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6. Spine MCQs

Practice Set 279 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 5561

Topic: 6. Spine

An infant presents with severe hypotonia and absent reflexes. While genetic testing for the SMN1 gene deletion is pending, an electromyogram (EMG) is performed. Which of the following EMG findings is most characteristic of Spinal Muscular Atrophy and helps differentiate it from a primary myopathy?

. Short-duration, low-amplitude motor unit potentials.
. Decremental response to repetitive nerve stimulation.
. Fibrillation potentials and large-amplitude, long-duration motor unit potentials.
. Normal insertional activity with early recruitment.
. Myotonic discharges described as a "dive bomber" sound.

Correct Answer & Explanation

. Fibrillation potentials and large-amplitude, long-duration motor unit potentials.

Explanation

Correct Answer: CSpinal Muscular Atrophy is a lower motor neuron disease caused by the degeneration of anterior horn cells. The characteristic EMG findings reflect this denervation and subsequent reinnervation process. Active denervation is indicated by fibrillation potentials and positive sharp waves. As surviving motor neurons sprout collateral axons to reinnervate orphaned muscle fibers, they create enlarged motor units, which appear on EMG as large-amplitude, long-duration motor unit potentials. In contrast, primary myopathies typically show short-duration, low-amplitude potentials.

Question 5562

Topic: 6. Spine

A 9-year-old non-ambulatory boy with Spinal Muscular Atrophy Type II is scheduled for a posterior spinal fusion to treat a progressive 75-degree neuromuscular scoliosis. Prior to surgery, a total spine MRI is ordered. The primary rationale for this imaging study in this specific patient population is to rule out which of the following conditions?

. Occult vertebral body fractures
. Syringomyelia or tethered cord
. Paraspinal muscle pseudohypertrophy
. Dural ectasia
. Atlantoaxial rotatory subluxation

Correct Answer & Explanation

. Syringomyelia or tethered cord

Explanation

Correct Answer: BPatients with neuromuscular scoliosis, including those with SMA, have a significantly higher incidence of intraspinal neural axis abnormalities compared to patients with idiopathic scoliosis. These abnormalities include syringomyelia, tethered cord syndrome, and diastematomyelia. A total spine MRI is a crucial preoperative step because correcting a severe spinal deformity in the presence of an unrecognized tethered cord or syrinx can lead to catastrophic neurological injury during the distraction and derotation maneuvers of the fusion surgery.

Question 5563

Topic: 6. Spine

A 2-month-old infant recently diagnosed with Spinal Muscular Atrophy Type 1 receives an intravenous infusion of onasemnogene abeparvovec. This therapeutic agent exerts its primary effect through which of the following mechanisms?

. Modifying the pre-mRNA splicing of the SMN2 gene to include exon 7.
. Inhibiting the degradation of the SMN protein by the ubiquitin-proteasome system.
. Delivering a fully functional copy of the SMN1 gene via an adeno-associated virus vector.
. Binding to and inhibiting myostatin to promote skeletal muscle hypertrophy.
. Acting as a small molecule to enhance the transcription rate of the endogenous SMN1 gene.

Correct Answer & Explanation

. Delivering a fully functional copy of the SMN1 gene via an adeno-associated virus vector.

Explanation

Correct Answer: COnasemnogene abeparvovec (Zolgensma) is a targeted gene replacement therapy. It utilizes a non-replicating adeno-associated virus serotype 9 (AAV9) vector to deliver a fully functional, episomal copy of the humanSMN1gene directly into the nucleus of motor neurons. This allows the cells to produce adequate levels of the full-length Survival Motor Neuron (SMN) protein, addressing the root genetic cause of the disease. In contrast, nusinersen and risdiplam work by modifying the splicing of the backupSMN2gene.

Question 5564

Topic: 6. Spine

A 12-year-old male with Spinal Muscular Atrophy Type II undergoes a posterior spinal fusion from T2 to the pelvis for a severe, progressive neuromuscular scoliosis. Postoperatively, the surgeon is particularly concerned about the risk of pseudarthrosis and instrumentation failure. Which of the following factors most significantly contributes to this specific risk in the SMA population?

. Hyperactive osteoblast activity leading to heterotopic ossification.
. Profoundly poor bone stock and osteopenia secondary to lack of mechanical loading and the underlying disease process.
. Increased risk of deep surgical site infection due to inherent immunodeficiency.
. Severe postoperative spasticity causing mechanical pull-out of pedicle screws.
. Rapid progression of the underlying genetic mutation post-surgery.

Correct Answer & Explanation

. Profoundly poor bone stock and osteopenia secondary to lack of mechanical loading and the underlying disease process.

Explanation

Correct Answer: BPatients with SMA, particularly those who are non-ambulatory, develop severe osteopenia and profoundly poor bone stock. This is a multifactorial issue resulting from a lack of mechanical loading (Wolff's law) due to immobility, severe muscle weakness, and potentially direct metabolic effects of SMN protein deficiency on bone cells. This extremely poor bone quality makes achieving solid biomechanical fixation with spinal instrumentation highly challenging. It significantly increases the risk of screw pull-out, hardware failure, and subsequent pseudarthrosis (failure of the spine to fuse) compared to patients with idiopathic scoliosis.

Question 5565

Topic: 6. Spine

A 9-year-old girl with Spinal Muscular Atrophy (SMA) Type II is undergoing a posterior spinal fusion for a progressive 80-degree neuromuscular scoliosis. During the induction of general anesthesia, the anesthesiologist explicitly avoids the use of succinylcholine. What is the primary physiological rationale for this contraindication in a patient with SMA?

. High risk of triggering a malignant hyperthermia crisis.
. Severe exacerbation of underlying restrictive lung disease leading to prolonged intubation.
. Risk of acute, life-threatening hyperkalemia due to extrajunctional receptor depolarization.
. Prolonged neuromuscular blockade due to delayed hepatic metabolism of the drug.
. Induction of severe, refractory bradycardia and complete heart block.

Correct Answer & Explanation

. Risk of acute, life-threatening hyperkalemia due to extrajunctional receptor depolarization.

Explanation

Correct Answer: CSpinal Muscular Atrophy (SMA) is a lower motor neuron disease characterized by the degeneration of anterior horn cells, leading to profound muscle denervation. In denervating conditions (such as SMA, spinal cord injury, or severe burns), there is a massive upregulation and proliferation of immature, extrajunctional acetylcholine receptors across the muscle membrane. When a depolarizing neuromuscular blocker like succinylcholine is administered, it activates all these receptors simultaneously, causing a massive efflux of potassium from the intracellular to the extracellular space. This can result in acute, life-threatening hyperkalemia and subsequent fatal cardiac arrhythmias. Malignant hyperthermia is classically associated with myopathies like Duchenne Muscular Dystrophy (DMD) or central core disease, not typically SMA. Non-depolarizing agents (e.g., rocuronium) are safe to use in SMA.

Question 5566

Topic: 6. Spine
A 14-year-old male with Osteogenesis Imperfecta Type III presents to the clinic with new-onset, severe occipital headaches, hyperreflexia in his upper extremities, and a deteriorating, spastic gait. A sagittal MRI of the cervical spine is obtained. Which of the following pathophysiological mechanisms best explains these new neurological findings?
. Atlantoaxial rotatory subluxation due to severe ligamentous laxity.
. Upward migration of the odontoid process into the foramen magnum.
. Syringomyelia secondary to a tethered spinal cord.
. Epidural hematoma from a minor, unrecognized cervical spine trauma.
. Ossification of the posterior longitudinal ligament causing central canal stenosis.

Correct Answer & Explanation

. Upward migration of the odontoid process into the foramen magnum.

Explanation

The patient is presenting with classic signs of myelopathy and lower cranial nerve/brainstem compression (occipital headaches, hyperreflexia, spastic gait). In severe forms of Osteogenesis Imperfecta (Types III and IV), the skull base is extremely soft due to poor bone mineralization. Over time, the weight of the head causes the skull base to settle onto the cervical spine, a condition known as basilar invagination or cranial settling. This leads to the upward migration of the odontoid process (dens) into the foramen magnum, compressing the cervicomedullary junction. This is a life-threatening complication of severe OI that requires prompt recognition with MRI or CT and often necessitates complex occipitocervical decompression and fusion.

Question 5567

Topic: 6. Spine

When planning a posterior spinal fusion for a non-ambulatory 11-year-old with Spinal Muscular Atrophy Type II who presents with a 75-degree thoracolumbar curve and 25 degrees of pelvic obliquity, which of the following construct designs is most critical to achieve the primary functional goals of the surgery?

. Selective thoracic fusion to preserve lumbar mobility for transfers.
. Extension of the fusion construct distally to include the pelvis.
. Use of anterior-only vertebral body tethering to allow for continued spinal growth.
. Avoidance of pedicle screws in favor of sublaminar wires to prevent pedicle fracture.
. Termination of the construct at L4 to preserve the lumbosacral junction.

Correct Answer & Explanation

. Extension of the fusion construct distally to include the pelvis.

Explanation

Correct Answer: BIn non-ambulatory patients with neuromuscular scoliosis (such as SMA Type II), the primary goals of spinal fusion are to halt curve progression, improve sitting balance, relieve pain, and optimize pulmonary function. A critical component of sitting balance is a level pelvis. When significant pelvic obliquity is present (typically >15 degrees), stopping the fusion short of the pelvis (e.g., at L4 or L5) will fail to correct the obliquity and often leads to the "crankshaft" phenomenon or continued decompensation below the construct. Therefore, extending the fusion to the pelvis (using iliac or S2-alar-iliac screws) is essential to provide a stable, level foundation for sitting. Preserving lumbar mobility is a goal in idiopathic scoliosis but is superseded by the need for stability and balance in severe neuromuscular curves.

Question 5568

Topic: 6. Spine

A 13-year-old female with Spinal Muscular Atrophy Type II undergoes a successful T2-to-Pelvis posterior spinal fusion for severe scoliosis. On postoperative day 4, she develops acute respiratory distress, significant abdominal distension, and copious bilious emesis. Upright abdominal radiographs demonstrate a markedly dilated stomach and proximal duodenum with an abrupt cutoff of gas in the third portion of the duodenum. What is the most likely diagnosis?

. Postoperative paralytic ileus
. Superior mesenteric artery (SMA) syndrome
. Acute appendicitis
. Clostridium difficile colitis
. Acute cholecystitis

Correct Answer & Explanation

. Superior mesenteric artery (SMA) syndrome

Explanation

Correct Answer: BThe patient has developed Superior Mesenteric Artery (SMA) syndrome, also known as cast syndrome. This is a known, potentially life-threatening complication following major spinal deformity correction. When a severe scoliotic or kyphotic curve is acutely straightened and the spine is lengthened, it can decrease the aortomesenteric angle (the angle between the abdominal aorta and the superior mesenteric artery). This acute anatomical change compresses the third portion of the duodenum as it passes between these two vessels, leading to a mechanical proximal bowel obstruction. Symptoms include bilious emesis, abdominal distension, and weight loss. It is particularly common in thin, asthenic patients with neuromuscular disorders. Treatment involves gastric decompression (NG tube), fluid resuscitation, positioning (left lateral decubitus or prone), and nutritional support; surgery (duodenojejunostomy) is reserved for refractory cases.

Question 5569

Topic: 6. Spine

A 9-year-old boy with Spinal Muscular Atrophy (SMA) Type II presents with a progressive 75-degree neuromuscular scoliosis and pelvic obliquity. He is currently treated with intrathecal nusinersen. When planning posterior spinal fusion with spinopelvic fixation for this patient, which of the following surgical modifications is most critical to incorporate?

. Anterior release and fusion to prevent crankshaft phenomenon.
. Creation of a lumbar interlaminar window or use of a specialized access port.
. Sublaminar wiring instead of pedicle screws to preserve the spinal canal.
. Extending the fusion proximally to the upper cervical spine to prevent basilar invagination.
. Avoiding pelvic fixation to allow for future hip contracture releases.

Correct Answer & Explanation

. Creation of a lumbar interlaminar window or use of a specialized access port.

Explanation

Nusinersen is an antisense oligonucleotide administered via regular intrathecal injections. During posterior spinal fusion for SMA, surgeons must leave an interlaminar defect (typically L3-L4 or L4-L5) or place a specialized catheter/port to allow continued intrathecal access.

Question 5570

Topic: 6. Spine
A 14-year-old female with Osteogenesis Imperfecta Type IV presents with occipital headaches, hyperreflexia, and recent onset of difficulty swallowing. Which of the following is the most appropriate next step in evaluating this patient's new symptoms?
. Flexion-extension cervical spine radiographs.
. MRI of the craniovertebral junction.
. CT myelogram of the cervical spine.
. Electromyography and nerve conduction studies.
. Audiogram to assess for associated cranial nerve VIII deficits.

Correct Answer & Explanation

. MRI of the craniovertebral junction.

Explanation

The patient's symptoms (headaches, dysphagia, hyperreflexia) suggest basilar invagination, a dangerous complication of severe OI caused by softening of the cranial base. MRI of the craniovertebral junction is the imaging modality of choice to assess for brainstem and upper cervical cord compression.

Question 5571

Topic: 6. Spine

A 12-year-old boy with SMA Type 2 and a progressive 85-degree neuromuscular scoliosis is scheduled for posterior spinal fusion. He is currently receiving Nusinersen (Spinraza) therapy. Which of the following technical modifications is essential during his surgical procedure?

. Use of sublaminar wires instead of pedicle screws to preserve the canal
. Extension of the fusion construct to the cervical spine
. Creation of a lumbar interlaminar window or placement of an intrathecal catheter
. Harvesting autologous iliac crest bone graft to augment fusion
. Routine performance of an anterior spinal release

Correct Answer & Explanation

. Creation of a lumbar interlaminar window or placement of an intrathecal catheter

Explanation

Nusinersen is administered via repeated intrathecal injections. During spinal fusion, surgeons must leave a translaminar window or place an indwelling catheter to ensure future access for the medication.

Question 5572

Topic: 6. Spine

A 9-year-old non-ambulatory girl with Spinal Muscular Atrophy Type 2 is incidentally found to have a painless, unilateral left hip dislocation on a pelvic radiograph obtained for scoliosis monitoring. Physical examination reveals a level pelvis when seated and no pain with hip range of motion. What is the most appropriate management?

. Closed reduction and spica casting
. Open reduction with femoral varus derotation osteotomy
. Proximal femoral resection (Castle procedure)
. Observation and continuation of seating modifications
. Bilateral varus derotation osteotomies with pelvic osteotomies

Correct Answer & Explanation

. Observation and continuation of seating modifications

Explanation

Painless hip dislocations in non-ambulatory SMA patients are generally observed. Surgical reduction does not improve functional outcomes, has a high complication and recurrence rate, and may cause postoperative stiffness.

Question 5573

Topic: 6. Spine

A 14-year-old patient with Osteogenesis Imperfecta Type IV presents with new-onset lower extremity hyperreflexia, sleep apnea, and difficulty swallowing. Lateral cervical spine radiographs are difficult to interpret due to marked osteopenia. Which of the following is the most appropriate next step in diagnostic imaging?

. Dynamic flexion-extension radiographs to assess the atlanto-dens interval
. Magnetic Resonance Imaging (MRI) of the craniocervical junction
. Computed Tomography (CT) scan to measure the space available for the cord
. Bone scintigraphy of the skull base
. Diagnostic cerebral angiography

Correct Answer & Explanation

. Magnetic Resonance Imaging (MRI) of the craniocervical junction

Explanation

The patient's symptoms are classic for basilar invagination, a dangerous complication of severe OI. MRI of the craniocervical junction is the gold standard for assessing brainstem compression and odontoid migration.

Question 5574

Topic: Cervical Spine

A 12-year-old girl with Osteogenesis Imperfecta Type IV presents with progressively worsening occipital headaches, hyperreflexia in all four extremities, and a positive Hoffmann's sign. Which of the following radiographic parameters on a lateral cervical spine radiograph is most appropriate to evaluate her suspected condition?

. McGregor's line
. Cobb angle
. Anterior atlantodental interval
. Space available for the cord
. Wiberg angle

Correct Answer & Explanation

. McGregor's line

Explanation

Basilar invagination is a recognized complication of Osteogenesis Imperfecta, presenting with brainstem or upper cervical cord compression. It is radiographically evaluated using McGregor's line or Chamberlain's line to assess the position of the odontoid tip relative to the skull base.

Question 5575

Topic: 6. Spine

A 6-year-old boy with Spinal Muscular Atrophy (SMA) Type II requires a posterior spinal fusion for a progressive neuromuscular scoliosis of 85 degrees. He is currently receiving treatment with nusinersen. How does this medical therapy impact the surgical planning for his spinal fusion?

. It requires a 6-month washout period to prevent pseudarthrosis.
. It necessitates leaving interlaminar access windows or placing a lumbar port for future intrathecal administration.
. It relies on intravenous administration and has no impact on spinal instrumentation planning.
. It significantly increases the risk of malignant hyperthermia during anesthesia.
. It promotes rapid curve reversal, often negating the need for surgical intervention.

Correct Answer & Explanation

. It necessitates leaving interlaminar access windows or placing a lumbar port for future intrathecal administration.

Explanation

Nusinersen is an antisense oligonucleotide administered intrathecally to treat SMA by modifying SMN2 splicing. Surgical planning for spinal fusion must include interlaminar windows, laminotomies, or an intrathecal catheter/port to allow for continued drug administration postoperatively.

Question 5576

Topic: 6. Spine

A 5-year-old non-ambulatory boy with Spinal Muscular Atrophy Type II is noted to have an asymptomatic, unilateral right hip dislocation on routine surveillance radiographs. He uses a custom-molded wheelchair and reports no pain with sitting or diaper changes. What is the most appropriate management?

. Closed reduction and spica casting.
. Open reduction and femoral varus derotational osteotomy.
. Varus derotational osteotomy and Dega pelvic osteotomy.
. Proximal femoral resection (Girdlestone procedure).
. Observation and continued use of his seating system.

Correct Answer & Explanation

. Observation and continued use of his seating system.

Explanation

Hip subluxation or dislocation is common in SMA Type II but is typically painless and does not significantly impair sitting balance. Surgical reconstruction is rarely indicated for painless dislocations in non-ambulatory patients due to high recurrence rates and poor functional benefit.

Question 5577

Topic: 6. Spine

A 4-year-old girl with Spinal Muscular Atrophy Type II is evaluated for a progressive collapsing thoracolumbar scoliosis measuring 45 degrees. A custom thoracolumbosacral orthosis (TLSO) is prescribed. Which of the following best describes the expected outcome of brace treatment in this patient?

. It will permanently halt the progression of the scoliosis.
. It will correct the curve to less than 20 degrees.
. It provides truncal support to improve sitting balance and frees the upper extremities.
. It prevents the development of restrictive lung disease.
. It is contraindicated due to the risk of exacerbating chest wall restriction.

Correct Answer & Explanation

. It provides truncal support to improve sitting balance and frees the upper extremities.

Explanation

In paralytic/neuromuscular scoliosis associated with SMA, orthoses generally do not stop curve progression. Their primary goal is to provide postural support, improve sitting balance, and allow the child to use their upper extremities for function rather than propping.

Question 5578

Topic: 6. Spine
A 14-year-old male with Spinal Muscular Atrophy Type III is scheduled for a posterior spinal fusion for an 80-degree scoliosis. Preoperative pulmonary function testing is obtained. Which of the following parameters is the most critical predictor of his requirement for prolonged postoperative mechanical ventilation?
. Forced expiratory volume in 1 second (FEV1) > 80% predicted.
. Forced vital capacity (FVC) < 30% predicted.
. Total lung capacity (TLC) > 100% predicted.
. Residual volume (RV) < 50% predicted.
. Diffusing capacity for carbon monoxide (DLCO) > 90% predicted.

Correct Answer & Explanation

. Forced vital capacity (FVC) < 30% predicted.

Explanation

Patients with SMA often have severe restrictive lung disease. A preoperative FVC of less than 30% to 40% of the predicted value is a strong indicator of high risk for postoperative respiratory failure and the need for prolonged mechanical ventilation.

Question 5579

Topic: 6. Spine

A 7-year-old boy with a known type II collagen (COL2A1) mutation is scheduled for bilateral hip reconstruction due to coxa vara. Preoperative assessment must include which of the following imaging modalities?

. Echocardiogram
. Renal ultrasound
. Flexion-extension radiographs of the cervical spine
. MRI of the lumbar spine
. DEXA scan

Correct Answer & Explanation

. Flexion-extension radiographs of the cervical spine

Explanation

Spondyloepiphyseal dysplasia congenita (SEDc) is associated with odontoid hypoplasia and atlantoaxial instability. Preoperative cervical spine clearance is mandatory to prevent catastrophic spinal cord injury during anesthesia intubation.

Question 5580

Topic: 6. Spine

A 9-year-old girl presents with waddling gait, short stature, and early-onset osteoarthritis of the hips. Her facial features are entirely normal. Radiographs reveal delayed, fragmented epiphyseal ossification and normal interpedicular distances in the lumbar spine. Which gene is most likely mutated?

. FGFR3
. COMP
. COL1A1
. SLC26A2
. RUNX2

Correct Answer & Explanation

. COMP

Explanation

Pseudoachondroplasia is caused by mutations in the Cartilage Oligomeric Matrix Protein (COMP) gene. Unlike achondroplasia, these patients have normal facial features, normal intelligence, and lack spinal stenosis (due to normal interpedicular distances).

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