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6. Spine MCQs

Practice Set 379 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 7561

Topic: 6. Spine

On a standardized long-leg standing anteroposterior radiograph, the mechanical axis of the lower extremity is drawn from the center of the femoral head to the center of the ankle mortise. In a normal knee, where does this line typically pass?

. Exactly through the center of the knee joint
. 8 +/- 7 mm medial to the center of the knee joint
. 8 +/- 7 mm lateral to the center of the knee joint
. Through the medial tibial spine
. Through the lateral tibial spine

Correct Answer & Explanation

. 8 +/- 7 mm medial to the center of the knee joint

Explanation

The normal mechanical axis of the lower extremity demonstrates a slight physiologic varus relative to the joint center. It typically passes approximately 8 mm (+/- 7 mm) medial to the absolute geometric center of the knee.

Question 7562

Topic: 6. Spine

A 9-year-old boy with Neurofibromatosis type 1 (NF1) presents with a rapidly progressive thoracic scoliosis. Radiographs reveal a short, sharp curve with severe apical rotation, vertebral scalloping, and rib penciling. What is the most appropriate surgical management for this specific type of spinal deformity?

. Bracing until skeletal maturity
. Anterior spinal fusion alone
. Posterior spinal fusion alone with pedicle screws
. Combined anterior and posterior spinal fusion

Correct Answer & Explanation

. Combined anterior and posterior spinal fusion

Explanation

Correct Answer: Combined anterior and posterior spinal fusionThe clinical and radiographic description (short, sharp curve, vertebral scalloping, rib penciling, severe rotation) is classic for dystrophic scoliosis in Neurofibromatosis type 1. Dystrophic curves are notoriously aggressive, progress rapidly, and have a very high rate of pseudarthrosis and implant failure if treated with posterior fusion alone. Therefore, the gold standard surgical management for dystrophic NF1 scoliosis is a combined anterior and posterior spinal fusion (often with robust bone grafting) to ensure solid arthrodesis and prevent curve progression or 'crankshaft' phenomenon.

Question 7563

Topic: 6. Spine

A 5-year-old boy with a known history of Spondyloepiphyseal Dysplasia Congenita (SEDC) is scheduled for elective bilateral femoral osteotomies to correct severe coxa vara. Preoperatively, which of the following evaluations is absolutely critical to perform?

. Echocardiogram to assess for aortic root dilation
. Renal ultrasound to rule out hydronephrosis
. Pulmonary function tests to assess for restrictive lung disease
. Flexion-extension cervical spine radiographs to rule out atlantoaxial instability
. Coagulation profile to assess for von Willebrand disease

Correct Answer & Explanation

. Flexion-extension cervical spine radiographs to rule out atlantoaxial instability

Explanation

SEDC, caused by a COL2A1 mutation, is highly associated with odontoid hypoplasia resulting in atlantoaxial instability. Flexion-extension cervical radiographs are critical prior to any general anesthesia to prevent catastrophic spinal cord injury during intubation.

Question 7564

Topic: 6. Spine

A 7-year-old girl with Morquio syndrome (Mucopolysaccharidosis Type IV) presents with worsening clumsy gait, hyperreflexia, and clonus. Her intelligence is completely normal. Which of the following enzyme deficiencies and corresponding spinal pathologies best explains her current neurological symptoms?

. Alpha-L-iduronidase deficiency; severe thoracolumbar kyphosis
. Iduronate-2-sulfatase deficiency; foramen magnum stenosis
. N-acetylgalactosamine-6-sulfatase deficiency; atlantoaxial instability
. Arylsulfatase B deficiency; basilar invagination
. Beta-galactosidase deficiency; tethered cord syndrome

Correct Answer & Explanation

. N-acetylgalactosamine-6-sulfatase deficiency; atlantoaxial instability

Explanation

Morquio syndrome (MPS IV) is caused by a deficiency in N-acetylgalactosamine-6-sulfatase (GALNS). Patients typically have normal intelligence but are at severe risk for cervical myelopathy due to odontoid hypoplasia causing atlantoaxial instability.

Question 7565

Topic: 6. Spine

A 14-month-old male with achondroplasia presents with delayed motor milestones, hypotonia, and central sleep apnea. What is the most critical initial diagnostic imaging step for this patient?

. Echocardiogram to evaluate for cor pulmonale
. Cervical spine MRI to evaluate foramen magnum stenosis
. Flexion-extension radiographs of the cervical spine
. Whole-body skeletal survey to assess for kyphosis
. CT scan of the chest to evaluate thoracic volume

Correct Answer & Explanation

. Cervical spine MRI to evaluate foramen magnum stenosis

Explanation

Achondroplasia (FGFR3 gain-of-function mutation) often features a narrowed foramen magnum leading to cervicomedullary compression, which causes central sleep apnea and hypotonia. An MRI of the craniocervical junction is essential for timely evaluation and potential surgical decompression.

Question 7566

Topic: 6. Spine

A 7-year-old child presents with severe genu valgum, a short trunk, and corneal clouding. Cognitive development is completely normal. A urine spot test is strongly positive for keratan sulfate. What is the most critical orthopedic evaluation required for this patient prior to any surgical intervention?

. Echocardiogram for aortic root dilation
. Pulmonary function tests for restrictive lung disease
. Flexion/extension cervical radiographs for odontoid hypoplasia
. Skeletal survey to rule out impending pathologic fractures
. Renal ultrasound to evaluate for nephrocalcinosis

Correct Answer & Explanation

. Flexion/extension cervical radiographs for odontoid hypoplasia

Explanation

Morquio syndrome (MPS IV) involves a deficiency of N-acetylgalactosamine-6-sulfatase, leading to keratan sulfate accumulation. Patients commonly have severe odontoid hypoplasia leading to atlantoaxial instability, making preoperative cervical spine evaluation critical to prevent iatrogenic spinal cord injury.

Question 7567

Topic: Cervical Spine

A 6-year-old boy with normal intelligence presents with a disproportionately short trunk, severe genu valgum, and progressive corneal clouding. Flexion-extension cervical spine radiographs show pronounced atlantoaxial instability secondary to profound odontoid hypoplasia. Which of the following metabolites is accumulating in this patient's tissues?

. Heparan sulfate
. Dermatan sulfate
. Keratan sulfate
. Chondroitin-6-sulfate
. Hyaluronic acid

Correct Answer & Explanation

. Keratan sulfate

Explanation

Morquio syndrome (Mucopolysaccharidosis Type IV) is caused by a deficiency in N-acetylgalactosamine-6-sulfatase (Type IVA) or beta-galactosidase (Type IVB), leading to the accumulation of keratan sulfate. It uniquely causes severe odontoid hypoplasia and atlantoaxial instability, requiring careful monitoring and potential cervical fusion.

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