction.

Explanation

Correct Answer: CThe case content emphasizes the critical distinction between compensatory and fixed pelvic obliquity. If the pelvic line is not parallel to the floor (tilted pelvis), the obliquity could be compensatory (driven by a true LLD) or fixed (driven by a primary spinal deformity or, more commonly for the hip surgeon, a fixed soft tissue contracture). The presence of a 'fixed adduction contracture of the right hip' strongly suggests that the pelvic obliquity is fixed and driven by this soft tissue contracture. Correcting a femoral deformity to level the knees in the presence of an unrecognized fixed pelvic obliquity will result in a disastrous postoperative imbalance. Therefore, this fixed obliquity must be addressed before or concurrently with any femoral correction.Option A is incorrectbecause while there is an LLD, the presence of a fixed contracture suggests the obliquity is not solely due to a true structural LLD that would be resolved by simple lengthening. The obliquity itself is a primary problem.Option B is incorrectbecause the presence of a 'fixed' adduction contracture indicates that the pelvic obliquity is not merely compensatory for a true LLD but is a primary, fixed issue that needs direct attention.Option D is incorrectbecause while fixed pelvic obliquity can create an apparent LLD, the problem statement also mentions a 3 cm LLD, which could be a combination of true and apparent. The key is that the obliquity is fixed and needs to be addressed.Option E is incorrectbecause while scoliosis can cause fixed pelvic obliquity, the vignette specifically provides a more direct cause relevant to the hip surgeon: a fixed hip adduction contracture.

Question 1929

Topic: 6. Spine

During the execution of a Paley double-level PSO, precise alignment of the distal femoral segment is crucial. When applying the distal block of a monolithic external fixator, how is the correct coronal alignment established?

. By referencing the anatomic axis of the proximal femur
. By placing the reference pins exactly parallel to the knee joint line
. By aligning the frame with the patient's acetabular inclination
. By referencing the anterior superior iliac spine
. By placing pins perpendicular to the mechanical axis of the tibia

Correct Answer & Explanation

. By placing the reference pins exactly parallel to the knee joint line

Explanation

To ensure accurate realignment of the knee, distal fixation is achieved by placing reference pins parallel to the true knee joint line. When the frame is manipulated to correct the deformity, the joint orientation is reliably restored.

Question 1930

Topic: Thoracolumbar Spine & Deformity

According to Paley's principles, how is the ideal magnitude of the proximal valgus angle calculated when planning a pelvic support osteotomy?

. Maximum adduction angle + 15 degrees
. Maximum abduction angle + 15 degrees
. Neutral alignment (0 degrees of valgus)
. Maximum adduction angle + 30 degrees
. Exactly 45 degrees of valgus universally

Correct Answer & Explanation

. Maximum adduction angle + 15 degrees

Explanation

The proximal osteotomy must compensate for the maximum adduction of the hip and add an additional 15 degrees. This overcorrection accommodates normal pelvic tilt during gait and ensures solid ischial abutment.

Question 1931

Topic: Thoracolumbar Spine & Deformity

During a pelvic support osteotomy for an adolescent with a neglected hip dislocation, the surgeon notes a fixed 30-degree hip flexion contracture. How should this deformity be addressed at the proximal osteotomy site?

. Incorporating 30 degrees of flexion into the osteotomy.
. Incorporating 30 degrees of extension into the osteotomy.
. Performing an isolated distal femoral extension osteotomy.
. Aggressive postoperative physical therapy without intraoperative bony correction.
. Releasing the posterior capsule of the hip.

Correct Answer & Explanation

. Incorporating 30 degrees of extension into the osteotomy.

Explanation

Hip flexion contractures are common in chronic dislocations and are addressed by incorporating extension into the proximal osteotomy. Adding an extension component compensates for the contracture and prevents an excessive anterior pelvic tilt during ambulation.

Question 1932

Topic: Thoracolumbar Spine & Deformity

A 40-year-old patient with a 2.5 cm limb length discrepancy (LLD) due to a previous distal femoral fracture is scheduled for a standing long-leg alignment radiograph. The patient typically compensates for the LLD by flexing the contralateral knee and tilting their pelvis.

What is the most appropriate technique to ensure accurate alignment assessment and prevent compensatory mechanisms from affecting the measurements?

. Instruct the patient to stand naturally without any intervention
. Ask the patient to flex the contralateral knee to level the pelvis
. Place a lift of appropriate height under the shorter limb to level the pelvis
. Obtain the radiograph in a non-weight-bearing supine position
. Have the patient stand on one leg, bearing full weight on the longer limb

Correct Answer & Explanation

. Place a lift of appropriate height under the shorter limb to level the pelvis

Explanation

Correct Answer: CThe text clearly states that if there is a limb length discrepancy (LLD), the shorter limb should be elevated on blocks adjusted to the approximate discrepancy (Fig. 3-8). This technique prevents the patient from using compensatory mechanisms such as contralateral knee flexion, ipsilateral ankle equinus, pelvic tilt, and scoliosis, which can alter alignment and leg length measurements. These compensatory mechanisms cause uneven loading of the limbs and can lead to inaccurate radiographic assessment. Options A, B, and E describe scenarios where compensatory mechanisms would be present or exacerbated, leading to inaccurate measurements. Option D, while eliminating weight-bearing compensation, does not assess functional standing alignment.

Question 1933

Topic: 6. Spine

When assessing the lower extremity mechanical axis on a full-length standing radiograph (a line drawn from the center of the femoral head to the center of the ankle), where does this line normally pass in relation to the knee joint?

. 10-15 mm lateral to the center of the knee.
. 1-8 mm medial to the center of the knee.
. 25 mm medial to the center of the knee.
. Through the center of the lateral tibial spine.
. Through the lateral compartment.

Correct Answer & Explanation

. 1-8 mm medial to the center of the knee.

Explanation

In a normally aligned lower limb, the mechanical axis passes slightly medial to the exact center of the knee joint, typically yielding a Mechanical Axis Deviation (MAD) of 1 to 8 mm medial to the center.

Question 1934

Topic: 6. Spine

In a structurally normal lower extremity, where should the mechanical axis of the lower limb pass in relation to the knee joint?

. Through the lateral aspect of the lateral femoral condyle
. Through the center or slightly medial (0-8 mm) to the center of the knee joint
. 15-20 mm medial to the medial tibial spine
. 10-15 mm lateral to the center of the knee joint
. Directly through the fibular head

Correct Answer & Explanation

. Through the center or slightly medial (0-8 mm) to the center of the knee joint

Explanation

The normal mechanical axis of the lower extremity passes exactly through the center of the knee joint or slightly medial to it. Deviations beyond 8 mm medial or lateral indicate a pathological alignment.

Question 1935

Topic: 6. Spine

A 38-year-old male presents with progressive knee pain and a noticeable bowing deformity of his left lower extremity. A full-length weight-bearing radiograph is obtained, and the surgeon begins the Paley method of deformity analysis. The initial step involves drawing a line from the center of the femoral head to the center of the talar dome. This line is observed to pass 25 mm medial to the center of the knee joint. The surgeon then identifies the intersection point of the proximal and distal mechanical axes of the deformed bone segment, as shown in the diagram below.

Which of the following statements accurately describes the initial findings and their significance in this patient's case?

. The patient has a valgus deformity with a Mechanical Axis Deviation (MAD) of 25 mm lateral, indicating excessive lateral compartment loading.
. The patient has a varus deformity with a Mechanical Axis Deviation (MAD) of 25 mm medial, which is the primary biomechanical driver of premature osteoarthritis.
. The identified intersection point represents the Center of Rotation of Angulation (CORA), which dictates the magnitude of the deformity and the required osteotomy level.
. The normal Mechanical Axis Deviation (MAD) should be 25 mm medial to the knee center, suggesting this patient's alignment is within normal limits.
. The CORA is primarily used to determine the normal joint orientation angles, such as the mLDFA and MPTA.

Correct Answer & Explanation

. The patient has a varus deformity with a Mechanical Axis Deviation (MAD) of 25 mm medial, which is the primary biomechanical driver of premature osteoarthritis.

Explanation

Correct Answer: BThe patient has a varus deformity with a Mechanical Axis Deviation (MAD) of 25 mm medial, which is the primary biomechanical driver of premature osteoarthritis. The text defines MAD as the perpendicular distance from the mechanical axis line to the center of the knee joint. A line passing medial to the knee center indicates a varus deformity, and a deviation of 25 mm is significant. This chronic maldistribution of force is explicitly stated as the primary biomechanical driver of premature osteoarthritis, ligamentous instability, and functional decline.Incorrect Options:A:A MAD of 25 mm medial indicates a varus deformity, not valgus. Valgus would be a lateral deviation.C:The identified intersection point is indeed the CORA, which dictates the apex of the deformity and guides the osteotomy. However, the MAD, not the CORA, quantifies themagnitudeof the deformity and its impact on the weight-bearing axis. The CORA tells youwherethe deformity originates, not its magnitude.D:In a neutrally aligned limb, the mechanical axis should pass slightly medial to the exact center of the knee, typically bisecting the medial tibial spine, but a 25 mm medial deviation is well outside the normal range and indicates a significant varus deformity, not normal alignment.E:The CORA dictates the rules of the osteotomy (angulation and translation), not the normal joint orientation angles. These angles (mLDFA, MPTA) are target values for correction, not determined by the CORA itself.

Question 1936

Topic: 6. Spine

A 62-year-old male presents with severe medial compartment knee osteoarthritis and a significant genu varum deformity. During gait analysis, he exhibits a pronounced lateral trunk lean to the affected side. His surgeon notes that this compensatory mechanism, while seemingly reducing pain, has significant biomechanical consequences. Which of the following statements accurately describes the primary effect of this lateral trunk lean on the lower extremity biomechanics, as depicted in the provided diagram?

. A. It shifts the ground reaction vector (GRV) medially, increasing the adduction moment at the knee.
. B. It primarily reduces the workload on the hip abductors of the ipsilateral limb.
. C. It shifts the ground reaction vector (GRV) laterally, increasing the workload on the hip abductors of the ipsilateral limb.
. D. It decreases shear forces across the lumbar spine by centralizing the passenger unit's center of gravity.
. E. It has no significant effect on the GRV but alters the foot progression angle.

Correct Answer & Explanation

. C. It shifts the ground reaction vector (GRV) laterally, increasing the workload on the hip abductors of the ipsilateral limb.

Explanation

Correct Answer: CThe provided diagram and case content clearly illustrate that a lateral trunk lean shifts the passenger unit's center of gravity (T10) laterally. This shift physically drags the ground reaction vector (GRV) laterally relative to the lower extremity. While this might paradoxically decrease the adduction moment at a severely varus knee (a common patient strategy to offload medial pain), it comes at a steep physiological price. This lateral shift of the GRV creates a larger external lever arm for the hip abductors, drastically increasing their workload to stabilize the pelvis during single-leg stance. It also creates abnormal shear forces across the lumbar spine and can accelerate contralateral joint wear.Option A is incorrectbecause a lateral trunk lean shifts the GRV laterally, not medially. A medial shift would increase the adduction moment at the knee, which is generally what patients try to avoid with a lateral lean.Option B is incorrectbecause the lateral shift of the GRV increases the external moment arm acting on the hip, thereby increasing the workload on the ipsilateral hip abductors, not reducing it.Option D is incorrectbecause shifting the passenger unit's center of gravity off-center, as occurs with a lateral trunk lean, increases abnormal shear forces across the lumbar spine, rather than decreasing them.Option E is incorrectbecause a lateral trunk lean significantly shifts the GRV. While gait compensations can involve altering the foot progression angle, the primary effect of a trunk lean is on the GRV's position relative to the joints.

Question 1937

Topic: Thoracolumbar Spine & Deformity

A patient with a severe fixed abduction deformity of the right hip will typically develop which compensatory deformity to maintain a level gaze and forward progression during gait?

. Left pelvic drop
. Lumbar scoliosis convex to the left
. Lumbar scoliosis convex to the right
. Knee recurvatum on the right side
. Right ankle equinus contracture

Correct Answer & Explanation

. Lumbar scoliosis convex to the left

Explanation

A fixed right hip abduction deformity causes an apparent lengthening of the right leg. To place the right foot flat and compensate, the pelvis drops on the left, leading to a compensatory lumbar scoliosis that is convex to the left to keep the head centered.

Question 1938

Topic: 6. Spine

A surgeon is evaluating a 50-year-old patient with a valgus knee deformity. A full-length weight-bearing radiograph demonstrates a Mechanical Axis Deviation (MAD) of 20 mm lateral to the center of the knee joint. The normal mechanical axis of the lower extremity should pass:

. Exactly through the center of the tibial spines.
. Approximately 8 to 10 mm medial to the center of the knee joint.
. Approximately 8 to 10 mm lateral to the center of the knee joint.
. Through the lateral compartment, bisecting the lateral femoral condyle.
. Directly through the center of the patella regardless of knee rotation.

Correct Answer & Explanation

. Approximately 8 to 10 mm medial to the center of the knee joint.

Explanation

In a normally aligned lower extremity, the mechanical axis line (drawn from the center of the femoral head to the center of the ankle mortise) passes slightly medial (about 8 to 10 mm) to the center of the knee joint.

Question 1939

Topic: 6. Spine

When evaluating a full-length standing lower extremity radiograph, the Mechanical Axis Deviation (MAD) is precisely measured. Which of the following represents the normal MAD in a healthy adult?

. 10 mm lateral to the center of the knee joint
. 1 to 8 mm medial to the center of the knee joint
. 5 to 15 mm lateral to the center of the knee joint
. Exactly centered between the femoral condyles
. 10 to 15 mm medial to the center of the knee joint

Correct Answer & Explanation

. 1 to 8 mm medial to the center of the knee joint

Explanation

The normal mechanical axis of the lower extremity passes 1 to 8 mm medial to the exact center of the knee joint, frequently intersecting the medial tibial spine.

Question 1940

Topic: 6. Spine

When calculating the Mechanical Axis Deviation (MAD) on a standing full-length radiograph, the normal mechanical axis line is drawn from the center of the femoral head to the center of the ankle mortise. Where does this line normally pass in relation to the center of the knee joint?

. Exactly through the center of the knee.
. Approximately 1 to 8 mm medial to the center of the knee.
. Approximately 1 to 8 mm lateral to the center of the knee.
. Through the lateral compartment of the knee.
. Through the medial tibial spine.

Correct Answer & Explanation

. Approximately 1 to 8 mm medial to the center of the knee.

Explanation

In a normally aligned lower extremity, the mechanical axis passes just medial to the geometric center of the knee joint, typically between 1 and 8 mm medial to the center. Deviations beyond this indicate varus or valgus malalignment.

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