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6. Spine MCQs

Practice Set 294 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 5861

Topic: Thoracolumbar Spine & Deformity

In patients with SMA, neuromuscular scoliosis often presents early and progresses rapidly. What is the typical curve pattern and sagittal profile associated with SMA scoliosis?

. Right thoracic curve with significant thoracic lordosis
. Left lumbar curve with hyperkyphosis
. Long, sweeping 'C'-shaped curve with pelvic obliquity and collapsed sagittal profile
. Short, sharp structural curve at the thoracolumbar junction
. Double major curve with preserved lumbar lordosis

Correct Answer & Explanation

. Long, sweeping 'C'-shaped curve with pelvic obliquity and collapsed sagittal profile

Explanation

Neuromuscular scoliosis, such as that seen in SMA, typically presents as a long, sweeping 'C'-shaped thoracolumbar curve that extends to the pelvis, leading to significant pelvic obliquity. Due to truncal weakness, these patients often have a collapsed sagittal profile (loss of physiological thoracic kyphosis and lumbar lordosis, often resulting in a global kyphosis when seated).

Question 5862

Topic: 6. Spine

A 4-year-old child with Spinal Muscular Atrophy Type II is scheduled for a posterior spinal fusion for progressive neuromuscular scoliosis. During the induction of anesthesia, which of the following agents is strictly contraindicated due to a specific severe adverse effect?

. Propofol
. Ketamine
. Succinylcholine
. Rocuronium
. Sevoflurane

Correct Answer & Explanation

. Succinylcholine

Explanation

Succinylcholine is a depolarizing neuromuscular blocker that is absolutely contraindicated in patients with motor neuron diseases, such as Spinal Muscular Atrophy (SMA), muscular dystrophies, and significant burns. In these conditions, there is an upregulation and spread of extrajunctional acetylcholine receptors. Depolarization by succinylcholine can lead to massive potassium efflux from muscle cells, resulting in sudden, life-threatening hyperkalemia and cardiac arrest.

Question 5863

Topic: 6. Spine

A 6-year-old patient with SMA Type II requires surgical stabilization for a progressive 80-degree neuromuscular scoliosis. The patient is currently receiving Nusinersen (Spinraza) therapy. What specific surgical consideration must be addressed during the spinal fusion?

. Withholding Nusinersen for 6 months postoperatively to ensure bone healing
. Performing an anterior-only fusion to preserve posterior elements for drug delivery
. Placing an intrathecal catheter or leaving an interlaminar window for future medication administration
. Using only titanium implants to avoid chemical interactions with the medication
. Performing the fusion before starting Nusinersen therapy is mandatory

Correct Answer & Explanation

. Placing an intrathecal catheter or leaving an interlaminar window for future medication administration

Explanation

Nusinersen (Spinraza) is an antisense oligonucleotide that alters the splicing of SMN2 pre-mRNA to increase functional SMN protein. It must be administered directly into the central nervous system via intrathecal injection every few months. In a patient undergoing posterior spinal fusion, the surgical team must plan a secure route for future intrathecal access, typically by leaving a lumbosacral interlaminar window or surgically placing a subcutaneous intrathecal port/catheter during the spinal procedure.

Question 5864

Topic: 6. Spine

A 14-year-old patient with Osteogenesis Imperfecta Type IV complains of new-onset occipital headaches, hyperreflexia, sleep apnea, and swallowing difficulties. Which of the following is the most appropriate next diagnostic step?

. Cervical spine flexion-extension radiographs
. MRI of the craniocervical junction
. CT scan of the temporal bones
. Lumbar puncture to measure opening pressure
. Electromyography and nerve conduction studies

Correct Answer & Explanation

. MRI of the craniocervical junction

Explanation

The patient's clinical presentation (occipital headaches, long tract signs like hyperreflexia, lower cranial nerve dysfunction, and sleep apnea) is highly suspicious for basilar invagination. This is a severe and potentially lethal complication seen in up to 25% of patients with severe OI (especially Type IV). An MRI of the craniocervical junction is the imaging modality of choice to assess for soft tissue impingement, brainstem compression, and syringomyelia.

Question 5865

Topic: 6. Spine
Spinal muscular atrophy is primarily caused by a homozygous deletion or mutation in the SMN1 gene. The clinical severity of the disease, which distinguishes between Types I, II, III, and IV, is most closely and inversely correlated with which of the following factors?
. The exact base pair size of the SMN1 gene deletion
. The number of copies of the SMN2 gene
. The level of maternal SMN protein transferred across the placenta
. The presence of a concomitant Duchenne muscular dystrophy mutation
. The age at which intensive physical therapy is initiated

Correct Answer & Explanation

. The number of copies of the SMN2 gene

Explanation

The SMN2 gene is a nearly identical paralog to SMN1, but a single nucleotide substitution causes altered splicing, resulting in only about 10-15% of the transcribed protein being fully functional. In patients lacking the SMN1 gene, their only source of functional SMN protein is the SMN2 gene. Therefore, a higher number of SMN2 gene copies yields more functional protein, which generally translates to a milder clinical phenotype (e.g., Type III or IV vs. the severe Type I).

Question 5866

Topic: Thoracolumbar Spine & Deformity

A 2-year-old with SMA Type II is being evaluated for orthotic management to aid in supported standing. Which of the following is the primary goal of standing programs and lower extremity orthoses in a non-ambulatory child with SMA?

. To permanently reverse fixed joint contractures
. To promote and eventually achieve independent walking
. To improve bone mineral density, bowel function, and respiratory mechanics
. To definitively halt the progression of neuromuscular scoliosis
. To upregulate SMN2 gene expression through mechanical loading

Correct Answer & Explanation

. To improve bone mineral density, bowel function, and respiratory mechanics

Explanation

In non-ambulatory children with SMA (Type II), supported standing programs (using standers or Knee-Ankle-Foot Orthoses) are highly recommended. While they do not teach the child to walk independently, reverse fixed contractures, or cure scoliosis, they are crucial for improving/maintaining bone mineral density, preventing severe contractures, aiding bowel and bladder function, and improving psychological well-being and respiratory mechanics.

Question 5867

Topic: 6. Spine

A 5-year-old with SMA Type II presents with a progressive thoracolumbar neuromuscular scoliosis measuring 35 degrees. The child is a functional sitter. What is the most appropriate role for a Thoracolumbosacral Orthosis (TLSO) in the management of this patient?

. To definitively halt curve progression until skeletal maturity is reached
. To permanently correct the structural spinal deformity
. To provide truncal support, free the upper extremities for function, and delay surgical intervention
. To forcefully correct pelvic obliquity and prevent hip subluxation
. Bracing is contraindicated in SMA due to inevitable respiratory compromise

Correct Answer & Explanation

. To provide truncal support, free the upper extremities for function, and delay surgical intervention

Explanation

In paralytic/neuromuscular scoliosis associated with SMA, bracing (TLSO) does not alter the natural history of the curve or provide permanent correction. However, a lightweight, custom-molded TLSO (often with abdominal cutouts to permit diaphragmatic breathing) is highly beneficial for providing truncal stability. This improves sitting balance, frees the upper extremities for functional use, and can help delay surgical spinal fusion until the child is older and larger.

Question 5868

Topic: 6. Spine

In a patient with Spinal Muscular Atrophy Type II undergoing evaluation for posterior spinal fusion, which preoperative pulmonary function test parameters are the most critical predictors of postoperative extubation success and respiratory complications?

. FEV1/FVC ratio and Maximum Voluntary Ventilation (MVV)
. Total Lung Capacity (TLC) and Functional Residual Capacity (FRC)
. Peak Cough Flow (PCF) and Forced Vital Capacity (FVC)
. Residual Volume (RV) and Diffusion Capacity of Carbon Monoxide (DLCO)
. Arterial Blood Gas (ABG) pO2 and pCO2 levels alone

Correct Answer & Explanation

. Peak Cough Flow (PCF) and Forced Vital Capacity (FVC)

Explanation

In neuromuscular patients (including those with SMA), Forced Vital Capacity (FVC) and Peak Cough Flow (PCF) are critical to assess preoperatively. An FVC < 30% of predicted indicates severe restrictive lung disease. A low PCF indicates bulbar/respiratory muscle weakness and an inability to clear secretions effectively. These findings combined strongly predict a high risk for prolonged postoperative intubation, need for BiPAP, or tracheostomy following spinal fusion.

Question 5869

Topic: 6. Spine

Spinal Muscular Atrophy primarily causes weakness through the degeneration of which specific neural structures?

. Upper motor neurons in the primary motor cortex (Betz cells)
. Sensory neurons in the dorsal root ganglia
. Alpha motor neurons in the anterior horn of the spinal cord and brainstem nuclei
. Purkinje cells in the cerebellar cortex
. Preganglionic sympathetic neurons in the intermediolateral nucleus

Correct Answer & Explanation

. Alpha motor neurons in the anterior horn of the spinal cord and brainstem nuclei

Explanation

Spinal Muscular Atrophy is a lower motor neuron disease. The deficiency of the SMN protein leads to the selective, progressive degeneration and death of alpha motor neurons located in the anterior horn of the spinal cord and lower brainstem nuclei. This results in progressive skeletal muscle denervation, weakness, and atrophy, with sparing of sensory and upper motor neuron pathways.

Question 5870

Topic: 6. Spine

A 10-year-old boy with Spinal Muscular Atrophy (SMA) Type II is scheduled for a posterior spinal fusion to correct a severe, progressive neuromuscular scoliosis. He is currently receiving Nusinersen (Spinraza) therapy. What specific surgical modification must be planned to facilitate his ongoing medical treatment?

. Avoidance of pedicle screws at the L4-L5 level
. Creation of an interlaminar window in the lower lumbar spine
. Placement of a permanent epidural catheter during fusion
. Fusion termination at L3 to maintain lumbar flexion
. Use of sublaminar wires exclusively in the lumbar spine

Correct Answer & Explanation

. Creation of an interlaminar window in the lower lumbar spine

Explanation

Nusinersen is administered via repeated intrathecal injections. In patients undergoing posterior spinal fusion, leaving an interlaminar window (typically L3-L4 or L4-L5) without bone graft or hardware obstruction is critical to allow future access.

Question 5871

Topic: 6. Spine

Which of the following genetic profiles determines the phenotypic severity of Spinal Muscular Atrophy in a patient with a homozygous deletion of the SMN1 gene?

. Mutations in the dystrophin gene
. The number of SMN2 gene copies
. Presence of the IFITM5 mutation
. Heterozygosity of the PMP22 gene
. Trinucleotide repeat expansion length

Correct Answer & Explanation

. The number of SMN2 gene copies

Explanation

SMA is caused by a loss of the SMN1 gene. The severity of the disease inversely correlates with the number of copies of the paralogous SMN2 gene, which produces a small amount of functional survival motor neuron protein.

Question 5872

Topic: Thoracolumbar Spine & Deformity

During preoperative evaluation for scoliosis surgery in a 12-year-old with SMA Type II, the pulmonologist performs spirometry. Which of the following pulmonary function test findings indicates an increased risk of prolonged postoperative mechanical ventilation?

. Forced Vital Capacity (FVC) less than 30% of predicted
. FEV1/FVC ratio greater than 80%
. Total lung capacity (TLC) greater than 120% of predicted
. Peak Expiratory Flow Rate (PEFR) greater than 80% of predicted
. Normal maximum inspiratory pressure (MIP)

Correct Answer & Explanation

. Forced Vital Capacity (FVC) less than 30% of predicted

Explanation

Patients with SMA have restrictive lung disease due to intercostal muscle weakness. An FVC of less than 30% to 40% of predicted is a major risk factor for postoperative pulmonary complications and the need for prolonged ventilation.

Question 5873

Topic: 6. Spine
A patient with severe osteogenesis imperfecta (Type III) develops progressive upper motor neuron signs, hyperreflexia, and lower cranial nerve deficits. What is the most likely diagnosis?
. Syringomyelia
. Basilar invagination
. Atlantoaxial rotatory subluxation
. Spinal muscular atrophy overlap syndrome
. Tethered cord syndrome

Correct Answer & Explanation

. Basilar invagination

Explanation

Basilar invagination occurs in severe OI due to softening of the skull base, leading to upward migration of the odontoid into the foramen magnum. It presents with brainstem compression, myelopathy, and lower cranial nerve dysfunction.

Question 5874

Topic: 6. Spine

A 10-year-old girl with SMA Type II presents with severe, collapsing neuromuscular scoliosis.

When planning a posterior spinal fusion for this patient, what is the most appropriate distal foundation to prevent future deformity?

. Fusion to L4
. Fusion to L5
. Fusion to the sacrum without pelvic instrumentation
. Fusion to the pelvis using iliac or sacropelvic screws
. Anterior tethering of the lumbar spine

Correct Answer & Explanation

. Fusion to the pelvis using iliac or sacropelvic screws

Explanation

In non-ambulatory patients with severe SMA and collapsing scoliosis, fusion must include the pelvis (e.g., iliac or S2-alar-iliac screws). This is essential to correct and prevent recurrence of pelvic obliquity, thereby maintaining sitting balance.

Question 5875

Topic: 6. Spine

A 3-year-old child with Spinal Muscular Atrophy (SMA) Type II is being evaluated for motor milestones. The severity of the clinical phenotype in SMA is primarily determined by the copy number of which of the following genes?

. SMN1
. SMN2
. COL1A1
. DMD
. PMP22

Correct Answer & Explanation

. SMN1

Explanation

All SMA patients have a homozygous deletion or mutation of the SMN1 gene. Disease severity is inversely proportional to the number of copies of the SMN2 backup gene, which produces a small amount of functional SMN protein.

Question 5876

Topic: 6. Spine

A 14-year-old girl with Osteogenesis Imperfecta Type IV is scheduled for posterior spinal fusion for a progressive 75-degree thoracic scoliotic curve. During preoperative planning, the surgeon must account for which characteristic intraoperative challenge specific to OI?

. High incidence of malignant hyperthermia with volatile anesthetics
. Severe rigidity of the curve preventing any intraoperative correction
. High risk of pedicle screw pullout due to poor bone mineral density
. Obligatory need to fuse exclusively to the cervical spine
. Inability to achieve a bony fusion mass

Correct Answer & Explanation

. High risk of pedicle screw pullout due to poor bone mineral density

Explanation

Scoliosis surgery in OI is fraught with instrumentation failure, particularly pedicle screw pullout, due to profoundly poor bone quality. Surgeons often employ multiple points of fixation and accept lesser curve corrections to prevent hardware failure.

Question 5877

Topic: 6. Spine

A 6-year-old boy with SMA Type II requires surgical intervention for a progressive 80-degree neuromuscular scoliosis with 20 degrees of pelvic obliquity. He is scheduled for magnetically controlled growing rods. Which of the following is a critical surgical principle regarding spinal instrumentation in this specific population?

. Avoidance of pelvic fixation to preserve hip motion
. Mandatory extension of the instrumentation to the pelvis
. Use of dynamic rather than rigid distal anchors
. Strict avoidance of sublaminar wires
. Anterior-only approach to spare posterior extensor muscles

Correct Answer & Explanation

. Mandatory extension of the instrumentation to the pelvis

Explanation

In SMA patients with severe scoliosis and pelvic obliquity, spinal instrumentation must almost always be extended to the pelvis (e.g., iliac or S2AI screws). Failure to include the pelvis leads to progressive pelvic obliquity and sitting imbalance.

Question 5878

Topic: 6. Spine
A 15-year-old boy with severe osteogenesis imperfecta (type III) presents with worsening occipital headaches, hyperreflexia in the lower extremities, and fine motor clumsiness in the hands. Which of the following is the most appropriate next step in diagnosis?
. Electroencephalogram (EEG)
. Lumbar puncture
. MRI of the cervical spine and craniocervical junction
. Nerve conduction studies (NCS)
. Cranial vault ultrasound

Correct Answer & Explanation

. MRI of the cervical spine and craniocervical junction

Explanation

This patient's symptoms suggest basilar invagination, a recognized and potentially fatal complication of severe OI caused by upward migration of the cervical spine into the foramen magnum. MRI is the modality of choice to assess neurovascular compression at the craniocervical junction.

Question 5879

Topic: 6. Spine

A 12-year-old boy with SMA Type II presents for posterior spinal fusion. During anesthetic induction, which of the following medications must be strictly avoided due to the risk of severe, life-threatening hyperkalemia?

. Propofol
. Ketamine
. Rocuronium
. Succinylcholine
. Sevoflurane

Correct Answer & Explanation

. Succinylcholine

Explanation

Succinylcholine, a depolarizing muscle relaxant, is contraindicated in patients with neuromuscular diseases like SMA or muscular dystrophies. Denervated muscles have upregulated extrajunctional acetylcholine receptors, which release massive amounts of potassium when depolarized.

Question 5880

Topic: 6. Spine

Spinal Muscular Atrophy (SMA) is an autosomal recessive neuromuscular disorder caused by a mutation in the SMN1 gene. Which of the following genetic factors serves as the primary determinant for the phenotypic severity of the disease in these patients?

. The specific exon deleted in the SMN1 gene
. The number of SMN2 gene copies
. The presence of a concurrent dystrophin mutation
. The extent of DNA methylation at the SMN1 promoter
. The rate of apoptosis in the anterior horn cells

Correct Answer & Explanation

. The number of SMN2 gene copies

Explanation

The severity of SMA is inversely correlated with the number of copies of the SMN2 gene. SMN2 produces a small amount of functional Survival Motor Neuron (SMN) protein, so more copies lead to a milder phenotype.

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